High-performance 640 x 512 pixel hybrid InGaAs image sensor for night vision

Through collaboration between III-V Lab and CEA-Leti, a 640 x 512 InGaAs image sensor with 15 μm pixel pitch has been developed. Based on a thinned substrate, the photodiode array detects the light from the visible to the near infrared wavelength (0.4 to 1.7 μm) with a dark current lower than 18 fA per pixel at room temperature. The readout IC (ROIC) design in a standard CMOS 0.18 μm technology is presented. The pixel circuit is based on a capacitive transimpedance amplifier (CTIA) stage with two selectable charge-to-voltage conversion gains. The input stage has been optimized for low noise performance in the high gain mode. In this mode, the charge-to-voltage conversion factor is 17.6 μV/electron and the full well capacity is above 105 x 103 electrons. The integration time can be set up to the frame period thanks to a rolling shutter approach. The frame rate can be up to 120 fps or 60 fps if the Correlated Double Sampling (CDS) capability of the circuit is enabled. The readout noise measured in CDS with short exposure time is around 30 electrons for a dynamic range of 71 dB in high-gain mode and 108 electrons and 79 dB in low-gain mode.