Microelectromechanical systems (MEMS) is the technology of the very small, and merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. Nanoelectromechanical systems or NEMS are similar to Microelectromechanical systems (MEMS but smaller Nanotechnology, sometimes shortened to nanotech, refers to a field of Applied science whose theme is the control of matter on an Atomic and Molecular MEMS are also referred to as micromachines (in Japan), or Micro Systems Technology - MST (in Europe). Micromachines are mechanical objects that are fabricated in the same general manner as Integrated circuits. MEMS are separate and distinct from the hypothetical vision of Molecular nanotechnology or Molecular Electronics. Molecular nanotechnology (MNT is the concept of engineering functional mechanical systems at the molecular scale For quantum mechanical study of the Electron distribution in a molecule see Stereoelectronics. MEMS are made up of components between 1 to 100 micrometers in size (i. e. 0. 001 to 0. 1 mm) and MEMS devices generally range in size from a 20 micrometers (20 millionth of a meter) to a millimeter (thousandth of a meter). The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to They usually consist of a central unit that processes data, the microprocessor and several components that interact with the outside such as microsensors. 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. Electrostatics is the branch of Science that deals with the Phenomena arising from what seems to be stationary Electric charges Since Classical Wetting is the contact between a liquid and a solid surface resulting from intermolecular interactions when the two are brought together The vis insita or innate force of matter is a power of resisting by which every body as much as in it lies endeavors to preserve in its present state whether it be of rest or of moving
The potential of very small machines was appreciated long before the technology existed that could make them—see, for example, Feynman's famous 1959 lecture There's Plenty of Room at the Bottom. There's Plenty of Room at the Bottom is the title of a famous lecture given by physicist Richard Feynman at an American Physical Society meeting MEMS became practical once they could be fabricated using modified semiconductor fabrication technologies, normally used to make electronics. Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical 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. In Microfabrication, wet etching is Chemical etching performed with a Liquid etchant as opposed to a plasma. Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]] Tetramethylammonium hydroxide (TMAH or TMAOH is a Quaternary ammonium salt with the molecular formula (CH34NOH Dry etching refers to the removal of material typically a masked pattern of Semiconductor material by exposing the material to a bombardment of Ions (usually a Electrical Discharge Machining (or EDM) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques
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 is the material used to create most integrated circuits used in consumer electronics in the modern world. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside 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. In Mechanics, and Physics, Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system 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. Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate
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. Injection molding (British moulding Embossing is the process of creating a three-dimensional image or design in Paper and other Ductile materials Stereolithography is a common Rapid manufacturing and Rapid prototyping technology for producing parts with high accuracy and good surface finish Microfluidics deals with the behavior precise control and manipulation of Fluids that are geometrically constrained to a small typically sub-millimeter scale
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. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 WikipediaNaming Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen
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). Electroplating is the process of using electrical current to reduce Cations of a desired material from a solution and coat a conductive object Sputter deposition is a Physical vapor deposition (PVD method of depositing Thin films by Sputtering, i Physical vapor deposition (PVD is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit Thin films by the condensation Chemical vapor deposition (CVD is a Chemical process used to produce high-purity high-performance solid materials
Lithography in MEMS context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light. Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If a photosensitive material is selectively exposed to radiation (e. g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs.
This exposed region can then be removed or treated providing a mask for the underlying substrate. Photolithography is typically used with metal or other thin film deposition, wet and dry etching.
There are two basic categories of etching processes: wet and dry etching. In the former, the material is dissolved when immersed in a chemical solution. In the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant. See Williams and Muller or Kovacs, Maluf and Peterson for a somewhat dated overview of MEMS etching technologies.
Wet chemical etching consists in a selective removal of material by dipping a substrate into a solution that can dissolve it. In Microfabrication, wet etching is Chemical etching performed with a Liquid etchant as opposed to a plasma. Due to the chemical nature of this etching process, a good selectivity can often be obtained, which means that the etching rate of the target material is considerably higher than that of the mask material if selected carefully.
Some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate. This is known as anisotropic etching and one of the most common examples is the etching of silicon in KOH (potassium hydroxide), where Si <111> planes etch approximately 100 times slower than other planes (crystallographic orientations). Crystallography is the experimental science of determining the arrangement of Atoms in Solids In older usage it is the scientific study of Crystals The Therefore, etching a rectangular hole in a (100)-Si wafer will result in a pyramid shaped etch pit with 54. 7° walls, instead of a hole with curved sidewalls as it would be the case for isotropic etching, where etching progresses at the same speed in all directions. Long and narrow holes in a mask will produce v-shaped grooves in the silicon. The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate.
Electrochemical etching (ECE) for dopant-selective removal of silicon is a common method to automate and to selective control etching. An active p-n diode junction is required, and either type of dopant can be the etch-resistant ("etch-stop") material. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Boron is the most common etch-stop dopant. In combination with wet anisotropic etching as described above, ECE has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. Selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon.
In reactive ion etching (RIE), the substrate is placed inside a reactor in which several gases are introduced. Reactive ion etching ( RIE) is an etching technology used in Microfabrication. A plasma is struck in the gas mixture using an RF power source, breaking the gas molecules into ions. The ions are accelerated towards, and react with, the surface of the material being etched, forming another gaseous material. This is known as the chemical part of reactive ion etching. There is also a physical part which is similar in nature to the sputtering deposition process. If the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction. It is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. By changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical.
A special subclass of RIE which continues to grow rapidly in popularity is deep RIE (DRIE). Deep reactive-ion etching ( DRIE) is a highly Anisotropic etch process used to create deep steep-sided holes and trenches in wafers with In this process, etch depths of hundreds of micrometres can be achieved with almost vertical sidewalls. The primary technology is based on the so-called "Bosch process", named after the German company Robert Bosch which filed the original patent, where two different gas compositions are alternated in the reactor. Currently there are two variations of the DRIE. The first variation consists of three distinct steps (the Bosch Process as used in the UNAXIS tool) while the second variation only consists of two steps (ASE used in the STS tool). In the 1st Variation, the etch cycle is as follows: (i) SF6 isotropic etch; (ii) C4F8 passivation; (iii) SF6 anisoptropic etch for floor cleaning. In the 2nd variation, steps (i) and (iii) are combined.
Both variations operate similarly. The C4F8 creates a polymer on the surface of the substrate, and the second gas composition (SF6 and O2) etches the substrate. The polymer is immediately sputtered away by the physical part of the etching, but only on the horizontal surfaces and not the sidewalls. Since the polymer only dissolves very slowly in the chemical part of the etching, it builds up on the sidewalls and protects them from etching. As a result, etching aspect ratios of 50 to 1 can be achieved. The process can easily be used to etch completely through a silicon substrate, and etch rates are 3-6 times higher than wet etching.
Xenon difluoride (XeF2) is a dry vapor phase isotropic etch for silicon originally applied for MEMS in 1995 at University of California, Los Angeles. Xenon difluoride is a powerful Fluorinating agent, with the chemical formula, is one of the most stable Xenon compounds. Primarily used for releasing metal and dielectric structures by undercutting silicon, XeF2 has the advantage of a stiction-free release unlike wet etchants. Stiction is an informal Portmanteau of the term "static Friction " ( μ s perhaps also influenced by the verb " stick Its etch selectivity to silicon is very high, allowing it to work with photoresist, SiO2, silicon nitride, and various metals for masking. Its reaction to silicon is "plasmaless", is purely chemical and spontaneous and is often operated in pulsed mode. Models of the etching action are available, and university laboratories and various commercial tools offer solutions using this approach.
Bulk micromachining is the oldest paradigm of silicon based MEMS. Bulk micromachining is a process used to produce Micromachinery or Microelectromechanical systems (MEMS The whole thickness of a silicon wafer is used for building the micro-mechanical structures.  Silicon is machined using various etching processes. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that have changed the shape of the sensor industry in the 80's and 90's. A pressure sensor measures the Pressure, typically of Gases or Liquids. An accelerometer is a device for measuring Acceleration and gravity induced reaction forces
Surface micromachining uses layers deposited on the surface of a substrate as the structural materials, rather than using the substrate itself. Surface micromachining is a process used to produce Micromachinery or MEMS.  Surface micromachining was created in the late 80's to render micromachining of silicon more compatible with planar integrated circuit technology, with the goal of combining MEMS and integrated circuits on the same silicon wafer. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside The original surface micromachining concept was based on thin polycrystalline silicon layers patterned as movable mechanical structures and released by sacrificial etching of the underlaying oxide layer. Interdigital comb electrodes were used to produce in-plane forces and to detect in-plane movement capacitively. This MEMS paradigm has enabled the manufacturing of low cost accelerometers for e. An accelerometer is a device for measuring Acceleration and gravity induced reaction forces g. automotive air-bag systems and other applications where low performance and/ or high g-ranges are sufficient. Analog Devices have pioneered the industrialization of surface micromachining and have realized the co-integration of MEMS and integrated circuits. Analog Devices ( is an American multinational producer of Semiconductor devices
Both bulk and surface micromachining are still used in industrial production of sensors, ink-jet nozzles and other devices. But in many cases the distinction between these two has diminished. New etching technology, deep reactive ion etching has made it possible to combine good performance typical to bulk micromachining with comb structures and in-plane operation typical to surface micromachining. Deep reactive-ion etching ( DRIE) is a highly Anisotropic etch process used to create deep steep-sided holes and trenches in wafers with Bulk micromachining is a process used to produce Micromachinery or Microelectromechanical systems (MEMS Surface micromachining is a process used to produce Micromachinery or MEMS. While it is common in surface micromachining to have structural layer thickness in the range of 2 µm, in HAR micromachining the thickness is from 10 to 100 µm. The materials commonly used in HAR micromachining are thick polycrystalline silicon, known as epi-poly, and bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also have been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR micromachining. The consensus of the industry at the moment seems to be that the flexibility and reduced process complexity obtained by having the two functions separated far outweighs the small penalty in packaging.
Commercial applications include:
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. The phrase research and development (also R and D or more often R&D) according to the Organization for Economic Co-operation and Development, refers
Researchers in MEMS use various engineering software tools to take a design from concept to simulation, prototyping and testing. Finite element analysis is often used in MEMS design. Simulation of dynamics, heat, and electrical domains, among others, can be performed by ANSYS and COMSOL. Other software, such as MEMS-PRO, is used to produce a design layout suitable for delivery to a fabrication firm. Once prototypes are on-hand, researchers can test the specimens using various instruments, including laser doppler scanning vibrometers, microscopes, and stroboscopes.
The global market for micro-electromechanical systems, which includes products such as automobile airbag systems, display systems and inkjet cartridges totalled $40 billion in 2006 according to Global MEMS/Microsystems Markets and Opportunities, a comprehensive new market research report from SEMI and Yole Developpement. Semiconductor Equipment and Materials International ( SEMI) is a Trade organization of Manufacturers of equipment and materials used in the fabrication of 
MEMS devices are defined as die-level components of first-level packaging, and include pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, micro fluidic devices, etc. The materials and equipment used to manufacture MEMS devices topped $1 billion worldwide in 2006. Materials demand is driven by substrates, making up over 70 per cent of the market, packaging coatings and increasing use of chemical mechanical planarization (CMP). While MEMS manufacturing continues to be dominated by used semiconductor equipment, there is a migration to 200mm lines and select new tools, including etch and bonding for certain MEMS applications.