PSF and non-uniformity in a monolithic, fully depleted, 4T CMOS image sensor

Abstract

Lateral charge diffusion is one of the main contributors to the Point Spread Function (PSF) in CMOS image sensors, due to the small depth to which they can be depleted. This can have an adverse effect on the spatial resolution of the sensor and the measured shape of the observed object. In this paper, PSF measurements are made on a novel CMOS detector capable of reverse bias and full depletion. The PSF is measured with the Virtual Knife Edge (VKE) technique at five wavelengths, from 470 nm to 940 nm, to ascertain wavelength dependence. The inter- and intra-pixel non-uniformity is examined to determine the difference between pixels as well as within the pixels themselves. Finally, the pixel structure is also evaluated using a 1 µm spot of light to examine the effect of the internal layout of a pixel on the sensitivity to light. These factors all impact precision astronomical measurements and so need to be understood before use in science missions.