The ATLAS ITk Strip Detector for the Phase-II LHC Upgrade

The inner detector of the present ATLAS experiment has been designed and developed to function in the environment of the current Large Hadron Collider (LHC). At the ATLAS Phase-II upgrade, the particle densities and radiation levels will exceed current levels by a factor of ten. The instantaneous luminosity is expected to reach unprecedented values, resulting in up to 200 proton-proton interactions in a typical bunch crossing. The new detectors must be faster, more highly segmented, and they require much greater power delivery to the front-end systems (~10 mW/cm2). The sensors closest to the beam pipe will face radiation levels over 10¹6 neq/cm2 fluence and around 10 MGy total ionising dose, reason why they also need to be far more resistant to radiation. At the same time, they cannot introduce excess material which could undermine tracking performance. To meet these requirements a new all-silicon design, the ATLAS Inner Tracker (ITk), is being constructed, and it will replace the Inner Detector (ID) in 2027. The ITk detector is contained in a cylinder of 6 m long with a diameter of 2 m. The innermost layers will be composed of silicon pixel sensors, and the outer layers will consist of silicon microstrip sensors. This contribution focuses on the strip region of ITk. The central part of the strip tracker (Barrel) is composed of rectangular short (~2. 5 cm) and long (~5 cm) strip sensors. The forward regions of the strip tracker (End-Caps) consist of six disks per side, with trapezoidal shaped sensors of various lengths and strip pitches. After the completion of final design reviews in key areas, such as Sensors, Modules, Front-End electronics, and ASICs, a large scale prototyping program has been completed. This paper provides an overview of the Strip System, highlighting final design choices for sensors, module designs, and ASICs. It summarises results achieved during prototyping and the current status of pre-production and production on various detector components, with an emphasis on QA and QC procedures. An update is also provided on the progress since the conference till the writing of this paper.