CMOS pixel structures optimised for scientific imaging applications

Abstract

In this paper we present the results from a pilot project at e2v technologies to examine the performance of CMOS Active Pixel Sensors for scientific applications. We describe the characterisation of two prototype 128 × 128 pixel imaging devices with scanning circuitry, as well as 5 × 5 pixel test structures with further variation in pixel design. The main variation in the design is the type of photodiode. In this process two types of diode were available, a 'shallow' n+/p-well diode and 'deep' n-well/p-substrate diode. The characterisation includes the use of photon transfer curves to measure output responsivity and we quantify dark signal variations between pixel structures and reset noise levels. A source of additional dark signal is found to be light emission from the in-pixel transistors. We also present results from an optical characterisation of the stand alone devices, including QE response, MTF and PSF measurements. Finally we outline the considerations to produce such a device using a more advanced process with a smaller feature size.

Predicting the effect of radiation damage on dark current in a space-qualified high performance CMOS image sensor

“…All devices' BOL dark current histograms displayed a small proportion of higher dark current pixels extending up to approximately 20 electrons s −1 . This feature originates mostly from preexisting defects, but also in part from a "glow" in the corner corresponding to pixel (row 1, col 1) that was seen in all devices (see figure 2b for an example), and which is thought to be a result of hot carrier effects (the generation of optical photons by circuitry outside the image area [7]). One device (15901-17-19) had a greater number of pixels with higher dark currents due to an additional proofs JINST_099P_0919 bright region centred on pixel (row 1, col 376) at the corner of column block 1, which would have declassified the device from being suitable for flight.…”