Measuring Dynamic On Resistance in GaN Transistors at MHz Frequencies

Gallium nitride (GaN) transistors are desirable for use in power electronics because of their low resistance and capacitance as compared to silicon devices. However, when switched at high frequencies, GaN transistors experience high dynamic on resistance which is both detrimental and difficult to measure. We propose a technique to measure dynamic on resistance of GaN transistors while exposing them to voltage and current waveforms that are similar to those seen in high-frequency (HF) power converters. The technique can be performed at high frequency while disambiguating loss in the output capacitance (P
_oss
) and can be applied across frequency, temperature, and off-state voltage. The result is a lumped R
_on
value which is easily incorporated into device models to provide a more accurate basis for design, analysis, and simulation of HF converters. We apply this technique to evaluate commercial GaN transistors at 3 MHz and find that dynamic R
_on
is roughly 4-6 times the room-temperature static R
_on
values usually quoted in datasheets, with device-dependent temperature and off-state voltage dependence.