CN117070895A - Ultra-low refractive index film, device and manufacturing method thereof - Google Patents

Abstract

The invention discloses an ultralow refractive index optical film, and belongs to the field of optical films. The ultra-low refractive index film is obtained through magnetron co-sputtering and selective chemical etching, and any ultra-low refractive index film with the refractive index of 1.1-1.46 can be accurately prepared through the method; the prepared film has good uniformity, the thickness and equivalent refractive index of the film layer with ultra-low refractive index can be precisely controlled by simply controlling the sputtering power proportion and the sputtering time of the target material in the sputtering stage, and the preparation process is suitable for large-area batch production and is expected to be widely applied to products such as solar batteries, LED illumination, display panels, sensors and the like.

Description

Ultra-low refractive index film, device and manufacturing method thereof

Technical Field

The invention belongs to the field of optical films, and particularly relates to an ultra-low refractive index film, a device and a manufacturing method thereof.

Background

The low refractive index film is a material widely applied in the technical field of photoelectrons. With the upgrade of products in the application fields of photovoltaics, illumination, display panels, sensors and the like, the requirements on optical elements/optical devices are also increasing. The low refractive index film can reduce the reflectivity of light, thereby improving the transmittance, and making the light easier to pass through the material, which makes the film very suitable for solar panels, liquid crystal displays and other applications requiring high transmittance, and helps to improve the performance of the optical device; in imaging systems such as lenses and lenses, low refractive index films have the ability to reduce scattering and distortion, thereby improving imaging quality.

However, the availability of low refractive index materials in nature is extremely limited, magnesium fluoride, the lowest refractive index material in the visible band in nature, has a refractive index of 1.38, whereas empirically, ultra low refractive index materials having a refractive index of less than 1.15 are required for the production of wide-angle broadband anti-reflection coatings.

Previous studies have shown that the introduction of nanoscale voids into a material is one possible way to reduce the refractive index of the material, with which various methods of preparing ultra-low refractive index films have been developed. For example, grazing incidence deposition is an effective method for preparing a nano columnar ultra-low refractive index film, the effective refractive index can reach n=1.05, but the quality of the deposited film is unstable, and the difficulty in obtaining a uniform film on a large-area substrate is a defect of the method. Immersing the film in deionized water for chemical reaction to obtain grass-like alumina is also an effective method for obtaining the film with ultralow refractive index, but the fragile mechanical property of the grass-like nano structure makes the film prepared by the process more suitable for the inner surface of a lens of an optical system.

Nanoporous films prepared by sacrificial induced pore-forming methods have also been widely studied. Sol-gel processing methods based on this concept can produce nanoporous films that are more suitable for industrial applications than nanopillar films. However, sol-gel processing techniques still suffer from drawbacks such as difficulty in controlling film thickness and poor surface uniformity of the resulting films.

Disclosure of Invention

The invention provides an ultralow refractive index film and a preparation method thereof, wherein the method can prepare the ultralow refractive index film with controllable refractive index by utilizing the magnetron radio frequency co-sputtering and selective chemical etching technology, the refractive index can be accurately regulated and controlled to prepare in the range of 1.1-1.46, the thickness of the prepared film is stable and controllable, and the repeatability of the preparation process is high. In particular, the ultra-low refractive index film with the lowest equivalent refractive index of n=1.1 can be prepared, and the preparation process of the ultra-low refractive index film is simple and is suitable for large-area and batch production.

The invention provides the following technical scheme:

an ultralow refractive index film comprises a substrate and a silicon oxide film arranged on the substrate, wherein the silicon oxide film is a film with a uniform void structure.

The substrate may be any of a variety of existing substrate materials, or may be a specific surface of a device or component, etc.

Preferably, the nanostructured ultra-low refractive index film layer is a silica nanostructured layer.

As a further preferred aspect, the uniform void structure within the silicon oxide film is a network of nanopores. In actual use, the air is in the void structure.

The pore size in the silicon oxide film is 100nm, and is mainly determined by the sputtering power ratio of co-sputtering.

Preferably, the silicon oxide film is prepared by the following method: preparing a silicon dioxide-aluminum oxide composite film on a substrate by adopting magnetron radio frequency co-sputtering; and then etching and removing the alumina to obtain the silicon oxide film with the uniform air gap structure.

The etching may be chemical etching, for example, phosphoric acid solution may be used.

Preferably, the physical thickness and the equivalent refractive index of the silicon oxide film are effectively controlled by controlling the sputtering power (ratio) and the sputtering time of the aluminum target and the silicon target in sputtering.

Preferably, the silicon dioxide-aluminum oxide composite film is prepared by adopting a mode of co-sputtering a silicon target material and an aluminum target material and introducing oxygen for reaction co-sputtering. Preferably, the silicon dioxide-aluminum oxide composite film can be etched by using a phosphoric acid solution heated by a water bath to obtain the nano-structure ultra-low refractive index film layer structure, and the temperature for heating by the water bath can be set to be 40-60 ℃ (preferably 50 ℃), and the etching time is 10-25 min (preferably 15 min).

Preferably, the ultra-low refractive index film has a refractive index in the range of 1.1 to 1.46.

Preferably, the nanostructured ultra-low refractive index film layer provides an equivalent film layer that matches the low refractive index film layer (preferably, the nanostructured ultra-low refractive index film layer has an equivalent refractive index of 1.1-1.46).

A wide-angle broadband antireflection device, wherein the silicon superoxide thin film according to any one of the above technical schemes is used as an outermost layer film.

In actual preparation, the equivalent refractive index of the ultra-low refractive index film is input into optimization software of a large-angle broadband antireflection device, the types and thicknesses of other layers of materials can be obtained, and if the thickness of the ultra-low refractive index film is also used as one of optimization parameters, the physical thickness of the ultra-low refractive index film is obtained simultaneously after optimization. Then the preparation of the wide-angle broadband anti-reflection device is carried out by adopting the existing method.

A method for preparing an ultra-low refractive index film, comprising: and preparing a composite film on the substrate by adopting magnetron radio frequency co-sputtering, and preparing the nano-structure ultralow refractive index film by wet etching the composite film.

Further, the preparation method of the ultra-low refractive index film according to any one of the above technical schemes comprises the following steps:

before preparation, determining the power ratio and the co-sputtering time of each target in the magnetron co-sputtering process according to the required equivalent refractive index and physical thickness;

the preparation process is as follows:

(1) Optionally, cleaning the substrate;

(2) Depositing a silicon dioxide-aluminum oxide composite film on a substrate by utilizing magnetron sputtering, and changing the composition ratio and thickness of the composite film by controlling the sputtering power ratio and the sputtering time between two targets;

(3) And (3) carrying out selective chemical solution etching on the composite film to finally obtain the nanostructure ultra-low refractive index film layer.

Further, a method for preparing the ultra-low refractive index film according to any one of the above claims, comprising:

(1) Optionally, the substrate is cleaned: putting the substrate into an acetone solution for ultrasonic treatment, and then cleaning the substrate by ethanol; then putting the substrate into ethanol solution for ultrasonic treatment, and then cleaning the substrate by deionized water; finally, putting the substrate into deionized water for ultrasonic treatment, and then cleaning the substrate again by using the deionized water;

(2) The magnetron sputtering is adopted to deposit a composite film on a substrate by utilizing the co-sputtering, and the component ratio and the thickness of the composite film are changed by controlling the sputtering power ratio and the sputtering time between two targets

(3) And (3) carrying out selective chemical solution etching on the composite film to finally obtain the nanostructure ultra-low refractive index film layer.

Taking a nano-structure silicon dioxide film as an example, the preparation steps of the low refractive index film of the invention during actual processing are as follows:

(1) And cleaning the substrate by adopting solutions such as ethanol, acetone, ethanol diethyl ether and the like.

(2) Depositing a silicon dioxide-aluminum oxide composite film on a substrate by adopting magnetron co-sputtering

(3) And placing the substrate deposited with the silicon dioxide-aluminum oxide composite film in a heated dephosphorization acid solution for etching for 15 minutes, taking out, washing with deionized water and isopropanol successively, and finally drying with nitrogen.

In the preparation method, the solution adopted by the chemical solution etching is phosphoric acid solution.

A preparation method of a large-angle broadband anti-reflection device comprises the following steps:

obtaining parameters of each layer by using optimization software;

processing each layer of film by using the existing film preparation method;

finally:

(i) Depositing a silicon dioxide-aluminum oxide composite film on the surface of the prepared film by utilizing magnetron co-sputtering, and changing the composition ratio and thickness of the composite film by controlling the sputtering power ratio and the sputtering time between two targets;

(ii) And (3) carrying out selective chemical solution etching on the composite film to finally obtain the wide-angle broadband anti-reflection device with the nano-structure ultra-low refractive index film layer.

The invention utilizes the chemical reaction of phosphoric acid solution and alumina to selectively etch alumina component in the silica-alumina composite film, thereby preparing the nano-structure silica film with ultralow refractive index. The specific process is that after the silicon dioxide-aluminum oxide composite film is immersed in a hot phosphoric acid solution, aluminum oxide components in the film are etched by phosphoric acid to leave nano-sized holes, the silicon dioxide components which do not react with the hot phosphoric acid mutually form a net structure, a silicon dioxide ultralow refractive index film layer with a nano-hole structure is prepared, then the transmittance spectrum of a substrate coated with the porous silicon dioxide film is measured, and the equivalent refractive index and the physical thickness of the prepared porous silicon dioxide film can be fitted through a spectrometry.

The nano-pore silica film layer with the ultralow refractive index can realize effective regulation and control of the physical thickness and the equivalent refractive index of the nano film layer by controlling the sputtering power and the sputtering time of an aluminum target and a silicon target in sputtering.

According to the requirement of the target film on the refractive index, the sputtering power of the aluminum target can be fixed to a certain higher value during co-sputtering, the sputtering power of the silicon target is set to a certain lower value, the power determines the equivalent refractive index of the nano-pore silica film after phosphoric acid solution etching, the sputtering time is set to a certain value of 0-10h, and the physical thickness of the nano-pore silica film after phosphoric acid solution etching is determined by the sputtering time and the sputtering power together. The sputtering power of the aluminum target and the silicon target has a certain difference in different equipment, and the factors such as the size of a cavity of the equipment, the size of a target material and the like need to be considered, so that the sputtering power can be adjusted according to specific situations. Before actual preparation, the relation between the sputtering power (ratio) of the aluminum target and the silicon target corresponding to specific equipment and the equivalent refractive index and the physical thickness of the silicon dioxide film can be obtained through limited experiments; and further guiding the subsequent actual needs and actual preparation according to the relation.

The invention has no limitation on the substrate material, wherein the substrate can be selected from glass materials such as K9, fused quartz, float glass and the like, semiconductor materials such as silicon wafers, germanium wafers and the like, and organic polymer materials such as organic glass (acrylic, PMMA, polymethyl methacrylate and the like) and the like which are not easy to be corroded by acid. The ultra-low refractive index film can be directly prepared on a blank substrate, can be combined with the existing multilayer anti-reflection film, and can be prepared on the existing multilayer anti-reflection film, and the equivalent refractive index obtained by fitting is substituted into the anti-reflection film design to form the composite anti-reflection film of the multilayer film and the ultra-low refractive index film.

In the invention, the component ratio of silicon dioxide and aluminum oxide in the prepared composite film can be changed by changing the ratio of the power of the silicon target and the power of the aluminum target in the magnetic control co-sputtering, and the thickness of the prepared composite film can be changed by controlling the deposition time. Immersing the composite film into phosphoric acid solution for etching, wherein the alumina component in the composite film can be completely etched, and the silica component which does not react with the phosphoric acid solution is recombined into a network structure with nano holes, so that the prepared nano hole silica film has different porosities according to the proportion of the alumina component in the composite film, and the larger the porosity is, the lower the equivalent refractive index of the film is. Compared with the composite film before etching, the thickness of the film after etching can be reduced according to the component content of alumina in the composite film before etching, so that the prepared ultralow refractive index film with any thickness and any refractive index within the range of 1.1-1.46 can be accurately controlled by calibrating the refractive index and thickness of the film.

The film prepared by the method has good uniformity based on a co-sputtering film deposition technology and a simple and rapid solution selective etching method, the thickness and equivalent refractive index of the film with the ultra-low refractive index can be precisely controlled by simply controlling the sputtering power proportion and the sputtering time of the target material in the sputtering stage, and the prepared film with the ultra-low refractive index is suitable for large-area batch production and is expected to be widely applied to products such as solar cells, LED illumination, display panels, sensors and the like.

Drawings

FIG. 1 is a schematic diagram of an ultralow refractive index film according to the present invention, wherein 1 represents an ultralow refractive index film layer and 2 represents a substrate;

FIG. 2 is a flow chart of the preparation of an ultra-low refractive index film according to the present invention;

FIG. 3 is a graph showing the fitting result of test spectrum and theoretical spectrum for obtaining the equivalent refractive index and thickness of the ultra-low refractive index film in example 1, wherein the substrate is K9, the sputtering power of the silicon target is 50W, the sputtering power of the aluminum target is 350W, the deposition time is 1.5h, the corrosion time of the deposited composite film in phosphoric acid solution is 15min, and the graph is the transmission spectrum of the K9 substrate after the ultra-low refractive index film is deposited on the actually measured single side and the simulated K9 substrate coated with the film with the 87nm average refractive index of 1.3 on the single side in the 380nm-780nm wave band;

FIG. 4 is a graph showing the variation of the refractive index of the porous silica film fitted according to the present invention with the sputtering power of the silicon target in the sputtering deposition stage, wherein the sputtering power of the fixed aluminum target is 350W, and the sputtering power of the silicon target is adjusted within the range of 43W-80W;

FIG. 5 is a graph showing the transmittance curve of a blank K9 substrate and a double-sided deposited ultra-low refractive index film after the deposition, wherein the anti-reflection effect of the ultra-low refractive index film of the embodiment 3 of the invention on the visible band of 380nm-780nm is shown when the film is applied as the anti-reflection film, wherein the substrate is K9, the sputtering power of a silicon target in the sputtering deposition stage is 48W, the sputtering power of an aluminum target is 350W, the deposition time is 1.5h, and the corrosion time of the deposited composite film in a phosphoric acid solution is 15 min;

FIG. 6 is a surface and cross-sectional topography of a porous silica structure in an ultra-low refractive index film according to the present invention;

FIG. 7 shows the reflection spectra of the composite antireflection film of example 4 of the present invention combined with the conventional multilayer antireflection film at different incident angles.

Detailed Description

The following description of the embodiments of the present invention will be made more complete and clear by reference to the figures and detailed description, wherein it is to be understood that the embodiments described are merely some, but not all, of the embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The present invention will be described in detail with reference to the accompanying drawings.

As shown in fig. 1, the optical film includes a film layer 1 and a substrate 2, the film layer 1 is attached to the substrate 2 and forms an overlapped structure, and the constituent material of the film layer 1 is silica having a porous structure.

The material of the substrate 2 is not limited, and the substrate may be selected from glass materials such as K9, fused silica, float glass, semiconductor materials such as silicon wafer and germanium wafer, and plastic materials such as acrylic glass which are not easily reacted with acid.

The preparation method of the low refractive index optical film, as shown in fig. 2, comprises the following steps of:

(1) Alternatively, the substrate is washed with a solution of ethanol, acetone, ethyl alcohol, or the like.

(2) Depositing a silicon dioxide-aluminum oxide composite film on a substrate by adopting magnetron co-sputtering

(3) And placing the substrate deposited with the silicon dioxide-aluminum oxide composite film in a heated phosphoric acid solution for etching for a period of time (5-30 min), taking out, sequentially flushing with deionized water and isopropanol, and finally drying with nitrogen.

Example 1

The preparation method comprises the following steps:

(1) Cleaning a substrate: when the substrate is cleaned, the K9 substrate can be wiped by ethanol/diethyl ether mixed solution, and the substrate can be cleaned by a solution ultrasonic method; for example, the K9 substrate can be placed in an acetone solution for ultrasonic treatment, and then the substrate is cleaned by ethanol removal; then putting the substrate into ethanol solution for ultrasonic treatment, and then cleaning the substrate by deionized water; finally, putting the substrate into deionized water for ultrasonic treatment, and then cleaning the substrate again by using the deionized water.

(2) Preparing a silicon dioxide-aluminum oxide composite film on a K9 substrate by utilizing magnetron co-sputtering; the sputtering power of the silicon target is 50W; the sputtering power of the aluminum target is 350W; the film deposition temperature is room temperature and the deposition time is 1.5h.

(3) And wiping the sample plated with the silicon dioxide-aluminum oxide composite film by using an ethanol/diethyl ether mixed solution, putting the sample into a phosphoric acid solution with the temperature of 50 ℃ for etching for 15min, taking out the sample, washing the sample by using deionized water and isopropanol in sequence, and drying the sample by using nitrogen.

(4) The single-sided reflectivity of the porous silica film is calculated by using a cary7000 spectrophotometric machine to measure, the result is imported into film design software, the thickness and the equivalent refractive index of the porous silica film are fitted by utilizing a spectrometry method, and the fitting result proves that the equivalent refractive index of the prepared porous silica film with the ultralow refractive index is 1.3, as shown in figure 3.

Example 2

Based on the preparation flow of example 1, by fixing the sputtering power of the aluminum target to 350W and gradually changing the sputtering power of the silicon target, composite films with different silicon dioxide and aluminum oxide content ratios can be obtained, and after the composite films are etched, an ultralow refractive index film with controllable refractive index (n=1.1-1.46) can be obtained, and the relation between the sputtering power of the silicon target and the refractive index of the finally obtained porous silicon dioxide film is shown in fig. 4.

Example 3

Based on the preparation flow of the embodiment 2, the preparation process of the ultra-low refractive index film is controlled: the sputtering power of the silicon target in the sputtering deposition stage is 48W, the sputtering power of the aluminum target is 350W, the deposition time is 1.5h, and the corrosion time of the deposited composite film in the phosphoric acid solution is 15min. An ultra-low refractive index film with an equivalent refractive index n=1.23 can be obtained for single wavelength antireflection of K9 substrates. The transmittance of the ultra-low refractive index film sample with the equivalent refractive index of n=1.23 and the transmittance of the blank K9 substrate are shown in fig. 5, and the transmittance of the ultra-low refractive index film layer of the K9 substrate in the visible waveband can be greatly improved.

The surface and cross-sectional morphology of the film were characterized using a scanning electron microscope, as shown in fig. 6, and the surface and cross-section of the ultra-low refractive index film exhibited good uniformity.

Example 4

The ultra-low refractive index film with the refractive index of 1.1 prepared by the invention is taken as the outermost layer film, and TiO is used ₂ And SiO ₂ The material is a multilayer antireflection film with the wave band of 400nm-1100nm, and the structure is as follows: k9 substrate|sio ₂ (36.9nm)|TiO ₂ (10.0nm)|SiO ₂ (65.9nm)|TiO ₂ (24.2nm)|SiO ₂ (42.7nm)|TiO ₂ (46.4nm)|SiO ₂ (20.0nm)|TiO ₂ (64.2nm)|SiO ₂ (26.8nm)|TiO ₂ (30.8nm)|SiO ₂ (112.2 nm) porous SiO ₂ (112.2 nm), adopting electron beam evaporation to deposit each film layer and using the process of the invention to prepare the outermost film to realize the large-angle broadband antireflection effect, wherein the antireflection effect at each incident angle is shown in figure 7, and the average reflectivity of 6 DEG, 30 DEG and 60 DEG is 0.11%,0.19% and 2.41% in the visible light and near infrared light wave bands of 400-1100 nm.

Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.

The invention is not limited to the specific embodiments described above. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, as well as to any novel one, or any novel combination, of the steps of the method or process disclosed.

Claims (9)

1. An ultra-low refractive index film is characterized by comprising a substrate and a silicon oxide film arranged on the substrate, wherein the silicon oxide film is a film with a uniform void structure.

2. The ultra-low refractive index film according to claim 1, wherein the pore size is 100nm.

3. The ultra-low refractive index film according to claim 1, wherein the silicon oxide film is prepared by the following method: preparing a silicon dioxide-aluminum oxide composite film on a substrate by adopting magnetron radio frequency co-sputtering; and then etching and removing the alumina to obtain the silicon oxide film with the uniform air gap structure.

4. The ultra-low refractive index thin film according to claim 3, wherein effective control of physical thickness and equivalent refractive index of the silicon oxide thin film is achieved by controlling sputtering power and sputtering time of the aluminum target and the silicon target during sputtering.

5. The ultra-low refractive index film according to claim 1, wherein said uniform void structure is a network of nanopores.

6. The ultra-low refractive index film according to claim 1, wherein the refractive index is in the range of 1.1 to 1.46.

7. A wide-angle broadband antireflection device, characterized in that the silicon oxide film according to any one of claims 1 to 6 is used as an outermost film.

8. A method for producing the ultra-low refractive index film according to any one of claims 1 to 6, comprising:

before preparation, determining the power ratio and the co-sputtering time of each target in the magnetron co-sputtering process according to the required equivalent refractive index and physical thickness;

the preparation process is as follows:

(1) Optionally, cleaning the substrate;

(2) Depositing a silicon dioxide-aluminum oxide composite film on a substrate by utilizing magnetron sputtering, and changing the composition ratio and thickness of the composite film by controlling the sputtering power ratio and the sputtering time between two targets;

(3) And (3) carrying out selective chemical solution etching on the composite film to finally obtain the nanostructure ultra-low refractive index film layer.

9. The method for preparing a film with ultra-low refractive index according to claim 8, wherein the solution used for chemical solution etching is phosphoric acid solution.