In-situ Raman testing device and method for memristor mechanism under electric field coupling

Abstract

The invention provides an in-situ Raman testing device and method for a memristor mechanism under electric field coupling. The device comprises a special PCB (Printed Circuit Board) substrate, is provided with four copper electrodes corresponding to a source end, a drain end, a grid end and a standby electrode of the transverse memristor, is connected with an external digital source meter, is used for applying direct-current voltage and is matched with a Raman spectrometer to realize in-situ Raman spectrum imaging. The testing method comprises the steps of preparing a two-dimensional material by utilizing a micromechanical stripping method, photoetching and thermally evaporating and depositing an electrode, performing Ar atmosphere thermal annealing and ultraviolet ozone passivation post-treatment, performing gold wire lead bonding connection, applying voltage, imaging and the like. By means of the device and the method, the dynamic migration process of the oxygen ions during resistance state switching can be visually displayed, the valence band conversion mechanism of the two-dimensional material transverse memristor can be deeply understood, and a powerful tool is provided for related research.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical properties and analysis of two-dimensional materials, and in particular to an in-situ Raman testing device and method for a memristor mechanism under electric field coupling. Background Art

[0002] Two-dimensional materials are widely used in the research of non-volatile memristive storage due to their unique physical and chemical properties, including ultra-thin and flexible layered structures, high carrier mobility, atomic-level thickness, adjustable electronic properties, and excellent thermal stability. At present, non-volatile memristive devices based on two-dimensional materials have the advantages of high-density and fast storage, excellent mechanical flexibility, high switching ratio, and low energy consumption, and have shown significant application prospects in the development of new generation storage technology, artificial neuromorphic simulation, and complex logic operations.

[0003] Although two-dimensional material lateral memristors (especially MoS2 memristor devices) have been developed to be relatively mature and perfect, their complex resistive switching mechanism (involving multiple physical processes, such as electron migration, ion migration, charge trap effect, etc.), metal / semiconductor interface effects, various interface engineering, etc. will affect the electrical properties and memristive characteristics of the material. At present, conventional electrical test analysis, such as transfer, output hysteresis curve, etc., and spectroscopy analysis, such as Raman, photoluminescence, X-ray photoelectron and other spectra, can only reflect the macroscopic electrical properties of the device and the microscopic properties of a specific stage, but cannot reveal the changes in the microscopic properties of the material under different storage states. The in-situ Raman technique can monitor the structural changes of two-dimensional materials in real time under electric field coupling, including chemical bond vibration modes, charge transfer processes, and provide chemical and electronic structure information at the interface, providing direct evidence for the understanding and analysis of the resistive switching mechanism. However, there is currently no in-situ detection device suitable for two-dimensional material lateral memristors. Therefore, it is urgent to develop an in-situ monitoring device suitable for the above-mentioned devices to achieve dynamic observation of Raman signals of molecular vibration groups on the surface of the material through external electric field coupling.

[0004] In situ Raman spectroscopy can realize real-time detection of material changes in exploring the resistive switching mechanism of lateral memristors of two-dimensional materials: detecting structural changes such as the vibration mode of chemical bonds of two-dimensional materials and the charge transfer process, which is crucial to understanding the electronic structure and ion migration path of materials driven by electric fields; and can reveal the charge injection, adsorption and desorption phenomena at the contact interface between two-dimensional materials and electrodes, to reveal the influence of interface effects on memristive properties. Summary of the invention

[0005] The present invention aims to solve the problem that there is a lack of in-situ Raman testing device and method for the resistance change mechanism of two-dimensional material lateral memristor in the prior art. To this end, the present invention provides an in-situ Raman testing device and method for the memristor mechanism under electric field coupling. A stable and accurate connection between an external digital source meter and the two-dimensional material memristor electrode is achieved through a special PCB substrate. It is applied to oxygen-passivated MoS2 lateral memristor, and the Raman spectrum imaging at the channel of the in-situ Raman test device under the drive of an external electric field is used to discover the dynamic migration process of oxygen ions with the resistance state, which intuitively proves the Raman signal change of the molecular vibration group on the surface of the material in the valence band transition mechanism of the oxygen-passivated MoS2 memristor. At the same time, the equipment is simple to prepare, the effect is stable, it can be recycled, and it has a certain industrial promotion value.

[0006] To achieve the above-mentioned purpose, the present invention provides an in-situ Raman testing device of a memristor mechanism under electric field coupling, characterized in that it comprises a special substrate on which four electrodes are provided, respectively corresponding to a source end, a drain end, a gate end and a spare electrode of a lateral memristor, the copper electrodes on the special substrate are connected to an external digital source meter for applying a DC voltage to a two-dimensional material device, and performing in-situ Raman spectral imaging using a Raman spectrometer under the drive of an external electric field.

[0007] Furthermore, the special substrate is a special PCB substrate, and the electrode material is copper.

[0008] Furthermore, the length of the specially made PCB substrate ranges from 1.5 cm to 2.5 cm, the width ranges from 0.8 cm to 1.2 cm, the thickness ranges from 0.8 mm to 1.2 mm, and the electrode thickness ranges from 30 μm to 40 μm.

[0009] The present invention also provides an in-situ Raman testing method according to the above-mentioned testing device, comprising the following steps: Device preparation steps: Prepare two-dimensional materials using micromechanical lift-off method, transfer the separated two-dimensional materials onto a p-type heavily doped silicon substrate with silicon oxide, and then use mask lithography to form metal electrode patterns; use thermal evaporation coating to achieve deposition of source and drain electrodes; Device post-processing steps: the device is subjected to Ar atmosphere rapid thermal annealing and UV ozone passivation post-processing in sequence; Connection step: placing the device on the special substrate of the in-situ Raman test device, and connecting the source electrode and the drain electrode to the corresponding electrodes on the special substrate by using a gold wire bonding machine; Test steps: Connect the electrodes on the special substrate to an external source meter to apply a DC voltage to the device; and use a Raman spectrometer to perform in-situ Raman spectroscopy imaging under the drive of an external electric field to achieve dynamic observation of the Raman signals of molecular vibration groups on the surface of the two-dimensional material memristor during operation.

[0010] Furthermore, the distance between the source electrode and the drain electrode ranges from 5 μm to 7 μm.

[0011] Furthermore, the temperature range of rapid thermal annealing in Ar atmosphere is 320° C. to 380° C., and the processing time range is 3 min to 7 min; the temperature range of UV ozone passivation is 40° C. to 60° C., and the processing time range is 3 min to 7 min.

[0012] Furthermore, the two-dimensional material is molybdenum disulfide with a thickness of 1nm-6nm.

[0013] Furthermore, the micromechanical peeling process is to use transparent Scotch tape to repeatedly stick the bulk material placed thereon to separate it to obtain a two-dimensional material.

[0014] Furthermore, the transfer is to transfer the separated two-dimensional material to the surface of a p-type heavily doped silicon substrate having silicon oxide using low-viscosity PDMS.

[0015] Furthermore, the source electrode and the drain electrode are Cr / Au electrodes, and the structure of the electrodes is Cr as an adhesion layer and Au as a conductive layer. The thickness of the adhesion layer ranges from 3nm to 7nm, and the thickness of the conductive layer ranges from 45nm to 55nm. Although Cr / Au is a commonly used electrode material, in some cases, other material combinations can also be considered, depending on the design and application requirements of the device. Titanium (Ti) is also a commonly used adhesion layer material. Similar to chromium, titanium can provide good adhesion and low contact resistance with two-dimensional materials. Platinum has excellent chemical stability and conductivity and can also be used as a conductive layer. Nickel can also be used as an electrode material in some cases, especially when it is necessary to form a good contact with a specific two-dimensional material. In some special applications, graphene or carbon nanotubes can also be used as electrode materials, especially in flexible electronic devices.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention prepares a special PCB substrate for in-situ Raman testing of two-dimensional materials. One side of the substrate is covered with copper electrodes, which correspond to the source, drain, gate and spare electrodes of the lateral memristor. The substrate can achieve a stable connection between the sample and the PCB board, and between the PCB board and the external digital source meter, and can effectively apply a DC voltage to the three ports of the device, providing an ideal experimental platform for in-situ Raman detection of memristors under electric field coupling. In addition, the PCB substrate has the advantages of compact structure, simple preparation process, low cost and recyclability.

[0017] (2) The present invention also provides an in-situ Raman test device and method for the memristor mechanism under electric field coupling. Through rapid Ar atmosphere thermal annealing and low-temperature ozone doping process, efficient and controllable p-type oxygen doping of MoS2 lateral memristor was successfully achieved, and it was used as a test sample in the in-situ Raman test device of the present invention. Through the electric field regulation of the external digital source meter, the device can achieve reversible switching between different resistance states. At the same time, through in-situ Raman spectroscopy imaging, the dynamic migration process of oxygen ions during the resistance state switching process is intuitively demonstrated. This method has important scientific significance for a deep understanding of the valence band conversion mechanism of the two-dimensional material lateral memristor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work. In the drawings: Figure 1 This is an optical image of a few layers of MoS2 on a silicon substrate according to Example 1 of the present invention.

[0019] Figure 2 This is an optical image of the MoS2 lateral memristor on a silicon substrate after the rapid thermal annealing and low-temperature rapid ultraviolet ozone treatment described in Example 1 of the present invention.

[0020] Figure 3 It is a Raman spectrum diagram of the device described in Example 1 of the present invention in the initial state, rapid thermal annealing and low-temperature rapid ultraviolet ozone treatment.

[0021] Figure 4 It is a PL spectrum diagram of the device described in Example 1 of the present invention in the initial state, rapid thermal annealing and low-temperature rapid ultraviolet ozone treatment.

[0022] Figure 5 This is an AFM image of the MoS2 lateral memristor described in Example 1 of the present invention.

[0023] Figure 6 It is a schematic diagram of the device and in-situ Raman test described in Example 1 of the present invention.

[0024] Figure 7 This is a diagram of an in-situ Raman testing device in which a digital source meter, a special substrate, a test sample and a Raman spectrometer are interconnected as described in Example 1 of the present invention.

[0025] Figure 8 The device described in Example 1 of the present invention is in the initial state (Pristine state) (source-drain voltage V ds=0V) Raman imaging diagram.

[0026] Fig. 9 The device described in Example 1 of the present invention is in a low resistance state (LRS) (source-drain voltage V ds =5V) Raman imaging diagram.

[0027] Fig.10 The device of Embodiment 1 of the present invention is in a high resistance state (HRS) (source-drain voltage V ds =-5V) Raman imaging diagram. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections.

[0030] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0031] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0032] In the embodiments shown in the drawings, the indications of directions (such as up, down, left, right, front and back) used to explain the structure and movement of the various components of the present invention are not absolute but relative. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, the indications of these directions also change accordingly.

[0033] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation of the present invention will be described below with reference to the accompanying drawings.

[0035] This embodiment provides an in-situ Raman testing device and method for a memristor mechanism under electric field coupling, comprising the following steps: 1) Micromechanical exfoliation and transfer of MoS2 thin film operation process: Use transparent Scotch tape to repeatedly stick the bulk material on it to separate it into dispersed multi-layer two-dimensional materials; Use low-viscosity PDMS to transfer the separated two-dimensional materials on the Scotch tape to the surface of SiO2 / P-type heavily doped silicon substrate; Find suitable few-layer MoS2 materials under an optical microscope, such as Figure 1 shown.

[0036] 2) Device preparation: Use mask lithography to form metal electrode patterns; use thermal evaporation coating to achieve the deposition of Cr / Au metal electrodes.

[0037] The structure of the metal electrode is Cr as the adhesion layer and Au as the conductive layer. Chromium is usually used as the adhesion layer because it can combine well with two-dimensional materials (such as MoS2) and substrates (such as SiO2), providing good adhesion and preventing electrode peeling. The thickness of chromium is usually thin (such as 5nm), and its main function is to enhance the adhesion between the gold layer and the substrate. Gold, as a conductive layer, has excellent conductivity and chemical stability. The thickness of gold is usually thicker (such as 50nm) to ensure low resistance and good electrical contact of the electrode. Gold is not easily oxidized in the air and can maintain stable electrical properties.

[0038] 3) Device post-processing: The MoS2 lateral memristor is rapidly annealed in an Ar atmosphere (350°C for 5 min) to reduce the impact of lattice damage, impurities and other defects on device performance; followed by low-temperature rapid ozone treatment (50°C for 5 min) to achieve mild and controllable P-type doping of MoS2, such as Figure 2 Shown is an optical image of the MoS2 lateral memristor after annealing and oxygen passivation. The device structure is complete, there are no obvious impurities on the surface of the channel material, and the channel spacing is 6μm.

[0039] Take the MoS2 lateral memristor prepared in this experiment as an example and use it as a sample of the in-situ Raman test device: Figure 3 It is the Raman spectrum of the device described in Example 1 in the initial state, rapid thermal annealing and low-temperature rapid ultraviolet ozone treatment. Analysis shows that: the characteristic peak of MoS2 is still retained under thermal annealing and ultraviolet ozone irradiation, indicating that ozone irradiation will not cause changes in the material composition; after rapid thermal annealing in Ar atmosphere, the Raman characteristic peak does not shift and the peak intensity is significantly improved, confirming that thermal annealing effectively repairs the internal defects of MoS2 film; the characteristic peak of MoS2 blue shifts during the oxidation process, which is caused by the introduction of oxygen defects on the surface of MoS2 by ozone irradiation, which weakens the interaction between MoS2 layers.

[0040] Figure 4 The PL spectra of the device described in Example 1 in the initial state, rapid thermal annealing, and low-temperature rapid ultraviolet ozone treatment. Analysis shows that there is a significant difference between the exciton peak of MoS2 after ozone irradiation and the exciton peak in the initial state, which may be caused by the adsorption of oxygen atoms by MoS2 to form P-type doping, resulting in changes in the electronic structure and band gap of the material. No excess MoS2 defect peaks were found in the observed Raman and PL spectra, which means that the MoS2 film will maintain high crystalline quality after oxygen passivation.

[0041] Figure 5 This is an AFM image of the MoS2 lateral memristor described in Example 1. Analysis shows that the surface morphology of the MoS2 film is good and its thickness is ~6nm.

[0042] Figure 6 It is a schematic diagram of the device and the in-situ Raman test device described in Example 1, the device includes a special substrate, and four electrodes are provided on the special substrate, which correspond to the source end, drain end, gate end and spare electrode of the lateral memristor respectively. The copper electrode on the special substrate is connected to an external digital source meter, which is used to apply a DC voltage to the two-dimensional material device, and use a Raman spectrometer to perform in-situ Raman spectroscopy imaging under the drive of an external electric field. A stable and accurate connection between the external digital source meter and the two-dimensional material memristor electrode is achieved through a special PCB substrate. It is applied in Example 1, and Raman spectroscopy imaging at the channel of the in-situ Raman test device is achieved through a Raman spectrometer under the drive of an external electric field. Figure 7 This is a diagram of the actual device for in-situ Raman testing in which the digital source meter, the special substrate, the test sample and the Raman spectrometer described in Example 1 are interconnected.

[0043] Figure 8 , Fig. 9 , Fig.10 The devices described in Example 1 are respectively in the initial state (source-drain voltage V ds =0V), low resistance state (source-drain voltage V ds =5V), high impedance state (source-drain voltage V ds =-5V) Raman imaging. Analysis shows that the dotted boxes on both sides represent the source and drain, and the black box signal represents E 1 2g and A 1gIn the original state, the Raman characteristic peak shows a slight blue shift, which is related to the chemical adsorption of O2 on sulfur vacancies. In the set state (also called LRS), the spatial distribution of the Raman characteristic peak intensity in the channel is roughly uniform. In addition, the switch from the set state to the reset state (also called HRS) involves the lateral migration of oxygen defects in the channel to the drain, which leads to an increase in peak intensity due to the enhanced electron-phonon coupling on the source electrode side. In the HRS state, the signal from the area near the source end side is sharply enhanced.

[0044] The above test results show that the in-situ Raman test device and method based on the memristor mechanism of two-dimensional materials under electric field coupling can intuitively reflect the dynamic migration process of oxygen ions during the resistance state switching process, which is of great significance for understanding and analyzing the valence band conversion mechanism of two-dimensional material lateral memristors.

[0045] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. An in-situ Raman test device for memristor mechanism under electric field coupling, characterized in that: It includes a special substrate, on which four electrodes are arranged, corresponding to the source, drain, gate and spare electrode of the lateral memristor respectively. The copper electrodes on the special substrate are connected to an external digital source meter to apply a DC voltage to the two-dimensional material device, and perform in-situ Raman spectroscopy imaging using a Raman spectrometer under the drive of an external electric field.

2. The in-situ Raman testing device of memristor mechanism under electric field coupling according to claim 1, characterized in that: The special substrate is a special PCB substrate, and the electrode material is copper.

3. The in-situ Raman testing device of memristor mechanism under electric field coupling according to claim 1, characterized in that: The specially made PCB substrate has a length ranging from 1.5 cm to 2.5 cm, a width ranging from 0.8 cm to 1.2 cm, a thickness ranging from 0.8 mm to 1.2 mm, and an electrode thickness ranging from 30 μm to 40 μm.

4. An in-situ Raman testing method according to the testing device according to any one of claims 1 to 3, characterized in that: The following steps are involved: Devices Preparation steps: Prepare the two-dimensional material by micromechanical stripping, transfer the separated two-dimensional material onto a p-type heavily doped silicon substrate with silicon oxide, and then use mask lithography to form a metal electrode pattern; use thermal evaporation coating to achieve the deposition of source and drain electrodes; Device post-processing steps: the device is subjected to Ar atmosphere rapid thermal annealing and UV ozone passivation post-processing in sequence; Connection step: placing the device on the special substrate of the in-situ Raman test device, and connecting the source electrode and the drain electrode to the corresponding electrodes on the special substrate by using a gold wire bonding machine; Test steps: Connect the electrodes on the special substrate to an external source meter to apply a DC voltage to the device; and use a Raman spectrometer to perform in-situ Raman spectroscopy imaging under the drive of an external electric field to achieve dynamic observation of the Raman signals of molecular vibration groups on the surface of the two-dimensional material memristor during operation.

5. The in-situ Raman testing method according to claim 4, characterized in that: The distance between the source electrode and the drain electrode ranges from 5 μm to 7 μm.

6. The in-situ Raman testing method according to claim 4, characterized in that: The temperature range of rapid thermal annealing in Ar atmosphere is 320° C. to 380° C., and the processing time range is 3 min to 7 min. The temperature range of UV ozone passivation is 40° C. to 60° C., and the processing time range is 3 min to 7 min.

7. The in-situ Raman testing method according to claim 4, characterized in that: The two-dimensional material is molybdenum disulfide with a thickness of 1nm-6nm.

8. The in-situ Raman testing method according to claim 4, characterized in that: The micromechanical peeling process is to use transparent Scotch tape to repeatedly stick the bulk material placed thereon to separate it to obtain a two-dimensional material.

9. The in-situ Raman testing method according to claim 4, characterized in that: The transfer is to transfer the separated two-dimensional material to the surface of a p-type heavily doped silicon substrate with silicon oxide by using low-viscosity PDMS.

10. The in-situ Raman testing method according to claim 4, characterized in that: The source electrode and the drain electrode are Cr / Au electrodes, and the structure of the electrodes is that Cr is used as an adhesion layer and Au is used as a conductive layer. The thickness of the adhesion layer ranges from 3nm to 7nm, and the thickness of the conductive layer ranges from 45nm to 55nm.

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