Improved Noise Performance of CMOS Poly Gate Single-Photon Avalanche Diodes

The noise performance of three types of n(+)/p-well single-photon avalanche diodes (SPADs) fabricated in a standard 180 nm CMOS technology is studied. The SPADs had different poly gate configurations: no poly gate (SPAD_NG), a dummy floating poly gate (SPAD_DG), and a field poly gate connected to the n(+) cathode (SPAD_FG). The measurement results of dark count rate and afterpulsing showed that the SPAD_DG had better noise performance compared to the SPAD_NG. This is because the dummy poly gate pushed the shallow trench isolation away from the active region of the SPAD, thus reducing the dark noise generated from the Si-SiO2 interface. The measurement results also revealed that the noise performance can be further improved by connecting the poly gate to the n(+) cathode. The voltage on the poly gate in SPAD_FG reduced the electric field in the n-well guard ring (GR) region, thus reducing the carriers from the GR region that can enter the active region of SPADs and initiate dark counts.

Automated summary

The noise performance of three types of n(+)/p-well single-photon avalanche diodes (SPADs) fabricated in a standard 180 nm CMOS technology was studied. It was found that the SPADs with dummy floating poly gate (SPAD_DG) had better noise performance compared to the ones without poly gate (SPAD_NG). Connecting the poly gate to the n(+) cathode (SPAD_FG) further improved the noise performance.