RADIATION EFFECTS ON BREAKDOWN CHARACTERISTICS OF MULTIGUARDED DEVICES

Multiguard structures are used in order to enhance the breakdown volta ge of microstrip detectors. In this work we studied the electrical pro perties of devices designed in four different layouts on n-Si substrat es, based on a central diode surrounded by various p(+) and/or n(+) fl oating rings. In particular we measured the main DC characteristics an d we compared the experimental results with those simulated by a two-d imensional drift-diffusion computer model. Device noise was also measu red for the central diode as a function of the applied voltage. We rep eated all measurements after neutron and gamma irradiation, in view of the application of these devices to silicon microstrip detectors for future high energy physics experiments. For example at the LHC the lev el of radiation damage expected during the detector lifetime implies v ery high bias voltages for the detector operation. Multiguards can off er a solution, provided the optimisation of the design takes into acco unt the radiation effects.