DESIGN OF MICROWAVE BAND STOP AND BAND PASS FILTERS BASED ON BST THIN FILM VARACTOR TECHNOLOGY Thesis Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree Master of Science in Electrical Engineering by Jaya Chandra Ramadugu UNIVERSITY OF DAYTON Dayton, Ohio December, 2013 DESIGN OF MICROWAVE BAND STOP AND BAND PASS FILTERS BASED ON BST THIN FILM VARACTOR TECHNOLOGY Name: Ramadugu, Jaya Chandra APPROVED BY: Guru Subramanyam, Ph.D. Monish Chatterjee, Ph.D. Advisory Committee Chairman Committee Member Department of Electrical and Department of Electrical and Computer Engineering Computer Engineering Weisong Wang, Ph.D. Committee Member Department of Electrical and Computer Engineering John G. Weber, Ph.D. Tony E. Saliba, Ph.D. Associate Dean Dean, School of Engineering School of Engineering & Wilke Distinguished Professor © Copyright by Jaya Chandra Ramadugu All rights reserved 2013 ABSTRACT DESIGN OF MICROWAVE BAND STOP AND BAND PASS FILTERS BASED ON BST THIN FILM VARACTOR TECHNOLOGY Name: Ramadugu, Jaya Chandra University of Dayton Advisor: Dr. Guru Subramanyam This thesis presents a design of band stop and band pass filters for microwave applications. These filters are based on coplanar waveguide (CPW) transmission lines on a 500 µm thick sapphire substrate. 0.25 µm thin film barium strontium titanate (BST) thin film is used as the tunable dielectric layer. The design of the band stop filter is based on the traditional varactor shunt switch (designed by Dr. Subramanyam and his team) coupled to the ground using an inductive path. Thus, the design symbolizes a single pole standard band stop filter with the potential for frequency tunability. The capacitive overlap makes the device tunable. Several designs of the band stop filter based on the same concept, but different capacitive overlaps, inductive configurations and overall device dimensions were designed and studied. The center frequency for these designs varied from 1 to 5GHz. The band pass filter is mostly single layered and represents a microstrip based structure although it is CPW fed. It is shunted to the ground with varactors on either side of the device. The idea of having varactors were to achieve tunability. It has 4 resonant iii traps representing a 4-pole filter. The design, simulation results, experimental results and analyses are presented. iv ACKNOWLEDGEMENTS My special thanks go to Dr. Guru Subramanyam, my advisor who has been very supportive right from the day I planned to transfer to the University of Dayton. He introduced me to microwave lab in my senior year, and that was when I developed my interest in this field. I would like to thank him for giving me this wonderful opportunity and supporting me professionally and financially throughout the program. Without him, I probably would not have been where I stand today in my professional career. I would like to thank Dustin Brown, who taught me the basics of RF engineering. He has always been there whenever I had a question. He is extremely knowledgeable and a big asset to our team. Thank you Dustin for every question of mine that you answered and for being there to troubleshoot any issue that I had throughout my time here. I would like to thank my all other team members Dr.Weisong Wang, Dr.Eunsung Shin, Hailing Yue, Wang Shu, Mark Connor, Kuan-Chang Pan, and Kelvin Freeman. Everybody has been very helpful and supportive whenever needed. It has been a pleasure working with you all. I would like to thank Chenhao Zhang, one of our teammates in the past. The initial design of the band pass filter design that I am discussing in my thesis was initiated by him. He also let me shadow him to learn to run the ECE 304L that I have been a teaching assistant for since August 2012. v I would like to thank the graduate school and all the professors that taught me. Finally, I would like to thank my other committee members Dr. Monish Chatterjee and Dr. Weisong Wang for agreeing to be on my committee and for reviewing my work. vi TABLE OF CONTENTS ABSTRACT ....................................................................................................................III ACKNOWLEDGEMENTS ............................................................................................... V TABLE OF CONTENTS ............................................................................................... VII LIST OF FIGURES ........................................................................................................ IX LIST OF TABLES ......................................................................................................... XII CHAPTER 1 INTRODUCTION ......................................................................... 1 1.1 BACKGROUND .................................................................................................... 1 1.2 SCOPE ................................................................................................................. 5 1.3 OUTLINE .............................................................................................................. 6 CHAPTER 2 LITERATURE REVIEW ............................................................... 7 2.1 FERROELECTRIC MATERIALS ........................................................................... 7 2.2 THIN FILM BARIUM STRONTIUM TITANATE (BST) ..........................................11 2.3 MICROWAVE DEVICES BASED ON BST ...........................................................12 2.4 FILTERS ..............................................................................................................15 CHAPTER 3 BST VARACTOR TECHNOLOGY ..............................................27 3.1 DESIGN ...............................................................................................................27 3.2 DATA ANALYSIS .................................................................................................30 3.3 FABRICATION PROCEDURE .............................................................................35 vii 3.4 MEASUREMENT SET UP ...................................................................................40 CHAPTER 4 BAND STOP FILTER DESIGN AND ANALYSIS ........................43 4.1 DESIGN ...............................................................................................................43 4.2 MEASURED RESULTS AND DATA ANALYSIS ..................................................48 CHAPTER 5 BAND PASS FILTER DESIGN AND ANALYSIS .........................55 5.1 DESIGN ...............................................................................................................55 5.2 MEASUREMENT RESULTS AND DATA ANALYSIS ...........................................62 CHAPTER 6 CONCLUSION AND FUTURE WORK ........................................71 6.1 CONCLUSION .....................................................................................................71 6.2 FUTURE WORK ..................................................................................................72 BIBLIOGRAPHY ............................................................................................................74 viii LIST OF FIGURES Figure 1-1 The electromagnetic spectrum [1] .................................................................. 1 Figure 1-2 Evolution of communication technology [2] .................................................... 2 Figure 1-3 Simplest RF front end of a receiver (top) and a transmitter (bottom) [3] ......... 4 Figure 2-1 Hysteresis loop of ferroelectric devices ......................................................... 8 Figure 2-2 Three dimensional view of a varactor shunt switch [25] ................................13 Figure 2-3 Simplest schematic of the four different types of filters .................................17 Figure 2-4 Ideal frequency response of the four different types of filters [3] ...................18 Figure 2-5 Practically realizable version of the different types of filters [31] ...................19 Figure 2-6 3D view of on-chip Inductor designed by Xu Yi [27] ......................................21 Figure 2-7 Guru Subramanyam’s microstrip band pass filter design [33] .......................23 Figure 2-8 Microstrip based dual band pass filter proposed by Cheng-Ying Hsu et. al. [39] ................................................................................................................................24 Figure 2-9 Multi-resonator RFID tag; Simulated and measured results of the RFID tag [41] ................................................................................................................................25 Figure 2-10 3D view and equivalent lumped element model of Chenhao Zang’s shunt IDC [42] .........................................................................................................................26 Figure 2-11 Simulation results from Chenhao Zang’s shunt IDC [42] .............................26 Figure 3-1 Top view of 5µm by 5µm varactor .................................................................28 Figure 3-2 3D view of a 5µm by 5µm varactor ...............................................................28 Figure 3-3 Top and bottom metal layers ........................................................................29 ix Figure 3-4 Equivalent schematic model .........................................................................30 Figure 3-5 Measured results of 5 µm x 5 µm varactor [39] .............................................32