MiniCACTUS: Sub-100 ps timing with depleted MAPS

Abstract

MiniCACTUS is a monolithic CMOS sensor demonstrator designed for time tagging individual Minimum Ionizing Particles with an accuracy better than 100ps. The sensor features an active array of 2 × 4 pixels surrounded by guard-rings used to bias the high-resistivity substrate, an analog and digital front-end per pixel, a slow control interface and internal programmable biases through DACs. The baseline pixel sizes are 1.0mm2 and 0.5mm2. The sensing element is a deep n-well/p-substrate diode without internal amplification. The analog front-ends and the discriminators for each pixel have been implemented outside the pixel, at the column level. After fabrication, the sensors have been thinned to 200µm and 100µm and then post-processed for backside biasing. As such, this sensor is a demonstrator chip for future large scale timing detectors, like upgrades of timing detectors at LHC, or future high energy physics detector projects. Measurements of noise, response to X and γ-rays are presented, as well as time resolution measurements using β decays from 90Sr. Some preliminary results from a test-beam campaign are also mentioned.