Transient self-heating effects in multifinger AlGaN/GaN HEMTs with metal airbridges

Abstract

Thermal behavior of a multifinger AlGaN/GaN/sapphire HEMT with a metal airbridge connecting five source contacts is investigated in the transient state using optical and electrical methods and using a 2D thermal model. The gate layout consists of eight fingers, each having 50 μm width/0.3 μm length, the pitch is 35 μm and the thickness of the electroplated airbridge is 7 μm. The device drain contact was pulsed by 10 μs long 10 V pulses, corresponding to ∼11.9 W/mm dissipating power density. The electrical characterization method shows that at the end of the pulse the temperature increase in the HEMT channel is ∼185 K while the transient interferometric mapping (TIM) optical method indicates that the airbridge structure serves also as a cooler removing approximately 10% of the heat energy. Surface temperature maps are constructed by using the TIM for a time window of 2–6 μs. An asymmetry in the temperature profiles was observed, e.g. the source contact was colder by ∼25% than the drain contact at t = 6 μs.