Impact of field limiting ring technique on breakdown voltage of irradiated Si sensors

The very intense radiation environment of high luminosity future colliding beam experiments (like LHC) makes radiation hardness the most important issue for Si detectors. One of the central issues concerning all LHC experiments is the breakdown performance of these detectors. The major macroscopic effect of radiation damage in determining the viability of long-term operation of Si sensors is the change in effective charge carrier concentration (N_eff), leading to type-inversion. Floating field limiting guard rings have been established as means of improving the breakdown performance of Si detectors. In this work the usefulness of the guard rings in improving the breakdown performance of detectors after type-inversion has been studied. Simulations are carried out to study the effect of change in N_eff on the breakdown performance of optimized guard ring structure using two dimensional device simulation program, TMA-MEDICI. Detailed calculations using Hamburg Model have allowed the parameterization of these effects to simulate the operation scenario of Si detectors over 10 years of LHC operation.