Foundation of MEMS

Chang Liu received his M.S. and Ph.D. degrees from the California Institute of Technology in 1991 and 1995, respectively. His Ph.D. thesis was titled Micromachined sensors and actuators for fluid mechanics applications. In January 1996, he joined the Microelectronics Laboratory of the University of Illinois as a postdoctoral researcher. In January 1997, he became an assistant professor with major appointment in the Electrical and Computer Engineering Department and joint appointment in the Mechanical and Industrial Engineering Department. In 2003, he was promoted to the rank of Associate Professor with tenure. In 2007, Chang Liu joined Northwestern University (Evanston, Illinois) as a full professor of engineering. He established the MedX Laboratory to conduct advanced engineering research for medicine and health care. Dr. Liu has 20 years of research experience in the MEMS area and has published 200 technical papers in journals and refereed conference proceedings. He teaches undergraduate and graduate courses covering broad-ranging topics, including MEMS, solid-state electronics, electromechanics, sensor technology, circuits, dynamics, and heat transfer. He won a campus "Incomplete list of teachers ranked as excellent" honor in 2001 for developing and teaching the MEMS class, a precursor to this book. He received the National Science Foundation's CAREER award in 1998 for his research proposal of developing artificial haircells using MEMS technology. He is currently a Subject Editor of the IEEE/ASME Journal of MEMS, and was an Associate Editor of the IEEE Sensors Journal. His work has been cited in popular media. Dr. Liu is a cofounder of Integrated Micro Devices (IMD) Corporation and a member of the scientific advisory board of NanoInk Corporation (Chicago, IL). In 2004, he won the University of Illinois College of Engineering Xerox Award for Faculty Research. In the same year, he was elected a Faculty Associate at the Center for Advanced Studies at the University of Illinois, to pursue research in large-format integrated sensors. He is a Fellow of the IEEE, the world's largest professional association for the advancement of technology.

Preface to Second Edition Preface to First Edition Note to Instructors About the Author Notational Conventions Chapter 1: Introduction 1.0. Preview 1.1. The History of MEMS Development 1.1.1. From the Beginning to 1990 1.1.2. From 1990 to 2001 1.1.3. 2002 to present 1.1.4. Future Trends 1.2. The Intrinsic Characteristics of MEMS 1.2.1. Miniaturization 1.2.2. Microelectronics Integration 1.2.3. Parallel Fabrication with Precision 1.3. Devices: Sensors and Actuators 1.3.1. Energy Domains and Transducers 1.3.2. Sensors Considerations 13.3. Sensor Noise and Design Complexity 1.3.4. Actuators Considerations Summary Problems References Chapter 2: First-Pass Introduction to Microfabrication 2.0. Preview 2.1. Overview of Microfabrication 2.2. Essential Overview of Frequently Used Microfabrication Processes 2.2.1. Photolithography 2.2.2. Thin film deposition 2.2.3. Thermal oxidation of silicon 2.2.4. Wet Etching 2.2.5. Silicon anisotropic etching 2.2.6. Plasma etching and reactive ion etching 2.2.7. Doping 2.2.8. Wafer dicing 2.2.9. Wafer bonding 2.3. The Microelectronics Fabrication Process Flow 2.4. Silicon-based MEMS Processes 2.5. Packaging and Integration 2.5.1. Integration Options 2.5.2. Encapsulation 2.6. New Materials and Fabrication Processes 2.7. Process Selection and Design 2.7.1. Points of Consideration for Deposition Processes 2.7.2. Points of Consideration for Etching Processes 2.7.3. Ideal Rules for Building a Process Flow 2.7.4. Rules for Building a Robust Process Summary Problems References Chapter 3: Review of Essential Electrical and Mechanical Concepts 3.0 Preview 3.1. Conductivity of Semiconductors 3.1.1. Semiconductor Materials 3.1.2. Calculation of Charge Carrier Concentration 3.1.3. Conductivity and Resistivity 3.2. Crystal Planes and Orientations 3.3. Stress and Strain 3.3.1. Internal Force Analysis: Newton's Laws of Motion 3.3.2. Definitions of Stress and Strain 3.3.3. General Scalar Relation between Tensile Stress and Strain 3.3.4. Mechanical Properties of Silicon and Related Thin Films 3.3.5. General Stress - Strain Relations 3.4. Flexural Beam Bending Analysis under Simple Loading Conditions 3.4.1. Types of Beams 3.4.2. Longitudinal Strain under Pure Bending 3.4.3. Deflection of Beams 3.4.4. Finding the Spring Constants 3.5. Torsional Deflections 3.6. Intrinsic Stress 3.7. Dynamic System, Resonant Frequency, and Quality Factor 3.7.1. Dynamic System and Governing Equation 3.7.2. Response under Sinusoidal Resonant Input 3.7.3. Damping and Quality Factor 3.7.4. Resonant Frequency and Bandwidth 3.8. Active Tuning of Spring Constant and Resonant Frequency 3.9. A List of Suggested Courses and Books Summary Problems References Chapter 4: Electrostatic Sensing and Actuation Section 4.0. Preview Section 4.1. Introduction to Electrostatic Sensors and Actuators Section 4.2. Parallel Plate Capacitor 4.2.1. Capacitance of Parallel Plates 4.2.2. Equilibrium Position of Electrostatic Actuator under Bias 4.2.3. Pull-in Effect of Parallel-Plate Actuators Section 4.3. Applications of Parallel-Plate Capacitors 4.3.1. Inertia Sensor 4.3.2. Pressure Sensor 4.3.3. Flow Sensor 4.3.4. Tactile sensor 4.3.5. Parallel-plate actuators Section 4.4. Interdigitated Finger Capacitors Section 4.5. Applications of Comb-Drive Devices 4.5.1. Inertia Sensors 4.5.2. Actuators Summary Problems Refer Chapter 5: Thermal Sensing and Actuation 5.0. Preview 5.1. Introduction 5.1.1. Thermal Sensors 5.1.2. Thermal Actuators 5.1.3. Fundamentals of Thermal Transfer 5.2. Sensors and Actuators Based on Thermal Expansion 5.2.1. Thermal Bimorph Principle 5.2.2. Thermal Actuators with a Single Material 5.3. Thermal Couples 5.4. Thermal Resistors 5.5. Applications 5.5.1. Inertia Sensors 5.5.2. Flow Sensors 5.5.3. Infrared Sensors 5.5.4. Other Sensors Summary Problems References Chapter 6: Piezoresistive Sensors 6.0. Preview 6.1. Origin and Expression of Piezoresistivity 6.2. Piezoresistive Sensor Materials 6.2.1. Metal Strain Gauges 6.2.2. Single Crystal Silicon 6.2.3. Polycrystalline Silicon 6.3. Stress Analysis of Mechanical Elements 6.3.1. Stress in Flexural Cantilevers 6.3.2. Stress and Deformation in Membrane 6.4. Applications of Piezoresistive Sensors 6.4.1. Inertial Sensors 6.4.2. Pressure Sensors 6.4.3. Tactile sensor 6.4.4. Flow sensor Summary Problems References Chapter 7: Piezoelectric Sensing and Actuation 7.0. Preview 7.1. Introduction 7.1.1. Background 7.1.2. Mathematical description of piezoelectric effects 7.1.3. Cantilever piezoelectric actuator model 7.2. Properties of Piezoelectric Materials 7.2.1. Quartz 7.2.2. PZT 7.2.3. PVDF 7.2.4. ZnO 7.2.5. Other Materials 7.3. Applications 7.3.1. Inertia Sensors 7.3.2. Acoustic Sensors 7.3.3. Tactile Sensors 7.3.4. Flow Sensors 7.3.5. Surface Elastic Waves Summary Problems References Chapter 8: Magnetic Actuation 8.0. Preview 8.1. Essential Concepts and Principles 8.1.1. Magnetization and Nomenclatures 8.1.3. Selected Principles of Micro Magnetic Actuators 8.2 Fabrication of Micro Magnetic Components 8.2.1. Deposition of Magnetic Materials 8.2.2. Design and Fabrication of Magnetic Coil 8.3. Case Studies of MEMS Magnetic Actuators Summary Problems References Chapter 9: Summary of Sensing and Actuation Methods 9.0. Preview 9.1. Comparison of Major Sensing and Actuation Methods 9.2. Other Sensing and Actuation Methods 9.2.1. Tunneling Sensing 9.2.3 Optical Sensing 9.2.4. Field Effect Transistors 9.2.5. Radio Frequency Resonance Sensing Summary Problems References Chapter 10: Bulk Micromachining and Silicon Anisotropic Etching 10.0. Preview 10.1. Introduction 10.2. Anisotropic Wet Etching 10.2.1. Introduction 10.2.2. Rules of Anisotropic Etching Simplest Case 10.2.3. Rules of Anisotropic Etching Complex Structures 10.2.4. Forming Protrusions 10.2.5. Interaction of Etching Profiles from Isolated Patterns 10.2.6. Summary of design methodology 10.2.7. Chemicals for Wet Anisotropic Etching 10.3. Dry Etching and Deep Reactive Ion Etching 10.4. Isotropic Wet Etching 10.5. Gas Phase Etchants 10.6. Native Oxide 10.7. Special Wafers and Techniques Summary Problems References Chapter 11: Surface Micromachining 11.0. Preview 11.1. Basic Surface Micromachining Processes 11.1.1. Sacrificial Etching Process 11.1.2. Micro Motor Fabrication Process A First Pass 11.2.3. Micro Motor Fabrication Process A Second Pass 11.1.4. Micro Motor Fabrication Process Third Pass 11.2. Structural and Sacrificial Materials 11.2.1. Material Selection Criteria for a Two-layer Process 11.2.2. Thin Films by Low Pressure Chemical Vapor Deposition 11.2.3. Other Surface Micromachining Materials and Processes 11.3. Acceleration of Sacrificial Etch 11.4. Stiction and Anti-stiction Methods Summary Problems References Chapter 12: Process Synthesis: Putting It all Together 12.0. Preview 12.1. Process for Suspension Beams 12.2. Process for Membranes 12.3. Psp; 12.3.1. SPM Technologies Case Motivation 12.3.2. General Fabrication Methods for Tips 12.3.3. Cantilevers with Integrated Tips 12.3.4. Cantilevers with Integrated Sensors 12.3.5. SPM Probes with Actuators 12.4. Practical Factors Affecting Yield of MEMS Summary Problems References Chapter 13: Polymer MEMS 13.0. Preview 13.1. Introduction 13.2. Polymers in MEMS 13.2.1. Polyimide 13.2.2. SU-8 13.2.3. Liquid Crystal Polymer (LCP) 13.2.4. PDMS 13.2.5. PMMA 13.2.6. Parylene 13.2.7. Fluorocarbon 13.2.8. Other Polymers 13.3. Representative Applications 13.3.1. Acceleration Sensors 13.3.2. Pressure Sensors 13.3.3. Flow sensors 13.3.4. Tactile Sensors Summary Problems Reference Chapter 14: Micro Fluidics Applications 14.0. Preview 14.1. Motivation for Microfluidics 14.2. Essential Biology Concepts 14.3. Basic Fluid Mechanics Concepts 14.3.1. The Reynolds Number and Viscosity 14.3.2. Methods for Fluid Movement in Channels 14.3.3. Pressure Driven Flow 14.3.4. Electrokinetic Flow 14.3.5. Electrophoresis and Dielectrophoresis 14.4. Design and Fabrication of Selective Components 14.4.1. Channels 14.4.2. Valves Summary Problems References Chapter 15: Case Studies of Selected MEMS Products 15.0. Preview 15.1. Case Studies: Blood Pressure (BP) Sensor 15.1.1. Background and History 15.1.2. Device Design Considerations 15.1.3. Commercial Case: NovaSensor BP Sensor 15.2. Case Studies: Microphone 15.2.1. Background and History 15.2.2. Design Considerations 15.2.3. Commercial Case: Knowles Microphone 15.3. Case Studies: Acceleration Sensors 15.3.1. Background and History 15.4.2. Design Considerations 15.4.1. Commercial Case: Analog Devices and MEMSIC 15.4. Case Studies: Gyros 15.4.1. Background and History 15.4.2. The Coriolis Force 15.4.3. MEMS Gyro Design 15.4.4. Single Axis Gyro Dynamics 15.4.4. Commercial Case: InvenSense Gyro 15.5 Summary of Top Concerns for MEMS Product Development 15.5.1. Performance and Accuracy 15.5.2. Repeatability and Reliability 15.5.3. Managing the Cost of MEMS Products 15.5.4. Market Uncertainties, Investment, and Competition Summary Problems References Appendix 1: Characteristics of selected MEMS material Appendix 2: Frequently Used Formula for Beams, Cantilevers, and Plates Appendix 3: Basic Tools for Dealing with a Mechanical Second-order Dynamic System Appendix 4: Most Commonly Encountered Materials Appendix 5: Most Commonly Encountered Material Removal Process Steps Appendix 6: A List of General Compatibility between General Materials and Processes Appendix 7: Comparison of Commercial Inertial Sensors Answers to selected problems Index