FD MOS SOI circuit to improve the threshold of detection of a co-integrated amorphous photodiode

Amorphous silicon (a-Si:H) photodetectors are widely used in low cost electronics as simple photodetectors, or integrated in a matrix of pixels. In the last years, much effort has been dedicated to the integration of these devices with MOSFET ASICs, the so called Thin Film on ASIC technology (TFA), which seems interesting for new applications, and provides separate design and optimization of the two components [1]. However, one of the drawbacks of these diodes is the high amount of dark current which is a problem in vision-like applications. In this work, we present for the first time a-Si:H photodetectors fabricated on top of a FD SOI MOSFET ASIC. In addition, we report the advantages of using a very simple circuit consisting of only two FD SOI MOSFET transistors to bias and sense the changes of current through the photodiode and at the same time provide a very significant detected ratio of illuminated to dark current. The ratio we obtained is several orders higher than what can be obtained using only the photodiode. At the output of the current mirror circuit, other circuits can be added to further process the output signal