Temperature dependence of single event transient in SiGe HBT for cryogenic application

We experimentally demonstrate that the dominant mechanism of single event transient in silicon-germanium heterojunction bipolar transistors (SiGe HBTs) can change with decreasing temperature from +20 ℃ to -180 ℃. This is accomplished by using a new well-designed cryogenic experimental system suitable for the pulsed laser platform. Firstly, when the temperature drops from +20 ℃ to -140 ℃, the increased carrier mobility drives a slight increase in transient amplitude. However, as the temperature decreases further below -140 ℃, the carrier freeze-out will bring about an inflection point which means the transient amplitude will decrease at cryogenic temperatures. To better understand this result, we analytically calculated the ionization rates of various dopants at different temperatures based on Altermatt’s new incomplete ionization model. And the parasitic resistivities with temperature on the charge collection pathway were extracted by the 2-D TCAD process simulation. In addition, we investigate the impact of temperature on the novel electron injection process from emitter to base under different bias conditions. The increasing of the emitter-base junction’s barrier height at low temperatures could suppress this electron injection phenomenon. We have also optimized the built-in voltage equations of HICUM compact model by introducing the impact of incomplete ionization. The present results and methods could provide a new reference for the effective evaluation of single event effects in bipolar transistors and circuits at cryogenic temperatures and provide new evidence of SiGe technology’s potential for applications in extreme cryogenic environments.