Physical effects of avalanche CMOS photodiodes

Three photodiodes of P-diffusion_N-well_P-substrate, N-well_P-substrate, N-diffusion_P-substrate photodiodes using the TSMC 0.35μm CMOS technology are implemented to understand their breakdown voltages at the Geiger mode. The measured results reveal that a photodiode with a larger perimeter yields a lower breakdown voltage. N-well_P-substrate and N-diffusion_P-substrate photodiodes have the largest breakdown voltage and the best current gain, respectively. Particularly, the electrical fields associated with photodiode´s structures are theoretically derived to support the measured results. The results from our experiments can be beneficial to the photodiode design of a 3D image sensor.