A method for preparing a composite resistive switching layer non-volatile memristor by anodic oxidation

Abstract

This invention belongs to the field of micro / nano devices and electrochemical technology, and relates to a method for fabricating a composite resistive switching layer non-volatile memristor using anodic oxidation. The fabrication method involves depositing an inert metal bottom electrode on a substrate, followed by depositing different types of composite metal layers and oxidizing them in an electrolyte to generate a partially oxidized oxide resistive switching layer; finally, a metal top electrode is deposited on top to fabricate a memristor with a composite resistive switching layer structure. This invention uses anodic oxidation technology to fabricate memristors, which not only improves fabrication efficiency and simplifies the process, but also introduces the concept of a composite oxide resistive switching layer based on the anodic oxidation of a single oxide layer, using a reasonable process to fabricate a non-volatile memristor with excellent stable cycling performance. The anodic oxidation-assisted fabrication method for composite resistive switching layer memristors provided by this invention holds promise for applications in fields such as simulating brain synaptic function and non-volatile storage.

Description

Technical Field

[0001] This invention relates to the fields of micro / nano device fabrication and electrochemistry, and more specifically, to a method for preparing a composite resistive switching layer non-volatile memristor by anodic oxidation. Background Technology

[0002] With the rapid development of information technology, the Internet of Things, and other fields, data processing places higher demands on computer performance. However, as transistor size approaches its physical limits, Moore's Law is nearing its end, making further miniaturization increasingly difficult. Simultaneously, traditional computer performance is limited by the von Neumann architecture, in which the processor and memory are separate, requiring data to be repeatedly transferred between them to complete computation. Most of the energy and time is consumed in data movement rather than computation. Furthermore, memory access speed is far slower than processor processing speed, resulting in significant wasted computing power. This process limits further improvements in computer performance and is known as the von Neumann bottleneck. Memristors are the fourth type of passive device, capable of changing their conductance by altering voltage. Non-volatile memristors, in particular, are memristors with multi-level adjustable and stable conductance, enabling synaptic function simulation, neuromorphic accelerated computing, and non-volatile storage. The advantages of in-memory computing can significantly reduce system power consumption and latency.

[0003] While current fabrication processes for micro / nano memristors can produce high-performance devices, they are generally hampered by expensive equipment and the need for high-vacuum, high-purity atmospheres, or heating conditions during deposition. Electrochemical anodizing offers advantages such as inexpensive equipment, no need for vacuum, heating, or specific atmosphere conditions, and rapid fabrication speed. It can be used to fabricate oxide resistive switching layers for memristors, improving fabrication efficiency and significantly reducing costs. Composite resistive switching layers, with their multi-layered oxide structures, create a localized electric field at the interface due to the different migration rates of oxygen ions in the two substances. This restricts oxygen ion migration and improves the linearity of the device's conductivity modulation. By appropriately adjusting the anodizing parameters, non-volatile memristors with high cycling performance and good tuning stability can be fabricated. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method for the anodic oxidation-assisted fabrication of composite resistive switching layer memristors. The aim is to utilize electrochemical anodic oxidation to fabricate memristors, thereby improving fabrication efficiency and reducing costs. Simultaneously, it introduces the concept of a composite resistive switching layer and implements it through anodic oxidation, selectively combining it with annealing to fabricate a stable composite layer non-volatile memristor. This method can simulate synaptic plasticity and achieve controllable adjustment of conductance states, holding promise for applications in neuromorphic computing and non-volatile storage.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a composite resistive switching layer non-volatile memristor by anodic oxidation is provided, comprising the following steps:

[0006] (1) Use photolithography to lithographically and develop the bottom electrode pattern on the substrate, and then deposit the bottom electrode;

[0007] (2) Deposit at least two different active metal layers on the bottom electrode obtained in step (1);

[0008] (3) Using the active metal layer obtained in step (2) as the anode and the inert metal electrode as the cathode, perform anodic oxidation in the electrolyte so that all the active metal layers above the bottom active metal layer are oxidized, and the part of the bottom active metal layer far from the bottom electrode is oxidized into metal oxide to obtain the resistive switching layer; the anodic oxidation time is 3s to 1min.

[0009] (4) The top electrode pattern is photolithographically etched and developed on the resistive switching layer obtained in step (3), and then the top electrode is deposited to prepare a memristor with a cross electrode structure.

[0010] According to another aspect of the present invention, a method for fabricating a composite resistive switching layer non-volatile memristor by anodic oxidation is provided, comprising the following steps:

[0011] (1) Use photolithography to lithographically and develop the bottom electrode pattern on the substrate, and then deposit the bottom electrode;

[0012] (2) Deposit at least two different active metal layers on the bottom electrode obtained in step (1);

[0013] (3) Using the active metal layer obtained in step (2) as the anode and the inert metal electrode as the cathode, perform anodic oxidation in the electrolyte so that all the active metal layers above the bottom active metal layer are oxidized, and the part of the bottom active metal layer far from the bottom electrode is oxidized into metal oxide to obtain a resistive switching layer; the anodic oxidation time is greater than 1 min and less than 10 min.

[0014] (4) Anneal the sample obtained in step (3) under vacuum or protective atmosphere;

[0015] (5) Photolithography and development of the top electrode pattern on the resistive switching layer after annealing in step (4), and then deposition of the top electrode to prepare a memristor with a cross electrode structure.

[0016] Preferably, the annealing temperature is 250℃~400℃, and the annealing time is 5~40min.

[0017] Preferably, the voltage of the anodizing is denoted as U, with the unit being V; the thickness of the bottommost active metal layer is denoted as d1, with the unit being nm; and the total thickness of the active metal layer is denoted as d, with the unit being nm; then the magnitude of the voltage U of the anodizing satisfies 1.5(d-d1)≤U≤1.5d.

[0018] Preferably, the thickness of the bottommost active metal layer is 50 nm to 150 nm, and the total thickness of the remaining active metal layers does not exceed 50 nm.

[0019] Preferably, the active metal layer is at least two of copper, tantalum, titanium, nickel, tungsten, hafnium, niobium, yttrium, zinc, cobalt, aluminum, silicon, and zirconium.

[0020] Preferably, the bottom electrode is Pt, Au, or Pd, and has a thickness of 30-200 nm;

[0021] The top electrode is made of platinum, gold, or titanium nitride, and has a thickness of 40–200 nm.

[0022] Preferably, the electrolyte is an acid solution, an alkaline solution, a salt solution, or an alcohol solution, and the concentration of the solute in the electrolyte is 0.02 M / L to 2 M / L; the temperature of the electrolyte is 10 to 30 °C.

[0023] According to another aspect of the present invention, a composite resistive switching layer non-volatile memristor prepared by any one of the methods is provided.

[0024] According to another aspect of the present invention, the application of the aforementioned composite resistive switching layer non-volatile memristor in synaptic function simulation or non-volatile storage is provided.

[0025] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0026] (1) This invention uses anodic oxidation to prepare oxide resistive switching layers. The platform is simple and the operation process is convenient, without the need for stringent conditions such as vacuum, temperature and atmosphere. Therefore, it improves the fabrication efficiency of memristors, reduces process energy consumption, and enables the fabrication process of memristors to be more widely expanded.

[0027] (2) In this invention, the bottom metal is partially oxidized. When a voltage is applied, the unoxidized metal reacts with oxygen ions to generate oxygen vacancies, which serve as oxygen vacancy sources to promote the formation of oxygen vacancy filaments, causing the memristor to exhibit a resistive switching effect. At the same time, since the migration ability of oxygen vacancies in the composite oxide layer is different, the excessive migration of oxygen vacancies is limited, which is beneficial to improving the linearity of conductivity regulation.

[0028] (3) The present invention has good universality and scalability. Within the scope of the present invention, almost all transition metal oxides can be used to form resistive switching layers, and their number of layers and stacking order can be adjusted, thereby preparing memristors with different performance, which greatly broadens the structure and function of memristors.

[0029] (4) The non-volatile memristor prepared by the present invention has good pulse cycle performance and IV cycle performance, and can be used for synaptic function simulation and non-volatile storage. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for preparing a composite resistive switching layer memristor with anodic oxidation assistance according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the anodizing apparatus of the present invention.

[0032] Figure 3 This is a schematic diagram of the composite resistive switching layer memristor prepared with anodic oxidation assistance provided by the present invention.

[0033] Figure 4 This is the IV cycle curve provided in Embodiment 1 of the present invention.

[0034] Figure 5 This refers to the high and low resistance states provided in Embodiment 1 of the present invention, which involve 500 pulse cycles.

[0035] Figure 6 This is the conductivity adjustment curve provided in Embodiment 1 of the present invention.

[0036] Figure 7 This is the IV cycle curve provided in Embodiment 2 of the present invention.

[0037] Figure 8 This is the IV curve of Embodiment 4 of the present invention.

[0038] Figure 9 This is the IV curve for Comparative Example 1.

[0039] Figure 10 This is the IV curve for Comparative Example 2. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] This invention discloses a method for anodic oxidation-assisted fabrication of composite resistive switching layer memristors. Figure 1 This is a flowchart of a method for anodic oxidation-assisted fabrication of a composite resistive switching layer memristor according to an embodiment of the present invention. The specific process is as follows:

[0042] S1. Preparation of the bottom electrode

[0043] Silicon wafers with a silicon oxide surface or non-conductive glass sheets are cleaned in acetone, isopropanol, and deionized water and then cut to specific dimensions. Inert metal bottom electrodes such as Pt, Au, and Pd with a thickness of 30-200 nm are then deposited using coating techniques such as magnetron sputtering or atomic layer deposition.

[0044] S2. Preparation of composite metal layer

[0045] A multilayer active metal layer with a thickness on the nanoscale is deposited on the bottom electrode prepared in step S1.

[0046] S3. Preparation of Oxidizing Electrolyte

[0047] To prepare the electrolyte for anodizing, weigh one or more acids, bases, salts, or alcohols and their complexes and dilute them to a certain concentration. Then, mechanically stir the electrolyte to ensure it is thoroughly mixed.

[0048] S4. Anodizing process

[0049] The multilayer metal layer prepared in step S2 is placed in the electrolyte prepared in step S3. An inert electrode is used as the cathode, and the wafer to be oxidized is used as the anode. The temperature is kept constant, and oxidation is carried out at a voltage and time corresponding to the thickness of the composite resistive switching layer. During the oxidation process, it is ensured that the bottom metal layer is not completely oxidized.

[0050] S5. Heat Treatment

[0051] After the composite resistive switching layer of the memristor is prepared, heat treatment is selectively performed according to the conditions of anodic oxidation. If the oxidation degree is high, there will be insufficient oxygen vacancies, requiring heat treatment under vacuum or nitrogen atmosphere to increase oxygen vacancies.

[0052] S6. Preparation of the top electrode

[0053] A metal top electrode of a certain material and thickness is further deposited on the obtained composite resistive switching layer to form a non-volatile memristor with a metal-oxide-metal sandwich structure and a composite resistive switching layer.

[0054] In some embodiments, the active metal layer is one or more of copper, tantalum, titanium, nickel, tungsten, hafnium, niobium, yttrium, zinc, cobalt, aluminum, silicon, and zirconium.

[0055] In some embodiments, the metal layer in step S2 is a composite metal layer, and the thickness of the bottom metal layer is between 50 nm and 150 nm, while the total thickness of the remaining metal layers does not exceed 50 nm.

[0056] In some embodiments, the electrolyte in step S3 is composed of an acid solution, an alkaline solution, or a salt solution; acids include commonly used phosphoric acid, hydrofluoric acid, sulfuric acid, acetic acid, etc.; alkalis include sodium hydroxide, potassium hydroxide, etc.; salts include sodium phosphate, sodium bicarbonate, ammonium fluoride, etc.; alcohols include glycerol, ethylene glycol, etc.

[0057] In some embodiments, the electrolyte concentration in step S4 is between 0.02 M / L and 2 M / L.

[0058] In some embodiments, the electrolyte temperature in step S4 should not be too high or too low, and should be controlled between 10 and 30°C; if it is too high, the oxide film surface will dissolve or loosen, and if it is too low, the oxidation rate will be reduced.

[0059] In some embodiments, the oxidation process in step S4 is as follows:

[0060] The oxidation voltage must correspond to the thickness of the deposited composite metal layer; let the oxidation voltage be denoted as v, the thickness of the bottom metal layer be denoted as d1, and the thickness of the overall metal layer be denoted as d, then 1.5(d-d1)≤U≤1.5d;

[0061] The oxidation time is 3 seconds to 10 minutes.

[0062] The heat treatment is determined based on the oxidation conditions. If the oxidation time is greater than 1 minute and the oxygen vacancy content in the oxide is low, then annealing at 250℃~400℃ for 5~40 minutes in a vacuum or nitrogen atmosphere is required.

[0063] The present invention shows a correlation between oxidation voltage and oxidation time: a higher oxidation voltage results in a shorter oxidation time, and vice versa.

[0064] Preferably, step voltage can also be used in step S3, that is, a voltage with a constant rise rate is used to increase to a specific value.

[0065] In some embodiments, in step S5, the top electrode is an inert metal electrode, such as platinum, gold, titanium nitride, etc.; oxygen vacancies are provided by the bottom electrode, allowing oxygen vacancy filaments to form near the top electrode; the shape of the top electrode can also be prepared by photolithography.

[0066] The anodic oxidation technology of this invention is used to assist in the efficient fabrication of non-volatile memristors with multilayer resistive switching layers, which have excellent stability and adjustable conductivity; they can be applied to non-volatile storage, synaptic function simulation, and neuromorphic computing.

[0067] The following are specific embodiments.

[0068] Example 1

[0069] This embodiment provides a method for anodic oxidation-assisted fabrication of a composite resistive switching layer memristor, including the following steps:

[0070] Fabrication of the bottom electrode: The cleaned substrate was placed in a magnetron sputtering apparatus, and Ti and Pt targets were mounted on the target material. The vacuum level inside the cavity was evacuated to 2 × 10⁻⁶. -6 Below Torr, high-purity argon gas was introduced, and 5nm Ti and 50nm Pt were sputtered as bottom electrodes, respectively. The sputtering power of the Ti target was 50W and the time was 150s. The sputtering power of the Pt target was 20W and the time was 1000s.

[0071] Preparation of composite metal layer: The wafer from step (1) is attached to the sample stage of the magnetron sputtering equipment, the Ta target and Ti target are installed, and then the cavity vacuum is evacuated to 2×10 -6 Below Torr, deposition was performed under an argon protective atmosphere. First, Ta metal was deposited at a sputtering power of 20 W for 3500 s, followed by Ti metal deposition at a sputtering power of 40 W for 100 s. The prepared Ta metal was approximately 70 nm thick, and the Ti metal was approximately 5 nm thick.

[0072] Preparation of anodic oxidation electrolyte: Prepare a 0.4 M / L dilute phosphoric acid solution, and then stir it with a stirring rod for 6 hours to ensure it is fully mixed.

[0073] Anodizing is used to prepare resistive switching layers: such as Figure 2 As shown, a sheet with deposited bottom metal was placed as the anode, and a Pt electrode was used as the cathode. Oxidation was performed under constant voltage conditions: 8V for 15s. After oxidation, the sheet was rinsed with deionized water and dried with a nitrogen gun. The oxidized TiO₂... x and TaO x The unoxidized Ta metal at the bottom is combined as an intermediate composite resistive switching layer.

[0074] Top electrode fabrication: A metal mask is placed on top of the resistive switching layer, and a Pt metal top electrode is deposited by magnetron sputtering. The vacuum level is 2 × 10⁻⁶. -6 Torr was used in an argon atmosphere. The sputtering power of the target was 19.5 W, and the time was 800 s, resulting in a top electrode with a thickness of approximately 50 nm. The final product was Ta / TaO. x / TiO x / Pt non-memory-free resistor. Figure 3 This is a schematic diagram of the composite resistive switching layer memristor prepared with anodic oxidation assistance provided by the present invention.

[0075] Figure 4The IV cycle curve for this example is shown after 50 cycles. It can be seen that this memristor is a non-volatile memristor, and the IV cycle curve has good repeatability, with relatively concentrated set / reset voltages.

[0076] Figure 5 For the pulse-regulated high and low resistance state curves of this example, 500 sets of 1.3V / 100μs positive pulses and -1V / 100μs negative pulses were applied. It can be seen that very stable high and low resistance state changes can be achieved under pulse regulation.

[0077] Figure 6 The conductivity regulation curves for this example under multiple positive and negative pulses are shown, read at a read voltage of 0.1V. It can be seen that the conductivity gradually increases under multiple positive pulses and gradually decreases under multiple negative pulses. This device exhibits good conductivity regulation performance and can be used to simulate synaptic weight changes or implement non-volatile memory.

[0078] Example 2

[0079] Same as step (1) in Example 1

[0080] Same as step (2) in Example 1.

[0081] Same as step (3) in Example 1.

[0082] Anodizing was used to prepare the oxide resistive switching layer: a wafer with the deposited bottom metal was placed at the anode, and a Pt electrode was used as the cathode. Oxidation was performed under constant voltage conditions, with an oxidation voltage of 18V and a time of 15s. After oxidation, the wafer was washed with deionized water and dried with a nitrogen gun. The upper Ti was completely oxidized, while the bottom Ta was partially oxidized, leaving some Ta metal at the bottom.

[0083] Annealing under nitrogen atmosphere: Place the wafer in a vacuum tube furnace, first evacuate the furnace, then introduce high-purity nitrogen. Increase the temperature to 300°C at a rate of 5°C / min, and hold for 5 minutes.

[0084] Same as step (5) in Example 1.

[0085] The electrical properties were tested using a 4200 semiconductor characterization system. Ta was connected to the positive electrode of the instrument, and Pt was connected to the negative electrode. The IV curve after 30 cycles is shown below. Figure 7 As shown, the curve sets around 0.9V and resets around -0.9V, and the cycles basically overlap, indicating good IV cycle stability.

[0086] Example 3

[0087] Same as step (1) in Example 1

[0088] Preparation of composite metal layer: Place the wafer prepared in step (1) on the deposition stage, install the Ta target and Ti target, and then evacuate the cavity to 2×10 -6 Below Torr, deposition was performed under an argon protective atmosphere. First, Ta metal was deposited at a sputtering power of 20 W for 3500 s, followed by Ti metal deposition at a sputtering power of 40 W for 100 s. Then, Ta metal deposition continued at a sputtering power of 20 W for 300 s. The resulting bottom Ta metal was approximately 70 nm, the Ti metal approximately 5 nm, and the top Ta metal approximately 6 nm.

[0089] Preparation of anodic oxidation electrolyte: Prepare a 0.7 M / L dilute citric acid solution, and then stir it with a stirring rod for 6 hours to ensure it is fully mixed.

[0090] Anodizing was used to prepare the oxide resistive switching layer: a sheet with deposited bottom metal was placed at the anode, and a Pt electrode was used as the cathode. Oxidation was performed under constant voltage conditions: 20V for 10s. After oxidation, the layer was rinsed with deionized water and dried with a nitrogen gun. The upper Ta and Ti layers were completely oxidized to TaO. x and TiO x The Ta portion at the bottom is oxidized to TaO. x The bottom retains some Ta metal.

[0091] Annealing under nitrogen atmosphere: Place the wafer in a vacuum tube furnace, first evacuate the furnace, then introduce high-purity nitrogen. Increase the temperature to 300°C at a rate of 5°C / min, and hold for 10 min.

[0092] Same as step (5) in Example 1.

[0093] The prepared composite layer memristor exhibits certain conductivity non-volatility.

[0094] Example 4

[0095] Same as step (1) in Example 1

[0096] Preparation of composite metal layer: The wafer from step (1) was attached to the sample stage of the magnetron sputtering equipment, the Ta target and Ti target were installed, and then the cavity vacuum was evacuated to 2×10 -6 Below Torr, deposition was performed under an argon protective atmosphere. Ti metal was deposited first at a sputtering power of 40 W for 2000 s, followed by Ta metal deposition at a sputtering power of 20 W for 300 s. The prepared Ti metal was approximately 60 nm thick, and the Ta metal was approximately 6 nm thick.

[0097] Preparation of anodic oxidation electrolyte: Prepare a 0.6 M / L dilute sulfuric acid solution, and then stir it with a stirring rod for 6 hours to ensure it is fully mixed.

[0098] Anodizing was used to prepare the oxide resistive switching layer: a sheet with the deposited bottom metal was placed at the anode, and a Pt electrode was used as the cathode. Oxidation was performed under constant voltage conditions: 10V for 10s. After oxidation, the sheet was washed with deionized water and dried with a nitrogen gun. The upper Ta was completely oxidized to TaO. x The Ti portion at the bottom is oxidized to TiO. x The bottom retains some Ti metal.

[0099] Same as step (4) in Example 1.

[0100] Comparative Example 1

[0101] Same as step (1) in Example 4.

[0102] Same as step (2) in Example 4.

[0103] Same as step (3) in Example 4.

[0104] Anodizing was used to prepare the oxide resistive switching layer: a wafer with the deposited bottom metal was placed at the anode, and a Pt electrode was used as the cathode. Oxidation was performed under constant voltage conditions: 25V for 80s. After oxidation, the wafer was washed with deionized water and dried with a nitrogen gun. The upper Ta was completely oxidized to TaO. x The Ti portion at the bottom is oxidized to TiO. x The bottom retains some Ti metal.

[0105] Same as step (5) in Example 4.

[0106] Comparative Example 2

[0107] Same as step (1) in Comparative Example 1

[0108] Same as step (2) in Comparative Example 1

[0109] Same as step (3) in Comparative Example 1

[0110] Same as step (4) in Comparative Example 1

[0111] The peroxide-coated wafers were placed in a vacuum tube furnace. A vacuum was first created, and then high-purity nitrogen gas was introduced. The temperature was increased to 300°C at a rate of 5°C / min and held for 5 minutes.

[0112] Same as step (5) in Comparative Example 1.

[0113] Figure 8 The IV curve is from Example 4, and Figure 9The IV curves for Comparative Example 1 show that when the oxidation voltage and time are suitable, a non-volatile memristor with resistive switching effect can be fabricated. However, in Comparative Example 1, increasing the oxidation time leads to a decrease in the number of oxygen vacancies. Therefore, oxygen vacancy filaments cannot be formed, such as... Figure 9 As shown, the corresponding resistive switching effect cannot be produced. Figure 10 To compare with the IV curve of Example 2, it can be seen that after annealing under oxygen-deficient conditions, the number of oxygen vacancies increases, and under a large voltage scan, oxygen vacancy filament channels are formed, thus exhibiting resistive switching properties.

[0114] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite resistive switching layer non-volatile memristor by anodic oxidation, characterized in that, Includes the following steps: (1) Use photolithography to photolithographically print and develop the bottom electrode pattern on the substrate, and then deposit the bottom electrode; (2) Deposit at least two different active metal layers on the bottom electrode obtained in step (1); (3) Using the active metal layer obtained in step (2) as the anode and the inert metal electrode as the cathode, perform anodic oxidation in the electrolyte so that all the active metal layers above the bottom active metal layer are oxidized, and the part of the bottom active metal layer far from the bottom electrode is oxidized into metal oxide to obtain the resistive switching layer; the anodic oxidation time is greater than 1 min and less than 10 min. (4) Anneal the sample obtained in step (3) under vacuum or a protective atmosphere; (5) Photolithography and development of the top electrode pattern on the resistive switching layer after annealing in step (4), and then deposition of the top electrode to prepare a memristor with a cross electrode structure.

2. The method as described in claim 1, characterized in that, The annealing temperature is 250 °C to 400 °C, and the annealing time is 5 to 40 min.

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