Yasuharu Shimomoto

Striped optical filters composed of multi-layered TiO2 and SiO2 films deposited by RF sputtering

Abstract Striped optical filters (cyan, magenta and yellow) are fabricated using a multi-target RF sputtering apparatus. These filters are made of 13 layers of TiO 2 and SiO 2 , with refractive indices of 2.50 and 1.47, respectively, at 546.1 nm. The spectra for these filters do not shift more than ±2 nm after baking at 500°C for 1 h in air. The filter layers are deposited alternately in one pump-down vacuum. The pitch, length and number of stripes are 20 micro m, 10 mm and about 700 lines respectively. The stripes are photoetched with conventional lift-off techniques, using two layers of Al and Cr. Each layer is deposited by placing the substrate holder under the TiO 2 and SiO 2 target for appropriate time intervals calculated from the deposition rate. Deviations in the deposition rate are within ±2%, as the result of automatically controlling RF power and sputtering gas pressure. The electric signal output from each color channel of these striped filters in tri-electrode pickup tube is increased by 6 dB over that of conventional R, G and B filters. The related moire signal-to-noise ratio has been decreased by 6 dB.

Optical Characteristics of Corning 7059 Glass Films Deposited by RF Sputtering

Corning 7059 glass films deposited by rf sputtering under certain conditions showed coloration phenomena. From thermodynamical calculations for oxides in 7059 glass, it was deduced that BaO became oxygen diffident to absorb visible light. This was supported by the experiments. Refractive indices of rf sputtered 7059 films were a few percents higher than that of 7059 bulk. The increase in refractive indices was explained by the change in the compositions, which were detected by electron microprobe analyzer. BaO and Al2O3 in the films were increased by 5–10%, while SiO2 was decreased by 5–10% and B2O3 remained practically unchanged.

Optical and Electrical Properties of Nitrogen Doped a-Si: H Films for Solid-State Image Pickup Devices

Hydrogenated amorphous silicon (a-Si: H) films deposited by RF sputtering and doped with nitrogen have been found to have high dark resistivity (1013 Ωcm) and high photoconductivity at a low field. The Fermi level is shifted by 0.2 eV toward the conduction band, compared with undoped film. The spectral response of this film covers the visible region well and a peak quantum efficiency of 1.0 has been obtained at a wavelength of 500 nm. The γ-value of the film is nearly equal to unity for visible radiation. Rise and fall time constants are shorter than 500 µs for a pulsed radiation of 550 nm emitted from an LED. We have found that nitrogen doped n-type a-Si: H films are quite suitable as a photoconductive material for a solid state color imager.

Amorphous Silicon Image Pickup Tubes

Reactively sputtered a-Si:H is used in a photoconductive target of an image pickup tube. When a-Si:H is used for a color imager, high resistivity and wide optical band gap are required. A blocking type target structure is effective in reducing dark current and producing rapid photo response. Low doping of boron into a-Si:H serves to increase both hole and electron mobilities. The imaging tube using this a-Si:H has high photosensitivity, high resolution, and no sticking or burning. By using high velocity electron beam for scanning, lag property is drastically improved.