ITO film preparation method for promoting ITO room temperature crystallization

Abstract

The invention belongs to the field of photoelectric materials, and particularly relates to an ITO (indium tin oxide) film preparation method for promoting ITO room-temperature crystallization, which comprises the following steps: providing a substrate; preparing a crystal assisting layer on the substrate, wherein the material of the crystal assisting layer is silver; and depositing an ITO thin film on the assistant crystal layer by adopting a plasma technology. According to the method, the crystallization assisting layer is introduced in the film preparation process, the ITO film is prepared in combination with the plasma assisting technology, crystallization of the ITO film is promoted under the room temperature or low temperature condition, damage to a substrate material caused by high-temperature treatment can be avoided, and the production cost can be reduced. According to the preparation method of the ITO thin film, the performance of the ITO thin film material is improved.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic materials, and relates to a preparation technology of indium tin oxide (ITO) thin films, specifically a method for preparing ITO thin films that promotes room-temperature crystallization of ITO. Background Art

[0002] ITO (Indium Tin Oxide) is an important transparent conductive thin film material, which is widely used in the optoelectronic field, such as touch screens, liquid crystal displays, photovoltaic devices, light-emitting diodes (LEDs), solar cells, etc. Due to its excellent optical transparency and electrical conductivity, ITO has become one of the core functional materials in the optoelectronic field. However, the performance of ITO thin films highly depends on their crystal structure, crystallinity, and microtopography. The crystallization degree of ITO plays a decisive role in its optoelectronic properties, especially in terms of carrier mobility, electrical conductivity, and optical transparency. As an n-type semiconductor, the carrier concentration of ITO mainly comes from oxygen vacancies and tin doping. With the increase in crystallization degree, the scattering effect between grains weakens, the carrier mobility increases, and the resistivity decreases, thereby significantly improving the electrical conductivity. In addition, the crystallization process can effectively reduce the defects and scattering centers in the thin film and improve the transmittance in the visible light band. Generally, the transparency of crystalline ITO thin films is better than that of amorphous thin films, and at the same time, they show better environmental stability in terms of oxidation resistance and chemical corrosion resistance. Moreover, ITO thin films with a higher crystallization degree also have more excellent adhesion and mechanical stability.

[0003] Under normal circumstances, due to factors such as low deposition temperature, high deposition rate, low particle kinetic energy, the influence of tin doping, and lack of sufficient external excitation (such as thermal annealing or plasma treatment), conventionally grown ITO thin films are usually amorphous. Under such conditions, the deposited atoms or molecules do not have enough energy to arrange into an ordered crystal structure, resulting in the ITO thin film remaining amorphous. To improve the electrical and optical properties of ITO thin films, crystallization processes such as heat treatment or laser annealing are usually required. These methods promote the rearrangement of the indium and tin oxide lattices in the ITO thin film through heating or high-energy excitation, thereby improving its electrical conductivity and transparency. The heat treatment temperature is generally between 300°C and 500°C. However, high temperatures can affect some substrate materials (such as plastics, flexible substrates), and may also cause changes in the thickness and morphology of the thin film. Other high-energy annealing methods use relatively expensive equipment, and it is difficult to ensure the uniformity of the annealing area. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing an ITO thin film that promotes the crystallization of ITO at room temperature. By introducing a crystallization assisting layer during the thin film preparation process and combining with plasma-assisted technology to prepare the ITO thin film, partial crystallization of the ITO thin film at room temperature is achieved, thereby improving its optoelectronic performance and broadening its application scope in flexible electronic devices.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing an ITO thin film that promotes the crystallization of ITO at room temperature, comprising the steps of:

[0007] Providing a substrate;

[0008] Preparing a crystallization assisting layer on the substrate, and the material of the crystallization assisting layer is silver;

[0009] Depositing an ITO thin film on the crystallization assisting layer by using plasma technology.

[0010] Further, the substrate is a transparent rigid substrate or a flexible substrate, which is used to support the ITO thin film and is selected according to actual application requirements. It includes but is not limited to transparent glass, MgO, MgF2, ZnS, PET, PC, CPI, PMMA, PDMS, PP, PA, PS.

[0011] Further, the crystallization assisting material includes but is not limited to Ag nanowires, Ag nanoparticles, and Ag metal films.

[0012] Further, the preparation method of the crystallization assisting layer includes but is not limited to spin coating method, Mayer rod coating method, spraying method, hydrothermal method, electrodeposition method, magnetron sputtering method, thermal evaporation method.

[0013] Further, the method for depositing the ITO thin film on the crystallization assisting layer includes but is not limited to methods with plasma technology such as physical vapor deposition method, chemical vapor deposition method, such as magnetron sputtering method, electron beam evaporation method, atomic beam deposition method, plasma spraying method, plasma enhanced chemical vapor deposition method, etc.

[0014] Further, the tin content of the ITO thin film is 1-15 wt%.

[0015] Further, the thickness range of the ITO thin film is 25-200 nm.

[0016] The ITO thin film preparation method of the present invention promotes the crystallization of the ITO thin film at room temperature or low temperature by introducing a crystallization assisting layer during the thin film preparation process and combining with plasma-assisted technology. Since the crystallization assisting layer is single crystal or polycrystalline and has a good crystal structure, it can effectively reduce the ITO crystallization barrier and induce the room temperature crystallization of ITO. At the same time, the plasma technology provides a certain amount of energy to ITO atoms or atomic groups, enabling them to migrate or diffuse when deposited on the substrate, further promoting their room temperature crystallization. This method can not only avoid damaging the substrate material due to high-temperature treatment, but also reduce production costs and improve the performance of ITO thin film materials. The ITO thin film preparation method of the present invention is applicable to the design and preparation of a variety of transparent conductive devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the ITO thin film prepared by the ITO thin film preparation method for promoting the room temperature crystallization of ITO of the present invention;

[0018] Figure 2 XRD patterns of ITO thin films with different thicknesses grown by magnetron sputtering without a crystallization assisting layer in Example 1;

[0019] Figure 3 XRD patterns of composite films of ITO with different thicknesses grown by magnetron sputtering with a silver nanowire crystallization assisting layer in Example 2;

[0020] Figure 4 For the composite film of ITO with different thicknesses grown by magnetron sputtering with a silver nanowire crystallization assisting layer in Example 2, its transmittance and sheet resistance in the visible light band (400 - 800 nm); where a is the transmittance and b is the sheet resistance;

[0021] Figure 5 TEM images of ITO composite films with a silver nanowire rotation speed of 300 rpm and ITO thicknesses of 15 nm (left) and 75 nm (right) in Example 2, where the ITO in the left figure is amorphous and the ITO in the right figure is partially crystalline;

[0022] Figure 6 XRD patterns of ITO composite films with different silver nanowire spin coating speeds in Example 3;

[0023] Figure 7 XRD pattern of a silver nanowire / ITO composite film with a PI substrate and an ITO thickness of 75 nm in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solution of the present invention will be described in detail below with reference to the drawings and examples.

[0025] In the embodiment of the present invention, the material used for the seed layer is silver nanowires, the concentration of the silver nanowire dispersion is 5 mg / ml, the dispersant is isopropanol, the diameter is in the range of 25 - 30 nm, the average aspect ratio is 1000, and the preparation method of the ITO thin film is magnetron sputtering method.

[0026] Example 1

[0027] A method for preparing an ITO thin film, comprising the following steps:

[0028] Step 1, ultrasonically clean a square PET substrate with a side length of 1 cm and a thickness of 125 μm for 5 min each using deionized water and absolute ethanol, and then dry it with nitrogen for standby.

[0029] Step 2, grow an ITO thin film on the PET substrate obtained in Step 1 by vacuum magnetron sputtering. Place the sample in a vacuum chamber, evacuate to 3×10 -5 Pa, the radio frequency sputtering power is 15 W, the sputtering gas pressure is 0.2 Pa, the oxygen - argon ratio is 0.3%, control the sputtering time to grow the ITO thin film.

[0030] Five samples were prepared according to the steps of this embodiment. The thicknesses of the ITO thin films grown on the PET substrate for the five samples are 25 nm, 50 nm, 75 nm, 100 nm, and 125 nm respectively. Perform XRD tests on the five ITO thin film samples of this embodiment, and the test results are as Figure 2 .

[0031] Example 2

[0032] A method for preparing an ITO thin film to promote room - temperature crystallization of ITO, comprising the steps:

[0033] Step 1, ultrasonically clean a square PET substrate with a side length of 1 cm and a thickness of 125 μm for 5 min each using deionized water and absolute ethanol, and then dry it with nitrogen for standby.

[0034] Step 2, disperse silver nanowires with a diameter of 25 - 30 nm and an average aspect ratio of 1000 in high - purity isopropanol to obtain a dispersion with a concentration of 5 mg / ml;

[0035] Step 3, adsorb the PET treated in Step 1 on a spin coater, and use a two - step spin - coating method to prepare a silver nanowire seed layer. Set the spin - coating parameters. The rotation speed in the first step is 300 rpm, the acceleration is 2000 rpm / s, and the coating time is 3 s; the rotation speed in the second step is 300 rpm, the acceleration is 2000 rpm / s, and the coating time is 60 s. Drop 100 μL of the silver nanowire dispersion in the middle of the PET and perform spin - coating.

[0036] Step 4: Place the silver nanowire seeding layer obtained in Step 3 on a pre-heated heating stage and perform heat treatment for a certain period of time (while keeping the temperature constant) to dry the silver nanowire film and remove the excess dispersant, thereby obtaining the silver nanowire seeding layer. Set the temperature to 70 °C and heat for 2 min.

[0037] Step 5: Grow an ITO film on the silver nanowire seeding layer obtained in Step 4 by means of vacuum magnetron sputtering. Specifically: Place the sample in a vacuum chamber, evacuate to 3×10 -5 Pa, with a radio frequency sputtering power of 15 W, a sputtering gas pressure of 0.2 Pa, an oxygen-to-argon ratio of 0.3%, and control the sputtering time to grow the ITO film. Finally, obtain the ITO film as shown in Figure 1 the figure.

[0038] Multiple ITO films were prepared according to the steps of this embodiment. The difference among the multiple ITO films lies in the different thicknesses of the ITO films grown on the silver nanowire seeding layer, which are 5 nm, 10 nm, 15 nm, 25 nm, 50 nm, 75 nm, 100 nm, 125 nm, and 150 nm respectively.

[0039] XRD, optoelectronic property, and TEM tests were respectively conducted on the multiple ITO films with different ITO thicknesses prepared in this embodiment. Among them, the XRD pattern is as shown in Figure 3 the figure, and its transmittance and sheet resistance in the visible light band (400 - 800 nm) are as shown in Figure 4 the figure. The TEM of the ITO composite films with a silver nanowire rotation speed of 300 rpm and ITO thicknesses of 15 nm and 75 nm respectively is as shown in Figure 5 the figure.

[0040] Example 3

[0041] A method for preparing an ITO film that promotes the crystallization of ITO at room temperature, comprising the steps:

[0042] Step 1: Ultrasonically clean a square PET substrate with a side length of 1 cm and a thickness of 125 μm in deionized water and absolute ethanol for 5 min each, and then dry it with nitrogen for standby.

[0043] Step 2: Disperse silver nanowires with a diameter of 25 - 30 nm and an average aspect ratio of 1000 in high-purity isopropyl alcohol to obtain a dispersion with a concentration of 5 mg / ml;

[0044] Step 3: Adsorb the PET treated in Step 1 on a spin coater, and use the two-step spin coating method to prepare a silver nanowire seeding layer. Set the spin coating parameters. The rotation speed in the first step is 300 rpm, the acceleration is 2000 rpm / s, and the coating time is 3 s; the rotation speed in the second step is n, the acceleration is 2000 rpm / s, and the coating time is 60 s. Drop 100 μL of the silver nanowire dispersion in the middle of the PET and perform spin coating.

[0045] Step 4: Place the silver nanowire seed layer obtained in Step 3 on a heating table preheated to 70 °C and keep the temperature constant to dry the silver nanowire film and remove the excess dispersant, thereby obtaining the silver nanowire seed layer. Set the temperature to 70 °C and heat for 2 min.

[0046] Step 5: Grow an ITO film on the silver nanowire seed layer obtained in Step 4 by vacuum magnetron sputtering. Specifically: Place the sample in a vacuum chamber, evacuate to 3×10 -5 Pa, with a radio frequency sputtering power of 15 W, a sputtering gas pressure of 0.2 Pa, an oxygen-to-argon ratio of 0.3%, control the sputtering time, and grow an amorphous ITO with a thickness of 100 nm.

[0047] Multiple ITO films were prepared according to the steps of this embodiment. The multiple ITO films differ in that during the preparation of the silver nanowire seed layer, the spin coating speeds in the second step are different. The spin coating speeds of the multiple ITO films in the second step of this embodiment are 300 rpm, 400 rpm, 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, and 3000 rpm respectively.

[0048] XRD tests were respectively performed on the multiple ITO films prepared in this embodiment, and the results are as Figure 6 shown.

[0049] Example 4

[0050] A method for preparing an ITO film to promote room-temperature crystallization of ITO, comprising the steps of:

[0051] Step 1: Ultrasonically clean a square PI substrate with a side length of 1 cm and a thickness of 125 μm in deionized water and absolute ethanol for 5 min each, and then dry it with nitrogen for standby.

[0052] Step 2: Disperse silver nanowires with a diameter of 25 - 30 nm and an average aspect ratio of 1000 in high-purity isopropanol to obtain a dispersion of 5 mg / ml.

[0053] Step 3: Adsorb the PI treated in Step 1 on a spin coater and use a two-step spin coating method to prepare a silver nanowire seed layer. Set the spin coating parameters. The rotation speed in the first step is 300 rpm, the acceleration is 2000 rpm / s, and the coating time is 3 s; the rotation speed in the second step is 300 rpm, the acceleration is 2000 rpm / s, and the coating time is 60 s. Drop 100 μL of the silver nanowire dispersion in the middle of the PI and perform spin coating.

[0054] Step 4: Place the silver nanowire seeding layer obtained in Step 3 on a heating stage preheated to 70°C, keep the temperature constant, and remove the excess dispersant. Set the temperature to 70°C and heat for 2 min.

[0055] Step 5: Grow an ITO thin film on the silver nanowire seeding layer obtained in Step 4 by vacuum magnetron sputtering. Place the sample in the vacuum chamber, evacuate to 3×10 -5 Pa, with a radio frequency sputtering power of 15 W, a sputtering gas pressure of 0.2 Pa, an oxygen-to-argon ratio of 0.3%, control the sputtering time, and grow an ITO with a thickness of 75 nm.

[0056] Step 6: Perform XRD testing on the prepared thin film, as Figure 7 shown.

[0057] Based on the above characterization tests, it is shown that a crystalline ITO thin film can be successfully prepared at room temperature by this method, and this ITO thin film has good light transmittance and conductivity (as Figure 6 ). It can be seen from Figure 2 , 3 , and 5 that the crystallization degree of the ITO thin film can be regulated by precisely controlling the spin-coating speed (density of silver nanowires) of the silver nanowires and the thickness of the ITO. Moreover, by adding the seeding layer, it can be seen that the crystallization degree of the ITO thin film is higher, which proves the feasibility of the method for promoting room-temperature crystallization of the ITO thin film proposed in the present invention. It provides a new idea for the research on room-temperature crystallization of ITO thin films and also expands the application of ITO thin films.

Claims

1. A method for preparing an ITO thin film that promotes crystallization of ITO at room temperature, characterized in that: Includes steps: providing a substrate; A crystal-assisting layer is prepared on the substrate, wherein the crystal-assisting layer material is silver; The ITO thin film is deposited on the auxiliary crystal layer using plasma technology.

2. A method for preparing an ITO film that promotes ITO room temperature crystallization according to claim 1, characterized in that, The substrate material is transparent glass, MgO, MgF2, ZnS, PET, PC, CPI, PMMA, PDMS, PP, PA or PS.

3. A method for preparing an ITO film that promotes ITO room temperature crystallization according to claim 1, characterized in that, The auxiliary crystal material is Ag nanowire, Ag nanoparticle or Ag metal film.

4. A method for preparing an ITO film that promotes ITO room temperature crystallization according to claim 1, characterized in that, The preparation method of the silver crystal-assisting layer adopts a spin coating method, a Meyer rod coating method, a spray coating method, a hydrothermal method, an electrodeposition method, a magnetron sputtering method or a thermal evaporation method.

5. A method for preparing an ITO film that promotes ITO room temperature crystallization according to claim 1, characterized in that, The method for depositing the ITO film on the auxiliary crystal layer adopts magnetron sputtering, electron beam evaporation, atomic beam deposition, plasma spraying or plasma enhanced chemical vapor deposition.

6. A method for preparing an ITO film that promotes ITO room temperature crystallization according to claim 1, characterized in that, The tin content of the ITO film is 1-15wt%.

7. A method for preparing an ITO thin film that promotes ITO room temperature crystallization according to any one of claims 1 to 6, characterized in that: The thickness of the ITO film ranges from 25 to 200 nm.

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