Memristor based on flexoelectric effect and preparation method thereof

Abstract

The application discloses a kind of memristor based on flexoelectric effect and preparation method thereof, the memristor is supported metal as electrode in two ends, and suspended and curved indium selenide is used as channel.First, patterned substrate is prepared using electron beam lithography technology, and electrode matrix is obtained;Indium selenide crystal is thinned by mechanical stripping special blue adhesive tape;Then, the wafer crystal is taken off from the blue adhesive tape by polydimethylsiloxane and thinned again, and the sample is selected under optical microscope;Then, the selected sample is transferred to the electrode matrix by means of two-dimensional material directional transfer auxiliary platform, thereby the memristor is prepared.The material used in the application is safe and environmentally friendly, low in cost, simple in structure, easy to operate in preparation process, and further expands the application of two-dimensional materials.

Description

Technical Field

[0001] This invention relates to the field of memristor fabrication technology based on the flexoelectric effect of two-dimensional layered thin films. It utilizes EBL technology to pattern the substrate and uses suspended and curved indium selenide as the channel. The flexoelectric effect is induced by the curved structure, thereby realizing the function of a high-performance memristor. Background Technology

[0002] Two-dimensional materials possess advantages such as tunable band gaps, the transition from indirect to direct band gaps with reduced layer count, and strong spin-orbit coupling caused by inversion symmetry breaking. These unique properties make two-dimensional materials very promising for optoelectronic and electromechanical applications.

[0003] Indium selenide (ISS) is a two-dimensional material with excellent electrical properties, possessing superior fundamental characteristics such as ultra-high carrier mobility, tunable interlayer bandgap, and large elastic deformation capability, making it a rising star among two-dimensional layered semiconductor materials. The monolayer bandgap of ISS is 1.2–1.8 eV, with a bandgap as high as 1000 cm⁻¹. 2 V −1 s −1 Indium selenide's inherent electron mobility and relatively small effective electron mass make it an excellent candidate for low-power devices and special switching devices. Compared to traditional memristor devices, memristors based on floating and curved indium selenide channels can achieve high on / off ratios and large-window memristor functions, further enriching the application scenarios of indium selenide devices, and also providing a new approach for the development of memristors based on two-dimensional materials. Summary of the Invention

[0004] The purpose of this invention is to provide a memristor based on the flexural effect and its fabrication method. The fabrication method is applicable to memristors using suspended and bent indium selenide as the channel. This method involves fabricating pre-designed patterned electrodes on a cleaned silicon / silicon dioxide substrate using electron beam lithography and thermal evaporation. Then, mechanically peeled-off few-layer two-dimensional indium selenide material is directionally transferred onto the patterned electrodes using a dry process. This method can induce and generate a flexural effect in the channel region, thereby improving the performance of the memristor device.

[0005] The specific technical solution for achieving the objective of this invention is as follows:

[0006] A method for fabricating a memristor based on the flexural effect, comprising the following specific steps:

[0007] Step 1: Fabrication of the electrode matrix

[0008] A1: Cleaning the substrate

[0009] Using a diamond knife, a P-type heavily doped silicon substrate with a surface layer of 90-300 nm thick silica is cut into squares with a side length of 1-4 cm. The squares are then placed in acetone, isopropanol, and deionized water in sequence and ultrasonically cleaned for 10-20 minutes. After cleaning, the surface is dried with a nitrogen gun and set aside for later use. This completes the cleaning of the substrate.

[0010] A2: Patterned substrate

[0011] A 300-350 nm thick layer of polymethyl methacrylate photoresist is spin-coated onto a clean conductive substrate; then electron beam exposure is performed according to a pre-designed electrode pattern; after exposure, development and fixing are performed, and the exposed photoresist dissolves in the developer, leaving the electrode structure.

[0012] A3: Source and drain electrodes of vapor-deposited memristor

[0013] The patterned substrate is fixed onto the sample plate on top of the thermal evaporation coating instrument. Two to three gold particles and two to three copper particles are placed in the two tungsten boats for evaporation, respectively. The chamber door is wiped with alcohol and then the chamber is closed. Then the mechanical pump and molecular pump are turned on to evacuate the chamber to a vacuum state. First, a copper film of 100-200 nm is deposited, and then a gold film of 50-100 nm is deposited.

[0014] A4: Remove adhesive

[0015] The patterned substrate after evaporation is immersed in acetone solution to remove the photoresist. The photoresist removed from the substrate surface is blown off with acetone solution using a dropper. After the photoresist is removed, it is dried with a nitrogen gun to obtain an electrode matrix with a spacing of 1-5 micrometers. This completes the preparation of the electrode matrix.

[0016] Step 2: Prepare the indium selenide channel layer

[0017] B1: Preparation of Indium Selenide Channel Layer

[0018] Clean the experimental equipment, including tweezers, scalpel, and glass slide, with alcohol. Cut the blue film tape to 2 cm × 5 cm. Use tweezers to pick up a 2 mm × 2 mm indium selenide block and place it in the center of the blue film tape. Fold it repeatedly to reduce the indium selenide block to a few layers. Select a 1 cm × 1 cm piece of PDMS and attach it to a clean glass slide. Then, stick the blue film tape containing the few layers of indium selenide onto the flat PDMS. Press it lightly a few times and then slowly lift it to separate the blue film tape from the PDMS. Turn on the optical microscope and adjust its sensitivity. Place the glass slide with the indium selenide material under the optical microscope to observe it. Look for a uniform indium selenide layer with a thickness of 30 μm × 30 μm as the target material. Then, use a scalpel to cut the PDMS to 5 mm × 5 mm as the target glass slide.

[0019] Step 3: Transfer of indium selenide thin film material

[0020] C1: Transfer indium selenide thin film material

[0021] Turn on the control switch of the transfer stage and the microscope screen, then turn on the nitrogen cylinder to level the air-float stage; check the level of the transfer stage with a level, and adjust it to be level if it is not; place the substrate prepared in step 1 on the stage, and focus on the substrate surface by adjusting the zoom ring and the coarse / fine adjustment knob, and center the target substrate in the microscope field of view by adjusting the X / Y axis of the stage movement, then turn on the mechanical pump to allow the substrate to adhere to the stage; fix one end of the target slide prepared in step B1 on the fixture stage and move it into the microscope field of view, locate the target indium selenide prepared in step B1 under low magnification, and focus the microscope on the surface of the target indium selenide material by adjusting the coarse / fine adjustment knob; Control the Z-axis knob of the stage to slowly lower the target slide to a position 1-2 cm from the substrate. Adjust the magnification of the microscope to mark the outline of the target indium selenide material and the position of the target substrate at maximum magnification. Adjust the X / Y axes of the stage and the stage to align their positions. Then, control the Z-axis of the stage to lower it close to the substrate surface while adjusting the focal length to ensure that it is always focused on the PDMS on the slide and the target substrate. When ripples are seen on the microscope screen, quickly press down to make the target indium selenide material adhere to the substrate. After they are completely aligned, slowly move the Z-axis upward until the PDMS and the target indium selenide material are completely separated. This completes the transfer of the indium selenide layer. Remove the substrate after the transfer of the indium selenide layer to obtain the memristor based on the flexural effect.

[0022] A memristor based on the flexural effect prepared by the above method.

[0023] Compared with the prior art, the biggest advantage of this invention is that the operation process is simpler and the cost is lower. Based on the traditional two-dimensional material memristor, a suspended and curved indium selenide is introduced as a channel. The flexural effect induced in the channel region can significantly improve the performance of the device. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of the indium selenide memristor prepared by the method described in this invention;

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of an indium selenide memristor prepared in comparison.

[0026] Figure 3 The typical current-voltage curve of the threshold switch of the indium selenide memristor of the present invention under quasi-DC voltage scanning is shown.

[0027] Figure 4The typical current-voltage curves of the threshold switch under quasi-DC voltage sweep are shown for comparison with indium selenide memristors. Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings, embodiments, and comparative examples.

[0029] See Figure 1 The indium selenide transistor based on the flexoelectric effect of the present invention includes a gate electrode 4, a dielectric layer 3, a copper / gold electrode 2, and an indium selenide channel layer 1; wherein, the gate electrode 4 is a p-type heavily doped silicon substrate; the dielectric layer 3 is a silicon dioxide layer; the electrode 2 is a copper / gold electrode prepared by thermal evaporation deposition; and the channel layer 1 is an indium selenide layer obtained by mechanical stripping. Example

[0030] Fabrication of indium selenide memristors based on the flexoelectric effect:

[0031] (1) A P-type heavily doped silicon substrate with a 280 nm thick silica layer on its surface was cut into squares with a side length of 1 cm using a diamond cutter. The squares were then placed in acetone, isopropanol, and deionized water and ultrasonically cleaned for 15 min. After cleaning, the surface was dried with a nitrogen gun for later use. A 330 nm thick polymethyl methacrylate photoresist was spin-coated onto the cleaned conductive substrate. Electron beam exposure was then performed according to the pre-designed electrode pattern. After exposure, development and fixing were performed. The exposed photoresist dissolved in the developer, leaving the electrode structure. The patterned substrate was fixed onto the sample plate on top of the thermal evaporation coating instrument. Three gold particles and two copper particles were placed in the two tungsten boats for evaporation, respectively. The chamber door was wiped with alcohol and then the chamber was closed. The mechanical pump and molecular pump were then turned on to evacuate the chamber to a vacuum state. A 150 nm copper film was deposited first, followed by a 100 nm copper film. A gold film of nm is deposited; the patterned substrate after evaporation is immersed in acetone solution to remove the photoresist. The photoresist removed from the substrate surface is blown off with a dropper of acetone solution. After the photoresist is removed, it is dried with a nitrogen gun to obtain an electrode matrix with a spacing of 2 μm × 2 μm. The preparation of the electrode matrix is ​​thus completed.

[0032] (2) Clean the experimental equipment with alcohol, such as tweezers, blades, and glass slides. Cut the blue film tape to 2 cm × 5 cm. Use tweezers to pick up a 2 mm × 2 mm indium selenide block and place it in the center of the blue film tape. Fold it repeatedly to make the indium selenide block into a few layers. Select a 1 cm × 1 cm piece of PDMS and stick it on a clean glass slide. Then stick the blue film tape containing the few layers of indium selenide on the flat PDMS. Press it lightly a few times and then slowly lift it to separate the blue film tape from the PDMS. Turn on the optical microscope and adjust its sensitivity. Place the glass slide with the indium selenide material under the optical microscope to observe and find an indium selenide layer with uniform texture, thickness, and 30 μm × 30 μm as the target material. Then use a blade to cut the PDMS to 5 mm × 5 mm as the target glass slide for the next step.

[0033] (3) Turn on the control switch of the transfer stage and the microscope screen, and then turn on the nitrogen cylinder to make the air flotation stage horizontal; check the horizontal state of the transfer stage with a level, and adjust it to be horizontal if it is not horizontal. Place the substrate prepared in step (1) on the stage, and focus on the substrate surface by adjusting the zoom ring and the coarse / fine adjustment knob. Adjust the X / Y axis of the stage to place the target substrate in the center of the microscope field of view, and then turn on the mechanical pump to make the substrate adsorbed on the stage; fix one end of the target slide prepared in step (2) on the fixture stage and move it into the microscope field of view. Under low magnification, find the target indium selenide prepared in step (2) and focus the microscope on the surface of the target indium selenide material by adjusting the coarse / fine adjustment knob. By controlling the Z-axis knob of the stage, the target slide is slowly lowered to a position 1 cm from the substrate. The magnification of the microscope is adjusted to mark the outline of the target indium selenide material and the position of the target substrate at maximum magnification. The X / Y axes of the stage and stage are adjusted to align their positions. Then, the Z-axis of the stage is lowered to near the substrate surface while the focus is adjusted to ensure that it remains focused on the PDMS on the slide and the target substrate. When ripples are visible on the microscope screen, the stage is quickly pressed down to adhere the target indium selenide material to the substrate. After they are fully aligned, the Z-axis is slowly moved upward until the PDMS and target indium selenide material are completely separated. This completes the fabrication of the indium selenide memristor, the structure of which is shown below. Figure 1 As shown.

[0034] Indium selenide transistor fabrication

[0035] (1) Select a P-type heavily doped silicon substrate with a silicon dioxide layer thickness of 280 nm, cut it into a square with a side length of 1 cm using a diamond knife, and perform ultrasonic cleaning. Place it in a drying oven to evaporate excess moisture to obtain a clean silicon / silicon dioxide wafer.

[0036] (2) Cut the blue ink tape to a size of 2 cm × 5 cm, place the indium selenide material in the center of the blue film tape, and obtain a blue film tape containing a few layers of indium selenide material by repeatedly folding the blue film tape; cut the PDMS to a size of 1 cm × 1 cm and stick it on a clean glass slide, then stick the blue film tape with a few layers of indium selenide material on the PDMS, press it lightly by hand and peel off the blue film tape to complete the transfer of two-dimensional material to PDMS, then place the PDMS with indium selenide material under an optical microscope to observe, and look for a target sample with uniform texture, appropriate size and thickness; finally, cut off the excess PDMS with a knife for later use, thus completing the preparation of the indium selenide layer.

[0037] (3) Transfer the indium selenide prepared in step (2) to a clean substrate using a transfer stage. Turn on the control switch of the transfer stage and the microscope screen, and then turn on the nitrogen cylinder to make the air-floating stage horizontal. Check the horizontal state of the transfer stage with a level. If it is not horizontal, adjust it to be horizontal. Place the substrate prepared in step (1) on the stage, and focus on the substrate surface by adjusting the zoom ring and the coarse / fine adjustment knob. Adjust the X / Y axis of the stage to make the target substrate in the center of the microscope field of view, and then turn on the mechanical pump to make the substrate adsorb onto the stage. Fix one end of the target slide prepared in step (2) on the fixture stage and move it into the microscope field of view. Look for the target indium selenide prepared in step (2) under low magnification and focus the microscope on the surface of the target indium selenide material by adjusting the coarse / fine adjustment knob. By controlling the Z-axis knob of the stage, the target slide is slowly lowered to a position 1 cm from the substrate. The magnification of the microscope is adjusted to mark the outline of the target indium selenide material and the position of the target substrate at the maximum magnification. The X / Y axes of the stage and the stage are adjusted to correspond their positions. Then, the Z-axis of the stage is lowered to near the substrate surface while the focal length is adjusted to always focus on the PDMS on the slide and the target substrate. When ripples are seen on the microscope screen, the target indium selenide material is quickly pressed down to adhere to the substrate. After they are completely aligned, the Z-axis is slowly moved up until the PDMS and the target indium selenide material are completely separated. This completes the transfer of the indium selenide layer.

[0038] (4) Apply a suitable length of high-temperature tape around the mask as a spare. Turn on the control switch of the transfer stage and the microscope screen, and use a level to adjust the X / Y axis of the transfer stage to be horizontal. Place the substrate containing the indium selenide layer in the substrate and fix it on the stage, and fix the mask on the fixture stage. Adjust the microscope zoom ring and coarse / fine focus knob to focus the microscope on the substrate surface, and adjust the X / Y axis of the stage to place the target sample in the center of the microscope field of view; control the Z axis of the fixture stage to slowly lower until the mask contacts the substrate surface, and finely adjust the relative position of the mask and the sample on the substrate; after adjustment, make the mask and the substrate fully adhere, and slowly lift the fixture stage to gradually separate the fixture stage from the mask. The patterning process of the sample is now complete. The sample was placed in a thermal evaporation coating apparatus. Three gold particles and two copper particles were placed in two tungsten boats for evaporation, respectively. After wiping the chamber door with alcohol, the chamber was closed. The mechanical pump and then the molecular pump were sequentially turned on to evacuate the chamber to a vacuum. The current was slowly increased to control the melting and evaporation rates of the copper and gold particles. First, a 150 nm copper film was deposited, followed by a 100 nm gold film, completing the electrode fabrication. This completed the entire fabrication of the indium selenide transistor, whose structure is shown below. Figure 2 As shown.

[0039] The electrical parameters of the memristor based on a suspended and curved indium selenide channel prepared in the examples are compared with those of the transistor based on a planar indium selenide channel prepared in the comparative examples, as shown below:

[0040] Figure 3 This is a typical current-voltage curve of a threshold switch under quasi-DC voltage scanning of a memristor with a floating and curved indium selenide channel. Figure 4 This is a typical current-voltage curve for threshold switching under quasi-DC voltage scanning of a transistor with a flat indium selenide channel.

[0041] from Figure 3 , Figure 4 It can be seen that the typical current-voltage curve of the threshold switching of a transistor with a flat indium selenide channel under quasi-DC voltage scanning does not show a clear window and has no memristor performance. In contrast, the curve of a memristor with a floating and curved indium selenide channel shows obvious memristor performance, with an on / off ratio as high as 10. 6 The window is approximately 10 4 Compared to traditional indium selenide transistors, using suspended and bent indium selenide as the channel can effectively induce the flexural effect, thus significantly improving the performance of memristors. Therefore, the flexural effect-based memristor fabricated according to this invention is simple and easy to manufacture, optimizes the structure of traditional two-dimensional transistors, and is of great significance for the further application of two-dimensional materials.

Claims

1. A method for fabricating a memristor based on the flexural effect, characterized in that, The method includes the following specific steps: Step 1: Fabrication of the electrode matrix A1: Cleaning the substrate Using a diamond knife, a P-type heavily doped silicon substrate with a surface layer of 90-300 nm thick silica is cut into squares with a side length of 1-4 cm. The squares are then placed in acetone, isopropanol, and deionized water in sequence and ultrasonically cleaned for 10-20 minutes. After cleaning, the surface is dried with a nitrogen gun and set aside for later use. This completes the cleaning of the substrate. A2: Patterned substrate A 300-350 nm thick layer of polymethyl methacrylate photoresist is spin-coated onto a cleaned substrate; then electron beam exposure is performed according to a pre-designed electrode pattern; after exposure, development and fixing are performed, and the exposed photoresist dissolves in the developer, leaving the electrode structure. A3: Source and drain electrodes of vapor-deposited memristor The patterned substrate is fixed onto the sample plate on top of the thermal evaporation coating instrument. Two to three gold particles and two to three copper particles are placed in the two tungsten boats for evaporation, respectively. The chamber door is wiped with alcohol and then the chamber is closed. Then the mechanical pump and molecular pump are turned on to evacuate the chamber to a vacuum state. First, a copper film of 100-200 nm is deposited, and then a gold film of 50-100 nm is deposited. A4: Remove adhesive The patterned substrate after evaporation is immersed in acetone solution to remove the photoresist. The photoresist removed from the substrate surface is blown off with acetone solution using a dropper. After the photoresist removal is completed, it is dried with a nitrogen gun to obtain an electrode matrix with a spacing of 1-5 micrometers. This completes the preparation of the electrode matrix. Step 2: Prepare the indium selenide channel layer B1: Preparation of Indium Selenide Channel Layer Clean the experimental equipment, including tweezers, scalpel, and glass slide, with alcohol. Cut the blue film tape to 2 cm × 5 cm. Use tweezers to pick up a 2 mm × 2 mm indium selenide block and place it in the center of the blue film tape. Fold it repeatedly to reduce the indium selenide block to a few layers. Select a 1 cm × 1 cm piece of PDMS and attach it to a clean glass slide. Then, stick the blue film tape containing the few layers of indium selenide onto the flat PDMS. Press it lightly a few times and then slowly lift it to separate the blue film tape from the PDMS. Turn on the optical microscope and adjust its sensitivity. Place the glass slide with the indium selenide material under the optical microscope to observe it. Look for a uniform indium selenide layer with a thickness of 30 μm × 30 μm as the target material. Then, use a scalpel to cut the PDMS to 5 mm × 5 mm as the target glass slide. Step 3: Transfer of indium selenide thin film material C1: Transfer indium selenide thin film material Turn on the control switch of the transfer stage and the microscope screen, and then turn on the nitrogen cylinder to make the air flotation stage horizontal. Use a level to check the levelness of the transfer stage. If it is not level, adjust it to be level. Place the substrate prepared in step 1 on the stage. Focus on the substrate surface by adjusting the zoom ring and the coarse / fine adjustment knob. Adjust the X / Y axis of the stage to center the target substrate in the microscope's field of view, and then turn on the mechanical pump to allow the substrate to adhere to the stage. Fix one end of the target slide prepared in step B1 to the fixture stage and move it into the microscope's field of view. Locate the target indium selenide prepared in step B1 under low magnification and focus the microscope on the surface of the target indium selenide material by adjusting the coarse / fine adjustment knob. Slowly lower the target slide to the desired position by controlling the Z-axis knob of the fixture stage. At a distance of 1-2 cm from the substrate, adjust the magnification of the microscope to mark the outline of the target indium selenide material and the position of the target substrate at maximum magnification. Adjust the X / Y axes of the stage and the fixture to align their positions. Then, control the Z-axis of the fixture to descend close to the substrate surface while adjusting the focal length to ensure that it is always focused on the PDMS on the slide and the target substrate. When ripples are seen on the microscope screen, quickly press down to make the indium selenide material on the PDMS adhere to the substrate. After they are completely overlapped, slowly move the Z-axis upward until the PDMS and the target indium selenide material are completely separated. This completes the transfer of the indium selenide layer. Remove the substrate with the transferred indium selenide layer to obtain the memristor based on the flexural effect.

2. A memristor based on the flexural effect prepared by the method of claim 1.

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