Wafer-level testing of the readout chip of the CMS Inner Tracker for HL-LHC

Abstract

The CMS Inner Tracker, in the High Luminosity LHC (HL-LHC) phase, will be instrumented with approximately 13 × 103 CMS Readout Chips (CROCs). This integrated circuit has been developed by the RD53 Collaboration in order to work reliably in the high hit rates and radiation doses of HL-LHC. The CMS Readout Chip includes a novel powering scheme, a very complex digital circuitry, and a low power analogue front-end. The first batch of prototype CROC wafers has been received in the third quarter of 2021 and several wafers have been tested in 2022 with the wafer-level testing (WLT) setup developed at INFN Torino. The WLT data are being used to produce prototype detector modules, to characterise the CROC v1 before the submission of the final version of the chip, and to estimate wafer yields. This paper describes the wafer-level testing apparatus and the major results obtained in the first waferprobing campaign.