MiniCACTUS: A 65 ps Time Resolution Depleted Monolithic CMOS Sensor

Abstract

International audienceMiniCACTUS is a monolithic sensor prototype optimized for timing measurement of charged particles. It has been designed in a standard 150 nm CMOS process without dedicated amplification layer. It is intended as a demonstrator chip for future large-scale timing detectors, like upgrades of timing detectors at LHC, or future high-energy physics detector projects. The sensor features an active array of $2\times4$ diodes, analog and digital front-ends (FEs), a slow control interface, and bias circuitry programmable through internal DACs. The sensing element is a deep n-well/p-substrate diode. Thanks to the optimized guard-rings surrounding the whole chip, it is possible to apply safely more than −450 V on the high-resistivity substrate allowing fast charge collection. The baseline pixel dimensions are $1.0\times1.0$ mm and $0.5\times1.0$ mm. The analog FEs and the discriminators for each pixel are implemented outside the pixel, at the column level. The power consumption is approximately 300 mW/cm2, which is compatible with cooling infrastructure available at LHC experiments, and making integration of this concept viable in future high-energy physics experiments. After fabrication, the sensors have been thinned to 100, 200, and $300~\mu \text{m}$ total thickness and then postprocessed for backside biasing. The time resolution of several sensors with different thicknesses has been measured in three testbeam campaigns using high-energy muons minimum ionizing particles (MIPs) at CERN SPS in 2021 and 2022. A resolution of 65.3 ps has been measured with ON-chip FE and discriminator. This article will focus on the results of these testbeam campaigns