A multi-state memory based on a two-dimensional ferroelectric heterojunction and its design method

Abstract

This invention belongs to the field of semiconductor technology, specifically relating to a multi-state memory based on a two-dimensional ferroelectric heterojunction and its design method. The multi-state memory based on a two-dimensional ferroelectric heterojunction includes: a two-dimensional ferroelectric van der Waals heterojunction, formed by vertically stacking a first two-dimensional material layer and a second two-dimensional ferroelectric material layer, wherein the second two-dimensional ferroelectric material layer has a reversible non-volatile polarization orientation; at least two sets of source and drain electrodes, respectively in contact with the first two-dimensional material layer, and the connection direction of the two sets of source and drain electrodes is respectively arranged along different crystal orientations of the two-dimensional ferroelectric van der Waals heterojunction, for applying read voltages in different directions. This invention achieves at least four different resistance states on a single heterojunction by independently controlling the polarization orientation of the two-dimensional ferroelectric material layer and the gating direction of the two sets of source and drain electrodes. Compared with existing FTJs that can only achieve binary storage, the single-device storage capacity of this invention is doubled, significantly improving data storage density.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a multi-state memory based on a two-dimensional ferroelectric heterojunction and its design method. Background Technology

[0002] In the post-Moore's Law era, improving chip performance requires collaborative efforts from multiple perspectives, including the development of new materials and processes, as well as the design of novel device architectures and circuits. For example, Tan et al. pioneered a dual epitaxial strategy, successfully achieving the directional integration of wafer-level two-dimensional Bi2O2Se / Bi2SeO5 fin oxide heterojunction arrays on an insulating substrate. By employing low-temperature UV-assisted intercalation oxidation technology, they constructed atomically smooth epitaxial interfaces, resulting in two-dimensional fin field-effect transistor devices exhibiting excellent performance. Meanwhile, Pazos et al. proposed a strategy that uses specific (non-traditional) biases to make conventional complementary metal-oxide-semiconductor transistors exhibit neuronal and synaptic behaviors. By cascading an additional CMOS transistor, they constructed a multifunctional dual-transistor unit with tunable synaptic responses, significantly simplifying the structure and size of the basic building blocks required to realize artificial neural networks. However, these methods require additional transistors and complex circuitry, significantly increasing area overhead.

[0003] Two-dimensional ferroelectric materials, due to their atomic-level thickness, tunable ferroelectric polarization characteristics, and compatibility with modern semiconductor processes, have become a cutting-edge field of research in post-Moore's Law electronic devices. Since the experimental confirmation of room-temperature ferroelectricity in CuInP2S6 and In2Se3, significant breakthroughs have been made in the research of two-dimensional ferroelectric devices, including ferroelectric field-effect transistors and ferroelectric tunnel junctions (FTJs). These devices, with their ultra-low power consumption, high on / off ratio, and potential for nanoscale integration, show broad application prospects in neuromorphic computing and in-memory computing architectures.

[0004] Interface engineering of ferroelectric / two-dimensional semiconductor heterojunctions can further enhance polarization stability and reversibility, providing a new paradigm for developing high-performance, multifunctional integrated electronic systems (such as MoS2 / AlScN, MSi2P4 / Sc2CO2 (M=Mo, W), and α-tellurene / In2Se3). However, existing FTJ devices typically only achieve two stable resistive states (binary operation), which fundamentally limits data storage density. Furthermore, due to the instability of the ferroelectric structure and the influence of a large depolarization field, FTJ devices struggle to maintain high tunneling resistance at atomically thin ferroelectric layers.

[0005] Furthermore, many two-dimensional materials exhibit anisotropic transport properties, primarily stemming from their intrinsic lattice symmetry breaking and orientation-dependent electronic structure. This manifests as significant changes in physical quantities such as electrical conductivity, carrier mobility, and thermal conductivity with orientation. In recent years, anisotropic two-dimensional materials have been widely applied in the design of novel devices, such as polarization-sensitive photodetectors, orientation-selective transistors, and multilevel memory devices. However, existing research typically explores and utilizes non-volatile ferroelectric polarization and anisotropic transport properties as independent physical properties. The effective integration of the non-volatility of two-dimensional ferroelectrics with the anisotropic transport properties of two-dimensional materials remains largely unexplored. Therefore, achieving effective synergy between these two properties to enhance device functionality is of significant research importance. Summary of the Invention

[0006] The primary objective of this invention is to provide a multi-state memory based on a two-dimensional ferroelectric heterojunction, which collaboratively utilizes two orthogonal and independent control degrees of freedom—carrier transport direction and ferroelectric polarization orientation—to achieve at least four stable and distinct resistance states in a single device. This design significantly reduces the area overhead required for the memory and provides a novel physical mechanism for realizing high-density in-memory computing architectures.

[0007] Another objective of this invention is to provide a design method for the multi-state memory based on a two-dimensional ferroelectric heterojunction.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a multi-state memory based on a two-dimensional ferroelectric heterojunction. The multi-state memory based on the two-dimensional ferroelectric heterojunction includes a two-dimensional ferroelectric van der Waals heterojunction, which is formed by vertically stacking a first two-dimensional material layer and a second two-dimensional ferroelectric material layer, and the second two-dimensional ferroelectric material layer has a reversible non-volatile polarization orientation; at least two sets of source and drain electrodes are respectively in contact with the first two-dimensional material layer, and the connection direction of the two sets of source and drain electrodes is respectively arranged along different crystal orientations of the two-dimensional ferroelectric van der Waals heterojunction for applying read voltages in different directions.

[0010] Furthermore, the first two-dimensional material layer is GaTe; the second two-dimensional ferroelectric material layer is In2Se3.

[0011] Furthermore, the connection directions of the two sets of source and drain electrodes are respectively along the armchair direction and the sawtooth direction of the two-dimensional ferroelectric van der Waals heterojunction.

[0012] Furthermore, the polymorphic memory applies a first electrical signal to the source-drain electrode pair to flip the polarization orientation and applies a second electrical signal to the source-drain electrode pair to read the tunneling resistance value, thereby achieving at least four distinguishable resistance states on a single heterojunction by independently controlling the polarization orientation and the selected source-drain electrode pair.

[0013] Furthermore, the at least four distinguishable resistance states are determined by a combination of a first input variable and a second input variable, wherein the first input variable corresponds to the polarization orientation of the second two-dimensional ferroelectric material layer, and the second input variable corresponds to the carrier transport direction determined by the selected source-drain electrode pair.

[0014] Furthermore, when the first input variable is 0, the corresponding ferropolarization direction is downward polarization, and when it is 1, the corresponding ferropolarization direction is upward polarization; when the second input variable is 0, the corresponding carrier transport direction is a sawtooth direction, and when it is 1, the corresponding ferropolarization direction is upward polarization; the output resistance state varies with the input combination 00, 01, 10, 11, and successively exhibits a low resistance state, a medium-low resistance state, a medium-high resistance state, and a high resistance state.

[0015] Furthermore, the first electrical signal is a voltage pulse with an amplitude greater than the coercive voltage of the second two-dimensional ferroelectric material layer; the second electrical signal is a continuous voltage with an amplitude less than the coercive voltage of the second two-dimensional ferroelectric material layer.

[0016] The present invention also provides a design method for the above-mentioned multi-state memory based on a two-dimensional ferroelectric heterojunction, comprising the following steps:

[0017] (1) Construct a lattice-matched heterojunction model of a first two-dimensional material layer / a second two-dimensional ferroelectric material layer;

[0018] (2) Analyze the binding energy of the heterojunction through first-principles calculations to determine the heterojunction with energy stability; calculate the band structure, work function and interlayer charge transfer of the heterojunction under different polarization states, and screen out the best heterojunction model with significant polarization reversal effect on band structure regulation.

[0019] (3) Based on the selected optimal heterojunction model, at least two sets of source and drain electrodes are set along different crystal orientations to construct a multi-electrode multi-channel ferroelectric tunnel junction;

[0020] (4) Density functional theory combined with the non-equilibrium Green's function method is used to simulate the current-voltage characteristics of the multi-electrode multi-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations, verify the distinguishability of the multi-resistance state, and determine the working voltage window.

[0021] Furthermore, the optimal heterojunction model is the GaTe / In2Se3 heterojunction model.

[0022] Compared with the prior art, the main advantages of the present invention are as follows:

[0023] 1. This invention achieves at least four stable and distinct resistive states by synergistically utilizing two degrees of freedom—ferroelectric polarization orientation and carrier transport direction—within a single ferroelectric tunnel junction. Compared to existing ferroelectric tunnel junctions that can only achieve binary (0 / 1) storage (such as MoS2 / AlScN, MSi2P4 / Sc2CO2, etc.), the single-device storage capacity of this invention is doubled, significantly improving data storage density. Simultaneously, this design avoids the enormous area overhead required to achieve multi-state storage through cascading multiple transistors, providing a compact solution for high-density memory architectures in the post-Moore's Law era.

[0024] 2. This invention utilizes density functional theory combined with non-equilibrium Green's functions to predict and verify the polarization modulation behavior and transport characteristics of GaTe / In2Se3 heterojunctions at the atomic scale. By calculating the band structure, work function difference, Bader charge transfer, and current-voltage curves, on-demand material screening and device performance prediction are achieved. This theory-driven research paradigm significantly shortens the development cycle of novel memory devices, reduces the high time and material costs associated with traditional trial-and-error experiments, and provides precise theoretical guidance for experimental fabrication. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a multi-state memory based on a GaTe / In2Se3 two-dimensional ferroelectric heterojunction.

[0026] Figure 2 Top view (a) and side view (b) of GaTe / In2Se3 ferroelectric heterojunction;

[0027] Figure 3 The diagram shows a GaTe / In2Se3 ferroelectric heterojunction with the source and drain contact electrodes aligned along the armchair and sawtooth crystal orientations, respectively. (a) is a top view, with arrows indicating different transport orientations; (b) is a side view.

[0028] Figure 4 The four resistor state bitmap is as follows (the input signals corresponding to the low resistance state LRS, the mid-low resistance state mid-LRS, the mid-high resistance state mid-HRS, and the high resistance state HRS are encoded as "00", "01", "10", and "11" respectively).

[0029] Figure 5 The effect of strain on the band structure of GaTe (a) and In2Se3 (b) is shown, where the black solid line represents the eigenstate and the blue solid line represents the state after strain is applied.

[0030] Figure 6The projected band structure of the GaTe / In2Se3 ferroelectric heterojunction in polarization-up (P↑) and polarization-down (P↓) states is shown in (a) (the orange and blue solid lines represent the projected weights of the GaTe and In2Se3 components, respectively, and the Fermi level is set to zero) and the band alignment between the GaTe and In2Se3 monolayers before contact (P↑ and P↓) is shown in (b).

[0031] Figure 7 The polarization flip barrier diagram for the GaTe / In2Se3 ferroelectric heterojunction;

[0032] Figure 8 The current-voltage characteristic curves of GaTe / In2Se3 ferroelectric heterojunction under different polarization states and transport directions are shown. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention.

[0034] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0035] A multi-state memory based on a two-dimensional ferroelectric heterojunction includes:

[0036] A two-dimensional ferroelectric van der Waals heterojunction is formed by vertically stacking a first two-dimensional material layer and a second two-dimensional ferroelectric material layer, wherein the second two-dimensional ferroelectric material layer has a reversible non-volatile polarization orientation.

[0037] At least two sets of source and drain electrodes are respectively in contact with the first two-dimensional material layer, and the connection direction of the two sets of source and drain electrodes is respectively arranged along different crystal orientations of the two-dimensional ferroelectric van der Waals heterojunction, for applying read voltages in different directions.

[0038] Example 1

[0039] This embodiment uses a GaTe / In2Se3 two-dimensional ferroelectric van der Waals heterojunction as an example to illustrate the polymorphic memory provided by the present invention.

[0040] like Figure 1 As shown, the multi-state memory based on GaTe / In2Se3 two-dimensional ferroelectric heterojunction includes a GaTe / In2Se3 two-dimensional ferroelectric van der Waals heterojunction and at least two sets of source and drain electrodes, wherein the GaTe / In2Se3 two-dimensional ferroelectric van der Waals heterojunction is used to store data, and the source and drain electrodes are used to apply read voltages in different directions.

[0041] In this embodiment, the first two-dimensional semiconductor material layer of the two-dimensional ferroelectric heterojunction is gallium telluride (GaTe), and the second two-dimensional ferroelectric material layer is indium triselenide (In2Se3). A GaTe monolayer is vertically stacked on top of an In2Se3 monolayer to construct a GaTe / In2Se3 bilayer heterojunction. Figure 2 The images show a top view (a) and a side view (b) of the GaTe / In₂Se₃ ferroelectric heterojunction. The heterojunction comprises nine atoms in total: three selenium atoms, two indium atoms, two tellurium atoms, and two gallium atoms. Both the GaTe and In₂Se₃ monolayers exhibit a hexagonal structure with lattice constants of 4.133 Å and 4.103 Å, respectively. Both GaTe and In₂Se₃ monolayers exhibit indirect band gaps of 1.408 eV and 0.775 eV, respectively.

[0042] Two sets of source and drain electrodes are respectively in contact with the GaTe material layer and are positioned in the armchair and serrated crystal orientations of the GaTe / In2Se3 two-dimensional ferroelectric van der Waals heterojunction. Figure 3 The diagram shows a GaTe / In2Se3 ferroelectric heterojunction with its source and drain contact electrodes aligned along the armchair and serrated crystal orientations, respectively. (a) is a top view, with arrows indicating different transport orientations; (b) is a side view. Figure 3 As shown in (b), the serrated electrode region consists of two orthogonal unit cells with a lattice constant of 4.12 Å along the transport direction and a central scattering region length of 4.12 nm; the armchair-shaped electrode region consists of one orthogonal unit cell with a corresponding lattice constant of 7.18 Å and a central scattering region length of 4.31 nm.

[0043] like Figure 3 As shown in (a), the polymorphic memory of this embodiment applies a first electrical signal to the source-drain electrode pair to flip the polarization orientation, and applies a second electrical signal to the source-drain electrode pair to read the tunneling resistance value, thereby performing different resistance state switching in two non-volatile states by independently controlling the polarization orientation and the selected source-drain electrode pair.

[0044] The device incorporates two input variables: a first input variable "A" (controlled by a first electrical signal) representing the ferropolarization direction, and a second input variable "B" (controlled by a second electrical signal) representing the carrier transport direction. For input variable "A", a logic value of "0" indicates a downward ferropolarization direction, and a logic value of "1" indicates an upward ferropolarization direction. For input variable "B", a logic value of "0" indicates a zigzag carrier transport direction, and a logic value of "1" indicates an armchair carrier transport direction. Figure 4 This is a bitmap showing the state of four resistors, such as... Figure 4As shown, when the input variables are combined as “00”, “01”, “10”, and “11”, the corresponding output resistance states are low resistance (LRS), mid-low resistance (mid-LRS), mid-high resistance (mid-HRS), and high resistance (HRS), respectively. This device can achieve four significantly different resistance states by combining and controlling two independent input variables, thus realizing multi-bit non-volatile storage functionality in a single device structure.

[0045] A design method for a multi-state memory based on a two-dimensional ferroelectric heterojunction includes the following steps:

[0046] (1) Construct a lattice-matched heterojunction model of a first two-dimensional material layer / a second two-dimensional ferroelectric material layer;

[0047] A vertical heterojunction model of a first two-dimensional material layer / second two-dimensional ferroelectric material layer is constructed by stacking a first two-dimensional material layer on top of a second two-dimensional ferroelectric material layer. First, the geometric and electronic structures of the first two-dimensional material layer / second two-dimensional ferroelectric material layer are determined, and the lattice mismatch rate is obtained according to the mismatch rate calculation formula.

[0048] The formula for calculating the mismatch rate is as follows:

[0049] ,

[0050] Where a1 and a2 are the lattice constants of the unit cells of the first two-dimensional material layer and the second two-dimensional ferroelectric material layer, respectively.

[0051] Then, the band structure of the first two-dimensional material layer and the second two-dimensional ferroelectric material layer under lattice mismatch strain was analyzed to explore the effect of strain caused by lattice mismatch on the electronic structure of each component. If the lattice mismatch has a weak effect on the band structure of the two isolated materials, then the lattice is matched.

[0052] (2) Analyze the binding energy of the heterojunction through first-principles calculations to determine the heterojunction with energy stability; calculate the band structure, work function and interlayer charge transfer of the heterojunction under different polarization states, and screen out the best heterojunction model with significant polarization reversal effect on band structure regulation.

[0053] S1: Based on first-principles calculations, analyze the binding energy of the heterojunction of the first two-dimensional material layer / the second two-dimensional ferroelectric material layer, and verify the stability of the heterojunction of the first two-dimensional material layer / the second two-dimensional ferroelectric material layer.

[0054] The formula for binding energy is as follows:

[0055] ,

[0056] in , and These represent the total energy of the heterojunction (first two-dimensional material layer / second two-dimensional ferroelectric material layer), the first two-dimensional material layer, and the first two-dimensional material layer, respectively. If the binding energy of the heterojunction is negative, the structure exhibits energy stability.

[0057] S2: Calculate the band structure, work function, and interlayer charge transfer of the heterojunction of the first two-dimensional material layer / second two-dimensional ferroelectric material layer under different polarization states, and study the modulation effect of polarization reversal on the band structure.

[0058] S201: The band structure of a heterojunction with a first two-dimensional material layer and a second two-dimensional ferroelectric material layer is studied using electron wavefunction and electron density. Based on the projected band structure of the heterojunction under different polarization states, a heterojunction model that can significantly modulate the band structure by ferroelectric polarization reversal is selected.

[0059] S202: Calculate the work function and Bader charge analysis of the heterojunction of the first two-dimensional material layer / second two-dimensional ferroelectric material layer, study the regulation of interlayer interaction by ferroelectric polarization reversal, and select a heterojunction model whose ferroelectric bistable characteristics are good and whose regulation of interlayer interaction by ferroelectric polarization reversal is not obvious.

[0060] The work function is defined as the difference between the vacuum level and the Fermi level. When two materials form a heterojunction, charge tends to transfer from the material with the lower work function to the material with the higher work function, and the extent of the transfer depends on the difference in their work functions.

[0061] (3) Based on the selected optimal heterojunction model, at least two sets of source and drain electrodes are set along different crystal orientations to construct a multi-electrode multi-channel ferroelectric tunnel junction; wherein, the left and right electrodes of the source and drain electrodes are both n-type doped by the compensation charge method.

[0062] (4) Density functional theory combined with the non-equilibrium Green's function method is used to simulate the current-voltage characteristics of the multi-electrode multi-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations, verify the distinguishability of the multi-resistance state, and determine the working voltage window.

[0063] S1: Density functional theory combined with the non-equilibrium Green's function method is used to simulate the current-voltage characteristics of the multi-electrode multi-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations, and to verify the distinguishability of multiple resistance states.

[0064] Applying a forward bias voltage across the electrodes generates a corresponding response current, and the current through the device is calculated using the Landauer-Büttiker formula:

[0065] ,

[0066] in, and Let Fermi-Dirac distribution functions of the left and right electrodes be represented respectively. This represents the transmission probability of electrons with different energies in the device. Based on the current-voltage curves of the device within the bias range, we analyze whether the device has stable and different resistance values ​​within the measurement bias window, verifying the distinguishability of multiple resistance states.

[0067] S2: Multi-state storage operation is achieved by orthogonally controlling the carrier transport direction and the ferroelectric polarization direction, and the working voltage window is determined.

[0068] First, by orthogonally controlling the carrier transport direction and the ferroelectric polarization direction, the aforementioned multi-electrode multi-channel ferroelectric tunnel junction is operated to perform different resistance state switching in two non-volatile states. In specific implementation, the device is configured with two input variables: the first input variable "B" represents the ferroelectric polarization direction, and the second input variable "A" represents the carrier transport direction. Then, under the premise of ensuring non-destructive readout, the voltage range that can best distinguish each resistance state without causing state switching or degradation is found, thus obtaining the operating voltage window.

[0069] Example 2

[0070] This embodiment uses a GaTe / In2Se3 two-dimensional ferroelectric van der Waals heterojunction as an example to illustrate the design method of the multi-state memory provided by the present invention.

[0071] (1) Constructing a lattice-matched GaTe / In2Se3 heterojunction model

[0072] A vertical GaTe / In2Se3 bilayer heterojunction was constructed by stacking GaTe monolayers on top of In2Se3 monolayers. The mismatch rate of the GaTe / In2Se3 heterojunction was calculated using the mismatch rate calculation formula:

[0073] ,

[0074] Where a1 and a2 are the lattice constants of GaTe and In2Se3 unit cells, respectively.

[0075] The mismatch rate of the GaTe / In2Se3 heterojunction was calculated to be 0.36%. The band structure of the GaTe and In2Se3 monolayers under 0.36% strain was analyzed, and the results are as follows: Figure 5 As shown, the results indicate that the lattice mismatch has a weak effect on the band structure of the two isolated materials, suggesting that the GaTe / In2Se3 heterostructure has a matched lattice.

[0076] (2) Analyze the binding energy of GaTe / In2Se3 heterojunction through first-principles calculations to determine whether GaTe / In2Se3 has energy stability; calculate the band structure, work function and interlayer charge transfer of GaTe / In2Se3 heterojunction under different polarization states to study the modulation effect of polarization reversal on band structure.

[0077] S1: Based on first-principles calculations, the binding energy of the GaTe / In2Se3 heterojunction is analyzed to verify the stability of the GaTe / In2Se3 ferroelectric heterojunction.

[0078] The formula for binding energy is as follows:

[0079] ,

[0080] in , and The values ​​represent the total energies of the GaTe / In₂Se₃ heterojunction, GaTe monolayer, and In₂Se₃ monolayer, respectively. The calculation results show that the binding energy of the heterojunction is negative, where E0 is the total energy of the GaTe / In₂Se₃ heterojunction. b-P↑ =-2.441eV, E b-P↓ = -2.481eV, P↑ and P↓ represent the upward and downward polarization states of the In2Se3 monolayer, respectively, indicating that the structure has energy stability.

[0081] S2: Calculate the band structure, work function, and interlayer charge transfer of GaTe / In2Se3 heterojunction under different polarization states, and study the modulation effect of polarization reversal on the band structure.

[0082] S201: The band structure of the GaTe / In₂Se₃ ferroelectric heterojunction was studied using electronic wavefunction and electron density. Based on the projected band structure of the GaTe / In₂Se₃ ferroelectric heterojunction under different polarization states, the study analyzed whether ferroelectric polarization reversal could significantly modulate the band structure. Results are as follows: Figure 6 As shown in (a), the band gaps of the GaTe / In2Se3 ferroelectric heterojunction when polarized upward and downward are 0.87 eV and 0.19 eV, respectively, indicating that ferroelectric polarization reversal can significantly modulate the band structure.

[0083] By comparing the projected band structures of the two polarization states, it was found that this phenomenon mainly originates from the change in the position of the In2Se3 band edge caused by the reversal of ferropolar polarization. Specifically, in upward polarization, the bottom of the In2Se3 conduction band is far from the Fermi level, while the top of its valence band is close to the Fermi level; conversely, in downward polarization, the bottom of the In2Se3 conduction band approaches the Fermi level, while the top of its valence band is far from the Fermi level.

[0084] S202: The work function of GaTe / In2Se3 ferroelectric heterostructures was calculated and Bader charge analysis was performed to study the modulation effect of ferroelectric polarization reversal on interlayer interactions.

[0085] Calculations show that the work functions of GaTe monolayer and In2Se3 monolayer in the upward and downward polarized states are 4.57, 4.73, and 5.92 eV, respectively. Figure 6 As shown in (b), since the work function of the In2Se3 monolayer is greater than that of the GaTe monolayer in both polarization states, electrons always transfer from the GaTe layer to the In2Se3 layer during heterojunction formation, regardless of whether the In2Se3 monolayer is in the P↑ or P↓ state. Moreover, there is a difference in the amount of interlayer charge transfer between the two polarization states, resulting in a phenomenon where ferroelectric polarization reversal causes the bandgap position of the In2Se3 monolayer to shift, that is, the electron doping concentration in the In2Se3 monolayer changes with the polarization state.

[0086] To quantify interlayer charge transfer in the GaTe / In₂Se₃ heterojunction, Bader charge analysis was performed. The calculations show that the number of electrons transferred from the GaTe monolayer to the In₂Se₃ monolayer in the P↑ and P↓ states are 0.018e and 0.024e, respectively. This indicates that the ferroelectric polarization reversal in the GaTe / In₂Se₃ heterojunction does not significantly modulate the interlayer interaction; therefore, no semiconductor-metal transition occurs in this system, and its ferroelectric bistable characteristics are well maintained. Figure 7 This is a polarization flip barrier diagram for the GaTe / In2Se3 ferroelectric heterojunction.

[0087] (3) Using the GaTe / In2Se3 heterojunction as a two-dimensional ferroelectric van der Waals heterojunction, two sets of source and drain electrodes are set along its armchair crystal orientation and serrated crystal orientation to construct a four-electrode dual-channel ferroelectric tunnel junction. The left and right electrodes of the source and drain electrodes are both n-type doped by the compensation charge method, and the doping concentration is set to 0.15e / atom.

[0088] (4) Using density functional theory combined with the non-equilibrium Green's function method, the current-voltage characteristics of the four-electrode dual-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations are simulated to verify the distinguishability of multiple resistance states and determine the working voltage window.

[0089] S1: Density functional theory combined with the non-equilibrium Green's function method is used to simulate the current-voltage characteristics of the four-electrode dual-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations, and to verify the distinguishability of multiple resistance states.

[0090] Applying a forward bias voltage across the electrodes generates a corresponding response current, and the current through the device is calculated using the Landauer-Büttiker formula:

[0091] ,

[0092] in, and Let Fermi-Dirac distribution functions of the left and right electrodes be represented respectively. This represents the transmission probability of electrons with different energies in the device. Figure 8 The current-voltage characteristic curves of GaTe / In2Se3 ferroelectric heterojunction under different polarization states and transport directions are shown. The current-voltage curves within the bias range [0.0, 0.4] V are displayed. Each curve shows a significantly different slope and maintains good linearity, indicating that the device has stable and different resistance values ​​within the measurement bias window, proving that it has good bias stability and anisotropic electric transport characteristics.

[0093] S2: Multi-state storage operation is achieved by orthogonally controlling the carrier transport direction and the ferroelectric polarization direction, and the working voltage window is determined.

[0094] By orthogonally controlling the carrier transport direction and the ferroelectric polarization direction, the aforementioned four-electrode dual-channel ferroelectric tunnel junction can perform different resistance state switching in two non-volatile states. In specific implementation, the device sets two input variables: the first input variable "A" represents the ferroelectric polarization direction, and the second input variable "B" represents the carrier transport direction. For input variable "A", a logic value "0" indicates that the ferroelectric polarization direction is downward, and a logic value "1" indicates that the ferroelectric polarization direction is upward; for input variable "B", a logic value "0" indicates that the carrier transport direction is along the zigzag direction, and a logic value "1" indicates that the carrier transport direction is along the armchair direction. When the input variable combinations are "00", "01", "10", and "11", the corresponding output resistance states are low resistance state (LRS), mid-low resistance state (mid-LRS), mid-high resistance state (mid-HRS), and high resistance state (HRS), respectively. This shows that the device can achieve four significantly different resistance states by combining and controlling two independent input variables. Finally, while ensuring non-destructive reading, the voltage range that can best distinguish the two resistive states without causing state flipping or degradation is found, thus obtaining the operating voltage window.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A multi-state memory based on a two-dimensional ferroelectric heterojunction, characterized in that, include: A two-dimensional ferroelectric van der Waals heterojunction is formed by vertically stacking a first two-dimensional material layer and a second two-dimensional ferroelectric material layer, wherein the second two-dimensional ferroelectric material layer has a reversible non-volatile polarization orientation. At least two sets of source and drain electrodes are respectively in contact with the first two-dimensional material layer, and the connection direction of the two sets of source and drain electrodes is respectively arranged along different crystal orientations of the two-dimensional ferroelectric van der Waals heterojunction, for applying read voltages in different directions.

2. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 1, characterized in that, The first two-dimensional material layer is GaTe, and the second two-dimensional ferroelectric material layer is In2Se3.

3. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 1, characterized in that, The connection directions of the two sets of source and drain electrodes are respectively along the armchair direction and the sawtooth direction of the two-dimensional ferroelectric van der Waals heterojunction.

4. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 1, characterized in that, The polymorphic memory applies a first electrical signal to the source-drain electrode pair to flip the polarization orientation and applies a second electrical signal to the source-drain electrode pair to read the tunneling resistance value, thereby achieving at least four distinguishable resistance states on a single heterojunction by independently controlling the polarization orientation and the selected source-drain electrode pair.

5. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 4, characterized in that, The at least four distinguishable resistance states are determined by a combination of a first input variable and a second input variable, wherein the first input variable corresponds to the polarization orientation of the second two-dimensional ferroelectric material layer and the second input variable corresponds to the carrier transport direction determined by the selected source-drain electrode pair.

6. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 5, characterized in that, When the first input variable is 0, the corresponding ferroelectric polarization direction is downward polarization, and when it is 1, the corresponding ferroelectric polarization direction is upward polarization; when the second input variable is 0, the corresponding carrier transport direction is sawtooth direction, and when it is 1, the corresponding carrier transport direction is armchair direction; the output resistance state varies with the input combination 00, 01, 10, 11, and successively presents a low resistance state, a medium-low resistance state, a medium-high resistance state, and a high resistance state.

7. The multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 4, characterized in that, The first electrical signal is a voltage pulse with an amplitude greater than the coercive voltage of the second two-dimensional ferroelectric material layer; the second electrical signal is a continuous voltage with an amplitude less than the coercive voltage of the second two-dimensional ferroelectric material layer.

8. A design method for a multi-state memory based on a two-dimensional ferroelectric heterojunction as described in claim 1, characterized in that, Includes the following steps: (1) Construct a lattice-matched heterojunction model of a first two-dimensional material layer / a second two-dimensional ferroelectric material layer; (2) Analyze the binding energy of the heterojunction using first-principles calculations to determine the heterojunction with energy stability; The band structure, work function, and interlayer charge transfer of heterojunctions under different polarization states were calculated, and the optimal heterojunction model with significant polarization reversal effect on band structure regulation was selected. (3) Based on the selected optimal heterojunction model, at least two sets of source and drain electrodes are set along different crystal orientations to construct a multi-electrode multi-channel ferroelectric tunnel junction; (4) Density functional theory combined with the non-equilibrium Green's function method is used to simulate the current-voltage characteristics of the multi-electrode multi-channel ferroelectric tunnel junction under different transport directions and different polarization state combinations, verify the distinguishability of the multi-resistance state, and determine the working voltage window.

9. The design method of a multi-state memory based on a two-dimensional ferroelectric heterojunction according to claim 8, characterized in that, The optimal heterojunction model is the GaTe / In2Se3 heterojunction model.

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