OPTICAL LIMITATIONS TO CELL-SIZE REDUCTION IN IT-CCD IMAGE SENSORS

We have determined the practical limits of cell size reduction in inte rline-transfer charge-coupled device (IT-CCD) image sensors, limits re sulting from diffraction occurring at the aperture above the photodiod e. We have found that image cell size cannot be reduced to a level for which aperture width would fall below about 0.2 mu m. We have also fo und, however, that image cells with greater than 0.2 mu m aperture siz e are sensitive over the entire wavelength range of visible light, and that sensitivity can be increased by thinning the photoshield film.