Hybrid Pixel Readout Chip Verification, Characterization and Wafer Level Testing for the ATLAS-ITK Upgrade at the HL-LHC

Abstract

The HL-LHC upgrade starting in 2026 will provide an opportunity for new high-energy physics experiments, but also present challenges for its tracking detectors, particularly the pixel detectors close to the interaction point, which will be subjected to significantly higher vertex density and radiation damage. <br /> To address this, new high resolution, radiation tolerant readout chips are being developed, and efforts are being made to establish ITk production processes to assemble the final ITk detector. <br /> In this thesis, the verification, characterization, and mass testing of the ITkPixV1.1 readout chip for the ITk upgrade at the HL-LHC is presented. <br /> The ITkPixV1.1 is a prototype readout chip for the pixel detector system. Their designs and functionality are described in detail. The signal generation processes in the tracking detector and the design of the silicon hybrid pixel detector, which incorporates ITkPix, are also outlined. A new BDAQ53 testing environment and accompanying software are introduced to verify the performance of ITkPixV1.1. <br /> The BDAQ53 testing environment, in combination with the RD53B interface cards, provide a robust platform for verifying the performance of ITkPixV1.1. During verification, ITkPixV1.1s digital logic in pixel matrix and chip bottom is tested in simulation and continuous DAQ compatibility is ensured using continuous integration in the BDAQ53 repository. <br /> During ITkPixV1.1 characterization, individual chips are tested and the general performance of analog and digital blocks is verified. Here, a few ITkPixV1.1 bugs, including unexpected behaviour during data merging and a time dependent detection threshold, is found. Many of the discovered bugs have led to fixes to ITkPixV1.1’s successor, called ITkPixV2. This has drastically increased the chances of a well working ITk-detector. In addition to that it is verified, that ITkPixV1.1 fulfills the RD53 analog front end specifications, with an analog current consumption of 3 µA to 5.5 µA per pixel, prior to irradiation. <br /> During wafer probing, the functionality of 6600 ITkPixV1.1 is tested, with a yield of 86 %, which is a significant improvement over 60 % during RD53A wafer probing, despite stricter requirements. <br /> In the future, four probe sites will use the wafer probing setup and software developed during this thesis, to probe ITkPixV2 for ITk production. In the event, that one probe site fails, the reduction of probe time has high priority, which is discussed and a reduction from 48 h to 30 h per wafer is expected. In addition to that new tests are recommended to be added to the testing routine. <br /> All in all the work in this thesis has significantly contributed to the development of ITkPixV2, and thus to the development of the new inner tracker detector ITk at the HL-LHC.