Gallium nitride MEMS resonators

Abstract

As a wide band-gap semiconductor, with large breakdown fields and saturation velocities, Gallium Nitride (GaN) has been increasingly used in high-power, high-frequency electronics and monolithic microwave integrated circuits (MMICs). At the same time, GaN also has excellent electromechanical properties, such as high acoustic velocities and low elastic losses. Together with a strong piezoelectric coupling, these qualities make GaN ideal for RF MEMS resonators. Hence, GaN technology offers a platform for the seamless integration of low-loss, piezoelectric RF MEMS resonators with high power, high frequency electronics. Monolithic integration of MEMS resonators with ICs would lead to reduced parasitics and matching constraints, enabling high-purity clocks and frequency-selective filters for signal processing and high-frequency wireless communications. This thesis highlights the physics and resonator design considerations that must be taken into account in a monolithically integrated solution. We then show devices that achieve the highest frequency-quality factor product in GaN resonators to date (1.56 x 1013). We also highlight several unique transduction mechanisms enabled by this technology, such as the ability to use the 2D electron gas (2DEG) channel of High Electron Mobility Transistors (HEMTs) as an electrode for transduction. This enables a unique out-of-line switching capability which allowed us to demonstrate the first DC switchable solid-state piezoelectric resonator. Finally, we discuss the benefits of using active HEMT sensing of the mechanical signal when scaling to GHz frequencies, which enabled the highest frequency lithographically defined resonance reported to date in GaN (3.5 GHz). These demonstrated features sh