MODEL FOR SUSPENDED GATE FIELD EFFECT TRANSISTORS USED IN

LABORATORY ANIMAL CAGE MONITORING

By

KAREN E. SUPAN

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2005

Copyright 2005

by

Karen E. Supan

This document is dedicated to my parents, Mary Jo and Fred Timm.

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ACKNOWLEDGMENTS

First, I would like to thank my advisor, Dr. Herbert Ingley, for his constant support

and encouragement of this work. From our first meeting, he has been a great mentor to

me in engineering, teaching, and life in general. I thank him for the countless words of

wisdom he imparted to me. I acknowledge my appreciation to Dr. David Hahn for the

generous amount of time he devoted to this project by providing technical assistance on

the experimental portion of this project, offering his expertise in a new area to me and for

serving on my committee. I also express gratitude to Dr. Sherif Sherif, Dr. Bill Lear, and

Dr. Jason Weaver for being committee members and providing guidance in their area of

proficiency.

I am grateful to Osman Ahmed of Siemens Building Technology for the inception

and financial support for this project. Danke schön to Roland Pohle, Peter Gulden, and

many others who made the trek across the Atlantic from Siemens Core Technology in

Munich, Germany, to collaborate on this project. Special thanks go to Dr. Gus Battles

and Mike Cormier from Animal Care Services for opening their facilities for this project

and answering many questions along the way.

It is impossible to forget all the friends and colleagues I have met at UF who have

made the time here so enjoyable.

Above all, I express thanks to my parents and family for creating an environment

where education was a high priority and paving the way for me to follow in their tracks.

My deepest gratitude goes to my husband, Brian, for providing encouragement to pursue

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this degree. I will be forever indebted to him for the distances he went to help me

achieve this accomplishment.

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TABLE OF CONTENTS Page

ACKNOWLEDGMENTS ................................................................................................. iv

LIST OF TABLES............................................................................................................. ix

LIST OF FIGURES .............................................................................................................x

ABSTRACT..................................................................................................................... xiii

CHAPTER

1 BACKGROUND ..........................................................................................................1

Comparison of Static Isolator Cages to Ventilated Caging Systems............................4 The Macroenvironment ................................................................................................7 The Microenvironment .................................................................................................9

Ammonia .............................................................................................................10 Carbon Dioxide ...................................................................................................14 Other Contaminants.............................................................................................16 Contact Bedding ..................................................................................................17 Relative Humidity ...............................................................................................19 Ventilation ...........................................................................................................20 Additional Environmental Factors ......................................................................21

Previous Environmental Studies.................................................................................22 Cost Analysis for Current Husbandry Practices .........................................................29 Air Sampling Techniques ...........................................................................................30

Semiconductors ...................................................................................................31 Field Effect Transistors .......................................................................................33 Gas Sensing .........................................................................................................35

Summary.....................................................................................................................40

2 EXPERIMENTAL FACILITIES AND METHODS .................................................42

Experimental Setup.....................................................................................................42 Experimental Procedures ............................................................................................48

Carbon Dioxide Sensor........................................................................................48 Ammonia Sensor .................................................................................................49

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3 THEORETICAL MODELING ..................................................................................54

Gibbs Free Energy ......................................................................................................54 Adsorption ..................................................................................................................58 Surface Reaction Rate Expressions ............................................................................60

Langmuir Adsorption Isotherm ...........................................................................60 Dissociative Adsorption ......................................................................................62 Competitive Adsorption ......................................................................................63

Proposed Mechanisms ................................................................................................64 Ammonia and Hydroxide ....................................................................................64 Ammonia Dissociation ........................................................................................66 Molecular Adsorption..........................................................................................72

Reaction Kinetics........................................................................................................74 Summary.....................................................................................................................77

4 RESULTS AND DISCUSSION.................................................................................78

Drift Tests ...................................................................................................................78 Ammonia Sensor Results............................................................................................79

Sensor Response and Mechanism .......................................................................80 Diffusion..............................................................................................................87 Temperature Effects ............................................................................................89 Sensor Performance.............................................................................................91

Gradual ramping tests...................................................................................94 Cross-sensitivity to humidity and carbon dioxide........................................96

Carbon Dioxide Sensor Results ..................................................................................99 Summary...................................................................................................................104

5 SUMMARY AND CONCLUSIONS.......................................................................106

Summary of Results..................................................................................................106 Ammonia Sensor ...............................................................................................106

Sensor response and mechanism................................................................106 Performance and feasibility........................................................................107

Carbon Dioxide Sensor......................................................................................108 Recommendations.....................................................................................................109 Future Work..............................................................................................................110

APPENDIX

A ENVIRONMENTAL STUDIES ..............................................................................112

B DETAILS OF FIELD EFFECT TRANSISTOR ......................................................116

C ANALYS