Date of Award

8-2010

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

Advisor

Rosemary Smith

Second Committee Member

Nuri Emantoglu

Third Committee Member

Scott Collins

Abstract

The goal of this project was to design, fabricate and test a multi-level micro coil, encased in parylene, to serve as part of a wireless resonant sensing circuit for a biomedical sensor. The goal was motivated by researchers at The Jackson Laboratory, a biological testing facility on Mount Desert Island, who are seeking a means to monitor, wirelessly the intraocular pressure in mouse eyes to study the genetics and progression of glaucoma. A mouse's eye is approximately 1 mm in diameter, so any sensor that is to be physically attached or implanted has to be very small. Additionally, in order to perform long term monitoring (days) on an unanesthetized, freely moving mouse requires wireless interrogation. To address this problem, a microfabricated resonating bio-implantable pressure sensor no greater than 100 um in all three dimensions is proposed. For this purpose multilayer micro coils with outer diameters from 100 um to 1000 um in size were designed and fabricated using microelectronic device fabrication techniques. Theoretical equations were applied to an equivalent circuit model of a multilayer micro coil with which the equivalent circuit component values were determined based on coil geometry. The coils' S11 parameters were measured using a vector network analyzer, and non linear regression was used to determine the equivalent circuit component values from the S11 data. Coils bound to the substrate on which they were fabricated and released coils were both tested. Also, the temperature response of the coils was examined. The experimental measurement results are compared with the theoretical values for the electrical characteristics of the micro coils. Poor correlation was obtained for the values of intermetal insulator resistance which is attributed to a failure in fabrication. During fabrication pin holes formed along the edge of the lower metal layer when the via holes were etched, resulting in shorting of the top and lower metal layers. Based on the theoretical results, a device with parameters that satisfy the estimated requirements for mouse intraocular pressure sensing can be fabricated, once the process is optimized to eliminate the pinholes.

Share