Date of Award

2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Electrical & Systems Engineering

First Advisor

Mark G. Allen

Abstract

Traditional microfabrication techniques for microelectromechanical systems (MEMS) have emphasized silicon and silicon-related materials. As more MEMS applications emerge, including the Internet of Things (IoT) and biodegradable applications, widely expanded materials sets are being considered. Since iron (Fe) has good electrical and magnetic properties, it undergoes degradation in moist or oxygenated environments, and since it is prevalent in both biological and environmental systems, it is being seriously considered as a candidate material to satisfy these new needs. In this dissertation, we developed iron-based microstructures for use in biodegradable and non-biodegradable applications. Specifically, electrical interconnects were developed with biodegradable iron/polymer composites. From the materials perspective, electrical, mechanical, and electrochemical properties of the composite material under physiological degradation were investigated. Stable electrical resistivity of the composite was shown over 20 days in degradation, even if under mechanical straining. Good adhesion to similarly biodegradable substrates of the composite was also shown in degradation. Further, the biodegradability of the composite was demonstrated by characterizing its degradation behavior. From the application perspective, a functional lifetime of over 4 days of the electrical interconnects with the packaging was achieved under physiological degradation to prove the capability of iron-based materials in biodegradable applications. In addition, miniaturized step-up transformers with laminated electrodeposited iron-alloy cores were developed. From the materials perspective, the magnetic permeability of the iron-alloy thin films at micro-scale thicknesses was characterized to demonstrate the retained magnetic properties of these materials at smaller scales. From the application perspective, the performance of the transformers was characterized at the device and circuit level to demonstrate the utility of iron-based bulk material in non-biodegradable magnetic applications. Finally, electrostatically tunable inductors fabricated from iron/ceramic composites were developed. From the materials perspective, the magnetic permeability tunability of the iron/ceramic composites was demonstrated. From the application perspective, the reasonable tuning ability of the device with minimum power consumption was shown to prove the utility of iron-based composite materials in non-biodegradable magnetic applications.

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