Impact of Vth Instability on Time-Resolved Characteristics of MIS-HEMT-Based GaN Power IC

The impact of dynamic threshold voltage (
${V}_{{\text {th}}}$
) on the real-time characteristics of GaN direct-coupled FET logic (DCFL) inverter is investigated using an in-situ voltage tracking method. Due to the electrons’ trapping/de-trapping process at the gate dielectric/AlGaN-barrier interface, a two-step positive shift of the threshold input (
${V}_{{\text {T}}}$
) is observed in the device-under-test (DUT) inverter circuit, including the start-up periods and the self-adjusted dynamic equilibrium periods. The dependence of the dynamic
${V}_{{\text {T}}}$
upon different temperatures, input voltage magnitude, and operating frequency, is systematically studied and the underlying mechanism is revealed. Compared with the dc
${V}_{\text {T}}$
of the inverter of 3.6 V, the dynamic
${V}_{\text {T}}$
at 1 MHz switching with 8 V input amplitude shifts to ~5 V, which poses a challenge to GaN power integrated circuit (IC).