1. Main process technology of optical vacuum coating
Optical vacuum coating mainly adopts physical vapor deposition (PVD), chemical vapor deposition (CVD) and ion beam assisted deposition (IAD). Different processes are suitable for different types of film preparation and have unique technical advantages and limitations.
A. Physical Vapor Deposition (PVD)
Physical vapor deposition (PVD) is the most common optical coating method, including evaporation and sputtering.
1. Evaporation coating
Evaporation coating technology vaporizes the target by heating it, and then deposits the gas molecules onto the substrate surface to form a film in a vacuum environment. According to different heating methods, evaporation coating is divided into thermal evaporation and electron beam evaporation.
Thermal evaporation: Thermal evaporation coatings use resistance to heat the target, causing it to sublimate or melt into steam. Commonly used thermal evaporation materials are aluminum, silver, magnesium fluoride and so on. The method is simple and easy to operate, but it requires high temperature control, which is easy to introduce impurities due to overheating and affect the purity of the film.
Electron beam evaporation: Electron beam evaporation uses an electron gun to heat the target and bombards the surface of the target with high-energy electron beams to cause partial sublimation. The heating efficiency of electron beam evaporation is high, and it is suitable for coating materials with high melting point (such as metal oxides and fluoride). It is widely used in the preparation of high-quality optical films, such as anti-reflection films and anti-reflection films.
The advantage of evaporation coating is that the film structure is uniform, which is suitable for large-area optical coating. However, due to the weak adhesion of the film, it is usually used in low-demand environments.
2. Sputtering coating
Sputtering coating is a technique in which the atoms of the material are removed from the surface of the target and deposited onto the substrate by bombarding the target with high-energy particles. The main sputtering technologies include DC sputtering, RF sputtering and magnetron sputtering.
Dc sputtering: The use of direct current electric field to bombard the target plasma, suitable for conductive materials, but not for insulating materials. Dc sputtering has low cost, but relatively low efficiency.
Radio-frequency sputtering: plasma bombarded by high-frequency electric fields can be used for conductive materials and insulating materials. Rf sputtering has good film uniformity and adhesion, which is suitable for high quality optical film preparation.
Magnetron sputtering: A magnetic field is installed near the target to restrain the movement of electrons, increase the plasma density, and improve the deposition rate. Magnetron sputtering is often used for the fine preparation of multilayer films, such as applications in high reflectors and filter films.
Sputtering coating has good film density and adhesion, which is suitable for high quality and high stability of optical film preparation.
B. Chemical Vapor Deposition (CVD)
Chemical vapor deposition (CVD) is a chemical reaction-based film deposition technique that converts gaseous materials into solid films through chemical reactions. Common CVD technologies include low-voltage CVD (LPCVD) and plasma enhanced CVD (PECVD).
Low pressure CVD (LPCVD) : Chemical vapor deposition at low pressure is suitable for the preparation of uniform and dense films. LPCVD is commonly used to deposit silicon oxide and silicon nitride films, and is widely used in optical filters and wave-plate films.
Plasma Enhanced CVD (PECVD) : The reaction gas is excited by plasma so that it is deposited on the substrate at a lower temperature. The PECVD process enables the preparation of high-quality film layers at lower temperatures and is suitable for the preparation of films on heat-sensitive substrates, such as optical film layers in display screens.
CVD technology is mainly used in optical coating for the preparation of dielectric films, especially high-quality anti-reflection and wave plate films.
C. Ion Beam Assisted Deposition (IAD)
Ion beam assisted deposition (IAD) is the addition of an ion beam during evaporation or sputtering deposition to enhance the density and adhesion of the film. The ion beam can change the surface energy and structure of the film, making the film more dense and improving its mechanical properties.
IAD technology has important applications in optical films that require high adhesion and high durability, such as highly reflective and damage resistant films for laser optical components.
2. Optical vacuum coating material
Different coating materials give different optical properties and physical properties of the film. Common coating materials are divided into metal materials, dielectric materials and composite materials.
A. Metal materials
Metallic materials have high reflectivity and good electrical conductivity, and are often used in reflective films and bandpass filters.
Aluminum: High reflectivity and low cost, suitable for visible light and infrared reflective films.
Silver: Extremely high reflectivity, excellent performance in near-infrared and visible wavelengths, often used in high-precision mirrors.
Gold: Excellent performance in the infrared region, often used in infrared optical devices.
The optical properties of metal films lie in their high reflectance and good electrical conductivity, but at the same time, their high absorption rate limits their application in transparent films.
B. Medium material
Dielectric materials are mainly used in optical coatings for anti-reflection and filter films. Common dielectric materials include high-index materials (such as TiO₂, ZnS) and low-index materials (such as SiO₂, MgF₂).
High refractive index materials such as titanium dioxide (TiO₂) and zinc sulfide (ZnS) can improve the optical interference effect of the film layer.
Low refractive index materials such as silica (SiO₂) and magnesium fluoride (MgF₂) are used to reduce reflection and achieve broadband anti-reflection.
The dielectric material forms interference structure through the difference of refractive index between layers to achieve the effect of anti-reflection and light filtering.
C. Composite materials
Composite materials are usually composed of multiple layers of different materials, and by optimizing the layer number and refractive index distribution, broadband anti-reflection and high reflectivity can be achieved.
Multilayer composite films are widely used in optical coatings, such as high reflectors and bandpass filters. These materials are complex to design, but can achieve optimal optical performance.
3. Structure design and performance optimization of optical vacuum coating
The design and optimization of thin film structure is the core of optical vacuum coating technology, which directly affects the spectral, mechanical and thermal properties of thin films.
A. Multilayer film design
The design principle of the multilayer film is based on interference enhancement and extinction effect. With computer-aided design (CAD) tools, the number of layers, thickness and refractive index of the film can be precisely designed to achieve optimal optical performance.
For example, a typical anti-reflection film uses a double or triple layer structure to achieve broadband low reflection through interference extinction of each layer.
B. Spectral performance optimization
By adjusting the thickness of the film and the refractive index of the material, the bandwidth, center wavelength and cut-off wavelength of the film can be controlled, and the spectral performance can be optimized. Bandwidth regulation is very important in optical filters.
C. Optimization of mechanical and thermal properties
Through the appropriate process (such as IAD) and material selection, the adhesion, wear resistance and thermal stability of the film can be improved, suitable for optical films in high temperatures and harsh environments.
4. Typical applications of optical vacuum coating
Optical vacuum coating technology is very important in various optical applications.
A. Anti-reflection film
Anti-reflection films are widely used in camera lenses, optical instruments and optoelectronic devices to significantly improve the imaging quality of devices by reducing reflection and improving light transmittance.
B. High reflector
High reflectors are used in lasers and astronomical telescopes, often with multilayer designs to improve reflectivity. The highly reflective film in the laser system needs to be stable at high power, so it is often combined with the IAD process to enhance the film strength.
C. Optical filters
Optical filters (such as bandpass filters, long wave pass filters and short wave pass filters) are widely used in spectrometers, microscopes and communication systems to achieve light filtering effects by selectively transmitting specific wavelengths.
Related NewsIn the magnificent map of the optical industry, Xu...
Optical components are regarded as the "eyes" of e...
The necessity of the coating as an optical element...
Hot Selling Product：