Selenium crystal intrinsic oxidation preparation of memristor functional layer material, memristor and method

Abstract

This invention provides a memristor functional layer material, a memristor, and a method for preparing a memristor based on the intrinsic oxidation of selenide crystals, belonging to the field of microelectronic devices. The functional layer material includes Re2O7 formed by the intrinsic oxidation of ReSe2, with the intrinsic oxide layer located above the ReSe2 two-dimensional material layer. Oxygen vacancy conductive filaments connect the ReSe2 and the oxidized Re2O7 intrinsic oxide layer. The memristor comprises four parts: a top electrode, a bottom electrode, a ReSe2 two-dimensional material layer, and a Re2O7 intrinsic oxide layer. The ReSe2 two-dimensional material layer itself has low resistance, which can effectively improve the contact characteristics with the electrode to form an ohmic contact. Its oxide, Re2O7, has a very high resistance, which can significantly increase the high resistance of the device, thereby reducing leakage current and increasing the on / off ratio of the device. This invention also provides a method for preparing the above-mentioned memristor. This invention employs a novel memristor functional layer material that can increase the on / off ratio of memristor devices.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic device technology, and more specifically, relates to a memristor functional layer material, memristor, and method for intrinsic oxidation of selenide crystals. Background Technology

[0002] Memristors are considered the fourth type of passive basic circuit element, alongside resistors, capacitors, and inductors. The resistance of a memristor changes with the amount of charge flowing through it and maintains its resistance when the current is interrupted, thus achieving non-volatile information storage. Research has shown that the non-volatile information storage capability of memristors allows them to be used for high-density information storage or non-volatile state logic operations. Furthermore, some memristors possess continuously adjustable conductance, enabling them to be used as synaptic devices in neuromorphic computing. Memristors achieve the integration of storage and computation in a single device, making them one of the fundamental components for building non-von Neumann computing architectures.

[0003] Currently, memristors based on the theory of conductive filaments have advantages such as simple structure, low power consumption, and fast read / write speed, making them one of the most promising memory technologies. However, memristor research has only been conducted for a short time, and many problems still need to be solved. On the one hand, the migration of ions in the dielectric material of a memristor forms conductive filaments, and the connection and breakage of these filaments cause changes in the conductivity of the device. [See the following two references: SUN H, LIU Q, LI C, et al. Direct Observation of Conversion Between Threshold Switching and Memory Switching Induced by Conductive Filament Morphology[J]. 2014; YANG Y, GAO P, GABA S, et al. Observation of conducting filament growth in nanoscale resistive memories[J]. 2012, 3(732.)].

[0004] On the one hand, heterogeneous integrated memristor devices suffer from poor interface conditions and low resistance of the functional layer material, leading to device failure, high power consumption, and low switching efficiency. This severely limits the storage capacity of memristor memory chips and poses significant challenges to the large-scale integration and circuit design of memristors. On the other hand, epitaxial growth of memristor functional layer materials involves complex processing conditions, and the functional layer thickness cannot be infinitely reduced, resulting in high design costs, hindering the control of device power consumption, and limiting the design of peripheral circuits for artificial neural networks.

[0005] Currently, the following work has been applied to reduce the power consumption of memristors:

[0006] For example, Liu et al. prepared HfSeO based on the intrinsic oxidation of two-dimensional HfSe2 materials. x Memristor functional layer material, utilizing HfSeO x The large bandgap and high resistivity of memristor functional layer materials enable low-power applications of memristors. [LIU L,LI Y,HUANG X,et al.Low-Power Memristive Logic Device Enabled by Controllable Oxidation of 2D HfSe2 for In-Memory Computing[J].2021,8(15):2005038.]. Zhao et al. prepared ultrathin BNOx memristor functional layer materials based on intrinsic oxidation of hBN, using Ag active electrode material for the top electrode, and thinned the material to an ultrathin monolayer of 0.9 nm, realizing single-point atomic-level growth of conductive filaments, and achieving ultra-low power consumption of memristors at the fJ level. [ZHAO H,et al.Advanced Materials,2017,29(47):1703232].

[0007] Furthermore, Chinese patent application No. 202111165610.3, entitled "An Island-Shaped Low-Resistance Memristor Functional Layer Material, Memristor, and Preparation Method," discloses a memristor formed from selenides and their oxidation products. However, it limits the selenides to those of group IV, V, and VI transition metals. Its internal microstructure is relatively complex, with selenide oxidation products containing trigonal selenium crystal clusters. These clusters are dispersed in an island-like pattern within the oxidation product layer, and oxygen vacancy conductive filaments connect the trigonal selenium crystal clusters to the unoxidized remaining selenide portion.

[0008] The above methods may have problems such as complex processes, high costs, or unstable performance. Therefore, it is necessary to develop a new type of low-resistivity memristor functional layer material and memristor. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a memristor functional layer material, memristor, and method prepared by intrinsic oxidation of selenide crystals. A novel material system is designed to form an oxide layer by in-situ oxidation of the selenide layer, which is a ReSe2 selenide layer and a Re2O7 layer obtained by intrinsic oxidation of ReSe2. The bilayer functional layer memristor device is prepared solely by intrinsic oxidation, resulting in good interface contact, high resistance, and easy reduction of device power consumption.

[0010] To achieve the above objectives, this invention provides a memristor functional layer material prepared by intrinsic oxidation of selenide crystals. It comprises a ReSe2 selenide layer and an intrinsic oxide layer obtained by in-situ oxidation of ReSe2 on the ReSe2 selenide layer. The ReSe2 selenide layer and its intrinsic oxide layer are tightly stacked to form a whole. The intrinsic oxide layer contains oxygen vacancy conductive filaments that connect the ReSe2 selenide layer and the top electrode. This ReSe2 selenide layer and its intrinsic oxide layer have never appeared in any memristor functional layer material system, representing a novel memristor functional layer material.

[0011] Furthermore, ReSe2 selenide has a two-dimensional structure and inherent metallic properties, enabling the establishment of ohmic contacts between the intrinsic oxide layer and the external electrode.

[0012] Furthermore, the resistivity of the intrinsic oxide obtained by in-situ oxidation with ReSe2 is not less than 1.0 × 10⁻⁶. 8 The intrinsic oxide, which possesses memristor characteristics, produces devices with low operating current. In this invention, the resistance of the intrinsic oxide obtained by in-situ oxidation of ReSe2 refers to the intrinsic resistance before the formation of conductive filaments in the functional layer. The test method involves applying a small voltage (10mV) between the upper and lower electrodes before cyclic operation and measuring its intrinsic resistance (approximately 100MΩ). Memristor characteristics refer to the ability of the device to cycle through the formation and breakage of conductive filaments in the functional layer by applying voltages of opposite polarity across the electrodes, thereby transitioning from a high-resistivity state to a low-resistivity state, and then back to a high-resistivity state.

[0013] According to a second aspect of the present invention, a memristor comprising a memristor functional layer material prepared by intrinsic oxidation of selenide crystal as described above is also provided. The memristor includes a top electrode, a bottom electrode, a ReSe2 selenide layer, and an intrinsic oxide layer obtained by in-situ oxidation of ReSe2. The bottom electrode is disposed on the ReSe2 selenide layer, and the top electrode is disposed on the intrinsic oxide layer. The ReSe2 selenide layer is used to improve the contact characteristics between the intrinsic oxide layer and the bottom electrode to form an ohmic contact.

[0014] Furthermore, the thickness of the ReSe2 selenide layer is 5 nm to 12 nm, and the thickness of the intrinsic oxide layer is 10 nm to 20 nm. Preferably, the thickness of the intrinsic oxide layer is 15 nm to 20 nm.

[0015] According to a third aspect of the present invention, a method for preparing the memristor as described above is also provided, characterized in that it comprises the following steps:

[0016] S1: Fabricate the bottom electrode on the substrate.

[0017] S2: Apply ReSe2 selenide to the bottom electrode prepared in step S1 to form a ReSe2 selenide layer.

[0018] S3: Perform oxidative annealing on the ReSe2 selenide layer. Specifically, first anneal at 90℃~110℃ in an atmospheric atmosphere for 45min~75min, then raise the temperature to 180℃~220℃ and anneal in a vacuum environment for 8min~12min to obtain the intrinsic oxide layer of ReSe2. The intrinsic oxide of ReSe2 is Re2O7.

[0019] S4: Fabricate the top electrode on the intrinsic oxide layer.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention have the following advantages:

[0021] Beneficial effects:

[0022] The memristor functional layer material of this invention is composed of a two-dimensional ReSe2 material and its corresponding Re2O7 oxide material stacked together. Such a functional layer material has not been previously designed, invented, or used; it is entirely novel. The stacked structure of the two-dimensional ReSe2 material and its corresponding Re2O7 oxide material utilizes both the low resistivity and easy integration advantages of the van der Waals layered structure of two-dimensional ReSe2, and the high resistivity and memristor function of its intrinsic oxide Re2O7. This results in memristor devices with good interface contact and low operating current. The fabrication method of this invention is simple and inexpensive. Attached Figure Description

[0023] Figure 1 This is a device structure diagram of a novel two-dimensional ReSe2 crystal intrinsically oxidized to prepare a memristor functional layer according to an embodiment of the present invention;

[0024] Figure 2 This is a flowchart illustrating the process of fabricating memristors using functional layer materials obtained from the intrinsic oxidation of novel two-dimensional ReSe2 crystals according to an embodiment of the present invention.

[0025] Figure 3 The XRD characterization spectrum of the two-dimensional ReSe2 material according to an embodiment of the present invention is shown.

[0026] Figure 4 The electrical DC characteristics of a memristor device fabricated by intrinsic oxidation of a novel two-dimensional ReSe2 crystal according to the present invention are shown in the figure.

[0027] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0028] 1 is the bottom electrode, 2 is the ReSe2 selenide layer, 3 is the oxygen vacancy conductive filament, 4 is the intrinsic oxide layer, and 5 is the top electrode. Detailed Implementation

[0029] 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.

[0030] This invention relates to the preparation of a memristor functional layer material, a memristor, and a method for preparing the memristor using intrinsic oxidation of a two-dimensional ReSe2 crystal. The functional layer material consists of a ReSe2 layer and a Re2O7 layer formed by intrinsic oxidation of ReSe2. The intrinsic oxide layer is located above the ReSe2 two-dimensional material layer, and the two are stacked to form a whole. Oxygen vacancy conductive filaments connect the oxidized Re2O7 intrinsic oxide layer and the ReSe2 two-dimensional material layer. The memristor comprises four parts: a top electrode, a bottom electrode, a ReSe2 two-dimensional material layer, and a Re2O7 intrinsic oxide layer. From bottom to top, the order is: bottom electrode, ReSe2 two-dimensional material layer, Re2O7 oxide layer, and top electrode. The ReSe2 two-dimensional material layer itself has low resistance, which can effectively improve the contact characteristics with the electrode to form an ohmic contact. Its oxide, Re2O7, has a high resistance, which can significantly increase the high resistance of the device, thereby reducing leakage current and increasing the on / off ratio of the device. This invention employs a novel memristor functional layer material, memristor, and preparation method, while also increasing the on / off ratio of the memristor device. The increased on / off ratio of the memristor specifically refers to the ratio of the memristor's resistance in its high-resistance state to its resistance in its low-resistance state; in this example, it is 3 × 10⁻⁶. 6 .

[0031] Figure 1 The diagram shows the structure of a memristor fabricated by intrinsic oxidation of a novel two-dimensional ReSe2 crystal according to the present invention. As shown, it includes a top electrode 5, a bottom electrode 1, an unoxidized remaining ReSe2 selenide layer 2, and an intrinsic oxide layer 4 obtained by in-situ oxidation of the ReSe2 selenide (the intrinsic oxide layer 4 is a functional layer with memristor properties formed after an oxidation annealing process). The ReSe2 selenide layer 2 is disposed on the bottom electrode 1, and the top electrode 5 is disposed on the intrinsic oxide layer 4. The ReSe2 selenide layer and the intrinsic oxide layer are tightly stacked to form a whole. The intrinsic oxide layer is obtained by in-situ oxidation of the ReSe2 selenide on the selenide layer. An oxygen vacancy conductive filament 3 connects the top electrode 5 and the unoxidized remaining unoxidized ReSe2 selenide layer 2.

[0032] In this invention, the selenide layer is a two-dimensional ReSe2 crystal. This two-dimensional ReSe2 has low resistivity, enabling the establishment of an ohmic contact between the oxide product layer and the external electrode. The intrinsic oxide layer is a Re2O7 oxide layer formed by the intrinsic oxidation of two-dimensional ReSe2, exhibiting high resistivity and memristor characteristics.

[0033] Figure 2 This is a flowchart illustrating the process of fabricating a memristor using a novel two-dimensional ReSe2 crystal intrinsically oxidized functional layer material according to an embodiment of the present invention. As shown in the figure, the method for fabricating the memristor of the present invention includes four key steps, as detailed below:

[0034] S1: Fabricate the bottom electrode on the substrate.

[0035] S2: Apply ReSe2 selenide to the bottom electrode prepared in step S1 to form a ReSe2 selenide layer.

[0036] S3: Perform oxidation annealing on the ReSe2 selenide layer. Specifically, anneal at 90℃~110℃ in an atmospheric atmosphere for 45min~75min to oxidize the surface of the selenide layer and obtain an oxidation product layer.

[0037] In practice, plasma can be used to oxidize the selenide layer simultaneously, followed by vacuum annealing. Specifically, oxidation can be carried out under plasma oxidation conditions with a power of 30W for 5 minutes.

[0038] Then, the temperature is raised to 180℃~220℃ and annealed in a vacuum environment for 8min~12min. The lattice damaged by oxidation in the oxidized ReSe2 layer is repaired during this annealing process.

[0039] S4: Fabrication of the top electrode on a two-dimensional material layer.

[0040] The method for preparing this novel memristor functional layer memristor will be further described in detail below with reference to more specific embodiments.

[0041] Example 1

[0042] The entire process of this embodiment is roughly divided into four steps, which will be described in turn below:

[0043] The first step involves fabricating a bottom electrode on a silicon substrate for subsequent two-dimensional material transfer. Specifically, a Si substrate with a 300nm silicon oxide epitaxial layer is used. After cleaning with acetone, ethanol, and deionized water, AZ5214 photoresist is dropped onto the silicon wafer and spin-coated using a spin coater. It is then pre-baked on a hot plate at 97°C for two minutes. Next, photolithography is performed to transfer the electrode pattern from the photomask to the photoresist; the pre-exposure takes 1.2 seconds. Then, the silicon wafer, after the above treatment, is post-exposure on a hot plate at 115°C for 2 minutes. It is then post-exposure under a photolithography machine for 12 seconds. Following this, development is performed using a dedicated AZ5214 developer for 30 seconds to obtain the desired pattern. Finally, electron beam evaporation is used for metallization, and excess metal is stripped to obtain the bottom electrode. It is important to note that the bottom electrode should not be too thick, generally less than 40nm. Excessive thickness will affect the transfer of two-dimensional materials and is detrimental to device fabrication. After this step, a bottom electrode is formed as shown in the image. Figure 1 The corresponding bottom electrode 1 is generally an electrode material containing an adhesive layer to prevent it from falling off.

[0044] The second step is to perform two-dimensional material transfer. The material used in this invention is 1T-ReSe2. ReSe2 has multiple crystal forms, and 1T-ReSe2 is one of the metallic ReSe2.

[0045] Specifically, the purchased two-dimensional material single-crystal bulk was mechanically exfoliated to obtain a single-crystal ReSe2 thin film with a diameter of less than 20 nm. Then, a metallographic microscope was used for targeted transfer, specifically to transfer the film to the previously prepared bottom electrode location, namely the tip of a 3 μm wide metal strip electrode. This step resulted in a film resembling... Figure 1 The first two-dimensional material in the middle is also the ReSe2 selenide layer 2. This two-dimensional selenide layer plays two roles. First, it has good metallic properties, which can establish ohmic contact between the functional layer and the electrode. Second, it can be oxidized to form the Re2O7 functional layer.

[0046] The third step is oxidation annealing. Specifically, in this embodiment, oxidation is performed in an atmospheric environment under the following conditions: 100°C for 60 minutes. Alternatively, plasma oxidation can be used with the following conditions: gas flow rate 100 sccm; oxidation power 30 W; oxidation time 5 min. After oxidation, the sample is placed in a vacuum annealing furnace, heated to 200°C, and annealed in a vacuum environment for 10 minutes. The first sub-step oxidizes the surface layer of the two-dimensional thin film material transferred to the bottom electrode to obtain a corresponding oxide layer with memristor properties, which is also a functional layer. The second sub-step repairs the lattice damaged during oxidation. After this step, a... Figure 1Intrinsic oxidation product layer 4.

[0047] The fourth step is to fabricate the top electrode, forming a crossbar structure to create a complete memristor device. This step is the same as the bottom electrode fabrication step described above, except that the electrode thickness is not subject to strict requirements; an appropriate thickness is sufficient. After this step, the top electrode 5 is formed.

[0048] In this invention, the device comprises a bottom electrode, an unoxidized two-dimensional ReSe2 material layer, an intrinsic oxide layer Re2O7, and a top electrode. The conductivity mechanism is explained as follows: When a positive voltage is applied to the top electrode and the bottom electrode is grounded, oxygen atoms at the negative electrode combine with electrons to generate oxygen ions. Due to the electric field, the oxygen ions move towards the positive electrode, leaving oxygen vacancies where oxygen atoms were originally located at the negative electrode. The oxygen atoms moving towards the positive electrode lose electrons upon reaching the vicinity of the positive electrode. Simultaneously, oxygen vacancies grow from the negative electrode towards the positive electrode along with the generation and movement of oxygen ions. The conductive channel formed by this accumulation of oxygen vacancies is called an oxygen vacancy conductive filament. After this conductive filament connects the negative electrode to the positive electrode, it forms a low-resistance path between the positive and negative electrodes, causing the memristor to undergo a threshold transition from high resistance to low resistance. Conversely, when a negative voltage is applied to the top electrode and the bottom electrode is grounded, the metal ions remaining at the oxygen vacancy combine with the oxygen ions formed after gaining electrons, and the oxygen vacancy disappears. When the conductive filament channel of the oxygen vacancy between the positive and negative electrodes is completely broken, the memristor undergoes a resistance transition from low to high. The above two processes describe a complete threshold switching electrical cycle of the memristor.

[0049] Figure 3 The figure shows the XRD characterization spectrum of the two-dimensional ReSe2 material in an embodiment of the present invention. As can be seen from the figure, by keeping the oxidation temperature constant, the intensity of the same peak position becomes lower and lower as the oxidation time increases, indicating that the content of the remaining two-dimensional material layer is decreasing. The prepared two-dimensional material is gradually oxidized into its intrinsic oxide. At 60 min, the two-dimensional material layer reaches the minimum value before it is completely oxidized. At this time, the oxide layer thickness is the largest and the two-dimensional layer thickness is the smallest.

[0050] Figure 4 The figure shows the DC cycling characteristics of the island-shaped memristor functional layer device implemented according to the present invention. As can be seen from the figure, the DC cycling electrical characteristics of the memristor device prepared according to the above process conditions are: the high-low group switching ratio is very large, approximately 3 × 10⁻⁶. 6 It can operate at a low current, approximately 10nA.

[0051] Example 2

[0052] This embodiment is the same as Embodiment 1, except that in the third step, the ReSe2 selenide layer is subjected to oxidation annealing. Specifically, the surface of the selenide layer is first annealed at 90°C in an atmospheric atmosphere for 75 minutes to oxidize the selenide layer and obtain an oxidation product layer. Then, the temperature is raised to 180°C and annealed in a vacuum environment for 8 minutes to obtain the intrinsic oxide layer of ReSe2, which is Re2O7.

[0053] Example 3

[0054] This embodiment is the same as that in embodiment 1, except that in the third step, the ReSe2 selenide layer is subjected to oxidation annealing. Specifically, the surface of the selenide layer is oxidized at 110°C in an atmospheric atmosphere for 45 minutes to obtain an oxidation product layer. Then, the temperature is raised to 220°C and annealed in a vacuum environment for 8 minutes to obtain the intrinsic oxide layer of ReSe2, which is Re2O7.

[0055] Example 4

[0056] This embodiment is the same as that in embodiment 1, except that in the third step, the ReSe2 selenide layer is subjected to oxidation annealing. Specifically, the surface of the selenide layer is oxidized at 95°C in an atmospheric atmosphere for 50 minutes to obtain an oxidation product layer. Then, the temperature is raised to 180°C and annealed in a vacuum environment for 12 minutes to obtain the intrinsic oxide layer of ReSe2, which is Re2O7.

[0057] This invention fabricates a ReSe2-Re2O7 bilayer thin film structure through several process steps. The Re2O7 oxide layer formed by intrinsic oxidation exhibits high resistivity, which significantly improves the device's on / off ratio and achieves lower operating current. The fabrication method involves two steps of oxidation annealing. The first step oxidizes the selenide surface layer transferred to the bottom electrode to obtain a corresponding intrinsic oxidation product layer with memristor characteristics. The second step repairs lattice damage generated during oxidation, reducing interface contact defects between different layers of the device. The intrinsic oxidation method avoids introducing additional epitaxial growth steps during the fabrication of functional layers, thus preventing impurity contamination and interface damage. This invention's method is simple, easy to operate, uses readily available materials, and is low-cost, making it promising for widespread application.

[0058] 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 memristor functional layer material prepared by intrinsic oxidation of selenide crystals, characterized in that, It comprises a ReSe2 selenide layer and an intrinsic oxide layer obtained by in-situ oxidation of ReSe2 on the ReSe2 selenide layer. The ReSe2 selenide layer and the intrinsic oxide layer are tightly stacked to form a whole. The intrinsic oxide layer contains oxygen vacancy conductive filaments, which connect the ReSe2 selenide layer and the top electrode. Specifically, the in-situ oxidation of ReSe2 involves annealing at 90℃~110℃ in an atmospheric atmosphere for 45min~75min, then heating to 180℃~220℃ and annealing in a vacuum environment for 8min~12min to obtain the intrinsic oxide Re2O7.

2. The memristor functional layer material prepared by intrinsic oxidation of selenide crystals as described in claim 1, characterized in that, ReSe2 selenide has a two-dimensional structure and good metallic properties, enabling it to establish ohmic contacts between the intrinsic oxide layer and the external electrode.

3. The memristor functional layer material prepared by intrinsic oxidation of selenide crystals as described in claim 2, characterized in that, The intrinsic oxides obtained by in-situ oxidation of ReSe2 have a resistivity of not less than 1.0 × 10⁻⁶. 8 Ω itself has memristor properties.

4. A memristor comprising a memristor functional layer material prepared by intrinsic oxidation of selenide crystals as described in any one of claims 1-3, characterized in that, It includes a top electrode, a bottom electrode, a ReSe2 selenide layer, and an intrinsic oxide layer obtained by in-situ oxidation of ReSe2. The bottom electrode is disposed on the ReSe2 selenide layer, and the top electrode is disposed on the intrinsic oxide layer. The ReSe2 selenide layer is used to improve the contact characteristics between the intrinsic oxide layer and the bottom electrode to form an ohmic contact.

5. The memristor as described in claim 4, characterized in that, The thickness of the ReSe2 selenide layer is 5 nm to 12 nm, and the thickness of the intrinsic oxide layer is 10 nm to 20 nm.

6. A method for preparing a memristor as described in claim 4 or 5, characterized in that, It includes the following steps: S1: Fabricate the bottom electrode on the substrate. S2: Apply ReSe2 selenide to the bottom electrode prepared in step S1 to form a ReSe2 selenide layer. S3: Perform oxidative annealing on the ReSe2 selenide layer. Specifically, first anneal at 90℃~110℃ in an atmospheric atmosphere for 45min~75min, then raise the temperature to 180℃~220℃ and anneal in a vacuum environment for 8min~12min to obtain the intrinsic oxide layer of ReSe2. The intrinsic oxide of ReSe2 is Re2O7. S4: Fabricate the top electrode on the intrinsic oxide layer.

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