Silicon sensors with various pixel geometries adapted for a common readout ASIC

Abstract

ATLAS is proposing to replace the entire tracking system for HL-LHC operation. The ``Letter of Intent'' baseline pixel size at higher radii was 50 × 250μm2 (φ × η), based on the FE-I4 readout chip, and this was optimized for the central barrel region. The detector tracking performance in the end-cap pixel disks can benefit from enhanced resolution in the radial direction to improve the impact parameter resolution in z-coordinate (along the beam line) for high η tracks, which is critical in the high pile-up environment of the HL-LHC. So called ``strixel'' geometries, with long narrow pixels, can be proposed at higher z in the barrel where tracks pass through at large angles. Larger pixels may also be considered for an additional pixel layer if this could reduce the requirements, and therefore costs, for the outer part of the tracker.While ATLAS pixel upgrade plans are evolving, the demonstration of providing a variety of sensor pixel shapes and sizes for a common ASIC pixel geometry will be of general application, whatever the final ASIC design.This paper will report on the development and testing of pixel sensors with several different dimensions assembled into modules with the FE-I4 readout chip. Some of these were irradiated (with protons, 1015 neq/cm2) and evaluated at the DESY test beam. These, together with the test beam results with non-irradiated sensors, will be shown, as well as the results from laboratory characterization.