Cryogenic/sub-ambient cooling of electronics: revisited

Operation of electronic devices at cryogenic temperatures has been considered a compelling option for enhancing their performance since long. Literature abounds with studies on cooling of electronics using liquid nitrogen from pool boiling to single and two-phase jet impingement. In spite of the performance benefits and the existing knowledgebase, attempts to operate microprocessors at cryogenic/sub-ambient temperature have not met with commercial success. Instead, scaling of CMOS (Complementary Metal Oxide Semiconductor) devices through reduction of gate length has proved to be a more viable option over the past few decades. However, as lithography scales approach a few times the atomic dimensions ("5 nm node"), further performance enhancement using traditional approaches may not be possible. Even at "50 nm" technology node, the sub-threshold power becomes comparable to the active power, due to the increase in leakage current at small gate lengths. As a result, operating electronic devices at low temperature again emerges as an attractive approach to performance enhancement. In the present work, a model for comparing different candidate technologies for realizing sub-ambient cooling is presented. Using this model, some promising candidate refrigeration technologies are analyzed. Continued interest in the use of liquid nitrogen for electronics cooling is reviewed. Some technologies, which can be used for integration of cryocoolers to electronic chips, are discussed.