A method for regulating intrinsic defects of boron nitride and application thereof to resistive random access memory

Abstract

The application discloses a boron nitride intrinsic defect regulation method and application thereof to resistive random access memory, wherein the boron vacancy defect density is successfully regulated by controlling the content of carbon powder in a growth source during the growth of a boron nitride crystal, and then the boron nitride film with defects is used as a resistive random access memory resistive layer, inert metal is used as a top electrode and a bottom electrode, and a metal / resistive layer / metal structure resistive random access memory is constructed. The boron vacancy defects can be rearranged under the excitation of a voltage, so that the resistance state of the resistive random access memory is changed. By controlling the mass ratio of the carbon powder, the resistive random access memory can exhibit better transport performance, including low turn-on voltage and turn-off voltage, large resistive random access memory switching ratio, and high resistive random access memory switching stability, and can be applied to resistive random access memory array processing and application.

Description

Technical Field

[0001] This invention belongs to the field of novel memory device technology, and relates to a method for controlling intrinsic defects of boron nitride and its application in resistive switching memory. Background Technology

[0002] In recent years, the information industry has developed rapidly, and the amount of information processed has increased dramatically, placing higher demands on the integration density and processing speed of memory. Current memory technology employs a multi-level storage architecture, including fast-response volatile memory and highly integrated non-volatile memory. However, such complex systems are struggling to meet the demands of high-speed information processing in the intelligent era, and the "memory wall" bottleneck remains insurmountable. Developing new types of non-volatile memory that simultaneously possess low power consumption and fast response is a feasible solution to the "memory wall" bottleneck.

[0003] Previous studies have shown that oxide-based non-volatile memories exhibit stable resistive switching phenomena and a well-defined resistive switching mechanism. However, the random implantation of active metal ions into the oxide resistive switching layer leads to a decrease in the device's retention capacity. Resistive switching memories using two-dimensional materials as the resistive switching layer have advantages such as fast switching, low power consumption, and simple structure. They also possess good transparency and flexibility. The sandwich structure of the device can reduce the size of the resistive switching memory to the nanometer scale. These advantages make it a promising candidate for next-generation memories.

[0004] Chemical vapor deposition (CVD) is one of the current methods for growing boron nitride resistive switching layers. CVD-grown boron nitride contains numerous defects, which are difficult to control. Furthermore, the number of defects in commercially available high-quality boron nitride crystals is very limited, making them unsuitable for use as resistive switching layers. Therefore, there is an urgent need to develop a method for growing boron nitride resistive switching layers with controllable defects. In addition, the use of active metal electrodes in resistive switching memories (RSMs) leads to reduced device durability and requires improved stability, necessitating the application of a large voltage for activation (forming process) upon initial power-on. Therefore, it is essential to develop RSMs based on intrinsic defects in boron nitride and to study and optimize the performance and operating mechanism of boron nitride RSMs with different defect densities. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controlling intrinsic defects in boron nitride, establishing the relationship between the carbon content in the growth source and the boron vacancy defect density, and constructing a boron nitride resistive switching memory based on the principle of boron vacancy conductive filaments. This solves the problems of unclear relationship between defect density and electrical performance, high operating voltage, and unstable device performance in existing boron nitride resistive switching memories.

[0006] The technical solution adopted in this invention is as follows:

[0007] According to a first aspect of this specification, a method for controlling intrinsic defects in boron nitride is provided, comprising: adjusting the proportion of carbon powder in the growth source during the growth of boron nitride crystals by atmospheric pressure high temperature metal solvent method, thereby controlling the density of boron vacancy defects in boron nitride.

[0008] Furthermore, the growth source is a mixture of nickel-chromium alloy, boron nitride powder, and carbon powder, wherein the mass percentage of carbon powder is 0-6.8%.

[0009] According to a second aspect of this specification, a resistive switching memory based on intrinsic defects of boron nitride is provided, characterized in that a boron nitride thin film with intrinsic defects is used as the resistive switching layer of the resistive switching memory, and inert electrodes are used as the top electrode and bottom electrode to form a resistive switching memory with a metal / boron nitride / metal sandwich structure.

[0010] Furthermore, the boron vacancy defect density of the resistive switching layer corresponds to the mass ratio of carbon powder in the growth source.

[0011] Furthermore, the top electrode and the bottom electrode are made of inert metals, and the material is any one or a combination of the following: gold, tungsten, or platinum.

[0012] Furthermore, the conductive filaments in the resistive switching memory are formed by the aggregation of boron vacancies, establishing a dependency relationship between the defect density of the resistive switching layer and the formation of conductive filaments, determining the proportion of carbon powder in the growth source to ensure a moderate boron vacancy defect density, and achieving stable high and low resistance state switching.

[0013] Furthermore, the low-resistivity state resistance of the resistive switching memory decreases with increasing temperature, which conforms to the vacancy-type conductive filament mechanism. This proves that the boron vacancy defect density directly affects the formation process and physical properties of the conductive filament, thereby determining the electrical performance of the resistive switching memory.

[0014] According to a third aspect of this specification, a method for fabricating a resistive switching memory based on intrinsic defects of boron nitride is provided, comprising: fabricating a bottom electrode array on a substrate using photolithography and magnetron sputtering techniques; then transferring boron nitride sheets with intrinsic defects to the bottom electrodes using a transfer technique; and finally fabricating a top electrode array using laser direct writing and magnetron sputtering techniques.

[0015] Furthermore, boron nitride thin film transfer can be performed using PDMS dry transfer or PVA wet transfer.

[0016] The beneficial effects of this invention are as follows: CVD-grown boron nitride films have very high defect densities, while boron nitride films peeled from high-quality boron nitride crystals have very low defect densities. Compared with these two boron nitride materials, this invention prepares boron nitride crystals with adjustable boron vacancy defect densities by controlling the mass ratio of carbon powder in the growth source and using an atmospheric pressure high-temperature metal solvent method. The boron nitride films obtained by mechanically peeling boron nitride crystals have similar defect densities, good two-dimensional structure, thermal stability, and chemical stability. They are compatible with traditional micro-nano fabrication processes and are suitable for array integration. Resistive switching memories (RSMs) constructed using boron nitride films with varying boron vacancy defect densities as resistive switching layers exhibit different device performances: at low boron vacancy defect densities, vacancy-conducting filaments are difficult to form, and resistive switching is not observed; at high boron vacancy defect densities, multiple vacancy-conducting filaments compete for growth, resulting in poor filament stability; boron nitride films with a carbon powder content of 0.6% by mass have a moderate boron vacancy defect density, and the RSM constructed from them exhibits excellent resistive switching performance, including low device turn-on (+2V) and turn-off voltages (-1.4V), high device stability (up to 200 cycles), and high storage durability (up to 10). 4 This boron nitride resistive switching memory (BNSMemory) achieves high-to-low resistance switching based on the formation and disconnection of boron vacancy conductive filaments. The device performance is highly dependent on the defect density in the resistive switching layer. This method can achieve resistive switching functionality using inert metal electrodes for both the upper and lower electrodes, avoiding the adverse effects of metal ion embedding in the resistive switching layer. Therefore, this method has a positive promoting effect on the development of boron nitride resistive switching memory. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the boron nitride resistive switching memory device structure provided in an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the fabrication process of a boron nitride resistive switching memory device provided in an embodiment of the present invention.

[0019] Figure 3 A schematic diagram of a 5×5 array boron nitride resistive switching memory provided in an embodiment of the present invention.

[0020] Figure 4 The forming process of the boron nitride resistive switching memory provided in the embodiments of the present invention.

[0021] Figure 5 The electrical IV scan curve of the boron nitride resistive switching memory provided in the embodiments of the present invention reflects the dependence of electrical performance on boron vacancy defect density.

[0022] Figure 6The resistance of a boron nitride resistive switching memory with a carbon powder content of 0.6% in the mass ratio provided in this embodiment of the invention changes with temperature in the low-resistivity state.

[0023] In the figure, 1 is the bottom electrode and 2 is the top electrode. Detailed Implementation

[0024] The following are specific embodiments of the present invention, further illustrating the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms fall within the scope defined by the appended claims.

[0025] During the growth of boron nitride crystals by atmospheric pressure and high temperature metal solvent method, carbon powder with different mass ratios is doped to regulate the boron vacancy defect density in boron nitride, thereby affecting the formation of boron vacancy conductive filament pathways and the electrical performance of resistive switching memory.

[0026] Furthermore, in the sandwich structure of the designed device, a boron nitride thin film with boron vacancy defects is used as the resistive switching layer, and an inert metal is used as the top electrode and bottom electrode to form a resistive switching memory array.

[0027] Furthermore, a flat, wrinkle-free boron nitride thin film was selected as the resistive switching layer material.

[0028] Furthermore, during device fabrication, the boron nitride resistive switching layer is transferred onto a substrate with an inert metal bottom electrode array using a dry or wet method, and then a top electrode array is fabricated on the resistive switching layer.

[0029] Furthermore, by applying a voltage to individual devices, the boron vacancies are redistributed to form conductive filaments. When the carbon powder content in the growth source is 0.6%, the resistive switching memory constructed from this boron nitride thin film exhibits excellent device performance. The initial formation of the conductive filaments requires an activation voltage of +4.2V (forming voltage, the voltage required for the initial power-on of the resistive switching memory), followed by an on-state voltage of +2V and a off-state voltage of -1.4V, resulting in 10 6 The resistance switching ratio results in a larger storage window.

[0030] Example 1

[0031] The method for preparing boron nitride crystals with boron vacancy defects in this embodiment includes the following steps:

[0032] Before material preparation, the CVD furnace tube and crucible were rinsed sequentially with deionized water and ethanol, and then allowed to dry. Boron nitride powder was placed in the crucible, and carbon powder was added. After mixing evenly, nickel-chromium alloy was placed on top of the powder. The mass ratio of nickel-chromium alloy, boron nitride powder, and carbon powder was 100:10:(0-8). The crucible was then placed in an alumina crucible boat, which was then placed in the tube furnace. The inlet and outlet valves at both ends of the tube furnace were closed, and a vacuum pump was used to evacuate the furnace to 5 × 10⁻⁶ ppm. -2 After the pressure drops below Pa, turn off the vacuum pump and introduce nitrogen gas to atmospheric pressure. Repeat this process 3-5 times to purge the air from the tube. Then, introduce a nitrogen flow at a rate of 60-100 sccm. Heat the sample to 1400-1700℃ and maintain the temperature for 5-20 hours. Then, reduce the temperature to 1200℃ at a rate of less than 10℃ / h. Finally, allow the sample to cool naturally and remove it. Boron nitride with various defect densities was obtained.

[0033] Example 2

[0034] In this embodiment, the resistive switching memory structure based on boron nitride defects is as follows: Figure 1 As shown, the substrate is a silicon oxide wafer with a surface silicon oxide layer thickness of 285 nm. The single-crystal silicon is p-type heavily doped silicon with a resistivity of 0.001-0.005 Ω·cm. Above the silicon oxide is a bottom electrode array, and the boron nitride resistive switching layer is boron nitride with various defect densities prepared in Example 1. Above the resistive switching layer is a top electrode array. The bottom and top electrode arrays are made of inert metals, including but not limited to gold, platinum, and tungsten.

[0035] Example 3

[0036] Figure 2 This is a schematic flowchart of a method for fabricating a resistive random access memory (RRAM) according to Embodiment 3 of the present invention. The RRAM fabrication process in this embodiment includes the following steps:

[0037] (1) The substrate is a p-type silicon wafer with a SiO2 layer, the thickness of which is 285 nm, so that the thickness of the boron nitride nanosheets can be confirmed under an optical microscope. The selected substrate layer is then cleaned using the standard RCA (wet chemical cleaning) process.

[0038] (2) The pre-designed bottom electrode pattern and alignment marker pattern are fabricated on the substrate using photolithography. The process is as follows: 5350 photoresist is selected, and the spin-coating parameters are: low speed 1000 r / min for 20 s, high speed 4000 r / min for 30 s, and drying at 105℃ for 300 s. The photolithography power is 4 mW, the exposure time is 3 s, and the development time is 30 s. The bottom electrode width and electrode spacing in the cross-array pattern can be set to 2-5 μm. A 20 nm thick gold film is grown on the substrate as the bottom electrode using DC magnetron sputtering. The substrate is immersed in acetone for 30 min to remove the photoresist, rinsed with isopropanol, and then dried to obtain the bottom electrode with the pre-designed pattern.

[0039] (3) Mechanical stripping of boron nitride crystals with different defect densities: Take out the boron nitride crystal grown in Example 1 and place it on a transparent tape. Fold and tear the tape five times to ensure that the boron nitride is evenly distributed on the tape. Lay the tape with boron nitride on the substrate treated in step (2) to ensure that the boron nitride and the substrate are in full contact. After bonding for 24 hours, no obvious air bubbles are observed between the tape and the substrate. Tear off the tape to obtain the substrate with boron nitride. Perform the above steps on boron nitride crystals with different defect densities.

[0040] (4) Wet transfer of boron nitride from PVA to the bottom electrode: Place the substrate with boron nitride under an optical microscope and find boron nitride nanosheets of suitable size and thickness. Here, boron nitride nanosheets with a diameter of 20 μm to 60 μm and a thickness of 5 to 15 nm are selected. Fix the PVA film to the PDMS film with adhesive tape. Use a two-dimensional material transfer platform to attach the fixed PVA film to the substrate with the target boron nitride. After heating to 60°C and naturally cooling to room temperature, lift the PVA film with the attached boron nitride and remove the adhesive tape used for fixing, so that the PVA and PDMS can be separated. Align the boron nitride on the PVA film and place it on the bottom electrode prepared in step (3). Heat to 80°C to separate the PVA from the PDMS. At this time, the PVA with the target boron nitride is tightly attached to the bottom electrode. Taking advantage of the water solubility of PVA, immerse the substrate in deionized water for 1 to 2 hours to remove the PVA film. A double-layer stacked structure with boron nitride on the bottom electrode is obtained.

[0041] (5) Growth of the top electrode on the boron nitride resistive switching layer: Based on the size of the boron nitride nanosheets, a suitable top electrode pattern was designed. The top electrode was fabricated using laser direct writing and magnetron sputtering techniques. The specific steps are as follows: 5350 photoresist was selected, and the spin-coating parameters were 1000 r / min for 20 s at low speed and 4000 r / min for 30 s at high speed. The substrate was dried at 105℃ for 300 s. The laser direct writing power was 30 mW, and the development time was 60 s. A 40 nm thick gold film was fabricated as the top electrode using DC magnetron sputtering. The substrate was immersed in acetone for 30 min to remove the photoresist, rinsed with isopropanol, and then dried to obtain the top electrode with the preset pattern. Figure 3 This is a schematic diagram of a boron nitride resistive switching memory with an array size of 5×5.

[0042] Three types of boron nitride crystals with different defect densities were selected, with carbon powder mass percentages of 0%, 0.6%, and 1.8% respectively during crystal growth. These three crystals were peeled off into thin films and fabricated into resistive switching memory (RSM) modules. Comparative tests were performed, and the forming process was as follows: Figure 4 As shown, the boron nitride resistive switching memory with a carbon powder content of 0.6% in the growth source exhibits the lowest forming voltage of +4.2V. Electrical properties are as follows... Figure 5 As shown in the IV scan curves, the defect density of boron nitride can adjust the turn-on voltage, turn-off voltage, and on / off ratio of the resistive switching memory. Specifically, the boron nitride resistive switching memories with a carbon powder mass ratio of 0.6% and 1.8% in the growth source achieved a larger 10... 6 With a high on / off ratio, a boron nitride resistive switching memory with a carbon powder mass ratio of 0.6% in the growth source achieved the lowest +2V turn-on voltage and -1.4V turn-off voltage, realizing performance optimization of boron nitride resistive switching memory based on boron vacancy conductive filaments.

[0043] Temperature-dependent electrical tests were performed on a boron nitride resistive switching memory with a carbon powder content of 0.6% in the growth source. Figure 6 As shown, in the temperature range of 250K to 350K, the low-resistivity resistance of the boron nitride resistive switching memory based on boron vacancy conductive filaments decreases with increasing temperature, which is consistent with the vacancy-type conductive filament mechanism.

[0044] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A resistive switching memory based on intrinsic defects of boron nitride, characterized in that, Using a boron nitride thin film with intrinsic defects as the resistive switching layer of the resistive switching memory, and using inert electrodes as the top and bottom electrodes, a resistive switching memory with a metal / boron nitride / metal sandwich structure is formed. The conductive filaments in the resistive switching memory are formed by the aggregation of boron vacancies. The formation and physical properties of the boron vacancy conductive filaments are controlled by the boron vacancy defect density. During the growth of boron nitride crystals by atmospheric pressure high temperature metal solvent method, the mass ratio of carbon powder in the growth source composed of nickel-chromium alloy, boron nitride powder and carbon powder is adjusted to 0.6%, thereby regulating the boron vacancy defect density in boron nitride to a moderate range, and thus realizing the regulation of the conductive filament formation process and the electrical performance of the resistive switching memory.

2. The resistive random access memory as described in claim 1, characterized in that, Both the top electrode and the bottom electrode are made of inert metal, and the material is any one or a combination of the following: gold, tungsten or platinum.

3. The resistive random access memory as described in claim 1, characterized in that, The activation voltage of the resistive switching memory is related to the mass percentage of toner in the growth source: when the mass percentage of toner is 0.6%, the resistive switching memory has an activation voltage of +4.2 V.

4. A method for fabricating a resistive switching memory according to any one of claims 1-3, characterized in that, First, a bottom electrode array is fabricated on a substrate. Then, a boron nitride thin film with intrinsic defects is transferred to the bottom electrode using a transfer technique. Finally, a top electrode array is fabricated.

5. The method as described in claim 4, characterized in that, Boron nitride thin film transfer uses either PDMS dry transfer or PVA wet transfer.

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