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Fabrication of Hollow Optical Waveguides on Planar Substrates Brigham Young University BYU ScholarsArchive Theses and Dissertations 2006-10-16 Fabrication of Hollow Optical Waveguides on Planar Substrates John P. Barber Brigham Young University - Provo Follow this and additional works at: https://scholarsarchive.byu.edu/etd Part of the Electrical and Computer Engineering Commons BYU ScholarsArchive Citation Barber, John P., "Fabrication of Hollow Optical Waveguides on Planar Substrates" (2006). Theses and Dissertations. 799. https://scholarsarchive.byu.edu/etd/799 This Dissertation is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. FABRICATION OF HOLLOW OPTICAL WAVEGUIDES ON PLANAR SUBSTRATES by John P. Barber A dissertation submitted to the faculty of Brigham Young University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Electrical and Computer Engineering Brigham Young University December 2006 Copyright © 2006 John P. Barber All Rights Reserved BRIGHAM YOUNG UNIVERSITY GRADUATE COMMITTEE APPROVAL of a dissertation submitted by John P. Barber This dissertation has been read by each member of the following graduate committee and by majority vote has been found to be satisfactory. Date Aaron R. Hawkins, Chair Date Milton L. Lee Date Gregory P. Nordin Date Stephen M. Schultz Date Richard. H. Selfridge BRIGHAM YOUNG UNIVERSITY As chair of the candidate’s graduate committee, I have read the dissertation of John P. Barber in its final form and have found that (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill university and department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the graduate committee and is ready for submission to the university library. Date Aaron R. Hawkins Chair, Graduate Committee Accepted for the Department Michael J. Wirthlin Graduate Coordinator Accepted for the College Alan R. Parkinson Dean, Ira A. Fulton College of Engineering and Technology ABSTRACT FABRICATION OF HOLLOW OPTICAL WAVEGUIDES ON PLANAR SUBSTRATES John P. Barber Department of Electrical and Computer Engineering Doctor of Philosophy This dissertation presents the fabrication of hollow optical waveguides integrated on planar substrates. Similar in principle to Bragg waveguides and other photonic crystal waveguides, the antiresonant reflecting optical waveguide (ARROW) is used to guide light in hollow cores filled with liquids or gases. Waveguides with liquid or gas cores are an important new building block for integrated optical sensors. The fabrication method developed for hollow ARROW waveguides makes use of standard microfabrication processes and materials. Dielectric layers are deposited on a silicon wafer using plasma-enhanced chemical vapor deposition (PECVD) to form the bottom layers of the ARROW waveguide. A sacrificial core material is then deposited and patterned. Core materials used include aluminum, SU-8 and reflowed photoresist, each resulting in a different core geometry. Additional dielectric layers are then deposited, forming the top and sides of the waveguide. The sacrificial core is then removed in an acid solution, resulting in a hollow ARROW waveguide. Experiments investigating the mechanical strength of the hollow waveguides and the etching characteristics of the sacrificial core suggest design rules for the different core types. Integration of solid-core waveguides is accomplished by etching a ridge into the top dielectric layer of the ARROW structure. Improved optical performance can be obtained by forming the waveguides on top of a raised pedestal on the silicon substrate. Loss measurements on hollow ARROW waveguides fabricated in this manner gave loss coefficients of 0.26 cm-1 for liquid-core waveguides and 2.6 cm-1 for air-core waveguides. Fluorescence measurements in liquid-core ARROW waveguides have achieved single-molecule detection sensitivity. Integrated optical filters based on ARROW waveguides were fabricated, and preliminary results of a capillary electrophoresis separation device using a hollow ARROW indicate the feasibility of such devices for future investigation. ACKNOWLEDGMENTS This dissertation and the research behind it would not be possible without the support of many people. My adviser, Dr. Aaron Hawkins, has provided needed guidance throughout the duration of my research. The collaboration with Dongliang Yin and Dr. Holger Schmidt at UCSC has been very beneficial due to their hard work on this project. Additional support and funding was provided by Dr. David Deamer at UCSC and Dr. Milton Lee at BYU. Dr. Richard Selfridge provided my first research opportunity, and the experience I gained during that time has been invaluable to my later work. Many fellow students have made invaluable contributions to the research presented here. Don Conkey, Evan Lunt, Matt Smith, J. Ryan Lee, Ghassan Sanber, Tao Sheng, Matt Holmes, Bridget Peeni, John Edwards, Neal Hubbard and Craig Christianson all have helped in many ways, and I am indebted to them for their efforts. Elizabeth Despain, Zack George and Jeffrey Maas provided excellent SEM imagery, as can be seen throughout this dissertation. TABLE OF CONTENTS LIST OF TABLES .......................................................................................................... xii LIST OF FIGURES .......................................................................................................xiv 1 Introduction............................................................................................................... 1 1.1 Integrated Optical Sensors.................................................................................. 1 1.2 Integrated Optical Waveguides with Hollow Cores ........................................... 3 1.3 Contributions ...................................................................................................... 5 2 Optical Waveguiding in Low-Index Materials....................................................... 7 2.1 Introduction......................................................................................................... 7 2.2 Index Guiding..................................................................................................... 7 2.3 Photonic Crystals.............................................................................................. 10 2.3.1 Introduction................................................................................................... 10 2.3.2 Bragg Waveguides ........................................................................................ 11 2.3.3 Two-dimensional Photonic Crystals............................................................. 12 2.4 ARROW Waveguides....................................................................................... 13 2.4.1 Introduction................................................................................................... 13 2.4.2 Optical Characteristics of ARROW Waveguides ......................................... 15 2.4.3 ARROW-based Optical Filters..................................................................... 19 2.5 Conclusions....................................................................................................... 22 3 Hollow Waveguide Fabrication Process ............................................................... 23 3.1 Introduction....................................................................................................... 23 viii 3.2 Process Overview............................................................................................. 25 3.3 Microfabrication Processes............................................................................... 27 3.3.1 PECVD ......................................................................................................... 27 3.3.2 Wafer Cleans................................................................................................. 42 3.3.3 Photolithography........................................................................................... 43 3.3.4 Etching .......................................................................................................... 45 3.4 Waveguide Evaluation...................................................................................... 46 3.4.1 Fabrication Complexity ................................................................................ 46 3.4.2 Mechanical Strength..................................................................................... 47 3.4.3 Optical Performance ..................................................................................... 49 4 Aluminum Sacrificial Core .................................................................................... 51 4.1 Introduction....................................................................................................... 51 4.2 Fabrication Process........................................................................................... 52 4.2.1 Aluminum Deposition and Patterning .......................................................... 52 4.2.2 Core Removal ............................................................................................... 56 4.3 Mechanical Strength........................................................................................
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