Yield, noise and timing studies of ALICE ITS3 stitched sensor test structures: the MOST

TL;DR

This paper evaluates the performance of stitched sensor test structures for the ALICE ITS3 upgrade, focusing on yield, noise, timing, and data transmission capabilities of the MOST and MOSS prototypes.

Contribution

It introduces and validates the MOST stitched sensor with high-density pixel circuitry and 1 Gb/s data transmission, demonstrating key functionalities for the ALICE ITS3 upgrade.

Findings

MOST validates power domain switching and data transmission over 26 cm lines

Performance of stitched sensors meets design expectations for ALICE ITS3

Yield and uniformity studies inform future sensor improvements

Abstract

In the LHC long shutdown 3, the ALICE experiment upgrades the inner layers of its Inner Tracker System with three layers of wafer-scale stitched sensors bent around the beam pipe. Two stitched sensor evaluation structures, the MOnolithic Stitched Sensor (MOSS) and MOnolithic Stitched Sensor with Timing (MOST) allow the study of yield dependence on circuit density, power supply segmentation, stitching demonstration for power and data transmission, performance dependence on reverse bias, charge collection performance, parameter uniformity across the chip, and performance of wafer-scale data transmission. The MOST measures 25.9 cm x 0.25 cm, has more than 900,000 pixels of 18x18 $\mu$m$^2$ and emphasizes the validation of pixel circuitry with maximum density, together with a high number of power domains separated by switches allowing to disconnect faulty circuits. It employs 1 Gb/s 26 cm long data transmission using asynchronous, data-driven readout. This readout preserves information on pixel address, time of arrival and time over threshold. In the MOSS, by contrast, regions with different in-pixel densities are implemented to study yield dependence and are read synchronously. MOST test results validated the concept of power domain switching and the data transmission over 26 cm stitched lines which are to be employed on the full-size, full-functionality ITS3 prototype sensor, MOSAIX. Jitter of this transmission is still under study. This proceeding summarizes the performance of the stitched sensor test structures with emphasis on the MOST.