Optical limitations to cell size reduction in IT-CCD image sensors

We have determined the practical limits of cell size reduction in interline-transfer CCD image sensors, limits resulting from diffraction occurring at the aperture above the photodiode. We have found that image cell size cannot be reduced to a level for which aperture width would fall below about 0.2 /spl mu/m. We have also found, however, that image cells with greater than 0.2 /spl mu/m aperture size are sensitive over the entire wavelength range of visible light, and that sensitivity can be increased by thinning the photoshield film.