An electro-thermal modeling of modern SiGe and Si bipolar transistor structures using TCAD Sentaurus Synopsys has been carried out. It has been shown that for SiGe heterojunction bipolar transistors, operating at high current density, the internal temperature is higher than for identical Si transistors. As a result a stronger degradation of the device parameters and electrical characteristics is observed.
The effects of proton irradiation on SiGe heterojunction bipolar transistor (HBT) are investigated using Synopsys/ISE TCAD tool. To account for the impact of proton irradiation models for carrier lifetime degradation under irradiation are included in the program. The results of modeling the impact of protons of different energies are presented. For SiGe HBT increase in the base current for low-energy protons is more intense than for high-energy protons. We also present the simulation results of SiGe HBT dc and ac performance after proton exposure. The simulation results are in good agreement with experimental data.
Radiation response of bipolar devices irradiated under various electrical modes and dose rates at high doses has been studied. A nonlinear numerical model including ELDRS effects and electric field reduction at high doses has been developed and validated. Dose degradation of a bipolar transistor's gain factor at different dose rates and electrical modes has been simulated and explained in a unified way, based on dependence of the charge yield in isolation oxides on dose rates and electric fields. It has been shown that at high doses one needs to use a nonlinear, self-consistent numerical approach, accounting for simultaneous suppression of the oxide electric field induced by trapped charge. Correspondingly, two types of degradation saturation have been revealed: (i) due to simultaneous thermal annealing, and (ii) due to total dose dependent electric field reduction in oxides. The former implies proportionality of the saturation dose and degradation level to dose rate, the latter permits dose rate independent saturation levels of degradation.
The possibilities of commercial SPICE are expanded in the new field—space environment electronics design. For this purpose, the set of BJT and MOSFET models with account for radiation influence is included into commercial SPICE device library. The characteristics of devices and circuits subjected to space radiation exposure (gamma-rays, protons, neutrons, electrons, heavy ions) are presented and examined with emphasis on application for radiation hardened electronics systems.