The shift of breakdown voltage for silicon membrane strip detectors resulting from surface avalanche

Abstract

Silicon membrane strip photodetectors are fabricated based on thin silicon-on-insulator (SOI) wafers. The thin SOI wafer is realized by exploiting a thinning process on backside. Such detectors can be implemented in proton-beam position detection because its ultra-thin membrane substrate can reduce beam scattering and offer the considerable advantages of higher radiation hardness. A p-spray implantation process is typically performed at the silicon surface between the n +-strips in order to insulate them, without requiring an extra photolithographic mask. In this paper, the sources of leakage current in the detector are first studied by considering both activation energy and simulation analysis in Silvaco TCAD. While the device is operating below avalanche breakdown voltage, the Shockley-Read-Hall process and trap-assisted-tunneling process are dominantly contributing to leakage current. The dominant breakdown voltage is attributed to the premature breakdown in the junction of p - spray / n + region. The shift of this breakdown voltage under repeated avalanche processes is analyzed in-depth by both experiments and simulations, as a function of temperature and electrical stress conditions, which are introducing an important reliability problem. The electrical stress can be attributed to an increase in fixed charge density at the Si/ SiO 2 interface. The breakdown voltage finally increases by 4 V after successive avalanche breakdowns as a function of the applied excess bias voltage beyond breakdown voltage.