A silicon photomultiplier (SiPM) is a solid state alternative to photomultiplier tubes. The signal gain is roughly 106, providing a photodetector with single photon detection capability. RMD has fabricated prototype SiPMs for research, and because the fabrication was done using a standard CMOS process, designs included some signal processing circuitry. SiPMs are a compact low-voltage detector that RMD uses with our advanced scintillation materials for nuclear detection in fields ranging from science to security.
The sensitivity is sufficiently high that the device can to resolve individual photons. The device is made up of an array of Geiger photodiodes (GPD). In operation, the number of GPDs that fire is proportional to the intensity of the incident light. A few diodes that trigger in the array will produce a small pulse, where many diodes triggered will generate a large pulse.
Silicon wafer with various SiPM designs and integrated circuitry
The spectrum shown was captured from a small SiPM array, illustrating the ability to resolve extremely low-intensity light pulses events where multiples of photons ranging from 1 to 20 are detected.