Active Pixel Sensors in ams H18/H35 HV-CMOS Technology for the ATLAS HL-LHC Upgrade

TL;DR

This paper explores HV-CMOS active pixel sensors in ams H18/H35 processes as radiation-hard, high-efficiency detectors for the ATLAS HL-LHC upgrade, demonstrating promising test results and large-scale feasibility.

Contribution

It presents the development and testing of HV-CMOS sensors in ams H18/H35 processes as potential replacements for current ATLAS pixel sensors, including irradiation tolerance and large-scale demonstrator fabrication.

Findings

Sensors tolerate ionizing doses of 1 Grad.

High detection efficiency after neutron irradiation.

Enlarged depletion zone up to 100um after irradiation.

Abstract

Deep sub micron HV-CMOS processes offer the opportunity for sensors built by industry standard techniques while being HV tolerant, making them good candidates for drift-based, fast collecting, thus radiation-hard pixel detectors. For the upgrade of the ATLAS Pixel Detector towards the HL-LHC requirements, active pixel sensors in HV-CMOS technology were investigated. These implement amplifier and discriminator stages directly in insulating deep n-wells, which also act as collecting electrodes. The deep n-wells allow for bias voltages up to 150V leading to a depletion depth of several 10um. Prototype sensors in the ams H18 180nm and H35 350nm HV-CMOS processes have been manufactured, acting as a potential drop-in replacement for the current ATLAS Pixel sensors, thus leaving higher level processing such as trigger handling to dedicated read-out chips. Sensors were thoroughly tested in lab measurements as well as in testbeam experiments. Irradiation with X-rays and protons revealed a tolerance to ionizing doses of 1Grad. An enlarged depletion zone of up to 100um thickness after irradiation due to the acceptor removal effect was deduced from Edge-TCT studies. The sensors showed high detection efficiencies after neutron irradiation to 1e15 n_eq cm-2 in testbeam experiments. A full reticle size demonstrator chip, implemented in the H35 process is being submitted to prove the large scale feasibility of the HV-CMOS concept.