CMOS Avalanche Photodiode Embedded in a Phase-Shift Laser Rangefinder

This paper presents the design and the characterization of a CMOS avalanche photodiode (APD) working as an optoelectronic mixer. The P⁺N photodiode has been implemented in a commercial 0.35-mum CMOS technology after optimization with SILVACO. The surface of the active region is 3.78 middot10^-3 cm². An efficient guard-ring structure has been created using the lateral diffusion of two n-well regions separated by a gap of 1.2 mum. When biased at -2 V, the best responsitivity S_{lambda APD} = 0.11 A/W is obtained at lambda = 500 nm. This value can easily be improved by using an antireflection coating. At lambda = 472 nm, the internal gain is about 75 at -6 V and 157 at -7 V. When biased at -6 V, the APD achieves a dark current of 128 muA middotmm^-2 and an excess noise factor F = 20. Then, the APD is successfully used as an optoelectronic mixer to improve the signal-to-noise ratio of a low-voltage embedded phase-shift laser rangefinder.