256 × 256 CMOS Image Sensor Using a Pseudo 3-Transistor Active Pixel Sensor for Low-illumination Level Application

In this paper, a new CMOS image sensor is presented, which uses a PMOSFET-type photodetector with a transfer gate that has a high and variable sensitivity. The proposed CMOS image sensor has been fabricated using a 0.35 mum 2-poly 4-metal standard CMOS technology and is composed of a 256 times 256 array of 7.05 times 7.10 mum
²
pixels. The unit pixel has a configuration of a pseudo 3-transistor active pixel sensor (APS) with the PMOSFET-type photodetector with a transfer gate, which has a function of conventional 4-transistor APS. The generated photocurrent is controlled by the transfer gate of the PMOSFET-type photodetector. The maximum responsivity of the photodetector is larger than 1.1 times 10
³
A/W without any optical lens. Fabricated 256 times 256 CMOS image sensor exhibits a good response to low-level illumination as low as 5 lux.