Basic concepts of microfabrication technology and nanocrystalline metal oxide-based gas sensors are discussed in detail in the 12 chapters of this book. It is written for research-level students in various disciplines such as physics, materials science, chemistry, and mechanical engineering.
Chapter 1 starts with a detailed introduction to clean room technology and concepts. A brief history with an introduction to microelectromechanical systems (MEMS) and materials used in MEMS is discussed with appropriate illustrations. Chapter 2 covers various substrates (Si, Ge, GaAs) used for MEMS. The effects of surface contaminants as well as various cleaning and etching (e.g., wet and dry etching) processes are discussed in detail. Chapter 3 discusses various physical (thermal evaporation, sputtering, molecular epitaxy) and chemical vapor (plasma-enhanced CVD) deposition methods with diagrams showing appropriate experimental setups. Different metallization processes are discussed briefly. Chapter 4 covers properties of photoresists and their different types, along with various photolithographic processes.
Chapter 5 starts with a brief introduction to micromachining for gas sensors and talks about bulk and surface micromachining. Illustrations explaining the etching process and patterns are very useful. Chapter 6 discusses microheaters for gas sensors: types, properties, and needs. Software used and the physical properties affecting the heater properties are also discussed, accompanied by models and equations. Chapter 7 is an introduction to semiconductor gas sensors, their fundamentals, and their classification with working principles and variable parameters. Different types of gas sensors such as resistive-type and metal oxide-type are briefly discussed. Thick and thin films and various growth processes employed for gas-sensor fabrication are discussed in detail. Chapter 8 talks about graphene, including its different physical, chemical, and mechanical properties. Growth and characterization of graphene and its application for gas sensors are well discussed. The high-quality scanning electron microscope and transmission electron microscope images are very useful. Chapter 9 covers nanocrystalline ZnO-based microfabricated gas sensors. ZnO-based device structures and different growth mechanisms at low and high temperatures are discussed in detail. Chapter 10 briefly discusses volatile organic compounds, their different nanostructures, and their fabrication processes. Chapter 11 explains signal processing and different interfacing techniques along with appropriate flow diagrams. Chapter 12 talks briefly about the applications of MEMS and nanotechnology. References at the end of each chapter are relevant and include recent works.
It would have been helpful if the authors had included some problems and solutions in each chapter in order to make the book more useful to students. However, this book is an outstanding, broad overview of basics, concepts, specific materials used for each sensing application, and techniques employed in current, emerging, and possible future MEMS applications. I strongly recommend this book to all research students interested in MEMS and gas sensors.
Reviewer: K. Kamala Bharathi of the National Institute of Standards and Technology/University of Maryland, USA.
