Date of Award

Fall 2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Hai-Feng Ji

Abstract

This work focuses on the simulation, fabrication and characterization of novel microdevices for chemical and biological sensors for improved sensitivity, enhanced performance and applicability. Specifically, microbridge and microcoil sensors have been fabricated via advanced microfabrication technologies. Due to the potential application in chemical and biological sensing, the growth of gold and platinum nanowires during an electrolysis process have also been investigated.

A microbridge can be considered as the head-to-head fusion of two cantilevers and the middle of the bridge would deform in a way similar to a microcantilever. The microbridge sensing device is more stable than the microcantilever, especially in turbulent or vibrational conditions, since both ends are fixed. The trade-off is the low ΔR/R change (sensitivity) of the microbridge compared to that of the microcantilever. Simulation of the microbridge has been conducted via Finite Element Analysis (FEA). The width, thickness and doping level of the piezoresistor play an important part in the sensitivity of the microbridge. Based on the simulation results and following standard microfabrication technology, microbridges have been fabricated. The detection of Hg2+ based on the microbridge platform was investigated for sensor validation.

The microcoil hygrometer can be used as a universal tool for the detection of chemical species by depositing a chemical specific coating on one side of the coil. The coil movement can be readily observed by the human eye and it advances as a cost-effective and power-free device. A micro- or nano-scale sized coil provides an outstanding sensor platform with improved dynamic response, greatly reduced size, and the integration of micromechanical components with on-chip electronic circuitry. Following standard microfabrication techniques, an SiO2/Si/SU-8 microcoil has been fabricated. After surface modification by treating the coil with aminopropyltriethoxysilane (APS), the microcoil was exposed to acetic acid vapor in air for characterization. This microcoil device has a potential to be used as a novel microsensor for the detection of chemical and biological species both in air and in solutions.

A self-assembled approach to grow gold and platinum nanowires across the gap of two electrodes on a surface using an electrolysis process has been investigated. In this process, the anode electrode is oxidized to form nanowires on the cathode. The DC offset, AC signal frequency and the space between the two electrodes all play important roles in the growth of the nanowires.

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