Development of millimeter-wave broadband power amplifier MMICs using gallium nitride HEMTs

This dissertation utilizes the advancement in GaN HEMT technology to demonstrate ultra-broadband state-of-the-art MMICs up to the millimeter-wave frequency range. A distributed amplifier circuit topology is selected and an amplifier with a record 50 GHz bandwidth is demonstrated. This amplifier achieves a gain of 5 dB and output power of over 130 mW. The gain bandwidth product for this amplifier is 90 GHz.;The maximum available gain is enhanced using a dual-gate GaN HEMT device. This device is equivalent to a cascode pair of standard HEMTs and results in numerous improvements to the DC and high-frequency characteristics. A distributed amplifier using the dual-gate GaN HEMTs is demonstrated to have a gain of 12 dB and a bandwidth of 30 GHz pushing the gain-bandwidth product to 120 GHz. This is a 33% improvement over the distributed amplifier based on standard HEMT. The dual-gate HEMT distributed amplifier achieves a maximum saturated output power of 1 Watt.;The next design aims to push the power limits of this distributed amplifier topology. At the same time high gain is maintained by using a two-stage cascaded topology. The first stage acts as a driver and gain stage. The second stage uses capacitive division technique to enhance the power output. A novel inter-stage matching network is used to further increase the output power while keeping the MMIC compact. This amplifier achieves a gain of 20 dB, a bandwidth of 20 GHz and an output power of 2 Watts.;All the circuits were self-fabricated in the UCSB cleanroom. This meant a tremendous amount of semiconductor processing and development work. The MMIC fabrication process was continuously optimized to obtain a repeatable and high-yielding process. In addition, considerable effort was also directed toward extracting measurement-based models for the HEMTs and passives. In the end, a new large-signal model is developed to better simulate the non-linear behavior of the HEMTs. This model is used to design a novel, highly linear, differential distributed amplifier using derivative superposition method. Simulated results show that this amplifier achieves excellent second and third harmonic suppression over a wide bandwidth while consuming low DC power.