Resistive AC-Coupled Silicon Detectors: principles of operation and first results from a combined analysis of beam test and laser data

TL;DR

This paper introduces Resistive AC-Coupled Silicon Detectors (RSDs), a novel LGAD-based sensor technology that enables isotropic charge sharing and achieves high spatial and temporal resolutions demonstrated through laser and beam tests.

Contribution

The paper presents the design, operation principles, and first experimental results of RSDs, a new type of silicon sensor with resistive implants for improved spatial and temporal resolution.

Findings

Spatial resolution between 2.5 and 17 micrometers depending on geometry.

Temporal resolution around 40 picoseconds for 200-micrometer pitch devices.

Successful demonstration of isotropic charge sharing without floating electrodes.

Abstract

This paper presents the principles of operation of Resistive AC-Coupled Silicon Detectors (RSDs) and measurements of the temporal and spatial resolutions using a combined analysis of laser and beam test data. RSDs are a new type of n-in-p silicon sensor based on the Low-Gain Avalanche Diode (LGAD) technology, where the $n^+$ implant has been designed to be resistive, and the read-out is obtained via AC-coupling. The truly innovative feature of RSD is that the signal generated by an impinging particle is shared isotropically among multiple read-out pads without the need for floating electrodes or an external magnetic field. Careful tuning of the coupling oxide thickness and the $n^+$ doping profile is at the basis of the successful functioning of this device. Several RSD matrices with different pad width-pitch geometries have been extensively tested with a laser setup in the Laboratory for Innovative Silicon Sensors in Torino, while a smaller set of devices have been tested at the Fermilab Test Beam Facility with a 120 GeV/c proton beam. The measured spatial resolution ranges between $2.5\; \mu m$ for 70-100 pad-pitch geometry and $17\; \mu m$ with 200-500 matrices, a factor of 10 better than what is achievable in binary read-out ($bin\; size/ \sqrt{12}$). Beam test data show a temporal resolution of $\sim 40\; ps$ for 200-$\mu m$ pitch devices, in line with the best performances of LGAD sensors at the same gain.