CN114496353A - Transparent conductive film with high conductivity and high transmissivity and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the field of semiconductors, and discloses a transparent conductive film with high conductivity and high transmittance, and a preparation method and application thereof. The transparent conductive film is a CdO-based transparent conductive film, the average transmittance in the range of 400-2500nm is more than 70%, and the conductivity is more than 3000S/cm. In the process of preparing the transparent conductive film, the invention can prepare the transparent conductive oxide film with high transmissivity (average transmissivity > 70%) in the full spectrum, wherein the average transmissivity at 1000-2500nm can be > 80% and high conductivity (more than 3000S/cm) by controlling the substrate temperature, the working gas condition, regulating the concentration of impurities or alloy elements of the film, regulating the thickness of the film and carrying out proper annealing treatment, and can be applied to optoelectronic devices in the full spectrum (visible light, near infrared and even middle infrared bands) including corresponding flexible devices.

Description

Transparent conductive film with high electrical conductivity and high transmittance and its preparation method and application

technical field

The invention belongs to the field of semiconductors, and particularly relates to a transparent conductive film with high electrical conductivity and high transmittance, and a preparation method and application thereof.

Background technique

Transparent conductive oxides (TCOs) thin film materials occupy an important position in today's optoelectronics industry. As transparent conductors, they are widely used in optoelectronic fields such as flat panel displays, photovoltaic cells, thin film transistors, photodetectors, gas sensors, light-emitting diodes, and smart windows. From their first discovery in 1907 to their widespread application, a great deal of research and development has been done on TCOs. Due to the continuous emergence of new application requirements and some key problems in recent years, the research and development of TCOs is still very active. At present, the application of TCOs thin films has at least the following three problems. First, Sn-doped In ₂ O ₃ (ITO) dominates the current transparent conductive material market, but the content of In on the surface is very scarce, it will be in short supply in the future, and the price is becoming more and more expensive, it is difficult to meet the global growth of transparent conductive films. Demand (a market survey released by the market research agency Research and Markets in 2017 pointed out that the global transparent conductive film market is estimated to have an average annual growth rate of more than 9% from 2017 to 2026, and is expected to be about 8.5 billion US dollars in 2026). Second, the electron mobility (μ about 30cm ² /Vs) of conventional commercial TCOs films is not high, and the free carrier concentration (N about 10 ²¹ /cm ³ ) is relatively large, which makes the transparency of TCOs films in the near-infrared light band low. (caused by the light absorption and plasmonic reflection of free electrons), which limits the application of TCOs thin films in near-infrared optoelectronic devices. Third, the industrial trend of the rise of flexible electronics represented by flexible displays, flexible solar cells and flexible wearable devices has become increasingly clear, while the mechanical flexibility of conventional TCOs film materials represented by ITO is not good, and it is difficult to apply to today's flexible materials. optoelectronic devices. Therefore, the industry and academia urgently need to develop transparent conductive materials with low cost, high near-infrared light transparency, and high flexibility to vigorously promote the sustainable development of new (flexible) optoelectronics and other intelligent manufacturing fields. In response to the first problem, researchers developed low-cost TCOs thin film materials (such as Al-doped ZnO) and realized commercial applications. However, the existing low-cost TCOs thin film materials (such as ZnO or SnO ₂ ) are not widely used due to their inferior electrical properties and/or chemical stability than ITO. For the second problem, people generally obtain higher near _- infrared transmittance (such as doping _{In 2} O ₃ ) by reducing the electron concentration in TCOs thin films. lattice defects, so that its mobility and corresponding conductivity are not high. For flexible TCOs thin films, researchers mainly realize the realization by forming two or more binary oxides (the corresponding cations have obvious differences in valence and size) to form amorphous oxide alloys (such as non-crystalline oxides). TCOs thin films of crystalline In-Zn-O). However, higher In content (about 70%) is required to obtain amorphous In-Zn-O films with high conductivity. Therefore, it is necessary to develop new low-cost high-mobility TCOs thin film materials that can maintain high electrical conductivity at low carrier concentrations, so as to obtain high performance in the full spectral range (from visible to near-infrared). Transmittance and even flexible TCOs thin film materials.

The existing TCOs market is dominated by ITOs. As mentioned above, the surface content of In element in ITO is rare and the price will be increasingly expensive. In addition, the electron mobility of _{doped In2O3} (typically < ^40cm2 /Vs) and its high frequency dielectric constant are not too high, the corresponding free electron absorption and plasmonic reflection lead to near-infrared light (wavelength >1100nm) The transmittance is low (less than 70%); if the transmittance of near-infrared light is improved by reducing the electron concentration in doped In ₂ O ₃ (eg <10 ²⁰ cm ^-3 ), it is difficult to obtain higher transmittance conductivity (>3000 S/cm), which greatly limits its application in near-infrared optoelectronic devices. The existing flexible TCOs based on In ₂ O ₃ also suffer from poor mechanical flexibility.

Therefore, there is an urgent need to provide a new transparent conductive oxide film, which not only has low manufacturing cost, but also has high electrical conductivity at the same time, and has high performance in the full spectrum (visible light to near-infrared and even mid-infrared band). The characteristics of transmittance, and further have high electron mobility.

SUMMARY OF THE INVENTION

The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. Therefore, the present invention proposes a transparent conductive film with high electrical conductivity and high transmittance, as well as a preparation method and application thereof.

The transparent conductive oxide film based on CdO of the present invention has high transmittance (average transmittance>70% in the whole spectrum (visible light to near-infrared and even mid-infrared band, corresponding to 400-2500 nm), and even the average transmittance at 1000-2500 nm can be >80%), high electrical conductivity (over 3000 S/cm, eg 3100-14000 S/cm), further high electron mobility (>50 cm ² /Vs, even > 100 cm ² /Vs), and excellent mechanical flexibility. Therefore, the high-performance transparent conductive oxide film based on CdO of the present invention is suitable for full-spectrum (visible light to near-infrared and even mid-infrared band) optoelectronic devices, including corresponding flexible devices. In addition, CdO-based transparent conductive oxides (TCOs) films also have significant advantages in terms of cost compared to In ₂ O ₃ -based films.

A first aspect of the present invention provides a high-conductivity, high-transmittance transparent conductive film.

Specifically, a transparent conductive film with high conductivity and high transmittance, the transparent conductive film is a CdO-based transparent conductive film, and the average transmittance of the transparent conductive film in the range of 400-2500 nm is greater than 70%, and the conductivity is greater than 3000S/cm.

Preferably, the average transmittance of the transparent conductive film in the range of 1000-2500 nm is greater than 80%.

Preferably, the electrical conductivity of the transparent conductive film is 3100-14000 S/cm, for example, 3100-13000 S/cm.

Preferably, the electron mobility of the transparent conductive film is >50 cm ² /Vs; further preferably, the electron mobility of the transparent conductive film is > 60 cm ² /Vs; more preferably, the electron mobility of the transparent conductive film >100cm ² /Vs.

Preferably, the transparent conductive film is doped with at least one of In, Ga, V or Ti.

Preferably, the thickness of the transparent conductive film does not exceed 130 nm; further preferably, the thickness of the transparent conductive film does not exceed 100 nm, more preferably 20-50 nm.

A second aspect of the present invention provides a method for preparing the above-mentioned high-conductivity, high-transmittance transparent conductive film.

Specifically, the above-mentioned preparation method of the transparent conductive film with high electrical conductivity and high transmittance includes the following steps:

The substrate is heated to 240-320° C., and a CdO target or a doped CdO target is used to coat the substrate to obtain the transparent conductive film. A working gas needs to be used during the coating process. Oxygen-free;

or,

The substrate is heated to 70-120° C., and a CdO target material and another oxide target material are used to coat the substrate to obtain the transparent conductive film. The coating process needs to use a working gas. The gas does not contain oxygen.

Preferably, the substrate is heated to 250-300° C., the substrate is coated with a CdO target or a doped CdO target, and then annealed to obtain the transparent conductive film.

Preferably, the temperature of the annealing treatment is 500-600° C., and the time of the annealing treatment is 5-10 minutes.

Preferably, the impurity element of the doped CdO target material is at least one of In, Ga, V or Ti, and the mole fraction of the impurity element is less than 5%.

Preferably, the another oxide target is an In ₂ O ₃ target or a Ga ₂ O ₃ target. Using a CdO target and another oxide target, coating the substrate, adjusting the power of each sputtering target gun, the obtained amorphous transparent conductive film is an oxide alloy (such as Cd _x In _1-x O _{1+ δ} ) film, where x is 0.1-0.55, and δ is greater than 0 and less than 0.5.

Preferably, the substrate is glass or flexible plastic, such as PET (polyethylene terephthalate).

Preferably, the coating process can use conventional physical or chemical vapor deposition methods, such as metal organic chemical vapor deposition (MOCVD), pulsed laser deposition (PLD), electron beam evaporation (EBE), plasma enhanced chemical vapor deposition (PECVD) ), atomized vapor deposition (mist-CVD), low pressure vapor deposition (LPCVD) and other methods for coating.

Preferably, the working gas is argon; the pressure of the working gas is 0.1-0.5Pa.

Preferably, before the substrate is heated, it is cleaned with acetone and deionization.

Preferably, the coating process is performed under a vacuum with a pressure less than 5×10 ^-4 Pa.

The third aspect of the present invention provides the application of the above-mentioned high-conductivity, high-transmittance transparent conductive film.

Application of the above-mentioned high-conductivity, high-transmittance transparent conductive film in the preparation of electronic products.

Preferably, the electronic products include flat panel displays, photovoltaic cells, thin film transistors, light detectors, gas sensors, light emitting diodes or smart windows.

With respect to the prior art, the beneficial effects of the present invention are as follows:

(1) The transparent conductive oxide film based on CdO of the present invention has high transmittance (average transmittance>70%, average transmittance at 1000-2500nm) in the full spectrum (visible light to near-infrared and even mid-infrared band, corresponding to 400-2500nm). rate can be >80%), high electrical conductivity (over 3000S/cm, such as ^3100-13000S /cm), further high electron mobility (>50cm2/Vs, even > ^100cm2 /Vs), and excellent mechanical Flexible. Therefore, the high-performance transparent conductive oxide film based on CdO of the present invention is suitable for full-spectrum (visible light to near-infrared and even mid-infrared band) optoelectronic devices, including corresponding flexible devices. In addition, CdO-based transparent conductive oxides (TCOs) films also have significant advantages in terms of cost compared to In ₂ O ₃ -based films.

(2) The preparation method of the present invention can obtain the above-mentioned high transmittance ( The average transmittance>70%, the average transmittance at 1000-2500nm can be>80%), high conductivity (over 3000S/cm, such as 3100-13000S/cm) transparent conductive oxide thin film.

Description of drawings

1 is a diagram of the transmittance of the transparent conductive films prepared in Example 1 and Comparative Examples 1-2 of the present invention to 400-3000 nm light waves;

2 is a diagram of the transmittance of the transparent conductive films prepared in Examples 3-5 of the present invention to 400-2500 nm light waves;

3 is a graph showing the transmittance of the transparent conductive films prepared in Examples 6-7 and Comparative Example 3 of the present invention to light waves of 400-3000 nm.

Detailed ways

In order to make those skilled in the art understand the technical solutions of the present invention more clearly, the following examples are now given for illustration. It should be noted that the following examples do not limit the protection scope of the present invention.

The raw materials, reagents or devices used in the following examples can be obtained from conventional commercial channels unless otherwise specified, or can be obtained by existing known methods.

Example 1: Preparation of Transparent Conductive Oxide Thin Films Using Undoped CdO Target Coating

A method for preparing a transparent conductive film with high electrical conductivity and high transmittance, comprising the following steps:

Take the glass substrate, first ultrasonically clean it with acetone for ₅ minutes, then ultrasonically clean it with ethanol for 5 minutes, and finally ultrasonically clean it with deionized water for 5 minutes. The bottom is placed on the chamber sample stage of the magnetron sputtering deposition system;

Evacuate the magnetron sputtering deposition chamber until the pressure in the chamber is less than 5×10 ^-4 Pa, then pass argon (Ar) into the magnetron sputtering deposition system through the gas pipeline and adjust the working pressure to about 0.5Pa ;

Heat the glass substrate to 250°C, close the substrate shutter, apply RF (radio frequency) to the CdO target (the working gas is pure Ar, the sputtering power density is 4W/cm ² ), and pre-sputter for 5 minutes to remove Contaminants on the surface of the CdO target, then open the substrate shutter, and use the CdO target to coat the substrate (the working gas is pure Ar, the working gas does not contain oxygen, and the sputtering power density is 4W/cm ² ), and the start In the film deposition, when the film thickness of the film is about 125 nm, the sputtering is stopped, and then the temperature is lowered to a room temperature of 20° C. to obtain a transparent conductive film with a thickness of 125 nm.

Comparative Example 1

Compared with Example 1, the substrate in Comparative Example 1 was not heated, the substrate in Comparative Example 1 was at room temperature of 20° C., and the rest of the process was the same as Example 1.

Comparative Example 2

Compared with Example 1, in the process of coating film on the substrate in Comparative Example 2, the working gas contained oxygen with a flow fraction of 1%, and the rest of the process was the same as that of Example 1.

Example 2

Compared with Example 1, in Example 2, the prepared transparent conductive film was also annealed at 500° C. in air for 6 minutes. The rest of the procedure is the same as in Example 1.

Example 3: Preparation of Transparent Conductive Oxide Thin Films Using Doped CdO Target Coating

Compared with Example 1, in Example 3, a doped CdO target material (wherein the impurity element can be any one of In, Ga, V and Ti, and the mole fraction of the impurity element is less than 5%) is used instead of Example 1. The thickness of the transparent conductive oxide film obtained is 100 nm (the thickness of the transparent conductive oxide film can be controlled by controlling the sputtering time), and the rest of the process is the same as that of Example 1.

Example 4

Compared with Example 3, the difference of Example 4 is that the sputtering time is shortened, so that the thickness of the prepared transparent conductive oxide film is 50 nm, and the rest of the process is the same as that of Example 3.

Example 5

Compared with Example 3, the difference of Example 5 is that the sputtering time is shortened, so that the thickness of the prepared transparent conductive oxide film is 25 nm, and the rest of the process is the same as that of Example 3.

Example 6: Preparation of Transparent Conductive Oxide Thin Films by Coating with CdO Target and Another Oxide Target

A method for preparing a transparent conductive film with high electrical conductivity and high transmittance, comprising the following steps:

Take the glass substrate, first ultrasonically clean it with acetone for ₅ minutes, then ultrasonically clean it with ethanol for 5 minutes, and finally ultrasonically clean it with deionized water for 5 minutes. The bottom is placed on the chamber sample stage of the magnetron sputtering deposition system;

Evacuate the magnetron sputtering deposition chamber until the pressure in the chamber is less than 5×10 ^-4 Pa, then pass argon (Ar) into the magnetron sputtering deposition system through the gas pipeline and adjust the working pressure to about 0.5Pa ;

Heat the glass substrate to 100°C, close the substrate shutter first, and apply RF (radio frequency) to the CdO target and another oxide target (In ₂ O ₃ target) (the working gas is pure Ar, the sputtering power is The density is 3W/cm ² ), pre-sputtering for 5 minutes to remove the contaminants on the surface of the CdO target and the In ₂ O ₃ target, then open the substrate shutter, and use the CdO target and the In ₂ O ₃ target on the lining Co-sputter coating on the bottom (the working gas is pure Ar, the working gas does not contain oxygen, and the sputtering power density is 3W/cm ² ), and the film deposition starts. When the film thickness is about 100 nm, the sputtering is stopped, and then the temperature is lowered. At room temperature of 20°C, a transparent conductive film was obtained.

Example 7

Compared with Example 6, the difference of Example 7 is that the sputtering time is shortened, so that the thickness of the prepared transparent conductive oxide film is 50 nm, and the rest of the process is the same as that of Example 6.

Comparative Example 3

Compared with Example 6, the substrate in Comparative Example 3 was not heated, the substrate in Comparative Example 3 was at room temperature of 20°C, and the rest of the process was the same as Example 6.

Sample effect test

1. Analyze the results of Example 1-2 and Comparative Example 1-2

The conductivity of the transparent conductive film prepared in Example 1 is 4210S/cm, the electron mobility is 173cm ² /Vs, and the electron concentration is 1.52×10 ²⁰ cm ³ ; the conductivity of the transparent conductive film prepared in Example 2 is 3370S /cm, the electron mobility was 234 cm ² /Vs, and the electron concentration was 9×10 ¹⁹ cm ³ . The conductivity of the transparent conductive film prepared in Comparative Example 1 is 2610 S/cm, the electron mobility is 62 cm ² /Vs, and the electron concentration is 2.6×10 ²⁰ cm ³ ; the conductivity of the transparent conductive film prepared in Comparative Example 2 is 560 S /cm, the electron mobility is 67 cm ² /Vs, and the electron concentration is 5.2×10 ¹⁹ cm ³

Fig. 1 is the transmittance diagram of the transparent conductive film made by Example 1 and Comparative Examples 1-2 of the present invention to 400-3000nm light waves; It can be seen that the transmittance of the transparent conductive film prepared in Example 1 to light waves with a wavelength of 400-2500 nm is higher than that in Comparative Examples 1-2, especially in the wavelength range of 1000-2500 nm, the transparent conductive film prepared in Example 1 The transmittance of the transparent conductive film to light waves is obviously better than that of Comparative Examples 1-2, and the average transmittance of the transparent conductive film prepared in Example 1 to light waves of 400-2500 nm exceeds 80%. It can be seen that the substrate temperature and whether oxygen is contained in the working gas have a significant impact on the light wave transmittance of the prepared transparent conductive film.

In addition, the light wave transmittance of the transparent conductive film prepared in Example 2 is increased by about 3% compared with Example 1, and it can be seen that the annealing treatment helps to further improve the average transmittance for 400-2500 nm light waves.

2. Analyze the results of Examples 3-5

The electrical conductivity of the transparent conductive film prepared in Example 3 is 13392S/cm, the electron mobility is 110cm ² /Vs, the electron concentration is 7.6×10 ²⁰ cm ³ , and the sheet resistance (Rs) is about 7.5Ω/€; Example The electrical conductivity, electron mobility and electron concentration of the transparent conductive film prepared in 4-5 are the same as in Example 3; the sheet resistance (Rs) of the transparent conductive film prepared in Example 4-5 is respectively about 15Ω/€, 30Ω /€.

Figure 2 is a diagram of the transmittance of the transparent conductive film made in Example 3-5 of the present invention to 400-2500nm light waves; from Figure 2 (the abscissa "Wavelength" in Figure 2 represents the wavelength, and the ordinate "T" represents the transmittance) It can be seen that the transparent conductive film of Example 5 is relatively thin, and has the highest average transmittance for 400-2500 nm light waves, and the transmittance for 1000-2500 nm light waves is close to 90%. It can be seen that the film thickness has an important influence on the light wave transmittance of the transparent conductive film.

3. Analyze the results of Examples 6-7 and Comparative Example 3

The electrical conductivity of the transparent conductive film prepared in Example 6 is 3114S/cm, the electron mobility is 54cm ² /Vs, the electron concentration is 3.6×10 ²⁰ cm ³ , and the sheet resistance (Rs) is about 32Ω/€; Example 7 The electrical conductivity of the prepared transparent conductive film is 3114 S/cm, the electron mobility is 54 cm ² /Vs, the electron concentration is 3.6×10 ²⁰ cm ³ , and the sheet resistance (Rs) is about 64Ω/€. The electrical conductivity of the transparent conductive film prepared in Comparative Example 3 was 2950 S/cm, the electron mobility was 42 cm ² /Vs, the electron concentration was 4.38×10 ²⁰ cm ³ , and the sheet resistance (Rs) was about 34Ω/€.

Figure 3 is a diagram of the transmittance of the transparent conductive films prepared in Examples 6-7 and Comparative Example 3 to 400-3000 nm light waves, from Figure 3 (the abscissa "Wavelength" in Figure 3 represents the wavelength, and the ordinate "T" It can be seen that the average transmittance of the transparent conductive film prepared in Example 6 to 400-2500nm light waves is greater than 70%, and the average transmittance of the transparent conductive film prepared in Example 6 to 400-2500nm light waves is greater than 80% %.

If the glass substrate in Example 6 is replaced by a PET substrate, the obtained transparent conductive film has the same optoelectronic properties as Example 6, and also has flexibility.

Application example

A photodetector, comprising the transparent conductive film prepared in Example 1.

In addition, it should be noted that within the scope of protection of the present invention, a transparent conductive film with similar effect can also be obtained by changing some process parameters, such as the heating temperature of the substrate.

Claims (10)

1. The transparent conductive film is characterized in that the transparent conductive film is a CdO-based transparent conductive film, the average transmittance of the transparent conductive film in the range of 400-2500nm is more than 70%, and the conductivity of the transparent conductive film is more than 3000S/cm.

2. The transparent conductive film as claimed in claim 1, wherein the transparent conductive film has an average transmittance of more than 80% in the range of 1000-2500 nm.

3. The transparent conductive film as claimed in claim 1, wherein the conductivity of the transparent conductive film is 3100-.

4. The transparent conductive film according to claim 1, wherein the transparent conductive film has an electron mobility>50cm²/Vs。

5. The transparent conductive film according to claim 1, wherein the transparent conductive film is doped with at least one of In, Ga, V, or Ti.

6. The transparent conductive film according to claim 1, wherein the thickness of the transparent conductive film is not more than 130 nm.

7. The method for preparing a transparent conductive film according to any one of claims 1 to 6, comprising the steps of:

heating the substrate to 240-320 ℃, and coating a film on the substrate by using a CdO target or a doped CdO target to prepare the transparent conductive film, wherein working gas is required to be used in the film coating process, and oxygen is not contained in the working gas;

or the like, or, alternatively,

heating the substrate to 70-120 ℃, and coating a film on the substrate by using the CdO target and another oxide target to prepare the transparent conductive film, wherein working gas is required to be used in the film coating process, and the working gas does not contain oxygen.

8. The method as claimed in claim 7, wherein the substrate is heated to 300 ℃ and then coated with CdO target or CdO-doped target, followed by annealing to obtain the transparent conductive film.

9. The method as claimed in claim 8, wherein the temperature of the annealing treatment is 500-600 ℃, and the time of the annealing treatment is 5-10 minutes; the impurity element of the doped CdO target material is at least one of In, Ga, V or Ti.

10. Use of the transparent conductive film of any one of claims 1-6 for the preparation of electronic products.

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