CMOS pixel structures optimised for scientific imaging applications

摘要

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.