Timing Parameters of 3D Si Sensors with Hexagonal Electrodes Layout

Abstract This study focuses on the timing performance of double-sided 3D Si sensors fabricated at the Centro Nacional de Microelectrónica (CNM) within the RD50 collaboration. The investigated devices originate from a dedicated CNM production run targeting the optimization of 3D sensors for fast-timing applications at the high-luminosity colliders such as HL-LHC. The studied detectors had columnar electrodes positioned in a hexagonal (HEX) structure instead of the standard square configuration. Two parameters of the signal generated using the Two-Photon Absorption Transient Current Technique (TPA-TCT) were investigated to characterize the timing performance of the sensors: the Time of Arrival (ToA) and the Rise Time (RT). The results show that the timing performance of the 3D HEX columnar-electrode sensor depends on the depth at which charge is generated within the active volume of the device. A strong dependence on the applied bias voltage and a moderate dependence on the laser pulse energy were also observed. Finally, the results for the HEX sensor were compared with those obtained for a detector featuring the standard square electrode configuration. In our single-cell measurements, square 3D Si cells exhibit better timing performance, with a smaller ToA spread of approximately 50 ps compared to 115 ps at a bias voltage of 20 V and a depth of 185 μm (in both cases under fully depleted conditions) and at a laser pulse energy of 650 pJ. This improvement is not solely a consequence of how the p + columns are arranged around the n + column, but rather reflects the combined influence of the cell layout, the cell size, and the length of the inter-electrode distance between the n + and p + column electrodes.