Memristor and method for manufacturing the same

Abstract

The application discloses a memristor and a preparation method thereof. The resistive change medium layer of the memristor is formed by titanium dioxide and rare earth oxide, so that the memristor device has at least four stable resistance states, and even more resistance states can be introduced, thereby overcoming the problems of unstable resistance state and poor robustness existing in the memristor device based on a single material. Moreover, the memristor has the characteristics of better stability and lower leakage current. Meanwhile, the preparation method proposed by the application gives the titanium dioxide medium a higher oxygen vacancy concentration, so that a conductive filament is more easily formed, and the device shows a faster switching speed.

Description

Technical Field

[0001] This invention relates to the fields of microelectronics and storage devices, specifically to a memristor based on various resistive switching media and its fabrication method. Background Technology

[0002] Traditional transistors can only switch between two resistive states, "0" and "1," which cannot meet the demands of the highly integrated and high-speed computing IC industry. Therefore, there is an urgent need to find alternative multi-resistive-state novel storage or computing unit devices. The emergence of memristors has brought new hope to the industry. These are novel nanodevices whose resistance is related to the charge flowing through them and are non-volatile, enabling them to perform both storage and computing functions. Memristor-based random access memory (RAM) offers superior integration, power consumption, and read / write speeds compared to traditional RAM, and has broad application prospects in information storage, chaotic circuits, in-memory computing chips, artificial neural networks, and many other areas.

[0003] Currently, most memristor structures studied consist of three parts: a metal electrode, a resistive switching dielectric, and another metal electrode. The resistive switching dielectric is typically an oxide material. Under an applied electric field, oxygen vacancies are formed and migrated, thereby enabling the formation and disconnection of conductive filaments and achieving continuous and reversible switching between high-resistivity states and even multiple resistance states. Further achieving multi-valued storage will place higher demands on the stability and consistency of the device's multiple resistance states.

[0004] The resistive state of the aforementioned sandwich structure is primarily determined by the material of the intermediate resistive switching dielectric layer. Currently, titanium dioxide is a popular memristor material due to its abundant oxygen vacancy defects. Additionally, rare earth oxides, such as HfOx, TaOx, and IrOx, are also frequently studied memristor materials, all possessing abundant oxygen vacancy defects.

[0005] However, the control of multiple resistance states of a single material has a certain degree of randomness, and the reliability of its multiple resistance states will inevitably be affected by material changes over time, making it difficult to guarantee reliable data reading. Summary of the Invention

[0006] The purpose of this invention is to propose a memristor based on multiple resistive switching media and its fabrication method. Through the construction of a new structure, a stable multi-resistive state memristor device design with the fusion of multiple memristor materials can be achieved.

[0007] To address the aforementioned problems, this invention provides a memristor comprising an upper electrode, a resistive switching dielectric layer, and a lower electrode. The resistive switching dielectric layer comprises titanium dioxide and rare earth oxides. In the cross-section of the resistive switching dielectric layer, the structure of the resistive switching dielectric layer is a grid-like structure in which strip-shaped titanium dioxide and strip-shaped rare earth oxides are arranged alternately. Alternatively, in the cross-section of the resistive switching dielectric layer, the structure of the resistive switching dielectric layer is a structure in which rare earth oxides are latticeally embedded in titanium dioxide.

[0008] Preferably, the rare earth oxide material is HfOx, TaOx, or IrOx, or a mixture of at least two of them.

[0009] Preferably, the thickness of the upper and lower electrodes is 80-100 nm; the thickness of the resistive switching dielectric layer is 50-100 nm.

[0010] The present invention also provides a method for fabricating a memristor, the method comprising:

[0011] Step S1: Prepare a titanium dioxide thin film on the lower electrode;

[0012] Step S2: Prepare a patterned metal layer on the titanium dioxide thin film. The patterned metal layer is in the form of a strip grid or the area not covered by the patterned metal layer is in the form of a dot matrix.

[0013] Step S3: Using the patterned metal layer as a mask, etch the titanium dioxide thin film down to the lower electrode using reactive ion etching.

[0014] Step S4: Deposit a rare earth oxide layer, the rare earth oxide layer having the same thickness as the titanium dioxide film;

[0015] Step S5: Remove the patterned metal layer and the rare earth oxides above it to form a resistive switching dielectric layer with titanium dioxide as the first resistive switching dielectric and rare earth oxides as the second resistive switching dielectric.

[0016] Step S6: Deposit an electrode on the resistive switching dielectric layer to obtain a memristor.

[0017] Preferably, in step S1, a titanium dioxide thin film is prepared on the lower electrode using the sol-gel method, and the thickness of the titanium dioxide thin film is 50-100 nm.

[0018] Preferably, oxygen is introduced during the etching of the titanium dioxide thin film using reactive ion etching in step S3.

[0019] Preferably, the lower electrode is an electrode that is difficult to dissolve in aqua regia at room temperature; step S5 includes: immersing the structure obtained in step S4 in aqua regia at room temperature for 5-30 seconds, so that the patterned metal layer and the rare earth oxides above it naturally peel off.

[0020] Preferably, the rare earth oxide layer is made of HfOx, TaOx, or IrOx, or a mixture of at least two of them.

[0021] Preferably, the thickness of the patterned metal layer in step S2 is 30-50 nm, and the patterned metal layer is prepared by thermal evaporation, physical vapor deposition, chemical vapor deposition or photolithography.

[0022] Preferably, step S0 is included before step S1. Step S0 includes cleaning the surface of the silicon substrate, drying it with a nitrogen gun after cleaning, and then growing the lower electrode on the silicon substrate by thermal evaporation, physical vapor deposition or chemical vapor deposition.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) The memristor structure based on titanium dioxide and rare earth oxides proposed in this invention enables the memristor device to have at least 4 resistance states based on 2 materials, and even more resistance states can be introduced, overcoming the problems of unstable resistance states and poor robustness in memristor devices based on a single material.

[0025] (2) The memristor structure proposed in this invention has two vertically integrated conductive channels: titanium oxide and rare earth oxide. The conductive filaments are switched on and off in relatively independent spaces, resulting in better stability of the conductive filaments and lower leakage current.

[0026] (3) The memristor fabrication method proposed in this invention is simple and low in cost. The fabrication process imparts a higher oxygen vacancy concentration to the titanium dioxide dielectric, making it easier to form conductive filaments and resulting in faster switching speeds for the device.

[0027] (4) The secondary deposition of the dielectric layer results in a certain degree of protrusion at the ends of the titanium dioxide and rare earth oxides. The structure of these protrusions can guide the formation of conductive filaments, and during the device conduction process, a stable and reliable conductive channel is formed in a guided manner, thereby greatly improving the uniformity of the device. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a memristor.

[0029] Figure 2 These are schematic diagrams of two structures of resistive switching dielectric layers;

[0030] Figure 3 This refers to the fabrication method of memristors. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] like Figure 1As shown, the present invention proposes a memristor based on two or more resistive switching media. The memristor includes an upper electrode 10, a resistive switching media layer and a lower electrode 20, wherein the resistive switching media layer includes titanium dioxide 31 and rare earth oxide 32.

[0033] In one embodiment, the structure of the resistive switching dielectric layer is as follows: Figure 2 As shown in (a), the resistive switching dielectric layer has a grid-like structure in which strip-shaped titanium dioxide 31 and strip-shaped rare earth oxide 32 are arranged alternately on the cross-section. The thickness of the resistive switching dielectric layer is preferably 50-100 nm.

[0034] In another embodiment, the structure of the resistive switching dielectric layer is as follows: Figure 2 As shown in (b), in the cross-section of the resistive switching dielectric layer, rare earth oxides 32 are distributed in a lattice pattern within titanium dioxide 31. It is worth noting that the lattice structure formed by rare earth oxides 32 is not limited to... Figure 2 The structure shown in (b)

[0035] The rare earth oxide 32 is made of HfOx, TaOx, or IrOx, or a mixture of at least two of them. When the rare earth oxide 32 is a mixture, more resistive states can be introduced.

[0036] The thickness of the upper electrode 10 is preferably 80-100 nm. The thickness of the lower electrode 20 is preferably 80-100 nm.

[0037] All preparation methods available to those skilled in the art based on known processing and manufacturing techniques can be used to manufacture the aforementioned memristor. This invention proposes a preferred method for preparing the aforementioned memristor, such as... Figure 3 As shown, the preparation method includes:

[0038] Step S1: Prepare a titanium dioxide thin film on the lower electrode. The thickness of the titanium dioxide thin film is preferably 50-100 nm.

[0039] The lower electrode is a single-layer metal electrode that is extremely difficult to dissolve in aqua regia at room temperature, such as W, Ti, Mo, Ta, Re, Os, Ir, Rh, and Ag; or other double-layer metal composite electrodes and conductive metal oxide electrodes that are extremely difficult to dissolve in aqua regia at room temperature.

[0040] In one embodiment, a titanium dioxide thin film is prepared on the lower electrode using a sol-gel method. The titanium dioxide thin film prepared by the sol-gel method has more oxygen vacancy defects. Specific steps include spin-coating a 0.5 mol·L⁻¹ titanium dioxide film onto the lower electrode at 3000 rpm for 30 s. -1A dense titanium dioxide film can be obtained by annealing a bis(acetylacetonate)diisopropyl titanate sol at 350°C for 30 minutes. It is worth noting that the thickness of the titanium dioxide film can be controlled by multiple spin coatings. Furthermore, the crystal structure of titanium dioxide can be controlled by adjusting the annealing temperature, thus altering its resistive state.

[0041] In other embodiments, titanium dioxide thin films can also be prepared by methods such as atomic layer deposition, physical vapor deposition, or chemical vapor deposition.

[0042] In one embodiment, step S0 is included before step S1. Step S0 specifically includes cleaning the surface of the silicon substrate, drying it with a nitrogen gun after cleaning, and then growing a lower electrode on the silicon substrate using methods such as thermal evaporation, physical vapor deposition, or chemical vapor deposition. The thickness of the lower electrode is preferably 80-100 nm.

[0043] Step S2: A patterned metal layer is prepared on the titanium dioxide thin film. The patterned metal layer is in the form of a strip grid, or the areas not covered by the patterned metal layer are in the form of a dot matrix. Preferably, the patterned metal layer is a patterned gold layer of 30-50 nm.

[0044] Alternatively, the patterned metal layer can be prepared by methods such as thermal evaporation, physical vapor deposition, chemical vapor deposition, or photolithography. The preparation methods for the patterned metal layer described above are all common knowledge in the art and will not be elaborated further.

[0045] Step S3: Using the patterned metal layer as a mask, the titanium dioxide thin film is etched to the lower electrode using reactive ion etching to form a metal / titanium dioxide array.

[0046] By taking advantage of the difference in reaction between metals and titanium dioxide to etching gases, and using a patterned metal layer as a mask, the more reactive titanium dioxide is preferentially etched, thereby forming a metal / titanium dioxide array.

[0047] In one embodiment, oxygen is introduced during the etching of the titanium dioxide thin film using reactive ion etching, which helps to increase the oxygen vacancy concentration in the titanium dioxide, thereby making it easier to form conductive filaments and enabling the device to exhibit faster switching speeds.

[0048] Step S4: A rare earth oxide layer is deposited on the metal / titanium dioxide array. The rare earth oxide layer has the same thickness as the titanium dioxide layer, so that the rare earth oxide completely fills the voids formed after etching the titanium dioxide film. The rare earth oxide layer is made of HfOx, TaOx, or IrOx, or a mixture of at least two of them. It is worth mentioning that when the rare earth oxide layer is a mixture, more resistive states can be introduced.

[0049] Alternatively, the rare earth oxide layer can be prepared by methods such as thermal evaporation, physical vapor deposition, or chemical vapor deposition.

[0050] Step S5: Remove the patterned metal layer and the rare earth oxides above it to form a resistive switching dielectric layer with titanium dioxide as the first resistive switching dielectric and rare earth oxides as the second resistive switching dielectric.

[0051] In one embodiment, the specific steps for removing the patterned metal layer and the rare earth oxides thereon include immersing the structure obtained in step S4 in aqua regia at room temperature for 5-30 seconds, allowing the patterned metal layer and the rare earth oxides thereon to peel off naturally.

[0052] The secondary deposition of the dielectric layer and the removal of the patterned metal layer and the rare earth oxides above it using aqua regia result in certain protrusions at the ends of the titanium dioxide and rare earth oxides. These protrusions can guide the formation of conductive filaments, and during the device conduction process, they can guide the formation of stable and reliable conductive channels, thereby greatly improving the device uniformity.

[0053] Step S6: Deposit an electrode on the resistive switching dielectric layer to obtain a memristor device.

[0054] The upper electrode is a single-layer metal electrode, such as W, Al, Cu, Au, Ag, Pt, Ru, Ti, Ta, etc.; or a double-layer metal composite electrode, such as Pt / Ti, Cu / Au, Au / Cr, Cu / Al, etc.; or a conductive metal oxide electrode, such as TiN, TaN, ITO, IZO, etc. The thickness of the upper electrode is preferably 80-100 nm.

[0055] Alternatively, the upper electrode can be prepared by methods such as thermal evaporation, physical vapor deposition, or chemical vapor deposition.

[0056] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A memristor, characterized in that, The memristor includes an upper electrode, a resistive switching dielectric layer, and a lower electrode, wherein the resistive switching dielectric layer includes titanium dioxide and rare earth oxides. On the cross-section of the resistive switching dielectric layer, the structure of the resistive switching dielectric layer is a grid structure in which strips of titanium dioxide and strips of rare earth oxide are arranged alternately. Alternatively, on the cross-section of the resistive switching dielectric layer, the structure of the resistive switching dielectric layer is such that the rare earth oxides are lattice-embedded in the titanium dioxide. The memristor has at least four resistive states.

2. The memristor according to claim 1, characterized in that, The rare earth oxide is made of HfOx, TaOx, or IrOx, or a mixture of at least two of them.

3. The memristor according to claim 1, characterized in that, The thickness of the upper and lower electrodes is 80-100 nm; the thickness of the resistive switching dielectric layer is 50-100 nm.

4. A method for fabricating a memristor, characterized in that, The preparation method includes: Step S1: Prepare a titanium dioxide thin film on the lower electrode; Step S2: A patterned metal layer is prepared on the titanium dioxide thin film. The patterned metal layer is in the form of a strip grid or the area not covered by the patterned metal layer is in the form of a dot matrix. Step S3: Using the patterned metal layer as a mask, the titanium dioxide thin film is etched to the lower electrode using reactive ion etching. Step S4: Deposit a rare earth oxide layer, wherein the rare earth oxide layer has the same thickness as the titanium dioxide film; Step S5: Remove the patterned metal layer and the rare earth oxides above it to form a resistive switching dielectric layer with titanium dioxide as the first resistive switching dielectric and rare earth oxides as the second resistive switching dielectric. Step S6: Deposit an upper electrode on the resistive switching dielectric layer to obtain the memristor; The memristor has at least four resistive states.

5. The preparation method according to claim 4, characterized in that, In step S1, the titanium dioxide film is prepared on the lower electrode using the sol-gel method, and the thickness of the titanium dioxide film is 50-100 nm.

6. The preparation method according to claim 4, characterized in that, Oxygen is introduced during the etching of the titanium dioxide thin film using reactive ion etching in step S3.

7. The preparation method according to claim 4, characterized in that, The lower electrode is an electrode that is difficult to dissolve in aqua regia at room temperature; step S5 includes: immersing the structure obtained in step S4 in aqua regia at room temperature for 5-30 seconds, so that the patterned metal layer and the rare earth oxides above it naturally peel off.

8. The preparation method according to claim 4, characterized in that, The rare earth oxide layer is made of HfOx, TaOx, or IrOx, or a mixture of at least two of them.

9. The preparation method according to claim 4, characterized in that, The patterned metal layer in step S2 has a thickness of 30-50 nm and is prepared by thermal evaporation, physical vapor deposition, chemical vapor deposition or photolithography.

10. The preparation method according to claim 4, characterized in that, Before step S1, there is also step S0, which includes cleaning the surface of the silicon substrate, drying it with a nitrogen gun after cleaning, and then growing the lower electrode on the silicon substrate by thermal evaporation, physical vapor deposition or chemical vapor deposition.

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