Introduction and history of Capacitive Coupled Low Gain Avalanche Diode (AC-LGAD) detectors.

Particle detectors at future lepton or hadron colliders will require very large area trackers with O(10)um spatial resolution. A timing capability of O(10)ps in addition should allow more efficient and reliable reconstruction of particles from primary collisions in high intensity hadron colliders. Precision timing together with spatial information will be critical not only to disentangle spatially overlapping or other with ambiguous events but also to identify the particles with different mass as well as sensitive to the mass of heavy unknown charged particles. The Low Gain Avalanche Diode (LGAD) technology is now becoming mature achieving a 30ps time resolution. Concerning the spatial resolution, high granularity electrodes potentially introduce a non-uniformity of timing performance. The Capacitive coupled LGAD (AC-LGAD) sensors fabricated by Hamamatsu Photonics (HPK) and Brookhaven National Laboratory (BNL) have shown to achieve a 20-30ps timing resolution with the finely segmented electrodes fully uniformly. In this presentation, a general introduction and history of AC-LGAD detectors will be described.