TCAD simulations of pixel sensors for the ATLAS ITk upgrade and performance of annealed planar pixel modules

TL;DR

This paper uses TCAD simulations and experimental tests to optimize and evaluate pixel sensors for the ATLAS ITk upgrade, focusing on charge collection, radiation damage, and annealing effects.

Contribution

It introduces TCAD simulation-based optimization of pixel sensor layout and assesses the impact of annealing on sensor performance after irradiation.

Findings

Optimized sensor layout for 50x50 μm² pixels using TCAD simulations.

Quantified charge-collection efficiency and noise before and after irradiation.

Measured the effects of room-temperature annealing on sensor performance over one year.

Abstract

For the high luminosity phase of the Large Hadron Collider to start operation around 2026, a major upgrade of the ATLAS Inner Tracker (ITk) is in preparation. Thanks to their low power dissipation and high charge-collection efficiency after irradiation, thin planar pixel modules are the baseline option to instrument all, except for the innermost layer of the pixel detector. To optimise the sensor layout for a pixel cell size of $50\times50\,\mu m^2$, TCAD simulations are being performed. Charge-collection efficiency, electronic noise and electrical-field properties are investigated. A radiation-damage model is employed in TCAD simulations to estimate the performance before- and after irradiation. The impact of storage time at room temperature for the ITk pixel detector during maintenance periods are estimated using sensors irradiated up to a fluence of 5$\times10^{15}\,$n$_\text{eq}$/cm$^2$. Pixel sensors of $100-150\,\mu m$ thickness, interconnected to FE-I4 read-out chips with pixel dimensions of $50\times250\,\mu m^2$, are characterised using the testbeam facilities at the CERN-SPS and DESY. The charge-collection and hit efficiencies are compared before and after annealing at room temperature for up to one year.