Study of n-on-p sensors breakdown in presence of dielectrics placed on top surface

The ATLAS Experiment at LHC will have several upgrade projects for High Luminosity LHC operations. Its tracking system will be replaced to cope with the higher interaction rate and radiation levels. The Strip portion of the tracker will be significantly expanded in radius and instrumented area to control the occupancy and momentum resolution. The strip modules are based on large-area n-on-p sensors with short strips, designed to work with the larger particle fluxes and radiation hardness requirements. The strip module design has readout flex circuit glued directly on top of the sensors’ active area to facilitate the assembly process and minimize the radiation length. Adhesive spread outward to the guard ring (GR) region is typically avoided to control the sensor breakdown. However, due to the large number of modules to be constructed, on the order of 20000, such occasions may in principle happen, depending on the process precision control. Therefore, the adhesive influence on the sensor breakdown and the breakdown mechanism are of interest. In this contribution we report on the studies of the breakdown behavior with prototype sensors, where adhesives were placed on top of the sensor, either directly in the GR region, or in the active area far away from it. Several adhesives under consideration for module building were used in these measurements. The measurements after thermo-cycling and after irradiation were also performed.