Self-heating of cryogenic high electron-mobility transistor amplifiers and the limits of microwave noise performance

The fundamental limits of the microwave noise performance high electron mobility transistors (HEMTs) are scientific and practical interest for applications in radio astronomy quantum computing. Self-heating at cryogenic temperatures has been reported to be a limiting mechanism noise, but cooling strategies mitigate it, instance using liquid cryogens, have not evaluated. Here, we report measurements packaged two-stage HEMT amplifier immersed normal superfluid $^4$He baths vacuum from 1.6 - 80 K. We find that these cryogens unable thermal associated with self-heating. Considering this finding, examine implications lower bounds HEMTs. Our analysis supports general design principle HEMTs maximizing gain lowest possible power.