Design and Fabrication of Near Ultraviolet Enhanced Composite Single Photon Avalanche Diode for Fluorescence Lifetime Imaging

Abstract

The near ultraviolet photon detection probability (PDP) of single photon avalanche diodes (SPADs) is very important for the fluorescence lifetime imaging. However, the PDP of traditional SPAD (T-SPAD) devices in the near-ultraviolet is not ideal, which is difficult to meet the requirements of fluorescence lifetime imaging. In response to the above problems, this paper realizes a near ultraviolet enhanced composite SPAD (NUEC-SPAD) based on photogate. The device is based on a photogate and a PN junction formed by P+/N-Well to detect photons. Therefore, the PDP of the device in the near ultraviolet is greatly improved. In addition, the shallow trench isolation (STI) and multiplication regions are isolated by photogate, and the dark count rate (DCR) of the device is greatly reduced. The principle of NUEC-SPAD device is simulated and verified based on the Technology-Computer-Aided-Design (TCAD). The NUEC-SPAD device and the T-SPAD device are fabricated based on the 0.18 μm BCD process. The experimental data show that the avalanche breakdown voltage of NUEC-SPAD device is 12 V. The device has good PDP in the range of 360 nm to 700 nm. Under the excess bias voltage of 0.5 V, the PDP of NUEC-SPAD device is 43.81% (@460 nm), which is 45.50% higher than that of T-SPAD device. Under the excess bias voltage of 1 V, the DCR of NUEC-SPAD device is only 0.24 Hz/μm2.