First measurements with monolithic active pixel test structures produced in a 65 nm CMOS process

TL;DR

This paper reports on the initial testing of monolithic active pixel sensors produced in a 65 nm CMOS process for the upgraded ALICE ITS3 detector, demonstrating their potential for high-radiation environments.

Contribution

First evaluation of stitched wafer-scale monolithic pixel sensors in 65 nm CMOS for high-energy physics applications, including performance under radiation.

Findings

Sensors achieved high detection efficiency

Performance maintained after irradiation

Successful fabrication of different sensor variants

Abstract

The Inner Tracking System (ITS) of the ALICE experiment at CERN will undergo an upgrade during the LHC long shutdown 3, in which the three innermost tracking layers will be replaced. This upgrade, named the Inner Tracking System 3 (ITS3), employs stitched wafer-scale Monolithic Active Pixel Sensors fabricated in a 65 nm CMOS process. The sensors are 260 mm in length and thinned to less than 50 um then bent to form truly half-cylindrical half-barrels. The feasibility of this process for the ITS3 was explored with the first test production run (MLR1) in 2021, whose goal was to evaluate the charged particle detection efficiency and the sensor performance under non-ionising and ionising radiation up to the expected levels for ALICE ITS3 of $10^{13}$ $1$ MeV n$_{\mathrm{eq}}$ cm$^{-2}$ (NIEL) and 10 kGy (TID). Three sensor flavours were produced to investigate this process: Analog Pixel Test Structure (APTS), Circuit Exploratoire 65 (CE65) and Digital Pixel Test Structure (DPTS). This contribution gives an overview of the MLR1 submission and test results, describing the different sensor flavours and presenting the results of the performance measurements done with particle beams for various chip variants and irradiation levels.