A novel high-gain CMOS image sensor using floating N-well/gate tied PMOSFET

The development of low power CMOS imaging systems has received a lot of attention. The main obstacle comes from the low responsivity and unscalability of the photo sensor. In this work, we have designed and fabricated a highly responsive photo sensor from a standard MOSIS HP0.8 /spl mu/m n-well CMOS process. The photo sensor is obtained by connecting the n-well with the n/sup +/ polysilicon gate of a PMOSFET. From the experimental results, the output photo current from a 8.2 /spl mu/m/0.8 /spl mu/m device is of the order of ten /spl mu/A. The self-amplification, which gives the high responsivity can be further increased by technology scaling. A simple 32/spl times/32 sensor array chip has also been fabricated to demonstrate the feasibility for using the new device in a CMOS imaging circuit.