The proof-of-concept prototype of the Picosecond Avalanche
Detector, a multi-PN junction monolithic silicon detector with
continuous gain layer deep in the sensor depleted region, was tested
with a beam of 180 GeV pions at the CERN SPS. The prototype
features low noise and fast SiGe BiCMOS frontend electronics and
hexagonal pixels with 100 μm pitch. At a sensor bias voltage
of 125 V, the detector provides full efficiency and average time
resolution of 30, 25 and 17 ps in the overall pixel area for a
power consumption of 0.4, 0.9 and 2.7 W/cm2, respectively. In
this first prototype the time resolution depends significantly on
the distance from the center of the pixel, varying at the highest
power consumption measured between 13 ps at the center of the pixel
and 25 ps in the inter-pixel region.