THESIS
2015
iii leaves, iv-xvi, 116 pages : illustrations ; 30 cm
Abstract
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...[
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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.
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