On-Wafer Characterization of Electromagnetic Properties of Thin-Film RF Materials Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jun Seok Lee, B. S., M. S. Graduate Program in Electrical and Computer Engineering The Ohio State University 2011 Dissertation Committee Professor Roberto G. Rojas, Adviser Professor Patrick Roblin Professor Fernando L. Teixeira Copyright by Jun Seok Lee 2011 ABSTRACT At the present time, newly developed, engineered thin-film materials, which have unique properties, are used in RF applications. Thus, it is important to analyze these materials and to characterize their properties, such as permittivity and permeability. Unfortunately, conventional methods used to characterize materials are not capable of characterizing thin-film materials. Therefore, on-wafer characterization methods using planar structures must be used for thin-film materials. Furthermore, most new, engineered materials are usually wafers consisting of thin films on a thick substrate. Therefore, it is important to develop measurement techniques for on-wafer films that involve the use of a probe station. The first step of this study was the development of a novel, on-wafer characterization method for isotropic dielectric materials using the T-resonator method. Material characterization using a T-resonator provides more accurate extraction results than the non-resonant method. Although the T-resonator method provides highly accurate measurement results, there is still a problem in determining the effective T-stub length, which is due to the parasitic effects, such as the open-end effect and the T-junction effect. Our newly developed method uses both the resonant effects and the feed-line length of the T-resonator. In addition, performing the TRL calibration provides the exact length of ii the feed line, thereby minimizing the uncertainty in the measurements. As a result, our newly developed method showed more accurate measurement results than the conventional T-resonator method, which only uses the T-stub length of the T-resonator. The second step of our study was the development of a new on-wafer characterization method for isotropic, magnetic-dielectric, thin-film materials. The on-wafer measurement approach that we developed uses two microstrip transmission lines with different characteristic impedances, which allow the determination of the characteristic impedance ratio. Therefore, permittivity and permeability can be determined from the characteristic impedance ratio and the measured propagation constants. In addition, this method involves Thru-Reflect-Line (TRL) calibration, which is the most fundamental calibration technique for on-wafer measurement, and it eliminates the parasitic effects between probe tips and contact pads. Therefore, this novel characterization method provides an accurate way to determine relative permittivity and permeability. The third step of this study was the development of an on-wafer characterization method for magnetic-dielectric material using T-resonators. Similar to our second proposed method, this method uses two different T-resonators that have the same T-stub lengths and widths but different widths of feed lines. This method allows the determination of the ratio of the characteristic impedance to the effective refractive index of the magnetic-dielectric materials at the resonant frequency points. Therefore, permittivity and permeability can be determined. Although this method does not provide continuous extractions of material properties, it provides more accurate experimental results than the transmission line methods. iii The last step of this research was the evaluation and assessment of an anisotropic, thin-film material. Many of the new materials being developed are anisotropic, and previous techniques developed to characterize isotropic materials cannot be used. In this step, we used microstrip line structures with a mapping technique to characterize anisotropic materials, which allowed the transfer of the anisotropic region into the isotropic region. In this study, we considered both uniaxial and biaxial anisotropic material characterization methods. Furthermore, in this step, we considered a characterization method for biaxial anisotropic material that has misalignments between the optical axes and the measurement axes. Thus, our newly developed anisotropic material characterization method can be used to determine the diagonal elements in the permittivity tensor as well as the misalignment angles between the optical axes and the measurement axes. iv Dedication This document is dedicated to my family. v Acknowledgments First and foremost, it is a pleasure to thank my advisor, Prof. Roberto G. Rojas, for his guidance and efforts made this dissertation possible. He has always encouraged me to pursue a career in the electrical engineering. He has enlightened me through his wide knowledge of Electrical Engineering and his deep intuitions about where it should go and what is necessary to get there. I am also very grateful to my dissertation committee members, Prof. Fernando L. Teixeira and Prof. Patrick Roblin. Their academic guidance and input and personal cheering are greatly appreciated. I would like to thank my fellow graduate students at ElectroScience Laboratory (ESL) – Keum-su Song, Bryan Raines, Idahosa Osaretin, Brandan T Strojny, and Renaud Moussounda. It has been a great experience to work with them past four years. I also want to thank to other Korean graduate students at ESL - Gil Young Lee, James Park, Chun-Sik Chae, Haksu Moon, Jae Woong Jeong, and Woon-Gi Yeo. Finally, I would like to thank all my family members, specially my parents and parents-in-law, for their unconditional love, encouragement, and support over the years. Last but not least, I would like to express the deepest gratitude to my wife, Hyun-su Kim, for being with me through all of this. Without her, it would be much harder to finish this work. Thank you and I love you! vi Vita August, 2004 ..................................................B.S. Electrical Eng., Kyungpook National University, Daegu, South Korea June 2004 to June 2005 ..................................Assistant Engineer, Samsung Electronics, Tangjung, South Korea December, 2006 .............................................M.S. Electrical and Computer Eng. University of Rochester, Rochester, NY, USA September 2007 to present .............................Graduate Research Associate, ElectroScience Laboratory, The Ohio State University, Columbus, OH, USA Fields of Study Major Field: Electrical and Computer Engineering vii Table of Contents Abstract ............................................................................................................................... ii Dedication ............................................................................................................................v Acknowledgments.............................................................................................................. vi Vita .................................................................................................................................... vii List of Tables ..................................................................................................................... xi List of Figures ................................................................................................................... xii Chapter 1. Introduction ........................................................................................................1 Chapter 2. Review of Conventional On-Wafer Measurement Methods ............................11 2.1. Introduction .....................................................................................................11 2.2. Review of Conventional On-Wafer Measurement Methods for Dielectric Materials ................................................................................................................13 2.2.1. Overview of Non-Resonant Method ................................................15 2.2.1.1. Transmission Line Method - Theory ................................15 2.2.1.2. Transmission Line Method - Experiments ........................20 2.2.2. Overview of Resonant Method ........................................................26 2.2.2.1. T-Resonator Method - Theory ..........................................29 2.2.2.2. T-Resonator Method - Experiments..................................34 2.3. Review of Conventional On-Wafer Measurement Methods for Magnetic- Dielectric Materials ................................................................................................38 2.3.1. Transmission Line Method (Theory) ...............................................39 viii Chapter 3. An Improved T-Resonator Method for the Dielectric Material On-Wafer Characterization .................................................................................................................45 3.1. Introduction .....................................................................................................45 3.2. Method of Analysis .........................................................................................46 3.2.1. T-Resonator Matrix Model ..............................................................47 3.2.2. Consideration of Loss Measurements ..............................................51 3.3. T-Resonator Measurement Results .................................................................53