CHARACTERIZATION AND COMPARISON OF LITHIUM NIOBATE AND QUARTZ SURFACE ACOUSTIC WAVE DEVICES by BABURAO GHONGADE B.E., Solapur University, 2014 A thesis submitted to the Graduate Faculty of the University of Colorado Colorado Springs in partial fulfillment of the requirements for the degree of Master of Science Department of Electrical and Computer Engineering 2017 ii This thesis for the Master of Science degree by Baburao Ghongade has been approved for the Department of Electrical and Computer Engineering by T.S. Kalkur, Chair Carlos De Paz Araujo Heather Song Date: 12/14/2017 iii Ghongade, Baburao (M.S., Electrical Engineering) Characterization and Comparison of Lithium Niobate and Quartz Surface Acoustic Wave Devices Thesis directed by Professor T.S. Kalkur ABSTRACT Sensors became the very important part of our technological life now a day. Its accuracy and reliability became the matter of success or failure, death or life. That’s why we all are trying to make these sensors as accurate and reliable as possible. At the same time, we need them affordable as well. We can make them cheap but reliable and accurate by using latest and advanced technology we ever known. Basically, sensors give us very important numerical data regarding the condition or the behavior of the devices. To get this data most of the sensors need wired connections to the computers and power supply. This wiring obviously need to be done very accurately and smartly so that it will not disturb or interfere with sensors performance. This indirectly make system more complex and less robust. On the other hand, wireless systems are handy, robust and futuristic. Talking about wireless temperature sensors, they are required by the almost every scientific field. A temperature sensor plays an important role in various applications. For an example, regulating the temperature is a very important part of the processes used in the chemical industries, pharmaceutical industries, bio medical and almost all the electrical and electronics industries. For such important fields, the responsiveness and accuracy of the sensors can be critical. iv In this thesis, we have compared and characterized the existing (in use) Quartz SAW devices with the newly designed and manufactured Lithium Niobate SAW devices which can be compatible with wireless interrogation unit for wireless temperature sensing. v DEDICATION To My Lovely and Encouraging Family vi ACKNOWLEDGEMENTS I want to appreciate and be thankful to the people who were there for me and supported me during this beautiful journey. I am really thankful to my adviser Dr. T.S. Kalkur, for his encouragement, whose expertise, excellent guidelines and enormous support made it possible for me to study and work on the topic that was of great interest to me. It was a great experience working along with him. I would also like to thank all my professors for their confidence and support. I would like to express my deepest gratitude to Mr. Bogdan Crivin for all his help in the laboratories. My sincere thanks to Eva Wynhorst for her kindness and support. Thanks to Gauri, the most amazing person and the best friend I have met, who has been there with me for all times. Finally, I would like to thank my parents for their tired less effort and enormous encouragement throughout my masters. vii CONTENTS CHAPTER 1 INTRODUCTION 1 1.1 History ............................................................................................................ 1 1.2 Types of temperature sensors ............................................................................. 3 1.2.1 Contact Temperature Sensors ................................................................ 3 1.2.2 Non-contact Temperature Sensors .......................................................... 5 1.3 Temperature sensors in use ................................................................................ 6 1.4 Acoustic Wave Devices ........................................................................................ 8 1.5 Objective and Scope of Thesis ............................................................................ 9 1.6 Novelty of proposed work .................................................................................... 8 2 SURFACE ACOUSTIC WAVE DEVICES 10 2.1 Getting familiar with SAW ................................................................................................ 10 2.2 Development phases of SAW devices ................................................................ 11 2.2.1 Wedge and Comb model ......................................................................... 11 2.2.2 Mortley’s model ...................................................................................... 12 2.2.3 Constant pitch model ............................................................................. 13 2.2.4 Dispersive IDT model ............................................................................ 13 2.3 Modern SAW device model ................................................................................ 14 viii 2.3.1 Aperture(a) ............................................................................................. 15 2.3.2 Acoustic Wavelength (λ) ......................................................................... 15 2.3.3 Metallization Thickness (h) ................................................................... 15 2.3.4 Number of fingers in IDT ...................................................................... 15 2.4 Working Principle of SAW ................................................................................................. 16 2.5 Types of SAW devices ......................................................................................... 16 2.5.1 Resonator SAW devices .......................................................................... 16 2.5.2 One Port Resonator ............................................................................... 16 2.5.3 Two Port Resonator ............................................................................... 19 2.5.4 Reflective Delay Line Device ................................................................. 23 2.6 Materials for SAW devices ..................................................................................25 2.6.1 Properties of commonly used piezoelectric SAW substrates ............... 26 2.6.2 Quartz (SiO2) ...................................................................................... 26 2.6.3 Lithium Niobate(LiNbO3) ...................................................................... 28 2.6.4 Physical Characteristics ........................................................................ 30 3 WAFER PROCESSING AND MAPPING 31 3.1 What is wafer? ................................................................................................... 31 3.1.1 Ingot- the foundation for wafers ........................................................... 31 3.1.2 The lapping and polishing process ....................................................... 32 3.2 Wafer processing ............................................................................................... 33 3.3 Knowing the wafer ............................................................................................ 36 ix 3.3.1 Wafer nomenclature ............................................................................... 37 3.3.2 Wafer characteristics ............................................................................. 38 3.4 Calibrating the Network Analyzer ..................................................................... 38 3.5 Wafer mapping .................................................................................................. 40 4 CHARACTERIZATION AND COMPARISON 43 4.1 SAW device specification .................................................................................. 44 4.2 Frequency response of temperatures ................................................................ 44 4.3 Quality factor .................................................................................................... 46 4.4 Bandwidth ......................................................................................................... 48 4.5 S-parameter characterization ........................................................................... 50 4.6 Temperature Coefficient of Frequency ................................................................. 52 5 CONCLUSION AND FUTURE WORK 53 5.1 Conclusion .......................................................................................................... 53 5.2 Future work ………………………………………………………………………………………… 53 REFERENCES 55 x TABLES Table 1.1 Most common temperature sensors in the market [13] ..................................... 7 1.2 Types of sensors and their application [13] .................................................... 7 2.1 Properties of SAW piezoelectric materials [26] .................................................. 26 2.2 Characteristics of Lithium Niobate and Quartz [20] [29] ............................... 30 3.1 Physical characteristics of the Lithium Niobate wafer ................................... 38 4.1 Specification of Lithium Niobate devices ........................................................ 44 4.2 Specification of Quartz devices [15] ................................................................. 44 xi FIGURES Figure 1.1 Galileo Thermometer [5] ...……………………………………………………………………………… 2 1.2 Bimetallic Temperature Sensor [1] …………………………………………………………………...2 1.3 Weld pad surface temperature