Image Sensors Based on Thin-film on CMOS Technology: Additional Leakage Currents due to Vertical Integration of the a-Si:H Diodes

Image sensors based on thin-film on CMOS technology (TFC) have been developed. In this approach, amorphous silicon (a-Si:H) detectors are vertically integrated on top of a CMOS readout chip so as to form monolithic image sensors. In order to reduce as far as possible the dark current density (J dark ) of the TFC sensors, we have focused on analyzing and understanding the behavior of J dark in this type of detectors. Edge effects along the periphery and at the corners of the pixel, due to the non planar configuration of the vertically integrated photodiodes, are found to be responsible for an increase of the dark current. A new and adapted solution for the minimization of J dark is proposed, which combines the use of a metal-i-p a-Si:H diode configuration with a deposition on top of an unpassivated CMOS chip. Values of J dark as low as 12 pA/cm 2 at a reverse polarization of V = -1 V are measured on such TFC sensors.