Performance Measurements of CMOS Position Sensitive Solid-State Photomultipliers

We have designed position sensitive solid-state photomultipliers (PS-SSPM) using a complementary metal-oxide-semiconductor (CMOS) process. Four variations of the PS-SSPM design were fabricated, however, one of the variations did not function properly. The remaining three functional variations were characterized for their energy and coincidence timing resolution, spatial resolution, and scintillator array imaging. Each PS-SSPM is 1.5 × 1.5 mm², however, each device has different micro-pixel geometries and different micro-pixel electrical readout for event position sensing. When coupled to 1 × 1 × 20 mm³ LYSO, the energy resolution at 511 keV was measured as a function of bias. The same LYSO scintillator was used to measure the coincidence timing resolution. Results between the PS-SSPMs varied from 2.0 ns to 0.9 ns (FWHM) at 511 keV. Spatial resolution studies were conducted using a focused (15 μm beam spot diameter) pulsed 635 nm diode laser. For each PS-SSPM, the X and Y spatial resolution was measured between 70 and 75 μm (FWHM). Lastly, scintillator array images were generated using a CsI:Tl and LYSO array having 300 × 300 μm² and 500 × 500 μm² pixels respectively.