Preparation method of intermediate infrared transparent compatible electromagnetic shielding film

Abstract

The invention relates to a preparation method of a mid-infrared transparent compatible electromagnetic shielding film, and aims to solve the problem that conventional transparent conductive oxide has good transmittance in a visible light wave band but has poor transmittance in mid-infrared light. The preparation method comprises the following steps: 1, using an indium oxide target material and a cerium-doped indium oxide target material; 2, heating the sapphire substrate, controlling the radio-frequency power supply power of the indium oxide target material to be 60W and the radio-frequency power supply power of the cerium-doped indium oxide target material to be 50-70W, and carrying out magnetron sputtering coating treatment to obtain an In2O3: Ce film; and thirdly, annealing treatment is conducted at the temperature ranging from 280 DEG C to 300 DEG C. The In2O3: Ce thin film with high conductivity of 2422S / cm is prepared by selecting doping elements, controlling the doping content, proper substrate temperature, proper oxygen content and proper annealing process, the In2O3: Ce thin film has high transmittance in mid-infrared rays, and the average transmittance of 2-5 microns is not lower than 76%.

Description

TECHNICAL FIELD

[0001] The present application relates to the application of mid-infrared transparent (3-5 μm) transparent conductive oxide (TCO) materials and continuous thin films in the field of electromagnetic shielding, in particular, a method for preparing cerium-doped indium oxide thin films with excellent photoelectric properties by magnetron sputtering. BACKGROUND

[0002] With the rapid development of communication technology, the widespread use of electronic equipment, and the increasing use of military electronic countermeasures and electromagnetic weapons, the electromagnetic environment in the civil and defense fields is becoming increasingly complex. Various types of electronic equipment may be subject to electromagnetic interference (EMI), which can cause performance degradation or even complete failure. Long-term exposure to electromagnetic radiation can also pose potential risks to human health. At the same time, with the increasing demand for infrared imaging technology, such as night vision equipment and medical infrared imaging equipment, aircraft infrared window protection, infrared sensor protection, vehicle infrared sensing, and the development of emerging technologies such as virtual and augmented reality, there is an urgent need to expand the optical transmission range to the mid-infrared (3-5 μm) region. Therefore, it is both urgent and necessary to study effective electromagnetic shielding materials and technologies, especially in the mid-infrared region. The commonly used mesh structure has imaging quality problems when used for infrared transparent electromagnetic shielding, and the adhesion to the substrate is poor, which can easily fall off. Other electromagnetic shielding films such as ultra-thin metal films and metal nanowires have very poor infrared transmittance. Carbon materials and wave-absorbing materials require a certain thickness to achieve certain electromagnetic shielding performance, and also have poor infrared transmittance. Continuous transparent conductive oxide materials have strong adhesion to the substrate and do not have imaging quality problems. Traditional oxides and doped materials such as tin-doped indium oxide, gallium-doped zinc oxide, and fluorine-doped tin oxide have poor compatibility between mid-infrared transmittance and conductivity, and are not suitable for mid-infrared transparent and compatible electromagnetic shielding. SUMMARY

[0003] The purpose of the present application is to solve the problem that conventional transparent conductive oxides have good transmittance in the visible light band, but poor transmittance in the mid-infrared region, which cannot meet the growing demand for mid-infrared transparent and compatible electromagnetic shielding optical windows. The present application provides a method for preparing a mid-infrared transparent and compatible electromagnetic shielding thin film.

[0004] The method for preparing a mid-infrared transparent and compatible electromagnetic shielding thin film according to the present application is implemented according to the following steps:

[0005] I. Cleaning of the substrate:

[0006] The sapphire substrate is ultrasonically cleaned to obtain a clean substrate, and indium oxide target material and cerium-doped indium oxide target material are used.

[0007] II. Preparation of In2O3:Ce film:

[0008] a. Place the clean substrate on the sample stage in the chamber of the magnetron sputtering device, install the indium oxide target and the cerium-doped indium oxide target, control the heating temperature of the sapphire substrate to be 110-150 DEG C, and vacuumize the chamber;

[0009] b. Control the Ar flow rate to be 20 sccm, the O2 flow rate to be 0.16-0.24 sccm, the gas pressure to be 0.3-0.5 Pa, the radio frequency power of the indium oxide target to be 60 W, and the radio frequency power of the cerium-doped indium oxide target to be 50-70 W, and perform magnetron sputtering film deposition treatment;

[0010] c. Stop heating the substrate, turn off the radio frequency power of the target, open the exhaust valve, and obtain the In2O3:Ce film;

[0011] III. Post-annealing treatment of the In2O3:Ce film:

[0012] Place the In2O3:Ce film into a quartz tube, vacuumize the quartz tube to obtain a vacuum-sealed quartz tube, and then place the quartz tube into an annealing furnace, vacuumize the quartz tube, and perform annealing treatment at a temperature of 280-300 DEG C, so as to obtain a mid-infrared transparent and compatible electromagnetic shielding film.

[0013] The In2O3:Ce film prepared by the method has excellent mid-infrared transmittance characteristics when used as an electromagnetic shielding film.

[0014] The current transparent conductive film focuses on the light transmittance in the visible light band, and the existing commercially available or researched transparent conductive film represented by tin-doped indium oxide has a very poor infrared transmittance due to the excessively high carrier concentration. Most of the researches on infrared films are in the near-infrared band (0.78-2.5 μm), and the application fields such as medical infrared imaging, night vision helmet, aircraft infrared window, and vehicle infrared sensing need to widen the light transmittance range to the important atmospheric infrared window band of the mid-infrared band (3-5 μm), and the traditional transparent conductive film material and preparation process cannot meet the requirement. By controlling the selection and proportion of the doping elements, the deposition temperature, the oxygen content, and the annealing process, the present application finally prepares a high-mobility infrared transparent conductive film by appropriately reducing the carrier concentration, so that the infrared transparent conductive film is compatible with the mid-infrared transmittance and the wide-band electromagnetic shielding.

[0015] By selecting the doping elements and controlling the doping content, by using a suitable substrate temperature, oxygen content, and suitable annealing process, and by combining the magnetron sputtering and the annealing furnace annealing processes, the present application prepares an In2O3:Ce film with a high conductivity of 2422 S / cm, and the mobility is as high as 103 cm 2 / V·s, while the carrier concentration is suitable at 1.47×10 20 / cm 3 It exhibits high transmittance in the mid-infrared range, with a transmittance of no less than 73% at a wavelength of 4 μm and an average transmittance of no less than 76% at wavelengths of 2-5 μm. It achieves electromagnetic shielding performance of no less than 13 dB in the 5.4-18 GHz range. The high infrared transmittance combined with highly conductive In₂O₃:Ce thin films provides a new option for the fabrication of increasingly common infrared transparent electromagnetic shielding optical window films. Attached Figure Description

[0016] Figure 1 The electromagnetic shielding performance test diagrams of the mid-infrared transparent compatible electromagnetic shielding film obtained in the example are shown in (a) 5.4-8.2GHz, (b) 8.2-12.4GHz, (c) 11.9-18GHz bands, and (d) Fourier transform infrared transmission spectrum at 2-5μm.

[0017] Figure 2 (a) Conductivity test diagram of mid-infrared transparent compatible electromagnetic shielding films with different Ce doping contents obtained in the example, (b) Fourier transform infrared spectrum at 2-5 μm, (c) Conductivity test diagram of In2O3:Ce film with Ce doping content of 1.57% after 1 h of annealing at different temperatures, (d) Fourier transform infrared spectrum at 2-5 μm;

[0018] Figure 3 (a) Conductivity test diagram of mid-infrared transparent compatible electromagnetic shielding films obtained at different deposition temperatures in the examples; (b) Conductivity test diagram of In2O3:Ce films with different oxygen contents deposited at 110°C in the 2-5 μm Fourier transform infrared spectrum; (c) Conductivity test diagram of In2O3:Ce films deposited at 110°C in the 2-5 μm Fourier transform infrared spectrum.

[0019] Figure 4 As an example, the XRD (crystal structure) image of the (60W,60W)In2O3:Ce thin film was obtained after annealing at 300°C for 1 hour at a deposition temperature of 110°C and an oxygen content of 1.2%. Detailed Implementation

[0020] Specific Implementation Method 1: The preparation method of the infrared transparent compatible electromagnetic shielding film in this embodiment is carried out according to the following steps:

[0021] I. Substrate Cleaning:

[0022] The sapphire substrate was ultrasonically cleaned to obtain a clean substrate, using indium oxide target and cerium-doped indium oxide target.

[0023] II. Preparation of In2O3:Ce thin films:

[0024] a, place the clean substrate on the sample table in the chamber of the magnetron sputtering device, install the indium oxide target and the cerium-doped indium oxide target, control the substrate heating temperature to be 110-150℃, and vacuumize the chamber;

[0025] b, control the Ar flow rate to be 20sccm, the O2 flow rate to be 0.16-0.24sccm, the gas pressure to be 0.3-0.5Pa, the radio frequency power of the indium oxide target to be 60W, and the radio frequency power of the cerium-doped indium oxide target to be 50-70W, and perform magnetron sputtering film deposition treatment;

[0026] c, stop the substrate heating, turn off the radio frequency power of the target, open the exhaust valve, and obtain the In2O3:Ce film;

[0027] III. Post-annealing treatment of the In2O3:Ce film:

[0028] Place the In2O3:Ce film into a quartz tube, vacuumize the quartz tube to obtain a vacuum-sealed quartz tube, and then place the quartz tube into an annealing furnace, vacuumize the quartz tube, and perform annealing treatment at a temperature of 280-300℃, thereby obtaining a mid-infrared transparent and compatible electromagnetic shielding film.

[0029] Specific implementation method two: different from the specific implementation method one, the step one is to use sandpaper to polish the indium oxide target and the cerium-doped indium oxide target in advance.

[0030] Specific implementation method three: different from the specific implementation method one or two, the step one is that the mass fraction of CeO2 in the cerium-doped indium oxide target is 3%.

[0031] Specific implementation method four: different from any one of the specific implementation methods one to three, the step one is to sequentially place the sapphire substrate into acetone, alcohol, and deionized water for ultrasonic cleaning.

[0032] Specific implementation method five: different from any one of the specific implementation methods one to four, the step two is to control the radio frequency power of the indium oxide target to be 60W, and the radio frequency power of the cerium-doped indium oxide target to be 60W.

[0033] Specific implementation method six: different from any one of the specific implementation methods one to five, the step two is to perform pre-sputtering for 5-6min before the magnetron sputtering film deposition treatment.

[0034] Specific implementation method seven: different from any one of the specific implementation methods one to six, the step two is to obtain the In2O3:Ce film with a thickness of 50-100nm.

[0035] The thickness of the In2O3:Ce film in the specific implementation method should not exceed 100nm.

[0036] Eighth Embodiment: The difference between this embodiment and one of the first to seventh embodiments is that the temperature rising rate of the annealing furnace in step three is 10℃ / min.

[0037] Ninth Embodiment: The difference between this embodiment and one of the first to seventh embodiments is that the annealing treatment in step three is performed at a temperature of 300℃ for 1h.

[0038] Tenth Embodiment: The difference between this embodiment and one of the first to ninth embodiments is that the atomic ratio content of Ce in the mid-infrared transparent and compatible electromagnetic shielding film is 1.2At.%-3At.%.

[0039] Example: The preparation method of the mid-infrared transparent and compatible electromagnetic shielding film in this example is implemented according to the following steps:

[0040] I. Cleaning of the substrate:

[0041] Under the condition of ultrasonic power of 100W, the sapphire pieces with specifications of 34.9 mm × 15.8 mm, 22.9 mm × 10.2 mm and 15.8 mm × 7.9 mm (the above sizes are the sample sizes for testing different wave bands of electromagnetic shielding) are sequentially placed in acetone, alcohol and deionized water for cleaning for 15 min respectively, to obtain clean sapphire substrates, and the surface of the indium oxide target and the cerium-doped indium oxide target (CeO2 mass fraction of 3%) is polished for 2 min using fine sandpaper with a mesh size of 320;

[0042] II. Preparation of the In2O3:Ce film:

[0043] a. Place the clean substrate on the sample stage in the chamber of the magnetron sputtering equipment, install the indium oxide target and the cerium-doped indium oxide target, and set the target base distance and the rotation angle of the two targets to be the same, vacuumize the chamber to 3×10 -4 Pa, and control the substrate heating temperature to be 110℃;

[0044] b. Control the Ar flow rate to be 20sccm, the O2 flow rate to be 0.24sccm, the gas pressure to be 0.3Pa, control the radio frequency power of the indium oxide target to be 60W, and the radio frequency power of the cerium-doped indium oxide target to be 60W, perform pre-sputtering before opening the target shutter for formal film deposition, the pre-sputtering time is 5min, and then perform magnetron sputtering film deposition treatment for 13min;

[0045] c. Stop the substrate heating, turn off the radio frequency power of the target, open the exhaust valve, and exhaust to open the chamber, to obtain an In2O3:Ce film with a thickness of about 75nm;

[0046] III. Post-annealing treatment of the In2O3:Ce film:

[0047] In2O3:Ce thin film was put into a quartz tube, vacuumed to 3x10 -3 Pa, and then put into an annealing furnace, vacuumed to 0.5 Pa, and annealed at 300℃ for 1 h with a heating rate of 10℃ / min, to obtain a mid-infrared transparent and compatible electromagnetic shielding thin film.

[0048] Before studying the optimal oxygen content, Figure 2 (a-d)、 Figure 3 The deposition oxygen content of (a) and (b) is 0.8%.

[0049] Figure 1 (a-c) are the electromagnetic shielding performance of In2O3:Ce thin film samples after vacuum annealing at 300℃ for 1 h at 5.38-8.17 GHz, 8.2-12.4 GHz, and 11.9-18.0 GHz, respectively, reaching an electromagnetic shielding performance of 14.5 dB, 13.6 dB, and 13.0 dB, respectively, with an average electromagnetic shielding performance of no less than 13 dB, measured by a vector network analyzer. Figure 1 (d) is the Fourier infrared transmission spectrum of the In2O3:Ce thin film sample at 2-5 μm, with a transmission rate of no less than 73% at 4 μm and an average transmission rate of no less than 76% at 2-5 μm.

[0050] Figure 2 (a) and (b) are the electro-optic performance diagrams of In2O3:Ce thin films with different Ce doping contents. The change in the doping content is achieved by changing the power of the target material. The power values of the indium oxide target and the cerium-doped indium oxide target are: (60W, 0W), (60W, 10W), (60W, 30W), (60W, 60W), and (0W, 60W). The cerium doping atomic ratio At.%(Ce / Ce+In) content of the prepared In2O3:Ce thin film is 0, 0.49%, 1.04%, 1.57%, and 2.89%. Since the electrical properties of the In2O3:Ce thin film sample without heating or annealing are unstable, Figure 2 The samples in (a) and (b) were annealed at 300℃ in vacuum for 1 h. Through analysis of the electrical properties, it is known that increasing the cerium doping content can increase the carrier concentration, but too much cerium can cause ionized impurity scattering, resulting in a decrease in mobility. Therefore, the power of the indium oxide target is selected as 60W, and the power of the cerium-doped indium oxide target is selected as 60W. Figure 2 (c) and (d) are the electro-optic performance diagrams of the (60W, 60W) sample after vacuum annealing at different temperatures for 1 h. Annealing at 300℃ can reduce the carrier concentration and increase the mobility, ensuring the infrared transmission capability at 2-5 μm.

[0051] Figure 3(a), (b) are the electro-optical performance of In2O3:Ce thin film samples deposited at different temperatures. The carrier concentration decreases and the mobility increases with the increase of deposition temperature, which improves the transmittance of 2-5 pm. Therefore, 110 °C is selected as the deposition temperature. Figure 3 (c), (d) are the electro-optical performance of In2O3:Ce thin film samples deposited at 110 °C with different oxygen contents. The oxygen vacancy concentration and the valence state of cerium can be effectively changed by adjusting the oxygen content, which can effectively control the photoelectric performance. The optimal oxygen content of (60W, 60W) is around 1.2%.

[0052] Figure 4 For the In2O3:Ce thin film deposited at 110 °C with 1.2% oxygen content, the XRD pattern of the (60W, 60W) thin film after annealing at 300 °C for 1 h shows that the main component of the film is cubic indium oxide, and cerium does not exist as an independent phase but replaces In 3+ exists in the crystal structure.

Claims

1. A method for preparing a mid-infrared transparent and compatible electromagnetic shielding film, characterized in that The preparation method of the mid-infrared transparent compatible electromagnetic shielding film is realized according to the following steps: I. Cleaning of the substrate: The sapphire substrate is ultrasonically cleaned to obtain a clean substrate, and indium oxide target and cerium-doped indium oxide target are used; II. Preparation of the In2O3:Ce film: a. Place the clean substrate on the sample stage in the chamber of the magnetron sputtering equipment, install the indium oxide target and the cerium-doped indium oxide target, control the heating temperature of the sapphire substrate to be 110-150 DEG C, and vacuumize the chamber; b. Control the Ar flow rate to be 20 sccm, the O2 flow rate to be 0.16-0.24 sccm, the gas pressure to be 0.3-0.5 Pa, the radio frequency power of the indium oxide target to be 60 W, and the radio frequency power of the cerium-doped indium oxide target to be 50-70 W, and perform magnetron sputtering film deposition treatment; c. Stop heating the substrate, turn off the radio frequency power of the target, open the exhaust valve, and obtain the In2O3:Ce film; III. Post-annealing treatment of the In2O3:Ce film: Place the In2O3:Ce film in a quartz tube, vacuumize the quartz tube to obtain a vacuum-sealed quartz tube, and then place the quartz tube in an annealing furnace, vacuumize the annealing furnace, and perform annealing treatment at a temperature of 280-300 DEG C to obtain the mid-infrared transparent compatible electromagnetic shielding film.

2. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step I, the indium oxide target and the cerium-doped indium oxide target are respectively polished using sandpaper in advance.

3. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step I, the mass fraction of CeO2 in the cerium-doped indium oxide target is 3%.

4. The method of claim 1, wherein the transparent and compatible electromagnetic shielding film in mid-infrared region is prepared by the steps of In step I, the sapphire substrate is sequentially placed in acetone, alcohol and deionized water for ultrasonic cleaning.

5. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step II, the radio frequency power of the indium oxide target is controlled to be 60 W, and the radio frequency power of the cerium-doped indium oxide target is controlled to be 60 W.

6. The method of claim 1, wherein the transparent, compatible electromagnetic shielding film is a mid-infrared transparent, compatible electromagnetic shielding film. In step II, the magnetron sputtering film deposition treatment is preceded by 5-6 min of pre-sputtering.

7. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step II, the thickness of the obtained In2O3:Ce film is 50-100 nm.

8. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step III, the heating rate of the annealing furnace is controlled to be 10 DEG C / min.

9. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... In step III, the annealing treatment is performed at a temperature of 300 DEG C for 1 h.

10. The method for preparing a mid-infrared transparent compatible electromagnetic shielding film according to claim 1, characterized in that... The atomic ratio content of Ce in the mid-infrared transparent compatible electromagnetic shielding film is 1.2-3 At.%.

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