Striped optical filters composed of multi-layered TiO 2 and SiO 2 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 moiré signal-to-noise ratio has been decreased by 6 dB.