4D Trackers Based on AC-LGAD with Long Strip Readout Electrodes*

Silicon-based sensors that can deliver a timing resolution of a few tens of ps along with a significantly better spatial resolution (O(few µm)) have been studied extensively in recent years. In AC-coupled Low-Gain Avalanche Diode (LGAD), a highly-doped p+ gain layer is implanted between a continuous n+ layer and p-type bulk to form a high-field multiplication region. Electrical signals in the n+ layer are AC-coupled to metal electrodes that are separated from the n+ layer by a thin insulator layer. Signal sharing among the adjacent electrodes in AC-LGAD sensors enables a significantly better spatial resolution while maintaining the excellent fast-timing resolution offered by the conventional LGAD sensors. The AC-LGAD technology has been suggested to use for particle identification (PID), tracking, and far-forward detectors at Electron-Ion Collider (EIC). Precision timing detectors in EIC will provide PID capabilities below the threshold of Cherenkov PID detectors. We demonstrated for the first time the performance of large-area AC-LGAD sensors produced by Brookhaven National Laboratory (BNL) [1], which achieved an excellent spatial resolution of around 10 - 80 µm, and timing resolution of around 30 - 50 ps depending on the length of the strip. Despite the excellent performance of AC-LGADs in this prototyping run, we observed a significant non-uniformity of the gain layer [1]. A follow-up production was performed at BNL in order to improve the gain layer uniformity. In this presentation, we will present the signal characteristics and charge sharing of AC-LGADs from the latest production batch with laser and test beam measurements.

References:

[1] Madrid, Christopher, et al. “First survey of centimeter-scale AC-LGAD strip sensors with a 120 GeV proton beam.” arXiv preprint arXiv:2211.09698 (2022).