A considerable amount of research is being carried out concerning the design and development of existing systems that reach down into micro- and nanometer scale levels. A technology that considers microscale sensors, actuators, valves, gears, and mirrors embedded in semiconductor chips is referred to as microelectromechanical systems, MEMS in short. In essence, MEMS are small, integrated devices that combine electronics, electrical as well as mechanical elements (Fig. 2.1). The size is in the order of a micrometer level. MEMS design technology is an extended form of traditional fabrication techniques used for IC (Integrated Circuit) manufacturing. MEMS add passive elements such as capacitors and inductors including mechanical elements such as springs, gears, beams, flexures, diaphragms, etc. MEMS are thus the integration of these elements on a single substrate (wafer) developed through more advanced microfabrication and micromachining technology. While the ICs are fabricated by the use of IC process, the mechanical micro components are fabricated using micromachining processes. This process helps in etching away the parts of the selected portions of the wafer. The process can also add new structural layers to form mechanical as well as electromechanical components. Thus, MEMS technology promises to revolutionise many products by combing microfabrication-based microelectronics with micromachining process sequences on silicon, making it possible for the realisation of a complete systems-on-a-chip (SoC). The technology allows for the development of smart systems and products inheriting increased computational capability, perception and control attributes. Smart systems can lead to expand the scope of possible solutions to diagnostics for target applications. It has been mentioned that microelectronic integrated circuits can be thought of as the brains of a system while MEMS augments the decision-making capability with eyes and arms, to allow microsystems to sense and control the environment ( mems/what-is.html). MEMS devices are manufactured by the use of batch fabrication techniques similar to those used for IC. Therefore, unparalleled levels of superiority, sophistication, functionality, reliability and availability can be achieved on a small silicon chip at a relatively low cost. Two important microsystems are microsensors and microactuators.

Sensors gather information from the environment. The commonly used transduction principles are chemical, thermal, biological, optical, magnetic and mechanical phenomena. Accordingly, there are various types of microsensors. The integrated electronics process the information derived from the sensors. In many cases the decision-making logics are integrated into the devices. The decision is mostly transmitted to the actuator in order to achieve moving, positioning, regulating, pumping or filtering actions. In this way, the environment can be controlled depending on the desired purpose. The study of MEMS accommodates the topics listed below. These principles are presented in this chapter.

• Fabrication processes

• Mechanical sensors and actuators

• Magnetic MEMS

• Micro-opto-electromechanical systems (MOEMS)

Fig. 2.1. Microelectromechanical systems

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