Conduction Lead Design and Optimization for Cryogenic Characterization of GaN HEMTs

Gallium Nitride (GaN) HEMTs present superior characteristics at cryogenic temperatures and becomes promising candidates for the lunar mission under the extreme cold environment down to 50 K. Extensive studies have been performed to characterize GaN HEMTs using cryogenic chamber with Liquid Nitrogen (LN2) down to 77 K, while few research focuses on cryocooler with Liquid Helium (LHe2) with limited trade study of cryogenic cabling between electrical resistance and heat flow. This paper proposes a methodology to optimize lead design for cryogenic device characterization. First, the temperature evolution along the conduction lead during the pulse test is modeled with reasonable assumptions, finding that Joule heating effect is basically negligible. Then, the thermal load and load-line effect are analyzed to introduce the design constraints, by which the optimization is performed to achieve desirable voltage drop and thermal load. Finally, the proposed methodology is validated by several design examples, and the I-V characterization of a GaN HEMT is demonstrated at 50 K.