Design optimization of the inter-electrode structures in DC-RSD

Abstract

DC-coupled Resistive Silicon Detectors (RSD) share charge among electrodes through a resistive n$^+$ surface layer, and the choice of inter-electrode structure --- a trench, a resistive strip, or no structure at all --- directly determines the achievable position resolution and its uniformity. This paper addresses the question of which structure best optimises the spatial resolution. To answer it quantitatively, DCRSD_SurfaceSimulator was developed, a ROOT-based tool that models the resistive surface as a two-dimensional Kirchhoff resistive network and solves for charge sharing as a function of hit position, surface resistivity, and inter-electrode structure. The simulator is validated against test-beam data from FBK DC-RSD sensors with 300, 500, and 1000~$μ$m pixel pitch, reproducing the position resolution, its spatial uniformity, and the signal-sharing templates correctly. Using the validated simulator, trenches, resistive strips, and no containment are then compared on position resolution and its spatial uniformity, inter-electrode resistance, and signal leakage to outer pixels. Resistive strips are found to outperform trenches in resolution by approximately 25\% for all tested strip resistances (500--2000~$Ω$) and input impedances (0--100~$Ω$), at a surface resistivity of 1000~$Ω/\square$, and trace the origin of this difference to the spatial gradient of the charge-sharing fraction: trenches produce a markedly weaker and less uniform gradient, particularly away from the pixel centre, than either a resistive strip or a bare resistive surface.