Influence of self-heating on noise of SiGe heterojunction bipolar transistors at cryogenic temperatures

Cryogenic low noise transistor amplifiers (LNA) at microwave frequencies have long been of interest for radio astronomy and more recently for quantum computers. While high electron mobility transistors have been the primary device of choice for these applications, SiGe HBTs are increasingly competitive due to increases in cutoff frequency and their relatively high yield. However, an understanding of the influence of self-heating on noise at cryogenic temperatures is lacking. In this work, we report noise measurements on SiGe HBT LNAs from 4 – 50 K. The influence of self-heating on the temperature of electrons at the base-emitter junction is evaluated by comparing measurements in vacuum with those in liquid Helium baths. Our work helps to identify a path for SiGe HBTs to achieve noise figures competitive with those of HEMTs.