阅读说明：本技术 用于低温操作的金属磁性存储器装置及其操作方法 (Metal magnetic memory device for low temperature operation and method of operating the same ) 是由 Q.乐 Z.李 Z.白 P.冯德海杰登 M.霍 于 2019-08-16 设计创作，主要内容包括：一种MRAM装置包含自旋阀,其含有具有固定磁化方向的参考层、自由层,以及位于所述参考层和所述自由层之间的非磁性金属屏障层；金属辅助结构,其配置成在编程期间向所述自由层提供旋转自旋转移力矩来辅助所述自由层切换；以及第一非磁性金属间隔物层,其位于所述自由层和所述金属辅助结构之间。(An MRAM device includes a spin valve containing a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metal barrier layer between the reference layer and the free layer; a metal assist structure configured to provide a rotational spin transfer torque to the free layer during programming to assist the free layer switching; and a first nonmagnetic metal spacer layer between the free layer and the metal assist structure.)

1. An MRAM device, comprising:

a spin valve comprising a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer between the reference layer and the free layer;

a metal assist structure configured to provide a rotational spin transfer torque to the free layer during programming to assist the free layer switching; and

a first nonmagnetic metal spacer layer located between the free layer and the metal auxiliary structure.

2. The MRAM device of claim 1, wherein the metal assist structure comprises a negative magnetic anisotropy assist layer having a negative magnetic anisotropy that provides in-plane magnetization in a plane perpendicular to the fixed magnetization direction.

3. The MRAM device of claim 2, wherein:

the negative magnetic anisotropy auxiliary layer has an easy magnetization plane perpendicular to the fixed magnetization of the reference layer;

the negative magnetic anisotropy auxiliary layer does not have an easy axis direction in the easy magnetization plane;

the free layer has a positive magnetic anisotropy to provide a bistable magnetization state including a parallel state having a magnetization parallel to the fixed vertical magnetization and an anti-parallel state having a magnetization anti-parallel to the fixed vertical magnetization; and is

The magnetic energy of the negative magnetic anisotropy auxiliary layer is not changed under the condition that the magnetization of the negative magnetic anisotropy auxiliary layer rotates in the horizontal plane.

4. The MRAM device of claim 2, wherein the negative magnetic anisotropy auxiliary layer comprises a homogeneous negative magnetic anisotropy material.

5. The MRAM device of claim 4, wherein the negative magnetic anisotropy assist layer comprises a cobalt-iridium alloy or a cobalt-iron alloy.

6. The MRAM device of claim 5, wherein the negative magnetic anisotropy assist layer comprises the cobalt-iridium alloy comprising 70 to 90 at% cobalt and 10 to 30 at% iridium.

7. The MRAM device of claim 5, wherein the negative magnetic anisotropy assist layer comprises the cobalt-iron alloy, the cobalt-iron alloy comprising 90 to 99.5 at% cobalt and 0.5 to 10 at% iron.

8. The MRAM device of claim 1, wherein the negative magnetic anisotropy assist layer comprises a plurality of repeating multilayer stacks comprising a first magnetic material layer and a second magnetic material layer.

9. The MRAM device of claim 8, wherein:

the first magnetic material layer comprises cobalt; and is

The second magnetic material layer includes iron.

10. The MRAM device of claim 1, wherein the metal assist structure comprises:

a first magnetic auxiliary layer;

a second magnetic auxiliary layer;

an antiferromagnetically coupled spacer layer between the first magnetic assist layer and the second magnetic assist layer, wherein the antiferromagnetically coupled spacer layer is configured to provide antiferromagnetic coupling between a first magnetization direction of the first magnetic assist layer and a second magnetization direction of the second magnetic assist layer.

11. The MRAM device of claim 10, wherein the first magnetization direction and the second magnetization direction are configured to precess about a vertical axis parallel to the fixed magnetization direction of the reference layer upon application of a current through the first magnetic assist layer, the antiferromagnetic coupling spacer layer, and the second magnetic assist layer while maintaining antiferromagnetic alignment therebetween.

12. The MRAM cell of claim 11, wherein:

the free layer has a positive magnetic anisotropy to provide a bistable magnetization state including a parallel state having a magnetization parallel to the fixed vertical magnetization and an anti-parallel state having a magnetization anti-parallel to the fixed vertical magnetization; and is

The fixed magnetization direction of the reference layer maintains the same orientation upon application of the current through the reference layer.

13. The MRAM cell of claim 10, wherein:

the first magnetization direction is a first in-plane magnetization perpendicular to the fixed magnetization direction of the reference layer; and is

The second magnetization direction is a second in-plane magnetization perpendicular to the fixed magnetization direction of the reference layer.

14. The MRAM cell of claim 10, wherein:

the antiferromagnetically coupled spacer layer comprises ruthenium;

the first magnetic auxiliary layer comprises a first magnetic material having a first negative magnetic anisotropy; and is

The second magnetic auxiliary layer comprises a second magnetic material having a second negative magnetic anisotropy.

15. The MRAM cell of claim 14, wherein each of the first and second magnetic assist layers is selected from:

a homogeneous negative magnetic anisotropy material; and

a plurality of repeating multi-layer stacks comprising a first magnetic material layer and a second magnetic material layer.

16. The MRAM cell of claim 1, wherein the metal assist structure comprises a spin torque oscillator stack.

17. The MRAM cell of claim 16, wherein the spin torque oscillator stack comprises a spin torque layer, a spin polarizing layer, and a second nonmagnetic metal spacer located between the spin torque layer and the spin polarizing layer.

18. The MRAM cell of claim 17, wherein:

the spin torque layer is on the first nonmagnetic metal spacer layer, the second nonmagnetic metal spacer layer is on the spin torque layer, and the spin polarization layer is on the second nonmagnetic metal spacer layer;

the spin torque layer comprises a first magnetic material having a first tapered magnetization with respect to a vertical axis parallel to the fixed vertical magnetization direction of the reference layer; and is

The spin polarizing layer includes a second magnetic material having a second tapered magnetization with respect to the vertical axis parallel to the fixed vertical magnetization direction of the reference layer.

19. The MRAM cell of claim 1, wherein the non-magnetic metal barrier layer comprises a material selected from Cu, Ag, AgSn, Cr, Ge, Ta, TaN, or CuN.

20. The MRAM cell of claim 1, wherein the MRAM cell is free of any electrically insulating layer, and the MRAM cell is configured to operate at a temperature below 77 Kelvin.

21. A spin orbit torque memory device, comprising:

a spin valve comprising a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer between the reference layer and a first surface of the free layer;

a metal line contacting the second surface of the free layer, wherein the metal line consists essentially of at least one elemental metal having an atomic number of 72 to 79;

a first electrode electrically connected to a first end of the metal line and electrically connected to a first transistor;

a second electrode electrically connected to a second end of the metal line, wherein the second surface of the free layer contacts the metal line between the first electrode and the second electrode;

a third electrode electrically connected to the reference layer and electrically connected to a second transistor; and

a program controller configured to control the first transistor and the second transistor to provide a two-step programming process for magnetization of the free layer, wherein the two-step programming process comprises:

a first program pulse applying step in which the first transistor is turned on and the second transistor is turned off, and a first current flows through the metal line between the first electrode and the second electrode; and

a second programming pulse applying step in which the second transistor is turned on and the first transistor is turned off, and a second current flows through the spin valve between the third electrode and the second electrode.

22. The spin-orbit torque memory device of claim 21, further comprising a synthetic antiferromagnetic structure comprising the reference layer, a fixed ferromagnetic layer having a magnetization antiparallel to the fixed magnetization direction of the reference layer, and an antiferromagnetic coupling layer located between the reference layer and the fixed ferromagnetic layer.

23. A method of programming a spin orbit torque memory device, the spin orbit torque memory device comprising: a spin valve comprising a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer between the reference layer and a first surface of the free layer; a metal line contacting the second surface of the free layer; a first electrode electrically connected to a first end of the metal line; a second electrode electrically connected to a second end of the metal line; and a third electrode electrically connected to the reference layer, the method comprising:

applying a first programming pulse between the first electrode and the second electrode such that a first current flows through the metal line between the first electrode and the second electrode; and

applying a second programming pulse between the second electrode and the third electrode such that a second current flows through the spin valve between the third electrode and the second electrode;

wherein the method is performed at a temperature below 77 degrees kelvin.

24. The method of claim 23, wherein:

the first programming pulse duration is 5ns or less; and is

The second programming pulse duration is 5ns or less.

Technical Field

The present disclosure relates generally to the field of magnetic memory devices, and in particular to metal magnetic memory devices, such as Magnetoresistive Random Access Memory (MRAM) devices having at least one auxiliary layer; and a method of operating the same.

Background

Spin Transfer Torque (STT) refers to the effect of the orientation of a magnetic layer in a magnetic tunnel junction or spin valve being modified by a spin polarized current. Typically, the current is unpolarized with electrons having random spin orientations. Spin polarized current is a current in which electrons have a net non-zero spin due to a preferential spin orientation distribution. Spin polarized current may be generated by passing a current through a magnetic polarizer layer. When a spin-polarized current flows through the free layer of a magnetic tunnel junction or spin valve, electrons in the spin-polarized current may transfer at least some of their angular momentum to the free layer, thereby generating a torque that magnetizes the free layer. When a sufficient amount of spin-polarized current passes through the free layer, spin transfer torque can be employed to flip the spin orientation (e.g., change magnetization) in the free layer. Data may be stored in a Magnetoresistive Random Access Memory (MRAM) cell using a difference in resistance of a magnetic tunnel junction between different magnetization states of the free layer, depending on whether the magnetization of the free layer is parallel or antiparallel to the magnetization of the reference layer.

Disclosure of Invention

According to an aspect of the present disclosure, an MRAM device includes: a spin valve having a reference layer with a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer positioned between the reference layer and the free layer; a metal assist structure configured to provide a rotational spin transfer torque to the free layer to assist the free layer to switch during programming; and a first nonmagnetic metal spacer layer positioned between the free layer and the metal assist structure.

According to another aspect of the present disclosure, a spin orbit torque memory device includes: a spin valve comprising a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer positioned between the reference layer and a first surface of the free layer; a metal line contacting the second surface of the free layer, wherein the metal line consists essentially of at least one elemental metal having an atomic number of 72 to 79; a first electrode electrically connected to a first end of the metal line and electrically connected to the first transistor; a second electrode electrically connected to a second end of the metal line, wherein the second surface of the free layer contacts the metal line between the first electrode and the second electrode; a third electrode electrically connected to the reference layer and electrically connected to the second transistor; and a program controller configured to control the first transistor and the second transistor to provide a two-step programming process for magnetization of the free layer. The two-step programming process includes: a first program pulse applying step in which the first transistor is turned on and the second transistor is turned off, and a first current flows through the metal line between the first electrode and the second electrode; and a second program pulse applying step in which the second transistor is turned on and the first transistor is turned off, and a second current flows through the spin valve between the third electrode and the second electrode.

According to another aspect of the present disclosure, a method of programming a spin orbit torque memory device, the spin orbit torque memory device comprising: a spin valve comprising a reference layer having a fixed magnetization direction, a free layer, and a non-magnetic metallic barrier layer positioned between the reference layer and a first surface of the free layer; a metal line contacting the second surface of the free layer; a first electrode electrically connected to a first end of the metal line; a second electrode electrically connected to a second end of the metal line; and a third electrode electrically connected to the reference layer, the method including applying a first programming pulse between the first and second electrodes such that a first current flows between the first electrode and the second electrode through the metal line; and applying a second programming pulse between the second and third electrodes such that a second current flows through the spin valve between the third electrode and the second electrode. The method is performed at a temperature below 77 degrees kelvin.

Drawings

FIG. 1 is a schematic diagram of a memory device including magnetoresistive memory cells of the present disclosure in an array configuration.

Fig. 2A shows a first configuration of a first exemplary STT MRAM cell according to a first embodiment of the disclosure.

Fig. 2B shows a second configuration of the first exemplary STT MRAM cell according to the first embodiment of the disclosure.

Fig. 2C shows a third configuration of the first exemplary STT MRAM cell in accordance with the first embodiment of the disclosure.

Fig. 2D shows a fourth configuration of the first exemplary STT MRAM cell in accordance with the first embodiment of the disclosure.

Fig. 3A shows a first configuration of a second exemplary STT MRAM cell according to a second embodiment of the present disclosure.

Fig. 3B shows a second configuration of a second exemplary STT MRAM cell in accordance with a second embodiment of the present disclosure.

Fig. 3C shows a third configuration of a second exemplary STT MRAM cell in accordance with a second embodiment of the present disclosure.

Fig. 3D illustrates a fourth configuration of a second exemplary STT MRAM cell in accordance with a second embodiment of the present disclosure.

Fig. 4A shows a first configuration of a third exemplary STT MRAM cell according to a third embodiment of the present disclosure.

Fig. 4B shows a second configuration of a third exemplary STT MRAM cell according to a third embodiment of the present disclosure.

Fig. 4C shows a third configuration of a third exemplary STT MRAM cell in accordance with a third embodiment of the present disclosure.

Fig. 4D shows a fourth configuration of a third exemplary STT MRAM cell in accordance with a third embodiment of the present disclosure.

FIG. 5A shows a first step of a programming operation of an exemplary SOT MRAM cell according to a fourth embodiment of the disclosure.

FIG. 5B shows a second step of the programming operation of an exemplary SOT MRAM cell according to a fourth embodiment of the disclosure.

FIG. 5C illustrates a read operation of an exemplary SOT MRAM cell according to a fourth embodiment of the disclosure.

Fig. 6 shows a contact region between a free layer and a metal line within an exemplary SOT MRAM cell according to a fourth embodiment of the present disclosure.

Detailed Description

Quantum computing is expected to provide superior performance over conventional computing. However, quantum computing presents unique characteristics and challenges due to its specific requirements for operating conditions (in particular, temperature). Typically, quantum computing devices will need to operate at very low temperatures (e.g., below 77 degrees kelvin, such as below 10 degrees kelvin). One key challenge associated with perpendicular magnetic tunnel junction (pMTJ) type STT MRAM devices is that both the reference layer and the free layer magnetizations are along a direction perpendicular to the stacking plane. Thus, the initial moment during switching of the free layer is close to zero. In conventional pMTJ STT-MRAM, the initial "kick" for free layer switching comes from the random effective field induced by thermal fluctuations. For quantum computing environments at low temperatures, this thermal random field is close to zero, making the free layer switching much more difficult. Thus, the magnitude of the current used to cause a transition from a parallel state to an anti-parallel state or from an anti-parallel state to a parallel state at low temperatures is greater than desired (e.g., greater than the magnitude of the current required to cause the same transition at room temperature). Other desirable characteristics specific to MRAM devices in quantum computing environments include a much smaller perpendicular anisotropy for the free layer, and a much smaller resistance for the MRAM elements, which further imposes constraints on pMTJ MRAM devices that have much higher resistance, typically due to an electrically insulating tunneling layer (e.g., MgO) positioned between the free layer and the reference layer.

Embodiments of the present disclosure provide MRAM devices, such as STT and/or MRAM devices suitable for low temperature operation (e.g., temperatures below 77 degrees kelvin, such as below 10 degrees kelvin). In one embodiment, each MRAM cell contains a stack of only metal layers, and does not include any electrically insulating layer such as MgO. As used herein, the term "metal" means a layer that is electrically conductive and includes a pure metal or metal alloy. The conductive layer lacks the band gap between the valence and conduction bands typically found in semiconductor and electrically insulating layers. Thus, the MRAM cell lacks a tunneling layer, such as MgO (i.e., the MRAM cell is not an MTJ cell), but instead includes a nonmagnetic metal spacer layer, such as a Cu metal or AgSn metal alloy. The metal layer provides a long spin diffusion length and low resistivity to provide polarized spin current and spin torque while keeping the overall resistance of the MRAM cell layer stack low (e.g., <10 ohms, such as 0.1 to 9 ohms).

In one embodiment, the MRAM cell includes an auxiliary structure that can provide a rotational spin transfer torque to the free layer to assist the free layer in switching during the write process. In one embodiment, this will not only solve the zero initial torque problem due to the low temperature, but the rotating STT from the auxiliary structure can also provide torque to the free layer throughout the switching process, thus maximizing the auxiliary effect.

In some embodiments, the metal MRAM cells may be used at low temperatures for any suitable application, such as quantum computing applications. The effective anisotropy of the free layer is much lower (e.g., more than 10 times lower) than that of typical pMTJ STT-MRAM. This is due to the very low cryogenic operating temperature (and hence much lower k)_BT term) is possible, which makes the anisotropy required to maintain the same thermal stability factor for data retention much lower. This further reduces the required switching current.

The drawings are not drawn to scale. Where a single instance of an element is described, multiple instances of the element may be repeated unless explicitly described or otherwise clearly indicated to be absent from the repetition of the element. The same reference numerals refer to the same or similar elements. Elements having the same reference number are presumed to have the same material composition unless explicitly stated otherwise. Ordinal numbers such as "first," "second," and "third" are used merely to identify similar elements, and different ordinal numbers may be employed across the specification and claims of the present disclosure. As used herein, a first element that is "on" a second element may be located on the outside of a surface of the second element or on the inside of the second element. As used herein, a first element is "directly" on a second element if there is physical contact between a surface of the first element and a surface of the second element. As used herein, an "in-process structure" or a "temporary" structure refers to a structure that is subsequently modified. As used herein, "layer" refers to a portion of a material that includes a region having a thickness. The layer may extend over the entire underlying or overlying structure, or may have an extent that is less than the extent of the underlying or overlying structure. In addition, a layer may be a region of a homogeneous or heterogeneous continuous structure having a thickness less than the thickness of the continuous structure. For example, a layer may be positioned between the top and bottom surfaces of a continuous structure or between any pair of horizontal planes at the top and bottom surfaces of a continuous structure. The layers may extend horizontally, vertically, and/or along a tapered surface. The substrate may be a layer, may contain one or more layers therein, and/or may have one or more layers thereon, above, and/or below.

As used herein, "layer stack" refers to a stack of layers. As used herein, "line" or "line-type structure" refers to a layer having a predominant direction of extension (i.e., having a direction along which the layer extends the most).

As used herein, "field effect transistor" refers to any semiconductor device having a semiconductor channel through which current flows at a current density modulated by an external electric field. As used herein, "active region" refers to either a source region of a field effect transistor or a drain region of a field effect transistor. "top active region" refers to an active region of a field effect transistor that is located above another active region of the field effect transistor. "bottom active region" refers to an active region of a field effect transistor that is located below another active region of the field effect transistor.

As used herein, "semiconductive material" refers to a material having a resistivity of 1.0 × 10^-6S/cm to 1.0 × 10⁵As used herein, "semiconductor material" refers to a material having an electrical conductivity in the absence of an electrical dopant of 1.0 × 10^-6S/cm to 1.0 × 10⁵A material having an electrical conductivity in the range of S/cm and which is capable of yielding, upon suitable doping with an electrical dopant, a material having an electrical conductivity in the range of 1.0S/cm to 1.0 × 10⁵As used herein, "electrical dopant" refers to a p-type dopant that adds holes to a valence band within the band structure, or an n-type dopant that adds electrons to a conduction band within the band structure⁵As used herein, "insulator material" or "dielectric material" refers to a material having an electrical conductivity of less than 1.0 × 10^-6As used herein, "heavily doped semiconductor material" refers to a material that is doped with an electrical dopant at a sufficiently high atomic concentration to become electrically conductive (i.e., having an electrical conductivity greater than 1.0 × 10)⁵S/cm conductivity) the "doped semiconductor material" may be a heavily doped semiconductor material, or may be a material including a material providing 1.0 × 10^-6S/cm to 1.0 × 10⁵Semiconductor material of electrical dopants (i.e., p-type dopants and/or n-type dopants) at a concentration of conductivity in the range of S/cm. "intrinsic semiconductor material" refers to a semiconductor material that is not doped with an electrical dopant. Thus, the semiconductor material may be semiconducting or conductive, and may be an intrinsic semiconductor material or a doped semiconductor material. The doped semiconductor material may be semiconducting or conducting depending on the atomic concentration of the electrical dopant therein. As used herein, "metallic material" refers to a conductive material containing at least one metallic element therein. All measurements for conductivity were performed under standard conditions.

Referring to FIG. 1, a schematic diagram of a magnetic memory device including memory cells 180 of an embodiment of the present disclosure in an array configuration is shown. The magnetic memory device may be configured as an MRAM device 500 containing MRAM cells 180. As used herein, "MRAM device" refers to a memory device containing cells that allow random access, such as access to any selected memory cell following a command to read the contents of the selected memory cell.

The MRAM device 500 of embodiments of the present disclosure includes a memory array region 550 containing an array of respective MRAM cells 180 located at intersections of respective word lines (which may include the conductive lines 30 as shown, or as second conductive lines 90 in an alternative configuration) and bit lines (which may include the second conductive lines 90 as shown, or as first conductive lines 30 in an alternative configuration). MRAM device 500 may also contain a row decoder 560 connected to word lines, a sense circuit 570 (e.g., sense amplifiers and other bit line control circuitry) connected to bit lines, a column decoder 580 connected to bit lines, and a data buffer 590 connected to the sense circuit. Various examples of MRAM cells 180 are provided in an array configuration that forms MRAM device 500. As such, each of the MRAM cells 180 may be a two-terminal device including a respective first electrode and a respective second electrode. It should be noted that the location and interconnection of elements is schematic and that elements may be arranged in different configurations. Furthermore, MRAM cell 180 may be fabricated as a discrete device, i.e., a single isolated device.

Each MRAM cell 180 includes a magnetic spin valve having at least two different resistance states depending on the alignment of the magnetization of the different layers of magnetic material. The magnetic spin valve is disposed between the first and second electrodes within each MRAM cell 180. The configuration of MRAM cell 180 is described in detail in subsequent sections.

Referring to fig. 2A, a first configuration of a first exemplary STT MRAM cell 180 in accordance with a first embodiment is schematically illustrated. The STT MRAM cell 180 includes a spin valve 140. The spin valve 140 includes a reference layer 132 having a fixed vertical magnetization, a non-magnetic metal barrier layer 134 between the positioning reference layer 132 and the free layer 136. In one embodiment, the reference layer 132 is located below the nonmagnetic metal barrier layer 134, while the free layer 136 is located above the nonmagnetic barrier layer 134. However, in other embodiments, the reference layer 132 is located above the non-magnetic barrier layer 134 while the free layer 136 is located below the non-magnetic barrier layer 134, or the reference layer 132 and the free layer 136 may be located on opposite lateral sides of the non-magnetic barrier layer 134. In one embodiment, the reference layer 132 and the free layer 136 have respective positive uniaxial magnetic anisotropy.

Generally, a magnetic thin film has magnetic energy per unit volume, which depends on the orientation of magnetization of a magnetic material of the magnetic thin film. The magnetic energy per unit volume may be transferred through an angle theta (or sin) between the magnetization direction and a vertical axis perpendicular to the plane of the magnetic thin film (e.g., the top surface or the bottom surface of the magnetic thin film)²θ) and the azimuth angle φ between the magnetization direction and a fixed vertical plane perpendicular to the plane of the magnetic thin film. As sin²The first and second order terms of magnetic energy per unit volume of the function of θ contain K₁sin²θ+K₂sin⁴Theta. When K is₁Is negative and K₂Less than-K₁At/2, function K₁sin²θ+K₂sin⁴Theta has a minimum value where theta is at pi/2. If the magnetic anisotropy energy as a function of θ has a minimum only when θ is at π/2, then the magnetization of the magnetic film is entirely in the plane of the film and the film is said to have a "negative magnetic anisotropy". If the magnetic anisotropy energy as a function of θ has a minimum only when θ is at 0 or π, then the magnetization of the magnetic film is perpendicular to the plane of the film and the film is said to have "positive magnetic anisotropy". The magnetization of the thin crystal magnetic film having positive magnetic anisotropy is perpendicular to the plane of the thin crystal magnetic film, i.e., perpendicular to both directions along which the thin crystal magnetic film laterally extends. The magnetization of the thin crystal magnetic film having negative magnetic anisotropy is in the plane of the thin crystal magnetic film, i.e., parallel to the two directions along which the thin crystal magnetic film laterally extends.

The configuration in which the reference layer 132 and the free layer 136 have respective positive uniaxial magnetic anisotropies provides the free layer 136 with a bi-stable magnetization state. The bi-stable magnetization state includes a parallel state, in which the magnetization (e.g., magnetization direction) of the free layer 136 is parallel to the fixed vertical magnetization (e.g., magnetization direction) of the reference layer 132; and an anti-parallel state, in which the magnetization (e.g., magnetization direction) of the free layer 136 is anti-parallel to the fixed vertical magnetization (e.g., magnetization direction) of the reference layer 132.

The reference layer 132 may comprise a Co/Ni or Co/Pt multilayer structure. The reference layer 132 may additionally comprise a thin non-magnetic layer of tantalum having a thickness of 0.2nm to 0.5nm, and a thin CoFeB layer (thickness in the range of 0.5nm to 2 nm). The non-magnetic metal barrier layer 134 may include metal barrier materials such as Cu, Ag, AgSn, Cr, Ru, Ta, TaN, and CuN. The thickness of the non-magnetic metal barrier layer 134 may be 0.7nm to 1.3nm, for example, about 1 nm. The free layer 136 may include an alloy of one or more of Fe, Co, and/or Ni (e.g., CoFeB) in a composition that provides positive uniaxial magnetic anisotropy.

In one embodiment, the reference layer 132 may be provided as a component within a synthetic antiferromagnetic structure (SAF structure) 120. The SAF structure 120 can include a reference layer 132, a fixed ferromagnetic layer 112 having a magnetization antiparallel to a fixed vertical magnetization, and an antiferromagnetic coupling layer 114 located between the reference layer 132 and the fixed ferromagnetic layer 112 toward a first side of the reference layer 132 opposite a second side of the reference layer 132 toward the nonmagnetic barrier layer 134. The thickness of the antiferromagnetic coupling layer 114 induces antiferromagnetic coupling between the reference layer 132 and the fixed ferromagnetic layer 112. In other words, the antiferromagnetic coupling layer 114 can lock in antiferromagnetic alignment between the magnetization of the reference layer 132 and the magnetization of the fixed ferromagnetic layer 112 to lock in place the magnetization of the reference layer 132 and the magnetization of the fixed ferromagnetic layer 112. In one embodiment, the antiferromagnetic coupling layer can comprise ruthenium and can have a thickness in the range of 0.3nm to 1 nm.

The first nonmagnetic metal spacer layer 150 is provided over a second side of the free layer 136 opposite the first side of the free layer 136 facing the nonmagnetic metal barrier layer 134. The first nonmagnetic metal spacer layer 150 includes a nonmagnetic metal material such as Cu, Ag, AgSn, Cr, Ta, Ru, TaN, or CuN. In one embodiment, the first nonmagnetic metal spacer layer 150 may comprise a conductive metal material. The thickness of the first nonmagnetic metal spacer layer 150 may be in the range of 0.2nm to 2nm, although lesser and greater thicknesses may also be employed.

The negative magnetic anisotropy auxiliary layer 160 may be provided on the first nonmagnetic metal spacer layer150 and over the second side of the free layer 136. The negative magnetic anisotropy auxiliary layer 160 may have a negative magnetic anisotropy with a substantially negative K₁The value is such as to provide in-plane magnetization for the negative magnetic anisotropy assist layer 160. The in-plane magnetization is a magnetization oriented in the horizontal plane in fig. 2A that is perpendicular to the fixed vertical magnetization of the reference layer 132.

In one embodiment, the hard-axis is parallel to the direction perpendicular to the major surface of the negative magnetic anisotropy assist layer 160 (i.e., the axis is perpendicular to the plane of layer 160 and parallel to the fixed vertical magnetization of the reference layer 132), while the easy magnetization plane is parallel to the plane of the negative magnetic anisotropy assist layer 160 (i.e., the easy magnetization plane is perpendicular to the fixed vertical magnetization of the reference layer 132 in fig. 2A). In one embodiment, in the plane of the negative magnetic anisotropy auxiliary layer 160 (i.e., the easy magnetization plane), there is no easy axis direction. The negative magnetic anisotropy assist layer 160 is spin-coupled with the free layer 136 via the first nonmagnetic spacer layer 150.

In one embodiment, thermal energy at room temperature (i.e., k)_BT, wherein k_BBeing boltzmann constant, and T being 297.15 kelvin (which is room temperature)), the orientation-dependent component of the magnetic anisotropy of the negative magnetic anisotropy assist layer 160 may be zero or insignificant. For example, the maximum change in magnetic anisotropy per unit volume about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the negative magnetic anisotropy assist layer 160, the magnetization of the negative magnetic anisotropy assist layer 160 is free to precess in a horizontal plane parallel to the interface between the first nonmagnetic metal spacer layer 150 and the negative magnetic anisotropy assist layer 160. In one embodiment, the magnetic energy of the negative magnetic anisotropy auxiliary layer 160 may be unchanged under the condition that the magnetization of the negative magnetic anisotropy auxiliary layer 160 rotates in the horizontal plane.

In one embodiment, the negative magnetic anisotropy auxiliary layer 160 comprises a homogeneous negative magnetic anisotropy material. As used herein, "homogeneous" material refers to a material that has a uniform material composition throughout. In one embodiment, the negative magnetic anisotropy auxiliary layer 160 includesA cobalt-iridium alloy, and/or consists essentially of a cobalt-iridium alloy. The material composition of the cobalt-iridium alloy may be selected to provide negative magnetic anisotropy. In one embodiment, the cobalt-iridium alloy may include cobalt atoms at an atomic concentration in the range of 60% to 98% (e.g., 70% to 90%, such as 80%) and iridium atoms at an atomic concentration in the range of 40% to 2% (e.g., 30% to 10%, such as 20%). In one embodiment, the cobalt-iridium alloy contains only cobalt, iridium, and unavoidable impurities. In another embodiment, up to 5 atomic percent of elements other than cobalt and iridium may be added to the alloy. In the illustrative example, having the composition Co_0.8Ir_0.2Of cobalt-iridium alloy₁A value of about-0.6 x10⁶J/m³. In another embodiment, the negative magnetic anisotropy assist layer 160 comprises, and/or consists essentially of, a cobalt-iron alloy. The material composition of the cobalt-iron alloy may be selected to provide negative magnetic anisotropy. In one embodiment, the cobalt-iron alloy may include cobalt atoms at an atomic concentration in the range of 80% to 99.8% (e.g., 90% to 99.5%, such as 99%) and iron atoms at an atomic concentration in the range of 20% to 0.2% (e.g., 10% to 0.5%, such as 1%). In the illustrative example, having the composition Co_0.99Fe_0.1Of cobalt-iron alloy₁A value of about-0.99 x10⁶J/m³. The thickness of the negative magnetic anisotropy auxiliary layer 160 may be in the range of 1nm to 10nm, for example 1.5nm to 6nm, but smaller and larger thicknesses may also be employed.

In one embodiment, the non-magnetic capping layer 170 may be located over the negative magnetic anisotropy assist layer 160. The nonmagnetic capping layer 170 may comprise a nonmagnetic conductive (e.g., metallic) material, such as W, Ti, Ta, WN, TiN, TaN, Ru, and Cu. The thickness of the non-magnetic capping layer 170 may be in the range of 1nm to 20nm, although lesser and greater thicknesses may also be employed.

The layer stack including the material layers from the SAF structure 120 to the nonmagnetic capping layer 170 may be deposited up or down, i.e., from the SAF structure 120 toward the nonmagnetic capping layer 170 or from the nonmagnetic capping layer 170 toward the SAF structure 120. The layer stack may be formed as a stack of continuous layers and may be subsequently patterned into a discrete patterned layer stack for each MRAM cell 180.

MRAM cell 180 may include a first terminal 92 electrically connected to or including a portion of bit line 90 (shown in FIG. 1), and a second terminal 32 electrically connected to or including a portion of word line 30 (shown in FIG. 1). The positions of the first and second terminals may be switched such that the first terminal is electrically connected to the SAF structure 120 and the second terminal is electrically connected to the cap layer 170.

Alternatively, each MRAM cell 180 may include a dedicated steering device, such as an access transistor or diode, configured to activate the respective discrete patterned layer stack (120, 140, 150, 160, 170) upon application of a suitable voltage to the steering device. The steering device may be electrically connected between the patterned layer stack and one of the respective word lines 30 or bit lines 90 of the respective MRAM cell 180.

In one embodiment, the polarity of the voltage applied to the first terminal 92 may change depending on the polarity of the magnetization state to be programmed in the free layer 136. For example, a voltage of a first polarity may be applied to the first terminal 92 (relative to the second terminal 32) during a transition from an anti-parallel state to a parallel state, and a voltage of a second polarity (which is opposite the first polarity) may be applied to the first terminal 92 during a transition from the parallel state to the anti-parallel state. Moreover, variations in circuitry for activating the discrete patterned layer stack (120, 140, 150, 160, 170) are also contemplated herein.

The magnetization direction of the free layer 136 may be switched (i.e., from up to down, or vice versa) by passing a current through the stack of discrete patterned layers (120, 140, 150, 160, 170). The magnetization of the free layer 136 may precess around the vertical direction (i.e., the direction of flow of current) during the programming process until the magnetization direction flips 180 degrees, at which time the flow of current stops. In one embodiment, the magnetization of the negative magnetic anisotropy assist layer 160 may be free to rotate about a vertical axis parallel to the fixed magnetization direction of the reference layer 132 while a current is flowing through the discrete patterned layer stack (120, 140, 150, 160, 170). This configuration allows the negative magnetic anisotropy assist layer 160 to provide an initial non-zero moment to the magnetization of the free layer 136 during an initial phase in which the magnetization of the free layer 136 precesses around a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 after initiating the flow of a current through the MRAM cell 180.

In one embodiment, the MRAM cell 180 may be configured to provide coupling between the in-plane magnetization of the negative magnetic anisotropy assist layer 160 and the magnetization of the free layer 136 during precession of the magnetization of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132, and to provide synchronous precession of the in-plane magnetization of the negative magnetic anisotropy assist layer 160 and the magnetization of the free layer 136 while a current is flowing through the MRAM cell 180.

Due to the negative magnetic anisotropy, in one embodiment, the in-plane magnetization of the negative magnetic anisotropy assist layer 160 may provide an initial moment to the free layer to facilitate initiating switching of the free layer 136. Once precession of the free layer 136 begins, the free layer 136 may provide a spin torque to the negative magnetic anisotropy assist layer 160 to cause the negative magnetic anisotropy assist layer 160 magnetization to also precess. This precession of the negative magnetic anisotropy assist layer 160 may in turn further assist in the switching of the free layer 136. The embodiment negative magnetic anisotropy auxiliary layer 160 having an in-plane easy magnetization plane but lacking a fixed easy axis direction is more efficient than prior art auxiliary layers in which the magnetization direction (e.g., easy axis) of the auxiliary layer is fixed.

Referring to fig. 2B, a second configuration of the first exemplary spin transfer torque MRAM cell 180 may be derived from the first configuration of the first exemplary spin transfer torque MRAM cell 180 of fig. 2A by replacing the negative magnetic anisotropy assist layer 160 with a negative magnetic anisotropy assist layer 260 comprising a multi-layer stack (262, 264). The multi-layer stack (262, 264) may include multiple repetitions of the first magnetic material layer 262 and the second magnetic material layer 264. First magnetic material layer 262 may include and/or may consist essentially of a first magnetic material. The second magnetic material layer 264 may include, and/or may consist essentially of, a second magnetic material.

The composition and thickness of each first magnetic material layer 262 and the composition and thickness of each second magnetic material layer 264 may be selected such that the multi-layer stack (262, 264) provides in-plane magnetization, i.e., perpendicular magnetizationA magnetization that is perpendicular to the fixed magnetization direction of the reference layer 132 (i.e., an easy magnetization plane that is perpendicular to the fixed magnetization direction of the reference layer 132 and has no easy magnetization axis). The negative magnetic anisotropy auxiliary layer 260 may have a negative magnetic anisotropy with a substantially negative K₁The value is such as to provide in-plane magnetization for the negative magnetic anisotropy assist layer 260.

In one embodiment, the orientation dependent component of the magnetic anisotropy of the negative magnetic anisotropy assist layer 260 may be zero or insignificant compared to thermal energy at room temperature. For example, the maximum change in magnetic anisotropy per unit volume about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the negative magnetic anisotropy assist layer 260, the magnetization of the negative magnetic anisotropy assist layer 260 is free to precess in a plane parallel to the interface between the first nonmagnetic spacer layer 150 and the negative magnetic anisotropy assist layer 260. In one embodiment, the magnetic energy of the negative magnetic anisotropy auxiliary layer 260 may be unchanged under the condition that the magnetization of the negative magnetic anisotropy auxiliary layer 260 rotates in the horizontal plane.

In one embodiment, first magnetic material layer 262 includes cobalt and second magnetic material layer 264 includes iron. In one embodiment, first magnetic material layer 262 consists essentially of cobalt and second magnetic material layer 264 consists essentially of iron. The thickness of each first magnetic material layer 262 may be in the range of 0.3nm to 1nm, and the thickness of each second magnetic material layer 264 may be in the range of 0.3nm to 1 nm. The total number of repetitions within the negative magnetic anisotropy auxiliary layer 260 (i.e., the total number of pairs of the first and second magnetic material layers 262 and 264) may be in a range of 2 to 20, such as 4 to 10. In one embodiment, the multi-layer stack (262, 264) includes a periodic repetition of a unit layer stack including a first magnetic material layer 262 and a second magnetic material layer 264. In an illustrative example, a repeating cobalt-iron multilayer stack comprising a unit layer stack consisting of a cobalt layer and an iron layer having the same thickness may have about-1.1 x10⁶J/m³K1 value of (a).

Referring to fig. 2C, a third configuration of the first exemplary spin transfer torque MRAM cell 180 may be derived from the first configuration of the first exemplary spin transfer torque MRAM cell 180 of fig. 2A by interposing a second nonmagnetic metal spacer layer 190 and a pinned magnetization layer 192 between the negative magnetic anisotropy assist layer 160 and the nonmagnetic cap layer 170.

The second nonmagnetic metal spacer layer 190 may be located on the negative magnetic anisotropy auxiliary layer 160, on the side opposite to the first nonmagnetic metal spacer layer 150. The second nonmagnetic metal spacer layer 190 contains a nonmagnetic metal material such as Cu, Ag, AgSn, Cr, Ru, Ta, TaN, or CuN. In one embodiment, the second nonmagnetic metal spacer layer 190 may comprise a conductive (e.g., metal) material. The thickness of the second nonmagnetic metal spacer layer 190 may be in the range of 0.2nm to 2nm, although lesser and greater thicknesses may also be employed. The second nonmagnetic metal spacer layer 190 may comprise the same material as the first nonmagnetic metal spacer layer 150, or may comprise a material different from the material of the first nonmagnetic metal spacer layer 150.

The pinned magnetization layer 192 is a magnetic layer having positive uniaxial magnetic anisotropy. In other words, K₁Is positive and the term K₁sin²θ dominates all other higher order terms and terms that depend on sin (n φ) (or cos (n φ)) in the amount of magnetic anisotropy per volume of the material of pinned magnetization layer 192. The positive uniaxial magnetic anisotropy of the pinned magnetization layer 192 provides a magnetization that is parallel or antiparallel to the fixed vertical magnetization of the reference layer 132. In one embodiment, K of pinned magnetization layer 192₁May be greater than K of the free layer 136₁Such that the magnetization of the pinned magnetization layer 192 remains pinned along the vertical direction (i.e., perpendicular to the interface between the layers of the discrete patterned layer stack (120, 140, 150, 160, 190, 192, 170)) during programming of the MRAM cell 180. The magnetization of the pinned magnetization layer 192 may remain parallel or antiparallel to the magnetization of the reference layer 132.

In one embodiment, the pinned magnetization layer 192 may comprise a Co/Ni or Co/Pt multilayer structure. The pinned magnetization layer 192 may additionally include a thin nonmagnetic layer composed of tantalum having a thickness of 0.2nm to 0.5nm, and a thin CoFeB layer (having a thickness in the range of 0.5nm to 2 nm). The pinned magnetization layer 192 may cause in-plane magnetization oscillation of the negative magnetic anisotropy assist layer 160. Oscillation of the in-plane magnetization of the negative magnetic anisotropy assist layer 160 may generate a rotating spin torque on the magnetization of the free layer 136 during programming, and thus may facilitate switching of the magnetization of the free layer 136 with a lower current through the discrete patterned layer stack (120, 140, 150, 160, 190, 192, 170). In one embodiment, the combination of the magnetizations of the pinned magnetization layer 192 and the negative magnetic anisotropy assist layer 160 applies a non-horizontal and non-vertical magnetic field (i.e., a field neither parallel nor perpendicular to the magnetization direction of the reference layer 132) to the magnetization of the free layer 136 to reduce the magnitude of a required current through the discrete patterned layer stack (120, 140, 150, 160, 190, 192, 170) during switching of the magnetization of the free layer 136.

Referring to fig. 2D, a fourth configuration of the first exemplary spin-transfer torque MRAM cell 180 may be derived from the third configuration of the exemplary spin-transfer torque MRAM cell 180 of fig. 2A by replacing the negative magnetic anisotropy assist layer 160, which has a homogeneous material composition, with a negative magnetic anisotropy assist layer 260 that contains a plurality of repeated multi-layer stacks (262, 264) including a first magnetic material layer 262 and a second magnetic material layer 264, described above with respect to fig. 2B.

Referring to all configurations of the exemplary spin transfer torque MRAM cell 180 shown in FIGS. 1-2D, the exemplary spin transfer torque MRAM cell 180 may be individually programmed and read. Reading (i.e., sensing) the magnetization state of the free layer 136 may be performed by applying a read bias voltage across the first and second terminals 92, 32 of the selected discrete patterned layer stack 120, 140, 150, (160 or 260), 170} or 120, 140, 150, (160 or 260), (190, 192), 170 }. The parallel or anti-parallel alignment between the magnetizations of the free layer 136 and the reference layer 132 determines the resistance of the selected discrete patterned layer stack in each MRAM cell 180, and thus determines the magnitude of the current flowing between the first terminal 92 and the second terminal 32. The magnitude of the current may be sensed to determine the magnetization state of the free layer 136 and the data encoded by the detected magnetization state.

Programming of the first example spin transfer torque MRAM cell 180 to the relative magnetization state of the free layer 136 may be performed by flowing a current through the selected discrete patterned layer stack 120, 140, 150, (160 or 260), 170} or 120, 140, 150, (160 or 260), (190, 192), 170} and by inducing a flip (i.e., switching) of the magnetization direction of the free layer 136. In particular, a current may be flowed through a selected stack of discrete patterned layers including the spin valve 140, the first nonmagnetic metal spacer layer 150, and the negative magnetic anisotropy assist layer (160 or 260). After an initial current flows through the spin valve 140, the first nonmagnetic metal spacer layer 150, and the negative magnetic anisotropy assist layer (160 or 260), the in-plane magnetization of the negative magnetic anisotropy assist layer (160 or 260) provides an initial non-zero moment to the magnetization of the free layer 136 during an initial phase of precession of the magnetization of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132.

In one embodiment, the in-plane magnetization of the negative magnetic anisotropy assist layer (160 or 260) couples with the magnetization of the free layer 136 during precession of the magnetization of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 to provide synchronous precession of the in-plane magnetization of the negative magnetic anisotropy assist layer (160 or 260) with the magnetization of the free layer 136 while a current is flowing through the MRAM cell 180. In one embodiment, the in-plane magnetization of the negative magnetic anisotropy assist layer (160 or 260) and the magnetization of the free layer 136 may remain in the same rotational vertical plane during switching of the magnetization of the free layer 136. The coupling between the magnetization of the free layer 136 and the horizontal (in-plane) component of the in-plane magnetization of the negative magnetic anisotropy assist layer (160 or 260) may be antiferromagnetic or ferromagnetic.

Referring to fig. 3A, a first configuration of a second exemplary MRAM cell in accordance with a second embodiment is schematically illustrated. The first configuration of the second exemplary MRAM cell 180 may be derived from the first configuration of the first exemplary MRAM cell 180 of fig. 2A by replacing the negative magnetic anisotropy assist layer 160 with a magnetic assist layer stack 460.

The magnetic assist layer stack 460 includes, from side to side, a first magnetic assist layer 162, an antiferromagnetically coupled spacer layer 164, and a second magnetic assist layer 166. The first magnetic assist layer 162 may be disposed on the first nonmagnetic metal spacer layer 150. First magnetic auxiliary layer 162Comprising a first magnetic material having a first magnetic anisotropy. In one embodiment, the first magnetic auxiliary layer 162 may have a first negative magnetic anisotropy having a substantially negative K₁The value provides a first in-plane magnetization for the first magnetic assist layer 162. The in-plane magnetization is a magnetization that is oriented in a horizontal plane perpendicular to the fixed vertical magnetization direction of the reference layer 132.

In one embodiment, thermal energy at room temperature (i.e., k)_BT, wherein k_BIs boltzmann constant, and T is 297.15 kelvin (which is room temperature)), the orientation-dependent component of the first magnetic anisotropy of the first magnetic auxiliary layer 162 may be zero or insignificant. For example, the maximum change in magnetic anisotropy energy per unit volume around a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the first magnetic assist layer 162, the magnetization of the first magnetic assist layer 162 precesses freely in a horizontal plane parallel to the interface between the first nonmagnetic metal spacer layer 150 and the first magnetic assist layer 162. In one embodiment, the magnetic energy of the first magnetic assist layer 162 may be invariant under rotation of the magnetization of the first magnetic assist layer 162 in the horizontal plane.

In one embodiment, a material with negative magnetic anisotropy, such as the first magnetic assist layer 162, has a hard axis parallel to the direction perpendicular to the major surfaces of the layers (i.e., the axis is perpendicular to the plane of the layers and parallel to the fixed vertical magnetization direction of the reference layer 132), while an easy magnetization plane is parallel to the plane of the layers (i.e., the easy magnetization plane is perpendicular to the fixed vertical magnetization direction of the reference layer 132 in FIG. 3A). In one embodiment, there is no easy axis direction in the easy magnetization plane.

In one embodiment, the first magnetic auxiliary layer 162 comprises a homogeneous negative magnetic anisotropy material. As used herein, "homogeneous" material refers to a material that has a uniform material composition throughout. In one embodiment, the first magnetic assist layer 162 includes and/or consists essentially of a cobalt-iridium alloy. The material composition of the cobalt-iridium alloy may be selected to provide negative magnetic anisotropy.In one embodiment, the cobalt-iridium alloy may include cobalt atoms at an atomic concentration in the range of 60% to 98% (e.g., 70% to 90%, such as 80%) and iridium atoms at an atomic concentration in the range of 40% to 2% (e.g., 30% to 10%, such as 20%). In one embodiment, the cobalt-iridium alloy contains only cobalt, iridium, and unavoidable impurities. In another embodiment, up to 5 atomic percent of elements other than cobalt and iridium may be added to the alloy. In the illustrative example, having the composition Co_0.8Ir_0.2Of cobalt-iridium alloy₁A value of about-0.6 x10⁶J/m³. In another embodiment, the first magnetic auxiliary layer 162 comprises and/or consists essentially of a cobalt-iron alloy having a hexagonal crystal structure. The material composition of the cobalt-iron alloy may be selected to provide negative magnetic anisotropy. In one embodiment, the cobalt-iron alloy may include cobalt atoms at an atomic concentration in the range of 80% to 99.8% (e.g., 90% to 99.5%, such as 99%) and iron atoms at an atomic concentration in the range of 20% to 0.2% (e.g., 10% to 0.5%, such as 1%). In the illustrative example, having the composition Co_0.99Fe_0.1Of cobalt-iron alloy₁A value of about-0.99 x10⁶J/m³. The thickness of the first magnetic auxiliary layer 162 may be in the range of 1nm to 10nm (e.g., 1.5nm to 6nm), although lesser and greater thicknesses may also be employed.

In another embodiment, the first magnetic assist layer 162 includes a plurality of repeating multi-layer stacks including a first magnetic material layer and a second magnetic material layer. The first magnetic material layer may include, and/or may consist essentially of, the first magnetic material. The second magnetic material layer may include, and/or may consist essentially of, a second magnetic material. The composition and thickness of each first magnetic material layer and the composition and thickness of each second magnetic material layer may be selected such that the multilayer stack provides in-plane magnetization, i.e., magnetization perpendicular to the fixed magnetization direction of the reference layer 132. The first magnetic auxiliary layer 162 may have a negative magnetic anisotropy with a substantially negative K₁Is a value of the first magnetic auxiliary layer 162For in-plane magnetization in a first plane.

In one embodiment, the first magnetic material layer comprises cobalt and the second magnetic material layer comprises iron. In one embodiment, the first magnetic material layer consists essentially of cobalt and the second magnetic material layer consists essentially of iron. The thickness of each first magnetic material layer may be in the range of 0.3nm to 1nm, and the thickness of each second magnetic material layer may be in the range of 0.3nm to 1 nm. The total number of repetitions within the first magnetic auxiliary layer 162 (i.e., the total number of pairs of first and second magnetic material layers) may be in a range of 2 to 20, such as 4 to 10. In one embodiment, the multi-layer stack includes a periodic repetition of a unit layer stack including a first magnetic material layer and a second magnetic material layer.

The anti-ferromagnetic coupling spacer layer 164 may be located between the first and second magnetic assist layers, e.g., on the first magnetic assist layer 162, on an opposite side of the first nonmagnetic metal spacer layer 150 located between the free layer 136 and the first magnetic assist layer 162. The antiferromagnetic coupling spacer layer 164 includes a metallic material that induces a Ruderman-Kittel-Kasuya-yosida (rkky) coupling interaction between the first magnetic assist layer 152 and, in one embodiment, the second magnetic assist layer 166 positioned on the antiferromagnetic coupling spacer layer 164. In the RKKY coupling interaction, the local inner d-or f-shell electron spins defining the magnetization direction of a ferromagnetic metal layer interact via conduction electrons in an intervening non-magnetic material layer to define the orientation of a preferred magnetization direction in another ferromagnetic metal layer. The thickness of the antiferromagnetic coupling spacer layer 164 may be selected such that the second in-plane magnetization direction of the second magnetic assist layer 166 is antiparallel to the first in-plane magnetization direction of the first magnetic assist layer 162. In other words, the antiferromagnetic coupling spacer layer 164 may have a thickness in a range that provides antiferromagnetic coupling between the first magnetization direction of the first magnetic assist layer 162 and the second magnetization direction of the second magnetic assist layer 166. In one embodiment, the antiferromagnetic coupling spacer layer 164 includes or consists essentially of ruthenium and has a thickness in the range of 0.1nm to 1.0 nm.

The second magnetic auxiliary layer 166 may be disposed on the antiferromagnetic couplingAnd a spacer layer 164. The second magnetic assist layer 166 includes a second magnetic material having a second magnetic anisotropy, which may be the same as or different from the material of the first magnetic assist layer 162. In one embodiment, the second magnetic auxiliary layer 166 may have a second negative magnetic anisotropy having a substantially negative K₁The value provides a second in-plane magnetization direction for the second magnetic assist layer 166. The in-plane magnetization direction is a magnetization direction that is oriented in a horizontal plane perpendicular to the fixed vertical magnetization direction of the reference layer 132.

In one embodiment, thermal energy at room temperature (i.e., k)_BT, wherein k_BIs boltzmann constant, and T is 297.15 kelvin (which is room temperature)), the orientation-dependent component of the magnetic anisotropy of the second magnetic auxiliary layer 166 may be zero or insignificant. For example, the maximum change in magnetic anisotropy per unit volume about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the second magnetic assist layer 166, the magnetization of the second magnetic assist layer 166 is free to precess in a horizontal plane parallel to the interface between the antiferromagnetically-coupled spacer layer 164 and the second magnetic assist layer 166. In one embodiment, the magnetic energy of the second magnetic assist layer 166 may be invariant under rotation of the magnetization of the second magnetic assist layer 166 in the horizontal plane.

In one embodiment, the second magnetic auxiliary layer 166 includes a homogeneous negative magnetic anisotropy material. In one embodiment, the second magnetic assist layer 166 includes and/or consists essentially of a cobalt-iridium alloy or a cobalt-iron alloy as described with respect to the first magnetic assist layer 162. The material composition of the cobalt-iridium alloy may be selected to provide negative magnetic anisotropy. In one embodiment, the cobalt-iridium alloy may include cobalt atoms at an atomic concentration in the range of 20% to 80% and iridium atoms at the atomic concentration of the balance. The thickness of the second magnetic auxiliary layer 166 may be in the range of 1nm to 10nm, for example 1.5nm to 6nm, although lesser and greater thicknesses may also be employed.

In another embodiment, the second magnetic auxiliary layer 166 includes a first magnetic layerA plurality of repeating multi-layer stacks of magnetic material layers and second magnetic material layers. The first magnetic material layer may include, and/or may consist essentially of, the first magnetic material. The second magnetic material layer may include, and/or may consist essentially of, a second magnetic material. The composition and thickness of each first magnetic material layer and the composition and thickness of each second magnetic material layer may be selected such that the multilayer stack provides in-plane magnetization, i.e., magnetization perpendicular to the fixed magnetization direction of the reference layer 132. The second magnetic auxiliary layer 166 may have a negative magnetic anisotropy with a substantially negative K₁The value provides a second in-plane magnetization for the second magnetic assist layer 166.

In one embodiment, the first magnetic material layer comprises cobalt and the second magnetic material layer comprises iron. In one embodiment, the first magnetic material layer consists essentially of cobalt and the second magnetic material layer consists essentially of iron. The thickness of each first magnetic material layer may be in the range of 0.3nm to 1nm, and the thickness of each second magnetic material layer may be in the range of 0.3nm to 1 nm. The total number of repetitions within second magnetic assist layer 166 (i.e., the total number of pairs of first and second magnetic material layers) may be in a range of 2 to 20, such as 4 to 10. In one embodiment, the multi-layer stack includes a periodic repetition of a unit layer stack including a first magnetic material layer and a second magnetic material layer.

In general, each of the first and second magnetic assist layers 162, 166 may be independently selected from a homogeneous negative magnetic anisotropy material, and a multiple-layer stack comprising a plurality of repetitions of a first magnetic material layer and a second magnetic material layer. In one embodiment, each of the first and second magnetic assist layers 162, 166 may be independently selected from a cobalt-iridium alloy, a cobalt-iron alloy having a hexagonal crystal structure and low iron content, or a multiple repeating multilayer stack comprising a unit stack of cobalt and iron layers. In one embodiment, at least one of the first and second magnetic assist layers 162, 166 includes a periodically repeating multi-layer stack including a unit layer stack, and the unit layer stack includes a first magnetic material layer and a second magnetic material layer.

In one embodiment, the non-magnetic metal cap layer 170 described above with respect to fig. 2A may be located over the second magnetic assist layer 166. A layer stack including layers of material from the SAF structure 120 to the nonmagnetic metal cap layer 170 may be deposited up or down, i.e., from the SAF structure 120 toward the nonmagnetic metal cap layer 170 or from the nonmagnetic metal cap layer 170 toward the SAF structure 120. The layer stack may be formed as a stack of continuous layers and may be subsequently patterned into a discrete patterned layer stack for each MRAM cell 180.

As in the first embodiment shown in fig. 2A, the MRAM cell 180 of the second embodiment shown in fig. 3A may include a first terminal 92 electrically connected to or including a portion of the bit line 90 (shown in fig. 1), and a second terminal 32 electrically connected to or including a portion of the word line 30 (shown in fig. 1). The positions of the first and second terminals may be switched such that the first terminal is electrically connected to the SAF structure 120 and the second terminal is electrically connected to the nonmagnetic metal cap layer 170.

Optionally, each MRAM cell 180 may include a dedicated steering device, such as an access transistor or diode, configured to activate the respective discrete patterned layer stack (120, 140, 150, 162, 164, 166, 170) upon application of a suitable voltage to the steering device. The steering device may be electrically connected between the patterned layer stack and one of the respective word lines 30 or bit lines 90 of the respective MRAM cell 180.

In one embodiment, the polarity of the voltage applied to the first terminal 92 may change depending on the polarity of the magnetization state to be programmed in the free layer 136. For example, a voltage of a first polarity may be applied to the first terminal 92 (relative to the second terminal 32) during a transition from an anti-parallel state to a parallel state, and a voltage of a second polarity (which is opposite the first polarity) may be applied to the first terminal 92 during a transition from the parallel state to the anti-parallel state. Moreover, variations in circuitry for activating the discrete patterned layer stack (120, 140, 150, 162, 164, 166, 170) are also contemplated herein.

The magnetization direction of the free layer 136 may be switched (i.e., from up to down, or vice versa) by passing a current through the stack of discrete patterned layers (120, 140, 150, 162, 164, 166, 170). The magnetization direction of the free layer 136 may precess around the vertical direction (i.e., the direction of flow of current) during the programming process until the magnetization direction flips 180 degrees, at which time the flow of current stops.

For example, upon application of a current through the first magnetic assist layer 162, the antiferromagnetically-coupled spacer layer 164, and the second magnetic assist layer 166 during programming, the first magnetization direction of the first magnetic assist layer 162 and the second magnetization direction of the second magnetic assist layer 166 are free to precess about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132 while maintaining antiferromagnetic alignment therebetween. The fixed vertical magnetization direction of the reference layer 132 maintains the same orientation upon application of a current through the reference layer 132.

During operation of the magnetic memory device, current may flow through the spin valve 140, the first nonmagnetic metal spacer layer 150, the first magnetic assist layer 162, the antiferromagnetically coupled spacer layer 164, and the second magnetic assist layer 166.

In one embodiment, the first magnetic assist layer 162, the antiferromagnetically coupled spacer layer 164, and the second magnetic assist layer 166 help to maintain the electron spin of the free layer more in-plane to counteract the spin torque that tilts the electron spin out-of-plane. Due to the antiferromagnetic coupling, the antiferromagnetically-coupled auxiliary film comprising the combination of the first magnetic auxiliary layer 162, the antiferromagnetically-coupled spacer layer 164, and the second magnetic auxiliary layer 166 further facilitates a single domain within each layer, thus maintaining a more uniform magnetization during the process of auxiliary free layer 136 switching, which is desirable. An additional benefit of this embodiment is that flux confinement within the tri-layer auxiliary film can minimize stray fields from the anti-ferromagnetically coupled auxiliary film on the free layer 136, which will help improve the thermal stability and data retention of the MRAM cell 180.

In one embodiment, the combination of the first magnetic assist layer 162, the antiferromagnetically-coupled spacer layer 164, and the second magnetic assist layer 166 is configured to provide an initial non-zero moment to the magnetization of the free layer 136 during an initial phase of precession of the magnetization of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132 after an initiation current flows through the MRAM cell 180. The MRAM cell 180 is configured to provide magnetic coupling between the magnetization direction of the free layer 136 and the first magnetization direction of the first magnetic assist layer 162 during precession of the magnetization direction of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132, and to provide synchronous precession of the first magnetization direction of the first magnetic assist layer 162 and the magnetization direction of the free layer 136 while a current flows through the MRAM cell 180.

Referring to fig. 3B, a second configuration of the second exemplary spin-transfer torque MRAM cell 180 can be derived from the first configuration of the second exemplary spin-transfer torque magnetic memory device shown in fig. 3A by replacing the first magnetic assist layer 162 having a first in-plane magnetization with a first magnetic assist layer 262 comprising a first ferromagnetic material that does not have uniaxial magnetic anisotropy, and replacing the second magnetic assist layer 166 having a second in-plane magnetization with a second magnetic assist layer 266 comprising a second ferromagnetic material that does not have uniaxial magnetic anisotropy. In one embodiment, the first and second magnetic assist layers (262, 266) may have a non-uniaxial magnetic anisotropy. As used herein, "non-uniaxial magnetic anisotropy" refers to a magnetic anisotropy in which the minimum value of the magnetic anisotropy energy per volume does not occur in the direction of θ ═ 0, θ ═ pi, or θ ═ pi/2 (all values for Φ). In other words, the orientation of the magnetization in the magnetic film having non-uniaxial magnetic anisotropy is not a vertical direction perpendicular to the plane of the magnetic film or all in-plane directions of the set.

The thickness of the antiferromagnetic coupling spacer layer 164 is selected to provide antiferromagnetic coupling between the first magnetization of the first magnetic assist layer 262 and the second magnetization of the second magnetic assist layer 266. Thus, the first magnetization of the first magnetic assist layer 262 and the second magnetization of the second magnetic assist layer 266 may be antiferromagnetically coupled. Furthermore, the change in energy of magnetic anisotropy per volume as a function of the spatial orientation of the first and second magnetizations (which remain antiparallel to each other) can be correlated with thermal energy at room temperature (i.e., k)_BT, where T is 297.15 kelvin) is equal or less than the thermal energy at room temperature.

Each of the first and second magnetic auxiliary layers 262 and 266 includes a respective soft magnetic material that may be the same or different that does not have uniaxial magnetic anisotropy. In one embodiment, each of the first and second magnetic auxiliary layers 262 and 266 includes and/or consists essentially of a respective material selected from a CoFe alloy having more than 40 atomic percent iron (e.g., 45 to 70 atomic percent iron) and a balance of cobalt or a NiFe alloy.

The magnetization direction of the free layer 136 may be switched (i.e., from up to down, or vice versa) by passing a current through the stack of discrete patterned layers (120, 140, 150, 262, 164, 266, 170). The magnetization direction of the free layer 136 may precess around the vertical direction (i.e., the direction of flow of current) during the programming process until the orientation of the magnetization direction reverses 180 degrees, at which point the flow of current stops.

The magnetization direction of the free layer 136 can be programmed by flowing a current through the discrete patterned layer stack (120, 140, 150, 262, 164, 266, 170), for example, from a parallel state parallel to the fixed vertical magnetization direction of the reference layer 132 to an anti-parallel state anti-parallel to the fixed magnetization direction of the reference layer 132 or vice versa. For example, upon application of a current through the first magnetic assist layer 262, the antiferromagnetic coupling spacer layer 164, and the second magnetic assist layer 266 during programming, the first magnetization direction of the first magnetic assist layer 262 and the second magnetization direction of the second magnetic assist layer 266 precess freely about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132 at an angle between 0 degrees and 180 degrees relative to the vertical axis while maintaining antiferromagnetic alignment therebetween. As the tilt angle changes from 0 degrees to 180 degrees or from 180 degrees to 0 degrees relative to the vertical axis during programming of the MRAM cell 180, the tilt angles of the first magnetization direction of the first magnetic assist layer 262 and the second magnetization direction of the second magnetic assist layer 266 during programming are synchronized with the tilt angle of the magnetization direction of the free layer 136. The fixed vertical magnetization direction of the reference layer 132 maintains the same orientation after applying a current through the reference layer 132.

During operation of the magnetic memory device, a current may flow through the spin valve 140, the first nonmagnetic metal spacer layer 150, the first magnetic assist layer 262, the antiferromagnetically coupled spacer layer 164, and the second magnetic assist layer 266. The combination of the first magnetic assist layer 262, the antiferromagnetically-coupled spacer layer 164, and the second magnetic assist layer 266 is configured to provide an initial non-zero moment to the magnetization direction of the free layer 136 during an initial phase of precession of the magnetization direction of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132 after an initial current flows through the MRAM cell 180. The MRAM cell 180 is configured to provide magnetic coupling between the magnetization direction of the free layer 136 and the first magnetization direction of the first magnetic assist layer 262 during precession of the magnetization direction of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization direction of the reference layer 132, and to provide synchronous precession of the first magnetization direction of the first magnetic assist layer 262 and the magnetization direction of the free layer 136 while a current flows through the MRAM cell 180.

Referring to fig. 3C, a third configuration of the second exemplary spin transfer torque MRAM cell 180 may be derived from the first configuration of the second exemplary spin transfer torque MRAM cell 180 of fig. 3A by interposing a second nonmagnetic metal spacer layer 190 and a pinned magnetization layer 192 between the second magnetic assist layer 166 and the nonmagnetic cap layer 170.

A second nonmagnetic metal spacer layer 190 may be located on the second magnetic assist layer 166 on the opposite side of the antiferromagnetic coupling spacer layer 164. The second nonmagnetic metal spacer layer 190 contains a nonmagnetic material such as Cu, Ag, AgSn, Cr, Ru, Ta, TaN, or CuN. In one embodiment, the second nonmagnetic metal spacer layer 190 may comprise a conductive metal material. The thickness of the second nonmagnetic metal spacer layer 190 may be in the range of 0.2nm to 2nm, although lesser and greater thicknesses may also be employed. The second nonmagnetic metal spacer layer 190 may comprise the same material as the first nonmagnetic metal spacer layer 150, or may comprise a material different from the material of the first nonmagnetic metal spacer layer 150.

The pinned magnetization layer 192 is a magnetic layer having positive uniaxial magnetic anisotropy. In other words, K₁Is positive and the term K₁sin²Theta dominates all other higher-order terms and depends on sin (n phi) in the amount of per-volume magnetic anisotropy energy of the material of pinned magnetization layer 192) (or cos (n φ)) terms. The positive uniaxial magnetic anisotropy of the pinned magnetization layer 192 provides a magnetization that is parallel or antiparallel to the fixed vertical magnetization of the reference layer 132. In one embodiment, K of pinned magnetization layer 192₁May be greater than K of the free layer 136₁Such that the magnetization of the pinned magnetization layer 192 remains pinned along the vertical direction (i.e., perpendicular to the interface between the layers of the discrete patterned layer stack (120, 140, 150, 162, 164, 166, 190, 192, 170)) during programming of the MRAM cell 180. The magnetization of the pinned magnetization layer 192 may remain parallel or antiparallel to the magnetization of the reference layer 132.

In one embodiment, the pinned magnetization layer 192 may comprise a Co/Ni or Co/Pt multilayer structure. The pinned magnetization layer 192 may additionally include a thin nonmagnetic layer composed of tantalum having a thickness of 0.2nm to 0.5nm, and a thin CoFeB layer (having a thickness in the range of 0.5nm to 2 nm). The pinned magnetization layer 192 may cause in-plane magnetization oscillation of the second magnetic assist layer 166. The out-of-plane oscillation of the magnetization of the second magnetic assist layer 166 may generate a rotating spin torque on the magnetization of the free layer 136 during programming, and thus may facilitate switching of the magnetization of the free layer 136 with less current through the discrete patterned layer stack (120, 140, 150, 162, 164, 166, 190, 192, 170). In one embodiment, the combination of the magnetizations of the pinned magnetization layer 192, the first magnetic assist layer 162, and the second magnetic assist layer 166 applies a non-horizontal, non-vertical magnetic field (i.e., a field neither parallel nor perpendicular to the fixed magnetization direction of the reference layer 132) to the magnetization of the free layer 136 to reduce the magnitude of the required current through the discrete patterned layer stack (120, 140, 150, 162, 164, 166, 190, 192, 170) during switching of the magnetization of the free layer 136.

Referring to fig. 3D, a fourth configuration of the second exemplary spin-transfer torque MRAM cell 180 may be derived from the third configuration of the second exemplary spin-transfer torque magnetic memory device shown in fig. 3C by replacing the first magnetic assist layer 162 having a first in-plane magnetization with a first magnetic assist layer 262 comprising a first ferromagnetic material that does not have uniaxial magnetic anisotropy, and replacing the second magnetic assist layer 166 having a second in-plane magnetization with a second magnetic assist layer 266 comprising a second ferromagnetic material that does not have uniaxial magnetic anisotropy.

The thickness of the antiferromagnetic coupling spacer layer 164 is selected to provide antiferromagnetic coupling between the first magnetization of the first magnetic assist layer 262 and the second magnetization of the second magnetic assist layer 266. Thus, the first magnetization of the first magnetic assist layer 262 and the second magnetization of the second magnetic assist layer 266 may be antiferromagnetically coupled. Furthermore, the change in energy of magnetic anisotropy per volume as a function of the spatial orientation of the first and second magnetizations (which remain antiparallel to each other) can be correlated with thermal energy at room temperature (i.e., k)_BT, where T is 297.15 kelvin) is equal or less than the thermal energy at room temperature.

The second exemplary spin transfer torque MRAM cell 180 can be individually programmed and read. Reading (i.e., sensing) the magnetization state of the free layer 136 may be performed by applying a read bias voltage across the first and second terminals 92, 32 of the stack of discrete patterned layers 120, 140, 150, (162 or 262), 164, (166 or 266), (190, 192), 170 or 120, 140, 150, (162 or 262), 164, (166 or 266), (190, 192), 170. The parallel or anti-parallel alignment between the magnetizations of the free layer 136 and the reference layer 132 determines the resistance of the selected discrete patterned layer stack in each MRAM cell 180, and thus determines the magnitude of the current flowing between the first terminal 92 and the second terminal 32. The magnitude of the current may be sensed to determine the magnetization state of the free layer 136 and the data encoded by the detected magnetization state.

Referring to fig. 4A, a first configuration of a third exemplary STT MRAM cell 180 in accordance with a third embodiment is schematically illustrated. The first configuration of the second exemplary MRAM cell 180 may be derived from the first configuration of the first exemplary MRAM cell 180 of fig. 2A by replacing the first magnetic assist layer 160 with a magnetic assist layer stack (e.g., a spin torque oscillator stack) 360.

The magnetic assist layer stack 360 includes, from side to side, a first magnetic assist layer (e.g., spin torque layer) 362, a nonmagnetic spacer layer 364, and a second magnetic assist layer (e.g., spin polarization layer) 366.

The spin torque layer 362 includes a first magnetic material having a first tapered magnetization (e.g., magnetization direction) with respect to a vertical direction that is parallel to the fixed vertical magnetization (e.g., magnetization direction) of the reference layer 132. As used herein, "tapered magnetization" refers to a rotational magnetization (e.g., magnetization direction) having an angle greater than zero but less than 90 degrees (e.g., 10 to 80 degrees, such as 30 to 60 degrees) with respect to an axis parallel to a fixed vertical magnetization (e.g., magnetization direction) of the reference layer 132.

Tapered magnetization can be provided for various symmetric types of magnetic anisotropy energy per volume. For example, a ferromagnetic film having six-sided rotational symmetry about an axis perpendicular to the plane of the ferromagnetic film can have functional dependence on the tilt angle θ and azimuth angle φ relative to the vertical axis of the ferromagnetic film with a functional dependence of the form: E/V ═ K₁sin²θ+K₂sin⁴θ+K₃sin⁶θ cos (6 φ). If K is₁Is negative and K₂Greater than K₁And/2, the ferromagnetic film has a bidirectional cone of easy magnetization direction at two values of q. Cone angle theta of bidirectional cone easy to magnetize_c1And theta_c2Through theta_c2＝π-θ_c1And (4) correlating.

Ferromagnetic films with different magnetic anisotropy symmetries can provide tapered magnetization in a similar manner. For example, a ferromagnetic film with magnetic anisotropy energy per volume with tetrahedral symmetry may have a functional dependence on the tilt angle θ and azimuth angle φ relative to the vertical axis, of the form: E/V ═ K₁sin²θ+K₂sin⁴θ+K₃sin⁴θ sin (2 φ). Ferromagnetic films with rhombohedral symmetry having magnetic anisotropy energy per volume can have a functional dependence on the tilt angle θ and azimuth angle φ from the vertical axis of the form: E/V ═ K₁sin²θ+K₂sin⁴θ+K₃cosθsin³θ cos (3 φ). If K is₃Is zero or is 1/2k_BT is not significant (where k is_BBoltzmann's constant and T is room temperature in kelvin, i.e., 297.15 in magnetic anisotropy energy per volume), the conical magnetization is free to rotate about a vertical axis (e.g.,high frequency oscillation).

In one embodiment, thermal energy at room temperature (i.e., k)_BT, wherein k_BIs boltzmann constant, and T is 297.15 kelvin (which is room temperature)), the orientation-dependent component of the magnetic anisotropy of the spin torque layer 362 may be zero or insignificant. For example, the maximum change in magnetic anisotropy energy per unit volume around a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the spin torque layer 362, the tapered magnetization of the spin torque layer 362 is free to precess in a horizontal plane parallel to the interface between the first nonmagnetic metal spacer layer 150 and the spin torque layer 362. In one embodiment, the magnetic energy of the spin torque layer 362 may be invariant under the conditions of magnetization rotation of the spin torque layer 362 in the horizontal plane.

The spin torque layer 362 can include any ferromagnetic film that provides a tapered magnetization. For example, the spin torque layer 362 can include a tapered magnetization material, e.g., a rare earth element such as neodymium, erbium, or an alloy of at least one rare earth magnetic element with a non-rare earth element such as iron, boron, cobalt, copper, and/or zirconium. In one embodiment, the spin torque layer 362 can include a homogeneous tapered magnetization material, i.e., a homogeneous material that provides tapered magnetization. As used herein, "homogeneous" material refers to a material that has a uniform material composition throughout. The thickness of the spin torque layer 362 can be in the range of 0.6nm to 10nm, such as 1.2nm to 5nm, although lesser and greater thicknesses can also be used.

The nonmagnetic spacer layer 364 may be located on the spin torque layer 362, on the opposite side of the first nonmagnetic metal spacer layer 150. In one embodiment, the nonmagnetic spacer layer 364 comprises a metallic material that induces a Ruderman-Kittel-Kasuya-yosida (rkky) coupling interaction between a first magnetic assist layer (e.g., spin torque layer) 362 and a second magnetic assist layer (e.g., spin polarizing layer) 366 located on the opposite side of the nonmagnetic spacer layer 364 from the first magnetic assist layer 362. In one embodiment, the nonmagnetic spacer layer 364 comprises, and/or consists essentially of, ruthenium and may have a thickness in the range of 0.1nm to 1.0 nm.

In one embodiment, a second magnetic assist layer (e.g., spin polarizing layer) 366 may be disposed on the nonmagnetic spacer layer 364. In another embodiment, the order of formation of the spin torque layer 362 and the spin polarizing layer 366 may be reversed such that the spin polarizing layer 366 is positioned closer to the free layer 136 than the spin torque layer 362. In general, the spin torque oscillator stack (e.g., the auxiliary layer stack) 360 includes a nonmagnetic spacer layer 364 located between the spin torque layer 362 and the spin polarizing layer 366.

The spin polarizing layer 366 has a tapered magnetization referred to herein as a second tapered magnetization. The spin polarizing layer 366 may comprise a single layer of magnetic material or multiple layers of magnetic material. The second taper magnetization of the spin polarizing layer 366 can be provided by a single layer of magnetic material having a second taper magnetization, or can be provided by a set of layers of ferromagnetic material having in-plane magnetization and perpendicular (i.e., vertical or axial) magnetization. The in-plane magnetization component of the second magnetic material is perpendicular to the fixed vertical magnetization (e.g., magnetization direction) of the reference layer 132. The in-plane magnetization component of the second magnetic material is antiferromagnetically coupled to the in-plane component of the first taper magnetization.

FIG. 4A shows an embodiment in which the spin polarizing layer 366 is composed of a single layer of ferromagnetic material with a second tapered magnetization with respect to the vertical direction parallel to the fixed vertical magnetization of the reference layer 132. In one embodiment, the azimuthal dependent component of the magnetic anisotropy of the spin polarizing layer 366 may be zero, or related to thermal energy at room temperature (i.e., k)_BT, wherein k_BBoltzmann constant and T of 297.15 kelvin, which is room temperature), were less significant. For example, the maximum change in magnetic anisotropy energy per unit volume around a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 may be less than 1/2 times the thermal energy at room temperature. In such cases, upon application of a current through the spin polarizing layer 366, the tapered magnetization of the spin polarizing layer 366 precesses freely in a horizontal plane parallel to the interface between the first nonmagnetic spacer layer 150 and the spin torque layer 362. In one embodiment, the magnetic energy of the spin polarizing layer 366 can spin in the horizontal planeThe magnetization of the polarizing layer 366 is unchanged under the rotation condition.

In one embodiment, the spin polarizing layer 366 can include any ferromagnetic film that provides a tapered magnetization. For example, the spin polarizing layer 366 can include a tapered magnetized material, e.g., a rare earth element such as neodymium, erbium, or an alloy of at least one rare earth magnetic element with a non-rare earth element such as iron, boron, cobalt, copper, and/or zirconium. In one embodiment, the spin polarizing layer 366 can comprise a homogeneous taper magnetization material, i.e., a homogeneous material that provides a taper magnetization. The ferromagnetic materials of the spin torque layer 362 and the spin polarizing layer 366 can be the same or different. The thickness of the spin polarizing layer 366 may be in the range of 0.6nm to 10nm, such as 1.2nm to 5nm, although lesser and greater thicknesses may also be employed.

In the case where the magnetization of the spin polarization layer 366 is a tapered magnetization (i.e., a second tapered magnetization), the second tapered magnetization of the spin polarization layer 366 can be coupled with the first tapered magnetization of the spin torque layer 362 in various modes.

As shown in fig. 4A, the spin polarizing layer 366 may be provided as a single spin polarizing layer of homogeneous composition and may have a second tapered magnetization with respect to the vertical direction. In general, a single spin polarizing layer may have an axial magnetization component that is parallel or antiparallel to the axial magnetization component of the first tapered magnetization of the spin torque layer 362. In some embodiments, the spin polarizing layer 366 can have an axial magnetization component that is antiparallel to the axial component of the tapered magnetization of the spin torque layer 362 (i.e., a vertical magnetization component). In some embodiments, the spin polarizing layer 366 can have an axial magnetization component (i.e., a vertical magnetization component) that is parallel to the axial component of the tapered magnetization of the spin torque layer 362.

In one embodiment, the nonmagnetic metal cap layer 170 may be located above the spin polarizing layer 366. The nonmagnetic metal cap layer 170 may comprise nonmagnetic conductive materials such as W, Ti, Ta, WN, TiN, TaN, Ru, and Cu. The thickness of the nonmagnetic metal cap layer 170 may be in the range of 1nm to 20nm, although lesser and greater thicknesses may also be employed.

A layer stack including layers of material from the SAF structure 120 to the nonmagnetic metal cap layer 170 may be deposited up or down, i.e., from the SAF structure 120 toward the nonmagnetic metal cap layer 170 or from the nonmagnetic metal cap layer 170 toward the SAF structure 120. The layer stack may be formed as a stack of continuous layers and may be subsequently patterned into a discrete patterned layer stack for each MRAM cell 180.

As in the first embodiment shown in FIG. 2A, MRAM cell 180 may include a first terminal 92 electrically connected to or including a portion of bit line 90 (shown in FIG. 1), and a second terminal 32 electrically connected to or including a portion of word line 30 (shown in FIG. 1). The positions of the first and second terminals may be switched such that the first terminal is electrically connected to the SAF structure 120 and the second terminal is electrically connected to the nonmagnetic metal cap layer 170.

Alternatively, each MRAM cell 180 may include a dedicated steering device, such as an access transistor or diode, configured to activate the respective discrete patterned layer stack (120, 140, 150, 360, 170) upon application of a suitable voltage to the steering device. The steering device may be electrically connected between the patterned layer stack and one of the respective word lines 30 or bit lines 90 of the respective MRAM cell 180.

In one embodiment, the polarity of the voltage applied to the first terminal 92 may change depending on the polarity of the magnetization state to be programmed in the free layer 136. For example, a voltage of a first polarity may be applied to the first terminal 92 (relative to the second terminal 32) during a transition from an anti-parallel state to a parallel state, and a voltage of a second polarity (which is opposite the first polarity) may be applied to the first terminal 92 during a transition from the parallel state to the anti-parallel state. Moreover, variations in circuitry for activating the discrete patterned layer stack (120, 140, 150, 360, 170) are also contemplated herein.

The magnetization direction of the free layer 136 may be switched (i.e., from up to down, or vice versa) by passing a current through the stack of discrete patterned layers (120, 140, 150, 362, 364, 366, 170). The magnetization direction of the free layer 136 may precess around the vertical direction (i.e., the direction of flow of current) during the programming process until the magnetization direction flips 180 degrees, at which time the flow of current stops.

For example, after applying a current through the spin torque layer 362, the nonmagnetic spacer layer 364, and the spin polarizing layer 366 during programming, the first tapered magnetization of the spin torque layer 362 and the second tapered magnetization of the spin polarizing layer 366 precess freely about a vertical axis that is parallel to the fixed vertical magnetization of the reference layer 132. The fixed vertical magnetization of the reference layer 132 maintains the same orientation after applying a current through the reference layer 132. The first and second tapered magnetizations may have the same or different taper angles.

During operation of the MRAM cell, a current may flow through the spin valve 140, the first nonmagnetic metal spacer layer 150, the spin torque layer 362, the nonmagnetic spacer layer 364, and the spin polarization layer 366. The spin torque oscillator stack 360, which includes the combination of the spin torque layer 362, the nonmagnetic spacer layer 364, and the spin polarization layer 366, is configured to provide an initial non-zero torque to the magnetization of the free layer 136 during an initial phase in which the magnetization of the free layer 136 precesses around a vertical axis parallel to the fixed vertical magnetization of the reference layer 132 after an initiation current flows through the MRAM cell 180. The MRAM cell 180 is configured to provide magnetic coupling between the magnetization of the free layer 136 and the first magnetization of the spin torque layer 362 during precession of the magnetization of the free layer 136 about a vertical axis parallel to the fixed vertical magnetization of the reference layer 132, and to provide synchronous precession of the first magnetization of the spin torque layer 362 and the magnetization of the free layer 136 while a current flows through the MRAM cell 180.

Referring to fig. 4B, a second configuration of a third exemplary spin transfer torque MRAM cell 180 is shown. The spin polarizing layer 366 includes a layer stack of multiple layers (3662, 3664, 3666) having different material compositions. The spin polarizing layer 366 includes a layer stack of a first spin polarization component layer 3662 having a magnetization that is the same as the in-plane magnetization component of the second tapered magnetization. The first spin polarization component layer 3662 may have zero magnetic anisotropy or negative uniaxial magnetic anisotropy such that the magnetization of the first spin polarization component layer 3662 is parallel to the interfaces between the layers of the nonmagnetic spacer layer 364.

In one embodiment, the first spin polarization component layer 3662 includes and/or consists essentially of a cobalt-iridium alloy. The material composition of the cobalt-iridium alloy may be selected to provide negative uniaxial magnetic anisotropy. In one embodiment, the cobalt-iridium alloy may beContaining cobalt atoms at an atomic concentration in the range of 60% to 98% (e.g., 70% to 90%), and iridium atoms at the atomic concentration of the balance. In the illustrative example, having the composition Co_0.8Ir_0.2Of cobalt-iridium alloy₁A value of about-0.6 x106J/m³. In another embodiment, the first spin polarization component layer 3662 includes and/or consists essentially of a cobalt-iron alloy. The material composition of the cobalt-iron alloy may be selected to provide negative uniaxial magnetic anisotropy. In one embodiment, the cobalt-iron alloy may include cobalt atoms at an atomic concentration in the range of 80% to 99.8% (e.g., 90% to 99.5%), and iron atoms at the atomic concentration of the balance. In the illustrative example, having the composition Co_0.99Ir_0.1Of cobalt-iron alloy₁A value of about-0.99 x106J/m³. In another embodiment, the first spin polarization component layer 3662 includes and/or consists essentially of a cobalt-iron-boron (CoFeB) alloy. The thickness of the first spin polarization component layer 3662 may be in the range of 1nm to 10nm, such as 1.5nm to 6nm, although lesser and greater thicknesses may also be employed.

In another embodiment, the first spin polarization component layer 3662 includes a multi-layer stack containing a plurality of repetitions of a first magnetic material layer and a second magnetic material layer. The first magnetic material layer may include, and/or may consist essentially of, the first magnetic material. The second magnetic material layer may include, and/or may consist essentially of, a second magnetic material.

In one embodiment, the first magnetic material layer comprises cobalt and the second magnetic material layer comprises iron. In one embodiment, the first magnetic material layer consists essentially of cobalt and the second magnetic material layer consists essentially of iron. The thickness of each first magnetic material layer may be in the range of 0.3nm to 1nm, and the thickness of each second magnetic material layer may be in the range of 0.3nm to 1 nm. The total number of repetitions within the first spin polarization component layer 3662 (i.e., the total number of pairs of the first and second magnetic material layers) may be in the range of 2 to 20, such as 4 to 10. In one embodiment, the multilayer stack includes a first magnetic layerThe periodic repetition of the unit layer stack of the material layer and the second magnetic material layer. In an illustrative example, a repeating interleaved cobalt-iron multilayer stack comprising a unit layer stack consisting of cobalt and iron layers having the same thickness may have about-1.1 x10⁶J/m³K1 value of (a).

The spin polarizing layer 366 further includes a second spin polarization component layer 3666 having an axial magnetization that is parallel or antiparallel to the vertical direction of the reference layer 132. In one embodiment, the second spin polarization component layer 3666 comprises a multilayer stack of cobalt layers and platinum or palladium layers. The second spin polarization component layer 3666 may have a positive uniaxial magnetic anisotropy such that the magnetization of the second spin polarization component layer 3666 is axial, i.e., perpendicular to the interfaces between the layers of the MRAM cell 180. The axial magnetization of the second spin polarization component layer 3666 may be parallel or antiparallel to the fixed vertical direction of the magnetization of the reference layer 132.

In one embodiment, the second spin polarization component layer 3666 may be vertically spaced apart from the first spin polarization component layer 3662 by an optional nonmagnetic spacer layer 3664. The nonmagnetic spacer layer 3664 may comprise a nonmagnetic metal material such as Cu, Ag, AgSn, Cr, Ru, Ta, TaN, or CuN. In one embodiment, the first spin polarization component layer 3662 may contact the nonmagnetic spacer layer 364.

In this case, the combined magnetization of the first spin polarization component layer 3662 and the second spin polarization component layer 3666 provides a second tapered magnetization that is free to rotate (e.g., oscillate) about a vertical axis during programming of the MRAM cell 180. In this case, the combined magnetization of the first spin polarization component layer 3662 and the second spin polarization component layer 3666 provides an additional taper magnetization (i.e., a second taper magnetization) that is coupled to the first taper magnetization of the spin torque layer 362. During programming, upon application of a current through the spin torque layer 362, the nonmagnetic spacer layer 364, and the spin polarizing layer 366, the second tapered magnetization and the first tapered magnetization precess about a vertical axis parallel to the vertical direction of the magnetization of the reference layer 132. The first and second tapered magnetizations may have the same or different taper angles.

Referring to fig. 4C, a third configuration of the example spin transfer torque MRAM cell 180 in accordance with embodiments of the present disclosure may be derived from the second configuration of the example spin transfer torque MRAM cell 180 by exchanging the positions of the first spin polarization component layer 3662 and the second spin polarization component layer 3666. In this case, the second spin polarization component layer 3666 may contact the nonmagnetic spacer layer 364. The example spin transfer torque MRAM cell 180 in the third configuration may operate in the same manner as the example spin transfer torque MRAM cell 180 in the first and second configurations.

Fig. 4D illustrates a fourth configuration of an exemplary spin transfer torque MRAM cell 180 in accordance with embodiments of the present disclosure. The fourth configuration of the example spin-transfer torque MRAM cell 180 can be derived from the first, second, and third configurations of the example spin-transfer torque MRAM cell 180 by replacing the spin torque layer 362 having the first tapered magnetization with a spin torque layer 462 having an in-plane magnetization (i.e., having a negative uniaxial magnetic anisotropy). In other words, the axial component of the magnetization of the spin torque layer 462 can be zero, and the magnetization (e.g., magnetization direction) of the spin torque layer 462 can consist of an in-plane component (i.e., zero taper angle). In this case, the total magnetization of the spin torque layer 462 is the same as the in-plane magnetization component of the spin torque layer 462. In this configuration, the taper angles of the first and second magnetizations are different.

In one embodiment, the spin torque layer 462 comprises a homogeneous negative uniaxial magnetic anisotropy material. As used herein, "homogeneous" material refers to a material that has a uniform material composition throughout. In one embodiment, the spin torque layer 462 comprises and/or consists essentially of a cobalt-iridium alloy. The material composition of the cobalt-iridium alloy may be selected to provide negative uniaxial magnetic anisotropy. In one embodiment, the cobalt-iridium alloy may include cobalt atoms at an atomic concentration in the range of 60% to 98% (e.g., 70% to 90%), and iridium atoms at the atomic concentration of the balance. In the illustrative example, having the composition Co_0.8Ir_0.2Of cobalt-iridium alloy₁A value of about-0.6 x106J/m³. In another embodiment, the spin torque layer 462 comprises and/or consists essentially of a cobalt-iron alloy. The material composition of the cobalt-iron alloy can be selected toFor negative uniaxial magnetic anisotropy. In one embodiment, the cobalt-iron alloy may include cobalt atoms at an atomic concentration in the range of 80% to 99.8% (e.g., 90% to 99.5%), and iron atoms at the atomic concentration of the balance. In the illustrative example, having the composition Co_0.99Ir_0.1Of cobalt-iron alloy₁A value of about-0.99 x106J/m³. In another embodiment, the spin torque layer 462 comprises and/or consists essentially of a cobalt-iron-boron (CoFeB) alloy. The thickness of the spin torque layer 462 can be in the range of 1nm to 10nm, such as 1.5nm to 6nm, although lesser and greater thicknesses can also be used.

In another embodiment, the spin torque layer 462 includes a multiple repeating multilayer stack including a first magnetic material layer and a second magnetic material layer. The first magnetic material layer may include, and/or may consist essentially of, the first magnetic material. The second magnetic material layer may include, and/or may consist essentially of, a second magnetic material.

In one embodiment, the first magnetic material layer comprises cobalt and the second magnetic material layer comprises iron. In one embodiment, the first magnetic material layer consists essentially of cobalt and the second magnetic material layer consists essentially of iron. The thickness of each first magnetic material layer may be in the range of 0.3nm to 1nm, and the thickness of each second magnetic material layer may be in the range of 0.3nm to 1 nm. The total number of repetitions within the spin torque layer 462 (i.e., the total number of pairs of the first and second magnetic material layers) may be in a range of 2 to 20, such as 4 to 10. In one embodiment, the multi-layer stack includes a periodic repetition of a unit layer stack including a first magnetic material layer and a second magnetic material layer. In an illustrative example, a repeating interleaved cobalt-iron multilayer stack comprising a unit layer stack consisting of cobalt and iron layers having the same thickness may have about-1.1 x10⁶J/m³K1 value of (a). The spin torque layer 462 can be used with any of the spin polarizing layers 366 described above with respect to the first through third embodiments.

5A-5C, an exemplary Spin Orbit Torque (SOT) magnetic memory device is illustrated, in accordance with a fourth embodiment of the present disclosure. In one embodiment, the SOT magnetic memory device of FIGS. 5A-5C may include SOTMRAM memory cells 280 that include only metallic materials used for operation at low temperatures, such as in a quantum computing environment. In one embodiment, the SOT magnetic memory device of FIGS. 5A-5C uses a two-step programming operation. FIG. 5A shows the SOT magnetic memory device during a first step of a two-step programming operation, and FIG. 5B shows the SOT magnetic memory device during a second step of the two-step programming operation. FIG. 5C illustrates an SOT magnetic memory device during a sensing (e.g., read) operation.

The magnetic junction in the SOT magnetic memory device includes a combination of the SAF structure 120 and the spin valve 140. The combination of the SAF structure 120 and the spin valve 140 can include, from side to side, a fixed ferromagnetic layer 112, an antiferromagnetic coupling layer 114, a reference layer 132, a non-magnetic metal barrier layer 134, and a free layer 136. The combination of the SAF structure 120 and the spin valve 140 can form the SOTMRAM cell 280 in the same configuration as in the first, second and third embodiment MRAM cells 180. For example, the reference layer 132 may have a fixed magnetization direction, and the non-magnetic metallic barrier layer 134 may be located between the reference layer 132 and the free layer 136. The non-magnetic metal barrier layer 134 may be composed of at least one metal material selected from Cu, Ag, AgSn, Cr, Ru, Ta, TaN, or CuN to achieve low temperature operation. The free layer 136 has a bi-stable magnetization state that includes a parallel state having a magnetization parallel to the fixed vertical magnetization and an anti-parallel state having a magnetization anti-parallel to the fixed vertical magnetization.

In one embodiment, the metal line 200 is disposed directly on the surface of the free layer 136. The metal line 200 may include and/or may consist essentially of at least one heavy element metal to maximize spin transfer across the interface between the free layer 136 and the metal line 200. In one embodiment, the elemental metal may have an atomic number in the range of 72 to 79 (and including 72 and 79). For example, the at least one elemental metal may comprise one or more of Hf, Ta, W, Re, Os, Ir, Pt, and Au. In one embodiment, the metal line 200 may comprise, and/or consist essentially of, tungsten. In other words, in one embodiment, the metal line 200 is made of an undoped and unalloyed elemental metal except for inevitable impurities.

The first electrode 910 may be located at and electrically connected to a first end of the metal line 200. The first electrode 910 may be electrically connected to a first voltage source V1 via a first transistor T1. The second electrode 920 may be located at and electrically connected to the second end of the metal line 200. The second electrode 920 may be electrically connected to a second voltage source (which may be ground) V2. The contact surface of the free layer 136 contacting the metal line 200 may be located between the first electrode 910 and the second electrode 920. Referring to fig. 6, the area of the contact surface 137 between the first electrode 910 and the second electrode 920 may be increased by employing an elongated surface extending along the length direction of the metal line 200. The first, second and third voltage sources may comprise the same computer-controlled voltage source with different connections to the electrodes 910, 920 and 930 and/or two or three different voltage sources.

Referring back to fig. 5A-5C, the third electrode 930 can be electrically connected to the reference layer 132, either directly or via the fixed ferromagnetic layer 112 of the SAF structure 120. The third electrode 930 may be connected to a third voltage source V3 via a second transistor T2. A programming controller 700 may be provided that may be configured to control the first transistor T1 and the second transistor T2 to provide a two-step programming process for the magnetization of the free layer 136.

The two-step programming (i.e., writing) process may include a first programming pulse application step in which the first transistor T1 is turned on and the second transistor T2 is turned off. A first current flows through the metal line 200 as shown in fig. 5A. The magnetization of the free layer 136 changes due to the spin-orbit torque effect with a cartesian coordinate system in which the x-axis is parallel to the length direction of the metal line 200 and the y-axis is parallel to the plane of the contact surface 137 (shown in fig. 6). Current flows perpendicular to the stacking direction of the layers (132, 134, 136) of the spin valve 140 during application of the first programming pulse.

In this case, the spin-orbit torque τ applied during the first step of the programming operation_SOTMay be given by:

where e is the charge of the electron(s),is the Planck constant (Plank's constant) divided by 2 π, θ_SHIs a spin Hall angle, J_eIn order to be the current density,is the z-component of the magnetization vector of the free layer 136, anIs a unit vector along the y-direction. The program controller 700 may be configured to control the duration of the on-time of the first transistor T1 such that the first program pulse applying step rotates the magnetization of the free layer 136 from one of the bi-stable magnetization states to a transient state in which the magnetization of the free layer 136 is about 90 degrees, such as in the range of 80 degrees to 100 degrees, relative to the magnetization direction of the free layer 136 prior to applying the first program pulse applying step. The spin orbit torque effect can generate a high magnitude spin orbit torque during the first programming step.

The two-step programming process may include a second programming pulse application step in which the second transistor T2 is turned on and the first transistor T1 is turned off. In this case, a second current flows through the spin valve 140 and between the surface of the free layer 136 and the second electrode 920, as shown in fig. 5B. The magnetization of the free layer 136 changes due to the spin torque transfer effect. In this case, the spin transfer torque τ applied during the second step of the programming operation_STTMay be given by:

where e is the charge of the electron(s),is the Planck constant divided by 2 π, η is the spin transfer torque coefficient, J_eIn order to be the current density,is the y-component of the magnetization vector of the free layer 136, anIs a unit vector along the z direction. The program controller 700 may be configured to control the duration of the on-time of the second transistor T2 such that the second program pulse application step rotates the magnetization of the free layer 136 from the other of the bi-stable magnetization states (i.e., from the parallel state prior to the two-step programming operation) to the anti-parallel state after the two-step programming operation, or vice versa. Current flows parallel to the stacking direction of the layers (132, 134, 136) of the spin valve 140 during application of the second programming pulse.

Referring to FIG. 5C, a read operation may be performed by applying a low bias voltage across the second electrode 920 and the third electrode 930 and measuring the magnitude of the current through the spin valve 140. The magnitude of the read current through the spin valve 140 may be maintained at a level that does not disturb the magnetization state of the free layer 136, i.e., at a level insufficient to apply sufficient torque to the magnetization of the free layer 136 to inhibit a read disturbance.

The spin orbit torque magnetic memory device of the fourth embodiment of the present disclosure benefits from applying a maximum initial torque regardless of the magnetization state of the free layer 136 in each of the first and second programming steps. Each of the spin orbit torque mechanism and the spin transfer torque mechanism may provide a respective 90 degree rotation of the magnetization of the free layer 136, thereby producing a total of 180 degree rotation, i.e., flipping the magnetization of the free layer 136. The total switching power for the two-step programming process may be less than that of a spin-orbit torque mechanism alone or a spin-transfer torque mechanism alone. The duration of the first programming pulse in the first programming step may be less than 5ns, such as 1nm to 5nm, and the duration of the second programming pulse in the second programming step may be less than 5ns, such as 1nm to 5 nm. The metal layer provides low resistance at low temperatures. Accordingly, the three-terminal spin orbit torque magnetic memory device of the fourth embodiment of the present disclosure may be operated at low power at low temperatures, for example, at temperatures below or the same as the boiling point of nitrogen (i.e., about 77 degrees kelvin or-195.79 ℃).

While the foregoing is directed to certain preferred embodiments, it is to be understood that the disclosure is not so limited. Various modifications to the disclosed embodiments will be apparent to those of ordinary skill in the art and are intended to be within the scope of the present disclosure. Where embodiments employing particular structures and/or configurations are described in this disclosure, it is to be understood that the disclosure may be practiced with any other compatible structures and/or configurations that are functionally equivalent, provided that such alternatives are not explicitly disabled or otherwise deemed to be impossible by one of ordinary skill in the art. All publications, patent applications, and patents cited herein are hereby incorporated by reference in their entirety.