Gallium Nitride Based High Electron Mobility Transistors And MMIC Circuits For Ka-wave Applications

GaN HEMTs are considered as excellent candidates for the next-generation microwave power transistors due to their large output power at high frequencies. Nowadays, the research on GaN HEMTs and MMICs has stepped into the millimeter-wave bands. In this dissertation, GaN HEMTs and integrated power amplifiers for Ka-wave applications based on the domestic epitaxial materials are paid attention to, and the main results of this research are summarized as follows:1. A two-dimensional electrical simulation model for Al GaN/GaN HEMT is established in Atlas and successfully used to assist the device structure design.2. The key processes of device were improved for Ka-band Al GaN/GaN HEMT. the recessed- gate process is optimized with SF6 gas. T-shaped gate with the gate length of 100 nm is successfully fabricated through optimizing the exposure conditions in writing the multilayer e-beam photoresist.3. To solve the physical problems in Ka-wave GaN HEMTs, innovative design of the device structure is carried out. Gate-recessed Al GaN/GaN HEMTs with a gate length of 0.16?m are fabricated on a Si C substrate. The passivation layer of ALD-grown Al2O3 effectively suppresses the Schottky gate leakage current, leading to an off-state breakdown voltage increase of 27%.4. Al N back-barrier is inserted between the channel and buffer layers to enhance the carrier confinement, and thus suppresses the short channel effect and reduces the gate leakage current. The fabricated 0.16 ?m gate-length Al N back-barrier HEMT on a Sapphire substrate has a 19% higher fmax(~186 GHz) than that of the conventional device. At 30 GHz, 0.88 W/mm output power density could be generated with PAE=12.31%.5. A double-stage MMIC power amplifier using microstrip interconnect technology is designed with the HEMT device of Win company.