Studying AC-LGAD strip sensors from laser and testbeam measurements

TL;DR

This work develops a laser-based calibration setup to characterize AC-LGAD strip sensors and validates its measurements against a 120 GeV proton test beam. By calibrating laser intensity to reproduce MIP responses and using a combination of position-sharing and multi-channel timing, the study demonstrates comparable spatial and timing performance between laser- and MIP-driven measurements across multiple sensors. Simulation with Weightfield2 and Silvaco TCAD identifies non-jitter components in the time resolution and introduces scale factors to reconcile jitter estimates with observed results, highlighting areas for refining timing models. The results support laser-based measurements as a fast, reliable tool to augment testbeam data and accelerate R&D for 4D tracking detectors in High-Luminosity collider environments.

Abstract

This paper presents the setup assembled to characterize and measure the spatial and timing resolutions of AC-coupled Low Gain Avalanche Diodes (AC-LGADs), using a 1060 nm laser source to deposit initial charges with a defined calibration methodology. The results were compared to those obtained with a 120 GeV proton beam. Despite the differences in the charge deposition mechanism between the laser and proton beam, the spatial and temporal resolutions were found to be compatible between the two sources after calibration. With 4D tracking detectors expected to play a vital role in upcoming collider experiments, we foresee this work as a way to evaluate the performance of semiconductor sensors that can augment testbeam measurements and accelerate R$\&$D efforts. Additionally, simulation studies using Silvaco TCAD and Weightfield2 were carried out to understand the various contributing factors to the total time resolution in AC-LGAD sensors, measured using the laser source.

Figures (13)

• Figure 1: An image of a HPK strip-type sensor.
• Figure 2: (a) A schematic representation of various components of the experimental setup and (b) an image of the laser test setup.
• Figure 3: A plot of the electric field profiles as a function of sensor depth simulated using WF2 and TCAD for a 50 $\mu$m thick AC-LGAD sensor. The readout electrodes and gain layer are located near sensor depth = 0 $\mu$m, while the backplane electrode of the sensor lies at high sensor depth values (50 $\mu$m in WF2 and 60 $\mu$m in TCAD).
• Figure 4: The observed time resolution and predicted jitter from the leading channel plotted as a function of $x$ position for sensors S1, S2, and S4, based on amplitude, noise, and efficiency values observed in the measurements.
• Figure 5: The observed time resolution and predicted jitter at the mid-gap position as a function of the oscilloscope sampling rate, for a 50 $\mu$m thick sensor.