First prototypes of two-tier avalanche pixel sensors for particle detection

In this paper, we present the implementation and preliminary evaluation of a new type of silicon sensor for charged particle detection operated in Geiger-Mode. The proposed device, formed by two vertically aligned pixel arrays, exploits the coincidence between two simultaneous avalanche events to discriminate between particle-triggered detections and dark counts. A proof-of-concept two-layer sensor with per-pixel coincidence circuits was designed and fabricated in a 150 nm CMOS process and vertically integrated through bump bonding. The sensor includes a 48 x 16 pixel array with 50 mu m x 75 mu m pixels. This work describes the sensor architecture and reports a selection of results from the characterization of the avalanche detectors in the two layers. Detectors with an active area of 43 x 45 mu m(2) have a median dark count rate of 3 kHz at 3.3 V excess bias and a breakdown voltage non-uniformity lower than 20 mV. (C) 2016 Elsevier B.V. All rights reserved.