Speaker
Description
Summary
The high-luminosity upgrades of the LHC will lead to increased occupancy and radiation damage of the inner trackers, approaching fluences of a few 1016 neq/cm2 at the innermost layer and still some 1015 neq/cm2 at the outer pixel layers.
The ATLAS experiment plans to introduce an all-silicon inner tracker with the HL-LHC upgrade to cope with the elevated occupancy. With silicon, the occupancy can be adjusted by using the unit size (pixel, strip or short strip sensors) appropriate for the radiation environment. For radiation damage reasons, only electron-collecting sensors designs are considered (n-in-p and n-in-n): Beyond a fluence of about 1015 neq/cm2, trapping becomes the dominant radiation effect and electrons are trapped significantly less than holes.
To investigate the suitability of pixel sensors using the proven planar technology for the upgraded tracker, the ATLAS Planar Pixel Sensor R&D Project was established comprising 17 institutes and more than 80 scientists. Main areas of research are
* performance assessment and improvement of planar pixel sensors at HL-LHC fluences
* the achievement of slim or active edges to provide low geometric inefficiencies without the need for shingling of modules
* establishment of reliable device simulations for severely radiation-damaged pixel detectors
* the exploration of possibilities for cost reduction to enable the instrumentation of large areas with pixel detectors
Recently, it has been demonstrated with sensors from different vendors that planar pixel sensors can be operated and still yield more than 5000 electrons of signal charge even above 10**16 neq/cm2; hit efficiencies of well above 97% were obtained.
Special slim-edge designs have been implemented and tested and show a reduction of the inactive edges from 1100 µm in the current ATLAS Pixel Detector to only about ~200 µm. Further improvements towards fully active edges by SCP (scribe-cleave-passivate) and DRIE etching techniques are being investigated.
The presentation will give an overview of the recent achievements of the R&D project, among them
* beam test results with planar sensors irradiated up to 21016 neq/cm2 at different eta angles providing new insight into efficiencies and cluster sizes under realistic b-layer conditions
* results obtained with n-in-n pixel assemblies with sensors irradiated up to 1.41016 neq/cm2 while readout chips (FE-I3) remained unirradiated to disentangle sensor and FE-related effects
* first results from pixel assemblies based on the new ATLAS pixel readout chip FE-I4 irradiated to beyond 1*1016 neq/cm2
* systematic studies of the SCP technique to obtain almost active edges by post-processing already existing sensors based on scribing, cleaving and edge passivation
* comparisons of these experimental findings with initial TCAD device simulations
* first results towards fully active edges by means of anisotropic trench etching with planar technology
* experience with recent large-scale planar sensor productions in terms of yield and QA and status of future plans for sensor productions on 6” substrates
