A Study of Stray Minority Carrier Diffusion in CMOS Image Sensors

Noise minimization is an important issue for a single-chip CMOS image sensor. Stray minority carriers diffusing from the circuit region to the sensor array through the substrate are one possible source of noise. To study this effect, an nMOS transistor was deliberately placed close to the sensor array as a source of stray minority carriers. The influence on the image quality was then examined by varying the switching frequency applied to the transistor. The results provide useful information for CMOS imager designs to eliminate the effect of stray minority carrier diffusion.