A VO2 dual-threshold phase-change memory based on a diamond substrate and its fabrication method

Abstract

This invention discloses a VO2 dual-threshold phase-change memory based on a diamond substrate and its fabrication method, belonging to the field of phase-change memory materials. This invention achieves oriented growth of the VO2-M1 phase on a diamond substrate using chemical vapor deposition. Utilizing the interfacial strain introduced by the lattice mismatch between diamond and VO2-M1, the VO2-M2 phase is generated at the interface, exhibiting the coexistence of both M1 and M2 phases. Furthermore, this allows a single material to possess two volatile resistive switching windows, enabling two independent resistive state abrupt changes within different voltage ranges. This solves the problem of existing devices only achieving a single resistive state abrupt change and having limited functionality.

Description

Technical Field

[0001] This invention belongs to the field of phase change memory materials, specifically relating to a VO2 dual threshold phase change memory based on a diamond substrate and its preparation method. Background Technology

[0002] VO2, as a typical strongly correlated oxide phase transition material, undergoes a reversible structural phase transition near its critical temperature (approximately 68°C), transforming from a monoclinic phase (typically M1 or M2 phase) at low temperatures to a tetragonal rutile phase at high temperatures. Accompanying this phase transition, its physical properties, such as conductivity and transmittance, undergo abrupt changes of several orders of magnitude. This phase transition characteristic makes it promising for applications in storage, optoelectronic devices, and signal processing. Based on the volatile resistive switching effect of the VO2 phase transition, its advantages, including automatic recovery to a high-resistivity state after power failure, no need for additional erasure operations, and fast response speed, make it considered an ideal technological path for addressing the needs of low-power dynamic computing, neuromorphic computing, and high-speed signal processing.

[0003] Meanwhile, the phase transition characteristics of VO2 are highly sensitive to the growth substrate, fabrication process, and external control conditions. The processing conditions, deposition method, and substrate selection significantly affect the phase composition, crystallinity, and final device performance of VO2. Existing literature has fully confirmed this trend, and no study has yet achieved stable dual-volatile window resistive switching characteristics by controlling these factors. Regarding deposition methods, current VO2 preparation methods mainly include chemical vapor deposition (CVD), pulsed laser deposition (PLD), magnetron sputtering, sol-gel method, and hydrothermal method. VO2 prepared by different deposition methods exhibits significant differences in phase, crystallinity, and performance: VO2 films deposited on SiO2-coated sodium-calcium-silicon glass substrates using radio frequency reactive magnetron sputtering mainly exist as tetragonal distorted rutile structures at low temperatures, achieving only a single-amplitude resistance jump and failing to exhibit dual-threshold voltage characteristics; while VO2 microwires prepared by the hydrothermal method can obtain high-purity monoclinic phase (M1 phase) and possess… While exhibiting good reversible phase transition properties, it also only has a single phase transition window and cannot achieve a dual-threshold response. VO2 films deposited on mica or glass substrates using the sol-gel method can achieve growth in specific crystal orientations, but they only exhibit single volatile resistive switching behavior and lack dual-threshold voltage characteristics. Even when using the same CVD method as this scheme, existing studies mostly focus on the preparation of single-phase VO2. For example, VO2 films deposited on fluorine-doped tin oxide / borosilicate substrates using atmospheric pressure CVD can only achieve a single thermally induced phase transition response, and no dual volatile window resistive switching characteristics have been found. Furthermore, their performance is easily affected by deposition parameters and is unstable.

[0004] In existing technologies, VO2 thin films are mostly grown on traditional substrates such as silicon, sapphire, quartz, glass, and mica. These substrates have obvious defects and cannot induce dual-phase coexistence to achieve dual-threshold voltage characteristics: VO2 thin films grown on sapphire substrates maintain a phase transition temperature of around 68°C, achieving only a single phase transition without dual volatile windows. Furthermore, the limited thermal conductivity of the substrate easily leads to heat accumulation during resistive switching, affecting device stability. Although the phase transition temperature of VO2 thin films grown on quartz substrates is lower (around 50°C), only a single phase transition window exists. Moreover, the lattice mismatch between the substrate and VO2 is small, failing to introduce sufficient interfacial strain to induce the formation of the M2 phase. VO2 thin films grown on silicon substrates are prone to interfacial diffusion, leading to decreased crystal quality, unstable resistive switching performance, and the absence of dual-threshold voltage characteristics. Although VO2 thin films grown on glass and mica substrates can achieve certain crystal orientations, they can only achieve single volatile resistive switching and cannot form dual-threshold voltage characteristics.

[0005] Furthermore, there are currently no reports on achieving dual-volatile window resistive switching using the VO2-M2 and M1 phases, and there is a lack of effective control methods to precisely control key performance parameters such as the voltage range and on / off ratio of the dual-volatile window, thus failing to fully realize the multifunctional potential of VO2 materials. Therefore, developing a VO2 phase change material with dual volatile windows and providing corresponding precise control methods is of significant theoretical and practical value for promoting the development of phase change memory technology towards high integration, low power consumption, and multifunctionality, and meeting the application needs of emerging technology fields. Summary of the Invention

[0006] To address the aforementioned shortcomings in the prior art, this invention provides a VO2 dual-threshold phase-change memory based on a diamond substrate and its fabrication method.

[0007] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: The purpose of this invention is to provide a VO2 dual threshold phase change memory based on a diamond substrate, which includes a diamond substrate and a VO2 functional layer and an electrode layer sequentially deposited thereon in a direction away from the diamond substrate; the VO2 functional layer has two phases, M1 and M2, coexisting and has dual volatile resistive switching windows.

[0008] Furthermore, VO2 microwires are deposited on a diamond substrate to form a VO2 functional layer with a thickness of 100~1000 nm.

[0009] Furthermore, the VO2 functional layer achieved oriented growth of the VO2-M1 phase during the deposition process. Due to the interfacial strain induced by the lattice mismatch between diamond and VO2-M1, the VO2-M2 phase was generated, which has the characteristic of coexistence of the two phases.

[0010] Furthermore, the electrodes of the electrode layer are Ti / Au electrodes, the distance between the electrodes is 10~30 μm, and the Ti / Au thickness is 5 / 100 nm.

[0011] Another object of the present invention is to provide a method for fabricating the above-mentioned diamond substrate-based VO2 dual-threshold phase-change memory, comprising the following steps: After cleaning the diamond substrate, VO2 microwires are deposited on it; then Ti / Au electrodes are deposited at both ends of the VO2 microwires to obtain the VO2 dual threshold phase change memory.

[0012] Further, the diamond substrate was ultrasonicated for 10-20 minutes in a 100 W ultrasonic machine with acetone, anhydrous ethanol, and deionized water in sequence, and then dried with a nitrogen gun for later use.

[0013] Furthermore, the VO2 micrometer-thickness of the deposition line is 100~1000 nm, and the deposition method is chemical vapor deposition, the specific process of which is as follows: The V2O5 powder was placed upstream of the cleaned diamond substrate, and the temperature was increased to 800-850℃ at a rate of 5-10℃ / min under an argon atmosphere of 100 sccm. The substrate was then held at this temperature for 2-4 hours. After the heat treatment, the substrate was cooled to room temperature in an argon atmosphere.

[0014] Furthermore, Ti / Au electrodes were deposited at both ends of the VO2 micrometer line by photolithography and vacuum thermal evaporation, with the distance between the electrode patterns being 10~30 μm.

[0015] Furthermore, the process of depositing the Ti / Au electrode is as follows: Using photolithography, electrode patterns are exposed at both ends of the obtained VO2 micron-line sample, with a distance of 10~30 μm between the two electrode patterns. The photolithography process includes steps such as spin coating, pre-baking, exposure, post-baking, and development.

[0016] Then, under vacuum conditions, metal is evaporated onto the sample obtained in the photolithography step; a two-step evaporation method is used, first evaporating Ti (5 nm) and then evaporating Au (100 nm); the sample obtained in the vacuum thermal evaporation step is immersed in acetone, and after the pattern is completely clear, it is washed with anhydrous ethanol and deionized water in sequence, and then dried with a nitrogen gun, thus obtaining the Ti / Au / VO2 / Ti / Au resistive switching memory.

[0017] Two probes are attached to the two electrodes of the VO2 functional layer respectively. By controlling the limiting current and bias voltage, the insulating-metal phase transition in the VO2 functional layer is induced, thereby realizing the control of the function of the unipolar dual volatile resistive random access memory.

[0018] The beneficial effects of this invention are: 1. This invention achieves oriented growth of the VO2-M1 phase on a diamond substrate using chemical vapor deposition. The interfacial strain introduced by the lattice mismatch between diamond and VO2-M1 promotes the formation of the VO2-M2 phase at the interface. Utilizing the temperature difference between the M2 and M1 phase transitions to the R phase, a VO2 phase-change memory with dual threshold voltages is constructed. Furthermore, the VO2 crystal forms a covalent bond with the diamond substrate, exhibiting stable volatile resistive switching. This allows a single material to possess two volatile resistive switching windows, enabling two independent resistive state transitions within different voltage ranges. This solves the problem of existing devices only achieving a single resistive state transition and having limited functionality, effectively simplifying circuit design complexity, reducing device size and system power consumption, increasing system integration density, and broadening the application scenarios of VO2 phase-change materials in storage, signal processing, and neuromorphic computing.

[0019] 2. This invention selects diamond as the growth substrate for VO2 phase change material. Diamond has extremely high thermal conductivity (approximately 2200 W / (m·K)), which can quickly dissipate the heat generated during the VO2 phase change process, effectively suppressing heat accumulation and avoiding problems such as material phase change failure and resistance switching performance degradation caused by local overheating. At the same time, diamond has high breakdown field strength, good chemical stability and mechanical stability, which can further improve the working reliability, cycle life and long-term stability of VO2 phase change memory devices, making them suitable for high power density and high integration application scenarios, and further broadening the application range of the devices.

[0020] 3. The resistive switching functional layer constructed by this invention is a single layer, which does not require complex processes such as doping. By simply controlling the limiting current and the magnitude of the applied bias voltage, it can exhibit unipolar dual volatile resistive switching behavior on a single device, avoiding the introduction of complex ions. 4. Based on the VO2 phase-change memory obtained by the present invention, two volatile resistive switching windows can be realized in a single device by changing the applied limiting current and the applied bias voltage. This has important theoretical significance and practical application value for promoting the development of phase-change memory technology towards high integration, low power consumption and multi-functionality, and meeting the application needs of emerging technology fields. Attached Figure Description

[0021] Figure 1 Transmission electron microscopy characterization of the coexistence of M1 and M2 phases at the VO2 / diamond substrate interface provided in Example 1. Figure 2 A schematic diagram of the composition of a VO2 phase-change memory cell provided by the present invention; Figure 3 The 50-cycle IV curve of the VO2 phase change memory with two volatile resistive switching windows provided in Embodiment 2 of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] Example 1 The fabrication process of VO2 microwires based on diamond substrates is as follows: (1) First, the diamond substrate with a size of 3 cm × 3 cm was ultrasonicated for 15 min each in an ultrasonic machine with a power of 100 W using acetone, anhydrous ethanol and deionized water, and then dried with a nitrogen gun. (2) VO2 microwires were prepared on a diamond substrate using chemical vapor deposition (CVD). The specific steps included: taking approximately 5 mg of V2O5 powder, placing the powder and the cleaned diamond substrate in a crucible, ensuring that the V2O5 powder was upstream of the diamond sample, with a distance of 5 mm between the V2O5 powder and the diamond sample; heating to 850 °C at a rate of 10 °C / min under an argon atmosphere of 100 sccm; maintaining the temperature at 850 °C for 2 h; and allowing the sample to cool naturally in flowing argon gas after the heat treatment. The diamond was then removed after cooling to room temperature, thus obtaining well-oriented VO2 microwires on the diamond substrate.

[0024] VO2 / Diamond cross-sectional samples were prepared and characterized using focused ion beam technology; transmission electron microscopy was used to characterize the cross-sectional samples. For example... Figure 1 As shown, the VO2 microwires prepared by this invention have the characteristic of coexistence of two phases, M1 and M2.

[0025] Example 2 A schematic diagram of a VO2 dual-threshold phase-change memory based on a diamond substrate is shown below. Figure 2 As shown, the substrate includes a diamond substrate, and a VO2 functional layer and a Ti / Au electrode layer with a thickness of 500 nm deposited thereon. The fabrication method is as follows: (1) Using photolithography, an electrode pattern with a distance of 10 μm is exposed at both ends of the VO2 micron line obtained in Example 1. The photolithography process includes the following steps: spin coating, pre-baking, exposure, post-baking, and development. (2) Under vacuum conditions, metal is evaporated on the sample obtained in the photolithography step; a two-step evaporation method is used, first evaporating Ti (5 nm) and then evaporating Au (100 nm). (3) Immerse the sample obtained from the vacuum thermal evaporation step in acetone. After the pattern is completely clear, wash it with anhydrous ethanol and deionized water in sequence, and dry it with a nitrogen gun. Thus, the Ti / Au / VO2 / Ti / Au phase change memory is obtained.

[0026] Example 3 A schematic diagram of a VO2 dual-threshold phase-change memory based on a diamond substrate is shown below. Figure 2 As shown, the substrate includes a diamond substrate, and a VO2 functional layer and a Ti / Au electrode layer with a thickness of 1000 nm deposited thereon. The fabrication method is as follows: (1) Using photolithography, an electrode pattern with a distance of 30 μm is exposed at both ends of the VO2 micron line obtained in Example 1. The photolithography process includes the following steps: spin coating, pre-baking, exposure, post-baking, and development. (2) Under vacuum conditions, metal is evaporated on the sample obtained in the photolithography step; a two-step evaporation method is used, first evaporating Ti (5 nm) and then evaporating Au (100 nm). (3) Immerse the sample obtained from the vacuum thermal evaporation step in acetone. After the pattern is completely clear, wash it with anhydrous ethanol and deionized water in sequence, and dry it with a nitrogen gun. Thus, the Ti / Au / VO2 / Ti / Au phase change memory is obtained.

[0027] Test case A method for controlling a dual-volatile resistive window VO2 phase-change memory: S1. The VO2 phase change memory of Example 2 was subjected to electrical tests using a semiconductor characterization system. Two probes were attached to two Ti / Au electrodes respectively. The scanning voltage range was 0 V to -3.0 V, and the current limit was 0.2 mA. S2. Perform a negative IV scan on the phase-change memory cell, and the results are shown below. Figure 3 .

[0028] from Figure 3 As can be seen, when the negative scan voltage rises to near the threshold voltage (Vth) of the first volatile resistive switching window, the device's conductance increases rapidly, and the resistance changes from high to low. As the voltage further increases, when it reaches approximately -2.5 V, the device's conductance increases rapidly for the second time. When the scan voltage is retraced, when it drops to approximately -1.9 V, the device's conductance decreases rapidly for the first time. As the retracement voltage further decreases, when it drops to approximately -1.4 V, the device's conductance decreases rapidly for the second time, and the resistance changes from low to high. This indicates that the device exhibits volatility. Under different voltages, the device as a whole exhibits two volatile resistive switching windows, indicating that the present invention has successfully constructed a material with two volatile resistive switching windows when M1 and M2 coexist.

[0029] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A VO2 dual-threshold phase-change memory based on a diamond substrate, characterized in that, It includes a diamond substrate, and a VO2 functional layer and an electrode layer sequentially deposited thereon in a direction away from the diamond substrate; the VO2 functional layer has two phases, M1 and M2, coexisting and has a dual volatile resistive switching window.

2. The VO2 dual-threshold phase-change memory based on a diamond substrate according to claim 1, characterized in that, VO2 microwires are deposited on a diamond substrate to form a VO2 functional layer with a thickness of 100~1000 nm.

3. The VO2 dual-threshold phase-change memory based on a diamond substrate according to claim 1 or 2, characterized in that, During the deposition process, the VO2 functional layer achieved oriented growth of the VO2-M1 phase. Due to the interfacial strain induced by the lattice mismatch between diamond and VO2-M1, the VO2-M2 phase was generated, which has the characteristic of coexistence of the two phases.

4. The VO2 dual-threshold phase-change memory based on a diamond substrate according to claim 1, characterized in that, The electrodes of the electrode layer are Ti / Au electrodes, with a distance of 10~30 μm between the electrodes and a Ti / Au thickness of 5 / 100 nm.

5. A method for fabricating a VO2 dual-threshold phase-change memory based on a diamond substrate as described in any one of claims 1 to 4, characterized in that, Includes the following steps: After cleaning the diamond substrate, VO2 microwires are deposited on it; then Ti / Au electrodes are deposited at both ends of the VO2 microwires to obtain the VO2 dual threshold phase change memory.

6. The preparation method according to claim 5, characterized in that, The diamond substrate was ultrasonicated for 10-20 minutes in a 100 W ultrasonic machine with acetone, anhydrous ethanol and deionized water in sequence, and then dried with a nitrogen gun for later use.

7. The preparation method according to claim 5, characterized in that, The deposition thickness of VO2 micrometer lines is 100~1000 nm, and the deposition method is chemical vapor deposition. The specific process is as follows: The V2O5 powder was placed upstream of the cleaned diamond substrate, and the temperature was increased to 800-850℃ at a rate of 5-10℃ / min under an argon atmosphere of 100 sccm. The substrate was then held at this temperature for 2-4 h. After the heat treatment, the substrate was cooled to room temperature under an argon atmosphere.

8. The preparation method according to claim 5, characterized in that, Ti / Au electrodes were deposited at both ends of a VO2 micrometer line by photolithography and vacuum thermal evaporation, with a distance of 10~30 μm between the electrode patterns.

9. The preparation method according to claim 8, characterized in that, The process of depositing Ti / Au electrodes is as follows: (1) Electrode patterns are exposed at both ends of the obtained VO2 micron line sample by photolithography; (2) Under vacuum conditions, metal is evaporated onto the sample obtained in the photolithography step; a two-step evaporation method is used, first evaporating Ti and then evaporating Au; (3) Immerse the sample obtained from the vacuum thermal evaporation step in acetone. After the pattern is completely clear, wash it with anhydrous ethanol and deionized water in sequence, and dry it with a nitrogen gun to obtain the Ti / Au / VO2 / Ti / Au phase change memory.

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