Smear reduction in the interline CCD image sensor

An undesirable smear in a vertical-overflow-drain interline CCD image sensor (VOD IL-CCD) has been analyzed. This smear has been reduced by using a new structure. The main cause of the smear was identified, using an experimental linear CCD image sensor, as light leakage, i.e., oblique incident light effect, concave lens effect, diffraction effect, and waveguide effect, To reduce the light-leakage smear, a new structure is proposed, where the oxide thickness under the aluminum photoshield is as small as 0.2 µm. As a result, the photoshielding performance is improved, and the smear-to-signal ratio for 10-percent vertical height illumination in the new structure VOD IL-CCD obtained is 0.016 percent, or 12 times smaller than that in a conventional structure VOD IL-CCD.