Wide bandgap gallium nitride (GaN) and related compounds possess superior material properties, including high electron saturation velocity, large breakdown electric field, and sustainability at high operating temperatures. Because of strong spontaneous and piezoelectric polarization effects, GaN-based heterostructures forming a two-dimensional electron gas (2DEG) channel with large sheet carrier concentration and high electron mobility are ideal for high-frequency power electronics. In addition to other characteristics such as high acoustic velocity, high mechanical and thermal stability and inherent chemical inertness, GaN has also been considered as an attractive thin film piezoelectric material for fabrication of on-chip acoustic wave devices. This dissertation aims at the ex...[ Read more ]

Wide bandgap gallium nitride (GaN) and related compounds possess superior material properties, including high electron saturation velocity, large breakdown electric field, and sustainability at high operating temperatures. Because of strong spontaneous and piezoelectric polarization effects, GaN-based heterostructures forming a two-dimensional electron gas (2DEG) channel with large sheet carrier concentration and high electron mobility are ideal for high-frequency power electronics. In addition to other characteristics such as high acoustic velocity, high mechanical and thermal stability and inherent chemical inertness, GaN has also been considered as an attractive thin film piezoelectric material for fabrication of on-chip acoustic wave devices. This dissertation aims at the exploration of GaN-based device technologies and their integration for applications in novel sensors and high-frequency power electronics.

In this thesis, monolithic integration technology of acoustic wave devices with high electron mobility transistors (HEMTs) on AlGaN/GaN heterostructures has been demonstrated. High performance Lamb-wave sensors were designed and fabricated using a GaN-on-Si platform. Then two on-chip oscillators were implemented by monolithically integrating a Lamb-wave or a surface acoustic wave (SAW) delay line device with AlGaN/GaN HEMT circuitries. The monolithic oscillators in this work, which are suitable for sensor systems operating at high ambient temperature, could potentially be extended to high-frequency power applications.

A scalable gate-last self-aligned technology was developed for fabrication of GaN-based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs). Source/drain (S/D) regrowth and low-k benzocyclobutene (BCB) planarization techniques were employed to reduce the access resistance and parasitic capacitance, minimizing the RC-related delay. Thin AlN barriers and in-situ grown SiN_x gate dielectrics by metal-organic chemical vapor deposition (MOCVD) were incorporated to facilitate the device scaling, with increased gate control capabilities, maintaining high channel conductivity and suppressing the gate leakage. The fabricated gate-last self-aligned in-situ SiN_x/AlN/GaN MISHEMTs exhibited high performance, demonstrating great potential for the next-generation RF/microwave power applications.