Ultraviolet light modulated depletion type graphene field effect transistor and preparation method thereof
By using PMMA spin coating in graphene field effect tubes, the resistance regulation of the depleted graphene field effect transistor with ultraviolet modulation is achieved, solving the problems of ultraviolet modulation and uniform doping of quantum dots in the prior art, and the device has good repeatability and process compatibility.
Patent Information
- Application Number
- CN202510552812.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-07-29
AI Technical Summary
The existing graphene field effect tubes are difficult to control the current magnitude by ultraviolet modulation, and inorganic materials are difficult to uniformly incorporate quantum dot materials.
The organic material PMMA is used as the insulated gate, and quantum doped insulated gate is prepared by spin coating. Combined with CVD graphene film transfer technology, depleted graphene field effect transistors are prepared with ultraviolet light modulated, and the quantum dots are used to release hole-electron pairs under ultraviolet light irradiation to change the graphene carrier concentration.
The function of regulating the resistance of graphene field effect transistors through ultraviolet light is realized. The graphene conductivity decreases, the resistance increases, and the device is in a depleted state, with good repeatability and process compatibility.
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Figure CN120390429A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of nanoelectronic devices, and particularly relates to an ultraviolet light modulated depletion type graphene field effect transistor and a preparation method thereof. Background Art
[0002] The insulating gates of existing graphene field effect transistors (GFETs) are divided into two categories: inorganic materials and organic materials. Among them, inorganic materials mainly deposit inorganic oxides such as silicon oxide and aluminum oxide on the surface of graphene by means of electron evaporation, sputtering, atomic layer deposition, etc. to achieve the preparation of the insulating gate. It is very difficult to uniformly incorporate quantum dot materials into the material interior during the preparation process in this way. The present invention uses an organic material as the insulating gate electrode and adopts a spin coating method to prepare the insulating gate, so that the quantum dot materials can be uniformly incorporated into the insulating gate interior, thereby realizing the above functions of the UV-GFET. Taking PMMA (polymethyl methacrylate) as an example, the insulating gate is prepared by spin coating PMMA dissolved in a volatile oil-phase organic solvent such as ethyl acetate or toluene or chlorobenzene on the surface of graphene. The present invention designs a special doping technique to enable the quantum dots to be uniformly dispersed in the organic solvent, so that the quantum dots can be uniformly incorporated into the PMMA insulating gate to prepare the core structure of this new device.
[0003] Currently, there is no ultraviolet light modulated depletion type graphene field effect transistor (UV-GFET). Therefore, we provide a UV-GFET and a preparation method thereof, that is, the current magnitude of the graphene field effect transistor is controlled by the intensity of ultraviolet light illumination. Summary of the Invention
[0004] To solve the above problems, the present invention provides an ultraviolet light modulated depletion type graphene field effect transistor and a preparation method thereof.
[0005] The technical solution adopted by the present invention is as follows:
[0006] An ultraviolet light modulated depletion type graphene field effect transistor, which successively includes a Si / SiO2 base layer, a metal electrode layer, a graphene thin film sensing layer, and a quantum dot doped insulating gate layer from bottom to top.
[0007] The preparation method of the above ultraviolet light modulated depletion type graphene field effect transistor includes the following steps:
[0008] 1) Mix 5 mL of PMMA oil-phase solution with 1 mL of quantum dot aqueous solution, and use a vortex oscillator to mix the solution for 30 min. Let it stand for 2 h to obtain a solution with oil-water two-phase stratification. The upper layer is the PMMA oil-phase mixture doped with quantum dots, and the lower layer is the quantum dot aqueous solution. Separate the upper PMMA oil-phase mixture doped with quantum dots, and then add PMMA oil-phase solution for mixing and dilution to obtain a diluted PMMA oil-phase mixture doped with quantum dots, which is the extraction solution.
[0009] 2) Prepare a metal electrode on the Si / SiO2 substrate layer by the mask method.
[0010] 3) First, drop the extraction solution onto the copper-based CVD graphene film, spin-coat it at 500 rps for 5 s, and then spin-coat it at 6500 rps for 45 s to complete the spin-coating of the extraction solution. After etching away the copper substrate of the copper-based CVD graphene film, transfer the CVD graphene film onto the metal electrode. Then, place the silicon wafer substrate layer with the transferred graphene inclined for 2 h to naturally evaporate the moisture, and then anneal it at 40 °C for 1 h to prepare an ultraviolet light-modulated depletion-type graphene field-effect transistor UV-GFET.
[0011] Further, in the above preparation method, in step 1), the PMMA oil-phase solution is prepared by dissolving 1 g of PMMA with an average molecular weight of 350000 in 20 mL of ethyl acetate or toluene or chlorobenzene.
[0012] Further, in the above preparation method, in step 1), the concentration of the quantum dot aqueous solution is 10 mg / mL.
[0013] Further, in the above preparation method, in step 1), the quantum dot is a chitosan quantum dot.
[0014] Even further, in the above preparation method, the preparation method of the chitosan quantum dot is as follows: Take 1 g of chitosan powder, add 40 mL of deionized water, and then add 0.9 mL of acetic acid solution. Stir at 50 °C for 3 h to obtain a chitosan solution. Put the chitosan solution into a reaction kettle and react at 190 °C for 24 h to obtain a chitosan quantum dot mixture. Then, put the chitosan quantum dot mixture into a dialysis bag and dialyze for 48 h to obtain a pure chitosan quantum dot solution. Take the pure chitosan quantum dot solution and put it into a freeze dryer to freeze-dry for 48 h to obtain chitosan quantum dot powder.
[0015] Further, in the above preparation method, the specific operation steps of step 2) are as follows: Use a thermal evaporation instrument to first evaporate chromium on the Si / SiO2 substrate layer to obtain a 15-nm metal electrode, and then evaporate gold on the chromium metal electrode to obtain a 35-nm metal electrode, thereby completing the preparation of a composite metal electrode with a total thickness of 50 nm.
[0016] Further, in the above preparation method, in step 3), the specific operation steps for etching away the copper substrate of the copper-based CVD graphene film are as follows: Cut the copper-based CVD graphene film with the spin-coated extraction liquid layer into small pieces, and then place the small pieces of copper-based CVD graphene film in an ammonium persulfate solution in a suspended state with the extraction liquid layer on top and the copper substrate on the bottom for 12 h of immersion; after the etching is completed, the copper-based CVD graphene film changes from brass color to colorless and transparent film, and then transfer the CVD graphene film to deionized water for 30 min of immersion to remove the residual ammonium persulfate solution, and repeat the deionized water immersion process 2-3 times to complete the process of etching away the copper substrate of the copper-based CVD graphene film.
[0017] Preferably, the concentration of the ammonium persulfate solution is 5 wt%.
[0018] The beneficial effects of the present invention are as follows:
[0019] 1. In the traditional graphene liquid-phase transfer process, a volatile organic solvent containing a high molecular polymer (PMMA) is spin-coated on the surface of CVD graphene on a copper foil substrate to form a PMMA-assisted transfer layer as a fixed support framework during the transfer of the graphene film. After the graphene is transferred to the metal electrode, the PMMA layer needs to be removed by washing with an organic solvent such as acetone, and then annealed to completely remove the organic residue on the surface of the graphene. Then, a top gate is fabricated on top of the graphene by sputtering coating or other methods to finally obtain a GFET. Since the bandgap of graphene is zero, although the source-drain current of the GFET can be regulated by adjusting the gate voltage, it is impossible to completely turn off the conductive channel at both ends of the source and drain. It can be considered that the GFET device is in a normally-on state. Because its normally-on state has similar characteristics to that of a silicon-based depletion-type field-effect transistor, it is called a depletion-type graphene field-effect transistor.
[0020] A depletion-type UV-GFET modulated by ultraviolet light developed by the present invention can encapsulate quantum dots inside the insulating gate through a novel quantum dot-doped insulating gate technology. This technology can integrate the quantum dot-doped insulating gate with the CVD graphene film transfer technology. During the preparation process of this depletion-type field-effect transistor, a PMMA organic thin layer containing quantum dot doping is covered on top of the graphene as a gate insulating layer to fabricate an ultraviolet light-modulated depletion-type graphene field-effect transistor. When the quantum dots inside the PMMA thin layer release hole-electron pairs due to the photoelectric effect under ultraviolet light irradiation, the graphene layer at the bottom of the insulating layer can obtain extra electrons at this time, thereby changing the carrier concentration inside the graphene. Since the number of holes in CVD graphene is much larger than the number of free electrons, after absorbing the extra electrons, the conductivity of the graphene decreases and the resistance increases, thereby realizing the function of regulating the resistance of the depletion-type graphene field-effect transistor through ultraviolet light.
[0021] 2. Use a volatile oil-phase solvent (such as ethyl acetate, toluene, chlorobenzene, etc., organic solvents that can dissolve PMMA and are insoluble in water) to extract quantum dots in an aqueous solution to form an oil-phase mixture of PMMA and quantum dots. Use this oil-phase mixed solution and adopt the spin-coating method to prepare the insulating gate. After a short standing and annealing, the quantum dot doping and insulating gate preparation can be completed. This technology can be integrated with the CVD graphene liquid-phase transfer technology. After the insulating gate preparation is completed, the CVD graphene substrate etching and liquid-phase transfer can be directly continued without affecting the subsequent process flow. Description of the Drawings
[0022] Figure 1 It is a process flow chart for the preparation of a graphene field-effect transistor (GFET).
[0023] Figure 2 It is a vertical cross-sectional structure diagram of the ultraviolet light-modulated depletion-type graphene field-effect transistor (UV-GFET) of the present invention.
[0024] Figure 3 It is a preparation process diagram for extracting quantum dots with a PMMA mixed solution. Among them, A is 5 mL of PMMA oil-phase solution (1 g PMMA / 20 mL ethyl acetate), B is 1 mL of chitosan quantum dot solution (10 mg / mL), and C is the extraction solution (ethyl acetate + PMMA + carbon quantum dots).
[0025] Figure 4 It is the luminescence situation of the quantum dot and PMMA oil-phase mixed solution under natural light and ultraviolet light. a is the chitosan quantum dot solution under ultraviolet light irradiation, b is the solution with oil-water two-phase stratification, c is the solution with oil-water two-phase stratification under ultraviolet light irradiation, and d is the diluted PMMA oil-phase mixed solution doped with quantum dots under ultraviolet light irradiation.
[0026] Figure 5 It is a process diagram for the liquid-phase integration preparation of UV-GFET with graphene and electrodes.
[0027] Figure 6 It is a physical diagram of UV-GFET.
[0028] Figure 7 It is the R-T diagram of UV-GFET-1.
[0029] Figure 8 It is the R-T diagram of UV-GFET-2.
[0030] Figure 9 It is the structure diagram of UV-GFET. Detailed Embodiments
[0031] The present invention will be further illustrated by specific examples below. The present invention is not limited to the embodiments and is equally applicable to other volatile oil-phase solvents. Minor variations may be made without departing from the scope described above.
[0032] Example 1 Preparation of Graphene Field-Effect Transistor (GFET)
[0033] The steps for preparing the graphene field-effect transistor (GFET) are as Figure 1 shown. First, metal electrodes are deposited on a silica substrate by a mask method or a photolithography method. Secondly, a graphene film is covered at both ends of the metal electrodes by van der Waals integration using a wet transfer method. Finally, the redundant part of the graphene is etched away to leave a standard shape, completing the preparation of the GFET.
[0034] Example 2 Preparation of Ultraviolet Light-Modulated Depletion-Type Graphene Field-Effect Transistor (UV-GFET)
[0035] 1) Chitosan quantum dots are prepared by a hydrothermal method. The specific steps are as follows: Take 1 g of chitosan powder, add 40 mL of deionized water, and then add 0.9 mL of acetic acid solution. Stir at 50 °C for 3 h to obtain a chitosan solution. Put the chitosan solution into a reaction kettle and react at 190 °C for 24 h to obtain a chitosan quantum dot mixture. Then put the chitosan quantum dot mixture into a dialysis bag and dialyze for 48 h to obtain a pure chitosan quantum dot solution. Take the pure chitosan quantum dot solution and put it into a freeze dryer to freeze-dry for 48 h to obtain chitosan quantum dot powder.
[0036] 2) As Figure 3 shown in the steps, first mix 5 mL of the prepared PMMA oil-phase solution (1 g of PMMA / 20 mL of ethyl acetate, with an average molecular weight of PMMA at 350,000) with 1 mL of chitosan quantum dot solution (10 mg / mL). Use a vortex oscillator to mix the solution for 30 min and let it stand for 2 h to obtain an oil-water two-phase stratified solution as shown in Figure 4 b. The upper layer is a PMMA oil-phase mixture doped with quantum dots, and the lower layer is an aqueous quantum dot solution. The chitosan quantum dot solution has an obvious fluorescence phenomenon as shown in Figure 4 a under ultraviolet light irradiation. Figure 4 As can be observed in c, when the stratified liquid is irradiated with an ultraviolet lamp, both the upper and lower layer liquids have a fluorescence phenomenon, indicating that the upper layer PMMA oil-phase solution has successfully extracted chitosan quantum dots and is well dispersed. Take the separated upper layer PMMA oil-phase mixture doped with quantum dots and add the PMMA oil-phase solution without quantum dots (1 g of PMMA / 20 mL of ethyl acetate) in proportion for mixing to dilute the quantum dots. Obtain the diluted PMMA oil-phase mixture doped with quantum dots, which is the extraction solution. As Figure 4The diluted PMMA oil phase mixture doped with quantum dots shown in d still has fluorescence under ultraviolet irradiation, indicating that the quantum dots are evenly dispersed in the mixture.
[0037] 3) Metal electrodes are prepared on the Si / SiO2 substrate using a mask method.
[0038] A silicon wafer with a SiO2 layer was purchased and cut into small pieces (1*1 cm) to obtain a Si / SiO2 base layer. Chromium was first evaporated on the Si / SiO2 base layer using a thermal evaporation apparatus to obtain a 15nm metal electrode. Then, gold was evaporated on the chromium metal electrode to obtain a 35nm metal electrode, thereby completing the preparation of a composite metal electrode with a total thickness of 50nm.
[0039] The metal electrode produced by the mask method exhibits a uniform transition at the interface with the substrate, while the metal electrode produced by the photolithography method exhibits a non-uniform transition. The PMMA layer covered by the liquid-phase transferred graphene film has a certain hardness. When the metal electrode produced by the photolithography method is integrated with the graphene film, air gaps are easily formed, which hinders charge transfer. The metal electrode produced by the mask method, on the other hand, exhibits a uniform transition, which facilitates the graphene film to be better coated on the metal electrode through van der Waals integration.
[0040] 4) The process of integrating graphene film onto metal electrode through liquid phase transfer is as follows Figure 5 As shown, a graphene auxiliary transfer layer was prepared using an extraction solution via spin coating. The spin coating process involved dropping the extraction solution onto a copper-based CVD graphene film. The extraction solution was then spin-coated at 500 rps for 5 seconds, followed by 6500 rps for 45 seconds to complete the extraction process. The copper-based CVD graphene film, coated with the extraction solution layer, was then cut into small pieces (0.6 x 0.6 cm) according to the experimental requirements. The small pieces were then suspended in an ammonium persulfate solution ((NH4)2S2O8, 5wt%) for 12 hours, with the extraction solution layer on top and the copper substrate on the bottom. After etching, the copper-based CVD graphene film changed from a brass color to a colorless, transparent film. The CVD graphene film was then transferred to deionized water and soaked for 30 minutes to remove any residual (NH4)2S2O8. The deionized water soaking process was repeated 2-3 times to complete the etching of the copper-based CVD graphene film and remove the copper substrate. After etching away the copper substrate of the copper-based CVD graphene film, the graphene is transferred to the metal electrode. The silicon wafer substrate with the transferred graphene is tilted and placed for 2 hours to evaporate the water naturally, and then annealed at 40°C for 1 hour to obtain the following: Figure 6 The actual picture of UV-GFET is shown. At this point, the ultraviolet light modulated depletion-mode graphene field-effect transistor is completed.
[0041] In this UV-GFET device, a quantum dot-doped PMMA organic polymer thin film obtained by a spin-coating process is used as the insulating gate. The thickness of the GFET insulating gate can be adjusted by controlling the rotation speed and the number of spin-coating times of the PMMA layer.
[0042] Figure 2 This is the vertical cross-sectional structure diagram of the UV-GFET prepared in this embodiment. From bottom to top, it is a silicon / silicon dioxide base layer, a metal electrode layer, a graphene thin film sensing layer, and a quantum dot-doped insulating gate layer. Figure 9 This is the structure diagram of the UV-GFET.
[0043] Test experiment of Embodiment 3
[0044] Under light-shielding conditions, the UV-GFET-1 was measured using a probe station and a 2400 digital source meter, and the results are as Figure 7 shown. The resistance of the UV-GFET-1 is approximately 165 Ω. When the ultraviolet lamp is turned on to irradiate the gate of the device, the resistance of the UV-GFET-1 starts to rise from 165 Ω to 215 Ω and remains stable; when the ultraviolet lamp is turned off, the resistance of the UV-GFET-1 slowly drops from 215 Ω to 165 Ω and stabilizes. Another UV-GFET-2 prepared by the same process was used for repeated experiments. As Figure 8 shown, the test results of the UV-GFET-2 are basically the same as those of the UV-GFET-1. This shows that the UV-GFET prepared by the present invention has good repeatability.
Claims
1. A depletion-mode graphene field-effect transistor modulated by ultraviolet light, characterized in that The ultraviolet light modulated depletion type graphene field effect transistor comprises, from bottom to top, a Si / SiO2 substrate layer, a metal electrode layer, a graphene thin film sensing layer, and a quantum dot doped insulating gate layer.
2. The preparation method of a depletion-mode graphene field-effect transistor modulated by ultraviolet light according to claim 1, characterized in that, It includes the following steps: 1) Mix 5 mL of PMMA oil phase solution with 1 mL of quantum dot aqueous solution, and use a vortex oscillator to mix the solution for 30 min, then let it stand for 2 h to obtain a solution with oil-water two-phase stratification. The upper layer is the PMMA oil phase mixed solution doped with quantum dots, and the lower layer is the quantum dot aqueous solution; separate the upper layer of the PMMA oil phase mixed solution doped with quantum dots, and then add PMMA oil phase solution for mixing and dilution to obtain a diluted PMMA oil phase mixed solution doped with quantum dots, which is the extraction solution; 2) Prepare a metal electrode on the Si / SiO2 substrate layer by using a mask method; 3) First, drop the extraction solution onto the copper-based CVD graphene thin film, spin-coat it at 500 rps for 5 s, and then spin-coat it at 6500 rps for 45 s to complete the spin-coating of the extraction solution; after etching away the copper substrate of the copper-based CVD graphene thin film, transfer the CVD graphene thin film onto the metal electrode. Then, place the silicon wafer substrate layer with the transferred graphene inclined for 2 h to naturally evaporate water, and then anneal it at 40 °C for 1 h to prepare the ultraviolet light modulated depletion type graphene field effect transistor UV-GFET.
3. The preparation method according to claim 2, characterized in that, In step 1), the PMMA oil phase solution is prepared by dissolving 1 g of PMMA with an average molecular weight of 350000 in 20 mL of ethyl acetate or toluene or chlorobenzene.
4. The preparation method according to claim 2, characterized in that, In step 1), the concentration of the quantum dot aqueous solution is 10 mg / mL.
5. The preparation method according to claim 2, characterized in that, In step 1), the quantum dots are chitosan quantum dots.
6. The preparation method according to claim 5, wherein The preparation method of the chitosan quantum dots is as follows: Take 1 g of chitosan powder, add 40 mL of deionized water, and then add 0.9 mL of acetic acid solution, and stir at 50 °C for 3 h to obtain a chitosan solution; put the chitosan solution into a reaction kettle and react at 190 °C for 24 h to obtain a chitosan quantum dot mixture, and then put the chitosan quantum dot mixture into a dialysis bag and dialyze for 48 h to obtain a pure chitosan quantum dot solution; take the pure chitosan quantum dot solution and put it into a freeze dryer to freeze-dry for 48 h to obtain chitosan quantum dot powder.
7. The preparation method according to claim 2, characterized in that, The specific operation steps of step 2) are as follows: First, evaporate chromium on the Si / SiO2 substrate layer by using a thermal evaporation instrument to obtain a 15 nm metal electrode, and then evaporate gold on the chromium metal electrode to obtain a 35 nm metal electrode, thereby completing the preparation of a composite metal electrode with a total thickness of 50 nm.
8. The preparation method according to claim 2, wherein In step 3), the specific operation steps for etching away the copper substrate of the copper-based CVD graphene thin film are as follows: Cut the copper-based CVD graphene thin film spin-coated with the extraction solution layer into small pieces, and then put the small pieces of copper-based CVD graphene thin film into an ammonium persulfate solution and suspend and soak it for 12 h in the way that the extraction solution layer is on the top and the copper substrate is on the bottom; after the etching is completed, the copper-based CVD graphene thin film changes from brass color to colorless transparent film, and then transfer the CVD graphene thin film into deionized water and soak it for 30 min to remove the ammonium persulfate residue solution, and repeat the deionized water soaking process 2 - 3 times to complete the process of etching away the copper substrate of the copper-based CVD graphene thin film.
9. The preparation method according to claim 8, wherein The concentration of the ammonium persulfate solution is 5 wt%.