MEMS devices for circumferential scanned optical coherence tomography bio imaging

MEMS DEVICES FOR CIRCUMFERENTIAL-SCANNED OPTICAL COHERENCE TOMOGRAPHY BIOIMAGING MU XIAOJING (B.Eng, Chongqing University) (M.Eng, Chongqing University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 ACKNOWLEDGEMENTS Acknowledgements Herein I would like to gratefully acknowledge all those people who have helped me to complete this thesis First of all, I thank my supervisors from National University of Singapore, Prof Chau Fook Siong and Prof Zhou Guangya for their excellent guidance, generous support and precious encouragement throughout my four years’ research I also thank my co-supervisors from Institute of Microelectronics (IME), Dr Feng Hanhua, Dr Julius Ming-Lin Tsai and Dr Wang Ming-Fang for their erudite knowledge and invaluable suggestions given to me throughout my research project in IME I am very thankful to my thesis committee members, Prof Quan Chenggen and Prof Vincent Chengkuo Lee for reviewing the manuscript I also want to express appreciation to my colleagues from Micro and Nano Systems Initiative (MNSI) Laboratory, Department of Mechanical Engineering (ME), Dr Yu Hongbin, Dr Du Yu, Dr Wang Shouhua, Mr Kelvin Cheo Koon Lin, Dr Jason Chew Xiong Yeu, Ms Leung Huimin, Dr Tian Feng and Dr Shi Peng for valuable discussions about processing, testing issues and their selfless assistance I would like especially to thank my friends Mr Lou Liang and Mr Zhang Songsong from Laboratory of Sensors, MEMS and NEMS, Electrical and Computer Engineering (ECE) Department for supporting me not just in research but also in my personal life In addition, I am very thankful to my project colleagues Dr Xu Yingshun, Dr Yu Aibin, Dr Winston Sun, Mr Kelvin Wei Sheng Chen, Mr C S Premachandran and Dr Tan Chee Wee from Institute of Microelectronics (IME), A*STAR, Singapore for their helpful suggestions and full cooperation during the device fabrication process and characterization; also, I thank all those staff members who have ever helped me in ii ACKNOWLEDGEMENTS IME for their technical support I also acknowledge the leadership of Prof Kwong Dim-Lee, Executive Director of Institute of Microelectronics (IME), who has provided an excellent and highly efficient workplace for research and development Finally, I extend my deepest gratitude to my beloved parents, my wife Chen Jie and my daughter Jiayi for their great care and long-lasting spiritual support during all these years Giving my warmest thanks to you all, Mu Xiaojing NUS, Singapore 2012 iii TABLE OF CONTENTS Table of Contents Declaration i Acknowledgements ii Table of Contents iv Summary vii List of Tables ix List of Figures x List of Acronyms xvi List of Symbols xix Introduction 1.1 History of Endoscopy 1.2 History of Optical Coherence Tomography 1.3 Endoscopic OCT 12 1.4 MEMS based endoscope for OCT imaging 13 1.5 Organization of the Dissertation 18 Technological Development of the Optical MEMS 20 2.1 MEMS Optical Scanner 20 2.2 Actuation Mechanism of MEMS Scanner 22 2.2.1 Electrostatic Actuators 23 2.2.2 Electrothermal Actuators 30 2.2.3 Piezoelectric Actuators 44 2.2.4 Magnetic Actuators 46 Researches for Higher Performances 47 2.3.1 Large Rotation Angle with Low-Voltage Driving 47 2.3.2 Accurate Rotation Angle Control 50 2.3.3 Lightweight Flat Mirror 51 Conclusion 52 2.3 2.4 Bimorph Electrothermal Based MEMS Micromirror for OCT 3.1 OCT Imaging System in a Miniaturized Probe iv 53 54 TABLE OF CONTENTS 3.1.1 OCP930SR System 3.1.2 Miniature OCT Probe Design 58 3.1.4 MEMS Micromirrors/SiOB Assembly 66 3.1.5 Probe Housing Design 68 Experimental Results and Discussion 74 3.2.1 MEMS Device Characterizations 74 3.2.2 OCT Imaging Experiment 3.3 56 3.1.3 Optical MEMS Micromirror Design 3.2 54 77 Conclusion 80 Chevron Electrothermal Actuation Based MEMS Micro-scanner 81 4.1 Device Design 83 4.2 Fabrication and Assembly 90 4.2.1 Pyramidal Polygon Micro-reflector Fabrication Process 90 4.2.2 Chevron-beam Micro-actuator Fabrication Process 92 4.2.3 MEMS Micro-scanner Assembly 96 4.3 Experimental Results 97 4.4 Conclusion 100 Electrostatic Double T-shaped Spring Mechanism based MEMS 5.1 102 Device Design 105 5.1.1 Structure Design of Rotational Mechanism 105 5.1.2 Theoretical Study of the Two-stage Double T-shaped Spring Mechanism 107 5.1.3 Simulation 116 Device Fabrication 117 5.2.1 MEMS Actuator Fabrication 117 5.2.2 Pyramidal Polygon Micro-reflector Fabrication 119 5.2.3 MEMS Micro-scanner Assembly 121 5.3 Experimental and Results 123 5.4 Conclusion 126 5.2 Electrostatic Resonating MEMS micro-scanner 6.1 128 Device Design 129 6.1.1 Theoretical Modeling 129 6.1.2 Mechanical Design and Simulation 133 v TABLE OF CONTENTS 6.2 Fabrication 135 6.2.1 MEMS Micro-actuator Fabrication 135 6.2.2 Pyramidal Polygon Micro-reflector Fabrication 137 6.3 Experimental Results 139 6.4 Conclusion 141 Conclusion and Future Research Work 143 7.1 Conclusion 143 7.2 Future Research Work 145 Bibliography 147 Appendices 160 Appendix: List of Publications 160 vi SUMMARY Summary The optical coherence tomography (OCT) is a fundamentally new type of noninvasive optical imaging modality This technology promises the capability of providing 2D/3D high resolution in vivo and in situ images and excellent optical sectioning for imaging multilayer microstructures of internal organs Recently, in order to avoid destructive effects on tissues by using conventional excisional biopsy and reduce sampling errors, the idea of “optical biopsy” by utilizing endoscopic OCT (EOCT) has been introduced One main feature of EOCT is its miniaturization of the optical system and scanners in the sample arm of the OCT system Initially, most catheters developed for EOCT are based on the assemblies of microprisms and single mode fibers (SMF) which are stretched or rotated by external actuation mechanisms Their scanning speeds are quite limited due to the friction and inertia of the devices The recent rapid growth of microelectromechanical system (MEMS) benefits modern EOCT catheters by offering compact, robust, high speed scanning, lightweight micro devices In this thesis, a bimorph electrothermal actuation-based MEMS micromirror integrated OCT probe is developed and its integration with a commercial OCT system having a mm-diameter OCT probe is introduced In addition, we also investigate (1) the function of the MEMS micromirror and the effects of curvature of the mirror platform on the optical performance of the OCT system, (2) the influence of housing shape on the image astigmatism and replacing it with a toroidal-lens equipped housing as an attempt to alleviate the undesirable effect, and (3) ex vivo image-capturing experiments vii SUMMARY For some clinical applications, full circumferential scanning (FCS) is highly desired MEMS technology has recently demonstrated strong potential in biomedical imaging applications due to its outstanding advantages of, for instance, low mass, high scan frequency and convenience of batch fabrication However, due to the nature of microfabrication processes, micromirrors are normally much thinner than conventional macro-scanning mirrors, and therefore, at high scan frequencies, the mirror plate loses its rigidity and tends to deform dynamically during scanning due to high out-of-plane acceleration forces This introduces dynamic aberrations into the optical system and seriously degrades its optical resolution In order to alleviate dynamic aberration and the mirror curvature issue induced by residual stresses that might exist in traditional thin MEMS micro-mirrors, a pyramidal polygon MEMS micro-scanner is developed together with a foul-pieces-in-one fiber-pigtail GRIN lens bundle to realize a compact EOCT probe In this work, a large scanning range of 328° optical angle is provided by chevron-beam microactuator In order to make the MEMS device compatible with clinical applications, the surface temperature and the scanning speed are two key factors Two types of electrostatic actuation MEMS micro-scanner are developed One type is an electrostatic double T-shaped spring mechanism-based MEMS micro-scanner that provides static laser beam scanning with a 300° optical scanning angle, and the other one is an electrostatic micromachined resonating micro polygonal scanner that is capable of 240° optical angle scanning with a amplitude of 80 Vpp and a frequency of 180 Hz For each of the proposed MEMS micro-scanner or micromirror, the design configuration, fabrication, modeling, simulation and performance testing are presented and discussed in detail viii LIST OF TABLES List of Tables Table 1.1 Comparison of the current existing OCT probe 18 Table 2.1 Major actuators and their typical performance 23 Table 2.2 Physical properties of materials commonly used in micro37 fabrication Table 3.1 Material properties used in the simulation 61 Table 5.1 Material properties used in the simulation 119 Table 5.2 Final structure dimensions 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circumferential scanned endoscopic imaging probe”, Optics Express Vol 20, Iss 6, pp 6325–6339 (2012) (Selected by the Editors for publication in the most recent issue of the virtual Journal for Biomedical Optics (VJBO) - Apr 26, 2012 Vol.7, Iss.5) Hongbin Yu, Guangya Zhou, Yu Du, Xiaojing Mu and Fook Siong Chau, “MEMS-based tunable iris diaphragm” IEEE/ASME Journal of Microelectromechanical Systems (JMEMS), Vol.21, No.5, pp.1136-1145 (2012) Mu Xiaojing, Sun Winston, Feng Hanhua, Zhou Guangya, Chau Fook Siong, “Multi Degree-of-Freedom Micromotor Utilizing an Electrothermal Actuator Array and a Spherical Rotor”, Advanced Materials Research Vol.254, PP 115-119 (2011) Xiaojing Mu, Guangya Zhou, Hongbin Yu, Julius Ming-Lin Tsai, Dennis Wee Keong Neo, A Senthil Kumar, Fook Siong Chau, “Electrostatic MEMS Resonating Micro Polygonal Scanner for Circumferential Endoscopic Bio-imaging” 160 APPENDIX IEEE Photonics Technology Letters (PTL), Vol.25, No.8, pp.749-752 (2013) Xiaojing Mu, Guangya Zhou, Hongbin Yu, Julius Ming-Lin Tsai, Dennis Wee Keong Neo, A Senthil Kumar, Fook Siong Chau, “Electrostatic Double T-shaped Spring Mechanism based MEMS Device for Circumferential Scanning”, IEEE/ASME Journal of Microelectromechanical Systems (JMEMS) (Accepted) Wang, Haomin; Shen, Xiaonan; Yu, Hongbin; Mu, Xiaojing; Cong, Chunxiao; Shang, Jingzhi; Yu, Ting “Graphene Bubble Formation: Strong Adhesion of Graphene Conforming to Substrate Surface” Submitted to Nano Letters Conference papers X J Mu, G Y Zhou, H H Feng, Y S Xu, A B Yu, C W Tan, K W S Chen , J Xie, F S Chau, “A 3mm Endoscopic Probe with Integrated MEMS Micromirror for Optical Coherence Tomography Bioimaging”, Eurosensors XXIV, September 5-8, 2010, Linz, Austria Xiaojing Mu, Yingshun Xu, Janak Singh, Nanguang Chen, Hanhua Feng, Guangya Zhou, Aibin Yu, Chee Wei Tan, Kelvin Wei Sheng Chen, Fook Siong Chau, “A Large Rotational Angle Micromirror Based Hypocycloidal Electrothermal Actuators for Endoscopic Imaging”, Optical MEMS and Nanophotonics 2010, August 9-12, 2010, Sapporo, Japan Ming-Fang Wang, Yingshun Xu, C.S Prem, Kelvin Wei Sheng Chen, Jin Xie, Xiaojing Mu, Chee Wei Tan, Aibin Yu and Hanhua Feng, “Microfabricated 161 APPENDIX Endoscopic Probe Integrated MEMS Micromirror for Optical Coherence Tomography Bioimaging”, 32nd Annual International Conference of the IEEE EMBS, August 31-September 4, 2010, Buenos Aires, Argentina Kelvin Chen Wei Sheng, Yu Aibin, Mu Xiaojing, Feng Hanhua, Tan Chee Wei, “Miniaturized OCT System with Optimized Housing Design”, 12th Electronics Packaging Technology Conference, December 8-10, 2010, Singapore Xiaojing MU, Winston SUN, Hanhua FENG, Guangya ZHOU, Fook Siong CHAU, “Multi Degree-of-freedom Micromotor Utilizing an Electrothermal Actuator Array and a Spherical Rotor”, ICMAT 2011 International Conference on Materials for Advanced Technologies, 26 June-1 July, Singapore Winston SUN, Xiaojing MU, Hanhua FENG, “Compact Circumferential Scan 3arm Suspended Micromirror for OCT Applications”, ICMAT 2011 International Conference on Materials for Advanced Technologies, 26 June-1 July, Singapore Xiaojing Mu, Guangya Zhou, Hongbin Yu, Hanhua Feng, Yu Du, Julius Ming Lin Tsai and Fook Siong Chau, “A Novel Chevron-beam Actuator based MEMS Platform for Circumferential Scanned Endoscopic Imaging”, The 25th International Conference on Micro Electro Mechanical Systems IEEE MEMS 2012-Paris, France, 29January-2 February 2012 Xiaojing Mu, Guangya Zhou, Hongbin Yu, Hanhua Feng, Yu Du, Julius Ming Lin Tsai and Fook Siong Chau, “In-plane rotational MEMS scanner for optical coherence tomography”, The Sixth Asia-Pacific Conference on Transducers and Micro/Nano Technologies APCOT 2012-Nanjing, China, July-11 July 2012 Xiaojing Mu, Guangya Zhou, Hongbin Yu, Yu Du, A Sentil Kumar, Julius Ming Lin Tsai and Fook Siong Chau, “An electrostatic in-plane rotational MEMS micro- 162 APPENDIX scanner”, Optical MEMS & Nanophotonics Conference 2012, The Banff Centre, Banff, Alberta, Canada 10 Xiaojing Mu, Guangya Zhou, Hongbin Yu, Julius Ming-Lin Tsai, Wee Keong Neo, A Senthil Kumar and Fook Siong Chau, “Electrostatic MEMS Resonating Micro Polygonal Scanner for Circumferential Endoscopic Bio-imaging”, Photonics West, 2-7 February 2013, The Moscone Center, San Francisco, California, United States 11 Fook Siong Chau, Xiaojing Mu, Guangya Zhou, “Electrostatic Actuation based MEMS Micro-Scanner for Optical Coherence Tomography”, Joint International Conference of The 2nd International Symposium on Experimental Mechanics, The 11th Asian Conference on Experimental Mechanics, 2012 Society for Experimental Mechanics Fall Conference and 7th International Symposium on Advanced Science and Technology in Experimental Mechanics (ISEM-ACEM-SEM-7th ISEM’12Taipei), November 8-11,2012, The Grand Hotel, Taipei, Taiwan 12 Xiaojing Mu, Guangya Zhou, Hongbin Yu, Julius Ming-Lin Tsai and Fook Siong Chau, “MEMS Scanners for Circumferential Scanning Endoscopic Probes”, International Conference on BioElectronics, BioSensors, BioMedical Devices, BioMEMS/NEMS and Applications 2012, (Bio4Apps 2012), NUS, Singapore, Nov.19 and 20, 2012 13 Xiaojing Mu, Hongbin Yu, Hanhua Feng, and Julius Ming-Lin Tsai, “MEMS based Optical Coherence Tomography Probe for Bio-imaging”, International Conference on BioElectronics, BioSensors, BioMedical Devices, BioMEMS/NEMS and Applications 2012, (Bio4Apps 2012), NUS, Singapore, Nov.19 and 20, 2012 163 ... of Optical Coherence Tomography 1.3 Endoscopic OCT 12 1.4 MEMS based endoscope for OCT imaging 13 1.5 Organization of the Dissertation 18 Technological Development of the Optical MEMS 20 2.1 MEMS. .. TetraEthylOrthoSilicate MEMS MicroElectroMechanical Systems MOEMS Micro-Opto-Electro-Mechanical System MRI Magnetic Resonance Imaging NA Numerical Aperture OCM Optical Coherence Microscopy OCT Optical Coherence Tomography. .. actuation 2.1 MEMS Optical Scanners MEMS optical scanners can be divided into two categories, reflective and refractive scanners MEMS reflective optical scanners, also referred to as MEMS scanning