A Circuit for Evaluating GaN HEMT Dynamic Rds(on) at Cryogenic Temperatures

GaN HEMTs are promising power switching devices for cryogenic power converters in superconducting motor drives and space applications. However, GaN HEMTs experience dynamic on-resistance Rds(on) which is not well understood at cryogenic temperatures (CT). This paper presents a circuit for evaluating the dynamic Rds(on) of GaN HEMTs at CT by using on-the-fly measurements to capture off-state trapping transients. The evaluation circuit utilises a measurement circuit with a blocking switch to accurately measure the Vds. Due to the much lower Rds(on) at CT than room temperature (RT), an amplifier was implemented to amplify the output of the measurement circuit, for which the performance is validated using a coaxial shunt resistor. Results demonstrate that the circuit can successfully measure the dynamic Rds(on) 2 μs after the device turns on at both RT and 77 K.