Effects of Collector Profile on the SET Response of 130-nm High-Speed and High-Breakdown SiGe HBTs

A comparison of laser-induced single-event transients in silicon-germanium heterojunction bipolar transistor (SiGe HBT) variants designed for high-speed applications and high-breakdown applications is presented. A significantly lower-amplitude single-event transient (SET) response at low laser pulse energies was observed in the high-speed device compared to the high-breakdown device. At high laser pulse energies, however, the transient amplitudes converged and produced a nearly identical response. A three-dimensional technology computer-aided design (TCAD) model of a SiGe HBT was used to understand the differences between the observed SET responses. During an SET produced by a low laser pulse energy, the mean electric field in the collector-base (CB) junction of a simulated high-breakdown device is shown to have a greater magnitude across the depletion region compared to that of its high-speed counterpart. Motivated by the proportional relationship between drift current and CB junction electric field, a greater breakdown voltage device produced a larger SET response. During an SET produced by a high laser pulse energy, the charge from the SET exceeded the collector doping in both the high-speed and high-breakdown SiGe HBT. This creates a conductive path to the output terminal, removing the dependence of collector doping on SET amplitude. The results of this study should help inform design choices of which device breakdown variant should be used in a given circuit if SETs are a major consideration for the application.