GaN-based high-frequency devices and circuits: A Fraunhofer perspective
We present the current status of our technology for GaN-based HEMTs and MMICs as well as results ranging from the L-band up to the W-band. Epitaxial growth is carried out on 4HSiC(0001) substrates by both MOCVD and MBE. Processing is done using standard III-V equipment including both frontside and backside processing. For L-band power bars we arrive at output powers, efficiencies and gains beyond 100 W, 60% and 17 dB, all measured under cw conditions at 50V drain bias. The X-band MMICs are characterized by a high efficiency above 40% for two-stage amplifiers. Towards mm-wave applications we have fabricated HEMTs with transit frequencies above 100 GHz and W-band MMICs delivering 0.5W/mm at 94 GHz with 7% PAE. First quaternary InAlGaN barriers show promising results for this new materials system. Reliability tests return a very good long-term stability of our devices even at an elevated channel temperature of 200 8C with an extrapolated lifetime of 5 x 10(5). Initial space capability tests including total ion dose radiation insensitivity, radiation displacement damage, hydrogen poisoning and single event effect are successfully passed.