CMOS Solid-State Photomultiplier for Detecting Scintillation Light in Harsh Environments

A CMOS SSPM coupled to a scintillation crystal uses an array of CMOS Geiger-mode avalanche photodiode (GPD) pixels to collect light and produce a signal proportional to the energy of the radiation. Each pixel acts as a binary photon detector, but the summed output is an analog representation of the total photon intensity. We have fabricated arrays of GPD pixels in a CMOS environment, which makes possible the production of miniaturized arrays integrated with the detector electronics in a small silicon chip. In this work, we compare designs for the CMOS GPD pixel used in the SSPM detector and present preliminary results in constructing a solid-state photomultiplier. One pixel design achieves maximum detection efficiency for 632-nm photons approaching 30% with a room temperature dark count rate of less then 1 kHz for a 30-μm-diameter pixel. We characterize the after pulsing in a CMOS GPD pixel, and the crosstalk between CMOS GPD pixels. We examine SSPM design considerations and the effects of after pulsing and cross talk on the performance of the SSPM detector.