MMICs using gallium nitride HEMTs and thin-film BST capacitors

GaN HEMTs have been considered as candidate devices for next generation high-power microwave applications. They feature fast speed, high power density, and also low noise. Many research works are underway from material improvement, fabrication development and device optimization. An increasing number of microwave circuits based on GaN HEMTs have been demonstrated, but there are still many challenges to make high-performance integrated microwave circuits. One of these problems is the limited availability of high quality integrated passive components for Monolithic Microwave Integrated Circuits (MMIC). Therefore, the exploration and integration of novel integrated passive components is a key solution to broaden the functionality of GaN MMICs.; Barium Strontium Titanate (BST) tunable capacitors have been studied for years as microwave components because of their high tunability, compact structure, decent quality factor and high capacitance density. In order to optimize the loss in the BST capacitors, a geometry dependent RF model is established to analyze high frequency performance at the device level. Several tunable microwave circuits, such as tunable filters and phase shifters, are demonstrated using these design techniques. Also successful integration of the BST process with GaN HEMT circuits in the form of a 5 GHz GaN HEMT oscillator is presented. BST thin film technology is shown to be useful for the design of frequency agile circuits and reduction of layout area in various microwave application.; In this research, a full MMIC fabrication process has been developed based on GaN HEMTs. BST tunable capacitors, spiral inductors, metal-insulator-metal (MIM) capacitors and thin film resistors have been successfully integrated in GaN HEMT microwave integrated circuits. Field-plated GaN HEMT structures were also employed and analyzed to improve the power and efficiency performance of transistors. Various microwave circuits, including LNAs, oscillators and power amplifiers, were designed and fabricated to study high frequency noise, phase-noise and power behaviors. Results from these circuits show superior properties of GaN MMICs, especially from perspectives of power density and efficiency.