Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-24-2016 Tunable Terahertz Metamaterials with Germanium Telluride Components Christopher H. Kodama Follow this and additional works at: https://scholar.afit.edu/etd Part of the Engineering Science and Materials Commons Recommended Citation Kodama, Christopher H., "Tunable Terahertz Metamaterials with Germanium Telluride Components" (2016). Theses and Dissertations. 306. https://scholar.afit.edu/etd/306 This Thesis is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. Cover Page TUNABLE TERAHERTZ METAMATERIALS WITH GERMANIUM TELLURIDE COMPONENTS THESIS Christopher H. Kodama, Second Lieutenant, USAF AFIT-ENG-MS-16-M-025 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio DISTRIBUTION STATEMENT A. APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. AFIT-ENG-MS-16-M-025 TUNABLE TERAHERTZ METAMATERIALS WITH GERMANIUM TELLURIDE COMPONENTS THESIS Presented to the Faculty Department of Electrical and Computer Engineering Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Master of Science in Electrical Engineering Christopher H. Kodama, BS Second Lieutenant, USAF March 2016 DISTRIBUTION STATEMENT A. APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT-ENG-MS-16-M-025 TUNABLE TERAHERTZ METAMATERIALS WITH GERMANIUM TELLURIDE COMPONENTS Christopher H. Kodama, BS Second Lieutenant, USAF Committee Membership: Ronald A. Coutu, Jr., Ph. D. Chairman Michael Havrilla, Ph. D. Member Michael A. Marciniak, Ph. D. Member AFIT-ENG-MS-16-M-025 Abstract Terahertz (THz) technology is an emerging field with many exciting applications. THz waves can be used to locate explosives and illicit drugs in security applications, or DNA and other molecule resonances in medical applications. THz frequencies represent the next level of modern, high-speed computing, but they also can be used for covert battlefield communications links. Metamaterials are an integral part of THz technology because they can be used to create exotic material properties—permittivities and permeabilities—in a part of the frequency spectrum that is otherwise rather empty and passive. This work aims to acquire a fuller understanding of THz metamaterials in terms of background and theory, and then use this understanding to create a few novel, actively tunable structures using the phase-change material germanium telluride. iv Acknowledgements I would like to thank several people for helping me with my thesis. I could not have done it all without ample mentorship from my advisor, Dr. Coutu, especially during the fabrication and troubleshooting of my devices. The cleanroom lab technicians Rich Johnston and Adam Fritzche were invaluable in my project as well. Rich trained me on several pieces of equipment in the cleanroom and performed several metal deposition runs on my request; Adam helped set up much of the equipment that I used in the test lab. I am grateful to Maj Jim Sattler, Maj Tod Laurvick, and Capt Rob Lake for always being available for questions and discussion, as well as assisting me with various processes in the cleanroom such as mask generation and metal deposition. I would especially like to thank Capt Lake for revising the final drafts of my thesis. The assistance I received from Brian Crabtree for custom parts, Jason Hickey for metal evaporation, Doug McFarland for wafer dicing, and Eric Kreit for inkjet printing is greatly appreciated. My thanks also goes to Capt Alex Gwin, for helping me during the initial phases of my project and being willing to answer a few of my questions even after being transferred out-of-state. I would also like to thank Capt Jimmy Lohrman for being a great and cheerful fellow classmate and colleague. With a class of only two Master’s students total in the microelectronics program, my time here would have been a lot more solitary without him. Finally, I would like to thank my family for encouraging me to apply for AFIT, and Elena Chong Loo for her patient support and encouragement during the most difficult times of my thesis work. v Table of Contents Abstract .............................................................................................................................. iv Acknowledgements ............................................................................................................. v Table of Contents ............................................................................................................... vi List of Figures ................................................................................................................... xii List of Tables ................................................................................................................. xxiv 1. Introduction ..................................................................................................................... 1 2. Literature Review............................................................................................................ 4 2.1. The Terahertz Spectrum: Concepts and Applications ............................................. 4 2.1.1. THz Generation ............................................................................................... 4 2.1.2. THz Applications: Communications ............................................................... 6 2.1.3. THz Applications: Spectroscopy ..................................................................... 7 2.1.4. Theory of THz Time-Domain Spectroscopy ................................................. 10 2.1.5. Analysis of THz-TDS data ............................................................................ 15 2.1.6. Summary ....................................................................................................... 25 2.2. Split-Ring Resonator Characterization .................................................................. 26 2.2.1. Inductance Modeling ..................................................................................... 28 2.2.2. Capacitance Modeling ................................................................................... 36 2.2.3. Substrate Effects ............................................................................................ 42 2.2.4. Plasmonic Resonances .................................................................................. 42 vi 2.2.5. Effective Homogeneous Properties of SRRs ................................................ 43 2.2.6. Summary ....................................................................................................... 47 2.3. Terahertz Metamaterials ........................................................................................ 47 2.3.1. Actively Tunable THz Metamaterials ........................................................... 47 2.3.2. Summary ....................................................................................................... 56 2.4. Phase Change Materials ......................................................................................... 57 2.4.1. Germanium Telluride .................................................................................... 59 2.4.2. Summary ....................................................................................................... 61 2.5. Heat Transfer: Theory and GeTe Switching Examples ......................................... 61 2.5.1. Joule Heating Theory .................................................................................... 62 2.5.2. Joule Heating Examples ................................................................................ 64 2.5.3. Laser Pulsing Theory .................................................................................... 66 2.5.4. Laser Pulsing Examples ................................................................................ 71 2.5.5. Summary ....................................................................................................... 71 2.6. Fabrication Processes ............................................................................................. 72 2.6.1. Bulk Micromachining ................................................................................... 72 2.6.2. Surface Micromachining ............................................................................... 73 2.6.3. Microforming ................................................................................................ 73 2.6.4. Additive Manufacturing ................................................................................ 74 2.7. Summary ................................................................................................................ 75 vii 3. Methodology ................................................................................................................. 76 3.1. Terahertz