Method for improving field effect performance of printed metal oxide thin film transistor through atmosphere annealing

Abstract

The invention belongs to the field of printed optoelectronic device preparation, and particularly relates to a method for improving field effect performance of a printed metal oxide thin film transistor through atmosphere annealing. The invention provides a method for improving the field effect performance of a printed thin film transistor. The method comprises the following steps: cutting a Si / SiO2 substrate and carrying out ultrasonic cleaning for 10 minutes; placing the substrate in a gas plasma generating device to remove impurities adsorbed on the surface of the substrate; dissolving zinc acetate dihydrate, stannous chloride dihydrate and indium nitrate hydrate in ethylene glycol monomethyl ether; printing an active layer of the thin film transistor device and carrying out 550 DEG C air atmosphere annealing treatment; in order to improve the field effect performance of the thin film transistor, annealing treatment is carried out on the metal oxide active layer material in a vacuum atmosphere at the temperature of 550 DEG C; and printing a source electrode and a drain electrode of the thin film transistor by using high-precision ink-jet printing equipment. According to the method provided by the invention, the field effect performance of the printed metal oxide thin film transistor can be improved, and the requirement of a current optoelectronic device on high electrical performance of a printed driving device is met.

Description

Technical Field

[0001] The invention belongs to the field of printed optoelectronic device preparation, and particularly relates to a method for improving the field effect performance of a printed metal oxide thin film transistor by atmosphere annealing. Background Art

[0002] As electronic devices develop towards printable manufacturing, the performance requirements for printed electronic components are also gradually increasing, including the improvement of the field effect performance of printed thin film transistors. In display devices, the field effect performance of thin film transistors is one of the key factors that determine image quality. At present, inorganic thin film transistors are mainly based on metal oxides represented by zinc oxide-based materials, and thin film transistor devices are constructed using vacuum deposition methods. However, this device construction method is limited by the vacuum deposition environment and the waste of film-forming materials caused by repeated lithography. To solve this problem, printable thin film transistor devices have attracted widespread attention. Among them, printed metal oxide thin film transistors have the advantages of good device stability and flexible control of the proportion of doping elements.

[0003] However, printed thin film transistors are in the emerging device preparation process, and the optimization of their field effect performance urgently needs further research and exploration. To solve this problem, the advantages of printed thin film transistors in the controllable patterning of the functional layer should be brought into play to optimize the channel structure design. However, this method still does not solve the problem of how to improve the performance of the active layer material itself. Therefore, at this stage, there is an urgent need for a method that is simple in process and effective in improving the field effect performance of printed metal oxide thin film transistors. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the field effect performance of printed metal oxide thin film transistors by atmosphere annealing in view of the poor electrical performance of existing printed oxide thin film transistors.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] A method for preparing a transparent grid electrode that can be folded arbitrarily is provided, comprising the following steps:

[0007] S1, thermally oxidize 285 nm silicon dioxide substrate (Si / SiO2) on cut silicon wafer, and ultrasonically clean the cut substrate in acetone, anhydrous ethanol, and deionized water for 10 minutes respectively;

[0008] S2, placing the cleaned substrate in a gas plasma generator to remove impurities adsorbed on the substrate surface and enhance the wettability of the substrate surface;

[0009] S3, zinc acetate dihydrate, stannous chloride dihydrate and hydrated indium nitrate are dissolved in ethylene glycol methyl ether respectively, and the solution concentration is 0.4 mol / L;

[0010] S4, printing the active layer of the thin film transistor using micro-nano material printing equipment;

[0011] S5. To effectively remove organic impurities in the solution, the metal oxide active layer material is annealed at 550 degrees Celsius in an air atmosphere for 1 hour;

[0012] S6. To improve the field effect performance of the thin film transistor, the metal oxide active layer material is annealed in a vacuum atmosphere at 550 degrees Celsius for 1 hour;

[0013] S7. Use high-precision inkjet printing equipment to print the source and drain electrodes of the thin film transistor.

[0014] In printable thin film transistor devices, metal oxides are preferred as active layer materials of the device due to their good stability. First, relying on a clean Si / SiO2 substrate as the bottom gate and insulating layer structure in the thin film transistor structure, it is necessary to maintain good surface wettability, which is more conducive to printing a patterned active layer on the substrate. Preferably, acetone, anhydrous ethanol, and deionized water are ultrasonically applied for 10 minutes at a time. The acetone solvent is used to clean the organic molecules adsorbed on the surface of the Si / SiO2 substrate, and the anhydrous ethanol solution is used to clean the residual acetone solution. Finally, deionized water is used to clean the organic reagents remaining on the surface. Use nitrogen to blow dry the surface of the Si / SiO2 substrate to avoid leaving water marks and the adsorption of other gas functional groups on the printed patterned active layer. The uniform dispersion of the substrate surface. The preferred Si / SiO2 substrate needs to be treated with surface plasma to further improve the substrate surface wettability and improve the better uniform dispersion of the printed active layer on the substrate surface. The power supply power of the gas plasma generator is set to 75W, and the plasma treatment time is controlled to 10s. The preferred gas is inert gas argon. The ions generated after ionization will not react chemically with the substrate, and the surface tension after plasma treatment will be significantly increased. The preferred plasma treatment time is 10s. When the treatment time is short, the surface wettability of the ink solution is poor when printing on the Si / SiO2 substrate, and liquid droplets are easily agglomerated. When the treatment time is too long, the surface wettability of the substrate is high, which will cause the printing solution to diffuse rapidly, which is not conducive to the preparation of the patterned active layer.

[0015] The preferred indium tin zinc oxygen active layer printing ink is prepared by dissolving zinc acetate dihydrate, stannous chloride dihydrate and hydrated indium nitrate in ethylene glycol methyl ether respectively. The preferred configuration solution concentration is 0.4 mol / L. Too high a solution molar concentration is not conducive to the printing accuracy of the active layer graphics, and an active layer printing ink with too low a concentration is not easy to obtain a good transistor field effect performance. The configured solution is placed in a three-necked bottle equipped with a condensing device, and the condensing device is more conducive to maintaining the configuration concentration of the solution. The indium tin zinc oxygen active layer printing ink is obtained by heating at 150 degrees Celsius and stirring for 1h in an oil bath.

[0016] The preferred active layer pattern has a length and width of 840 microns and 560 microns, respectively. A printing needle with a diameter of 5 microns is selected, and the printing voltage is set to 0.6 volts. The preferred printing line spacing is 40 microns. If the spacing is set too narrow, the solution printing pattern thickness will be larger, and the subsequent annealing treatment will easily cause the active layer graphics to break. If the printing spacing is set too wide, the printed active layer graphics will be discontinuous. After the graphic active layer is printed, it needs to be placed on a 90-degree Celsius hot plate for curing for 3 minutes, and then annealed to remove organic impurities added during the printing ink configuration process. The Si / SiO2 substrate carrying the patterned active layer is placed in an air atmosphere at 550 degrees Celsius for annealing for 1 hour, and the heating rate is 5 degrees Celsius / minute. Traditional air atmosphere annealing will cause more functional patterns to be adsorbed on the surface of the active layer, which will affect the carrier transport at the interface of the thin film transistor device. In order to solve the formation of defect states at such interfaces, the printed metal oxide active layer was annealed at 550 degrees Celsius in a vacuum atmosphere for 1 hour, with a heating rate of 5 degrees Celsius per minute and an annealing pressure of 0.5 hPa in a vacuum environment.

[0017] Use high-precision inkjet printing equipment to print electrode ink composed of silver nanoparticles on the patterned active layer to form the source and drain electrodes of the thin-film transistor device. After the preferred source and drain electrode layers are printed, they need to be heated on a 90-degree Celsius hot plate for 5 minutes to evaporate the solvent, and then placed in an annealing furnace for 1 hour at 200 degrees Celsius to optimize the conductivity of the silver nanoparticle electrodes. The overall construction of the printed metal oxide thin-film transistor is completed. This type of thin-film transistor has a bottom-gate top contact structure. By testing the output characteristic curve and transfer characteristic curve of the thin-film transistor, the current regulation ability and field effect performance of the thin-film transistor can be judged, such as field effect mobility, threshold voltage, and current switching ratio. Figure 2 a, 3a, the gate voltage (V G ) leakage current from 0 to 40V (I SD ) and source-drain voltage (V SD ) output characteristics. The curve shows the typical field effect properties of n-type thin film transistors. After air atmosphere annealing, the indium tin zinc oxide thin film transistor has an obvious transition from linear to saturation. G The leakage current value is also gradually increased with the continuous improvement, and the current can be controlled. When testing the transfer characteristics of the device, V SD The applied voltage is 20V, V G From -30V to 30V, by Figure 2 b, 2c show that, by calculation, the air-annealed IZN / I TFT device exhibits a threshold voltage (V T) is -10.1V, and the subthreshold swing (SS) is 2.91V dec -1 , switching ratio (I on / I off ) is 1.4×10 5 and field effect mobility (μ) is 0.14 cm 2 / Vs. Relative contrast, by Figure 3 b, 3c It can be calculated that the vacuum annealed InSnZnO thin film transistor device exhibits V T is -9.2V, SS is 1.07V dec -1 , I on / I off 3.6×10 5 and field effect mobility μ is 0.16 cm 2 / Vs. The thin film transistors prepared after annealing all showed good performance, among which the thin film transistor devices annealed in a vacuum atmosphere showed better performance and had a lower turn-on current I on , a higher off-state current I off , the off-state current is reduced by annealing in an air atmosphere. In terms of the current switching ratio, the printed thin film transistor device after vacuum annealing is twice that of the air annealing device. Part of the carriers in the channel come from oxygen vacancies. Annealing the printed active layer in an air atmosphere can provide neutral oxygen atoms for the film and fill the oxygen vacancies in the active layer. The vacuum environment can effectively prevent the incorporation of oxygen during the annealing process and avoid the filling of oxygen vacancies, resulting in a higher carrier concentration, which increases the number of controllable carriers under the same field effect, and can also effectively reduce the interference of noise signals when the thin film transistor device is working. Therefore, a method for improving the field effect performance of printed metal oxide thin film transistors by atmosphere annealing is formed. Since vacuum annealing can effectively control the number of oxygen vacancies in the active layer of the thin film transistor, the processing method is simple and does not change the device stacking structure, which provides a new idea for regulating electrical properties by atmosphere annealing in improving the field effect performance of printed metal oxide thin film transistor devices. This provides strong support for the future application of printable electronic components in electronic skin and wearable devices. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The overall preparation process of printed metal oxide thin film transistors; Figure 2 (a) Output characteristic curve of thin film transistor prepared after printing indium tin zinc oxygen air annealing treatment; (b, c) Transfer characteristic curve of thin film transistor prepared after printing indium tin zinc oxygen air annealing treatment; Figure 3 (a) Output characteristic curve of thin film transistor prepared after printing indium tin zinc oxygen vacuum annealing treatment; (b, c) Transfer characteristic curve of thin film transistor prepared after printing indium tin zinc oxygen vacuum annealing treatment.

Claims

1. A method for improving the field effect performance of printed metal oxide thin film transistors by atmosphere annealing, characterized in that: The following steps are involved: S1, thermally oxidize 285 nm silicon dioxide substrate (Si / SiO2) on cut silicon wafer, and ultrasonically clean the cut substrate in acetone, anhydrous ethanol, and deionized water for 10 minutes respectively; S2, placing the cleaned substrate in a gas plasma generator to remove impurities adsorbed on the substrate surface and enhance the wettability of the substrate surface; S3, zinc acetate dihydrate, stannous chloride dihydrate and hydrated indium nitrate are dissolved in ethylene glycol methyl ether respectively, and the solution concentration is 0.4 mol / L; S4, printing the active layer of the thin film transistor using micro-nano material printing equipment; S5. To effectively remove organic impurities in the solution, the metal oxide active layer material is annealed at 550 degrees Celsius in an air atmosphere for 1 hour; S6. To improve the field effect performance of the thin film transistor, the metal oxide active layer material is annealed in a vacuum atmosphere at 550 degrees Celsius for 1 hour; S7. Use high-precision inkjet printing equipment to print the source and drain electrodes of the thin film transistor.

2. The preparation method according to claim 1, characterized in that: In the step S1, the Si / SiO2 substrate is cut into a square size of about 15 mm in length and width, and the substrate is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water in sequence and then blown dry with nitrogen.

3. The preparation method according to claim 1, characterized in that: In step S2, the power of the gas plasma generating device is set to 75W, and the plasma processing time is controlled to 10s.

4. The preparation method according to claim 1, characterized in that: In step S3, zinc acetate dihydrate, stannous chloride dihydrate and indium nitrate hydrate are respectively dissolved in ethylene glycol methyl ether to prepare a solution concentration of 0.4 mol / L, placed in a three-necked flask equipped with a condenser, heated in an oil bath at 150 degrees Celsius and stirred for 1 hour.

5. The preparation method according to claim 1, characterized in that: In step S4, the length and width of the active layer pattern are 840 microns and 560 microns respectively, a printing needle with a diameter of 5 microns is selected, the printing voltage is set to 0.6 volts, and the printing line spacing is 40 microns.

6. The preparation method according to claim 1, characterized in that: In the step S5, the printed metal oxide active layer is annealed in an air atmosphere at 550 degrees Celsius for 1 hour, with a heating rate of 5 degrees Celsius per minute.

7. The preparation method according to claim 1, characterized in that: In the step S6, the metal oxide active layer prepared by printing is annealed in a vacuum atmosphere at 550 degrees Celsius for 1 hour, the heating rate is 5 degrees Celsius / minute, and the annealing pressure in the vacuum environment is 0.5 hPa.

8. The preparation method according to claim 1, characterized in that: In step S7, after the source and drain electrode layers are printed, they need to be heated on a hot plate at 90 degrees Celsius for 5 minutes to evaporate the solvent, and then placed in an annealing furnace at 200 degrees Celsius for 1 hour.

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