阅读说明：本技术 一种自旋轨道矩磁存储器及其制备方法 (Spin orbit torque magnetic memory and preparation method thereof ) 是由 卢世阳 张静 商显涛 刘宏喜 曹凯华 王戈飞 于 2021-08-27 设计创作，主要内容包括：本发明公开了一种自旋轨道矩磁存储器及其制备方法,涉及隧穿磁电阻领域,该自旋轨道矩磁存储器包括：底电极层和设置于所述底电极层之上的磁隧道结,其中,所述底电极层包括衬底和顺次覆盖于所述衬底之上的底部重金属层,顶部重金属层。可见,本发明示意的自旋轨道矩存储器,通过将原重金属层的单层结构变更为多层结构,使衬底之上的重金属层结构厚度增加,增大了刻蚀制程中对刻蚀精度和刻蚀时间的调节范围,降低了因刻蚀精度异常引发的制程不良的风险。且由于多层金属层结构在实际应用中也具有更大的自旋霍尔角,从而更利于降低电流翻转密度,利于器件的集成。(The invention discloses a spin orbit torque magnetic memory and a preparation method thereof, relating to the field of tunneling magnetoresistance, wherein the spin orbit torque magnetic memory comprises: the bottom electrode layer comprises a substrate, and a bottom heavy metal layer and a top heavy metal layer which are sequentially covered on the substrate. Therefore, the spin orbit torque memory disclosed by the invention has the advantages that the single-layer structure of the original heavy metal layer is changed into the multi-layer structure, so that the thickness of the heavy metal layer structure on the substrate is increased, the adjusting range of the etching precision and the etching time in the etching process is enlarged, and the risk of poor process caused by abnormal etching precision is reduced. And because the multilayer metal layer structure also has a larger spin Hall angle in practical application, the current overturning density is more favorably reduced, and the integration of devices is favorably realized.)

1. A spin orbit torque magnetic memory, comprising: a bottom electrode layer and a magnetic tunnel junction (3) arranged above said bottom electrode layer,

the bottom electrode layer comprises a substrate, and a bottom heavy metal layer (1) and a top heavy metal layer (2) which are sequentially covered on the substrate.

2. The spin-orbit torque magnetic memory according to claim 1, wherein the magnetic tunnel junction (3) is disposed above the top heavy metal layer (2), the magnetic tunnel junction (3) comprising a free layer, a non-magnetic barrier layer, a fixed layer and a capping layer, wherein the free layer is disposed above the top heavy metal layer (2), the non-magnetic barrier layer is disposed above the free layer, the fixed layer is a free layer, the non-magnetic barrier layer is disposed above the free layer, and the capping layer is disposed above the magnetic tunnel junction.

3. A spin-orbit-torque magnetic memory according to claim 1 or 2, characterized in that the magnetic tunnel junction (3) further comprises: a pinned layer and an antiferromagnetic layer, the pinned layer being located above the fixed layer, the antiferromagnetic layer being located above the pinned layer, and the capping layer being located below the capping layer, wherein the fixed layer, the pinned layer and the antiferromagnetic layer serve as an artificial antiferromagnetic coupling layer (4).

4. Spin-orbit torque magnetic memory according to claim 1, characterized in that the bottom heavy metal layer (1) is obtained from a metal that can generate spin hall angles.

5. The spin-orbit torque magnetic memory of claim 1, wherein the class of top heavy metal layer (2) materials includes at least one of: heavy metal simple substance, heavy metal oxide, heavy metal nitride, alloy, antiferromagnetic magnetic material, crystal film, polycrystalline film, amorphous film, peril semimetal, two-dimensional electron gas and non-magnetic metal simple substance.

6. A spin-orbit torque magnetic memory according to claim 1, wherein the bottom heavy metal layer (1) square resistance is at least 2 times the top heavy metal layer (2) square resistance.

7. A method of fabricating a spin-orbit torque magnetic memory, the method comprising:

building a bottom heavy metal layer on the bottom electrode layer;

building the top heavy-metal layer over the bottom heavy-metal layer;

and constructing a magnetic tunnel junction on the top heavy metal layer.

8. The method of claim 7, wherein the building a bottom heavy metal layer over a bottom electrode layer comprises:

constructing a bottom heavy metal layer on the bottom electrode layer in a sputtering mode;

building the top heavy-metal layer over the bottom heavy-metal layer;

and constructing the top heavy metal layer on the bottom heavy metal layer by means of sputtering.

9. The method of claim 7, wherein after said building said top heavy metal layer over said bottom heavy metal layer and before said top heavy metal layer builds a magnetic tunnel junction, further comprising:

and constructing a magnetic tunnel junction film layer on the top heavy metal layer in a sputtering mode.

10. The method of claim 7, wherein the magnetic tunnel junction is constructed by three ways: gluing, developing and etching.

Technical Field

The embodiment of the invention relates to the field of electronics, in particular to a preparation method of a magnetic random access memory.

Background

As the development process of emerging memories is continuously developed and matured, Spin Orbit Torque Magnetic Memory (SOT-MRAM) is widely applied. The SOT-MRAM has the advantages of nonvolatility, high-speed low-power-consumption data writing capability, high device durability and the like, is gradually becoming a new generation Random Access Memory following a Spin Transfer Torque Random Access Memory (STT-MRAM), and becomes a key technology which is expected to break through the power consumption bottleneck of the integrated circuit in the later Moore era.

However, there are two main problems in the preparation of SOT-MRAM in practice: 1) the surface roughness process of a Complementary Metal Oxide Semiconductor (CMOS) substrate is difficult to process and complicated, so that the roughness of the CMOS substrate is difficult to reach the required standard, and the performance of a device is influenced; 2) the size of the whole heavy metal layer of the Magnetic Tunnel Junction (MTJ) with the core structure is small, the thickness is about 3-5 nm, the requirement on the precision of an etching process in the preparation process is high, the adjustable range of the instant etching precision and the etching time is small, and the yield loss of devices caused by the over-etching phenomenon due to abnormal etching precision is easy to occur.

Disclosure of Invention

The embodiment of the invention provides a spin orbit torque magnetic memory and a preparation method thereof, which can improve the surface roughness of a CMOS and reduce the abnormal risk of etching in the preparation process.

In order to solve the above-described problems, a first aspect of the present invention proposes a spin orbit torque magnetic memory comprising: a bottom electrode layer and a magnetic tunnel junction 3 arranged above said bottom electrode layer,

the bottom electrode layer comprises a substrate, and a bottom heavy metal layer 1 and a top heavy metal layer 2 which are sequentially covered on the substrate.

In some embodiments, the spin-orbit torque magnetic memory, the magnetic tunnel junction 3 is disposed over the top heavy metal layer 2, the magnetic tunnel junction 3 comprises a free layer, a non-magnetic barrier layer, a fixed layer, and a capping layer, wherein the free layer is disposed over the top heavy metal layer 2, the non-magnetic barrier layer is disposed over the free layer, the fixed layer is a free layer, the non-magnetic barrier layer is disposed over the free layer, and the capping layer is disposed over the magnetic tunnel junction top layer.

In some embodiments, the magnetic tunnel junction 3 structure comprises: the magnetic tunnel junction 3 further includes: a pinned layer and an antiferromagnetic layer, the pinned layer being located above the fixed layer, the antiferromagnetic layer being located above the pinned layer, and the capping layer being located below the capping layer, wherein the fixed layer, the pinned layer and the antiferromagnetic layer serve as the artificial antiferromagnetic coupling layer 4.

In some embodiments, the bottom heavy metal layer 1 is derived from a spin hall angle generable metal comprising: w (tungsten), Ta (tantalum), Pt (platinum).

In some embodiments, the bottom heavy metal layer 1 final state is embodied as a nitride that can produce a spin hall angle metal, including: WN (tungsten nitride).

In some embodiments, the top heavy metal layer 2 material category selection includes: heavy metal simple substance, heavy metal oxide, heavy metal nitride, alloy, antiferromagnetic magnetic material, crystal film, polycrystalline film, amorphous film, foreign semimetal, two-dimensional electron gas and non-magnetic metal simple substance, heavy metal simple substance and non-magnetic metal simple substance include at least: ta, W, Pt, Pd (palladium), Hf (hafnium), Au (gold), Mo (molybdenum), and Ti (titanium);

the top heavy metal layer 2 may also be made of an oxide or nitride capable of generating a self-selected hall angle metal, and the oxide or nitride capable of generating the self-selected hall angle metal comprises: WO (tungsten oxide), WN (tungsten nitride) and mixed layer structures WO/WN;

the top heavy metal layer 2 can also be made of alloy with different atomic ratios of metal capable of generating self-selected Hall angle, and at least comprises Au_0.93W_0.07、Au_0.9Ta_0.1、Au_xPt_100-x；

The top heavy metal layer 2 material can also select the anti-ferromagnetic magnetic material for use, and the anti-ferromagnetic magnetic material includes: IrMn, PtMn, FeMn, PdMn, L10-IrMn, poly-IrMn;

the material of the top heavy metal layer 2 can also be selected from a crystal film, a polycrystalline film, an amorphous film, a peril semimetal or other structures capable of generating spin current, and at least comprises: bi₂Se₃、Bi₂Te₃、Sb₂Te₃、(Bi_xSb_1-x)₂Te₃、Bi_xSe_1-x、WTe₂、MoTe₂、Mo_xW_1-xTe₂And a two-dimensional electron gas.

In some embodiments, the ferromagnetic material of the free layer or the fixed layer may be selected from CoFeB, CoFe, Co, and combinations of the three, wherein the combined materials include: co₂₀Fe₆₀B₂₀、Co₄₀Fe₄₀B₂₀、Co₆₀Fe₂₀B₂₀、Co₇₀Fe₃₀、Co₇₅Fe₂₅Or Co₈₅Fe₁₅。

In some embodiments, the non-magnetic barrier layer material comprises at least: MgO and Al₂O₃。

In some embodiments, the bottom heavy metal layer 1 square resistance value is set to be at least 2 times the top metal layer 2 square resistance value.

In some embodiments, the resistivity of the bottom heavy metal layer 1 and the top heavy metal layer 2 may be selected as follows: rho_BHM>2ρ_THMWhere ρ represents the material resistivity.

In some embodiments, the bottom heavy metal layer 1 andthe thickness of the top heavy metal layer 2 may be selected according to the following rule: t is t_THM<2t_BHMWhere t represents the material film layer thickness.

In a second aspect of the present application, there is also provided a method of manufacturing a spin orbit torque magnetic memory, the steps including:

building a bottom heavy metal layer on the bottom electrode layer;

building the top heavy-metal layer over the bottom heavy-metal layer;

and constructing a magnetic tunnel junction on the top heavy metal layer.

In some embodiments, the bottom heavy metal layer and the top heavy metal layer may be formed by sputtering.

In some embodiments, the magnetic tunnel junction film layer structure may be formed by sputtering.

In some embodiments, the process of processing the magnetic tunnel junction film layer structure into a magnetic tunnel junction can be implemented by the following three ways: gluing, developing and etching.

The embodiment of the invention provides an SOT-MRAM with a multilayer heavy metal layer structure and a preparation method thereof. The upper layer structure is made of a material with a spin Hall angle, so that the function of converting current into spin current and further realizing the magnetic field overturning function after being electrified is realized. Due to the introduction of the multilayer heavy metal layer structure, the thickness of the multilayer heavy metal layer structure is increased, the etching window is enlarged, the adjusting range of the etching precision and the etching time in the etching process is enlarged, and the risk of poor processing caused by small etching precision window is reduced. And because the multilayer metal layer structure also has a larger spin Hall angle in practical application, the charge current-spin current conversion efficiency is higher, the current turnover density is more favorably reduced, and the integration of devices is favorably realized.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application.

FIG. 1 is a schematic diagram of a SOT-MRAM architecture according to a conventional technique of the present invention;

FIG. 2a is a schematic diagram of a pre-etched structure of a magnetic tunnel junction of a multilayer heavy metal layer structure according to an embodiment of the present invention;

FIG. 2b is a schematic diagram of a magnetic tunnel junction etched back structure of a multilayer heavy metal layer structure according to an embodiment of the present invention;

FIG. 2c is a schematic diagram of a top view structure of a multilayer heavy metal layer structure after etching of a magnetic tunnel junction according to an embodiment of the present invention;

FIG. 3a is a diagram of a small-mode SOT-MRAM structure for etching windows according to an embodiment of the invention;

FIG. 3b is a diagram of a small-mode two-SOT-MRAM structure for etching windows according to an embodiment of the invention;

FIG. 4 is a schematic diagram of a current distribution of a heavy metal layer according to an embodiment of the present invention;

FIG. 5 shows N during sputtering of a bottom heavy metal layer according to one embodiment of the present invention₂The relationship between the input amount and the resistivity of the film is shown schematically;

fig. 6 is a schematic diagram of a self-selected hall angle test result of the multilayer heavy metal layer structure according to an embodiment of the invention.

Detailed Description

In order to make the objects, features and advantages of the present invention more apparent and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It will be understood by those within the art that the terms "first", "second", etc. in this application are used only to distinguish one device, module, parameter, etc., from another, and do not denote any particular technical meaning or necessary order therebetween.

As shown in FIG. 1, the core structure of the conventional SOT-MRAM includes: heavy metal layer from bottom to top, free layer, non-magnetic barrier layer, fixed layer, antiferromagnetically coupled layer, pinned layer and cover layer. Wherein the heavy metal layer generates a spin hall effect. Spin (Spin) is an inherent angular momentum of electrons, the Spin hall effect refers to that under the condition of no external magnetic field, an electric field is introduced, a non-polarized current is injected, electrons which Spin upwards and Spin downwards move in opposite directions, however, the number of charges which move upwards and downwards is equal, and therefore, no net current flows, the main cause of the Spin hall effect is based on the Spin Orbit Coupling (SOC) of electrons in a material, namely, the interaction result of the Spin angular momentum and the Orbit angular momentum of the electrons, and therefore, the strength of the Spin hall effect result degree has a strong correlation with the selection of a used sample material. In the application of SOT-MRAM field, SOT-MRAM passes an in-plane current in the heavy metal layer, and utilizes the interaction between electron spin and orbit to generate unbalanced spin accumulation, so as to form spin current perpendicular to the current direction. The spin-polarized current entering the free layer rapidly interacts with the local magnetic moment to generate a spin-orbit torque (or a field) that induces a magnetic moment to flip if a critical current is reached. SOT-MRAM is capable of producing strong Spin-orbit coupling due to the Spin-orbit torque effect of heavy metal layers, the Spin source often having a certain Spin-to-charge conversion efficiency, i.e., Spin Hall Angle (SHA).

Generally, the pinned layer is not easily changed by an external stimulus because the magnetic moment is fixed in one direction, and the direction of the magnetic moment of the free layer can be changed by spin current excitation induced by an SOT current, thereby being switched in two directions of the easy magnetization axis. The change in direction is characterized by the high and low resistance states of the MTJ, which can be used to represent the state of the stored data "1" or "0" in this row memory field.

In general, SOT-MRAM suffers from a number of problems during the actual device self-fabrication process, which commonly include: 1) the roughness of the substrate does not meet the standard, and negative influence is brought to the performance of the device; 2) at the present stage, the thickness of the heavy metal layer is small, the requirement on the precision of the etching process is high, the difficulty is high, and poor products caused by small etching windows are easy to occur, as shown in fig. 3a and 3b, the phenomenon is represented as an over-etching phenomenon caused by the fact that the etching exceeds the preset precision. However, since the SOT-MRAM itself has a small device structure, for example, the thickness of a conventional heavy metal layer is usually 3 nanometers (nm) to 5nm, the difficulty of improving the process capability is large for both problems.

In one embodiment of the present application, in order to ensure the yield of the magnetic tunnel junction in the etching process and reduce the risk of poor products caused by abnormal etching precision, the SOT-MRAM is constructed by using a multilayer heavy metal layer.

FIG. 2a shows a schematic diagram of a SOT-MRAM pre-etching structure, which is a multilayer heavy metal layer SOT-MRAM, comprising a bottom electrode layer and a magnetic tunnel junction 3 disposed above the bottom electrode layer. The Bottom electrode layer comprises a substrate, and a Bottom Heavy Metal layer (BHM) 1 and a Top Heavy Metal layer (THM) 2 sequentially covering the substrate.

Due to the introduction of the multilayer heavy metal layer structure, the thickness of the multilayer heavy metal layer structure is larger than that of the traditional heavy metal layer structure. Therefore, in the etching process, under the condition of the same etching process capability, the influence of the etching error on the multi-layer heavy metal layer structure is smaller than that of the traditional heavy metal layer. Therefore, compared with the traditional heavy metal layer, the multi-layer heavy metal layer has larger adjustment range of etching thickness and etching time, namely has larger upper and lower limits of product specification. In other words, the introduction of the multilayer heavy metal layer strengthens the capability of resisting the abnormal influence of the etching precision of the product, so that the risk of poor products caused by the abnormal etching precision is reduced.

In one embodiment of the present application, to achieve improved roughness of the hybrid heavy-metal layer, the build material of the heavy-metal layer is defined by screening.

Optionally, the bottom heavy metal layer 1 is made of a metal capable of generating a spin hall angle, that is, the material of the bottom heavy metal layer 1 may be an amorphous material prepared from a metal material having a spin hall angle. The material still keeps the metal property, the amorphous characteristic is kept after annealing, the self roughness can be reduced by the amorphous characteristic, and therefore the influence on the device performance caused by larger substrate roughness is reduced.

Optionally, the metal material with a spin hall angle at least includes: w, Pt, Ta.

Optionally, the bottom heavy metal layer 1 may be formed by sputtering, and N may be introduced during sputtering₂To obtain an amorphous material of the sputtered metal.

Optionally, the resistivity of the material of the bottom heavy metal layer 1 and the sputtering process N₂The amount of the introduced substance is exponentially expressed, as shown in FIG. 5.

Optionally, the sputtering thickness of the bottom heavy metal layer 1 is 1-10 nm.

In one embodiment of the present application, the material of the top heavy metal layer 2 is selected to include:

optionally, the material of the top heavy metal layer 2 may be a heavy metal simple substance and a non-magnetic metal simple substance, and at least includes: ta, W, Pt, Pd (palladium), Hf (hafnium), Au (gold), Mo (molybdenum), and Ti (titanium).

Optionally, the material of the top heavy metal layer 2 may be a heavy metal oxide, nitride, and metal mixed layer structure, and at least includes: WO (tungsten oxide), WN (tungsten nitride) and mixed layer structure WO/WN.

Optionally, the material of the top heavy metal layer 2 may be an alloy of metals capable of generating a spin hall angle with different atomic ratios, and at least includes: au coating_0.93W_0.07、Au_0.9Ta_0.1、Au_xPt_100-x。

Optionally, the material of the top heavy metal layer 2 may be an antiferromagnetic magnetic material, and at least includes: IrMn, PtMn, FeMn, PdMn, L10-IrMn, poly-IrMn.

Optionally, the material of the top heavy metal layer 2Selecting a structure which can be a crystalline film, a polycrystalline film, an amorphous film, a peril semimetal or other structures capable of generating spin current, and at least comprising: bi₂Se₃、Bi₂Te₃、Sb₂Te₃、(Bi_xSb_1-x)₂Te₃、Bi_xSe_1-x、WTe₂、MoTe₂、Mo_xW_1-xTe₂And a two-dimensional electron gas.

In one embodiment of the present application, the sheet resistance of the bottom heavy metal layer 1 is at least 2 times the sheet resistance of the top heavy metal layer 2, i.e., R_BHM>2R_THM. This ensures that more current passes through the top heavy metal layer 2, as shown in fig. 4, resulting in a larger spin hall angle.

Optionally, a current I through the top heavy metal layer 2_sAnd a current I through the bottom heavy metal layer_cThe relationship is as follows: i is_s/I_c＝ρ_BHMt_THM/ρ_THMt_BHMWhere ρ is_BHMRepresents the resistivity, t, of the material of the bottom heavy metal layer 1_BHMRepresents the film thickness (unit: nm), rho, of the bottom top heavy metal layer 1_THMRepresents the material resistivity, t, of the top heavy metal layer 2_THMThe film thickness (unit: nm) of the top heavy metal layer 2 is shown.

Optionally, the resistivity selection rule for the materials of the bottom heavy metal layer 1 and the top heavy metal layer 2 may be as follows: rho_BHM>2ρ_THM。

Optionally, the thickness of the bottom heavy metal layer 1 and the top heavy metal layer 2 may be selected according to the following rule: t is t_THM<2t_BHM。

Further, wherein the magnetic tunnel junction 3 is disposed above the top heavy metal layer, in some embodiments, the magnetic tunnel junction 3 comprises a free layer, a non-magnetic barrier layer, a pinned layer, and a capping layer. The free layer is arranged on the top heavy metal layer, the nonmagnetic barrier layer is arranged on the free layer, the nonmagnetic barrier layer is arranged on the fixed layer, the free layer is arranged on the fixed layer, and the covering layer is arranged on the top layer of the magnetic tunnel junction.

In other embodiments, as shown in fig. 2b, the film layer structure of the magnetic tunnel junction 3 includes, from bottom to top: free Layer (FL), nonmagnetic barrier Layer (MgO, magnesium oxide), artificial antiferromagnetically coupled Layer (SAF), and capping Layer (Top, Mental). The structure of the artificial antiferromagnetic coupling Layer 4 is shown in fig. 1, and includes a fixed Layer (RL), an antiferromagnetic Layer and a pinning Layer.

Optionally, after the whole film of the SOT-MRAM is sputtered, the annealing direction needs to be perpendicular to the SOT current direction, as shown in fig. 2c, so that the fixed magnetic moment direction is perpendicular to the SOT current direction, and the magnetic moment inversion without external field can be realized.

Optionally, when the bottom heavy metal layer 2 is supplied with current, most of the current flows into the top heavy metal layer 2, spin polarization current perpendicular to the current direction is generated in the top heavy metal layer 2, and the spin polarization current enters the free layer to induce the magnetic moment to flip.

Optionally, the ferromagnetic material of the free layer or the fixed layer may be CoFeB, CoFe, Co, or a combination of different components of the foregoing three materials, and at least includes: co₂₀Fe₆₀B₂₀、Co₄₀Fe₄₀B₂₀、Co₆₀Fe₂₀B₂₀、Co₇₀Fe₃₀、Co₇₅Fe₂₅Or Co₈₅Fe₁₅。

Optionally, the nonmagnetic barrier layer material at least comprises: MgO and Al₂O₃。

In one embodiment of the present application, there is provided a method for fabricating an SOT-MRAM of a multi-layered heavy metal layer structure, comprising the steps of:

a bottom heavy metal layer is built on top of the bottom electrode layer.

Wherein, the bottom heavy metal layer can be constructed by adopting a sputtering process means. The sputtering process is a process of bombarding the surface of a solid with particles (particles or neutral atoms, molecules) with certain energy to make the atoms or molecules near the surface of the solid obtain enough energy to finally escape from the surface of the solid, and the sputtering process can be performed only under a certain vacuum state, and the growth of the mixed heavy metal layer here constitutes an optional sputtering process, but is not limited to this scheme, and other modes are also applicable.

Optionally, the sputtering process for growing and constructing the mixed heavy metal layer includes, but is not limited to, two-stage sputtering, three-stage sputtering or four-stage sputtering, magnetron sputtering, target sputtering, radio frequency sputtering, bias sputtering, asymmetric alternating current radio frequency sputtering, ion beam sputtering, reactive sputtering, and the like;

optionally, the metal material with a spin hall angle at least includes: w, Pt, Ta;

optionally, the bottom metal layer 1 may be formed by sputtering, and N may be introduced during sputtering₂Amorphous material for obtaining sputtered metal;

optionally, the sputtering thickness of the bottom heavy metal layer 1 is 1-10 nm.

Building the top heavy metal layer over the bottom heavy metal layer.

Wherein, the bottom heavy metal layer can be constructed by adopting a sputtering process means. The sputtering process is a process of bombarding the surface of a solid with particles (particles or neutral atoms, molecules) with certain energy to make the atoms or molecules near the surface of the solid obtain enough energy to finally escape from the surface of the solid, and the sputtering process can be performed only under a certain vacuum state, and the growth of the mixed heavy metal layer here constitutes an optional sputtering process, but is not limited to this scheme, and other modes are also applicable.

Optionally, the sputtering process for growing and constructing the hybrid heavy metal layer includes, but is not limited to, two-stage sputtering, three-stage sputtering or four-stage sputtering, magnetron sputtering, target sputtering, radio frequency sputtering, bias sputtering, asymmetric alternating current radio frequency sputtering, ion beam sputtering, reactive sputtering, and the like.

Optionally, the material of the top heavy metal layer 2 may be a heavy metal simple substance and a non-magnetic metal simple substance, and at least includes: ta, W, Pt, Pd (palladium), Hf (hafnium), Au (gold), Mo (molybdenum), and Ti (titanium).

Optionally, the material of the top heavy metal layer 2 may be a heavy metal oxide, nitride, and metal mixed layer structure, and at least includes: WO (tungsten oxide), WN (tungsten nitride) and mixed layer structure WO/WN.

Optionally, the material of the top heavy metal layer 2 may be an alloy of metals capable of generating a spin hall angle with different atomic ratios, and at least includes: au coating_0.93W_0.07、Au_0.9Ta_0.1、Au_xPt_100-x。

Optionally, the material of the top heavy metal layer 2 may be an antiferromagnetic magnetic material, and at least includes: IrMn, PtMn, FeMn, PdMn, L10-IrMn, poly-IrMn.

Optionally, the material of the top heavy metal layer 2 may be selected from a crystalline thin film, a polycrystalline thin film, an amorphous thin film, a peril semimetal or other structures capable of generating spin current, and at least includes: bi₂Se₃、Bi₂Te₃、Sb₂Te₃、(Bi_xSb_1-x)₂Te₃、Bi_xSe_1-x、WTe₂、MoTe₂、Mo_xW_1-xTe₂And a two-dimensional electron gas.

And constructing a magnetic tunnel junction on the top heavy metal layer.

The tunneling magnetic tunnel junction film layer structure can be constructed by adopting a sputtering process, and the construction effect is shown in fig. 2 a.

Optionally, the sputtering process constructed by the growth of the tunneling magnetic tunnel junction film layer includes, but is not limited to, two-stage sputtering, three-stage sputtering or four-stage sputtering, magnetron sputtering, target sputtering, radio frequency sputtering, bias sputtering, asymmetric alternating current radio frequency sputtering, ion beam sputtering, reactive sputtering, and the like.

And after the tunneling magnetic tunnel junction film layer structure grows completely, processing the tunneling magnetic tunnel junction structure, wherein the processing effect is shown as figure 2 b. Common processing steps include: gluing, developing and etching.

In an optional embodiment of the present application, a ready-made CMOS wafer of BEOL is selected as a substrate, and the bottom heavy metal layer 1 and the top heavy metal layer 2 are sputtered thereon, wherein the bottom heavy metal layer 1 is made of TaN (tantalum nitride), the thickness of the film layer is 5nm, the top heavy metal layer 2 is made of W (tungsten), and the thickness of the film layer is 3nm, so as to ensure that the sheet resistance of the bottom heavy metal layer is 2 times that of the top heavy metal layer.

Optionally, N in the TaN sputtering process₂The amount of (2) was selected to be 35sccm (standard ml/min);

optionally, the material selected for the free layer material is CoFeB, and the sputtering thickness is 1.2 nm.

Optionally, the nonmagnetic barrier layer is made of MgO, and the sputtering thickness is 1.5 nm.

Optionally, the fixed layer is made of CoFeB, and the sputtering thickness is 1.9 nm;

optionally, the selected material of the fixed layer can also be CoFe, and the sputtering thickness is 0.5 nm;

optionally, the antiferromagnetic coupling layer is made of Ru, and the sputtering thickness is 0.8 nm;

optionally, the pinning layer is made of IrMn, and the sputtering thickness is 7.5 nm;

optionally, the material of the covering layer is Ta, and the sputtering thickness is 2 nm;

optionally, the material selected for the covering layer can also be Ru with the sputtering thickness of 5 nm;

optionally, after the sputtering of the film stack of the magnetic tunnel junction 3 is completed, annealing is performed, where the annealing conditions include: the temperature is 300 ℃, the magnetic field intensity is 1T, and the annealing time is 1 h;

optionally, the annealing direction is perpendicular to the current direction in the heavy metal layer;

optionally, performing operations such as gluing, developing and etching on the film stack structure after annealing;

optionally, the MTJ is constructed in an elliptical structure with a cross-sectional length-to-minor axis dimension ratio of 3/1;

finally, a result obtained by testing the Hall device is shown in FIG. 6, a spin Hall angle of 0.46 is obtained after data processing, the spin Hall angle of W is also selected as the single-layer heavy metal layer material at the present stage to be 0.1, and compared with the spin Hall angle of the multi-layer heavy metal layer, the spin Hall angle of the multi-layer heavy metal layer is far larger than that of the single-layer heavy metal layer, so that the flip current density represented in the SOT-MRAM can be theoretically calculated and reduced by 4-5 times, and the reduction of the flip density is beneficial to the integration of the device. Further, the adjustment of this structure facilitates the integration of the device.

The embodiment of the invention provides an SOT-MRAM structure with a multilayer heavy metal layer structure and a preparation method thereof. The upper layer structure is made of materials with spin Hall angles, and the magnetic field overturning function after electrification is achieved. Due to the introduction of the multilayer heavy metal layer structure, the thickness of the multilayer heavy metal layer structure is increased, the adjusting range of the etching thickness and the etching time in the etching process is enlarged, and the risk of poor process caused by abnormal etching precision is reduced. And because the multilayer metal layer structure also has a larger spin Hall angle in practical application, the conversion efficiency between the charge current and the spin current is higher, the current overturning density is more favorably reduced, and the integration of the device is favorably realized.

The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, and any modifications, equivalents, improvements, etc. that are within the spirit and principle of the present invention should be included in the present invention.