Output Capacitance Loss of GaN HEMTs in Steady-State Switching

The output capacitance (
${C}_{\text{OSS}}$
) loss, a loss produced when the device's output capacitor is charged and discharged, has become a concern for GaN high electron mobility transistors (HEMTs) in high-frequency applications. This work presents a new, easy-to-implement method for the
${C}_{\text{OSS}}$
loss characterization based on the unclamped inductive switching setup. As compared with prior approaches, this method involves the device's
on
-state conduction and could measure the
${C}_{\text{OSS}}$
loss in a single pulse and the steady-state switching. The
${C}_{\text{OSS}}$
loss of three types of the mainstream commercial GaN HEMTs is characterized, which exhibit some common dependencies including a nonmonotonic relation with the
dv/dt
(or resonance frequency), a linear relation with the
on
-state current, a power-law relation with the peak blocking voltage, and a little temperature dependence. In addition, their
${C}_{\text{OSS}}$
losses all show minimal distinctions in a single pulse and the steady-state switching, despite the increased
on
-resistance in the steady-state switching. This suggests that the traps accounting for the
${C}_{\text{OSS}}$
loss possess different detrapping time constants as compared with the traps governing the dynamic
on
-resistance. Finally, a unified model is established to describe the
${C}_{\text{OSS}}$
loss of all three types of GaN HEMTs. These results provide important references for the high-frequency application of GaN HEMTs and new insights into the physical origin of their
${C}_{\text{OSS}}$
loss.