Memristors based on artificially constructed conductive filaments and their fabrication methods

Abstract

This invention discloses a memristor based on artificially constructed conductive filaments and its fabrication method. The memristor comprises, from bottom to top, a substrate, a bottom electrode, a resistive switching layer, and a top electrode. The resistive switching layer employs a sandwich structure, comprising multiple epitaxial layers with oxygen vacancy concentrations increasing and decreasing from bottom to top. Several artificially constructed conductive filaments are formed on the middle epitaxial layer. The memristor design proposed in this invention utilizes a resistive switching layer structure with multiple epitaxial layers, where the oxygen vacancy concentration increases and decreases from bottom to top. This structural design, through precise control of the oxygen vacancy concentration, promotes the generation of a highly efficient oxygen vacancy conductive filament network, not only enhancing the activity of oxygen vacancies but also accelerating their migration process within the memristor, thereby significantly enhancing the memristor's memory capability and nonlinear characteristics.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a memristor based on artificially constructed conductive filaments and its preparation method. Background Technology

[0002] Guided by Moore's Law, microelectronic devices, represented by Complementary Metal-Oxide-Semiconductor (CMOS) devices, have shown a rapid increase in both quantity and integration, while device size has further decreased. However, with the continuous development of science and technology, traditional silicon-based floating-gate memory structures are facing numerous physical limitations. Simultaneously, chip power consumption is rapidly increasing, and reducing device size requires higher costs and time. These issues have led to a gradual slowdown in the growth trend of device integration. Reactive RAM (RRAM) is one of the representative technologies that can solve these problems. As a new generation of non-volatile memory, RRAM has received widespread attention due to its advantages such as low cost, simple device structure, extremely small cell size, high speed and low power consumption, and compatibility with CMOS processes. It is considered the most suitable non-volatile memory for 3D integration. In traditional electronic computers, the von Neumann architecture creates a bottleneck known as the separation of computing modules and storage units. This bottleneck forces the central processing unit to read data from storage units and then execute the data in the form of commands, resulting in long latency and high power consumption. Previous research has found that computer structures that mimic the human brain, i.e., neuromorphic computers, are the only way to solve this bottleneck. Due to the integration of computing modules and storage units, the neural networks in the human brain can efficiently handle complex tasks. Therefore, to mimic and reproduce the structure of the human brain, academic and industrial researchers are actively exploring neuromorphic computers, which require the use of artificial bio-synaptic devices for information processing and storage. Memristors, nonlinear resistors with memory capabilities, are thus being used to implement artificial synapses. Memristors possess significantly superior data processing capabilities compared to current von Neumann architectures, allowing for better simulation and computation at a biological scale.

[0003] like Figure 1As shown, traditional gallium oxide memristors primarily employ a sandwich structure, consisting of three basic parts: two electrodes and a dynamic resistance-changing layer (also known as the resistive switching layer) located between them. The core of this resistive switching layer lies in its abundant oxygen vacancies, which control the memristor effect (the switching between the High Resistance State and the Low Resistance State). This switching process essentially involves the local migration and stable state changes of oxygen vacancies within the thin film. In conventional sandwich designs, increasing the number of oxygen vacancies in the resistive switching layer enhances the nonlinear response of the impedance, particularly by suppressing the effective recombination of photogenerated carriers (such as electron-hole pairs), thereby enhancing the so-called "permanent conductance" (PPC) phenomenon.

[0004] However, this traditional architecture has certain limitations. Although increasing the oxygen vacancy concentration can improve performance, the improvement is limited by the single structure of the resistive switching layer, affecting the stability of the memristor effect. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a memristor based on artificially constructed conductive filaments and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] In a first aspect, the present invention proposes a memristor based on artificially constructed conductive filaments, which includes, from bottom to top, a substrate, a bottom electrode, a resistive switching layer and a top electrode.

[0007] The resistive switching layer adopts a sandwich structure, which includes multiple epitaxial layers. The oxygen vacancy concentration of the multiple epitaxial layers is distributed in a way that first increases and then decreases from bottom to top. Furthermore, several artificially constructed conductive filaments are formed on the middle epitaxial layer.

[0008] Secondly, this invention proposes a method for fabricating a memristor based on artificially constructed conductive filaments, comprising:

[0009] A bottom electrode is formed on the substrate;

[0010] A first epitaxial layer with a first oxygen vacancy concentration is fabricated on the bottom electrode;

[0011] A second epitaxial layer with a second oxygen vacancy concentration is fabricated on the first epitaxial layer;

[0012] The second epitaxial layer is etched to form an artificially constructed conductive filament;

[0013] A third epitaxial layer with a third oxygen vacancy concentration is fabricated on the second epitaxial layer, thereby forming a complete resistive switching layer;

[0014] A top electrode is formed on the resistive switching layer, thereby completing the fabrication of a memristor based on artificially constructed conductive filaments.

[0015] The beneficial effects of this invention are:

[0016] This invention proposes a memristor based on artificially constructed conductive filaments. It employs a resistive switching layer structure comprising multiple epitaxial layers, where the oxygen vacancy concentration increases initially and then decreases from bottom to top. Several artificially constructed conductive filaments are formed on the middle epitaxial layer. This structural design includes alternating regions of low oxygen vacancy concentration, high oxygen vacancy concentration, and regions returning to low oxygen vacancy concentration. Precise control of the oxygen vacancy concentration promotes the generation of a highly efficient network of oxygen vacancy conductive filaments, enhancing not only the activity of oxygen vacancies but also accelerating their migration within the memristor. This significantly improves the memristor's memory capacity and nonlinear characteristics, overcoming the bottleneck in performance improvement of traditional resistive switching layer structures and achieving a more stable memristor effect.

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a traditional memristor with a sandwich-structured resistive switching layer.

[0019] Figure 2 This is a schematic diagram of a memristor based on artificially constructed conductive filaments provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of an artificially constructed conductive filament provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram illustrating the principle of the formation and breakage of conductive filaments provided in an embodiment of the present invention;

[0022] Figure 5 This is a schematic flowchart of a method for preparing a memristor based on artificially constructed conductive filaments provided in an embodiment of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The first aspect of the present invention provides a memristor based on artificially constructed conductive filaments, which includes, from bottom to top, a substrate, a bottom electrode, a resistive switching layer and a top electrode;

[0025] The resistive switching layer adopts a sandwich structure, which includes multiple epitaxial layers. The oxygen vacancy concentration of the multiple epitaxial layers is distributed in a way that first increases and then decreases from bottom to top. Furthermore, several artificially constructed conductive filaments are formed on the middle epitaxial layer.

[0026] As one implementation method, please refer to Figure 2 , Figure 2 This is a schematic diagram of a memristor based on artificially constructed conductive filaments provided in an embodiment of the present invention. The resistive switching layer comprises, from bottom to top, a first epitaxial layer, a second epitaxial layer, and a third epitaxial layer. The fixed oxygen vacancy concentration or highest oxygen vacancy concentration of the first and third epitaxial layers is lower than the fixed oxygen vacancy concentration or lowest oxygen vacancy concentration of the second epitaxial layer, and the fixed oxygen vacancy concentrations of the first and third epitaxial layers are the same. A plurality of artificially constructed conductive filaments are formed in the second epitaxial layer.

[0027] Preferably, the oxygen vacancy concentration in the first and third epitaxial layers can be 20%, and the oxygen vacancy concentration in the second epitaxial layer can be 40%.

[0028] Optionally, in this embodiment, the thickness of the first epitaxial layer and the thickness of the third epitaxial layer are the same; the thickness of the second epitaxial layer is greater than the thickness of the first epitaxial layer.

[0029] For example, the thickness of the first epitaxial layer and the third epitaxial layer can be 30-50 nm, and the thickness of the second epitaxial layer can be 100 nm.

[0030] In this embodiment, by etching the second epitaxial layer, several artificially constructed conductive filaments can be formed, such as... Figure 3 As shown, the formed conductive filaments are equivalent to oxygen vacancy columns with a spacing of 50–100 nm.

[0031] Please see Figure 4 , Figure 4 This is a schematic diagram illustrating the formation and breakage principle of the conductive filaments provided in this embodiment of the invention. By precisely controlling the oxygen vacancy concentration, this invention promotes the generation of a highly efficient oxygen vacancy conductive filament network. This not only enhances the activity of oxygen vacancies but also accelerates their migration process within the memristor, thereby significantly improving the memristor's memory capability and nonlinear characteristics. It breaks through the bottleneck in improving the performance of traditional resistive switching layer structures, achieving a more stable memristor effect.

[0032] Furthermore, in this embodiment, the substrate can be a silicon substrate, a sapphire substrate, or a diamond substrate; the resistive switching layer can be made of gallium oxide, or other hafnium oxide or aluminum oxide materials; the bottom electrode can be made of graphene two-dimensional material; and the top electrode can be made of any one of Ag, Ti, Pt, Au, W, Al, or Cu.

[0033] Gallium oxide (Ga2O3), as an emerging ultra-wide bandgap semiconductor material, possesses advantages such as good thermal stability, large bandgap, high ultraviolet absorption coefficient, and easy processing, making it a promising candidate material for solar-blind ultraviolet detection. Simultaneously, Ga2O3's high resistance and oxygen-sensitive conductivity also make it an ideal candidate material for memristors. Ga2O3 memristors can store signals from solar-blind photodetectors, potentially enabling the development of optical sensing image recognition and storage systems based on the solar-blind band. This significantly simplifies circuit complexity, effectively improves information processing efficiency, and reduces system power consumption, making it a cutting-edge research area in the application field.

[0034] Therefore, gallium oxide is preferred as the resistive switching layer material in this embodiment.

[0035] Understandably, the bottom electrode can be made of single-layer graphene, few-layer graphene, or multi-layer graphene. This invention uses graphene as the bottom electrode, which can alleviate the stress caused by lattice mismatch between the substrate and the epitaxial layer, ensuring the high quality of the gallium oxide crystal.

[0036] This invention proposes a memristor based on artificially constructed conductive filaments. It employs a resistive switching layer structure comprising multiple epitaxial layers, where the oxygen vacancy concentration increases initially and then decreases from bottom to top. Several artificially constructed conductive filaments are formed on the middle epitaxial layer. This structural design includes alternating regions of low oxygen vacancy concentration, high oxygen vacancy concentration, and regions returning to low oxygen vacancy concentration. Precise control of the oxygen vacancy concentration promotes the generation of a highly efficient network of oxygen vacancy conductive filaments, enhancing not only the activity of oxygen vacancies but also accelerating their migration within the memristor. This significantly improves the memristor's memory capacity and nonlinear characteristics, overcoming the bottleneck in performance improvement of traditional resistive switching layer structures and achieving a more stable memristor effect.

[0037] Furthermore, this invention uses gallium oxide as the resistive switching layer of the memristor. Due to the material's excellent solar-blind ultraviolet detection characteristics, it can store solar-blind photodetector signals, and develop a light-sensing image recognition and storage system based on the solar-blind band. This greatly simplifies circuit design, improves information processing speed, and reduces energy consumption, opening up new avenues for high-efficiency, low-power application scenarios.

[0038] Based on the same inventive concept, a second aspect of this invention also provides a method for fabricating a memristor based on artificially constructed conductive filaments. Please refer to [link to relevant documentation]. Figure 5 , Figure 5 This is a schematic flowchart illustrating a method for fabricating a memristor based on artificially constructed conductive filaments, as provided in an embodiment of the present invention. The method specifically includes:

[0039] Step 1: Form the bottom electrode on the substrate.

[0040] First, prepare a silicon substrate for later use.

[0041] Then, the graphene bottom electrode material prepared on the copper foil using CVD (Chemical Vapor Deposition) process is transferred to the substrate using a wet transfer method to serve as the bottom electrode.

[0042] The graphene bottom electrode can be a single layer, a few layers, or multiple layers of graphene.

[0043] Step 2: Fabricate a first epitaxial layer with a first oxygen vacancy concentration on the bottom electrode.

[0044] Specifically, taking a gallium oxide resistive switching layer as an example, a 30-50 nm thick gallium oxide film with a first oxygen vacancy concentration is van der Waals epitaxially grown on the bottom electrode as the first epitaxial layer. The oxygen vacancy concentration of the first epitaxial layer can be adjusted to the desired range using process parameters; for example, in this embodiment, the fixed oxygen vacancy concentration of the first epitaxial layer can be set to 20%.

[0045] Optionally, the epitaxial process of the first epitaxial layer can be any of the following processes: sputtering, atomic layer deposition, evaporation, pulsed laser deposition, thermal oxidation, or chemical vapor deposition.

[0046] Step 3: Fabricate a second epitaxial layer with a second oxygen vacancy concentration on the first epitaxial layer.

[0047] Specifically, a 100nm gallium oxide thin film with a certain oxygen vacancy concentration is epitaxially grown on the first epitaxial layer to serve as the second epitaxial layer.

[0048] Optionally, the epitaxial process of the second epitaxial layer can be any of the following processes: sputtering, atomic layer deposition, evaporation, pulsed laser deposition, thermal oxidation, or chemical vapor deposition.

[0049] Step 4: Etch the second epitaxial layer to form an artificially constructed conductive filament.

[0050] Specifically, by selectively etching the second epitaxial layer, several artificially constructed conductive filaments, i.e. oxygen vacancy pillars, can be obtained, thereby adjusting the oxygen vacancy concentration of the second epitaxial layer to the required range, such as 40% in this embodiment.

[0051] Step 5: Fabricate a third epitaxial layer with a third oxygen vacancy concentration on the second epitaxial layer to form a complete resistive switching layer.

[0052] Specifically, a 30-50 nm thick gallium oxide film with a third oxygen vacancy concentration is van der Waals epitaxially grown on the second epitaxial layer as the third epitaxial layer.

[0053] The concentration of the third oxygen vacancy can be the same as that of the first oxygen vacancy, both being 20%.

[0054] Thus, a resistive switching layer structure with a three-layer sandwich structure was formed.

[0055] Optionally, the epitaxial process of the third epitaxial layer can be any of the following processes: sputtering, atomic layer deposition, evaporation, pulsed laser deposition, thermal oxidation, or chemical vapor deposition.

[0056] It is understood that in this embodiment, the preparation processes of the first epitaxial layer, the third epitaxial layer and the second epitaxial layer can be the same or different. When the same process is used, different oxygen vacancy concentrations can be obtained by using different process parameters.

[0057] Step 6: Form the top electrode on the resistive switching layer to complete the fabrication of the memristor based on artificially constructed conductive filaments.

[0058] Specifically, Ag, Ti, Pt, Au, W, Al, or Cu metals are deposited on the resistive switching layer using electron beam evaporation deposition or shadow masking and magnetron sputtering processes to form the top electrode.

[0059] Optionally, as one implementation method, firstly, a forward photoresist (AZ 6112) is coated on the sandwich structure / monolayer graphene / silicon substrate at a rotation speed of 4000 rpm / min for 60 s, and then cured at 100°C for 90 s.

[0060] Then, Ti metal was deposited using electron beam evaporation as the top electrode.

[0061] Thus, the fabrication of a memristor based on artificially constructed conductive filaments was completed.

[0062] The method for preparing a memristor based on artificially constructed conductive filaments provided in the second aspect of the present invention can be used to prepare the memristor based on artificially constructed conductive filaments provided in the first aspect of the present invention. Therefore, it has similar beneficial effects to the memristor based on artificially constructed conductive filaments provided in the first aspect. For relevant details, please refer to the description of the device embodiments.

[0063] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0064] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0065] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0066] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A memristor based on artificially constructed conductive filaments, characterized in that, From bottom to top, it includes a substrate, a bottom electrode, a resistive switching layer, and a top electrode; The resistive switching layer adopts a sandwich structure, including multiple epitaxial layers. The oxygen vacancy concentration of the multiple epitaxial layers is distributed in a way that first increases and then decreases from bottom to top. Furthermore, several artificially constructed conductive filaments are formed in the middle epitaxial layer through etching.

2. The memristor based on artificially constructed conductive filaments according to claim 1, characterized in that, The resistive switching layer comprises, from bottom to top, a first epitaxial layer, a second epitaxial layer, and a third epitaxial layer; wherein, the fixed oxygen vacancy concentrations of the first epitaxial layer and the third epitaxial layer are equal and both are less than the fixed oxygen vacancy concentration of the second epitaxial layer; and a plurality of artificially constructed conductive filaments are formed in the second epitaxial layer.

3. The memristor based on artificially constructed conductive filaments according to claim 2, characterized in that, The oxygen vacancy concentration of the first epitaxial layer and the third epitaxial layer is 20%, and the oxygen vacancy concentration of the second epitaxial layer is 40%.

4. The memristor based on artificially constructed conductive filaments according to claim 2, characterized in that, The thickness of the first epitaxial layer is the same as the thickness of the third epitaxial layer; the thickness of the second epitaxial layer is greater than the thickness of the first epitaxial layer.

5. The memristor based on artificially constructed conductive filaments according to claim 1, characterized in that, The spacing between some of the artificially constructed conductive filaments is 50~100 nm.

6. The memristor based on artificially constructed conductive filaments according to claim 1, characterized in that, The substrate is a silicon substrate, a sapphire substrate, or a diamond substrate; the resistive switching layer is made of gallium oxide, hafnium oxide, or aluminum oxide; the bottom electrode is made of graphene; and the top electrode is made of any one of Ag, Ti, Pt, Au, W, Al, or Cu.

7. A method for fabricating a memristor based on artificially constructed conductive filaments, characterized in that, include: A bottom electrode is formed on the substrate; A first epitaxial layer having a first oxygen vacancy concentration is fabricated on the bottom electrode; A second epitaxial layer with a second oxygen vacancy concentration is fabricated on the first epitaxial layer; The second epitaxial layer is etched to form several artificially constructed conductive filaments; A third epitaxial layer with a third oxygen vacancy concentration is fabricated on the second epitaxial layer to form a complete resistive switching layer; the oxygen vacancy concentration of the multilayer epitaxial layers is distributed in a manner that first increases and then decreases from bottom to top. A top electrode is formed on the resistive switching layer, thereby completing the fabrication of a memristor based on artificially constructed conductive filaments.

8. The preparation method according to claim 7, characterized in that, Forming a bottom electrode on the substrate includes: A wet transfer method was used to transfer graphene prepared by CVD on copper foil onto a substrate to form a bottom electrode.

9. The preparation method according to claim 7, characterized in that, The fabrication of the first epitaxial layer, the second epitaxial layer, and the third epitaxial layer is achieved by sputtering, atomic layer deposition, evaporation, pulsed laser deposition, thermal oxidation, or chemical vapor deposition. During the fabrication process, different oxygen vacancy concentrations are achieved by adjusting the process parameters.

10. The preparation method according to claim 7, characterized in that, A top electrode is formed on the resistive switching layer, comprising: The top electrode is formed by depositing Ag, Ti, Pt, Au, W, Al or Cu metals on the resistive switching layer using electron beam evaporation deposition or shadow masking and magnetron sputtering processes.

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