A CMOS image sensor with high sensitivity and low dark current

A CMOS image sensor with a very low-leakage photodiode and a low voltage buried photodiode has been developed that has sensitivity comparable to that of conventional CCD imagers. Photodiode leakage current caused by stress originates in the surface damage and in the dislocations and defects near the local oxidation of silicon. Use of a dislocation-free stress-release process and of a buried photodiode reduced the damage and eliminates the stress. A 1/4 inch 330 K pixel CMOS image sensor using this buried photodiode structure and a sensor-specified process had a low dark current of 0.1 nA/cm2 in 5.6 μm pixels. The buried photodiode can operate in complete charge transfer mode at voltage as low as 3.3 V, thereby suppressing the image lag and FPN of the photodiode.