Using proton irradiation to probe the origins of low-frequency noise variations in SiGe HBTs

We use proton irradiation to probe the origins of the geometry-dependent variation of low-frequency noise in 120 GHz SiGe heterojunction bipolar transistors (HBTs). Before irradiation, small-sized transistors show a strong variation in noise magnitude across many samples, whereas the noise in larger devices is more statistically reproducible. Although the noise magnitude shows little degradation after 2×10¹³ p/cm² irradiation, the observed noise variation decreases. Its dependence on both geometry and bias is quantified. This fundamental geometrical scaling effect is investigated using theoretical calculations based on the superposition of generation/recombination (G/R) noise sources.