Reliability and Compact Modeling of Gamma-Irradiated 4H-SiC Bipolar Devices and Circuits
Tid: Må 2026-06-15 kl 10.00
Plats: Greta Woxén, Teknikringen 31, Stockholm
Videolänk: https://kth-se.zoom.us/j/64180405913
Språk: Engelska
Respondent: Alexey Metreveli , Elektronik och inbyggda system
Opponent: Doctor Muhammad Nawaz, Hitachi Energy Research, Västerås, Sverige
Handledare: Professor Carl-Mikael Zetterling, Elektronik och inbyggda system
QC 20260525
Abstract
This thesis investigates the radiation response of 4H-SiC bipolar junction transistors and integrated TTL inverter circuits under gamma irradiation, with emphasis on the role of bias conditions, dose rate, temperature, and oxide/interface processing. The work combines in-situ irradiation experiments using a 60Co source, device- and circuit-level electrical characterization, and compact modelling approaches to establish a consistent understanding of radiation-induced degradation mechanisms in this technology.
The results show that the dominant degradation mechanism in the studied devices is an increase in base current, leading to a reduction in current gain. This behaviour is attributed to radiation−induced charge trapping in oxide layers and the formation of interface states at the SiC/SiO2 boundary, which enhance surface recombination. Despite the wide bandgap of 4H-SiC and its intrinsically low carrier concentration, the radiation response is governed primarily by interface−controlled processes rather than by bulk material properties.
A key finding is the dependence of degradation on the electrical bias applied during irradiation. Passive or zero-bias conditions are shown to produce more severe degradation than active bias configurations.
Circuit-level experiments demonstrate that transistor degradation propagates into inverter behavior through shifts in transfer characteristics and changes in supply current. While circuits may remain operational after irradiation, their functional margins are reduced and become strongly dependent on the bias conditions.
The thesis also introduces a compact modelling framework that links radiation-induced physical mechanisms to SPICE-compatible parameters, enabling predictive circuit-level simulations under irradiation conditions.
The overall conclusion is that radiation hardness in 4H-SiC bipolar electronics in many cases can be much higher compared to silicon devices, but the radiation hardness should be understood as a condition-dependent system property, rather than as an intrinsic material characteristic.