Developments and first measurements of Ultra-Fast Silicon Detectors produced at FBK

Segmented silicon sensors with internal gain, the so called Ultra-FAST Silicon Detectors (UFSD), have been produced at FBK for the first time. UFSD are based on the concept of Low-Gain Avalanche Detectors (LGAD), which are silicon detectors with an internal, low multiplication mechanism (gain ~ 10). This production houses two main type of devices: one type where the gain layer is on the same side of the read-out electrodes, the other type where the gain layer is on the side opposite to the pixellated electrodes (reverse-LGAD). Several technological splits have been included in the first production run, with the aim to tune the implantation dose of the multiplication layer, which controls the gain value of the detector. An extended testing on the wafers has been performed and the results are in line with simulations: the fabricated detectors show good performances, with breakdown voltages above 1000 Volts, and gain values in the range of 5–60 depending on the technological split. The detectors timing resolution has been measured by means of a laboratory setup based on an IR picosecond laser. The sample with higher gain shows time resolution of 55 ps at high reverse bias voltage, indicating very promising performance for future particle tracking applications.