Abstract
Vertical integration of amorphous hydrogenated silicon diodes on CMOS readout chips offers several advantages compared to standard CMOS imagers in terms of sensitivity, dynamic range and dark current while at the same time introducing some undesired transient effects leading to image lag. Performance of such sensors is here reported and their transient behaviour is analysed and compared to the one of corresponding amorphous silicon test diodes deposited on glass. The measurements are further compared to simulations for a deeper investigation. The long time constant observed in dark or photocurrent decay is found to be rather independent of the density of defects present in the intrinsic layer of the amorphous silicon diode.
Highlights
Active pixel sensors (APS) in CMOS technology have recently gained a lot of interest
Non flat surface and the periphery of such diodes can significantly deteriorate the leakage current. This is especially critical in the case of thin-film on ASIC (TFA) sensors where the amorphous silicon (a-Si):H diode array is deposited over the chips passivation layers
We have analyzed the performance of a TFA image sensor
Summary
Active pixel sensors (APS) in CMOS technology have recently gained a lot of interest. Vertical integration of hydrogenated amorphous silicon (a-Si:H) sensors on top of readout electronics is a promising solution to this problem. This concept has been pioneered by the University of Siegen [1] with the demonstration of this technology for several applications, especially for vision sensors with high sensitivity [2,3] or high dynamic range [4]. This integration concept is known as thin-film on ASIC (TFA), thin-film on CMOS (TFC), above IC (integrated circuit) or elevated diode technology (in the cases where a diode is used) and has attracted a large interest, for imaging application and for particle detection, MEMS (micro electro-mechanical systems) or BioMEMS (biological MEMS) [5]
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