Pixel column issue in the ATLAS Inner Tracker modules

TL;DR

This paper investigates a recurring electrical malfunction in ATLAS ITk Pixel detector modules, focusing on the core column issue that affects module yield and requires further analysis to identify its root cause.

Contribution

It provides a detailed investigation of the core column issue, analyzing electrical behavior, production data, and visual inspection to understand its causes and impact.

Findings

Erratic behavior observed in pixel modules with ITkPix v1.1 and v2 chips.

Disabling pixel core columns can bypass the malfunction.

The origin of the issue remains unidentified, affecting module yield.

Abstract

Pixel modules are currently being built for the ATLAS ITk Pixel detector upgrade. During the preproduction phase, recurring chip malfunctioning was observed during electrical testing. It was possible to bypass this issue by disabling some pixel core columns in the ITkPix readout chip. Therefore the issue is called "core column issue" which is a direct disqualifier for a pixel module. A concerning number of cases has been observed in pixel modules with ITkPix v1.1 as well as v2 chips which significantly impacts the module yield. However, the behaviour is erratic and there is not any evidence hinting at the origin of this issue. These proceedings outline the investigations of the issue, highlighting the electrical behaviour during testing, present findings from the data collected via our production database and through visual inspection, and point towards possible causes of the issue.