A memristive crossbar array based on topological phase change material and a preparation method thereof

Abstract

This invention relates to the field of semiconductor information storage and neuromorphic computing devices, specifically to a memristor cross-array based on topological phase change material and its fabrication method. The fabrication method includes: forming a bottom electrode array on a substrate; performing in-situ heat treatment on the substrate with the bottom electrode array; depositing topological phase change material on the bottom electrode array and the exposed substrate in a frequency gradient increment to form a storage dielectric layer; and forming a top electrode array perpendicular to the bottom electrode array on the storage dielectric layer. This invention repairs edge lattice damage of the patterned bottom electrode through in-situ heat treatment of the bottom electrode, and, combined with a frequency gradient increment and in-situ heat preservation deposition process, effectively improves the coverage quality and crystallinity of the topological phase change material at the bottom electrode steps, eliminating edge leakage channels.

Description

Technical Field

[0001] This invention relates to the field of semiconductor information storage and neuromorphic computing device technology, specifically to a memristor cross array based on topological phase change materials and its fabrication method. Background Technology

[0002] With the explosive growth of artificial intelligence (AI), the Internet of Things (IoT), and big data technologies, the traditional von Neumann computing architecture faces a "memory wall" bottleneck due to the separation of storage and computing units, resulting in low energy efficiency and high latency. Neuromorphic computing, inspired by the working mechanism of the human brain, is considered a key technology to overcome this bottleneck. Among numerous electronic synaptic devices, memristors based on crossbar array structures have become a core component for building hardware neural networks due to their high integration density, ability to perform parallel matrix multiplication (VMM) operations, and plasticity similar to biological synapses.

[0003] Currently, mainstream memristor research focuses primarily on binary metal oxide materials, such as hafnium oxide (HfO). x ), aluminum oxide (AlO) x These oxides are typically amorphous or polycrystalline, making it easy to introduce highly random and unstable oxygen vacancy defect regions during thin film fabrication. This microstructural disorder makes it difficult to precisely control the growth path, morphology, and on / off positions of the conductive wires, resulting in significant fluctuations in the resistive switching parameters (such as cycle stability) of the device during cyclic testing. More seriously, this randomness is amplified during array integration, leading to poor device-to-device (D2D) performance consistency between different device units in the memristor array. This poor D2D characteristic results in low array weight update accuracy and decreased recognition rate, limiting its practical application in high-performance, high-precision neuromorphic computing.

[0004] To address the aforementioned randomness issue, materials based on long-range lattice order and topological phase transition (TPT) have attracted widespread attention. Strontium ferrite (SrFeO) is a prime example. x SFO and SrCoO xPerovskite oxides, represented by SCO, exhibit a resistance switching mechanism derived from the reversible migration of lattice oxygen ions between the heliocratic phase (BM phase, high resistance) and the perovskite phase (PV phase, low resistance). Unlike the random conductive filaments of binary oxides, the resistance switching of topological phase change materials is based on the ordered entry and exit of lattice oxygen ions within specific lattice channels (such as oxygen vacancy channels). This lattice-structure-based phase change mechanism is theoretically more stable than random filament growth, exhibiting higher thermodynamic stability and on / off uniformity, making it highly suitable for constructing highly reliable artificial synaptic arrays.

[0005] However, integrating complex oxides such as topological phase change materials (TOPC materials) into crossbar arrays presents significant technological challenges: First, photolithography incompatibility. TOPC CLC films typically require epitaxial growth using pulsed laser deposition (PLD) at high temperatures (>600 °C) and in oxygen-rich / high vacuum environments to ensure crystal quality. Traditional photoresists cannot withstand such high temperatures, resulting in carbonization, decomposition, or peeling, severely contaminating the film and leading to device failure. Conversely, if the film is deposited first and then etched (a subtractive process), it is difficult to find etchants with high selectivity due to the chemical stability of complex oxides, while dry etching (such as ion beam etching) easily introduces lattice damage, disrupting the stoichiometry and phase transition properties of the material surface. Second, the step coverage problem introduced by physical masks. To avoid photolithography contamination, hard masks are typically used for patterning. However, in crossbar array structures, the functional layer film must span and cover the patterned bottom electrode. Because the bottom electrode (such as SrRuO3) has a certain physical thickness (typically tens of nanometers), steep steps form at the electrode edges. For complex oxides that rely on atomic layer epitaxy, growth at these steps is extremely challenging. The abrupt geometric change at the steps leads to localized stress concentration, making it difficult to maintain perfect epitaxial growth of the topological phase change film. This easily results in structural defects such as dislocations and grain boundaries. These defects often become low-resistance current channels, causing short circuits or large leakage currents at the top and bottom electrodes at the steps. This step leakage can mask the intrinsic resistive switching properties of the material, significantly reducing device yield and thus obscuring the phase change advantages of the topological phase change material itself.

[0006] Furthermore, the laser repetition frequency in pulsed laser deposition (PLD) is a key parameter affecting the growth kinetics and final crystal quality of oxide thin films. During PLD growth, the laser frequency directly determines the deposition rate and pulse interval. While a higher deposition frequency can improve preparation efficiency, it leads to an excessively high plasma plume flux reaching the substrate surface per unit time. Adsorbed atoms lack sufficient thermal relaxation time for surface diffusion, migration, and lattice rearrangement before the arrival of the next pulse of particles. Especially in complex morphological regions with large surface energy differences and stress concentrations, such as the bottom electrode edge steps, an excessively fast deposition rate can easily cause atoms to accumulate disorderedly before finding the lowest-energy lattice sites, resulting in amorphous layers, columnar grain boundaries, or void defects, thus hindering high-quality single-crystal epitaxial growth.

[0007] Conversely, lower deposition frequencies can significantly extend the pulse interval, giving adsorbed atoms ample time to cross the potential barrier and migrate to the kink sites at the step edges, thus helping to improve step coverage and reduce lattice defects. However, relying entirely on low-frequency deposition (e.g., 1 Hz) for the entire functional layer fabrication process also presents significant disadvantages. Low-frequency deposition implies extremely low film formation rates, which, for oxide films typically requiring tens of nanometers in thickness, leads to a doubling of deposition time, severely reducing fabrication efficiency and yield, increasing process costs, and hindering practical applications and large-scale production. Furthermore, excessively long deposition cycles mean that samples need to be exposed to high-temperature, high-vacuum environments for longer periods, potentially leading to unintended surface reconstruction and negatively impacting the overall stoichiometric stability of the film. Therefore, neither simple low-frequency nor high-frequency deposition can simultaneously meet the dual requirements of "high-quality crystallization at step edges" and "efficient fabrication." This necessitates a strategy that combines the advantages of both: a "gradient frequency deposition" method that uses low frequency in the early stages of nucleation to ensure step coverage and high frequency in the bulk growth stage to guarantee efficiency.

[0008] Therefore, existing fabrication techniques struggle to simultaneously achieve the patterning accuracy, step coverage quality, and production efficiency of topological phase change memristor arrays. There is an urgent need to develop an innovative process that can circumvent photoresist compatibility issues and effectively address bottom electrode step leakage, in order to fully realize the potential of topological phase change materials in neuromorphic computing. Summary of the Invention

[0009] In view of this, this invention proposes a memristor cross array based on topological phase change materials and its fabrication method. This method combines bottom electrode annealing repair with gradient frequency deposition processes to achieve the fabrication of high-quality topological phase change arrays, aiming to solve the problems of poor uniformity in existing binary amorphous oxide arrays and step coverage and edge leakage current in the fabrication of complex oxide arrays. The technical solution of this invention is implemented as follows: In a first aspect, the present invention proposes a method for fabricating a memristor crossbar array based on a topological phase change material, comprising the following steps: S1. Form a bottom electrode array on the substrate; S2. Perform in-situ heat treatment on the substrate on which the bottom electrode array is formed; S3. Deposit a topological phase change material on the bottom electrode array and the exposed substrate in an increasing frequency gradient manner to form a storage medium layer; S4. A top electrode array perpendicularly intersecting the bottom electrode array is formed on the storage medium layer.

[0010] Preferably, the in-situ heat treatment temperature in step S2 is 650~750 ℃, the cavity atmosphere is oxygen, the gas pressure is 50~150 Pa, and the holding time is 5~25 min.

[0011] Preferably, the frequency gradient increasing deposition method in step S3 includes at least two deposition stages, with the laser pulse frequency in the later stage being higher than that in the earlier stage.

[0012] Preferably, the deposition method with increasing frequency gradient includes a first deposition stage, a second deposition stage, and a third deposition stage; the frequency of the first deposition stage is 0.5~1 Hz, the frequency of the second deposition stage is 2~3 Hz, and the frequency of the third deposition stage is 4~8 Hz.

[0013] Preferably, an in-situ heat preservation treatment is performed for 1 to 10 minutes between each deposition stage.

[0014] Preferably, the deposition temperature in step S3 is 650~750 ℃, the cavity atmosphere is oxygen, the gas pressure is 0.6~2 Pa, and the laser energy is 250~450 mJ.

[0015] In a second aspect, the present invention provides a memristor cross array obtained by the preparation method described in the first aspect, comprising: a substrate; a bottom electrode array formed on the substrate; a storage medium layer covering the bottom electrode array and the substrate, the storage medium layer being composed of a topological phase change material; and a top electrode array formed on the storage medium layer and perpendicularly intersecting the bottom electrode array.

[0016] Preferably, the composition of the bottom electrode array layer includes SrRuO3 or La.0.7 Sr 0.3 MnO3, the composition of the storage medium layer includes SrFeO 2.5 or SrCoO 2.5 .

[0017] Preferably, the substrate layer comprises SrTiO3, and the top electrode array comprises Pt or Au.

[0018] Thirdly, the present invention provides a neuromorphic computing system or storage device comprising a memristor cross array as described in the second aspect.

[0019] Compared with the prior art, the advantages of the present invention are as follows: (1) This invention reduces the step defect problem of physical mask process. By using the "gradient frequency deposition" process, the deposition rate is reduced in the initial stage of growth. Combined with "in-situ heat preservation" to give atoms sufficient relaxation time, the topological phase change material film can "climb" to cover the step edge of the bottom electrode with high quality, avoiding edge amorphization or fracture that may be caused by traditional constant high frequency deposition, eliminating edge leakage channels, and laying the foundation for subsequent scalable arrays.

[0020] (2) This invention avoids the randomness defects of binary oxides, compared with HfO x AlO x In this invention, amorphous materials such as SFO (superoxide dismutase) with lattice order are used as the storage medium, utilizing its intrinsic phase transition mechanism (BM phase). The PV phase replaces the random oxygen vacancy conductive filament mechanism, making it more suitable for high-precision neuromorphic computing.

[0021] (3) The all-physical mask of the present invention is compatible with high-temperature processes. The entire process does not require photoresist, avoids organic pollution, and ensures the cleanliness of the heterojunction interface. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a structural diagram of the topological phase-change memristor array of the present invention; Figure 2 This is a flowchart illustrating the fabrication process of the topological phase-change memristor array of the present invention. Figure 3 This refers to the hard mask used in the fabrication process of the topological phase change memristor array of the present invention. Figure 4 The IV cycle characteristic curve of the memristor array cell prepared in Example 1; Figure 5 The image shows the surface morphology of the memristor array cell prepared in Example 1. Figure 6 A transmission electron microscope image of the cross-section of the memristor array cell prepared in Example 1; Figure 7 The image shows the optical morphology of the memristor array cell prepared in Example 2. Figure 8 This is a high-resolution transmission electron microscope image of the cross-section of the memristor array unit prepared in Example 3; Figure 9 The IV cycle characteristic curve of the memristor array cell prepared for Comparative Example 1. Detailed Implementation

[0024] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] In this document, the terms “containing,” “comprising,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0027] In this document, the terms “optional,” “optionally,” or “optional” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0029] To achieve the above objectives, the present invention employs the following device structure, the schematic diagram of which is shown below. Figure 1 As shown, it includes: The substrate is composed of pure-phase SrTiO3 (STO) with the following crystal orientation: <100> Direction, dimensions 5×5×0.5mm; Bottom Electrode (BE) array, composed of pure-phase SrRuO3 (SRO) or La. 0.7 Sr 0.3 MnO3 (LSMO), its crystal orientation is <100> The direction, its edge steps have a smooth morphology reconstructed by high temperature; The storage medium layer is composed of pure-phase SrFeO. 2.5 (SFO) or SrCoO 2.5 (SCO), covering the bottom electrode array and the substrate, wherein the storage medium layer maintains a continuous lattice structure across the bottom electrode edge step and has no obvious penetrating grain boundary defects; The top electrode (TE) array, composed of pure-phase strip Pt or Au, is arranged perpendicularly to the bottom electrode array. This invention provides a method for fabricating the above-mentioned memristor structure, employing pulsed laser deposition (PLD) technology, with specific steps as follows: Figure 2 As shown, it includes: (1) The SrTiO3 (STO) substrate (purchased from Hefei Kejing Materials Technology Co., Ltd.) was cleaned with acetone, ethanol and deionized water; (2) Fix the strip hard mask (Mask A) onto the surface of the single crystal substrate and place it in the pulsed laser deposition (PLD) cavity; wherein the strip hard mask (Mask A) is as follows: Figure 3 As shown; (3) Use PLD to deposit bottom electrode material (such as SRO) to form a strip bottom electrode array; (4) Perform bottom electrode repair. After deposition, do not remove the sample. Maintain the cavity temperature and keep the bottom electrode in situ. This step uses the atomic thermal motion at high temperature to repair the lattice damage at the edge of the hard mask and smooth the step edge. (5) Replace the square hard mask (Mask B) to block both ends of the bottom electrode, and deposit the topological phase change material functional layer by using a gradient frequency increase and in-situ heat preservation method to obtain the storage dielectric layer; wherein the square hard mask (Mask B) is as follows Figure 3 As shown; (6) Cool down and sample, rotate the strip hard mask (Mask A) by 90 degrees, deposit the top electrode array, and complete the cross array preparation.

[0030] The device structure prepared by the above method is Au(Pt) / BM-SFO(BM-SCO) / SRO(LSMO).

[0031] Preferably, the process conditions for PLD deposition in step (3) include: a temperature of 650~750℃. o C, The cavity atmosphere is oxygen, the pressure is 10~20 Pa, the laser energy is 250~450 mJ, the laser frequency is 1~8 Hz, and the back-floor vacuum is 1×10⁻⁶. -7 ~9×10 -6 Pa, the distance between the substrate and the target is 40~60 mm.

[0032] Preferably, the in-situ heat preservation process conditions in step (4) are: a temperature of 650~750°C. o C, the cavity atmosphere is oxygen, the pressure is 50~150 Pa, and the holding time is 5~25 min.

[0033] Preferably, the pulsed laser deposition process conditions in step (5) are: a temperature of 650~750℃. o C. The cavity atmosphere is oxygen, with a pressure of 0.6–2 Pa. The laser energy is 250–450 mJ, and the laser frequency gradient increases progressively: 0.5–1 Hz in the first stage, 2–3 Hz in the second stage, and 4–8 Hz in the third stage. After each deposition stage, the in-situ heat preservation time is 1–10 min, and the back vacuum level is 1 × 10⁻⁶. -7 ~9×10 -6 Pa, the distance between the substrate and the target is 40~60 mm.

[0034] As a preferred option, the process conditions for electron beam evaporation of the metal top electrode in step (6) are: deposition rate of 2~2.5 nm / min and deposition time of 40 min.

[0035] In this embodiment, the laser source used in the pulsed laser deposition system is a KrF excimer laser with a wavelength of 248 nm, and the angle between the target and the laser beam is approximately 45°.

[0036] Example 1

[0037] This embodiment provides a method for fabricating a memristor crossbar array based on topological phase change materials, including the following steps: (1) To process the SrTiO3 (STO) substrate, the STO substrate was first placed in acetone, alcohol and deionized water in sequence and ultrasonically cleaned for 5 min each. Then, the substrate was fixed on the heating stage with conductive silver paste. The substrate was then covered with a stainless steel strip mask (Mask A). The substrate, SrRuO3 (SRO) and SrFeO were then processed. 2.5 The (SFO) target is fed onto the fixed support inside the pulsed laser deposition equipment cavity via a transfer rod. The distance between the target stage and the substrate is adjusted to 55 mm. The process continues until the molecular pump and mechanical pump pump pump 10... -7After obtaining a vacuum below mbar, the substrate temperature is heated to 700 °C at a heating rate of 25 °C / min. (2) Set the laser frequency to 5 Hz and the laser energy to 300 mJ. Close the suction valve, open the oxygen valve, and manually adjust the bypass valve to adjust the oxygen pressure to (1.5±0.2)×10. -1 mbar; Adjust the baffle, use laser to irradiate the SRO and SFO targets to generate plasma plume, deposit for 12 min to clean the targets; (3) After pre-deposition, remove the baffle, maintain the laser frequency at 2 Hz and the laser energy at 300 mJ, and formally deposit the SRO thin film for 1 h. The deposition process is monitored in situ, and the temperature and pressure environment inside the vacuum chamber are kept constant (temperature 700±5 ℃, pressure (1.5±0.2)×10). -1 After deposition, the oxygen pressure is increased to 100 Pa and annealed in situ at 700 °C for 20 min. This process utilizes a high-temperature oxygen-rich environment to repair the lattice distortion at the edge of the SRO strip caused by mask obstruction, making its step slope more gentle. (4) After the SRO fabrication is completed, cover both ends of the bottom electrode with a hard mask (Mask B) to deposit the SFO functional layer. The laser energy is 250 mJ, and the temperature and pressure environment in the vacuum chamber remain unchanged (temperature 700±5 ℃, pressure (1.0 ± 0.2)×10). -2 (mbar), set the gradient deposition frequency: ① The laser frequency is 1 Hz and the deposition time is 5 min. The low rate allows the Fe and Sr atoms at the step to have enough time to find low energy state positions and complete the initial epitaxy across the step. After deposition, the atoms are kept at the temperature in situ for 2 min to drive atomic rearrangement and eliminate grain boundary stress. ② The laser frequency is 2 Hz to serve as a buffer and transition, providing a robust and low-defect epitaxial template for subsequent high-frequency rapid growth. Deposition takes 10 min, followed by in-situ heat preservation for 2 min after deposition to improve the crystallinity of the film. ③ The laser frequency is 5 Hz to accelerate the deposition rate. The deposition time is 15 min. After the deposition is completed, the gas pressure is kept constant and the film is kept at the same temperature for 15 min to improve the crystallinity of the film. Then the heating is stopped. After the film cools down to room temperature naturally, the oxygen supply is stopped, the pulsed laser deposition system is turned off, the substrate is removed, and the SFO film preparation is completed. (5) Rotate the hard mask (Mask A) by 90 degrees so that it is perpendicular to the bottom electrode orientation, and deposit the Au top electrode by electron beam evaporation process.

[0038] See Figure 4 , Figure 4 The memristor array unit prepared in Example 1 IVCyclic characteristic curves. The curves show that the memristor array cell transitions from a high-resistivity state to a low-resistivity state under a positive voltage scan (0 V→1.7 V→0 V), and then returns from the low-resistivity state to the high-resistivity state under a negative voltage scan (0 V→-3 V→0 V), exhibiting typical bipolar resistive switching behavior. This indicates that the fabricated memristor array cell has no obvious leakage current and has good resistive switching characteristics.

[0039] See Figure 5 , Figure 5 The image shows the surface topography of the memristor array cell prepared in Example 1. The image shows a clear vertically intersecting structure with well-defined boundaries of the strip-shaped intersecting electrodes, indicating that the patterned electrodes were successfully deposited through a hard mask.

[0040] See Figure 6 , Figure 6 The image shows a transmission electron microscope (TEM) image of the cross-section of the memristor array cell prepared in Example 1. The horizontal superlattice-like fringes in the SFO thin film are clearly visible in the image. The film is continuous and dense at the bottom electrode step without any breaks or holes. This indicates that the gradient frequency deposition plus in-situ annealing method successfully avoids the problem of many defects at the step edge in the physical mask process, which leads to obvious leakage channels and poor film epitaxial quality.

[0041] Example 2

[0042] This embodiment provides a method for fabricating a memristor crossbar array based on topological phase change materials, including the following steps: (1) Processing the SrTiO3 (STO) substrate: First, the STO substrate was placed in acetone, alcohol, and deionized water in sequence and cleaned by ultrasonic vibration for 5 min each. Then, the substrate was fixed on the heating stage using conductive silver paste. The substrate was then covered with a stainless steel strip mask (Mask A). Finally, the substrate and La... 0.7 Sr 0.3 MnO3 (LSMO) and SrFeO 2.5 The (SFO) target is fed onto the fixed support inside the pulsed laser deposition equipment cavity via a transfer rod. The distance between the target stage and the substrate is adjusted to 55 mm. The process continues until the molecular pump and mechanical pump pump pump 10... -7 After obtaining a vacuum below mbar, the substrate temperature is heated to 650°C at a heating rate of 25 °C / min. (2) Set the laser frequency to 5 Hz and the laser energy to 300 mJ. Close the suction valve, open the oxygen valve, and manually adjust the bypass valve to adjust the oxygen pressure to (1.5±0.2)×10. -1 mbar; Adjust the baffle, use laser to irradiate the LSMO and SFO targets to generate plasma plume, deposit for 12 min to clean the targets; (3) After pre-deposition, remove the baffle, maintain the laser frequency at 2 Hz and the laser energy at 300 mJ, and formally deposit the LSMO thin film for 1 h. The deposition process is monitored in situ, and the temperature and pressure environment in the vacuum chamber are kept constant (temperature 650±5 ℃, pressure (1.5±0.2)×10). -1 After deposition, the oxygen pressure is increased to 50 Pa and annealed in situ at 650 °C for 5 min. This process utilizes a high-temperature oxygen-rich environment to repair the lattice distortion at the edge of the LSMO strip caused by mask blocking, making its step slope more gentle. (4) After the LSMO fabrication is completed, a hard mask (Mask B) is used to cover both ends of the bottom electrode to deposit the SFO functional layer. The laser energy is 250 mJ, and the temperature and pressure environment in the vacuum chamber are kept constant (temperature 650±5 ℃, pressure (0.6 ± 0.2)×10). -2 (mbar), set the gradient deposition frequency: ① Laser frequency 0.5 Hz, deposition for 10 min; after deposition, in-situ heat preservation for 2 min; ② Laser frequency 2 Hz, deposition for 10 min, and in-situ heat preservation for 1 min after deposition; ③ The laser frequency is 4 Hz, and the deposition time is 18 min. After the deposition is completed, the gas pressure is kept constant and the film is kept at the same temperature for 15 min. Then the heating is stopped and the film is allowed to cool naturally to room temperature. After that, the oxygen supply is stopped, the pulsed laser deposition system is turned off, the substrate is removed, and the SFO film preparation is completed. (5) Rotate the hard mask (Mask A) by 90 degrees so that it is perpendicular to the bottom electrode orientation, and deposit the Au top electrode by electron beam evaporation process.

[0043] See Figure 7 , Figure 7 The image shows the optical morphology of the memristor array unit prepared in Example 2. The upper and lower strip electrodes are vertically oriented and clearly defined. The two ends of the strip electrodes have square test endpoints (Pad), indicating that the memristor array prepared under the physical mask process meets the testing requirements of actual semiconductor testers and other equipment.

[0044] Example 3

[0045] This embodiment provides a method for fabricating a memristor crossbar array based on topological phase change materials, including the following steps: (1) To process the SrTiO3 (STO) substrate, the STO substrate was first placed in acetone, alcohol and deionized water in sequence and ultrasonically cleaned for 5 min each. Then, the substrate was fixed on the heating stage with conductive silver paste. The substrate was then covered with a stainless steel strip mask (Mask A). The substrate, SrRuO3 (SRO) and SrCoO3 were then processed.2.5 (SCO) The target material is delivered to the fixed support inside the pulsed laser deposition equipment cavity via a transfer rod. The distance between the target stage and the substrate is adjusted to 55 mm. The process continues until the molecular pump and mechanical pump pump pump 10... -7 After obtaining a vacuum below mbar, the substrate temperature is heated to 750 °C at a heating rate of 25 °C / min. (2) Set the laser frequency to 5 Hz and the laser energy to 300 mJ. Close the suction valve, open the oxygen valve, and manually adjust the bypass valve to adjust the oxygen pressure to (1.5±0.2)×10. -1 mbar; Adjust the baffle, use laser to irradiate the SRO and SCO targets to generate plasma plume, deposit for 12 min to clean the targets; (3) After pre-deposition, remove the baffle, maintain the laser frequency at 2 Hz and the laser energy at 300 mJ, and formally deposit the SRO thin film for 1 h. The deposition process is monitored in situ, and the temperature and pressure environment in the vacuum chamber are kept constant (temperature 750±5 ℃, pressure (1.5±0.2)×10). -1 After deposition, the oxygen pressure is increased to 150 Pa and annealed in situ at 750°C for 25 min. (4) After the SRO fabrication is completed, cover both ends of the bottom electrode with a hard mask (Mask B) to deposit the SFO functional layer. The laser energy is 450 mJ, and the temperature and pressure environment in the vacuum chamber remain unchanged (temperature 750±5 ℃, pressure (2.0 ± 0.2)×10). - 2 (mbar), set the gradient deposition frequency: ① Laser frequency 1 Hz, deposition for 5 min; after deposition, in-situ heat preservation for 2 min; ②Laser frequency 3 Hz, deposition 6 min, in-situ heat preservation 2 min after deposition; ③ The laser frequency is 8 Hz, and the deposition time is 9 min. After the deposition is completed, the gas pressure is kept constant and the film is kept at the same temperature for 10 min. Then the heating is stopped and the film is allowed to cool naturally to room temperature. After that, the oxygen supply is stopped, the pulsed laser deposition system is turned off, the substrate is removed, and the SFO film preparation is completed. (5) Rotate the hard mask (Mask A) by 90 degrees so that it is perpendicular to the bottom electrode orientation, and deposit the Au top electrode by electron beam evaporation process.

[0046] See Figure 8 , Figure 8 The image shown is a high-resolution transmission electron microscope image of the cross-section of the memristor array unit prepared in Example 3. The clear superlattice-like fringes of the topological phase transition functional layer can be clearly seen, further demonstrating the good crystallinity of the film under the deposition conditions at a more microscopic level.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that gradient frequency and intermediate heat preservation are not used in step (4). Step (4) is as follows: After the SRO preparation is completed, the two ends of the bottom electrode are covered with a hard mask (Mask B) to deposit the SFO functional layer. The laser energy is 250mJ, and the temperature and pressure environment in the vacuum chamber remain unchanged (temperature 700±5 ℃, pressure (1.0±0.2)×10). -2 The deposition frequency was set to 5 Hz (mbar), and the deposition time was 20 min. After deposition was completed, heating was stopped, and the film was allowed to cool naturally to room temperature. Oxygen was then stopped, the pulsed laser deposition system was turned off, and the substrate was removed. The SFO film preparation was then complete.

[0048] See Figure 9 , Figure 9 The image shows the IV cycle characteristic curves of the memristor array cell prepared in Comparative Example 1. The curves illustrate that the device current curve window is small under both positive and negative voltage sweeps, exhibiting significant leakage current.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that a gradient frequency is used in step (4), but no intermediate heat preservation is performed after the deposition stage. Instead, the next stage of thin film deposition is carried out directly. Step (4) is as follows: After the SRO preparation is completed, the two ends of the bottom electrode are covered with a hard mask (Mask B) to deposit the SFO functional layer. The laser energy is 250 mJ, and the temperature and pressure environment in the vacuum chamber remain unchanged (temperature 700±5 ℃, pressure (1.0±0.2)×10). -2 (mbar), set the gradient deposition frequency: ① Laser frequency 1 Hz, deposition 5 min; ② Laser frequency 2 Hz, deposition for 10 min; ③ The laser frequency is 5 Hz, and the deposition time is 15 min. Then the heating is stopped, and the film is allowed to cool naturally to room temperature. After that, the oxygen supply is stopped, the pulsed laser deposition system is turned off, the substrate is removed, and the SFO film preparation is completed.

[0050] The electrical performance of the memristor array prepared in Comparative Example 2 was tested using a semiconductor analyzer. It was found that the memristor array prepared without in-situ insulation also exhibited a large leakage current.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that a gradient frequency is used in step (4). The low-frequency and mid-frequency deposition frequencies remain at 1 Hz and 2 Hz, respectively, and the final high-frequency deposition frequency is increased from 5 Hz to 10 Hz. The deposition time is shortened to maintain a consistent total thickness. Step (4) is as follows: After the SRO preparation is completed, a hard mask (Mask B) is used to cover both ends of the bottom electrode to deposit the SFO functional layer. The laser energy is 250 mJ, and the temperature and pressure environment in the vacuum chamber remain unchanged (temperature 700±5 ℃, pressure (1.0±0.2)×10). - 2 (mbar), set the gradient deposition frequency: ① Laser frequency 1 Hz, deposition 5 min; ② Laser frequency 2 Hz, deposition for 10 min; ③ The laser frequency is 10 Hz, and the deposition time is 7.5 min. Then, the heating is stopped, and the film is allowed to cool naturally to room temperature. After that, the oxygen supply is stopped, the pulsed laser deposition system is turned off, the substrate is removed, and the SFO film preparation is complete.

[0052] The phase composition of the memristor array prepared in Comparative Example 3 was characterized by X-ray diffraction. It was found that the characteristic peaks of the SFO functional layer were weak, reflecting that the crystallinity of the functional layer film prepared at excessively high frequencies was poor.

[0053] The embodiments described above are some, but not all, of the embodiments of the present invention; the detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention; all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for fabricating a memristor crossbar array based on topological phase change materials, characterized in that, Includes the following steps: S1. Form a bottom electrode array on the substrate; S2. Perform in-situ heat treatment on the substrate on which the bottom electrode array is formed; S3. Deposit a topological phase change material on the bottom electrode array and the exposed substrate in an increasing frequency gradient manner to form a storage medium layer; S4. A top electrode array perpendicularly intersecting the bottom electrode array is formed on the storage medium layer; The frequency gradient increasing deposition method in step S3 includes at least two deposition stages, with the laser pulse frequency of the later stage being higher than that of the previous stage. The frequency gradient increasing deposition method includes a first deposition stage, a second deposition stage, and a third deposition stage; the frequency of the first deposition stage is 0.5~1 Hz, the frequency of the second deposition stage is 2~3 Hz, and the frequency of the third deposition stage is 4~8 Hz. Between each deposition stage, in-situ heat preservation treatment is performed for 1 to 10 minutes.

2. The preparation method according to claim 1, characterized in that, The in-situ heat treatment temperature in step S2 is 650~750 ℃, the cavity atmosphere is oxygen, the gas pressure is 50~150 Pa, and the heat treatment time is 5~25 min.

3. The preparation method according to claim 1, characterized in that, The deposition temperature in step S3 is 650~750℃, the cavity atmosphere is oxygen, the gas pressure is 0.6~2 Pa, and the laser energy is 250~450 mJ.

4. A memristor cross-array obtained by the preparation method according to any one of claims 1 to 3, characterized in that, include: Substrate; A bottom electrode array formed on the substrate; A storage medium layer covering the bottom electrode array and the substrate, the storage medium layer being composed of a topological phase change material; And a top electrode array formed on the storage medium layer that intersects the bottom electrode array perpendicularly.

5. The memristor cross-connect array according to claim 4, characterized in that, The composition of the bottom electrode array layer includes SrRuO3 or La. 0.7 Sr 0.3 MnO3, the composition of the storage medium layer includes SrFeO 2.5 or SrCoO 2.5 .

6. The memristor cross-connect array according to claim 4, characterized in that, The substrate layer is composed of SrTiO3, and the top electrode array is composed of Pt or Au.

7. A neuromorphic computing system or storage device, characterized in that, It includes the memristor cross array as described in any one of claims 4 to 6.

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