Investigation of signal characteristics and charge sharing in AC-LGADs with laser and test beam measurements

Abstract

AC-LGADs, also referred to as resistive silicon detectors, are a recent development of low-gain avalanche detectors (LGADs), based on a sensor design where the multiplication layer and n⁺ contact are continuous, and only the metal layer is patterned. In AC-LGADs, the signal is capacitively coupled from the continuous, resistive n⁺ layer over a dielectric to the metal electrodes. Therefore, the spatial resolution is not only influenced by the electrode pitch, but also the relative size of the metal electrodes. Signal propagation between the metallized areas and charge sharing between electrodes plays a larger role in these detectors than in conventional silicon sensors read out in DC mode. AC-LGADs from two manufacturers were studied in beam tests and with infrared laser scans. The impact of n⁺ layer resistivity and metal electrode pitch on the charge sharing and achievable position resolution is shown. For strips with 100 µm pitch, a resolution of ¡ 5 µm can be reached. The charge sharing between neighboring strips is investigated in more detail, indicating the induction of signal charge and subsequent re-sharing over the n⁺ layer. Furthermore, an approach to identify signal sharing over large distances is presented.