A double-layer and triple-layer graphene out-of-plane sliding ferroelectric material based on defect engineering and a regulation method thereof

Abstract

The application discloses a graphene sliding ferroelectric regulation method and device based on defect engineering and belongs to the technical field of two-dimensional ferroelectric materials. In the application, structural defects are introduced into specified monolayers of double-layer graphene, the lattice spatial symmetry is destroyed, and a defect double-layer graphene system with intrinsic polarity is constructed. Then, the system is polarized and regulated by using out-of-plane interlayer sliding, the out-of-plane ferroelectric polarization is reversibly flipped, and a non-typical sliding ferroelectric response is formed. Meanwhile, a three-layer graphene structure is constructed, defects are introduced into specific layer positions, and a defect three-layer graphene system with high polarization intensity is prepared. The system is subjected to double-mode sliding regulation, small-amplitude polarization is quickly switched by using low-barrier in-plane interlayer sliding, and super-high out-of-plane polarization is obtained by using out-of-plane interlayer sliding, and the polarization is reversibly flipped. The application breaks through the limitation of traditional two-dimensional sliding ferroelectric regulation, provides a new design idea for the research and development of high-performance van der Waals ferroelectric devices, and can be applied to the fields of high-density information storage, intelligent sensing and preparation of new microelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional ferroelectric materials technology, specifically relating to defective graphene sliding ferroelectric materials and their interlayer polarization regulation, which can be applied to information storage and novel microelectronic devices. Background Technology

[0002] Ferroelectric materials, due to their spontaneously polarizing properties, are widely used in multifunctional information storage devices such as ferroelectric memories, field-effect transistors, and tunnel junctions. Traditional perovskite ferroelectric materials exhibit a significant critical size effect, with ferroelectricity decreasing sharply as the thickness decreases to the nanometer scale. They also suffer from poor high-temperature processing compatibility and high mechanical brittleness, making it difficult to meet the demands of atomic-level miniaturization and flexible integration. Two-dimensional van der Waals materials offer a new path for the design of ultrathin ferroelectrics. Most non-polar two-dimensional materials can achieve sliding ferroelectricity through non-equivalent interlayer stacking, i.e., relying on in-plane interlayer slip to achieve out-of-plane polarization reversal.

[0003] Graphene, as a typical highly symmetric two-dimensional carbon material with a honeycomb lattice, cannot break symmetry through in-plane sliding due to its intrinsic bilayer structure, and therefore lacks out-of-plane ferroelectric polarization. The reported pure multilayer graphene sliding ferroelectric system has an out-of-plane polarization of only about 0.21 pC / m, and can only be controlled by in-plane sliding alone. The polarization is weak, the control methods are limited, and the application potential is limited.

[0004] Currently, two-dimensional sliding ferroelectric materials generally rely on in-plane slip mechanisms, lacking graphene-based systems that can achieve strong polarization reversal through out-of-plane interlayer slip. Existing technologies struggle to simultaneously achieve high out-of-plane polarization and multi-mode sliding control within graphene structures, failing to balance high signal response with low-energy switching. Therefore, it is urgent to break through the traditional in-plane sliding ferroelectric framework, utilize defect engineering to disrupt the inherent symmetry of graphene, and construct novel ferroelectric systems that combine high out-of-plane polarization with both in-plane and out-of-plane control capabilities, providing crucial technological support for the development of high-performance two-dimensional van der Waals ferroelectric devices. Summary of the Invention

[0005] This invention discloses a defect-engineered out-of-plane sliding ferroelectric material of two-layer and three-layer graphene and its polarization control method, belonging to the field of two-dimensional ferroelectric materials and microelectronic devices. The specific method steps are as follows:

[0006] Step 1: Prepare highly symmetric bilayer and trilayer graphene substrates, introduce structural defects at specified layers to disrupt lattice symmetry and induce out-of-plane ferroelectric polarization;

[0007] Step 2: Polarization reversal is achieved for defective bilayer graphene by out-of-plane interlayer sliding; polarization is controlled for defective trilayer graphene by in-plane / out-of-plane dual sliding.

[0008] Step 3: Verify the structural stability of the material and integrate the defective graphene ferroelectric system to fabricate a high-performance microelectronic device.

[0009] Further, in step 1, highly symmetric bilayer and trilayer graphene are selected as initial substrates and prepared using an AA stacking configuration. This ensures strict atomic alignment between layers and maintains complete six-fold symmetry of the lattice, guaranteeing the system's intrinsic nonpolarity and absence of spontaneous polarization. The bilayer graphene employs a structure with perfectly aligned upper and lower layers, while the trilayer graphene uses AAA symmetric stacking. Only weak van der Waals interactions exist between the layers, with no chemical bonding or lattice distortion. High-quality graphene films with atomically flat surfaces, free of impurities and pre-defects are obtained through vapor deposition, mechanical exfoliation, or epitaxial growth, with the interlayer rotation angle strictly controlled at 0° to ensure high system symmetry. Subsequently, atomic-scale structural defects, including single vacancies, double vacancies, or localized lattice distortions, are precisely introduced into the specified single or bilayer layers. These defects act only on the target layers without disrupting the overall graphene honeycomb framework. By disrupting the inherent spatial symmetry between graphene layers through defect modulation, the uniformity of charge distribution is destroyed, and directional charge transfer between layers is induced, transforming the system from a nonpolar paraelectric state to a ferroelectric state with strong out-of-plane spontaneous polarization. This provides a structural basis and polarization source for subsequent interlayer sliding polarization modulation.

[0010] Furthermore, in step 2, differentiated interlayer sliding polarization control is implemented for the defect-introduced bilayer and trilayer graphene. For defective bilayer graphene, an out-of-plane (OOP) interlayer sliding mode along the c-axis of the crystal is adopted. While maintaining the relative positions of atoms within the layers, the defect layer and the intrinsic graphene layer undergo controllable relative displacement in the vertical direction, overcoming the interlayer van der Waals barrier and achieving a completely reversible reversal of the out-of-plane ferroelectric polarization, thereby forming a stable and distinguishable ferroelectric bistable state. For defective trilayer graphene, a dual in-plane (IP) and out-of-plane (OOP) sliding mode can be adopted: through horizontal sliding between in-plane layers, rapid polarization switching with low barrier (5~50 meV) and low amplitude (0.1~0.6 pC / m) is achieved to meet the requirements of low-power and high-speed device applications. By vertically sliding out-of-plane interlayer along the c-axis, an ultra-high out-of-plane polarization of up to 5.92 pC / m is generated, and the reversible reversal of the strong polarization state is completed, which meets the requirements of high-sensitivity and high-reliability storage and sensing applications, and enables precise control of ferroelectric polarization intensity, reversal direction and switching energy consumption.

[0011] Furthermore, in step 3, the structural and thermal stability of the constructed defective bilayer and trilayer graphene ferroelectric systems are fully verified, and the device integration is completed.

[0012] Phonon spectrum simulations of the system were performed using first-principles calculations to ensure the absence of imaginary frequencies in the phonon spectrum, demonstrating the material's dynamical stability and reliability. First-principles molecular dynamics simulations at 300 K were conducted to monitor the evolution of the system's energy and atomic structure over time, confirming that the material exhibits excellent thermal stability and structural robustness within its actual operating temperature range, without structural distortion, defect migration, or interlayer dissociation.

[0013] After completing the material performance characterization and reliability verification, the above-mentioned defective graphene sliding ferroelectric system is used as the core functional layer and integrated with the electrode, dielectric layer and encapsulation layer to fabricate ferroelectric random access memory, ferroelectric field-effect transistor, ferroelectric tunnel junction or multi-state information storage device. By utilizing the in-plane / out-plane sliding controllable polarization characteristics, non-volatile data storage, high and low resistance state control and multi-bit logic output are realized, resulting in high-performance two-dimensional ferroelectric devices with excellent performance, flexible control and compatibility with silicon-based processes. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the out-of-plane sliding ferroelectric mechanism in defective graphene, where (a) is the in-plane sliding path of a traditional two-dimensional sliding ferroelectric. (b) proposes an out-of-plane sliding path along the c-axis of the crystal, where the sliding process requires overcoming interlayer van der Waals interactions.

[0015] Figure 2 To characterize the out-of-plane sliding ferroelectric properties of defective bilayer graphene, the yellow and red layers represent graphene (G) and defective graphene (D), respectively. (a) and (c) show six different stacking orders of the bilayer graphene: (a) indicates a defective top layer (called the DG configuration), and (c) indicates a defective bottom layer (called the GD configuration). (b) and (d) are schematic diagrams of the relative energy and vertical polarization distribution of the graphene bilayer under different stacking configurations, with orange arrows indicating polarization directions along the positive c-axis and green arrows indicating polarization directions along the negative c-axis.

[0016] Figure 3 This invention relates to the defect-induced ferroelectric polarization and regulation mechanism of three-layer graphene, wherein (a) the phonon spectrum of the DG-AB bilayer film; (b) the energy-time curve obtained from molecular dynamics simulation of the DG-AB bilayer film at T = 300 K; (c) the ferroelectric switching path along the

[001] direction, and the energy barrier of the bilayer graphene from the DG-AB configuration to the GD-BA configuration; (d) the differential charge density map of the DG-AA and GD-AA stacked structures and their top and side views based on Hirshfeld charge analysis, wherein the yellow and blue isosurfaces represent the electron accumulation region and the electron depletion region, respectively.

[0017] Figure 4The different stacking orders of the DD+1 and D+2 type graphene trilayer structures of the present invention are shown, where NP indicates a nonpolar configuration. (a) Interlayer slip of IP in DGD and GDG trilayer structures; (b) Interlayer slip of OOP in DGD and GDG trilayer structures. Detailed Implementation

[0018] This specific implementation is based on first-principles density functional theory (DFT) calculations and is simulated using the VASP software package. The exchange-correlation functional is selected using the PBE generalized gradient approximation, the cutoff energy is set to 480 eV, a 3×3×1 k-point grid is laid out using the Monkhorst-Pack method, uniform integral sampling is performed on the Brillouin zone, and the vacuum layer thickness is not less than 15 Å to avoid interlayer interactions.

[0019] First, the model was constructed and defects were introduced. This invention constructed an AA-stacking bilayer graphene supercell with lattice constants a = b = 2.46 Å and interlayer spacing d0 = 3.35 Å. Single-vacancy defects were introduced into the upper carbon atoms using a 4×4 graphene supercell model. One carbon atom vacancy defect was introduced into the single supercell structure, maintaining a constant defect atom percentage to form a DG configuration. Similarly, defects were introduced into the lower layer to form a GD configuration. For the three-layer graphene, AAA stacking was used, and defects were introduced into the 1st and 3rd layers (DGD), and the 2nd layer (GDG), respectively, with the defect location and concentration consistent with the bilayer system.

[0020] The spontaneous polarization intensity P of the system was calculated using the Berry phase method:

[0021]

[0022] Where: e is the elementary charge, Ω is the unit cell volume, Z is the effective charge, and r is the atomic displacement.

[0023] Next, we explored the out-of-plane sliding polarization modulation of defective bilayer graphene. A rigid interlayer displacement, Δz, was applied along the c-axis to the DG-configured bilayer graphene. The displacement range was 0 ~ 0.7 Å. The calculation results showed:

[0024] (1) Defect-induced equilibrium polarization intensity: 3.31 ~ 3.86 pC / m

[0025] (2) Out-of-plane glide barrier: ~300 meV / unit cell

[0026] (3) Polarization reversal is driven entirely by Δz, and in-plane displacement cannot change the polarization direction.

[0027] When the interlayer relative displacement reaches Δz = 0.35 Å, the polarization direction flips by 180°, satisfying:

[0028] P final = −P initial

[0029] Achieving a typical ferroelectric bistable state.

[0030] For the dual-mode sliding control of defective trilayer graphene, the first is the in-plane (IP) sliding mode. Interlayer translation is applied along the a / b axis, with a displacement Δx = 0 ~ 1.23 Å, polarization intensity: 0.1 ~ 0.6 pC / m, and sliding barrier: 5 ~ 50 meV. It is characterized by low energy consumption and rapid switching, making it suitable for low-power devices.

[0031] Out-of-plane (OOP) sliding mode: A vertical displacement Δz = 0 ~ 0.7 Å is applied along the c-axis. The highest polarization intensity reaches 5.92 pC / m. The sliding barrier is 280 ~ 320 meV. The polarization value is significantly higher than that of previously reported van der Waals interface ferroelectric systems.

[0032] Finally, stability was verified using phonon spectroscopy calculations and 300 K molecular dynamics simulations: the phonon spectrum showed no imaginary frequencies throughout the Brillouin zone, satisfying the dynamic stability condition. After a 10 ps simulation at 300 K, the maximum atomic displacement was less than 0.15 Å, the structure showed no distortion, no defect migration, and interlayer spacing fluctuations were less than 0.1 Å, maintaining the integrity of the van der Waals stacking structure.

[0033] Key performance indicators obtained in this embodiment:

[0034] Bilayer defect graphene: P ≈ 3.59 pC / m

[0035] Trilayer defect graphene: P_max = 5.92 pC / m

[0036] Control methods: Two-layer system supports out-of-plane sliding only; Three-layer system supports both in-plane and out-of-plane modes.

[0037] Compared to the pure graphene sliding ferroelectric system (P ≈ 0.21 pC / m), the polarization is improved by nearly 30 times.

[0038] This embodiment fully demonstrates that the present invention, through defect engineering and out-of-plane sliding along the c-axis, can realize a high-performance, multi-mode controllable graphene-based sliding ferroelectric system, which is suitable for next-generation non-volatile memory and low-power microelectronic devices.

Claims

1. A sliding ferroelectric material based on defect engineering, characterized in that: The material is bilayer or trilayer graphene with introduced structural defects. Bilayer graphene is of the DG or GD configuration with defects introduced in one layer. These defects disrupt the symmetry of the highly symmetric honeycomb lattice of graphene, thereby generating flippable out-of-plane ferroelectric polarization. Trilayer graphene is of the DGD, GDG, DDG, or GGD configuration with defects introduced in a specific single or bilayer, exhibiting both in-plane and out-of-plane ferroelectric modulation properties.

2. The sliding ferroelectric material according to claim 1, characterized in that, The out-of-plane ferroelectric polarization of the bilayer defect graphene is 3.31~3.86 pC / m, and the out-of-plane ferroelectric polarization of the trilayer defect graphene can reach up to 5.92 pC / m.

3. A method for controlling the ferroelectric polarization of bilayer defect graphene, comprising the following steps: (1) Highly symmetric nonpolar bilayer graphene was selected as the matrix; (2) Introduce structural defects into the upper or lower layer of bilayer graphene to obtain defective bilayer graphene with DG or GD configuration. (3) Reversible reversal of out-of-plane ferropolarization is achieved by out-of-plane (OOP) interlayer sliding, while in-plane sliding cannot change the polarization direction.

4. The control method according to claim 3, characterized in that, The out-of-plane interlayer sliding occurs along the c-axis of the crystal, while the relative positions of atoms within the layer remain unchanged, and the sliding switching energy barrier is approximately 300 meV / unit cell.

5. A method for controlling the ferroelectric polarization of three-layer defective graphene, comprising the following steps: (1) Construct a three-layer graphene structure and introduce structural defects in a specific single or double layer; (2) Low amplitude and low barrier polarization switching is achieved by in-plane (IP) interlayer sliding, with a polarization intensity of 0.1~0.6 pC / m and a sliding barrier of 5~50 meV. Alternatively, high amplitude polarization switching is achieved by out-of-plane (OOP) interlayer sliding, with a maximum polarization intensity of 5.92 pC / m.

6. The control method according to claim 5, characterized in that, The three-layer defective graphene can independently achieve the reversal and control of out-of-plane ferropolarization through in-plane or out-of-plane sliding.

7. The material or method according to any one of claims 1 to 6, characterized in that, The structural defects are used to break the spatial symmetry between graphene layers, induce interlayer charge transfer, and generate spontaneous out-of-plane polarization.

8. The application of the sliding ferroelectric material according to any one of claims 1 to 7 in ferroelectric memory, field-effect transistor, tunnel junction, and multifunctional information storage device.

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