Performance and design differences between PMOS and NMOS CMOS imagers

Abstract

NMOS and PMOS CMOS imager design comparisons and performance differences are reviewed for night vision and scientific applications. Parameters include pixel read noise, charge transfer efficiency, charge collection efficiency, pixel readout speed, dark current and radiation damage tolerance. Focus of the paper is given to pixel read noise and dark current since these are the only parameters that require further development for our CMOS imagers. Discussions reveal that PMOS read noise is limited to ~ 1 h+ rms by flicker noise and why PMOS can fundamentally achieve lower noise than NMOS. We will examine where flicker noise is apparently generated and discuss various experiments that have been tried to lower it. New design and fabrication remedies are explored to reduce read noise below 1 h+ rms floor without reducing 1/f noise. Data is presented showing that PMOS and NMOS imagers are generating the same amount of dark current that is limited by silicon wafer contamination sources introduced in the fabrication process. Test data from a new stitched PMOS/NMOS Mk x Nk x 10 um pixel CMOS sensor suited for space borne NASA scientific applications is presented.