First demonstration of a two-tier pixelated avalanche sensor for charged particle detection

This paper presents the first experimental demonstration of a pixelated two-layer Geiger-mode avalanche sensor designed for the direct detection of charged particles. In the proposed device, each pixel is formed by two vertically aligned avalanche detectors, exploiting the coincidence between two simultaneous avalanche events to discriminate between the detection of particles and dark counts. A 48 x 16 pixel array has been designed and fabricated in a 150-nm CMOS process and vertically integrated through bump bonding. The pixel, that includes passive quenching, comparator, and digital electronic circuits for coincidence processing and signal storage, has a size of 50 mu m x 75 mu m and a maximum fill factor of 51.6%. The operation of the particle sensor has been validated with the measurement of dark count rate distribution at different coincidence resolution times. An average dark count rate per pixel as low as 93 mHz, corresponding to 24 Hz/mm(2), was obtained at room temperature. A first sensor validation using a Sr-90 beta source is presented.