Vertically Integrated Optical Sensor With Photoconductive Gain > 10 and Fill Factor > 70%

A hybrid active pixel optical sensor for high-resolution and high-sensitivity imaging is proposed and experimentally demonstrated. The sensor vertically integrates an amorphous silicon p-i-n photodiode and a low-temperature polycrystalline silicon readout thin-film transistor (TFT). The vertical integration results in a high fill factor (>70%) and an enlarged photosensing area in the pixel. In the photodiode-gated TFT structure of the sensor, the output current is amplified by operating the TFT in the sub-threshold regime. A weak wavelength-dependent photoconductive gain >10 is obtained at visible wavelengths, enabling large area low-level light detection.