Microelectromechanical systems (MEMS)-based sensors and actuators have become remarkably popular in the past few decades. Rapid advances have taken place in terms of both technologies and techniques of fabrication of MEMS structures. Wet chemical–based silicon bulk micromachining continues to be a widely used technique for the fabrication of microstructures used in MEMS devices. Researchers all over the world have contributed significantly to the advancement of wet chemical–based micromachining, from understanding the etching mechanism to exploring its application to the fabrication of simple to complex MEMS structures. In addition to its various benefits, one of the unique features of wet chemical–based bulk micromachining is the ability to fabricate slanted sidewalls, such as 45° walls as micromirrors, as well as freestanding structures, such as cantilevers and diaphragms. This makes wet bulk micromachining necessary for the fabrication of structures for myriad applications.
This book provides a comprehensive understating of wet bulk micromachining for the fabrication of simple to advanced microstructures for various applications in MEMS. It includes introductory to advanced concepts and covers research on basic and advanced topics on wet chemical–based silicon bulk micromachining. The book thus serves as an introductory textbook for undergraduate- and graduate-level students of physics, chemistry, electrical and electronic engineering, materials science, and engineering, as well as a comprehensive reference for researchers working or aspiring to work in the area of MEMS and for engineers working in microfabrication technology.
A Brief Introduction of the Crystal Structure
Introduction
Crystal Structure
Unit Cell: Primitive and Nonprimitive
Symmetry Operations
Types of Lattices
Index System for Crystal Planes and Directions
Cubic Structures
Stereographic Projection
References
Brief Overview of Silicon Wafer Manufacturing and Microfabrication Techniques
What Is Silicon?
Why Is Silicon Used as a Material for ICs and MEMS?
What Are Microelectromechanical Systems?
Wafer Manufacturing
Silicon Microfabrication Processes
References
Isotropic Etching of Silicon and Related Materials
Isotropic Etching Properties
Isotropic Etching Solutions
Conditions for Isotropic Etching
Applications
References
KOH-Based Anisotropic Etching
Etching in Pure KOH Solutions
Effect of Alcohols and Surfactant Additives
References
TMAH-Based Anisotropic Etching
Introduction
The Etching Mechanism
Etch Rates
Surface Morphology
Undercutting and Etched Profiles
Why Are Etching Characteristics Affected When a Surfactant Is Added to TMAH?
Etched Profile Control
Summary
References
Convex and Concave Corners in Silicon Wet Bulk Micromachining
Introduction
Etch Rate, Underetching, and Undercutting
Role of Corner Undercutting in MEMS Fabrication
Why Does Undercutting Start at Convex Corners?
Etched Profiles at Sidewalls and Corners
Fabrication Techniques of Convex Corners
Summary
References
Alignment of Mask Patterns to Crystallographic Directions
Introduction
Role of Precise Alignment in Wet Bulk Micromachining
Alignment Techniques
Summary
References
Simple to Complex Structures Using Wet Bulk Micromachining
Introduction
Cavities, Channels, and Mesa Structures
Microstructures with 45° Slanted Sidewalls
Silicon Gratings
Suspended Microstructures
Microstructures with Perfectly Sharp Edges and Corners
Suspended Microfluidic Channels
AFM Cantilevers
Microvalves and Micropumps
Microstructures Inside a Silicon Wafer
Dry-Assisted Wet Etching
Silicon Molds for the Fabrication of PDMS Structures
Complex Patterns for Very-High-Aspect-Ratio Microstructures Using Photoelectrochemical
Etching
References
Biography
Prem Pal is associate professor in the Department of Physics, Indian Institute of Technology (IIT) Hyderabad, India. He obtained his MTech in solid state materials and PhD in MEMS from IIT Delhi, India, in 1999 and 2004, respectively. From July 2005 to June 2006, he was a postdoctoral researcher at Yonsei Microsystems Laboratory, School of Mechanical Engineering, Yonsei University, Seoul, South Korea. Then he worked in the Department of Micro-Nano Systems Engineering, Nagoya University, Japan, as Center of Excellence (COE) scientist from July 2006 to March 2008 and as JSPS fellow from March 2008 to March 2010. Dr. Pal has published more than 50 papers in peer-reviewed international journals and has made outstanding contributions to the area of silicon wet anisotropic etching, especially its application to the fabrication of MEMS components. His research interests include MEMS technology, MEMS-based sensors, silicon micromachining, and thin films for MEMS.
Kazuo Sato is emeritus professor at Nagoya University, Japan, and professor at the Aichi Institute of Technology, Japan, since 2012. He is also the founding chair of the Micro/Nano Science and Technology Division of the Japan Society of Mechanical Engineers. He received his BS from Yokohama National University, Japan, in 1970 and PhD from the University of Tokyo, Japan, in 1982. He worked with Hitachi Ltd. from 1970 to 1994. He was a professor at the Micromachining and MEMS Laboratory, Nagoya University, from 1994 to 2012. Prof. Sato started his MEMS research in 1983 and has published 151 journal papers, 219 conference papers, and 20 books/book chapters on MEMS technologies. His research areas are micro-/nanophysics in anisotropic etching and mechanical properties of single-crystal silicon, as well as applied microsystems such as sensors and actuators.
