INTRODUCTION OF MEMS ENGINEERING :
What Are MEMS?
In the United States, the technology is known as microelectromechanical systems (MEMS): in Europe, it is called microsystems technology (MST). A question asking for a more specific definition is certain to generate a broad collection of replies with few common characteristics other than “miniature.” But such apparent divergence in the responses merely reflects the diversity of applications this technology enables, rather than a lack of commonality. MEMS is simultaneously a toolbox, a physical product, and a methodology, all in one :
- It is a portfolio of techniques and processes to design and create miniature systems.
- It is a physical product often specialized and unique to a final application one can seldom buy a generic MEMS product at the neighborhood electronics store.
- “MEMS is a way of making things,” reports the Microsystems Technology Office of the United States DARPA . These “things” merge the functions of sensing and actuation with computation and communication to locally control physical parameters at the microscale, yet cause effects at much grander scales.
Although a universal definition is lacking, MEMS products possess a number of distinctive features. They are miniature embedded systems involving one or many micromachined components or structures. They enable higher level functions, though in and of themselves, their utility may be limited—a micromachined pressure sensor in one’s hand is useless, but, under the hood, it controls the fuel-air mixture of the car engine.
They often integrate smaller functions together into one package for greater utility (e.g., merging an acceleration sensor with electronic circuits for self diagnostics). They can also bring cost benefits directly through low unit
pricing or indirectly by cutting service and maintenance costs.
What Is Micromachining?
Micromachining is the set of design and fabrication tools that precisely machine and form structures and elements at a scale well below the limits of our human perceptive faculties—the microscale. Micromachining is the underlying foundation of MEMS fabrication; it is the toolbox of MEMS.
Arguably, the birth of the first micromachined components dates back many decades, but it was the well-established integrated circuit industry that indirectly played an indispensable role in fostering an environment suitable for the development and growth of micromachining technologies.
As the following chapters will show, many tools used in the design and manufacturing of MEMS products are “borrowed” from the integrated circuit industry. It should not then be surprising that micromachining relies on silicon as a primary material, even though the technology has certainly been demonstrated using other materials.