Speaker
Description
As part of the CMS Tracker upgrade for High-Luminosity LHC, the Inner Tracker community is developing an automated test system for the qualification of the front-end chip (CROC) before the wafer is sent to the company for dicing and hybridization. The procedure takes approximately one day for each wafer to be tested, thus allowing to fully verify the functionalities of all the chips in the tight timeline (18 months) allocated to the project. The talk will describe the test procedure and strategy, the setup and the results obtained on the first eigth wafers tested of the CROC prototype.
Summary (500 words)
For efficient operations at the High-Luminosity LHC (HL-LHC) the CMS experiment will use an improved silicon tracker. The innermost part, Inner Tracker, will be instrumented by hybrid pixels detectors capable of resolving the 200 pp collisions per bunch crossing expected on average at the luminosity 7.5e34 cm-2 s^-1.
The sensors of the Inner Tracker will be read out by the CMS Readout Chip (CROC), an ASIC developed in CMOS 65 nm technology. The CROC contains about 145 000 readout channels, more than one billion transistors, with a digital architecture of unprecedented complexity for High Energy Physics. It has the novelty to be powered from a constant current generator to allow chains of serially powered modules. The Inner Tracker will be equipped with 13256 CROCs. Verification of all the critical functionalities of the CROC has to be performed during production, and it is fundamental to guarantee a reliable performance of the CMS pixel detector, and therefore the success of the experiment.
The CROC chips will be delivered by the foundry on 12" wafers with 138 chips. Each chip will have to be tested at wafer level before being sent to the company for dicing and hybridization.
This talk will describe the procedure currently put in place for the automatic test of the CROC chips while they are still on wafer, during the construction of the Inner Tracker. The testing setup relies on a semi-automated probe system, a custom design probe card hosting a mezzanine equipped with a micro-controller and uses the Phase-2 Acquisition and Control Framework (Ph2_ACF) under development by the Data Acquisition team for the experiment.
The talk will illustrate the hardware, the software and the test procedures developed to validate the analog and the digital sections of the chip, and show the results from a first qualification campaign based on wafers from a production of the full-size prototype of the CROC delivered in August 2021.
