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Chip-Scale Thermoelectric Energy Harvester for Room Temperature Applications

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Chip-Scale Thermoelectric Energy Harvester for Room Temperature Applications Chip-Scale Thermoelectric Energy Harvester for Room Temperature Applications A Dissertation Presented By Samer A. Haidar to The Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the field of Electrical Engineering Northeastern University Boston, Massachusetts May 2020 2 To my family. 3 Abstract Thermoelectric energy harvesters have emerged as a solution for power generation by converting wasted heat directly into electrical energy through the Seebeck effect. As a result, they play a critical role in the development of the Internet-of-Things (IoT) wireless devices and sensors. High efficiency thermoelectric (TE) materials are important for power generation and help reduce our dependence on fossil fuels and reduce greenhouse gas emissions. Recent advances in fabrication technology have enabled these devices to be constructed at the chip-scale level promoting the use with low power devices such as wireless sensors and wearable applications. Thermoelectric n-type bismuth telluride (Bi2Te3) films and p-type antimony telluride (Sb2Te3) films are grown on SiO2/Si substrates using RF magnetron sputtering via physical vapor deposition (PVD) process. The objective of this dissertation is to study the crystal structure, grain size and elemental composition for 1µm and 10µm thermoelectric films deposited using different deposition conditions and using various heat treatment recipes. The thermoelectric properties of the films are found to be strongly dependent on the sputtering method and deposition temperature that lead to the design and fabrication of micro-scale thermoelectric energy generator (µTEG) based on the vertical architecture, which is geared towards IoT and wearable applications close to room temperature. It is observed that high temperature single-target sputtered depositions of n-type Bi2Te3 films result in a tellurium Te-deficient of stoichiometric films (Bi:Te = 2:3) due to the evaporation of tellurium. Two-target co-sputtered depositions using Bi2Te3 and Te targets 4 at room temperature and subsequent anneal at +250°C yielded a 10µm n-type film with - 102µV/K for the Seebeck coefficient and 0.7 mW/K2.m for the power factor. Similarly, prepared p-type Sb2Te3 film but using a single sputtering target yielded +110µV/K and 1.3 mW/K2.m for their Seebeck coefficient and power factor respectively. The design, fabrication and characterization of the proposed vertical µTEG using separate n-type and p-type wafers is demonstrated. Device power output as a function of the temperature difference measured as high as 1 mW for the vertical μTEG with ~13.8 mm2 footprint and device ΔT of ~7.5 K. We also introduce a second-generation µTEG based on patented pyramid architecture to overcome limitations of the vertical architecture such as thermal resistance and manufacturing constraints. In the pyramid design, the thermoelectric elements are deposited along a polyimide slope allowing more than 20µm of leg length for film depositions under 5µm thick. In this architecture, the heat flows at a slight angle compared to the top-down vertical architecture allowing for longer effective leg length and higher output performance. We present fabrication flow of the second-generation architecture and identify future age-related reliability stress test experiments post characterization to assess device performance under field conditions such as high temperature and humidity. Mechanical cross-sectioning Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analyses will be used for device enhancements to achieve the desired power output performance. 5 Acknowledgments This dissertation could not be completed without the guidance and support of many friends and colleagues who made this work possible. First, I would like to express my gratitude to my advisor Professor Nian Sun for his support and encouragement during the past five years. This dissertation could not be finished without his support especially during time critical milestones. He made difficult things look easy and this is very important for all part-time students. I still remember when we first met and discovered his openness towards research and especially his enthusiasm to work with innovative companies in the industry. He gave me the freedom to work on what interested me and encouraged me throughout the research. I’m thankful to my committee members, Dr. Baoxing Chen from Analog Devices Inc. for all his guidance and support throughout the research, Professor Hui Fang and Professor Yong-bin Kim from Northeastern University for their support and for their time to review my dissertation. I greatly appreciate their efforts and feedback. I would also thank my colleagues at Analog Devices Inc. very much specifically, Dr. Nigel J. Coburn, Dr. Jane E. Cornett, Dr. Jean-Jacques Hajjar, Dr. Kevin Lukas, Dr. Colm Glynn, Daniel McDaid, Arnaud Sow and my colleagues at Stanford university and Northeastern university, Dr. Marc T. Dunham (Stanford), Dr. Yuan Gao (Northeastern, Winchester Technologies) and Yifan He (Northeastern) in Professor Sun’s group. I appreciate everything they’ve done for me to make this research work possible. Special thanks to my friend James Griffin who gave me my first full-time job at Analog Devices Inc. and believed in me. 6 I also like to thank the entire product analysis group at Analog Devices Inc. for all the support during the past five years. This group is like family and I thank everyone for all the help. I would like to show my deep gratitude to mom and dad for their unconditional love and support. Finally, I would like to show my very special thanks and profound love and appreciation to my dear wife who always supported and encouraged me to finish this dissertation work while raising a beautiful family. I owe all my success to her and my parents and I’m eternally grateful. 7 List of Publications • Chip-Scale Thermal Energy Harvester Using Bi2Te3, Jane Cornett, Bill Lane, Marc Dunham, Mehdi Asheghi, Kenneth Goodson, Yuan Gao, Nian Sun, and Baoxing Chen, IECON 2015 - Yokohama 41st Annual Conference of the IEEE Industrial Electronics Society. • Fabrication and Characterization of Bi2Te3-Based Chip-Scale Thermoelectric Energy Harvesting Devices, Jane Cornett, Samer Haidar, Helen Berney, Pat McGuinness, Bill Lane, Yuan Gao, Yifan He, Nian Sun, Marc Dunham, Mehdi Asheghi, Ken Goodson, Yi Yuan and Khalil Najafi, Journal of Electronic Materials, Vol. 46, No. 5, 2017. • Experimental Characterization of Microfabricated Thermoelectric Energy Harvesters for Smart Sensor and Wearable Applications, Marc T. Dunham, Michael T. Barako, Jane E. Cornett, Yuan Gao, Samer Haidar, Nian Sun, Mehdi Asheghi, Baoxing Chen, and Kenneth E. Goodson, Adv. Mater. Technol. 2018, 1700383. • Deposition and Fabrication of Sputtered Bismuth Telluride and Antimony Telluride for Microscale Thermoelectric Energy Harvesters, Samer A. Haidar, Yuan Gao, Yifan He, Jane E. Cornett, Baoxing Chen, Nigel J. Coburn, Colm Glynn , Marc T. Dunham, Kenneth E. Goodson and Nian Sun, Pending acceptance in Thin Solid Films, 2020. 8 Table of Contents Abstract ........................................................................................................................................... 3 Acknowledgments .......................................................................................................................... 5 List of Publications ........................................................................................................................ 7 Table of Contents ........................................................................................................................... 8 List of Figures ............................................................................................................................... 11 List of Tables ................................................................................................................................ 16 Nomenclature ............................................................................................................................... 17 Chapter 1. Introduction .......................................................................................................... 18 1.1 Background .................................................................................................................... 18 1.2 Thermoelectric Effect .................................................................................................... 20 1.2.1 Seebeck Effect ........................................................................................................... 20 1.2.2 Peltier Effect .............................................................................................................. 22 1.2.3 Thomson Effect .......................................................................................................... 23 1.2.4 The Kelvin Relationships ........................................................................................... 23 1.3 Thermoelectric Materials ............................................................................................... 24 1.3.1 Bismuth Telluride ...................................................................................................... 26 1.3.2 Antimony Telluride .................................................................................................... 27 1.4 Thermoelectric Transport Properties ............................................................................
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