Study of electrical and X-ray induced degradation in 55-nm BiCMOS SiGe heterojunction bipolar transistors

In this work, the effect on the DC electrical characteristics of electrical stress and high X-ray Total Ionizing Dose (TID) exposures is studied and compared for SiGe HBTs of a 55-nm BiCMOS technology. HBTs were exposed to a maximum X-ray TID of 520 krad (SiO 2 ) and in terms of electrical stress, using a particular stress procedure, to a high current injection (i.e. V BE = 1.1 V in the direct gummel-plot configuration). For both stress techniques, the effect of the cumulative X-ray dose and electrical stress duration on the degradation of the base current, I B, is investigated. A linear degradation is observed after X-ray exposure. For the higher cumulative dose, the relative base current ∆I B /I B between pre-stress and post-stress is approximately 8. For electrical stress, degradation is generally more pronounced but increasing or decreasing erratically with the duration of the stress. To investigate a possible detrapping mechanism, a two-step annealing process was conducted at temperatures of 100 °C and 130 °C. Annealing results showed a significant difference between the two degradation processes. A recovery of 90% is measured after X-ray irradiation stress even after two cycles of high-dose X-irradiation, while no recovery is observed after electrical stress. TCAD simulations of X-ray irradiation effects were used to investigate and compare experimental data regarding the impact of created trap densities and emitter width on the degradation of DC characteristics. This enabled us to highlight the role of the EB junction, with a marked perimeter effect. When comparing degradation after stress, the two techniques studied here lead to the same effect, namely an increase in the generation-recombination component of the base current. However, analysis of the results leads us to consider a different location and kinetics for the induced traps.