Investigation of wide band gap semiconductors: InGaZnO TFTs for chemical sensing and hybrid GaN/organic high-frequency packaging and circuits
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Wide band gap (WBG) semiconductors offer a number of unique properties not achievable by traditional silicon, such as optical transparency in the visible wavelength regime, high carrier mobility and high voltage/high power operation. This thesis advances the development of two WBG semiconductors, indium gallium zinc oxide (InGaZnO) and gallium nitride (GaN), for chemical sensing and high-frequency applications, respectively. Whereas previous works have relied on high temperature fabrication and/or device operation that are incompatible with flexible and low-cost substrates, this work successfully exploits low temperature microfabrication methods to manufacture InGaZnO thin film transistors (TFTs) for chemical sensing at room temperature. Gas-phase sensing of volatile organic compounds has been demonstrated, and it is shown that sensitivity can be improved through the use of a polymer capping layer. For liquid-phase sensing, this thesis shows that low temperature atomic layer deposition of TiOx can be used to create dual-gate InGaZnO TFTs with Super Nernstian pH sensitivity and long term reliability within a liquid environment. GaN devices and circuits offer best-in-class high power performance, yet packaging remains a critical issue for practical applications. This work proposes a novel, flip-chip bonding packaging technique that involves GaN die encapsulation within multi-layer organic laminates that are both low-cost and low-loss. A 5.4 W hybrid GaN/organic encapsulated power amplifier operating in the X-Band is demonstrated for the first time. Moreover, the encapsulated package technique has been extended to realize a heterogeneous receiver achieves the widest bandwidth among heterogeneous receivers reported to date.