Microelectromechanical systems

Microelectromechanical systems (MEMS) is the technology of the very small, and merges at the nano-scale into nanoelectromechanical systems (NEMS) and Nanotechnology. MEMS are also referred to as micro machines, or Micro Systems Technology (MST). MEMS are separate and distinct from the hypothetical vision of Molecular nanotechnology or Molecular Electronics. MEMS generally range in size from a micrometer (a millionth of a meter) to a millimeter (thousandth of a meter). At these size scales, the standard constructs of classical physics do not always hold true. Due to MEMS' large surface area to volume ratio, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass. Finite element analysis is an important part of MEMS design.

The potential of very small machines was appreciated long before the technology existed that could make them. MEMS became practical once they could be fabricated using modified semiconductor fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing very small devices.

Companies with strong MEMS programs come in many sizes. The larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics. The successful small firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins. In addition, both large and small companies work in R&D to explore MEMS technology. Complexity and performance of advanced MEMS based sensors are described by different MEMS sensor generations.
MEMS description
Developments in the field of semiconductors are leading to integrated circuits with three-dimensional features and even moving parts. Such devices, called MicroElectroMechanical Systems (MEMS), can resolve many problems that a microprocessor plus software or hardwired ASIC(Application Specific Integrated Chip) cannot. MEMS technology can be implemented using a number of different materials and manufacturing techniques; the choice of which will depend on the device being created and the market sector in which it has to operate.
Silicon
Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking. The basic techniques for producing all silicon based MEMS devices are deposition of material layers, patterning of these layers by photolithography and then etching to produce the required shapes.
Polymers
Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to produce. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection moulding, embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.
Metals
Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability.
Metals can be deposited by electroplating, evaporation, and sputtering processes.
Commonly used metals include Gold, Nickel, Aluminum, Chromium, Titanium, Tungsten, Platinum and Silver.

MEMS processes: deposition

One of the basic building blocks in MEMS processing is the ability to deposit thin films of material. In this text we assume a thin film to have a thickness anywhere between a few nanometers to about 100 micrometers. Commonly used deposition processes are: Electroplating, Sputter deposition, Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD). The Chemical Vapor Deposition Process is a very intricate process which takes place in several steps.