Large-area CMOS solid-state photomultipliers and recent developments

Abstract

The CMOS solid-state photomultiplier (SSPM) is an array of Geiger avalanche photodiodes (GPD) read out in parallel. These devices are not susceptible to magnetic fields, less expensive to fabricate than many other photodetector technologies, compact, and allow for on-chip integration of signal processing circuits. A number of nuclear detection applications require detector sizes on the order of 1 cm. Standard silicon fabrication technology limits the size of the SSPM die, and tiling of the silicon die can result in large-area devices but results in dead space between die for bonding purposes. Radiation Monitoring Devices (RMD) has fabricated 1×1 cm SSPM arrays on a single die. The size of these devices is large enough to provide an alternative detector for scintillation detector applications compared to photomultiplier tubes. Although the size increases the dark noise, we will demonstrate that the large-area SSPM can provide a PMT-like response for 22Na gamma rays using an LYSO crystal. Each of the noise terms associated with the large-area SSPM is discussed, quantifying the cross talk and after pulse multipliers, which are scaling factors to the gain to account for the additional output charge from the SSPM. The excess noise factor associated with cross talk and after pulsing has a linear dependence on the multiplier term. The signal and noise terms have been compiled to provide the best operating voltage of roughly 6 V above breakdown for a 1×1 cm CMOS SSPM to be operated with a short integration time (<10 ns) and at 0 °C.