UC San Diego

This dissertation accentuates the significance of high-power gallium nitride (GaN) camel diode varactors for RF transmitter applications. Modern RF transmitters favor compact adaptive circuits for cost and power efficiency. Adaptive circuits include tunable filters, tunable matching networks, and antenna tuners, facilitating adjustments in resonate frequency or impedance. Crucially, these components need to exhibit robust power handling capability when operating below 6 GHz. Vertical Schottky diodes stand out as tuning elements in these high-power adaptive circuits due to their compactness, high power handling, and superior quality factor, with GaN holds promise for achieving the highest quality factor figure of merit (QFOM) owing to its outstanding breakdown electric field and favorable electron mobility.Popularly pursued GaN Schottky diode varactors suffer from leakage currents at high reverse voltage biases at their junctions and because of inherent threading dislocations in thin GaN layers on foreign substrates. We devised a novel device architecture to address these limitations. We employ an interdigitated anti-series multi-Fin camel diode structure composed of a thin p+-GaN top layer situated between the Schottky metal and an n-type GaN drift layer. The p-GaN layer raises the barrier height to suppress reverse leakage current to maintain a high Q factor at higher reverse biases than Schottky diodes. Additionally, we utilize GaN on Qromis Substrate Technology (QST) wafers that permit the growth of thick GaN layers with lower dislocation densities and lower leakage currents than GaN-on-Si and that are comparable to GaN-on-GaN. In this dissertation, we first propose a universal design flow for power varactors. Secondly, we experimentally validate the proposed methods for suppressing leakage current. Subsequently, a significant portion of this dissertation is dedicated to device optimizations encompassing epi-structure and device aspects. Detailed iterations of experiments and subsequent improvements are documented. The finalized fabrication flow and the DC, RF S-parameters of these diodes are reported, signifying their potential to outperform other power varactor technologies. Lastly, we demonstrate prototype bandpass filters using these diodes, underscoring the feasibility of real-world applications with further refinement and development efforts.