Fully depleted, thick, monolithic CMOS pixels with high quantum efficiency

Clarke, A.; Stefanov, K.; Johnston, N. and Holland, A. (2015). Fully depleted, thick, monolithic CMOS pixels with high quantum efficiency. Journal of Instrumentation, 10(4), article no. T04005.

DOI: https://doi.org/10.1088/1748-0221/10/04/T04005

Abstract

The Centre for Electronic Imaging (CEI) has an active programme of evaluating and designing Complementary Metal-Oxide Semiconductor (CMOS) image sensors with high quantum efficiency, for applications in near-infrared and X-ray photon detection.

This paper describes the performance characterisation of CMOS devices made on a high resistivity 50 μm thick p-type substrate with a particular focus on determining the depletion depth and the quantum efficiency. The test devices contain 8x8 pixel arrays using CCD-style charge collection, which are manufactured in a low voltage CMOS process by ESPROS Photonics Corporation (EPC).

Measurements include determining under which operating conditions the devices become fully depleted. By projecting a spot using a microscope optic and a LED and biasing the devices over a range of voltages, the depletion depth will change, causing the amount of charge collected in the projected spot to change. We determine if the device is fully depleted by measuring the signal collected from the projected spot. The analysis of spot size and shape is still under development.

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