Heat transfer in microwave transistors at cryogenic temperatures
Heat transfer in microwave transistors at cryogenic temperatures lead image
Low-noise microwave amplifiers are widely used in applications like radio astronomy, deep space communications, and quantum computing. For such applications, it is important these amplifiers add as little noise to the incoming signal as possible.
Noise associated with thermal motion is a major component of the noise of the amplifier, and knowledge of the local temperature of the transistor is important to interpreting the physical origin of the noise.
Choi et al. determine the first quantitative measurement of the local temperature of a microwave transistor when the surroundings are maintained at cryogenic temperatures. The researchers used various types of electrical measurements to determine the self-heating, the amount the transistor heats, for a given amount of electrical power.
“We found that the transistor heats much more compared to the expectations when the environment is at room temperature,” said author Austin Minnich. “This finding means the thermal noise is a much bigger contribution than assumed when the device is placed in a cryogenic environment.”
The researchers found the mechanism of heat transfer was not by diffusion as is typically assumed but rather by radiation of atomic vibrations in exact analogy to blackbody radiation of electromagnetic waves.
“Importantly, this result implies self-heating will be appreciable for any realistic low-noise application at cryogenic temperatures, setting a lower bound for the minimum thermal noise and hence overall noise performance of modern microwave transistors absent any improvements in thermal management,” said Minnich.
Because the researchers have identified self-heating as a mechanism that limits the noise performance of modern microwaves, they will explore how to mitigate it.
Source: “Characterization of self-heating in cryogenic high electron mobility transistors using Schottky thermometry,” by Alexander Y. Choi, Iretomiwa Esho, Bekari Gabritchidze, Jacob Kooi, and Austin J. Minnich, Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0063331 .
