A Monolithic Amorphous-Selenium/CMOS Visible-Light Imager With Sub-9-μm Pixel Pitch and Extended Full-Well Capacity

Autor: Peter M. Levine, Abdallah El-Falou, Rhiannon L. Lohr, Karim S. Karim, Christopher C. Scott, Mohamed Hamid, Yun Zhe Li
Rok vydání: 2021
Předmět:
Zdroj: IEEE Sensors Journal. 21:339-346
ISSN: 2379-9153
1530-437X
DOI: 10.1109/jsen.2020.3014073
Popis: We present a monolithic hybrid visible-light imager composed of an amorphous selenium (a-Se) photoconductor thin film integrated on a CMOS active pixel sensor (APS) array readout integrated circuit. We achieve more than 14-dB signal-to-noise ratio under monochromatic light at an illuminance of 0.04 lux in one quadrant of the imager containing $7.8\times 7.8-\mu \,\,\text{m}^{2}$ pixels using a 1.6-s exposure (integration) time without operating the a-Se sensor in avalanche mode. Long integration times are made possible by exploiting the low dark-current of a 20- $\mu \text{m}$ -thick a-Se sensor layer and by implementing dark-current reduction techniques in the APS, such as series stacking reset and protection devices. In addition, use of a relatively thick 20- $\mu \text{m}$ a-Se layer obviates the need for an additional planarization step of the sensing layer as was done with a previously-reported avalanche-mode a-Se/CMOS imager that incorporated a 0.5- $\mu \text{m}$ -thick sensing layer. We also demonstrate an improved APS design, with $7.8\times 8.7-\mu \,\,\text{m}^{2}$ dimensions, containing a programmable in-pixel integration capacitor to provide enhanced full-well capacity (FWC) for a-Se/CMOS imagers. Measured results show that our APS achieves a FWC of approximately 230 ke−, which is comparable to several previously-reported photodiode-based CMOS imagers with extended FWC. Our imager can also resolve an effective object size of approximately $12.5~\mu \text{m}$ , demonstrated through measurement of the modulation transfer function.
Databáze: OpenAIRE
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