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Leong Yonghui, Jonathan Lubrication and Tribological Performance Optimizations for Micro-Electro-Mechanical Systems by Leong Yonghui, Jonathan A Thesis submitted to Imperial College London in fulfilment of the degree of Doctor of Philosophy and the Diploma of Imperial College London February 2013 Tribology Group Department of Mechanical Engineering The Imperial College of Science, Technology and Medicine London Abstract Lubricants and lubrication have been of great interest to mankind since the introduction of machines with sliding/rolling surfaces into everyday life. With the recent trend of miniaturization, Micro-Electro-Mechanical Systems (MEMS) have taken centre stage, featuring components with scales in dimensions as small as nanometres. In this PhD study, two approaches to solving MEMS tribology problems have been pursued. First, a novel direct lubrication method using well-known lubricants such as perfluoropolyether (PFPE) and multiply alkylated cyclopentane (MAC) was developed and tested using reciprocating sliding and actual MEMS tribometry. The second approach utilized the concept of hydrodynamic lubrication and selective surface modification for MEMS. To combat spreading and starvation of lubricants in small contacts such as in MEMS, selective modification of the silicon surface with hydrophobic (non-wetting) and hydrophilic (wetting) portions was carried out and found to increase the force required to move a droplet of lubricant from a designated location on the surface. Octadecylamine and dodecylamine were also used as additives to successfully induce autophobicity in hexadecane, and the various spreading behaviours investigated. In conclusion, several new approaches to tackling tribological problems in MEMS have been researched. These methods are easily adapted to suitable MEMS devices and greatly reduce adhesion and friction, and increase wear and device life by several orders of magnitude. 1 Acknowledgements First of all, I would like to express my deep thanks to my supervisors Sujeet Sinha Kumar and Hugh Spikes, and also to Tom Reddyhoff for their patience and guidance throughout the research and dissertation writing. I have been honoured to work with each of you and have learned much indeed. I also wish to express my gratitude to the academic and technical staff in Materials Lab, National University of Singapore, and in the Tribology Lab, Imperial College London. I am extremely thankful to all my labmates in Imperial College for providing me a conducive and warm environment in which we could learn and have fun together! Thank you for the times we had working, playing and chatting together – special mention goes to Oana, “Ponjac”, Jason and Jessika; who have become true friends during my short time in London. I am grateful for all the guidance showered upon me by my elders and betters through the years of education, and I thank each of my teachers and mentors who have influenced me along the way. I am deeply indebted to my family and loved ones, without whom this PhD would have been much more difficult. Your support and encouragement has driven me all these years. Thanks go to my wife-to-be for being strong during this time. And lastly, to God Almighty, for His mercy and grace through this season. 2 Preface This thesis is submitted for the Joint Degree of Doctor of Philosophy with National University of Singapore and Imperial College London, under the supervision of Dr. Hugh Alexander Spikes and Dr Sujeet Kumar Sinha. The works presented in this thesis have been submitted, under review for publication or have been published for publication as listed below: Journal Papers and Patents: 1. Jonathan, L. Y., Harikumar, V., Satyanarayana, N. and Sinha, S. K. (2010). "Localized lubrication of micromachines: A feasibility study on Si in reciprocating sliding with PFPE as the lubricant." Wear 270(1-2): 19-31. 2. Sinha, S. K., Jonathan, L. Y., Satyanarayana, N., Yu, H., Harikumar, V. and Zhou, G. (2010). "Method of applying a lubricant to a micromechanical device." U.S. Provisional Patent, 61/314,627. Filing date: 17 March 2010 3. Hongbin, Y. Guangya Z., Sinha S. K. Leong J. Y. Fook Siong Chau, “Characterization and Reduction of MEMS Sidewall Friction Using Novel Microtribometer and Localized Lubrication Method”, Journal of Microelectromechanical Systems, 2011. 20(4): p. 991-1000. 4. J. Y. Leong, T. Reddyhoff, S. K. Sinha, A. S. Holmes, H. A. Spikes, Hydrodynamic Friction Reduction in a MAC-Hexadecane Lubricated MEMS Contact, Tribology Letters, 2013, 49, p. 217-225, ISSN:1023-8883 5. Leong Y. Jonathan, N. Satyanarayana and Sujeet K. Sinha, A tribological study of Multiply-Alkylated Cyclopentanes and Perfluoropolyether lubricants 3 for application to Si-MEMS devices, Tribology Letters, In Press 6. J. Y. Leong, T. Reddyhoff, S. K. Sinha, H. A. Spikes, A. S. Holmes, Liquid Containment on Silicon Surfaces, Manuscript prepared 7. J. Y. Leong, Tian Feng, Loy Xing Zheng Keldren, N. Satyanarayana, Sujeet K. Sinha, Localized Lubrication on sidewalls of reciprocating MEMS contacts using PFPE and MAC lubricants, Submitted to Tribology Letters Book Chapters: 1. L. Y. Jonathan, N. Satyanarayana and S. K. Sinha., “Localized Lubrication of Micromachines – A Novel Method of Lubrication on Micromechanical Devices”, in “Nano-Tribology and Materials Issues in MEMS” (Eds: S. K. Sinha, N. Satyanarayana and S. C. Lim), Springer-Verlag, Berlin, Germany, 2012, in press. Conference Papers/Presentations: TriboUK 2012, Southampton - Poster Presentation, “Lubricant Additives to Reduce Boundary and Hydrodynamic Friction in Silicon MEMS”, J. Y. Leong, L. Tonggang, T. Reddyhoff, S. K. Sinha, A. S. Holmes, H. A. Spikes, Imperial College London, UK & National University of Singapore, Singapore STLE 2010, Atlanta - Paper presentation, “Localized Lubrication of Micro-Machines”, J. Leong, H. Vijayan, N. Satyanarayana, S. Sinha, National University of Singapore, Singapore 4 - Poster Presentation, “Localized Lubrication – A Novel Method of Lubricant Application to MEMS Devices”, J. Leong, H. Vijayan, N. Satyanarayana, S. Sinha, National University of Singapore, Singapore 5 Declaration I hereby declare that the thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. Leong Yonghui, Jonathan 10 October 2012 6 Copyright Declaration The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work. 7 Table of Contents Abstract ..................................................................................................................................................... 1 Acknowledgements ............................................................................................................................... 2 Preface ...................................................................................................................................................... 3 Declaration ............................................................................................................................................... 6 Copyright Declaration .......................................................................................................................... 7 Table of Contents ................................................................................................................................... 8 List of Figures ...................................................................................................................................... 12 List of Tables ....................................................................................................................................... 18 List of Equations ................................................................................................................................. 20 Chapter 1 - Introduction ............................................................................................................. 21 1.1 Introduction to Tribology ................................................................................................ 22 1.2 Introduction to MEMS ..................................................................................................... 22 1.3 Objectives of study ........................................................................................................... 24 1.4 Scope of thesis ................................................................................................................... 26 Chapter 2 - Literature Review .................................................................................................. 28 2.1 Issues with MEMS reliability and difficulties in lubrication................................ 29 2.1.1 Release Stiction ......................................................................................................... 30 2.1.2 In-use Stiction ............................................................................................................ 32 2.1.3 Friction, Wear and Lubrication ...........................................................................
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