A resistive random access memory based on a composite film with tunable performance and a preparation method thereof

Abstract

The present invention relates to a resistive random access memory based on a composite thin film with adjustable performance and a preparation method thereof, belonging to the technical field of resistive random access memory preparation. The present invention discloses a resistive random access memory based on a composite thin film with adjustable performance, which is composed of a substrate, a bottom electrode, a resistive layer, and a top electrode stacked from bottom to top in sequence, wherein the resistive layer is a polymethyl methacrylate (PMMA) composite thin film doped with Cs<subgt;2< / subgt;AgSbBr<subgt;6< / subgt> nanocrystals. The resistive random access memory can achieve the regulation of storage performance by changing the mass ratio of the incorporated Cs2AgSbBr6 nanocrystals, and has the characteristics of bipolar non-volatile storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of resistive random access memories, and relates to a resistive random access memory based on a composite film with adjustable performance and a preparation method thereof. Background Art

[0002] In recent years, with the continuous innovation of semiconductor technology and the explosive growth of information, the current society has put forward higher requirements for information storage and information processing. At present, the mainstream non-volatile memory - Flash, due to problems such as high power consumption and thermal crosstalk between cells, can no longer meet the growing needs of people. Therefore, the development of new storage technologies has attracted more and more extensive attention from researchers.

[0003] Resistive random access memories are considered to be the most promising candidates for the next-generation new storage technologies due to their advantages such as stable performance, low cost, low power consumption, high integration, simple preparation, and fast storage speed. A resistive random access memory is a device that realizes data storage by changing the resistance value of a resistive material under the stimulation of electric fields with different intensities or polarities. Its device has a simple "sandwich" structure, which is composed of a top electrode, a resistive layer, and a bottom electrode. Among them, the top electrode and the bottom electrode are usually composed of metals or semiconductor materials with conductive properties, such as gold (Au), platinum (Pt), graphene, etc.; the resistive layer is usually composed of metal oxides or halide perovskite materials with resistive properties, such as SiO2, HfO2, CsPbBr3, etc. However, the preparation of metal oxide thin films often requires a high vacuum and high-temperature environment, and has a high dependence on equipment; although the resistive layer thin film of lead-based halide perovskite has excellent performance and does not require a high-temperature environment, due to the harm of lead elements to the environment, it is not conducive to the goal of green environmental protection. Therefore, lead-free halide perovskite materials have attracted more and more extensive attention due to their advantages such as high carrier mobility, adjustable bandgap width, and low-temperature preparation.

[0004] The performance parameters of resistive random access memories include switching voltage, cycling endurance, data retention, erase / write / read speed, etc. Among them, the switching voltage refers to the voltage value required for the resistive random access memory to change from the high-resistance state to the low-resistance state (write voltage), and the voltage value required for the change from the low-resistance state to the high-resistance state (erase voltage), which determines the power consumption of the resistive random access memory; the cycling endurance refers to the number of times the resistive random access memory switches between the high-resistance state and the low-resistance state, which determines the service life of the resistive random access memory; the data retention refers to the time for which the resistive random access memory can maintain the high-resistance state or the low-resistance state, which determines the retention ability of the resistive random access memory; the erase / write / read speed represents the speed of the resistive random access memory for data erase / write / read operations.

[0005] Therefore, adjusting the device performance parameters by changing the resistive layer material is currently one of the research hotspots in the field of resistive random access memories. Summary of the Invention

[0006] In view of this, one of the objectives of the present invention is to provide a resistive random access memory (RRAM) based on a composite film with adjustable performance; another objective of the present invention is to provide a preparation method for a resistive random access memory (RRAM) based on a composite film with adjustable performance.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] 1. A resistive random access memory (RRAM) based on a composite film with adjustable performance, which is stacked from bottom to top in sequence by a substrate 1, a bottom electrode 2, a resistive layer 3, and a top electrode 4, wherein the substrate 1, the bottom electrode 2, and the resistive layer 3 have the same shape and size;

[0009] The resistive layer 3 is a polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals.

[0010] Preferably, the substrate 1, the bottom electrode 2, and the resistive layer 3 are all square in shape, and the side length of the square is 1 - cm;

[0011] The substrate 1 is quartz glass or an organic polymer, and the thickness is 0.05 - 1 mm;

[0012] The bottom electrode 2 is indium tin oxide (ITO) or fluorine tin oxide (FTO) of transparent conductive glass, and the thickness is 200 - 500 nm;

[0013] The thickness of the resistive layer 3 is 50 - 200 nm;

[0014] The top electrode 4 is any one of silver, aluminum, or gold, the thickness is 100 - 200 nm, and the shape is circular or square. Among them, the diameter of the circle is 100 - 500 μm, and the side length of the square is 100 - 500 μm.

[0015] Preferably, the polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals is prepared according to the following method:

[0016] (1) Prepare a mixed solution of Cs2AgSbBr6 nanocrystals and polymethyl methacrylate: After taking Cs2AgSbBr6 nanocrystal powder and doping it into polymethyl methacrylate (PMMA) powder, add an organic solvent, and ultrasonically mix it evenly to form a mixed solution. The volume ratio of Cs2AgSbBr6 nanocrystal powder, polymethyl methacrylate (PMMA) powder, and organic solvent in the mixed solution is 0.91 - 5:90:6, mg:mg:mL;

[0017] (2) Preparation of polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals: Drop the mixed solution onto the cleaned bottom electrode 2, spin-coat it at a speed of 2000 - 4000 rpm for 40 - 60 s, then anneal it at 80 - 120 °C for 3 - 5 mins, and cool it to room temperature;

[0018] (3) Repeat step (2) 3 - 5 times. And after the last spin-coating, anneal it at 80 - 120 °C for 10 - 30 mins, and cool it to room temperature to form a polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals on the bottom electrode.

[0019] Further preferably, in step (1), the Cs2AgSbBr6 nanocrystals are prepared according to the following method:

[0020] a. Preparation of Cs2AgSbBr6 nanocrystal precursor solution: Add cesium bromide (CsBr), silver bromide (AgBr), and antimony tribromide (SbBr3) into a mixed solvent of dimethyl sulfoxide (DMSO), oleic acid (OA), and oleylamine, stir and mix them evenly at a temperature of 50 - 70 °C to obtain a clear orange-yellow solution, which is the Cs2AgSbBr6 nanocrystal precursor solution;

[0021] b. Preparation of Cs2AgSbBr6 nanocrystal powder: Cool the Cs2AgSbBr6 nanocrystal precursor solution to room temperature, drop it into isopropyl alcohol (IPA), stir and mix them evenly, rotate and centrifuge to obtain a layered supernatant and a yellow precipitate, pour off the supernatant, and take the precipitate for vacuum drying to obtain Cs2AgSbBr6 nanocrystals.

[0022] Further preferably, in step a, the mass-volume ratio of cesium bromide (CsBr), silver bromide (AgBr), antimony tribromide (SbBr3), dimethyl sulfoxide (DMSO), oleic acid (OA), and oleylamine (OAm) is 0.213:0.094:0.181:5:1:0.15, mg:mg:mg:mL:mL:mL;

[0023] In step b, the volume ratio of the Cs2AgSbBr6 nanocrystal precursor solution to isopropyl alcohol (IPA) is 0.5 - 1:8 - 10. The rotation and centrifugation are specifically: centrifuge at a speed of 5000 - 9000 rpm for 3 - 5 mins. The vacuum drying is specifically: dry in a vacuum drying oven at a temperature of 50 - 80 °C for 3 - 6 h.

[0024] Further preferably, in step (1), the volume ratio of the Cs2AgSbBr6 nanocrystal powder, polymethyl methacrylate (PMMA) powder and organic solvent is 0.91-5:90:6, mg:mg:mL, and the organic solvent is any one of chlorobenzene, toluene or isopropanol;

[0025] The mass fraction of Cs2AgSbBr6 nanocrystals in the polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals is 1% - 5.3%.

[0026] Further preferably, in step (2), the cleaning is specifically as follows: The substrate 1 combined with the bottom electrode 2 is successively ultrasonically treated with dishwashing liquid, deionized water, acetone, and absolute ethanol for 10 - 20 mins, and after drying, it is treated with ultraviolet-ozone for 5 - 10 mins.

[0027] 2. According to the above preparation method of the resistive random access memory, the preparation method includes the following steps:

[0028] First, the raw material of the bottom electrode 2 is deposited on one surface of the substrate 1 by magnetron sputtering to form the bottom electrode 2. After cleaning, the raw material of the resistive switching layer 3 is deposited on the surface of the bottom electrode by solution spin coating-annealing to form the resistive switching layer 3. Finally, the raw material of the top electrode 4 is prepared on the resistive switching layer 3 by vacuum evaporation to obtain the top electrode 4, and thus a resistive random access memory based on a composite film with adjustable performance can be formed.

[0029] Preferably, the vacuum evaporation method is specifically as follows: Cover the mask plate on the surface of the resistive switching layer 3, place it in a vacuum evaporation device, and deposit the material of the top electrode 4 with a thickness of 100 - 200 nm under the condition that the vacuum degree is less than or equal to 8.0×10 -5 Pa.

[0030] The beneficial effects of the present invention are as follows: The present invention discloses a resistive random access memory based on a composite film with adjustable performance, which is composed of a substrate 1, a bottom electrode 2, a resistive layer 3, and a top electrode 4 stacked in sequence from bottom to top. Among them, the resistive layer 3 is a polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals. This resistive random access memory can achieve the regulation of storage performance by changing the mass ratio of Cs2AgSbBr6 nanocrystals incorporated, and has the characteristics of bipolar non-volatile storage. The reasons are as follows: (1) Incorporating Cs2AgSbBr6 nanocrystals can reduce the switching voltage of the resistive random access memory and achieve the goal of low-power non-volatile storage; (2) Incorporating Cs2AgSbBr6 nanocrystals makes the switching voltage of the device more concentrated, improving the reliability and stability of the device; (3) The incorporation of Cs2AgSbBr6 nanocrystals increases the cycle tolerance of the device and improves the service life of the device. In addition, the raw materials used in the preparation process of the resistive random access memory of the present invention are easy to obtain, green, environmentally friendly and low-toxic, and the preparation process flow is simple, which is conducive to large-scale industrial utilization.

[0031] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0033] Figure 1 It is a structural diagram of the resistive random access memory based on a composite film with adjustable performance in Example 1;

[0034] Figure 2 It is a structural diagram of the memory based on a polymethyl methacrylate film in Comparative Example 1;

[0035] Figure 3 It is the I-V characteristic curve (a) and the high and low resistance value distribution diagram (b) of the memory based on a polymethyl methacrylate film (Cs2AgSbBr6 nanocrystal doping content 0%) in Comparative Example 1;

[0036] Figure 4 It is the I-V characteristic curve (a) and the high and low resistance value distribution diagram (b) of the resistive random access memory based on a composite film with adjustable performance (Cs2AgSbBr6 nanocrystal doping content 1%) in Example 1;

[0037] Figure 5I-V characteristic curve (a) and distribution diagrams of high and low resistance values (b) of the resistive random access memory based on the composite film with adjustable performance in Example 1 (doping content of Cs2AgSbBr6 nanocrystals: 3%);

[0038] Figure 6 I-V characteristic curve (a) and distribution diagrams of high and low resistance values (b) of the resistive random access memory based on the composite film with adjustable performance in Example 1 (doping content of Cs2AgSbBr6 nanocrystals: 5%). Detailed implementation manners

[0039] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following examples only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following examples and the features in the examples can be combined with each other.

[0040] Example 1

[0041] A memory based on a composite film with adjustable performance (its structure is as Figure 1 shown), from bottom to top in sequence: substrate 1 (made of quartz glass, with a thickness of 1 mm, a square shape, and a side length of 1 cm), bottom electrode 2 (made of indium tin oxide (ITO) transparent conductive glass, with a thickness of 190 nm, a square shape, and a side length of 1 cm), resistive switching layer (3) (made of a composite film of Cs2AgSbBr6 nanocrystals and polymethyl methacrylate, with a thickness of 100 nm, a square shape, and a side length of 1 cm), top electrode 4 (made of silver, with a thickness of 150 nm, a circular shape, and a diameter of 100 μm). The specific preparation method includes the following steps:

[0042] (1) Deposit ITO on one surface of the substrate by magnetron sputtering to form the bottom electrode. Ultrasonically treat it with dishwashing liquid, deionized water, acetone, and absolute ethanol for 20 mins in sequence, dry it, and then treat it with ultraviolet-ozone for 10 mins and set aside;

[0043] (2) Preparation of the resistive switching layer composite film: Using a high-speed spin coater, take 0.1 mL of the resistive switching layer mixed solution and drop it onto the bottom electrode 2 after cleaning, and spin at 4000 rpm for 60 s; then use an annealing furnace to anneal at 120 °C for 5 mins and cool to room temperature. Repeat the above steps 3 times, and after the last spin coating, anneal at 120 °C for 20 mins and cool to room temperature to obtain a poly(methyl methacrylate) (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals on the bottom electrode 2, forming the resistive switching layer 3;

[0044] (3) Preparation of the top electrode: Cover the mask template on the surface of the above resistive switching layer 3, place it in a vacuum evaporation equipment, use silver (Ag) as the target, and deposit a 150-nm-thick metallic silver electrode under the condition that the vacuum degree is less than or equal to 8.0×10 -5 Pa to form the top electrode 4 on the resistive switching layer 3, and obtain a resistive random access memory based on the composite film with adjustable performance.

[0045] The resistive switching layer mixed solution used in the above step (2) is prepared according to the following method:

[0046] a. Preparation of the Cs2AgSbBr6 nanocrystal precursor solution: Dissolve 0.213 g, 0.094 g, and 0.181 g of cesium bromide (CsBr), silver bromide (AgBr), and antimony tribromide (SbBr3) powders in a mixed solvent formed by 5 mL of dimethyl sulfoxide (DMSO), 1 mL of oleic acid (OA), and 0.15 mL of oleylamine (OAm), and stir well at 60 °C for 1 h to prepare a clear orange-yellow solution, which is the Cs2AgSbBr6 nanocrystal precursor solution;

[0047] b. Preparation of the Cs2AgSbBr6 nanocrystal powder: Slowly drop 1 mL of the Cs2AgSbBr6 nanocrystal precursor solution cooled to room temperature into 10 mL of isopropyl alcohol (IPA), stir well for 1 min, and then centrifuge at 9000 rpm for 5 mins in a centrifuge to obtain a layered supernatant and a yellow precipitate. Pour off the supernatant, take the precipitate and dry it in a vacuum drying oven at 60 °C for 6 h to obtain the Cs2AgSbBr6 nanocrystal powder;

[0048] c. Preparation of the resistive switching layer mixed solution: Take 0.91 mg, 2.78 mg, and 4.74 mg of the Cs2AgSbBr6 nanocrystal powder and incorporate them into 90 mg of poly(methyl methacrylate) (PMMA) powder, and then add 6 mL of chlorobenzene solution and ultrasonicate for 30 mins to form resistive switching layer mixed solutions with doping mass fractions of 1%, 3%, and 5% respectively.

[0049] Example 2

[0050] A memory based on a composite film with adjustable performance, from bottom to top in sequence: substrate 1 (made of quartz glass, with a thickness of 0.5 mm, a square shape, and a side length of 2 cm), bottom electrode 2 (made of indium tin oxide (ITO) transparent conductive glass, with a thickness of 200 nm, a square shape, and a side length of 2 cm), resistive switching layer 3 (made of a composite film of Cs2AgSbBr6 nanocrystals and polymethyl methacrylate, with a thickness of 120 nm, a square shape, and a side length of 2 cm), top electrode 4 (made of silver, with a thickness of 100 nm, a square shape, and a side length of 200 μm). The specific preparation method includes the following steps:

[0051] (1) Deposit ITO on one surface of the substrate by magnetron sputtering to form the bottom electrode. Ultrasonically treat it with dishwashing liquid, deionized water, acetone, and absolute ethanol in sequence for 10 minutes, dry it, and then treat it with ultraviolet-ozone for 5 minutes and set aside;

[0052] (2) Prepare the resistive switching layer composite film: Use a high-speed spin coater, take 0.1 mL of the resistive switching layer mixed solution, drop it onto the cleaned bottom electrode 2, and spin at 3000 rpm for 60 s; then use an annealing platform, anneal at 80 °C for 5 minutes, and cool to room temperature. Repeat the above spinning and annealing steps 5 times, and after the last spin coating, anneal at 80 °C for 20 minutes and cool to room temperature to obtain a polymethyl methacrylate (PMMA) composite film doped with Cs2AgSbBr6 nanocrystals on the bottom electrode 2, forming the resistive switching layer 3;

[0053] (3) Prepare the top electrode: Cover the mask on the surface of the above resistive switching layer 3, place it in a vacuum evaporation device, use silver (Ag) as the target, and deposit a 150-nm-thick metal silver electrode under the condition of a vacuum degree of 5.0×10 -5 Pa to form the top electrode 4 on the resistive switching layer 3, obtaining a resistive memory based on the composite film with adjustable performance.

[0054] The resistive switching layer mixed solution used in the above step (2) is prepared according to the following method:

[0055] a. Prepare the Cs2AgSbBr6 nanocrystal precursor solution: Dissolve 0.213 g, 0.094 g, and 0.181 g of cesium bromide (CsBr), silver bromide (AgBr), and antimony tribromide (SbBr3) powders in a mixed solvent composed of 5 mL of dimethyl sulfoxide (DMSO), 1 mL of oleic acid (OA), and 0.15 mL of oleylamine (OAm), and stir well at 50 °C for 1 h to prepare a clear orange-yellow solution, which is the Cs2AgSbBr6 nanocrystal precursor solution;

[0056] b. Preparation of Cs2AgSbBr6 nanocrystal powder: Slowly drop 0.5 mL of the Cs2AgSbBr6 nanocrystal precursor solution cooled to room temperature into 10 mL of isopropyl alcohol (IPA). After stirring well for 1 min, centrifuge at 5000 rpm for 5 mins in a centrifuge to obtain a layered supernatant and a yellow precipitate. Pour off the supernatant, take the precipitate and dry it in a vacuum drying oven at 50 °C for 6 h to obtain Cs2AgSbBr6 nanocrystal powder;

[0057] c. Preparation of the resistive switching layer mixed solution: Take 2.78 mg of Cs2AgSbBr6 nanocrystal powder and mix it into 90 mg of polymethyl methacrylate (PMMA) powder, then add 6 mL of chlorobenzene solution and ultrasonicate for 30 mins to form a resistive switching layer mixed solution with a doping mass fraction of 3%.

[0058] Example 3

[0059] A memory based on a composite film with adjustable performance, from bottom to top in sequence: Substrate 1 (made of quartz glass, with a thickness of 1 mm, a square shape, and a side length of 1.5 cm), bottom electrode 2 (made of transparent conductive glass indium tin oxide (ITO), with a thickness of 300 nm, a square shape, and a side length of 1.5 cm), resistive switching layer 3 (made of a composite film of Cs2AgSbBr6 nanocrystals and polymethyl methacrylate, with a thickness of 200 nm, a square shape, and a side length of 1.5 cm), top electrode 4 (made of silver, with a thickness of 200 nm, a square shape, and a side length of 100 μm). The specific preparation method includes the following steps:

[0060] (1) Deposit ITO on one surface of the substrate by magnetron sputtering to form the bottom electrode. Ultrasonically treat it with dishwashing liquid, deionized water, acetone, and absolute ethanol in sequence for 20 mins. After drying, treat it with ultraviolet-ozone for 10 mins and then set it aside;

[0061] (2) Preparation of the resistive switching layer composite film: Use a high-speed spin coater, take 0.1 mL of the resistive switching layer mixed solution, drop it onto the cleaned bottom electrode 2, and spin at 4000 rpm for 40 s; then use an annealing stage, anneal at 120 °C for 3 mins, and cool to room temperature. Repeat the above spinning and annealing steps 3 times, and after the last spin coating, anneal at 120 °C for 10 mins and cool to room temperature to obtain a composite film of polymethyl methacrylate (PMMA) doped with Cs2AgSbBr6 nanocrystals on the bottom electrode 2, forming the resistive switching layer 3;

[0062] (3) Preparation of the top electrode: Cover the mask template on the surface of the above resistive switching layer 3, place it in a vacuum evaporation device, use silver (Ag) as the target, and at a vacuum degree equal to 8.0×10 -5Under the condition of [[Pa]], depositing a 200 - nm - thick metallic silver electrode can form the top electrode 4 on the resistive - switching layer 3, and a resistive - switching memory based on a composite thin - film with adjustable performance is obtained.

[0063] The resistive - switching layer mixed solution used in the above step (2) is prepared according to the following method:

[0064] a. Prepare the Cs2AgSbBr6 nanocrystal precursor solution: Dissolve 0.213 g, 0.094 g, and 0.181 g of cesium bromide (CsBr), silver bromide (AgBr), and antimony tribromide (SbBr3) powders in a mixed solvent composed of 5 mL of dimethyl sulfoxide (DMSO), 1 mL of oleic acid (OA), and 0.15 mL of oleylamine (OAm). Stir well for 1 h at 60 °C to prepare a clear orange - yellow solution, which is the Cs2AgSbBr6 nanocrystal precursor solution.

[0065] b. Prepare the Cs2AgSbBr6 nanocrystal powder: Slowly drop 1 mL of the Cs2AgSbBr6 nanocrystal precursor solution cooled to room temperature into 8 mL of isopropyl alcohol (IPA). After stirring well for 1 min, centrifuge at a speed of 9000 rpm for 3 mins in a centrifuge to obtain a layered supernatant and a yellow precipitate. Discard the supernatant, and take the precipitate to dry in a vacuum drying oven at 80 °C for 3 h to obtain the Cs2AgSbBr6 nanocrystal powder.

[0066] c. Prepare the resistive - switching layer mixed solution: Take 4.74 mg of Cs2AgSbBr6 nanocrystal powder and incorporate it into 90 mg of polymethyl methacrylate (PMMA) powder. Then add 6 mL of chlorobenzene solution and ultrasonicate for 30 mins to form a resistive - switching layer mixed solution with a doping mass fraction of 5%.

[0067] Comparative Example 1

[0068] A memory based on a polymethyl methacrylate thin - film (its structure is as Figure 2 shown), from bottom to top in sequence: substrate 1 (made of quartz glass with a thickness of 1 mm); bottom electrode 2 (made of indium tin oxide (ITO) transparent conductive glass with a thickness of 190 nm); resistive - switching layer 3 (made of polymethyl methacrylate thin - film with a thickness of 100 nm); top electrode 4 (made of silver with a thickness of 150 nm). The specific preparation method includes the following steps:

[0069] (1) Deposit the ITO bottom electrode on the surface of the substrate by magnetron sputtering.

[0070] (2) Clean the substrate combined with the bottom electrode: Ultrasonically treat it with dishwashing liquid, deionized water, acetone, and absolute ethanol in sequence for 20 mins, dry it, and then treat it with ultraviolet - ozone for 10 mins.

[0071] (3) Preparation of polymethyl methacrylate solution: Take 90 mg of polymethyl methacrylate (PMMA) powder, add 6 mL of chlorobenzene solution, and ultrasonicate for 30 mins to form a solution with a doping mass fraction of 0% of Cs2AgSbBr6 nanocrystals;

[0072] (4) Preparation of the resistive switching layer film: Using a high-speed spin coater, take 0.1 mL of the above mixed solution, drop it onto the bottom electrode 2 after cleaning, and spin at 4000 rpm for 60 s; then use an annealing stage to anneal at 120 °C for 5 mins and cool to room temperature. The above steps are repeated 3 times, and after the last spin coating, anneal at 120 °C for 20 mins and cool to room temperature to obtain a resistive switching layer based on a polymethyl methacrylate film;

[0073] (5) Preparation of the top electrode: Cover the mask on the surface of the resistive switching layer 3 and place it in a vacuum evaporation equipment. Use silver (Ag) as the target material and deposit a 150 nm thick metal silver electrode under the condition that the vacuum degree is less than or equal to 8.0×10 -5 Pa.

[0074] Performance testing

[0075] Perform electrical performance testing on the resistive random access memory prepared in Example 1 and the memory in Comparative Example 1. The top electrode Ag is connected to the positive electrode of the semiconductor analyzer through a probe, and the bottom electrode ITO is connected to the ground terminal of the semiconductor analyzer through a probe. The writing process is a forward voltage scan (0 → 2V → 0), and the erasing process is a reverse voltage scan (0 → -4V → 0).

[0076] Figure 3 are the I-V characteristic curve (a) and the high and low resistance value distribution diagram (b) of the memory based on polymethyl methacrylate film in Comparative Example 1 (with a doping content of 0% of Cs2AgSbBr6 nanocrystals). It can be seen from Figure 3 that the performance parameters of the memory without doping Cs2AgSbBr6 nanocrystals are relatively unstable. The writing voltage range is 0.87V - 1.91V, the erasing voltage range is -0.61V - -1.26V, and the cycle tolerance is about 100 times.

[0077] Figure 4 are the I-V characteristic curve (a) and the high and low resistance value distribution diagram (b) of the resistive random access memory based on the composite film with adjustable performance in Example 1 (with a doping content of 1% of Cs2AgSbBr6 nanocrystals). It can be seen from Figure 4It can be seen that after adding Cs2AgSbBr6 nanocrystals with a mass fraction of 1%, the performance parameters of the resistive random access memory (RRAM) are greatly improved. The write voltage range is 0.56V - 1.01V, the erase voltage range is -0.72V - -0.82V, and the cycle tolerance is about 510 times.

[0078] Figure 5 It is the distribution diagram of the I-V characteristic curve (a) and the high and low resistance values (b) of the RRAM based on the composite film with adjustable performance in Example 1 (the doping content of Cs2AgSbBr6 nanocrystals is 3%). From Figure 5 It can be seen that as the mass fraction of Cs2AgSbBr6 nanocrystals increases to 3%, its write voltage and erase voltage can continue to be lower. The write voltage range is 0.59V - 0.81V, the erase voltage range is -0.41V - -0.62V, and the cycle tolerance is about 550 times.

[0079] Figure 6 It is the distribution diagram of the I-V characteristic curve (a) and the high and low resistance values (b) of the RRAM based on the composite film with adjustable performance in Example 1 (the doping content of Cs2AgSbBr6 nanocrystals is 5%). From Figure 6 It can be seen that when the mass fraction of Cs2AgSbBr6 nanocrystals continues to increase to 5%, the range and value of its write voltage and erase voltage continue to decrease. The write voltage range is 0.50V - 0.79V, the erase voltage range is -0.31V - -0.47V, and the cycle tolerance can reach about 820 times.

[0080] In Example 1 of the present invention, due to the addition of Cs2AgSbBr6 nanocrystals, the local electric field around the nanocrystals is enhanced, significantly improving the charge trapping ability, thereby preventing device failure caused by too weak local electric field. Compared with the memory in Comparative Example 1 without adding Cs2AgSbBr6 nanocrystals, the values of the erase and write voltages continue to decrease as the mass fraction of the doped nanocrystals increases, and the goal of a low-power memory can be achieved; at the same time, the ranges of the erase and write voltages continue to decrease as the mass fraction of the doped nanocrystals increases, which greatly improves the stability and reliability of the device; in addition, the cycle tolerance of the device also continues to increase as the mass fraction of the doped nanocrystals increases, indicating that the enhanced local electric field due to the incorporation of perovskite nanocrystals can improve the charge trapping ability of the device, thereby increasing the service life of the device.

[0081] Similarly, the above performance tests were carried out on the RRAMs based on the composite film with adjustable performance prepared in Example 2 and Example 3, and the results are similar to those of the RRAM based on the composite film with adjustable performance in Example 1, having good stability and cycle tolerance.

[0082] In summary, the present invention discloses a resistive random access memory based on a composite film with adjustable performance and a preparation method thereof. By regulating the mass fraction of Cs2AgSbBr6 nanocrystals in the Cs2AgSbBr6 nanocrystal-polymethyl methacrylate composite film, the jump voltage and power consumption of the device are reduced, the cycle tolerance of the device is improved, and the storage failure caused by too weak charge trapping ability of the device is prevented. The resistive switching layer of the present invention is prepared by solution spin coating at low temperature. The preparation process is simple, has low dependence on equipment, and does not contain lead elements, having the characteristics of green environmental protection and low toxicity. The memory structure based on the composite film with adjustable performance prepared by the present invention is, from bottom to top in sequence: a quartz glass substrate; an ITO bottom electrode; a Cs2AgSbBr6 nanocrystal-polymethyl methacrylate composite film resistive switching layer; a metal silver top electrode. The resistive random access memory prepared by the present invention is a non-volatile bipolar storage device with adjustable performance, showing excellent resistive switching characteristics. As the mass fraction of the incorporated Cs2AgSbBr6 nanocrystals increases, its erase and write voltages are lower than those of traditional resistive random access memories (both less than 0.7 V), and at the same time, it shows good cycle tolerance. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A resistive random access memory based on a composite thin film with adjustable performance, characterized in that The resistive random access memory is composed of a substrate (1), a bottom electrode (2), a resistive switching layer (3), and a top electrode (4) stacked in sequence from bottom to top, where the substrate (1), the bottom electrode (2), and the resistive switching layer (3) have the same shape and size; The resistive switching layer (3) is a polymethyl methacrylate composite film doped with Cs2AgSbBr6 nanocrystals.

2. The resistive random access memory according to claim 1, wherein The substrate (1), the bottom electrode (2), and the resistive switching layer (3) are all square in shape, and the side length of the square is 1 - cm; The substrate (1) is quartz glass or an organic polymer with a thickness of 0.05 - 1 mm; The bottom electrode (2) is indium tin oxide or fluorine tin oxide of transparent conductive glass with a thickness of 200 - 500 nm; The thickness of the resistive switching layer (3) is 50 - 200 nm; The material of the top electrode (4) is any one of silver, aluminum, or gold, with a thickness of 100 - 200 nm and a shape of circular or square, where the diameter of the circle is 100 - 500 μm and the side length of the square is 100 - 500 μm.

3. The resistive random access memory according to claim 1, wherein The polymethyl methacrylate composite film doped with Cs2AgSbBr6 nanocrystals is prepared according to the following method: (1) Prepare a mixed solution of Cs2AgSbBr6 nanocrystals and polymethyl methacrylate: After taking Cs2AgSbBr6 nanocrystal powder and mixing it into polymethyl methacrylate powder, add an organic solvent and ultrasonically mix them evenly to form a mixed solution. The volume ratio of Cs2AgSbBr6 nanocrystal powder, polymethyl methacrylate powder, and organic solvent in the mixed solution is 0.91 - 5:90:6, mg:mg:mL; (2) Prepare a polymethyl methacrylate composite film doped with Cs2AgSbBr6 nanocrystals: Drop the mixed solution onto the cleaned bottom electrode (2), spin - coat it at a speed of 2000 - 4000 rpm for 40 - 60 s, then anneal it at 80 - 120 °C for 3 - 5 mins, and cool it to room temperature; (3) Repeat step (2) 3 - 5 times, and after the last spin - coating is completed, anneal it at 80 - 120 °C for 10 - 30 mins and cool it to room temperature, then a polymethyl methacrylate composite film doped with Cs2AgSbBr6 nanocrystals is formed on the bottom electrode.

4. The resistive memory according to claim 3, wherein, In step (1), the Cs2AgSbBr6 nanocrystals are prepared according to the following method: a. Prepare a Cs2AgSbBr6 nanocrystal precursor solution: Add cesium bromide, silver bromide, and antimony bromide to a mixed solvent of dimethyl sulfoxide, oleic acid, and oleylamine, and stir and mix them evenly at a temperature of 50 - 70 °C to obtain a clear orange - yellow solution, which is the Cs2AgSbBr6 nanocrystal precursor solution; b. Prepare Cs2AgSbBr6 nanocrystal powder: Cool the Cs2AgSbBr6 nanocrystal precursor solution to room temperature, drop it into isopropyl alcohol, stir and mix them evenly, rotate and centrifuge to obtain a layered supernatant and a yellow precipitate, pour out the supernatant, and take the precipitate for vacuum drying to obtain Cs2AgSbBr6 nanocrystals.

5. The resistive random access memory according to claim 4, characterized in that, In step a, the mass-volume ratio of cesium bromide, silver bromide, antimony bromide, dimethyl sulfoxide, oleic acid and oleylamine is 0.213:0.094:0.181:5:1:0.15, mg:mg:mg:mL:mL:mL; In step b, the volume ratio of the Cs2AgSbBr6 nanocrystal precursor solution to isopropanol is 0.5-1:8-10. The rotation and centrifugation are specifically as follows: centrifuge at a speed of 5000-9000 rpm for 3-5 mins. The vacuum drying is specifically as follows: dry in a vacuum drying oven at a temperature of 50-80 °C for 3-6 h.

6. The resistive random access memory according to claim 3, characterized in that, In step (1), the volume ratio of the Cs2AgSbBr6 nanocrystal powder, polymethyl methacrylate powder and organic solvent is 0.91-5:90:6, mg:mg:mL. The organic solvent is any one of chlorobenzene, toluene or isopropanol; The mass fraction of Cs2AgSbBr6 nanocrystals in the polymethyl methacrylate composite film doped with Cs2AgSbBr6 nanocrystals is 1%-5.3%.

7. The resistive random access memory according to claim 3, wherein In step (2), the cleaning is specifically as follows: ultrasonically treat the substrate (1) combined with the bottom electrode (2) with dishwashing liquid, deionized water, acetone and absolute ethanol in sequence for 10-20 mins, and after drying, perform ultraviolet-ozone treatment for 5-10 mins.

8. The manufacturing method of the resistive random access memory according to any one of claims 1 to 7, characterized in that, The preparation method includes the following steps: First, deposit the raw material of the bottom electrode (2) on one surface of the substrate (1) by magnetron sputtering to form the bottom electrode (2). After cleaning, deposit the raw material of the resistive switching layer (3) on the surface of the bottom electrode by solution spin coating-annealing to form the resistive switching layer (3). Finally, prepare the raw material of the top electrode (4) on the resistive switching layer (3) by vacuum evaporation to obtain the top electrode (4), that is, a resistive memory based on a composite film with adjustable performance is formed.

9. The preparation method according to claim 8, characterized in that, The specific process of the vacuum evaporation method is as follows: Cover the mask plate on the surface of the resistive switching layer (3), place it in a vacuum evaporation device, and deposit the material of the top electrode (4) with a thickness of 100 - 200 nm under the condition that the vacuum degree is less than or equal to 8.0×10 -5 Pa.

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