AC-LGAD development in Japan

Adding timing measurement capabilities to semiconductor sensors with fine spatial resolution enables accurate track reconstruction in high-density environments such as the High-Luminosity LHC (HL-LHC) collisions, and also improves particle identification performance. AC-coupled LGAD is a new sensor that possesses both precise timing and spatial resolutions, making it suitable for these requirements. In recent years, extensive research has been conducted to assess its performance.

In Japan, research and development of HPK Pad-type, Strip-type, and Pixel-type sensors have been primarily carried out for the HL-LHC. This presentation will provide an update on the recent developments of AC-LGAD sensors. Basic properties were measured at various p⁺/n⁺ implant concentrations and coupling capacitance, yielding a time resolution of 30 to 40 ps. It has also been confirmed that a position resolution of approximately 10 μm can be achieved.

The radiation hardness of the AC-LGAD sensors was tested through proton beam irradiation and gamma source irradiation. Significant gain reduction was observed due to proton irradiation ranging from 10¹⁴ to 10¹⁵ n_eq/cm², which necessitates higher operating voltage. Gamma irradiation resulted in a slight increase in signal size and reduction in crosstalk.

Regarding the EIC, members of the EIC Japan Group from Hiroshima University, RIKEN, University of Tokyo, and Shinshu University are interested in developing AC-LGAD sensors and their readout systems primarily for the Barrel ToF detectors. This talk will present the recent progress of AC-LGAD research within the EIC-Japan group.