Flexible transistor based on comprehensive two-dimensional material and preparation method and application thereof

Abstract

The invention relates to the technical field of inorganic semiconductor nanomaterials, in particular to a flexible transistor based on a comprehensive two-dimensional material and a preparation method and application thereof, and the flexible transistor comprises a first graphene nanosheet, a hexagonal boron nitride nanosheet, a molybdenum disulfide nanosheet, a second graphene nanosheet and a third graphene nanosheet, the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet are sequentially arranged from bottom to top in the thickness direction of the transistor, and the second graphene nanosheet and the third graphene nanosheet are arranged on the molybdenum disulfide nanosheet at intervals. A transverse conducting channel is formed between the second graphene nanosheet and the third graphene nanosheet; the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet have completely vertical overlapped areas. The flexible transistor has excellent bending performance and electrical performance, and when the curvature radius reaches 5 mm, the flexible transistor can also have the switch ratio as high as 8 orders of magnitude.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic semiconductor nanomaterials, and in particular to a flexible transistor based on all-two-dimensional materials, and a preparation method and application thereof. Background Art

[0002] Traditional silicon-based semiconductors are difficult to apply to flexible electronic devices due to their high rigidity. However, due to their ultra-thin properties and ultra-high flexibility, two-dimensional layered materials show great application prospects in the field of flexible electronic devices. More importantly, these ultra-thin two-dimensional materials can be stacked arbitrarily and assembled into van der Waals heterojunctions with different functions. Therefore, in the application of wearable electronic devices, high-performance flexible electronic devices based on all-two-dimensional materials occupy a pivotal position.

[0003] At present, research on flexible two-dimensional material transistor devices has achieved certain results. By optimizing material synthesis methods, such as chemical vapor deposition (CVD) and mechanical peeling technology, researchers have successfully prepared a variety of two-dimensional materials, including graphene, transition metal sulfides, etc., and applied them to the manufacture of transistors. These devices exhibit good electronic properties on flexible substrates, including high mobility, low power consumption and excellent bending stability. In addition, by adopting new flexible substrate materials, such as polyimide (PI) and polydimethylsiloxane (PDMS), as well as advanced packaging technology, researchers have been able to manufacture flexible electronic devices that can remain stable in practical applications.

[0004] Nevertheless, the development of flexible two-dimensional material transistor devices still faces some challenges. First, the uniformity and quality control of two-dimensional materials are still a problem, which directly affects the performance and reliability of the device. For example, it is generally difficult to achieve a high switching ratio at a higher bending radius. Therefore, the manufacturing process of flexible electronic devices needs to be further optimized to further improve the performance of transistor devices on flexible substrates. Summary of the invention

[0005] The present invention provides a flexible transistor based on all-two-dimensional materials and a preparation method and application thereof, so as to solve the above-mentioned problems existing in the prior art.

[0006] According to a first aspect of the present invention, the present invention provides a flexible transistor based on all-two-dimensional materials, comprising a first graphene nanosheet, a hexagonal boron nitride nanosheet, a molybdenum disulfide nanosheet, a second graphene nanosheet and a third graphene nanosheet, wherein the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet are arranged in sequence from bottom to top along the thickness direction of the flexible transistor, the second graphene nanosheet and the third graphene nanosheet are arranged at intervals on the molybdenum disulfide nanosheet, and a lateral conductive channel is formed between the second graphene nanosheet and the third graphene nanosheet; the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet have a completely vertically overlapping area.

[0007] Graphene nanosheets have high specific surface area, excellent mechanical properties, high thermal conductivity and outstanding electrical properties. Hexagonal boron nitride nanosheets have a structure similar to graphene and are called "white graphene". They have high insulation and high thermal conductivity. Using hexagonal boron nitride as a dielectric layer can improve the thermal conductivity of the device, thereby effectively dissipating heat and improving the efficiency and life of the device. Molybdenum disulfide has excellent semiconductor properties and can improve the switching current ratio and field effect mobility of the device. The flexible transistor of the present invention is based on a fully two-dimensional material, with graphene nanosheets as electrodes, hexagonal boron nitride nanosheets as dielectric layers, and molybdenum disulfide as a conductive channel. It can have a larger bending radius. For example, when the radius of curvature reaches 5 mm, the transistor device can also have a higher switching ratio, up to 8 orders of magnitude.

[0008] In a specific embodiment, the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet have the same length and width and completely overlap. The completely overlapping method can bring better gate control effect and help improve the switching ratio of the transistor.

[0009] To form an electrical circuit, the vertical conductive channel of the flexible transistor is formed by the series connection of vertical graphene and molybdenum disulfide.

[0010] Furthermore, the thickness of the first graphene nanosheet is 0.3-50nm, preferably 0.3-5nm; the thickness of the hexagonal boron nitride nanosheet is 10-50nm, preferably 10-20nm; the thickness of the molybdenum disulfide nanosheet is 0.6-50nm, preferably 0.6-5nm. By limiting the thickness of the first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet to a reasonable range, the layers can play a better synergistic role, which is more conducive to improving the bending performance and electrical performance of the flexible transistor.

[0011] Furthermore, the flexible transistor also includes three metal electrodes: a metal electrode placed on the first graphene nanosheet as a gate electrode, a metal electrode placed on the second graphene nanosheet as a source electrode, and a metal electrode placed on the third graphene nanosheet as a drain electrode.

[0012] In a field effect transistor, the gate electrode, source electrode, and drain electrode are three key terminals, which together determine the working principle and performance of the transistor. The main function of the gate electrode is to control the conductive state of the transistor. By applying a voltage to the gate electrode, the conductivity of the transistor channel can be changed, thereby controlling the current flow between the source and the drain. The source electrode injects a majority of carriers (electrons or holes) into the conductive channel of the transistor, and these carriers will move from the source to the drain through the channel. The drain electrode collects the carriers that move from the source electrode through the conductive channel to form a current from the source to the drain. The coordinated work of these three electrodes enables the field effect transistor to amplify or switch electronic signals. By changing the voltage on the gate electrode, the current passing through the transistor can be accurately controlled, thereby achieving control of the circuit state. The gate electrode, source electrode, and drain electrode of the present invention are all graphene nanosheets. When the graphene nanosheet is used as a gate electrode, its high electron mobility and excellent conductivity can be used to control the conductive state of the channel. When used as source and drain electrodes, graphene nanosheets can provide low-resistance ohmic contacts, thereby reducing the contact resistance of the device and improving the efficiency of current injection. Graphene nanosheets have high thermal conductivity, which helps to quickly disperse heat in high-power devices and reduce heat accumulation, thereby improving the reliability and life of the device. Graphene nanosheets have extremely high mechanical strength, which helps to improve the structural stability of transistors, especially in flexible electronics and wearable devices. The flexibility and strength of graphene make it an ideal material for building bendable and stretchable electronic devices.

[0013] Furthermore, the width of the transverse conductive channel is 0.5-2um. If the width of the transverse conductive channel is less than 0.5um, the width is too small and will affect the conductive efficiency; if the width of the transverse conductive channel is greater than 2um, the width is too large and will affect the bending performance. Optionally, the width of the transverse conductive channel can be 0.5um, 0.6um, 0.7um, 0.8um, 0.9um, 1um, 1.1um, 1.2um, 1.3um, 1.4um, 1.5um, 1.6um, 1.7um, 1.8um, 1.9um or 2um, etc. In some specific embodiments, the width of the transverse conductive channel is 1um.

[0014] In a transistor, a conductive channel (also called a conductive channel or channel region) is a conductive region connecting the source and drain. It is the core part of the operation of the transistor. It is not only a channel for current, but also directly affects the electrical characteristics and performance of the transistor. In addition, the lateral conductive channel can increase the flexibility of the material without sacrificing the strength of the material. By creating notches or grooves on the flexible transistor, the flexible transistor can be more easily deformed when subjected to bending or twisting forces without breaking. By limiting the width of the lateral conductive channel within a reasonable range, it is beneficial to improve the bending performance of the flexible transistor and ensure the electrical performance of the flexible transistor.

[0015] Further, the metal electrode is formed by stacking a chromium layer and a gold layer; preferably, the thickness of the chromium layer is 5-15nm; the thickness of the gold layer is 20-100nm. More preferably, the thickness of the chromium layer is 5-8nm; the thickness of the gold layer is 20-40nm. In a specific embodiment, the thickness of the chromium layer is 5nm; the thickness of the gold layer is 30nm.

[0016] According to a second aspect of the present invention, the present invention also provides a method for preparing the above-mentioned flexible transistor based on all-two-dimensional materials, comprising the following steps: Firstly, a first graphene nanosheet as a gate electrode is placed on a flexible substrate, and then a hexagonal boron nitride nanosheet, a molybdenum disulfide nanosheet and a graphene nanosheet are placed on the graphene nanosheet in sequence, and then a second graphene nanosheet and a third graphene nanosheet are placed on the molybdenum disulfide nanosheet at intervals to obtain a graphene / molybdenum disulfide / hexagonal boron nitride / graphene heterojunction; The obtained graphene / molybdenum disulfide / hexagonal boron nitride / graphene heterojunction is connected to three metal electrodes to obtain a flexible transistor.

[0017] The preparation method of the invention is simple and can obtain a flexible transistor with stable structure and excellent performance.

[0018] Furthermore, the metal electrode is made by electron beam exposure and metal deposition, and the metal deposition sequence is to deposit chromium first and then gold.

[0019] Furthermore, the first graphene nanosheet, the hexagonal boron nitride nanosheet, the molybdenum disulfide nanosheet, the second graphene nanosheet and the third graphene nanosheet are prepared by mechanically exfoliating corresponding bulk materials.

[0020] The present invention does not impose any special restrictions on the material of the flexible substrate, as long as it is a flexible substrate. Further, the material of the flexible substrate can be one or more of polyimide, polydimethylsiloxane, polyvinyl alcohol, polyester, polyamic acid, and polyethylene naphthalate.

[0021] According to the third aspect of the present invention, the present invention also provides the application of the above-mentioned flexible transistor based on all-two-dimensional materials or the flexible transistor based on all-two-dimensional materials prepared by the above-mentioned preparation method in flexible devices.

[0022] Flexible equipment includes: Wearable electronic devices: Flexible transistors can be used to manufacture wearable devices such as smart watches, health monitors, heart rate sensors, etc. These devices need to fit closely to the skin and have good bending and stretching properties.

[0023] Flexible displays: In flexible electronic paper and curved displays, flexible transistors can be used as pixel drivers to achieve bendable display technology.

[0024] Biomedical sensors: Flexible transistors can be used to develop skin patches, health monitoring patches, etc. to monitor physiological parameters such as body temperature, blood sugar, muscle activity, etc.

[0025] Flexible energy storage: In flexible batteries and supercapacitors, flexible transistor technology can be used to build flexible electrodes and circuits to adapt to deformable energy storage systems.

[0026] Smart textiles: Integrating flexible transistors into textiles could create smart clothing that can monitor the wearer's health or environmental conditions.

[0027] Flexible sensor arrays: In robotics, flexible transistors can be used to make tactile sensor arrays, giving robots more refined tactile perception capabilities.

[0028] The flexible transistor based on all-two-dimensional materials provided by the present invention uses molybdenum disulfide as a conductive channel, graphene nanosheets as electrodes, and hexagonal boron nitride nanosheets as dielectric layers. It has excellent bending and electrical properties. When the curvature radius reaches 5 mm, the transistor device can also have a higher switching ratio, up to 8 orders of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a schematic structural diagram of a flexible transistor provided in Experimental Example 1 of the present invention.

[0031] Figure 2This is an optical microscope image of the flexible transistor of Example 1 of the present invention placed on a polyimide substrate.

[0032] Figure 3 This is a diagram of the state of the flexible transistor after being bent according to Example 1 of the present invention.

[0033] Figure 4 It is an output curve diagram of source-drain current versus source-drain voltage and a transfer curve diagram of source-drain current versus gate voltage of the flexible transistor before and after bending according to Example 1 of the present invention.

[0034] Figure 5 This is a transfer curve diagram of the source-drain current versus gate voltage of the flexible transistor before bending according to Example 1 of the present invention.

[0035] Reference numerals: 1: first graphene nanosheet; 2: hexagonal boron nitride nanosheet; 3: molybdenum disulfide nanosheet; 4: second graphene nanosheet; 5: third graphene nanosheet. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. 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.

[0037] Example 1

[0038] This embodiment provides a flexible transistor, such as Figure 1 As shown, it includes a first graphene nanosheet 1, a hexagonal boron nitride nanosheet 2, a molybdenum disulfide nanosheet 3, a second graphene nanosheet 4 and a third graphene nanosheet 5. The first graphene nanosheet 1, the hexagonal boron nitride nanosheet 2 and the molybdenum disulfide nanosheet 3 are arranged in sequence from bottom to top along the thickness direction of the flexible transistor. The second graphene nanosheet 4 and the third graphene nanosheet 5 are arranged at intervals on the molybdenum disulfide nanosheet 3, and a lateral conductive channel is formed between the second graphene nanosheet 4 and the third graphene nanosheet 5; the first graphene nanosheet 1, the hexagonal boron nitride nanosheet 2 and the molybdenum disulfide nanosheet 3 have a completely vertically overlapping area. As shown in Figure 2, the flexible transistor is placed on a polyimide substrate. The conductive channel is a lateral molybdenum disulfide channel, the dielectric layer is hexagonal boron nitride, and the electrode is graphene.

[0039] Among them, the length and width of the first graphene nanosheet 1 are 6um and 5um respectively, and the thickness is 0.3nm. The length and width of the hexagonal boron nitride nanosheet 2 are 6um and 5um respectively, and the thickness is 20nm. The length and width of the molybdenum disulfide nanosheet 3 are 6um and 5um respectively, and the thickness is 5nm. The length and width of the second graphene nanosheet 4 are 8um and 2um respectively, and the length and width of the third graphene nanosheet 5 are 8um and 2um respectively, and the width of the lateral conductive channel is 1um. The first graphene nanosheet 1, the second graphene nanosheet 4 and the third graphene nanosheet 5 are all single-layer graphene nanosheets.

[0040] The flexible transistor further includes three metal electrodes: a metal electrode is placed on the first graphene nanosheet 1 as a gate electrode, a metal electrode is placed on the second graphene nanosheet 4 as a source electrode, and a metal is placed on the third graphene nanosheet 5 as a drain electrode. The metal electrodes are stacked by a chromium layer and a gold layer, wherein the thickness of the chromium layer is 5 nm and the thickness of the gold layer is 30 nm.

[0041] The preparation method of the flexible transistor is as follows: (1) The first graphene nanosheet 1, hexagonal boron nitride nanosheet 2, molybdenum disulfide nanosheet 3, second graphene nanosheet 4 and third graphene nanosheet 5 are prepared by mechanically exfoliating the corresponding bulk materials. The first graphene nanosheet 1 is placed on a flexible polyimide substrate; the 20nm thick hexagonal boron nitride nanosheet, the 5nm thick molybdenum disulfide nanosheet and the other two single-layer graphene nanosheets (the second graphene nanosheet 4 and the third graphene nanosheet 5) are placed on a 300nm thick PPC plastic support film.

[0042] (2) With the help of an optical microscope, hexagonal boron nitride nanosheets 2 and molybdenum disulfide nanosheets 3 are sequentially placed on the first graphene nanosheet 1, and then the second graphene nanosheets 4 and the third graphene nanosheets 5 are placed on the molybdenum disulfide nanosheets 3 to obtain a graphene / molybdenum disulfide / hexagonal boron nitride / graphene heterojunction, requiring that the second graphene nanosheets 4 and the third graphene nanosheets 5 have no overlapping regions in the vertical direction. The stacking requirement is that the bottom first graphene nanosheets 1, hexagonal boron nitride nanosheets 2, molybdenum disulfide nanosheets 3 and the top second graphene nanosheets 4 and the third graphene nanosheets 5 have completely vertically overlapping regions, but the top second graphene nanosheets 4 and the third graphene nanosheets 5 have no vertically overlapping regions.

[0043] (3) The obtained graphene / MoS2 / HBN / graphene heterojunction is connected with three metal electrodes to obtain a fully two-dimensional material flexible transistor device. The metal electrodes are made by standard electron beam lithography and metal deposition. The metal deposition sequence is 5 nm thick chromium and 30 nm thick gold.

[0044] The flexible transistor of Example 1 was subjected to a bending test and a switching ratio test under a bending radius. The bending test method was to stick the polyimide substrate on a cylinder with a bending radius of 5 mm. The switching ratio test method was to connect the probe to the metal electrode using a probe station and use a semiconductor analysis tester to test the switching ratio of the transistor.

[0045] Figure 3 Figure a shows the fully two-dimensional material flexible transistor after bending. Figure 3 Figure b shows that the curvature radius of the fully two-dimensional material flexible transistor after bending can reach 5 mm.

[0046] Figure 4 Figure a shows the output curve of the source-drain current versus source-drain voltage of the fully two-dimensional material flexible transistor before and after bending. The symmetrical current magnitude under positive and negative biases shows good ohmic contact on the surface. Figure 4 Figure b shows the transfer curve of source-drain current with gate voltage of the fully two-dimensional material flexible transistor before and after bending. When the curvature radius after bending reaches 5 mm, it can still maintain a switching ratio of up to 8 orders of magnitude.

[0047] Comparative Example 1

[0048] This comparative example provides a flexible transistor, which is different from the embodiment in that: molybdenum ditelluride nanosheets are used instead of molybdenum disulfide nanosheets. Figure 5 The transfer curve of the unbent source-drain current versus gate voltage after the channel material is replaced with molybdenum ditelluride, a fully two-dimensional material flexible transistor. It can be seen that the on-state current of molybdenum ditelluride material is lower than that of molybdenum disulfide, so the transistor switching ratio performance is not as good as molybdenum disulfide. The switching ratio of the molybdenum ditelluride device obtained in this comparative example is only 6 orders of magnitude, and the performance is not as good as the present invention which uses molybdenum disulfide nanosheets as the conductive channel material.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible transistor based on all-two-dimensional materials, characterized in that: The flexible transistor includes a first graphene nanosheet, a hexagonal boron nitride nanosheet, a molybdenum disulfide nanosheet, a second graphene nanosheet and a third graphene nanosheet. The first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet are sequentially arranged from bottom to top along the thickness direction of the flexible transistor. The second graphene nanosheet and the third graphene nanosheet are arranged at intervals on the molybdenum disulfide nanosheet, and a lateral conductive channel is formed between the second graphene nanosheet and the third graphene nanosheet. The first graphene nanosheet, the hexagonal boron nitride nanosheet and the molybdenum disulfide nanosheet have a completely vertically overlapping area.

2. The flexible transistor based on all-two-dimensional materials according to claim 1, characterized in that: The thickness of the first graphene nanosheet is 0.3-50 nm, preferably 0.3-5 nm; the thickness of the hexagonal boron nitride nanosheet is 10-50 nm, preferably 10-20 nm; the thickness of the molybdenum disulfide nanosheet is 0.6-50 nm, preferably 0.6-5 nm.

3. The flexible transistor based on all-two-dimensional materials according to claim 1, characterized in that: The flexible transistor also includes three metal electrodes: a metal electrode placed on the first graphene nanosheet as a gate electrode, a metal electrode placed on the second graphene nanosheet as a source electrode, and a metal electrode placed on the third graphene nanosheet as a drain electrode.

4. The flexible transistor based on all-two-dimensional materials according to claim 3, characterized in that: The width of the lateral conductive channel is 0.5-2 um.

5. The flexible transistor based on all-two-dimensional materials according to claim 3, characterized in that: The metal electrode is formed by stacking a chromium layer and a gold layer; preferably, the thickness of the chromium layer is 5-15 nm; the thickness of the gold layer is 20-100 nm.

6. The method for preparing a flexible transistor based on all-two-dimensional materials according to any one of claims 1 to 5, characterized in that: The steps include: Firstly, a first graphene nanosheet as a gate electrode is placed on a flexible substrate, and then a hexagonal boron nitride nanosheet, a molybdenum disulfide nanosheet and a graphene nanosheet are placed on the graphene nanosheet in sequence, and then a second graphene nanosheet and a third graphene nanosheet are placed on the molybdenum disulfide nanosheet at intervals to obtain a graphene / molybdenum disulfide / hexagonal boron nitride / graphene heterojunction; The obtained graphene / molybdenum disulfide / hexagonal boron nitride / graphene heterojunction is connected to three metal electrodes to obtain a flexible transistor.

7. The preparation method according to claim 6, characterized in that: The metal electrode is made by electron beam exposure and metal deposition, and the metal deposition sequence is to deposit chromium first and then gold.

8. The preparation method according to claim 6, characterized in that: The first graphene nanosheet, the hexagonal boron nitride nanosheet, the molybdenum disulfide nanosheet, the second graphene nanosheet and the third graphene nanosheet are prepared by mechanically exfoliating corresponding bulk materials.

9. The preparation method according to claim 6, characterized in that: The material of the flexible substrate is one or more of polyimide, polydimethylsiloxane, polyvinyl alcohol, polyester, polyamic acid, and polyethylene naphthalate.

10. Application of the flexible transistor based on all-two-dimensional materials as described in any one of claims 1 to 5 or the flexible transistor based on all-two-dimensional materials prepared by the preparation method as described in any one of claims 6 to 9 in flexible devices.

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