Evaluation of junction termination for silicon X-ray detectors

Junction terminations intended for silicon strip X-ray detectors were evaluated experimentally and with simulations, with respect to their tolerance to radiation-induced surface charge. The terminations were designed with an inner guard ring biased to the same potential as the active anode and multiple p+-doped rings with metallic field plates at floating potential. Two designs, one with 9 and one with 14 floating rings were evaluated and applied to simple non-segmented test diodes. The test diodes were irradiated with X-rays to 72–74 kGy, the surface charge was determined from capaciatance–voltage measurements, and reverse breakdown voltage was determined from I–V-curves. Both simulations and experiments showed superior performance of the 14-ring design. The experimentally determined surface charge density after irradiation was in the order of +5×1011 cm−2, and the breakdown voltages were ∼900 and 1600 V for the 9-ring and 14-ring termination, respectively.