A hybrid CMOS APS pixel for wide-dynamic range imaging applications

In this paper, a new hybrid photodiode-photogate (HPDPG) CMOS APS pixel for high-dynamic range imaging applications is presented. The HPDPG pixel composes of a biased photogate, a photodiode and standard 3-transistors (3T) CMOS APS readout electronics. Biased photogate was connected in parallel with photodiode structure introducing a knee on the photoresponse curve. This new photodetection structure allows extension of the photoresponse range, providing wide dynamic range operation. New HPDPG pixel and a reference photodiode type 3T CMOS APS pixel were designed, fabricated, and tested using a 0.5μm double poly, triple metal (2P3M) CMOS process. It was shown that addition of a biased photogate structure in a standard photodiode type 3T CMOS APS pixel improve saturation exposure five times (5x) with the expense of reduced quantum efficiency, and increased dark current. Photogate in parallel with photodiode improves pixel full-well capacity ten times (10x) with the expected reduction in sensitivity and conversion gain.