Superficial Breakdown Analysis in 3d Detectors and in Active-Edge Planar Detectors through TCAD Simulations

This report describes the main results obtained from numerical simulations of silicon detectors with tridimensional electrodes and with active-edge and planar electrodes. The first type of detector, only recently proposed thanks to the great improvement of the micromachining processes, has electrodes penetrating vertically in the substrate. Differently from the conventional planar detectors in which the charge collection occurs on the surface of the device, the 3D architecture allows to decouple the active volume of the detector, determined by the thickness of the silicon wafer, from the distance that the carriers need to travel to be collected from the electrodes. This distance is equal to the one between the electrodes and can be reduced in the order of some ten of micrometers. This property allows to obtain very fast detectors that are, at the same time, very resistant to radiation damage, to be used in the particle tracking systems of the next generation’s accelerators. The second type of detectors combines planar structures with the 3D technology. They essentially are planar photodiodes but an active-edge is added using the 3D technology. With this trick it is possible to reduce the dead area around the device, ensuring less area waste and better distribution of the detectors on wide surfaces. The activity was focused on numerical simulations with particular attention to the breakdown dynamics, in order to understand how the phenomena occurs and to gain better knowledge of the critical areas of the devices before their realization in the FBK laboratories. The simulations were carried out applying an increasing reverse voltage to the devices and looking at the regions where the electric field is maximum. In the active-edge case, different configurations were tested in order to understand which one allowed to apply the higher voltage. At the end some transient simulations were made to assure that the introduction of the active-edge didn’t compromise the charge collection in the detectors.