Design and simulation of modified 3D-trench electrode sensors

Future experiments at high-luminosity hadron colliders will involve unprecedent levels of pile up, calling for ultrafast detectors in order to add time information to distinguish between particle tracks. The unique geometry of 3D sensors enables to achieve very good timing performance, with the additional benefit of high radiation hardness. Remarkable results in terms of temporal resolution have been reported for 3D sensors with columnar electrodes (-30 ps) and even better with trenched electrodes (-10 ps), because of a more uniform distribution of the electric field and weighting field. However, 3D-trench technology is more complex, and has still to be optimized in terms of both fabrication process and pixel layout. To this purpose, as an alternative to the existing design which features continuous (p+) ohmic trenches, we propose a new variant by introducing a gap (-10 mu m) in the p+ trenches and placed offset with respect to the readout (n+) trenches, so as to reduce the risk of lithographical defects that were observed in mm's long ohmic trenches, thus improving the fabrication yield.TCAD simulations confirmed that the impact of the gap on the uniformity of the electric and weighting field is minimum, and good charge collection efficiency performance is preserved up to large fluences. Further Monte Carlo time-resolved simulations are performed on both the standard and modified geometries showing comparable temporal resolutions.