Effects of Varying Substrate Thickness on the Collected Charge From Highly Irradiated Planar Silicon Detectors

The full exploitation of the physics potential of the LHC will require a significant upgrade program with detailed planning around proton-proton collisions running at 14 TeV with a target integrated luminosity of 3000 fb^-1 implying innermost detector radiation levels approaching up to 2×10¹⁶ n_eqcm^-2. Current experience with planar pixel sensors has been very positive in ATLAS, CMS and ALICE. Recent results by ourselves, and now by many others, have shown that the survival of planar processed silicon greatly exceeds expectations. It has been proposed that further advantages could be achieved by thinning detectors beyond the accepted standard of ~300 μm. In previous measurements, we have shown that thin detectors (140 μm) have higher collected charge and reverse current than standard thickness detectors (310 μm) after fluences of 2×10¹⁵ n_eqcm^-2, where n_eq denotes the 1 MeV neutron equivalent fluence. In this paper, we extended our comparisons of collected charge and reverse current properties of micro-strip devices to three different bulk thicknesses: thin (140 μm), standard (310 μm) and thick (500 μm). These measurements confirm the trends seen in our earlier results.