Silicon Photodiodes in Standard CMOS Technology

Silicon photodiodes (PDs) of 850-nm-wavelength, in standard 0.18-μm CMOS technology, are systematically presented and discussed in this study. A basic p-n PD can obtain high responsivity of 0.3 A/W and response of 1.6 GHz while biasing in the avalanche process. However, Si PDs from different CMOS foundries would result in different performance due to the different n-/p-well doping profile. A basic p-n PD with body contact can effectively remove the slow diffusion carrier in the Si substrate and demonstrate improved response. Both body contact and deep n-well design in an octagonal PD can improve the performance of basic p-n PD significantly. The response is improved to 8.7 GHz with 0.8 A/W before breakdown. The improvement is due to the block and elimination of slow diffusion carriers in the Si substrate. Finally, Si PD with built-in n-p-n bipolar junction transistor and edge-coupled PD are proposed to further improve responsivity and response.