Cross-dimensional phase change device based on semi-metal material, preparation method, phase change induction method and application
By realizing cross-dimensional structural phase transitions in half-metal materials such as PtBi2 and utilizing the "intra-layer splitting-inter-layer reconstruction" atomic mechanism, the problem of irreversible cross-dimensional phase transitions in existing technologies has been solved, and reversible switching between high-resistivity and low-resistivity states has been achieved. This is suitable for novel memory storage and logic operation units in the field of topological electronics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING INST OF TECH
- Filing Date
- 2025-12-30
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies struggle to achieve reversible cross-dimensional phase transitions while maintaining the chemical composition of materials, limiting their application in functional devices such as memory storage and logic switches.
By controlling external electrical excitation, a cross-dimensional structural phase transition between a two-dimensional ferroelectric phase and a three-dimensional topological T' phase is achieved in half-metal materials such as PtBi2. By utilizing the atomic mechanism of "intralayer splitting-interlayer reconstruction", a resistance hysteresis loop is formed, enabling reversible switching between high-resistivity and low-resistivity states.
This achievement realizes a cross-dimensional topological phase transition from two-dimensional spin Hall insulators to three-dimensional strong topological insulators, providing a new dimension for topological property control in the field of topological electronics, and is suitable for constructing novel memory storage and logic operation units.
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Figure CN122028652A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of topological quantum devices, and in particular to a cross-dimensional phase transition device based on a half-metal material, its preparation method, phase transition induction method, and its application. Background Technology
[0002] Phase transitions are one of the key means to control the electrical, optical and topological properties of materials. Traditional phase transitions, such as the 2H-1T' phase transition in molybdenum ditelluride (MoTe2), usually occur within the same dimension (such as two-dimensional to two-dimensional), and their atomic rearrangement is limited to the plane, which cannot achieve a change in the overall dimension of the material.
[0003] In recent years, although some studies have reported cross-dimensional phenomena such as the transformation of titanium selenide (TiSe2) to titanium nonoselenide (Ti2Se9), such phase transitions are often accompanied by changes in chemical composition and the process is usually irreversible, which severely limits their application in functional devices that require reversible operation (such as memory storage and logic switches).
[0004] Dimension, as a fundamental physical property of materials, directly affects their symmetry and electronic structure. Achieving controllable and reversible cross-dimensional phase transitions (such as from two-dimensional to three-dimensional) holds promise for inducing new property leaps that cannot be achieved by conventional phase transitions, such as the mapping and manipulation of topological quantum states between different dimensions.
[0005] However, how to achieve this reversible cross-dimensional phase transition while keeping the chemical composition of the material unchanged, and apply it to functional devices, remains a core technical challenge that urgently needs to be overcome in this field.
[0006] Topological half-metal materials, represented by platinum dibismuthide (PtBi2), are known to have a variety of stable two-dimensional phases. However, current research is mostly limited to the property control within the two-dimensional phase, and has not yet explored the technology of realizing new functions and quantum devices through cross-dimensional phase transitions.
[0007] In view of this, a novel cross-dimensional phase change device based on semi-metallic materials, its preparation method, phase change induction method, and its application are proposed to solve all or part of the above problems. Summary of the Invention
[0008] To address at least one of the aforementioned problems and deficiencies in the prior art, embodiments of the present invention provide a cross-dimensional phase transition device based on half-metallic materials, its fabrication method, phase transition induction method, and its application. By controlling the induced phase transition, a cross-dimensional structural phase transition between an isomeric, reversible two-dimensional ferroelectric phase and a three-dimensional topological T' phase is achieved in half-metallic materials such as PtBi2. This phase transition, based on a clear "intra-layer splitting-inter-layer reconstruction" atomic mechanism, breaks through the dimensional limitations of traditional phase transitions, exhibiting a "hat-shaped" resistance-voltage hysteresis loop. It achieves reversible, non-volatile switching between high-resistivity and low-resistivity states. By using "dimensionality" itself as a parameter driving the topological phase transition, a cross-dimensional topological phase transition from a two-dimensional spin Hall insulator to a three-dimensional strong topological insulator is realized, providing a new dimension for topological property control in the field of topological electronics. The technical solution is as follows:
[0009] According to one aspect of the present invention, a cross-dimensional phase change device based on a half-metallic material is provided. The cross-dimensional phase change device includes:
[0010] SiO2 / Si substrate;
[0011] A semi-metallic material layer is located on the upper surface of the SiO2 / Si substrate, and the initial state of the semi-metallic material layer is a two-dimensional ferroelectric phase;
[0012] The metal electrode is in electrical contact with the semi-metallic material layer; wherein
[0013] External electrical excitation causes a reversible cross-dimensional structural phase transition in the half-metal material layer through metal electrodes, with no change in composition, transforming it from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase, accompanied by a sudden change in the resistance state, forming a resistive hysteresis loop.
[0014] In some embodiments, specifically, the semi-metallic material is any one or any combination of PtBi2, PdBi2 and NiBi2, and the thickness of the semi-metallic material layer is 1-100 nm.
[0015] In some embodiments, the metal electrode is specifically a Cr / Au composite electrode, wherein the Cr layer thickness is 3-10 nm and the Au layer thickness is 40-60 nm.
[0016] In some embodiments, the metal electrode is specifically structured as a two-terminal crossbar structure, a Hall bar structure, or a three-terminal structure integrated with a field-effect transistor.
[0017] In some embodiments, the external electrical excitation specifically includes voltage scanning, current scanning, or pulsed electrical excitation. This external electrical excitation induces a transdimensional structural phase transition via the Joule heating effect, the critical temperature of which is 600-700 K.
[0018] In some embodiments, preferably when PtBi2 is used as a half-metal material, the atomic mechanism of the cross-dimensional structural phase transition includes:
[0019] In the two-dimensional ferroelectric phase of the PtBi2 material layer, the Bi-Bi-Pt-Pt-Bi-Bi six-membered ring undergoes in-plane deformation;
[0020] The Pt atomic layer splits, with some of the Pt atoms migrating vertically downwards and passing through the bottom Bi atomic layer to migrate to the van der Waals gap.
[0021] The migrating Pt atoms form covalent bonds with Bi atoms at the top of the adjacent PtBi2 material layer, reconstructing the Bi-Pt-Bi three-layer structure into a Bi-Pt-Bi-Pt four-layer structure, thus reconstructing the structure from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase.
[0022] In some embodiments, in the PtBi2 material layer, a portion of the region is a two-dimensional ferroelectric phase and another portion is a three-dimensional topological T' phase, forming a heterojunction in which the two-dimensional and three-dimensional phases coexist, and an interface topological boundary state is formed at the boundary of the regions to achieve quantum transmission.
[0023] In some embodiments, corresponding to a two-dimensional spin Hall insulator, the topological invariant of the two-dimensional ferroelectric phase is Z2=1; corresponding to a three-dimensional strong topological insulator, the topological invariant of the three-dimensional topological T' phase is (1; 000).
[0024] According to one aspect of the present invention, a method for fabricating a cross-dimensional phase change device based on a semi-metallic material is provided, for obtaining the cross-dimensional phase change device described above. The fabrication method includes:
[0025] Crystal flakes of semi-metallic materials are prepared by chemical vapor deposition or mechanical exfoliation, and then transferred to the upper surface of a SiO2 / Si substrate.
[0026] Metal electrodes are fabricated on crystal wafers using photolithography and electron beam evaporation.
[0027] Electrical tests were performed on the cross-dimensional phase change device, and the resistive hysteresis loop was verified using a dual-probe IV test. The critical voltage for the cross-dimensional structural phase transition was ±0.8-±1.6V.
[0028] According to one aspect of the present invention, a phase transition induction method for a cross-dimensional phase change device based on a half-metallic material is provided, for inducing the cross-dimensional phase change device described above to form a cross-dimensional structural phase transition reconstruction. The phase transition induction method includes:
[0029] Applying a positive external electrical excitation to the metal electrode raises the local temperature of the half-metal material layer to the critical point of cross-dimensional structural phase transition through the Joule heating effect, triggering the transformation from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase.
[0030] By applying a reverse external electrical excitation to the metal electrode, the three-dimensional topological T' phase is reversibly transformed into a two-dimensional ferroelectric phase through cooling via the Peltier effect;
[0031] The external electrical excitation is a voltage scan, with a scan voltage range of ±1.0-±2.0V.
[0032] According to one aspect of the present invention, an application of a cross-dimensional phase-change device based on a half-metal material in topological quantum devices is provided. The cross-dimensional phase-change device is either the cross-dimensional phase-change device described in the above aspect or a cross-dimensional phase-change device prepared by the preparation method described in the above aspect.
[0033] In some embodiments, the cross-dimensional phase change device achieves reversible switching between a high-resistivity state and a low-resistivity state through a resistive hysteresis loop.
[0034] In some embodiments, the cross-dimensional phase change device achieves topological state modulation from a two-dimensional spin Hall insulator to a three-dimensional strong topological insulator through a cross-dimensional structural phase change.
[0035] The embodiments of the present invention provide a cross-dimensional phase change device, fabrication method, phase change induction method, and application based on semi-metallic materials, which have at least one or a portion of the following advantages:
[0036] (1) By controlling the induced phase transition, a cross-dimensional structural phase transition between a two-dimensional ferroelectric phase and a three-dimensional topological T' phase with equal composition and reversibility was realized in half-metal materials such as PtBi2. This phase transition is based on a clear "intra-layer splitting-inter-layer reconstruction" atomic mechanism, which breaks through the dimensional limitation of traditional phase transitions.
[0037] (2) Based on the reproduction of cross-dimensional phase transition, the cross-dimensional phase transition device exhibits a unique “hat-shaped” resistance-voltage hysteresis loop, realizing reversible and non-volatile switching between high resistance state and low resistance state, which can be used to construct new memory storage or logic operation units.
[0038] (3) By taking the “dimension” itself as a parameter to drive the topological phase transition, a cross-dimensional topological phase transition from a two-dimensional spin Hall insulator (topological invariant Z2=1) to a three-dimensional strong topological insulator (topological invariant 1;000) was realized, providing a new dimension for the topological property control in the field of topological electronics.
[0039] (4) The cross-dimensional phase change device is based on conventional SiO2 / Si substrate and Cr / Au electrode. It is prepared by mature processes such as chemical vapor deposition or mechanical exfoliation. The phase change is triggered by external electrical excitation through the Joule heating effect. It is easy to operate, responds quickly, has good process compatibility, and is easy to realize large-area preparation and large-scale integration.
[0040] (5) Based on the clear atomic mechanism of “intralayer splitting-interlayer reconstruction”, the cross-dimensional structural phase transition process is completely reversible. After multiple cycles, the phase transition performance is stable and has practical application potential.
[0041] (6) The atomic mechanism of “intralayer splitting-interlayer reconstruction” is applicable to common half-metal materials (PtBi2, PdBi2, NiBi2) with similar layered structures and has wide applicability. Attached Figure Description
[0042] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:
[0043] Figure 1 This is a schematic diagram illustrating the overall structure of a cross-dimensional phase change device according to an embodiment of the present invention.
[0044] Figure 2 for Figure 1 A schematic diagram of the temperature field of a cross-dimensional phase change device when subjected to external electrical excitation;
[0045] Figure 3a This is a schematic diagram of an atomic migration process during a cross-dimensional structural phase transition in a PtBi2 half-metal material layer according to an embodiment of the present invention.
[0046] Figure 3b for Figure 3a A schematic diagram illustrating the changes in the combined structure of Pt and Bi atoms during atomic migration;
[0047] Figure 3c for Figure 3a A schematic diagram illustrating the changes in interlayer structure during atomic migration;
[0048] Figure 4 This is a schematic diagram of the boundary state characteristics of a 2D-3D cross-dimensional topological phase transition according to an embodiment of the present invention;
[0049] Figure 5 This is a schematic diagram of the steps in a method for fabricating a cross-dimensional phase change device based on a semi-metallic material according to an embodiment of the present invention;
[0050] Figure 6This is a schematic diagram illustrating the relationship between temperature and electrical properties during the simulated dual-probe IV test of a multidimensional phase change device.
[0051] Figure 7 A schematic diagram of the resistance-voltage hysteresis loop of a cross-dimensional phase-change device;
[0052] Figure 8 This is a schematic diagram of the current-voltage characteristic curve of a cross-dimensional phase change device.
[0053] Figure 9 The current-voltage characteristic curves of a cross-dimensional phase change device after multiple phase change cycles are shown. Detailed Implementation
[0054] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.
[0055] Embodiments of this invention provide a cross-dimensional phase transition device based on half-metallic materials. By controlling the induced phase transition, a cross-dimensional structural phase transition between an isomeric, reversible two-dimensional ferroelectric phase and a three-dimensional topological T' phase is achieved in half-metallic materials such as PtBi2. This phase transition, based on a clear "intra-layer splitting-inter-layer reconstruction" atomic mechanism, breaks through the dimensional limitations of traditional phase transitions, exhibiting a "hat-shaped" resistance-voltage hysteresis loop. It achieves reversible, non-volatile switching between high-resistivity and low-resistivity states. By using "dimensionality" itself as a parameter driving the topological phase transition, a cross-dimensional topological phase transition from a two-dimensional spin Hall insulator to a three-dimensional strong topological insulator is realized, providing a new dimension for topological property control in the field of topological electronics.
[0056] See Figure 1 The overall structure of a cross-dimensional phase change device based on a semi-metallic material, according to an embodiment of one aspect of the present invention, is shown. The cross-dimensional phase change device 100 includes:
[0057] SiO2 / Si substrate 10;
[0058] The semi-metallic material layer 20 is located on the upper surface of the SiO2 / Si substrate 10, and the initial state of the semi-metallic material layer 20 is a two-dimensional ferroelectric phase.
[0059] Metal electrode 30 is in electrical contact with half-metal material layer 20; wherein
[0060] External electrical excitation (e.g., by adjusting voltage / current) causes a reversible cross-dimensional structural phase transition in the half-metallic material layer 20 with unchanged composition through the metal electrode 30, transforming it from a two-dimensional ferroelectric phase (i.e., 2D FE phase) to a three-dimensional topological T' phase (i.e., 3D T' phase), accompanied by a sudden change in the resistance state, forming a resistance hysteresis loop.
[0061] In one example, preferably, the thickness of the PtBi2 semi-metallic material layer 20 is 1-100 nm to ensure that the semi-metallic material has good two-dimensional properties and can continuously and effectively undergo two-dimensional to three-dimensional phase transition.
[0062] In one example, preferably, the metal electrode 30 is a Cr / Au composite electrode, wherein the Cr layer serves as an adhesive layer with a thickness of 3-10 nm; and the Au layer serves as a conductive layer with a thickness of 40-60 nm.
[0063] For example, the specific electrode structure of the metal electrode 30 can be designed according to the actual functional requirements of the cross-dimensional phase change device 100. For instance... Figure 1 As shown, the electrode structure can be a simple two-terminal crossbar structure, a Hall bar structure for precise measurement of lateral transport, or a three-terminal structure integrated with a field-effect transistor (FET) to control phase transitions with gate voltage assistance. Furthermore, the above electrode structures can be combined to effectively control the effect of electrical excitation on the phase transition performance of the half-metallic material layer 20.
[0064] In one example, the external electrical excitation preferably includes voltage scanning, current scanning, or pulsed electrical excitation. Typically, voltage scanning or current scanning can effectively provide a stable electrical excitation process and offer rich data support for obtaining phase transition characteristics, while pulsed electrical excitation helps reduce overall power consumption and precisely control the phase transition region. Those skilled in the art can design and adjust the device according to the actual functional requirements of the multidimensional phase change device 100.
[0065] See Figure 2 , showed Figure 1 Temperature field of the cross-dimensional phase change device 100 when receiving external electrical excitation.
[0066] In one example, specifically, external electrical excitation induces a transdimensional structural phase transition via the Joule heating effect, with a critical temperature of 600-700 K. The transdimensional structural phase transition is primarily driven by the Joule heating effect generated by the external electrical excitation. When the local temperature of the half-metallic material layer 20 rises to the phase transition critical point (approximately 600-700 K, or approximately 650 K for PtBi2), the transdimensional structural phase transition is triggered.
[0067] See Figure 3aThis illustrates an atomic migration process in which a PtBi2 semimetal material layer undergoes a cross-dimensional structural phase transition, according to one embodiment.
[0068] See Figure 3b This shows, as Figure 3a The diagram illustrates the changes in the combined structure of Pt and Bi atoms during atomic migration.
[0069] See Figure 3c This shows, as Figure 3a The diagram illustrates the changes in interlayer structure during atomic migration.
[0070] exist Figures 3a-3c It can be clearly seen that the migration path of Pt atoms is an atomic migration mechanism of "intralayer splitting-interlayer reconstruction".
[0071] In one example, specifically using PtBi2, the atomic mechanism of the cross-dimensional structural phase transition of the PtBi2 half-metal material layer 20 includes:
[0072] In the two-dimensional ferroelectric phase of the PtBi2 material layer, the Bi-Bi-Pt-Pt-Bi-Bi six-membered ring undergoes in-plane deformation;
[0073] The Pt atom layer splits, and a portion of the Pt atoms (about 50% of the Pt atoms) migrate vertically downwards and through the bottom Bi atom layer to migrate to the van der Waals (vdW) gap.
[0074] The migrating Pt atoms form covalent bonds with Bi atoms at the top of the adjacent PtBi2 material layer, reconstructing the Bi-Pt-Bi three-layer structure into a Bi-Pt-Bi-Pt four-layer structure, thus reconstructing the structure from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase.
[0075] In one example, combined Figures 3a-3c The atomic migration process of the transdimensional structural phase transition in the PtBi2 half-metal material layer is explained in detail below:
[0076] The core of the Pt atom transition process is "intralayer splitting + interlayer reconstruction", which can be divided into two steps, and is reversible throughout while maintaining the same composition.
[0077] The first step involves a positive transition from the two-dimensional ferroelectric phase (FE phase) to the three-dimensional topological T' phase. Initially, PtBi2 in the 2D FE phase is a three-layer stacked structure of Bi-Pt-Bi with van der Waals gaps between the layers. Then, transition triggering occurs; after applying a forward bias, the Joule heating effect at the electrode interface provides the transition energy. Specifically, the Pt atomic layers first undergo intralayer splitting, with half of the Pt atoms detaching from their original layers and migrating through the bottom Bi layer to the van der Waals gaps between the layers. Ultimately, they form new covalent bonds with Bi atoms in adjacent layers, reconstructing the original three-layer structure into a gapless Bi-Pt-Bi-Pt four-layer structure, thus forming the three-dimensional topological T' phase.
[0078] The second step involves a reverse transition from the three-dimensional topological T' phase back to the two-dimensional ferroelectric phase. A reverse bias voltage is applied to trigger this transition, utilizing the Peltier effect to achieve interface cooling. Specifically, the covalent bonds between Pt atoms and adjacent Bi atoms in the interstitial layer break, and the Pt atoms migrate back to their original atomic layers. Van der Waals interstices reform, and the four-layer Bi-Pt-Bi-Pt structure reverts to the initial three-layer Bi-Pt-Bi structure, thus returning to the two-dimensional ferroelectric phase.
[0079] In one example, taking the PtBi2 half-metal material layer 20 as an example, the phase transition region can be precisely controlled in a single PtBi2 sheet by local electrical excitation (e.g., focused pulse), so that a part of the region remains in the two-dimensional ferroelectric phase and another part of the region transforms into the three-dimensional topological T' phase, thereby constructing a two-dimensional / three-dimensional heterojunction.
[0080] Specifically, in addition to achieving local phase transitions through "focused pulses," various spatially selective excitation methods can be used to precisely pattern within a single material sheet (such as PtBi2) to form designed two-dimensional / three-dimensional phase heterostructures. For example, using scanning probe induction, a local electric field or current can be applied to a specific region using a nanoscale probe of a conductive atomic force microscope (c-AFM) or a scanning tunneling microscope (STM), thereby enabling the writing of nanoscale phase transition regions and forming patterned two-dimensional / three-dimensional phase arrays.
[0081] Gate voltage can also be used to limit the phase transition. In a three-terminal device structure integrated with a field-effect transistor, the carrier concentration or electric field distribution of the material layer can be adjusted by adjusting the back gate or top gate voltage, thereby limiting the region where the phase transition occurs. Combined with source-drain voltage to trigger the phase transition, the electrical control design of the position and shape of the heterojunction can be realized.
[0082] The constructed two-dimensional / three-dimensional phase heterojunctions can be non-volatilely retained after the excitation is removed. By applying a reverse excitation (such as a reverse scanning voltage), the three-dimensional phase region can be reversibly restored to the two-dimensional phase, thereby realizing the erasure and reconstruction of the heterojunction and providing a material basis for programmable quantum circuits.
[0083] Furthermore, at the interface between the two-dimensional ferroelectric phase and the three-dimensional topological T' phase, a topologically protected one-dimensional chiral boundary state is formed due to the difference in topological order. Based on this controllable two-dimensional / three-dimensional phase heterojunction and its interface topological state, a variety of novel quantum device concepts can be derived.
[0084] For example, reconfigurable topological quantum wire networks can be "drawn" with interconnected three-dimensional phase channels, which are surrounded by two-dimensional phase regions, through electrical excitation. The boundaries between these three-dimensional phase channels then form a continuous, topologically protected conductive network. This network can be reconfigured in real time using electrical means to realize dynamic, programmable topological quantum circuits for simulating complex quantum systems or constructing novel logic architectures.
[0085] For example, topological quantum interference devices (QFIDs) are constructed by creating ring-shaped or interferometer structures containing two or more interface boundary state channels. Topologically protected quantum interference effects can be observed by adjusting the electronic phase in the channels through gate voltage or by introducing Aharonov-Bohm phase using a magnetic field. Such interferometers are insensitive to local perturbations and can serve as highly robust quantum sensors or phase-coherent devices.
[0086] For example, spin-charge separation devices utilize the spin polarization characteristics of interface topological boundary states. By injecting spin polarization current into a specific port of a heterojunction, efficient spin transport and detection can be achieved on the boundary states of another port, providing a new solution for low-power spintronic devices.
[0087] First-principles calculations (DFT) can verify the changes in topological properties accompanying the phase transition. For PtBi2, its two-dimensional ferroelectric phase was confirmed as a two-dimensional spin Hall insulator with topological invariant Z2=1; while its three-dimensional topological T' phase was confirmed as a three-dimensional strong topological insulator with topological invariant (1;000). This demonstrates that the cross-dimensional phase transition successfully induced a change in topological state.
[0088] For example, the semi-metallic material layer 20 can be made using a variety of existing semi-metallic materials, such as any one or any combination of PtBi2, PdBi2, and NiBi2. That is, the monolithic semi-metallic material layer 20 can be made using a single-component material, or it can be made using a mixture of two or more semi-metallic materials. For example, in a specific embodiment of the present invention, the semi-metallic material layer 20 in the multidimensional phase change device 100 is made using a single-component PtBi2.
[0089] In one example, PdBi2 and PtBi2 have similar layered crystal structures, with their two-dimensional ferroelectric phases formed by the stacking of Bi-Pd-Bi three-layer units via van der Waals forces. Under external electrical excitation (such as voltage scanning), PdBi2 also undergoes an atomic migration process of "intra-layer splitting-inter-layer reconstruction." When critical parameters are set, the critical temperature for the transdimensional phase transition of PdBi2 is approximately 580-650 K, slightly lower than that of PtBi2, but still within the range achievable through Joule heating.
[0090] In one example, the crystal structure of NiBi2 is similar to that of PtBi2 and PdBi2. In its two-dimensional ferroelectric phase, the Ni atom layers can also split and migrate under electrical excitation, achieving cross-dimensional reconstruction. The atomic migration path is similar to that of PtBi2, manifesting as interlayer migration and bonding reconstruction of Ni atoms. The critical phase transition temperature of NiBi2 is approximately 550-620 K. NiBi2 devices also exhibit significant resistance jumps and hysteresis characteristics during the phase transition process, making them suitable for non-volatile memory and logic switching applications.
[0091] Those skilled in the art will understand that PtBi2, PdBi2, and NiBi2 are all layered transition metal dibismuth compounds with similar crystal structures and half-metallic characteristics in their electronic state density near the Fermi level. Therefore, the "intralayer splitting-interlayer reconstruction" mechanism of this invention is applicable to this type of material system and can achieve cross-dimensional phase transitions and topological state manipulation.
[0092] See Figure 4 This demonstrates the boundary state characteristics of a 2D-3D cross-dimensional topological phase transition.
[0093] like Figure 4 As shown, the boundary state characteristics of 2D-3D cross-dimensional topological phase transitions are intuitively presented. Based on the theory of dimension-driven topological phase transitions, topological state switches can be designed.
[0094] Two-dimensional ferroelectric phase is a 2D spin Hall insulator. In-plane topological edge states exist only on a specific crystal plane (100). The boundary states of the 2D phase are limited to the in-layer edges.
[0095] The three-dimensional topological T' phase is a strong 3D topological insulator. It has topological surface states (such as Dirac cones) on crystal planes such as (100) and (010). The boundary states of the 3D phase cover the three-dimensional crystal surface, reflecting the direct influence of dimension on the topological boundary states.
[0096] And when it forms as Figure 4When considering the 2D-3D-2D topological heterostructure on the far right, it exhibits reversible controllability of cross-dimensional phase transitions. By using an external electric field (forward / reverse bias), the intermediate region can be switched between a two-dimensional ferroelectric phase and a three-dimensional topological T' phase, forming a 2D-3D-2D heterostructure. This heterostructure can serve as a design prototype for topological state switches. By switching the dimension of the intermediate region (and the corresponding topological phase), the connection mode of the overall topological boundary states can be controlled, providing an intuitive solution for designing multifunctional topological quantum devices.
[0097] See Figure 5 This paper illustrates the step-by-step process for fabricating a cross-dimensional phase change device based on semi-metallic materials. Figure 1 Taking the cross-dimensional phase change device 100 shown as an example, the fabrication method includes:
[0098] Step S110: Material preparation, preparing a crystal sheet of half-metal material (e.g., a PtBi2 crystal sheet) by chemical vapor deposition (CVD) or mechanical exfoliation, and transferring the crystal sheet (i.e., the half-metal material layer 20) to the upper surface of the SiO2 / Si substrate 10 (e.g., using a dry or wet transfer method).
[0099] Step S120: Device fabrication, metal electrode 30 is fabricated on a crystal thin film (semi-metallic material layer 20) by photolithography and electron beam evaporation;
[0100] Specifically, electrode patterns are defined on a PtBi2 crystal wafer using standard ultraviolet lithography or electron beam lithography. Then, Cr (e.g., 5 nm) and Au (e.g., 50 nm) metal layers are deposited sequentially using electron beam evaporation. Finally, the required metal electrodes 30 (e.g., two-terminal crossbars, Hall bars, three-terminal structures, etc.) are formed through a lift-off process.
[0101] Step S130: Performance verification. Electrical tests are performed on the cross-dimensional phase change device. The resistance hysteresis loop is verified using a dual-probe IV test, where the critical voltage for the cross-dimensional structural phase change is ±0.8-±1.6V.
[0102] See Figure 6 The figure illustrates the relationship between temperature and electrical properties during a simulated dual-probe IV test. It shows how the spatial distribution of temperature inside the device (especially within the half-metallic layer) changes with location due to the Joule heating effect when a voltage or current is applied to the transdimensional phase change device.
[0103] Specifically, the fabricated transdimensional phase change device 100 was simulated using a dual-probe IV characteristic test in a vacuum probe station or cryogenic environment. When the scan voltage exceeded the critical value (approximately ±1.5V at 300K, varying with temperature from ±0.8V to ±1.6V), a clear current jump and resistance hysteresis loop were observed, indicating that a phase change had occurred.
[0104] In one example, a specific method for inducing phase transition in a transdimensional phase transition device based on a semimetallic material includes: applying a positive external electrical excitation to the metal electrode 30 to raise the local temperature of the semimetallic material layer 20 to the critical point of the transdimensional structural phase transition through the Joule heating effect, triggering the transition from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase; applying a reverse external electrical excitation to the metal electrode 30 to reversibly transform the three-dimensional topological T' phase into a two-dimensional ferroelectric phase through Peltier cooling; wherein the external electrical excitation is a voltage scan with a scanning voltage range of ±1.0-±2.0V.
[0105] Specifically, during the positive external electrical excitation process, i.e., when a positive phase transition (from 2D FE phase to 3D T' phase) occurs, a positive scanning voltage (typically ±1.0V to ±2.0V) is applied to the metal electrode 30. The current generates Joule heating through the PtBi2 / electrode interface, causing the local temperature to rise to the phase transition critical point (approximately 650K), triggering the PtBi2 half-metal material layer 20 to transition from the two-dimensional ferroelectric phase to the three-dimensional topological T' phase. The resistance of the cross-dimensional phase change device 100 switches from a high-resistance state to a low-resistance state.
[0106] Specifically, during the reverse external electrical excitation process, i.e., when a reverse phase transition (from 3D T' phase to 2D FE phase) occurs, a reverse scanning voltage is applied to the metal electrode 30. The Peltier effect generated at the PtBi2 / electrode interface or other cooling mechanisms are used to cool the interface region, and the three-dimensional topological T' phase is reversibly transformed back to the two-dimensional ferroelectric phase. The resistance of the cross-dimensional phase change device 100 is restored to a high-resistance state.
[0107] The aforementioned forward and reverse phase transitions form a complete and reversible resistive hysteresis loop.
[0108] See Figure 7 The diagram illustrates the resistance-voltage hysteresis loop of a cross-dimensional phase-change device. The cross-dimensional phase-change device 100 exhibits a unique "hat-shaped" resistance-voltage hysteresis loop, demonstrating the reversible switching between high-resistivity and low-resistivity states caused by the cross-dimensional structural phase transition, which can be used to construct novel memory storage or logic units.
[0109] The RV curve (resistance-voltage curve) can distinguish the contributions of "device bulk resistance" and "electrode contact resistance," thus clarifying the location of the phase transition. The scanning path is consistent with the IV curve, synchronously recording the resistance value during voltage changes. The 2-probe test (blue curve) exhibits a "cap-shaped" hysteresis pattern, while the 4-probe test (green curve) remains relatively stable. The stable 4-probe curve indicates that the bulk resistance of PtBi2 does not change with voltage, and the phase transition does not occur within the material. The abrupt change in resistance in the 2-probe curve originates from the change in contact resistance at the electrode / material interface, confirming that the phase transition only occurs in the interface region, consistent with the phenomenon of Joule heating concentrated at the interface.
[0110] See Figure 8 The current-voltage characteristic curves of the cross-dimensional phase change device are shown.
[0111] The current-voltage (IV) curve (current-voltage curve) illustrates the current response of the PtBi2 device during the voltage scan process, directly reflecting the reversible switching between the "high resistance state (HRS)" and the "low resistance state (LRS)". The scan path is as follows: scan from 0V to 2V, then scan back to -2V, and finally scan back to 0V, forming a complete closed loop.
[0112] As the bias voltage increases in segment AB, the contact resistance increases, the Joule heat increases, and point B reaches the phase transition temperature. As the bias voltage decreases in segment CA, the Joule heat decreases, and the heat release is very slow. Due to the Peltier effect, segment CA stabilizes in another three-dimensional topological phase T', and vice versa.
[0113] The specific steps for phase transition verification may include: (1) Temperature-dependent test: In the range of 10K-300K, as the temperature increases, the critical voltage for triggering the phase transition increases from 0.8V to 1.6V at 240K, and then drops to 1.5V at 300K; (2) Structural characterization: Using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), it is observed that after applying a positive bias voltage, PtBi2 transforms from the 2DFE phase to the 3D T' phase, and there is a clear boundary between the two phases.
[0114] At 10K, a sudden current change occurs around ±0.8V, and at 300K, the voltage shifts to ±1.5V. When the forward voltage exceeds the critical value, the current increases sharply, corresponding to the phase transition from the 2D FE phase to the 3D T' phase (Joule heating driven); when the reverse voltage reaches the critical value, the current drops sharply, corresponding to the reverse phase transition from the 3D T' phase to the 2D FE phase (Peltier cooling driven). The hysteresis of the closed-loop curve proves that the phase transition is reversible.
[0115] See Figure 9The current-voltage characteristic curves of a cross-dimensional phase-change device after multiple phase-change cycles are shown. The overall curve shape of the IV curve of the same cross-dimensional phase-change device after 15 phase-change cycles is reproducible, proving that the cross-dimensional structural phase-change process is completely reversible based on the explicit "intra-layer splitting-inter-layer reconstruction" atomic mechanism, and the phase-change performance remains stable after multiple cycles.
[0116] The cross-dimensional phase change devices based on half-metal materials in the various embodiments of the present invention can be widely used in topological quantum devices.
[0117] For example, this cross-dimensional phase-change device achieves reversible switching between high-resistance and low-resistance states via a resistive hysteresis loop. Its reversible resistive switching characteristics can be utilized as a basic unit for non-volatile memories (such as RRAM) or reconfigurable logic circuits.
[0118] For example, this cross-dimensional phase-change device achieves topological state manipulation from a two-dimensional spin Hall insulator to a three-dimensional strong topological insulator through a cross-dimensional structural phase transition. Its cross-dimensional topological phase transition characteristics can be utilized to achieve active manipulation of topological quantum states (such as topological boundary states), providing a novel device platform for cutting-edge fields such as topological quantum computing and spintronics.
[0119] The embodiments of the present invention provide a cross-dimensional phase change device, fabrication method, phase change induction method, and application based on semi-metallic materials, which have at least one or a portion of the following advantages:
[0120] (1) By controlling the induced phase transition, a cross-dimensional structural phase transition between a two-dimensional ferroelectric phase and a three-dimensional topological T' phase with equal composition and reversibility was realized in half-metal materials such as PtBi2. This phase transition is based on a clear "intra-layer splitting-inter-layer reconstruction" atomic mechanism, which breaks through the dimensional limitation of traditional phase transitions.
[0121] (2) Based on the reproduction of cross-dimensional phase transition, the cross-dimensional phase transition device exhibits a unique “hat-shaped” resistance-voltage hysteresis loop, realizing reversible and non-volatile switching between high resistance state and low resistance state, which can be used to construct new memory storage or logic operation units.
[0122] (3) By taking the “dimension” itself as a parameter to drive the topological phase transition, a cross-dimensional topological phase transition from a two-dimensional spin Hall insulator (topological invariant Z2=1) to a three-dimensional strong topological insulator (topological invariant 1;000) was realized, providing a new dimension for the topological property control in the field of topological electronics.
[0123] (4) The cross-dimensional phase change device is based on conventional SiO2 / Si substrate and Cr / Au electrode. It is prepared by mature processes such as chemical vapor deposition or mechanical exfoliation. The phase change is triggered by external electrical excitation through the Joule heating effect. It is easy to operate, responds quickly, has good process compatibility, and is easy to realize large-area preparation and large-scale integration.
[0124] (5) Based on the clear atomic mechanism of “intralayer splitting-interlayer reconstruction”, the cross-dimensional structural phase transition process is completely reversible. After multiple cycles, the phase transition performance is stable and has practical application potential.
[0125] (6) The atomic mechanism of “intralayer splitting-interlayer reconstruction” is applicable to common half-metal materials (PtBi2, PdBi2, NiBi2) with similar layered structures and has wide applicability.
[0126] While some embodiments of the present general inventive concept have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.
Claims
1. A cross-dimensional phase change device based on a semi-metallic material, characterized in that, The cross-dimensional phase change device includes: SiO2 / Si substrate; A semi-metallic material layer is located on the upper surface of the SiO2 / Si substrate, and the initial state of the semi-metallic material layer is a two-dimensional ferroelectric phase; A metal electrode is in electrical contact with the semi-metallic material layer; wherein External electrical excitation causes a reversible cross-dimensional structural phase transition in the half-metal material layer through the metal electrodes, with no change in composition, transforming it from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase, accompanied by a sudden change in the resistance state, forming a resistance hysteresis loop.
2. The cross-dimensional phase change device according to claim 1, characterized in that, The semi-metallic material is any one of PtBi2, PdBi2, and NiBi2, or any combination thereof. The thickness of the semi-metallic material layer is 1-100 nm.
3. The cross-dimensional phase change device according to claim 2, characterized in that, The metal electrode is a Cr / Au composite electrode, wherein the Cr layer has a thickness of 3-10 nm and the Au layer has a thickness of 40-60 nm; The structure of the metal electrode is a two-terminal crossbar structure, a Hall bar structure, or a three-terminal structure integrated with a field-effect transistor.
4. The cross-dimensional phase change device according to claim 2, characterized in that, The external electrical excitation includes voltage scanning, current scanning, or pulse electrical excitation. The external electrical excitation induces the transdimensional structural phase transition through the Joule heating effect. The critical temperature for the cross-dimensional structural phase transition is 600-700K.
5. The cross-dimensional phase-change device according to any one of claims 1-4, characterized in that, When PtBi2 is used as a half-metal material, the atomic mechanism of the transdimensional structural phase transition includes: In the two-dimensional ferroelectric phase of the PtBi2 material layer, the Bi-Bi-Pt-Pt-Bi-Bi six-membered ring undergoes in-plane deformation; The Pt atomic layer splits, with some of the Pt atoms migrating vertically downwards and passing through the bottom Bi atomic layer to migrate to the van der Waals gap. The migrating Pt atoms form covalent bonds with Bi atoms at the top of the adjacent PtBi2 material layer, reconstructing the Bi-Pt-Bi three-layer structure into a Bi-Pt-Bi-Pt four-layer structure, thus reconstructing the structure from the two-dimensional ferroelectric phase to the three-dimensional topological T' phase.
6. The cross-dimensional phase change device according to claim 5, characterized in that, In the PtBi2 material layer, one region is a two-dimensional ferroelectric phase and another region is a three-dimensional topological T' phase, forming a heterojunction where the two-dimensional and three-dimensional phases coexist. At the boundary between the regions, an interface topological boundary state is formed to achieve quantum transmission.
7. The cross-dimensional phase change device according to claim 5, characterized in that, For a two-dimensional spin Hall insulator, the topological invariant of the two-dimensional ferroelectric phase is Z2=1; For a three-dimensional strong topological insulator, the topological invariant of the three-dimensional topological T' phase is (1; 000).
8. A method for fabricating a cross-dimensional phase change device based on a half-metallic material, the method being used to obtain the cross-dimensional phase change device according to any one of claims 1-7, characterized in that, The preparation method includes: Crystal flakes of semi-metallic materials are prepared by chemical vapor deposition or mechanical exfoliation, and the crystal flakes are transferred to the upper surface of a SiO2 / Si substrate. Metal electrodes are fabricated on the crystal wafer by photolithography and electron beam evaporation; Electrical tests were performed on the cross-dimensional phase change device, and the resistive hysteresis loop was verified using a dual-probe IV test. The critical voltage for the cross-dimensional structural phase transition was ±0.8-±1.6V.
9. A phase transition induction method for a cross-dimensional phase change device based on a half-metallic material, the phase transition induction method being used to induce a cross-dimensional structural phase transition reconstruction in the cross-dimensional phase change device according to any one of claims 1-7, characterized in that, The phase transition induction method includes: Applying a positive external electrical excitation to the metal electrode raises the local temperature of the half-metal material layer to the critical point of cross-dimensional structural phase transition through the Joule heating effect, triggering the transformation from a two-dimensional ferroelectric phase to a three-dimensional topological T' phase. By applying a reverse external electrical excitation to the metal electrode, the three-dimensional topological T' phase is reversibly transformed into a two-dimensional ferroelectric phase through Peltier effect cooling; wherein... The external electrical excitation is a voltage scan, with a scanning voltage range of ±1.0-±2.0V.
10. An application of a cross-dimensional phase change device based on a half-metal material in topological quantum devices, characterized in that, The cross-dimensional phase change device is the cross-dimensional phase change device according to any one of claims 1-7 or the cross-dimensional phase change device is the cross-dimensional phase change device obtained by the preparation method according to claim 8; The cross-dimensional phase change device achieves reversible switching between high-resistance and low-resistance states through a resistive hysteresis loop. The cross-dimensional phase change device achieves topological state modulation from a two-dimensional spin Hall insulator to a three-dimensional strong topological insulator through cross-dimensional structural phase transition.