阅读说明：本技术 范德华异质结构存储设备和切换方法 (Van der Waals heterostructure memory device and switching method ) 是由 陈伟 向都 刘陶 于 2021-06-09 设计创作，主要内容包括：一种在范德华异质结构的第一状态和第二状态之间切换的方法,存储设备,范德华异质结构存储设备,以及制造范德华异质结构存储设备的方法。所述范德华异质结构存储设备包括第一二维材料；和第二二维材料,其中,在所述存储设备的第一存储状态中,所述第一二维材料和所述第二二维材料之间的界面包括界面态；并且其中,相比于所述第一存储状态,在所述存储设备的第二存储状态中调节界面态。(A method of switching between a first state and a second state of a van der Waals heterostructure, a memory device, a van der Waals heterostructure memory device, and a method of manufacturing a van der Waals heterostructure memory device. The van der waals heterostructure memory device includes a first two-dimensional material; and a second two-dimensional material, wherein, in a first memory state of the memory device, an interface between the first two-dimensional material and the second two-dimensional material comprises an interface state; and wherein the interface state is adjusted in a second storage state of the storage device compared to the first storage state.)

1. A method of switching between a first state and a second state of a van der waals heterostructure memory device, the van der waals heterostructure memory device including a first two-dimensional material and a second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material, the method comprising the steps of:

exposing the interface to a laser beam while applying an erase voltage signal across the interface to create an interface state from a first storage state of the van der waals heterostructure storage device; and

applying a write voltage signal across the interface to adjust the interface state according to a second storage state of the van der Waals heterostructure storage device.

2. The method of claim 1, wherein the van der waals heterostructure memory device comprises the second two-dimensional material as a channel on the first two-dimensional material in a field effect transistor configuration comprising a gate, a source, and a drain, and the method comprises: the erase voltage signal is applied to the gate with zero bias between the source and the drain.

3. The method of claim 2, comprising: applying the write voltage signal to the gate with zero bias between the source and the drain.

4. The method of claim 2, wherein the gate is provided as a back gate electrode.

5. The method of claim 2, wherein the first storage state of the memory device is characterized by a first output current having a read voltage applied between the source and the drain in a dark condition.

6. The method of claim 5, wherein the second storage state of the storage device is characterized by a second output current that is greater than the first output current and has the same read voltage applied between the source and the drain in a dark condition.

7. The method of claim 1, wherein the first two-dimensional material comprises hexagonal boron nitride.

8. The method of claim 1, wherein the second two-dimensional material comprises molybdenum ditelluride or tungsten diselenide.

9. A van der waals heterostructure memory device, comprising:

a first two-dimensional material; and

a second two-dimensional material having a second dimension,

wherein, in a first memory state of the van der Waals heterostructure memory device, an interface between the first two-dimensional material and the second two-dimensional material comprises an interface state; and is

Wherein the interface state is adjusted in a second storage state of the van der Waals heterostructure memory device as compared to the first storage state.

10. The van der waals heterostructure memory device of claim 9, configured to expose the interface to a laser beam while applying an erase voltage signal on the interface to set the van der waals heterostructure memory device to the first memory state.

11. The van der waals memory device of claim 9, configured to apply an erase voltage signal on the interface to set the van der waals heterostructure memory device to the second memory state.

12. The van der waals heterostructure memory device of claim 9, comprising the second two-dimensional material as a channel on the first two-dimensional material in a field effect transistor configuration comprising a gate, a source, and a drain.

13. The van der waals heterostructure memory device of claim 12, configured to apply the erase voltage signal to the gate with zero bias between the source and the drain.

14. The van der waals heterostructure memory device of claim 12, configured to apply the write voltage signal to the gate with zero bias between the source and the drain.

15. The van der waals heterostructure memory device of claim 12, wherein the gate is provided as a back gate electrode.

16. The van der waals heterostructure memory device of claim 12, wherein the first memory state of the memory device is characterized by a first output current having a read voltage applied between the source and the drain in a dark condition.

17. The van der waals heterostructure memory device of claim 16, wherein the second memory state of the memory device is characterized by a second output current that is greater than the first output current and has the same read voltage applied between the source and the drain in a dark condition.

18. The van der waals heterostructure memory device of claim 9, wherein the first two-dimensional material comprises hexagonal boron nitride.

19. The van der waals heterostructure memory device of claim 9, wherein the second two-dimensional material comprises molybdenum ditelluride or tungsten diselenide.

20. A method of fabricating a van der waals heterostructure memory device, comprising the steps of:

providing a first two-dimensional material;

providing a second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material; wherein the interface is configured such that in the first memory state of the memory device, the interface between the first two-dimensional material and the second two-dimensional material comprises an interface state, and such that the interface state is adjusted in the second memory state of the memory device compared to the first memory state.

Technical Field

The present invention relates broadly to a method of switching between a first state and a second state of a van der waals heterostructure, a van der waals heterostructure memory device and a method of manufacturing a van der waals heterostructure memory device, and more particularly to a van der waals heterostructure memory device implemented with an artificial interface state.

Background

Any reference and/or discussion of prior art throughout the specification should in no way be taken as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

Two-dimensional (2D) layered materials are hot spots for the next generation of nanoelectronics material research due to their unique properties [1 ]. The discovery of graphene has led to a great interest in a variety of two-dimensional materials, including conductors, semiconductors with different band gaps (e.g., transition metals aluminum dichloride, black phosphorus), and insulators (e.g., boron nitride) [1 ]. The interactions between adjacent layers of these two-dimensional layered materials are generally characterized by van der waals forces, which have completely saturated chemical bonds at the surface of these two-dimensional layered materials, which makes heterogeneous integration of these two-dimensional materials on an atomic scale unconstrained by lattice mismatch and processing compatibility [2 ]. Furthermore, the design and stacking of large two-dimensional crystal libraries with selected properties enables the emergence of various van der Waals heterostructures such as memory devices, channel transistors, light emitting diodes, and atomically thin p-n junctions with new physical phenomena and device functions [3-8 ]. Among other things, the two-dimensional van der waals heterostructure memory devices have attracted considerable attention for their great potential in breaking the von neumann bottleneck in current computing architectures and increasing the storage capacity of memory device chips in the post-molar era. The two-dimensional atomic layer structure of the van der waals heterostructure memory device enables it to extend the capacity limits present in conventional mass storage devices. In addition, due to the abundant band structure of the two-dimensional material, a high-performance storage device having stable data storage capability can be realized by appropriate band engineering.

Although the nature of each individual component in van der waals heterostructures is very important for achieving the desired device functionality, the heterostructure interface still plays a dominant role in determining its practical performance due to the atomically thin structure and high surface to volume ratio of two-dimensional layered materials [8 ]. Previous work has focused on suppressing the appearance of interface states and charge traps to minimize unintended charge transfer and interaction between heterostructure stack layers [7 ]. However, there are still limitations to new architectures for two-dimensional memory devices and other two-dimensional electronic/optoelectronic devices. Embodiments of the present invention seek to address at least one of the above problems.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a method of switching between a first state and a second state of a van der waals heterostructure memory device, the van der waals heterostructure memory device comprising a first two-dimensional material and a second two-dimensional material, the second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material, the method comprising the steps of:

exposing the interface to a laser beam while applying an erase voltage signal across the interface to create an interface state from a first memory state of the memory device; and

applying a write voltage signal on the interface to adjust the interface state according to a second storage state of the storage device.

According to a second aspect of the present invention, there is provided a van der waals heterostructure memory device, comprising:

a first two-dimensional material; and

a second two-dimensional material having a second dimension,

wherein, in a first memory state of the memory device, an interface between the first two-dimensional material and the second two-dimensional material comprises an interface state; and is

Wherein the interface state is adjusted in a second storage state of the storage device compared to the first storage state.

According to a third aspect of the present invention, there is provided a method of manufacturing a van der waals heterostructure memory device, comprising the steps of:

providing a first two-dimensional material;

providing a second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material; wherein the interface is configured such that in the first memory state of the memory device, the interface between the first two-dimensional material and the second two-dimensional material comprises an interface state, and such that the interface state is adjusted in the second memory state of the memory device compared to the first memory state.

Brief description of the drawings

Embodiments of the present invention will be better understood and readily apparent to those skilled in the art from the following description, by way of example only, with reference to the accompanying drawings.

Fig. 1A shows a schematic cross-sectional view illustrating a manufacturing process of a van der waals heterostructure according to an exemplary embodiment.

Figure 1B illustrates a schematic perspective side view of a van der waals heterostructure in accordance with an example embodiment.

Fig. 1C shows an optical microscope image of a molybdenum ditelluride/hexagonal boron nitride van der waals heterostructure according to an exemplary embodiment.

FIG. 1D shows Raman characterization of the exfoliated molybdenum ditelluride/hexagonal boron nitride flakes of the Van der Waals heterostructure of FIG. 1C.

Fig. 1E shows the transfer characteristics, including linear and logarithmic (inset) scales, of a molybdenum ditelluride transistor in the van der waals heterostructure of fig. 1C on a hexagonal boron nitride substrate. Bias voltage V_sdIs 1.0V.

Fig. 2A illustrates transfer characteristics of a van der waals heterostructure memory device according to an exemplary embodiment in a dark condition after an initialization process.

FIG. 2B shows the device according to an exemplary embodiment as the read-out voltage V_readThe switching ratio of the function of (a).

Fig. 2C shows a diagram illustrating a dynamic write-erase process of a van der waals heterostructure memory device according to an example embodiment. The grey shading indicates that the laser beam is on. The inset shows the output current of the memory after erasing.

Fig. 3A illustrates the change in transfer characteristics of a van der waals heterostructure memory according to an example embodiment after erasing under different erase gates from 10V to 50V.

Figure 3B illustrates a memory device window as a function of an erase gate of a van der waals heterostructure memory device according to an example embodiment.

FIG. 3C shows a reading of the stored current of a Van der Waals heterostructure memory according to an example embodiment after writing at a different write gate of-20V to-80V. At a bias voltage V_sd0.1V and a gate voltage V_readThe current is read at 0V.

FIG. 3D illustrates output current as a function of a write gate of a Van der Waals heterostructure memory device, according to an example embodiment.

Fig. 4A illustrates a change in storage current versus retention time of a van der waals heterostructure memory device according to an example embodiment.

Fig. 4B illustrates a change in the switching ratio of the van der waals heterostructure memory device compared to the retention time according to an example embodiment.

Fig. 4C illustrates a change in the transfer characteristics of a van der waals heterostructure memory device at different cycle numbers according to an example embodiment.

Fig. 4D illustrates changes in the storage current extracted in state "0" and state "1" as a function of the number of cycles of the van der waals heterostructure storage device, according to an example embodiment.

Fig. 5 shows a flow diagram illustrating a method of switching between a first state and a second state of a van der waals heterostructure memory device including a first two-dimensional material and a second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material, according to an example embodiment.

Figure 6 illustrates a schematic diagram of a van der waals heterostructure memory device 600, according to an example embodiment.

Fig. 7 illustrates a flow diagram of a method of fabricating a van der waals heterostructure memory device, according to an example embodiment.

Fig. 8A illustrates transfer characteristics of the van der waals heterostructure memory device according to an exemplary embodiment in a dark condition after an initialization process.

FIG. 8B shows the device according to an exemplary embodiment as the read-out voltage V_readThe switching ratio of the function of (a).

Fig. 8C shows a diagram illustrating a dynamic write-erase process of a van der waals heterostructure memory device according to an example embodiment. The grey shading indicates that the laser beam is on. The inset shows the output current of the memory after erasing.

Detailed Description

Embodiments of the present invention may provide a two-dimensional (2D) non-volatile van der Waals heterostructure (vdWH) memory device by locating hexagonal boron nitride (hBN) and molybdenum ditelluride (MoTe)₂) The artificial interface state therebetween. According to an exemplary embodiment, the memory device derives from the micro-coupled optical and electrical response of van der Waals heterostructures, which is highly reliable by more than 10⁴s long data retention time and up to 100 write-erase cycles or more. Also, the memory current in the memory according to an exemplary embodiment can be precisely controlled by the write gate and the erase gate, thereby proving tunability of the memory state thereof.

In an exemplary embodiment, the optical and electrical responses of the van der Waals heterostructure can be controlled microscopically to effectively tune the interface states, resulting in different memory states in the memory.

Embodiments of the present invention enable high performance two-dimensional non-volatile van der Waals heterostructure memory devices.

Fabrication of two-dimensional molybdenum ditelluride/hexagonal boron nitride van der Waals heterostructure memory devices according to example embodiments

The mixed structure of molybdenum ditelluride and hexagonal boron nitride according to the exemplary embodiment was achieved by a dry transfer method in an argon atmosphere glove box. Referring to fig. 1A, a multilayer hexagonal boron nitride 110 sheet is first mechanically peeled onto a silicon substrate 112 coated with a 300 nm silicon dioxide dielectric. Hereinafter, use is made ofAn optical microscope aligns the thin sheet of molybdenum ditelluride 114 peeled from the transparent Polydimethylsiloxane (PDMS) substrate to the thin sheet of hexagonal boron nitride. After alignment, the polydimethylsiloxane film was pressed onto the silicon dioxide/silicon substrate 110 for about 2 minutes, followed by a slow lift during which the molybdenum ditelluride 114 flakes were transferred to the hexagonal boron nitride 110 flakes. After transfer, van der waals heterostructures (110, 114) were spin coated with Polymethylmethacrylate (PMMA)116 in the same glove box to prepare the devices. Standard Electron Beam Lithography (EBL) is performed to define the molybdenum ditelluride memory channels and electrical contacts, followed by the deposition of metal electrodes (chromium/gold) using thermal evaporation, such as metal electrode 104. After lifting the polymethylmethacrylate 115 layer in the acetone solution, the van der waals heterostructure memory device 100 according to the exemplary embodiment is wire bonded to a chip carrier and loaded into a high vacuum chamber (pressure about 10 a)^-7Mbar) for producing the properties.

Electrical characteristics of van der Waals heterostructure memory devices according to example embodiments

The apparatus according to the exemplary embodiment is in a high vacuum chamber (10)^-7Mbar). Electrical measurements were made using a source measurement unit model 2912A from agilent. Memory performance was tuned using a miniature laser beam with a wavelength of 405 nm. The intensity of the laser beam is calibrated by a power meter (PM 100A) of THORLABS gmbh.

Results and analysis of the exemplary embodiments

Referring again to fig. 1A, during fabrication of a device according to an exemplary embodiment, a small layer of hexagonal boron nitride 110 is mechanically stripped onto a silicon dioxide/silicon substrate 112 followed by dry transfer of a molybdenum ditelluride 114 flake. A metal contact (e.g., 104) is thermally deposited on the channel of the molybdenum ditelluride 114. Fig. 1C shows an optical microscope image of a molybdenum ditelluride/hexagonal boron nitride van der waals heterostructure memory device 100 fabricated according to an exemplary embodiment in a back gate Field Effect Transistor (FET) configuration. For each pair of contacts, e.g., contact 104, contact 105, there is one source and one drain. Since the contacts are symmetrical to each other, there is no limitation as to which contact is specifically referred to. The measurements given below were obtained at a time between a pair of contacts using a gate on the backside of the silicon/silicon dioxide substrate 112.

Raman measurements revealed the crystallinity of the molybdenum ditelluride flake (FIG. 1D), with three characteristic peaks, each at-172 cm^-1、235cm^-1And 291cm^-1To (3). Hexagonal boron nitride flakes in-1365 cm^-1Showing a single characteristic raman peak. FIG. 1E shows the bias voltage V_sdTransmission curve (I) on linear and logarithmic (inset) scales for pristine molybdenum ditelluride transistors on hexagonal boron nitride wafers at 1.0V_sd-V_g) Which exhibits a typical n-type dominated bipolar transmission behavior. It should be noted that in the reverse direction (V)_gFrom 50V to-80V) and forward direction (V)_gfrom-80V to 50V), the transfer curve shows a weak hysteresis, indicating that the trapped charge at the original molybdenum ditelluride/hexagonal boron nitride interface can be neglected.

Referring to FIGS. 1A and 1B, then at the positive gate V_gThe memory device 100 is exposed using the laser beam 118(λ 405nm) at 50V and zero bias, which is denoted as initialization. The laser beam 118 is fine focused on one channel (between a pair of electrodes) at a time. The laser intensity is calibrated at 200mW/cm²Left and right, exposure time was 2 s. After initialization, the transfer curve is scanned again in both the front and back directions under dark conditions (fig. 2A). Interestingly, during the bi-directional scan, the transfer characteristics exhibited a significant hysteresis and a threshold voltage of 60V (V)_th) The drift av (i.e. the memory window), which represents a significant memory behavior. To further investigate this memory behavior, a dynamic "write-erase" process was performed on the device according to the exemplary embodiment to set the device to state "1" and state "0", as shown in FIG. 2C. At V_sd1.0V and V_gThe reading of the original channel current at 0V is about-0.5 μ a, which is assigned to state "1" and is consistent with the transmission characteristics in fig. 1E. The same initialization process is then performed to erase the channel current, followed by a read operation. The output current dropped significantly to a low level of 0.15nA (fig. 2C inset), indicating that the device is in state "0". Electric currentThe reduction in charge is due to the charge being "dispersed" in the man-made interface state during the initialization process. In addition, at V_sdAt 1.0V, the erase current remains unchanged, which illustrates its non-volatility. Then using a negative gate pulse (V)_g-80V for-2 s) to restore the output current to its original level and the device returns to state "1". To evaluate the distinguishability of the storage states in the storage device, the switching ratio R is calculated as follows: r is ═ I_written/I_erasedThe switching ratio R is defined as the output current ratio between the state "1" and the state "0". As shown in fig. 2B, at V_readWhen it is 0V, R is estimated to be-3X 10³Which gradually decays as the read voltage increases to-50V. A large switching ratio represents a significant current difference between the written and erased states, which is very promising for multi-bit data storage applications according to example embodiments. It should be noted that the development of molybdenum ditelluride/hexagonal boron nitride van der waals heterostructure memories involves the integration of a miniature laser beam in the device chip according to an exemplary embodiment. By selecting appropriate materials or careful design of the chip structure [9,10 ]]High performance photonic chips capable of functioning as laser beam sources have been realized. Based on these advanced photonic chip technologies, according to an exemplary embodiment, a miniature laser beam can be integrated into the memory of the actual device package.

FIG. 3A shows the erase gates at different erase gates (V)_eraseFrom 10V to 50V) of the data transfer characteristic of the van der waals heterostructure memory according to an exemplary embodiment. As the erase gate increases from 10V to 50V, the reverse transfer curve remains positive, resulting in a gradually increasing hysteresis and a memory window from 40V to 60V (FIG. 3B). These results illustrate the performance tunable characteristics of van der waals heterostructure memories according to exemplary embodiments, which are achieved by controlling the erase gates. In addition to the erase gate, memory performance can also be adjusted by the write gate, as shown in FIGS. 3C and 3D. Write current I output in memory state "1_writtenGradually increases from 3.3nA to 500nA, and simultaneously writes a voltage V_writeIncrease from-10V to-80V, saidBright write current I_writtenTunable characteristics over a wide range.

In order to evaluate the reliability of the van der waals heterostructure memory device according to the exemplary embodiment, studies were made on data retention capability and cyclic write-erase endurance. FIG. 4a shows the output current (at V) in different memory states "0" and "1_sd1.0V and V_gIn the case of 0V) as high as 10⁴s, as a function of the latency. It should be noted that after erasing or writing, the memory remains isolated from output disturbances (e.g., electric field and light) and at 2 × 10³The output current is read at regular intervals of s. Although the output current gradually changes, the hold time is extended to 10⁴s, the write current and the erase current remain almost unchanged. In addition, the switching ratio R can still be kept at 1.1 × 10³(FIG. 4b) high level, which illustrates the high distinguishability of state "0" and state "1" throughout the retention period. These results show the excellent non-volatile characteristics of the storage device according to the exemplary embodiment. The write-erase dynamic process was also repeated 100 times, with the bidirectional transfer characteristic of the selected cycle as shown in FIG. 4C. The transfer curves at different cycles almost overlap each other in the front-to-back scanning direction, which represents a prominent reproducibility of the memory according to an exemplary embodiment. At V_readThe output currents in memory states "0" and "1" are extracted from the transfer characteristic at 0V, which is plotted as a function of the number of cycles in fig. 4D. The current showed a weak fluctuation in its corresponding storage state over 100 cycles. Furthermore, each V_readDeviation from the average value of the write current and the erase current is within 50%, further reflecting high reproducibility of the output current. The interface state assisted Van der Waals heterostructure memory has strong data retention capacity and cycle durability and shows great potential in nonvolatile data storage.

In another exemplary embodiment, a tungsten diselenide/hexagonal boron nitride memory was fabricated and analyzed. FIGS. 8A-C illustrate device performance of a tungsten diselenide/hexagonal boron nitride memory device according to an exemplary embodiment, which is similar to that of FIGS. 2A-CMolybdenum ditelluride/hexagonal boron nitride memory. Similarly, at the positive gate V_gThe device is exposed with a laser beam 118(λ 405nm) at 50V and zero bias, a process called initialization. The laser beam is fine focused on one channel at a time (between a pair of electrodes). The laser intensity is calibrated at 200mW/cm²Left and right, and exposure time is 2S. After initialization, the transfer curve is again scanned in both the front and back directions under dark conditions (fig. 8A). Likewise, during the bidirectional scanning, the transmission characteristic exhibits a significant hysteresis and a threshold voltage of 77V (V)_th) The offset Δ V (i.e., the memory window), which represents a significant memory behavior. To further investigate this memory behavior, a dynamic "write-erase" process was performed on the device according to the exemplary embodiment to set the device to state "1" and state "0", as shown in FIG. 8C. At V_sd1.0V and V_gIn the case of 0V, the original channel current reads 60nA, which is designated as state "1". The same initialization process is then performed to erase the channel current and then the read operation is performed. The output current dropped significantly to a low level of-60 pA (inset of fig. 8C), indicating that the device is in state "0". Likewise, the reduction in current is due to the charge being "dispersed" in the man-made interface state during initialization. In addition, at V_sdWhen 1.0V, the erase current remains unchanged, indicating that there is no fluctuation. Then using a negative gate pulse (V)_g-80V for-2 s) to restore the output current to its original level and the device returns to state "1". To evaluate the distinguishability of the storage states in the storage device, the switching ratio R is calculated as R ═ I_written/I_erasedIt is defined as the output current ratio between state "1" and state "0". Threshold voltage V of different devices/materials in the scan direction from positive to negative voltage_thThere are differences. In a molybdenum ditelluride plant (cf. FIG. 2), V_thAbout 0V, whereas in tungsten diselenide (compare FIG. 8), V is_thAbout 20V. The maximum value of the switching ratio R occurs at V_thAt the value.

Fig. 5 shows a flow diagram illustrating a method of switching between first and second states of a van der waals heterostructure memory device including a first two-dimensional material and a second two-dimensional material with an interface therebetween, according to an example embodiment. In step 502, the interface is exposed to a laser beam while an erase voltage signal is applied to the interface to create an interface state according to a first memory state of the memory device. At step 504, a write voltage signal is applied to the interface to adjust the interface state according to the second state of the memory device.

The van der waals heterostructure memory device can include a second two-dimensional material as a channel on the first two-dimensional material in a field effect transistor configuration including a gate, a source, and a drain, and the method includes applying an erase voltage signal to the gate between the source and the drain with a zero bias.

The method also includes applying a write voltage signal to the gate with zero bias between the source and the drain.

The gate may be provided as a back gate electrode. A first storage state of the memory device can be characterized by a first output current having a read voltage applied between the source and drain in a dark condition.

A second storage state of the memory device can be characterized by a second output current that is greater than the first output current and has the same read voltage applied between the source and drain in the dark state.

The first two-dimensional material may comprise hexagonal boron nitride or other materials, such as metal oxides, which contain a large number of defects.

The second two-dimensional material may comprise a dialkylene molybdenum or other two-dimensional semiconductor, such as molybdenum disulfide, tungsten diselenide.

Fig. 6 shows a schematic diagram of a van der waals heterostructure memory device 600 according to an example embodiment, the van der waals heterostructure memory device 600 includes a first two-dimensional material 602; and a second two-dimensional material 605, wherein, in a first memory state of the memory device 600, an interface 606 between the first two-dimensional material 602 and the second two-dimensional material 605 comprises an interface state, such as interface state 608; and wherein an interface state, such as interface state 608, is adjusted in a second storage state of the memory device 600 as compared to the first storage state.

The van der waals heterostructure memory device 600 can be configured to expose the interface 606 to a laser beam while applying an erase voltage signal on the interface 606 to set the van der waals heterostructure memory device 600 to the first memory state.

The van der waals heterostructure memory device 600 can be configured to apply an erase voltage signal on the interface 606 to set the van der waals heterostructure memory device 600 to the second memory state.

The van der waals heterostructure memory device 600 can include a second two-dimensional material 605 that serves as a channel on the first two-dimensional material 602 in a field effect transistor configuration that includes a gate, a source, and a drain.

The van der waals heterostructure memory device 600 can be configured to apply an erase voltage signal to the gate between the source and the drain with zero bias.

The van der waals heterostructure memory device 600 can be configured to apply a write voltage signal to the gate between the source and the drain with zero bias.

The gate may be provided as a back gate electrode.

A first storage state of the memory device 600 can be characterized by a first output current having a read voltage applied between the source and drain in the dark state.

A second storage state of the memory device 600 can be characterized by a second output current that is greater than the first output current and has the same read voltage applied between the source and drain in the dark state.

The first two-dimensional material 602 may comprise hexagonal boron nitride.

The second two-dimensional material 605 may comprise molybdenum ditelluride or tungsten diselenide.

FIG. 7 shows a flowchart 700 illustrating a method of fabricating a Van der Waals heterostructure memory device, according to an example embodiment. In step 702, a first two-dimensional material is provided. In step 704, a second two-dimensional material is provided, the second two-dimensional material having an interface between the first two-dimensional material and the second two-dimensional material, wherein the interface is configured such that in a first memory state of the memory device, the interface between the first two-dimensional material and the second two-dimensional material comprises an interface state, and such that the interface state is adjusted in a second memory state of the memory device compared to the first memory state.

As described above, a non-volatile van der waals heterostructure memory device according to an exemplary embodiment is provided with the aid of an artificial interface state between molybdenum ditelluride and hexagonal boron nitride. The dynamic write-erase process has been repeated for 100 cycles with little fluctuation in the transfer characteristic and the output current, which indicates the outstanding reliability of the memory device according to the exemplary embodiment. On the other hand, in-10⁴During the retention time of s, both the write and erase currents can be maintained without significant decay, which illustrates the excellent non-volatile characteristics of the memory according to example embodiments. Embodiments of the present invention provide artificial and efficiently regulated interface states in van der waals heterostructures, making it possible to implement high performance van der waals heterostructure memory devices, opening up new opportunities for the design and architecture of two-dimensional electronic and optoelectronic devices according to various embodiments to utilize interface state engineering techniques.

Embodiments of the invention may have one or more of the following features and associated advantages:

the above description of illustrated embodiments of the systems and methods is not intended to be exhaustive or to limit the systems and methods to the precise form disclosed. While specific embodiments of, and examples for, the system components and method are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the system, components and method, as those skilled in the relevant art will recognize. The teachings of the systems and methods provided herein may be applied to other processing systems and methods, not just the systems and methods described above.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. Furthermore, the present invention includes any combination of features described for different embodiments (including features described in the abstract section), even if the features or combinations of features are not explicitly stated in the claims or in the detailed description of the embodiments.

For example, other two-dimensional semiconductors such as molybdenum disulfide may also be used as the second two-dimensional material in different embodiments.

In general, in the following claims, the terms used should not be construed to limit the systems and methods to the specific embodiments disclosed in the specification and the claims, but should be construed to include all processing systems that operate under the claims. Accordingly, the system and method are not limited by the disclosure, but instead the scope of the system and method is to be determined entirely by the claims.

Throughout the specification and claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, unless the context clearly requires otherwise; that is, words using the singular or plural number also include the plural or singular number, respectively, in the sense of "including but not limited to". Furthermore, the words "herein," "below," "upper," "lower," and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word "or" is used to refer to a list of two or more items, the word contains all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

Reference to the literature

[1]Wang,Q.H.,Kalantar-Zadeh,K.,Kis,A.,Coleman,J.N.&Strano,M.S.Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.Nat.Nanotechnol.,7,699-712(2012).

[2]Lin,Z.,Huang,Y.&Duan,X.Van der Waals thin-film electronics.Nat.Electron.2,378-388,doi:10.1038/s41928-019-0301-7(2019).

[3]Liu,C.et al.A semi-floating gate memory based on van der Waals heterostructures for quasi-non-volatile applications.Nat.Nanotechnol.13,404-410,doi:10.1038/s41565-018-0102-6(2018).

[4]Lee,J.et al.Monolayer optical memory cells based on artificial trap-mediated charge storage and release.Nat.Commun.8,14734(2017).

[5]Li,J.et al.Symmetric Ultrafast Writing and Erasing Speeds in Quasi Nonvolatile Memory via van der Waals Heterostructures.Adv.Mater.31,1808035(2019).

[6]Novoselov,K.,Mishchenko,A.,Carvalho,A.&Neto,A.C.2D materials and van der Waals heterostructures.Science 353,aac9439(2016).

[7]Geim,A.K.&Grigorieva,I.V.Van der Waals heterostructures.Nature 499,419-425(2013).

[8]Liu,Y.et al.Van der Waals heterostructures and devices.Nat.Rev.Mater.1,16042(2016).

[9]Gundavarapu,S.et al.Sub-hertz fundamental linewidth photonic integrated Brillouin laser.Nat.Photon.13,60-67(2019).

[10]Zhou,Z.et al.On-chip light sources for silicon photonics.Light Sci.Appl.4,e358(2015).