Demonstration of 200-, 100-, and 50-$\mu$ m Pitch Resistive AC-Coupled Silicon Detectors (RSD) With 100% Fill-Factor for 4D Particle Tracking

Abstract

We designed, produced, and tested RSD (Resistive AC-Coupled Silicon Detectors) devices, an evolution of the standard LGAD (Low-Gain Avalanche Diode) technology where a resistive n-type implant and a coupling dielectric layer have been implemented. The first feature works as a resistive sheet, freezing the multiplied charges, while the second one acts as a capacitive coupling for readout pads. We succeeded in the challenging goal of obtaining very fine pitch (50, 100, and 200 µm) while maintaining the signal waveforms suitable for high timing and 4D-tracking performances, as in the standard LGAD-based devices.

High performance 4D tracking with 100% fill-factor and very fine pitch silicon detectors

“…For what concerns the transient properties, unirradiated RSD1 have been tested in the Silicon Laboratory at Università degli Studi di Torino and in the SSD Lab at CERN (EP-DT Department). Both campaigns confirmed that we succeeded in the challenging goal of producing very-fine-pitch Silicon detectors with internal gain and 100% fill-factor [1]. As an example, the 2D maps of charges obtained with a TCT (Transient Current Technique) [11] setup, and shown in panels (a) and (b) of Figure 5, demonstrate that we have been able to design a correct readout scheme with an effective segmentation down to a nominal pitch of 50×50 µm 2 .…”

“…RSD (Resistive AC-Coupled Silicon Detectors), a new generation of particle trackers with internal gain [1], are specifically intended for high-luminosity environments in near-future HEP experiments, in which Silicon sensors is the enabling technology to perform 4D particle detection [2]. Contrarily to the standard segmented LGAD (Low-Gain Avalanche Diode) [3], where each active area is surrounded by proper isolation implants (see panel (a) of Figure 1) needed to avoid short-circuit and early breakdown at edges, RSD are based on a continuous gain layer.…”

The second production of RSD (AC-LGAD) at FBK

“…In particular, TCT measurements, where a pulsed laser stimulated the secondary charge production through impact ionization, have been extensively used to provide 2D maps of charges induced on the AC-pads [1]. From these studies it was possible to point out that: (i ) signals are bipolar (due to the capacitive nature of the RSD readout scheme), (ii ) the charge, in general, is always induced in more than one pad and (iii ) the amplitude of signals decreases when the laser moves away from a pad, while the peak shifts in time.…”

Radiation-tolerant Silicon Detectors for the LHC Phase-II Upgrade and Beyond: Review of RD50 Activities

“…LGADs with a resistive sheet under the electrodes, also allowing for a uniform gain layer [24]. The most prominent radiation effect in LGAD sensors is the drastic reduction of gain achievable in the device, and shift of the same gain to higher bias voltages with irradiation (Fig.4a).…”