DC and RF Variability of SiGe HBTs Operating Down to Deep Cryogenic Temperatures

We present measurement results of commercially-available 90-nm SiGe HBTs at 300 K, 78 K, and 7 K. The data reveal increased variability of SiGe HBTs at 78 K and 7 K compared to that at 300 K. The variation of collector current, base current, and DC current gain (β) increase from 5% at 300 K to 50% at 7 K around the average measured values. Transconductance (gm) variation increases from 0.6% at 300 K to 5% at 7 K. Peak fT variation increases from 2.6% to 7.1%, while the fT at low injection increases from 1.8% at 300 K to 24.9% at 7 K. Increased variability is observed at lower injection levels at 78 K and 7 K and DC parameters tend to have more variation than RF parameters. The implications of increased variability for circuit designs supporting emerging cryogenic applications such as quantum computing are discussed.