Design and fabrication of a high-dynamic-range image sensor in TFA technology

Image sensors in thin film on ASIC (TFA) technology are composed of amorphous silicon (a-Si:H) thin-film detectors on top of crystalline ASIC's. With regard to advanced imaging systems, TFA provides enhanced performance and more flexibility than conventional technologies. Extensive an-chip signal processing is feasible, as well as small pixels for high-resolution imagers. Several prototypes of TPA sensors have been developed, optimized for considerably different applications. This paper focuses on a TFA sensor for automotive vision systems that allows each pixel to adapt its individual sensitivity to the local illumination intensity. By this means, a dynamic range of 120-dB minimum along with high local contrast is achieved. The recent second prototype array consists of 368 x 256 pixels with an area of 40 x 38 mu m(2) each. The ASIC's were fabricated in a 0.7-mu m CMOS technology, whereupon the a-Si:H thin film was deposited in a plasma-enhanced chemical vapor deposition cluster system.