Abstract
An ultra low dark signal and high sensitivity pixel has been developed for an embedded active-pixel CMOS image sensor, by using a standard 0.35-µm CMOS logic process. To achieve in-pixel dark current cancellation, we developed a combined photogate/photodiode photon-sensing device with a novel operation scheme. To eliminate the photosensitivity reduction resulting from the optically opaque salicide layer, a salicide blocking mask is adopted to obtain a sensitivity improvement of 110%. The experimental results demonstrate that the severe dark signal degradation of CMOS active pixel sensor (APS) is reduced more than an order of magnitude. Through varying the bias conditions on the photogate, dynamic sensitivity can be obtained by increasing the maximum allowable illumination level. Combining the above two operation schemes, the dynamic range of this new cell is extended by more than 20X.