In the plating of optical thin films, as the requirements for film quality increase, various plating methods have been continuously researched, and the test after plating has also been discussed in depth with the advancement of plating technology.
The materials required for plating are related to the results after plating. Although there are many materials that can be displayed, the ones that can be used in optical films are very limited. This makes us need to choose different materials in different spectral regions. The commonly used optical film materials and their characteristics are listed below:
Name: Yttrium (Y)
Yttrium trioxide, (Y2O3) is deposited using an electron gun. The properties of this material vary with the thickness of the film. The refractive index is about 1.8 at 500nm. It is very popular as an aluminum protective film, especially for high incidence in the 800-12000nm region. In terms of angle, it can be used as a protective film for glasses and exposed to moisture for 24 hours. Generally granular and flakes
Name: Cerium Dioxide (CeO2)
Use a high-density tungsten boat (used earlier) to evaporate, and vaporize cerium oxide on a substrate at 200°C to obtain a refractive index of about 2.2. At about 3000nm, there is an absorption band whose refractive index changes with the temperature of the substrate. Significant change. The refractive index in the 500nm region of the substrate at 300°C is 2.45, and there is absorption when the wavelength is shorter than 400nm. The traditional method of evaporation lacks compactness. Oxygen ion-assisted plating can obtain a low absorption film of n=2.35 (500nm), generally It is granular, and can also be used with an antireflection film and filter, etc.
Name: Magnesium Oxide (MgO)
An electron gun must be used to evaporate because the material is sublimated, hard and durable, and has good ultraviolet (UV) penetration, n=1.86 at 250nm, n=2.06 at 190nm. K-value at 166nm is 0.1, n=2.65. Can be used as ultraviolet light Thin film materials. The MGO/MGF2 membrane stack has good permeability from 200nm to 400nm, but the film layer is limited to 60 layers (due to film stress). When 500nm, n=1.70 is obtained on the environmental substrate. Due to the interference of atmospheric CO2, The exposed surface of MGO forms a fuzzy light blue scattering surface, which can successfully use the traditional MHL refractive index 3-layer AR film (MgO/CeO2/MgF2).
Name: Zinc Sulfide (ZnS)
The refractive index is 2.35, and the light transmission range of 400-13000nm has good stress and good environmental durability. ZnS is very easy to sublime when steaming at high temperature, so that it will form a non-adsorbed substrate on the substrate before the required film is attached. Therefore, it needs to be thoroughly cleaned and dried at the highest temperature. It takes several hours to eliminate the adverse effects of zinc. HASS et al. claim that ultraviolet (UV) has a greater impact on ZNS, due to ultraviolet rays in the atmosphere. The 15-20nm thick zinc sulfide film is completely converted into zinc oxide (ZnO).
Should have: splitting film, cold light film, decorative film, filter, high reflection film, infrared film.
Name: Titanium Dioxide (TIO2)
Because of its high refractive index and relative sturdiness, TIO2, people like to use this high refractive index material in the visible and near-infrared regions, but it is difficult to get a stable result by itself. TIO2, TI2O3. TIO, TI, these raw materials The simulated ratios of oxygen-titanium atoms are respectively: 2.0, 1.67, 1.5, 1.0, 0. It is found that the material with a ratio of 1.67 is relatively stable and generates a strong film with a repetitive refractive index of 2.21 at approximately 550 nm, with a ratio of 2. The first layer of the material produces a refractive index of about 2.06, and the refractive index of the subsequent film layers is close to 2.21. A material with a ratio of 1.0 requires 7 layers to reduce the refractive index from 2.38 to 2.21. These film materials are non-absorbent , Almost every TIO2 steaming follows a principle: to obtain negligible absorption in the usable spectral region, which can reduce the limit of oxygen pressure and the limit of temperature and steaming speed. TIO2 needs to use IAD to assist plating, and the oxygen input port is Below the bezel.
TI3O5 is more expensive than other types of oxides, but many people think that the risk of instability of this material is less.PULKER et al. pointed out that the final refractive index and non-absorption are changed with oxygen pressure and vaporization temperature. , The high temperature of the substrate results in a high refractive index. For example, the refractive index obtained at a wavelength of 550 nanometers when the substrate temperature is 400 ℃ is 2.63, but due to other reasons, high-temperature vaporization is usually undesirable, and ion-assisted plating It has become a commonly used method. It can get relatively high refraction at low temperatures or even at room temperature. It is usually necessary to provide enough oxygen to avoid it (because the absorption reduces the transmittance), but it may also need to reduce the absorption and increase Laser damage critical value (LDT). The refractive index of TIO2 has a great relationship with the degree of vacuum and evaporation speed, but this problem can be solved by sufficient pre-melting and IAD plating. Therefore, in the visible light and near-infrared spectra, TIO2 is very Be welcomed by people.
When IAD assists in plating TIO2, the use of shielded grid ion source evaporation requires 200EV, and the use of unshielded grid ion source evaporation requires 333EV or less, where the average energy is estimated to be about 60% of the driving voltage. If the ion energy exceeds the above value, TIO2 will absorb. And SIO2 has electron gun evaporation that can provide 600EV collision (ionizing radiation) energy without any adverse effects.
The driving voltage of 300EV is used in the TIO2/SIO2 process. The purpose is to use a gateless ion source in both materials, so as to avoid changing the driving voltage for each layer. The choice of driving voltage depends on the allowable range of TIO2. The streaming speed depends on the range allowed by the completely dense and non-absorbent film.
TIO2 is used for anti-reflection film, spectroscopic film, cold light film, filter, high reflection film, glasses film, heat mirror, etc., black granular and white flake, melting point: 1175℃
TIO2 is used for anti-reflection film, decorative film, filter, high-reflection film
TI2O3 is used for anti-reflection film, filter, high-reflection film, spectacle film