Date of Award

5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering (Holcomb Dept. of)

Committee Chair/Advisor

Goutam Koley

Committee Member

William R. Harrell

Committee Member

Judson Ryckman

Committee Member

Igor Luzinov

Abstract

Micro-electromechanical systems (MEMS)-based sensors have gained significant attention due to their ability to sense, measure, and process various physical, chemical, and biological parameters. The small size of MEMS sensors provides numerous advantages, including low power consumption, high sensitivity, and rapid response time, making them suitable for various applications in healthcare, automotive, aerospace, and consumer electronics.

In the past few years, AlGaN/GaN MEMS devices have been found to offer several advantages over silicon-based MEMS devices. One of the main advantages of AlGaN/GaN MEMS is their high sensitivity to surface stresses and forces due to their high piezoelectric coefficients. This sensitivity allows them to detect small changes in mass or mechanical properties of samples, making them ideal for applications requiring high sensitivity and resolution. Additionally, the high mechanical strength of AlGaN/GaN materials enables these devices to withstand harsh environments, including high temperatures, radiation, and corrosive substances. Moreover, the wide bandgap of AlGaN/GaN materials allows them to operate at higher temperatures and higher power levels, making them ideal for high-temperature sensing and power electronics applications. These advantages make AlGaN/GaN MEMS devices a promising option for various sensing and measurement applications, offering higher sensitivity, resolution, and durability than silicon-based MEMS devices.

Microcantilevers are MEMS-based sensors consisting of a thin beam or plate attached to a fixed base at one end, with the other free to move. These sensors can measure various physical, chemical, and biological parameters such as force, mass, pressure, and chemical reactions. Triangular microcantilevers have emerged as a promising platform for sensing applications due to their high surface area-to-volume ratio and ability to detect subtle changes in their electrical properties.

This work focuses on developing and characterizing a novel UV photodetector structure using dual AlGaN/GaN heterostructure-based two-dimensional electron gas (2DEG) channels and a semi-insulating GaN layer in a triangular microcantilever shape. Using a semi-insulating interchannel layer helped reduce the dark current and achieve a high photo-to-dark current ratio. A unique challenge is presented by the volatile organic compounds (VOCs) in air quality monitoring. VOCs emitted from various sources and mixtures are complex to monitor. We demonstrate a technique for real-time detection of VOCs with AlGaN/GaN dual-channel triangular microcantilevers. These cantilevers were exposed to various VOCs, and corresponding changes in electrical characteristics were recorded and monitored. A single-channel triangular microcantilever-based airflow sensor is also demonstrated in this work. This study also details the formation of indium tin oxide (ITO)-based transparent ohmic contacts for bulk n-GaN and HVPE-grown n-GaN thin films on c-face sapphire, with improved contact characteristics following SiCl4 plasma treatment. Overall, this work presents the design, fabrication, and characterization of AlGaN/GaN triangular microcantilevers for UV, VOCs, and airflow detection. This work contributes to advancing photodetector technology and sensor system development for various applications using III-Nitride triangular microcantilevers.

Author ORCID Identifier

https://orcid.org/0000-0001-7524-8850

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