A preparation method for realizing the protection of thin film transistors

Abstract

The present invention discloses a preparation method for realizing the protection of thin film transistors. First, a relatively thin barrier layer is spin-coated above the active layer in the present invention, and then through a printing and etching method, the barrier layer is etched in a positioned manner by using the solvent of the conductive ink. Under the outward Marangoni flow, the insulating barrier layer solute is migrated to the periphery, and a relatively thin, uniform and flat electrode layer is formed in the center, thereby improving the interface contact between the active layer and the conductive layer, and at the same time realizing the effective protection of the TFT device. The process is simple, time-consuming and suitable for large-area preparation.

Description

Technical Field

[0001] The present invention belongs to the field of printed electronics, and particularly relates to a preparation method for realizing the protection of thin film transistors. Background Art

[0002] With the continuous development of electronic devices, the solution method with low cost, good compatibility and environmental friendliness is considered to be the mainstream direction for future device preparation. Especially the inkjet printing technology with on-demand spraying can directly achieve high-precision patterning without a mask, and has great application potential. Thanks to the continuous progress of scientific research, there are already many kinds of inks that can be applied to the preparation of each functional layer of TFTs, providing a solid foundation for realizing all-solution or even all-printed preparation of high-performance TFTs.

[0003] Since metal-oxide semiconductor materials have excellent electrical properties, good uniformity and compatibility with various preparation processes, etc., many of the materials currently used for the active layer of TFTs are metal-oxide semiconductor materials. However, the interface of metal-oxide semiconductors is greatly affected by environmental water and oxygen, and is more likely to adsorb impurities. Moreover, during the subsequent deposition process of conductive ink, it is easily eroded by the ink, and atomic diffusion may also occur (especially silver and copper), resulting in a large number of defect states at the interface of the active layer, and finally the performance and stability of the prepared TFT devices are poor. Therefore, how to improve the interface contact between the metal and the active layer and isolate the influence of the environment on the active layer channel has become a problem that must be solved well in the future. Summary of the Invention

[0004] In order to solve the disadvantages and deficiencies of the prior art, the purpose of the present invention is to provide a preparation method for realizing the protection of thin film transistors.

[0005] The present invention first spin-coats a thin barrier layer above the active layer, and then through a printing and etching method, uses the solvent of the conductive ink to etch the barrier layer in a targeted manner. Under the outward Marangoni flow, the insulating barrier layer solute is migrated to the periphery, and a thin, uniform and flat electrode layer is formed in the center, thereby improving the interface contact between the active layer and the conductive layer, and at the same time realizing the effective protection of the TFT device. The process is simple, time-consuming and suitable for large-area preparation.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A preparation method for realizing the protection of thin film transistors, comprising the following steps:

[0008] (1) Perform oxygen plasma hydrophilic treatment on the metal oxide active layer, and then spin-coat the insulating material solution on the surface of the metal oxide active layer and cure it to form an insulating barrier layer;

[0009] The solvent of the insulating material solution is at least one of ethylene glycol, glycerol, and 2,3-butanediol;

[0010] (2) By means of inkjet printing, deposit the conductive ink onto the insulating barrier layer to form source and drain electrodes, remove the solvent, and obtain a protective thin-film transistor;

[0011] The solvent of the conductive ink is at least one of methanol, ethanol, isopropanol, ethylene glycol methyl ether, and triethylene glycol methyl ether.

[0012] The solvent of the insulating material solution in step (1) does not have an erosive effect on the underlying metal oxide active layer, and the solvent of the conductive ink in step (2) is miscible with the solvent of the insulating solution in step (1).

[0013] Preferably, the metal oxide active layer material in step (1) is at least one of IGZO, IZO doped with Nd, IZO doped with Pr, and SnO2.

[0014] Preferably, the power of the oxygen plasma hydrophilic treatment in step (1) is 40 - 70 W, more preferably 70 W; the treatment time is 10 - 30 min, more preferably 30 min.

[0015] Preferably, in the insulating material solution of step (1), the insulating material is at least one of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylamide (PAM), polymethyl methacrylate (PMMA), and ZrO2.

[0016] Preferably, the concentration of the insulating material solution in step (1) is 0.1 - 10 mg / mL; the spin coating speed is 2000 - 7000 rpm.

[0017] Preferably, the thickness of the insulating barrier layer in step (1) is 10 - 60 nm, more preferably 20 nm.

[0018] Preferably, the curing in step (1) is one of thermal curing, UV curing, or plasma sintering.

[0019] More preferably, the thermal curing temperature is T - 30 to T - 100 °C, more preferably T - 50 to T - 100 °C, where T is the highest boiling point temperature (°C) of the solvent in the insulating material solution; the curing time is 5 - 20 minutes, more preferably 10 minutes; the light intensity of the UV curing is 100%, the power is 200 - 800 W, and the time is 5 - 20 minutes, more preferably 10 minutes.

[0020] Preferably, the inkjet printing process in step (2) is: the ink droplet spacing is 1 to √2 times the radius r of the ink droplet; the ejection frequency is 1 - 7 kHz, more preferably 1 kHz; the substrate temperature is 30 - 60 °C.

[0021] Preferably, the solid content of the conductive ink in step (2) is 5-45 wt%.

[0022] Preferably, the functional material in the conductive ink in step (2) is at least one of silver, copper, aluminum, gold, and graphene.

[0023] Preferably, the conductive ink in step (2) is deposited on the insulating barrier layer, and the thickness of the insulating barrier layer after etching is 3-10 nm, preferably 3 nm.

[0024] Preferably, the method for removing the solvent in step (2) is heating evaporation, the temperature is between the highest boiling point of the solvent in the insulating material solution and 300 °C, and the time is 5-30 min.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) In the present invention, in a printing and etching manner, taking full advantage of the on-demand deposition of inkjet printing, a protective layer is first spin-coated and then the electrode layer is etched. Different from the stacking sequence of traditional bottom-gate top-contact TFTs, the protection of TFTs is achieved in a simple, fast and more effective way.

[0027] (2) The present invention effectively avoids the erosion of the lower layer by the conductive ink solvent during the printing process and also avoids the thermal diffusion phenomenon of conductive particles into the active layer, improving the thermal stability of the TFT device. Since there is still an ultra-thin polymer material between the printed electrode and the active layer, using the tunneling effect, the effective transfer of carriers between the electrode layer and the active layer can also be achieved, avoiding the degradation of device performance.

[0028] (3) The present invention effectively prevents the excessive back-channel defects in the TFT device because spin-coating is easier to obtain an ultra-thin and uniform film compared to inkjet printing, effectively improving the interfacial contact characteristics between the electrode layer and the active layer and avoiding the generation of defects at the interface.

[0029] (4) The present invention is beneficial to directly realizing protection in the TFT array. In the TFT circuit, the TFTs are interconnected through conductive lines. After depositing the active layer and the following functional layers in the substrate, an ultra-thin protective layer with high coverage, uniformity, and smoothness can be directly spin-coated, and then the electrode lines are patterned by etching, greatly reducing the preparation cost and improving the efficiency. Description of the Drawings

[0030] Figure 1Process flow chart for protecting the TFT array of the present invention; the markings in the figure are explained as follows: 11 - glass substrate, 12 - gate electrode, 13 - insulating layer, 14 - active layer, 15 - spin coating process, 16 - barrier layer, 17 - inkjet printing process, 18 - conductive layer.

[0031] Figure 2 Schematic diagram for etching and protection implemented by the present invention; the markings in the figure are explained as follows: 21 - redissolved solute; 22 - outward Marangoni flow.

[0032] Figure 3 Profile effect diagram of printing and etching of the present invention; the markings in the figure are explained as follows: 31 - insulating layer, 32 - conductive layer, 33 - coffee ring effect.

[0033] Figure 4 Microscope image obtained after printing and etching in Example 2 of the present invention; (a) is the effect without protection (i.e., obtained by omitting step (2) of Example 2), and (b) is the effect after introducing an ultra-thin barrier layer. The markings in the figure are explained as follows: 41 - insulating solute and a small amount of electrode material aggregated at the periphery due to the coffee ring effect, 42 - electrode layer.

[0034] Figure 5 Comparison of TFT performance with and without protection in Example 2 of the present invention; (a) is the TFT obtained by directly printing the electrode (i.e., obtained by omitting step (2) of Example 2), and (b) is the TFT obtained by printing the electrode after introducing an ultra-thin barrier layer. The markings in the figure are explained as follows: 51 - Vth = 0V, 52 - Vth = 5V, 53 - Vth = 10V, 54 - Vth = 15V, 55 - Vth = 20V. Detailed implementation manners

[0035] The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto.

[0036] For those conditions not specified in the embodiments of the present invention, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials, reagents, etc. that are not specified for the manufacturer can all be obtained as conventional products through commercial purchase.

[0037] Example 1

[0038] This embodiment provides a protection preparation method suitable for a thin film transistor array. The specific preparation steps are as follows:

[0039] 1) The preparation method of the TFT active layer and below is to magnetron sputter a 300-nm-thick Al:Nd layer on a cleaned glass substrate by DC magnetron sputtering. Then, the prepared gate film is immersed in an ethylene glycol solution of ammonium tartrate for oxidation to form an Al2O3:Nd insulating layer with a thickness of 200 nm. Next, a 20-nm-thick Pr_IZO layer is sputtered by radio frequency magnetron sputtering, annealed at 250 °C for 1 h and then cooled naturally to obtain the active layer. Finally, the active layer is treated with oxygen plasma. The instrument model is AutoGlow200, the power is 70 W, the treatment time is 30 min, and it is reserved after treatment.

[0040] 2) Add 0.5 g of PVP to 50 mL of ethylene glycol, and the solution is stirred at 400 rpm at 70 °C for 1 h to obtain a PVP ethylene glycol solution. Spin-coat 31 μL of the PVP solution onto the active layer at a high speed of 7000 rpm. First, use ultraviolet light. The instrument model is IntelliRay UV0832, the light intensity is 100%, the power is 600 W, the wavelength is 200 - 400 nm, the distance is about 40 cm, and it is cured for 3 min to obtain an uncrosslinked PVP film, and an insulating barrier layer with a thickness of about 40 nm is obtained.

[0041] 3) Use ANP DGP 40TE-20C (silver ink) as the conductive ink, and the ink solvent is triethylene glycol ethyl ether, and the solid content is about 42 wt%. Print the conductive ink onto the uncrosslinked PVP film. The printing parameters are: driving voltage 25 V, emission frequency 2 kHz, substrate temperature 60 °C, droplet spacing 25 μm. After printing, it is dried at 200 °C for 20 min to remove the solvent.

[0042] In this embodiment, triethylene glycol ethyl ether can be well miscible with ethylene glycol and can well dissolve PVP, meeting the basic conditions for printing and etching. Treating the active layer with oxygen plasma with moderate power can, on the one hand, repair some defects in the active layer such as oxygen vacancies, and on the other hand, increase the surface energy of the substrate, which is beneficial to the spreading of the PVP solution on the active layer, thereby obtaining a thinner PVP film.

[0043] In this embodiment, the inkjet printing system used is DMP-2800 (FUJIFILM, USA), and the loading nozzle diameter is 16 μm.

[0044] In this embodiment, when the ink is ejected onto the PVP, the PVP is dissolved. Since the evaporation rate at the edge of the ink droplet is faster than that at the center, the central solvent moves towards the edge to form an outward Marangoni flow (as Figure 2 ), driving the polymer solute to re-stack at the edge, while thinning the thickness of the electrode layer, and finally generating a contour effect as Figure 3As shown. After etching, there is a very thin insulating layer between the electrode layer and the active layer. However, due to the tunneling effect, effective carrier transport can still occur between the electrode layer and the active layer.

[0045] Example 2

[0046] This embodiment provides another protective preparation method suitable for a thin-film transistor array. The specific preparation steps are as follows:

[0047] 1) The preparation method for the TFT active layer and below is to sputter a 300-nm-thick Al:Nd layer on a cleaned glass substrate by DC magnetron sputtering. Then, soak the prepared gate film in an ethylene glycol solution of ammonium tartrate for oxidation to form an Al2O3:Nd insulating layer with a thickness of 200 nm. Next, sputter a 20-nm-thick Pr_IZO layer by radio-frequency magnetron sputtering, anneal at 250 °C for 1 h, and then cool naturally to obtain the active layer. Finally, perform oxygen plasma treatment on the active layer. The instrument model is AutoGlow200, the power is 70 W, the treatment time is 10 min, and it is set aside after treatment.

[0048] 2) First, dissolve polyacrylamide (PAM) in ethylene glycol at a concentration of 3.272 mg / mL, heat and stir at 45 °C for 5 h. Subsequently, dissolve zirconium oxychloride octahydrate (ZrOCl2·8H2O) in the polymer solution at a concentration of 0.3 mol / L, and stir for 20 minutes to fully dissolve it to obtain a zirconia precursor solution. Spin-coat 31 μL of this solution onto the active layer at a speed of 4000 rpm and cure at 120 °C for 10 min to obtain an insulating barrier layer with a thickness of about 17 nm.

[0049] 3) Use ANP DGP 40TE-20C (silver ink) as the conductive ink. The ink solvent is triethylene glycol monoethyl ether, and the solid content is about 42 wt%. Print the conductive ink onto the cured zirconia film. The printing parameters are: driving voltage 25 V, set the droplet spacing to 30 μm, substrate temperature 30 °C, and ejection frequency 2 kHz. After printing, dry at 200 °C for 20 min to remove the solvent.

[0050] In this embodiment, the solvent of the conductive ink, triethylene glycol monoethyl ether, and ethylene glycol can be well miscible. Under the action of outward Marangoni flow, the zirconia solute and silver particles re-aggregate towards the periphery. Since the printing spacing of the conductive ink is small, the silver particles between adjacent droplets can be quickly replenished, and finally a thin conductive layer can be obtained in the printing area. After annealing the device, the organic solvent is removed, and the particle flow is inhibited. A very thin zirconia layer is successfully etched between the conductive layer and the active layer, while achieving the protection of the active layer, reducing the defects at the back channel, and improving the contact characteristics between the two layers. Its polarized light micrograph is asFigure 4 As shown, the performance effect is as Figure 5 shown. Without protection, due to the printing erosion and diffusion of silver ink, an approximate short circuit occurs between the source and drain electrodes, resulting in the loss of the switching characteristics that a transistor should have. After protection, the barrier layer effectively blocks the influence of the printed conductive layer on the underlying layer, enabling the transistor to have a small leakage current when turned off and thus exhibiting good transistor characteristics.

[0051] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method for realizing the protection of thin film transistors, characterized in that, It includes the following steps: (1) Perform oxygen plasma hydrophilic treatment on the metal oxide active layer, and then spin-coat the insulating material solution onto the surface of the metal oxide active layer and cure it to form an insulating barrier layer; The solvent of the insulating material solution is at least one of ethylene glycol, glycerol, and 2,3-butanediol; (2) Deposit the conductive ink onto the insulating barrier layer by inkjet printing. The solvent of the conductive ink erodes the insulating barrier layer, and at the same time, the functional materials in the conductive ink form source and drain electrodes. Remove the solvent of the conductive ink to obtain a protected thin-film transistor; The solvent of the conductive ink is at least one of methanol, ethanol, isopropanol, ethylene glycol monomethyl ether, and triethylene glycol monomethyl ether; In step (1), the thickness of the insulating barrier layer is 10 - 60 nm; in step (2), after the conductive ink is deposited onto the insulating barrier layer and eroded, the thickness of the insulating barrier layer is 3 - 10 nm.

2. The preparation method for realizing the protection of thin film transistors according to claim 1, characterized in that, In the insulating material solution in step (1), the insulating material is at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylamide, polymethyl methacrylate, and ZrO2.

3. The preparation method for realizing the protection of thin film transistors according to claim 1, characterized in that, The material of the metal oxide active layer in step (1) is at least one of IGZO, IZO doped with Nd, IZO doped with Pr, and SnO2.

4. The preparation method for realizing the protection of a thin-film transistor according to claim 1, wherein, The curing in step (1) is one of thermal curing, UV curing, or plasma sintering; The thermal curing temperature is T - 30 to T - 100 °C, where T is the lowest boiling point temperature of the solvent in the insulating material solution; the curing time is 5 - 20 minutes; The light intensity of the UV curing is 100%, the power is 200 - 800 W, and the time is 5 - 20 minutes.

5. The preparation method for realizing the protection of a thin film transistor according to claim 1, wherein, The inkjet printing process in step (2) is: the ink droplet spacing is 1 to √2 times the ink droplet radius r; the jetting frequency is 1 - 7 kHz; the substrate temperature is 30 - 60 °C.

6. The preparation method for realizing the protection of a thin film transistor according to claim 1, wherein, The functional materials in the conductive ink in step (2) are at least one of silver, copper, aluminum, gold, and graphene; The solid content of the conductive ink is 5 - 45 wt%.

7. The preparation method for realizing the protection of a thin film transistor according to claim 1, wherein, The power of the oxygen plasma hydrophilic treatment in step (1) is 40 - 70 W, and the treatment time is 10 - 30 min.

8. The preparation method for realizing the protection of thin film transistors according to claim 1, wherein, The concentration of the insulating material solution in step (1) is 0.1 - 10 mg / mL; the rotation speed of the spin-coating is 2000 - 7000 rpm.

9. The preparation method for realizing the protection of a thin film transistor according to claim 1, wherein, The method for removing the solvent of the conductive ink in step (2) is heating evaporation, the temperature is between the highest boiling point of the solvent in the insulating material solution and 300 °C, and the time is 5 - 30 min.

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