Chien-Jen Tang

Rugate filter made with composite thin films by ion-beam sputtering

Composite films of Ta-Si oxide with refractive indices that varied from 1.48 to 2.15 were realized by using rf ion-beam sputtering. All the composite films were amorphous and had a surface roughness of less than 0.3 nm. The inhomogeneity of the composite was discussed, and a rugate filter was designed and fabricated by automatic computer control.

Residual stress in Ta2O5-SiO2 composite thin-film rugate filters prepared by radio frequency ion-beam sputtering

Ta-Si oxide composite thin-film rugate filters were prepared by radio frequency ion-beam sputtering and their residual stress and substrate deflections were measured. The residual stress and substrate deflection of these composite film rugate filters were less than that of notch filters made from a series of discrete quarter-wave layers with alternate high and low indices because of the smooth modulation of composition and no interface structure of the rugate filter.

TiO2--Ta2O5 composite thin films deposited by radio frequency ion-beam sputtering.

TiO2--Ta2O5 composite films were prepared by a radio frequency ion-beam sputtering deposition process, and the refractive indices and extinction coefficients of the composite films were found to be between those of the TiO2 and Ta2O5 films. The structure of the as-deposited films was amorphous, and the surface roughness was approximately 0.1 nm. The residual stress of the composite films was less than that of pure TiO2 film. The structure of the composite films after annealing was amorphous, with low surface roughness and slightly increased residual stress. The film containing 6.3% TiO2 displayed better properties than either the pure TiO2 or the pure Ta2O5 film.

Residual stress in obliquely deposited MgF2 thin films.

MgF(2) films with a columnar microstructure are obliquely deposited on glass substrates by resistive heating evaporation. The columnar angles of the films increases with the deposition angle. Anisotropic stress does not develop in the films with tilted columns. The residual stresses in the films depend on the deposition and columnar angles in a columnar microstructure.

Measurement of stress in aluminum film coated on a flexible substrate by the shadow moiré method

This investigation proposes the use of the shadow moiré method (SMM) to measure stress in a thin film that is coated on a flexible substrate. The technique defines the profile of the sample by contour lines without the application of an external force, and the radius of curvature is calculated from these contour lines. The SMM is insensitive to environmental noise and has the same advantages as the interference method, such as being nondestructive and easy to use. For Al film with a thickness of 120 nm coated on a polyimide substrate by a DC magnetron sputtering system (800 W, room temperature), the stress is 0.45 +/- 0.042 GPa.

Optical constants of electrochromic films and contrast ratio of reflective electrochromic devices.

This study investigates the optical constants of WO3 electrochromic films and NiO ion-storage films in bleached and colored states and that of a Ta2O5 film used as an ion conductor. These thin films were all prepared by electron-beam evaporation and characterized using a spectroscopic ellipsometer. The spectra obtained using a spectrophotometer and those calculated from the optical constants agreed closely. An all-solid thin-film reflective electrochromic device was fabricated and discussed. Its mean contrast ratio of reflectance in the range of 400-700 nm was 37.91.

Antireflection coating on metallic substrates for solar energy and display applications

Normally metallic films are required for solar energy and display related coatings. To increase the absorbing efficiency or contrast, it is necessary to apply an antireflection coating (ARC) on the metal substrate. However, the design of a metal substrate is very different from the design of a dielectric substrate, since the optical constant of metallic thin film is very dependent on its thickness and microstructure. In this study, we design and fabricate ARCs on Al substrates using SiO 2 and Nb 2 O 5 as the dielectric materials and Nb for the metal films. The ARC successfully deposited on the Al substrate had the following structure: air/SiO 2 /Nb 2 O 5 /Metal/Nb 2 O 5 /Al. The measured average reflectance of the ARC is less than 1% in the visible region. We found that it is better to use a highly refractive material than a low refractive material. The thickness of the metallic film can be thicker with the result that it is easier to control and has a lesser total thickness. The total thickness of the ARC is less than 200 nm. We successfully fabricated a solar absorber and OLED device with the ARC structure were successfully fabricated.

Reduction of residual stress in optical silicon nitcide thin films prepared by radio-frequency ion beam sputtering deposition

In this study, we investigate the deposition of SiNx thin films by radio-frequency ion-beam sputtering deposition. By varying the amount of N2 and Ar flow and ion-beam voltage, we can obtain an optimal refractive index of 2.07, extinction coefficient (at the central wavelength of 500 nm) of 3.44×10−4, and deposition rate of 0.166 nm/s. The x-ray photoelectron spectra of SiNx films deposited with different beam voltages are also analyzed. The residual stress of the SiNx films varied from −1.38 to −2.17 GPa, depending on the beam voltage. The residual stress is reduced from −2.17 to −1.40 GPa when the film is divided into four layers with three interfaces.

Enhancement of adhesion between antireflection coating and cellulose triacetate by surface pretreatment using argon-helium plasma.

The adhesion of optical thin films on cellulose triacetate (TAC) was enhanced with surface pretreatment by argon-helium plasma. The optical properties, water contact angle, surface morphology, and thin film adhesion of TAC substrate that had been treated with different plasma gases were also investigated. An antireflection coating adhered well to TAC with an appropriate interface layer.

Optical properties and residual stress in Nb-Si composite films prepared by magnetron cosputtering

This paper investigates Nb-Si metal composite films with various proportions of niobium in comparison to pure Nb films. Films were prepared by two-target RF-DC magnetron cosputtering deposition. The optical properties and residual stress were analyzed. A composition of Nb(0.74)Si(0.26) was chosen toward the design and fabrication of solar absorbing coatings having a high absorption in a broad wavelength range, a low residual stress, and suitable optical constants. The layer thicknesses and absorption characteristics of the Nb-Si composite films adhere more closely to the design than other coatings made of dielectric film materials.