Principles of Microelectromechanical Systems

Ki Bang Lee

• Publisher: Wiley-IEEE Press
• Year: 2011
• ISBN:
  9781118102244
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Microelectronics
• Index: Technology & Engineering

The building blocks of MEMS design through closed-form solutions

Microelectromechanical Systems, or MEMS, is the technology of very small systems; it is found in everything from inkjet printers and cars to cell phones, digital cameras, and medical equipment. This book describes the principles of MEMS via a unified approach and closed-form solutions to micromechanical problems, which have been recently developed by the author and go beyond what is available in other texts. The closed-form solutions allow the reader to easily understand the linear and nonlinear behaviors of MEMS and their design applications.

Beginning with an overview of MEMS, the opening chapter also presents dimensional analysis that provides basic dimensionless parameters existing in large- and small-scale worlds. The book then explains microfabrication, which presents knowledge on the common fabrication process to design realistic MEMS. From there, coverage includes:

• Statics/force and moment acting on mechanical structures in static equilibrium
  
  

• Static behaviors of structures consisting of mechanical elements
  
  

• Dynamic responses of the mechanical structures by the solving of linear as well as nonlinear governing equations
  
  

• Fluid flow in MEMS and the evaluation of damping force acting on the moving structures
  
  

• Basic equations of electromagnetics that govern the electrical behavior of MEMS
  
  

• Combining the MEMS building blocks to form actuators and sensors for a specific purpose
  
  

All chapters from first to last use a unified approach in which equations in previous chapters are used in the derivations of closed-form solutions in later chapters. This helps readers to easily understand the problems to be solved and the derived solutions. In addition, theoretical models for the elements and systems in the later chapters are provided, and solutions for the static and dynamic responses are obtained in closed-forms.

This book is designed for senior or graduate students in electrical and mechanical engineering, researchers in MEMS, and engineers from industry. It is ideal for radio frequency/electronics/sensor specialists who, for design purposes, would like to forego numerical nonlinear mechanical simulations. The closed-form solution approach will also appeal to device designers interested in performing large-scale parametric analysis.

CHAPTER 1

INTRODUCTION

1.1 MICROELECTROMECHANICAL SYSTEMS

MEMS, microelectromechanical systems, are systems that consist of small-scale electrical and mechanical components for specific purposes. MEMS were translated into systems with electrical and mechanical components but have extended their boundaries to include optical, radio-frequency, and nano devices. As a result, depending on the components included and applications desired, MEMS have different names: for example, MOEMS (micro-optoelectromechanical systems) for optical applications, RF MEMS (radio-frequency MEMS) to refer to radio-frequency components and applications, and NEMS (nanoelectromechanical systems) if the systems include at least one component whose dimension is less than 1 µm. When MEMS use bio-related material (e.g., strands of DNA) to detect desired targets or to manipulate cells, the corresponding MEM system is currently called bioMEMS. Different names may refer to MEMS: microsystems technology (MST) in Europe and micromachines in Japan. Throughout this book, MEMS will be referred to as systems that include at least one set of electrical and mechanical components for a specific purpose. Depending on the specific purpose, more components, such as a reflective surface for a micromirror, can be added to a MEMS device. A typical dimension of a component of MEMS varies from 1 µm to a few hundred micrometers, and the overall size is approximately less than 1 mm. In this book we describe MEMS principles via a unified approach and newly developed closed-form solutions. Readers are assumed to be familiar with mathematical background at the third-year college and university level.

1.2 COUPLED SYSTEMS

MEMS are coupled systems since they consist of electrical and mechanical components; the mechanical behavior of MEMS are in general coupled with the electrical behavior. For example, let us consider the first electrostatic MEMS device (Fig. 1.1), presented by Nathanson et al. in the 1960s to filter or amplify electrical signals using the resonance of an electroplated cantilever. When an input signal (electrical signal) is applied across the end of the cantilever and the actuation electrode on a substrate, the electrical attractive force, given by Coulomb’s law, actuates the cantilever, and a detection circuit formed under the cantilever detects the filtered or amplified electrical signal that is generated by the mechanical vibration of the cantilever.

Figure 1.1 Resonant gate transistor.

Since the development of the first MEMS device, many other MEMS have been developed. For example, as one of the important components of MEMS, the parallel plate shown in Fig. 1.2 (similar to the cantilever of Fig. 1.1) is widely used in many microdevices that employ electrostatic forces for actuation of a microstructure or detection of a physical quantity. The typical parallel plate shown in Fig. 1.2 illustrates the basic knowledge that is required to understand MEMS behavior. The parallel plate consists of a movable plate suspended by flexures, a stationary plate, and a voltage source to supply voltage or electrical charge to the movable and stationary plates. The flexures are used to support the movable plate and act as a spring. The gap between plates can be adjusted when a force (e.g., electrostatic force or inertial force) acts on the plate.

Figure 1.2 Parallel plate.

Let us suppose that we apply a voltage across the movable and stationary plates. Upon applying the voltage, positive charges (or negative charges, depending on the electrical connection) are accumulated on the movable plate while opposite charges are accumulated on the stationary plate. As a result, the positive and negative ...

Table of contents

• Cover
• Title page
• Copyright page
• Dedication
• PREFACE
• CHAPTER 1 INTRODUCTION
• CHAPTER 2 MICROFABRICATION
• CHAPTER 3 STATICS
• CHAPTER 4 STATIC BEHAVIOR OF MICROSTRUCTURES
• CHAPTER 5 DYNAMICS
• CHAPTER 6 FLUID DYNAMICS
• CHAPTER 7 ELECTROMAGNETICS
• CHAPTER 8 PIEZOELECTRIC AND THERMAL ACTUATORS
• CHAPTER 9 ELECTROSTATIC AND ELECTROMAGNETIC ACTUATORS
• CHAPTER 10 SENSORS
• APPENDIX
• REFERENCES
• Index