A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www.mems.sandia.gov

Microelectromechanical Systems (MEMS) is the technology of the very small, and merges at the nanoscale into "Nanoelectromechanical Systems" (NEMS) and Nanotechnology. In Europe, MEMS are often referred to as Micro Systems Technology (MST). It should not be confused with the hypothetical vision of Molecular nanotechnology or Molecular Electronics. ==of a metre) to a millimetre (thousandth of a metre). At these size scales, a human's intuitive sense of 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. They are fabricated using modified silicon fabrication technology (used to make electronics), 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. MEMS sometimes go by the names micromechanics, micro machines, or micro system technology (MST). A mite examines a gear chain produced using nanotechnology Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ... A mite examines a gear chain produced using nanotechnology Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ... Families Tetranychidae - Spider mites Eriophyidae - Gall mites Sarcoptidae - Sarcoptic Mange mites The mites and ticks, order Acarina or Acari, belong to the Arachnida and are among the most diverse and successful of all the invertebrate groups, although some way behind the insects. ... Spur gears found on a piece of farm equipment. ... NEMS or nanoelectromechanical systems are similar to MEMS but smaller. ... Molecular gears from a NASA computer simulation. ... It has been suggested that Molecular engineering be merged into this article or section. ... Molecular electronics (sometimes called moletronics) is a branch of applied physics which aims at using molecules as passive (e. ... metre or meter, see meter (disambiguation) The metre (in the U.S., chiefly meter) is a measure of length, approximately equal to 3. ... A millimetre (American spelling: millimeter, symbol mm) is an SI unit of length that is equal to one thousandth of a metre. ... The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density. ... Electrostatics is the branch of physics that deals with the forces exerted by a static (i. ... Wetting of different fluids. ... The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... The field of electronics is the study and use of systems that operate by controlling the flow of electrons (or other charge carriers) in devices such as thermionic valves and semiconductors. ... Wet etching is the removal of material by immersing the wafer in a liquid bath of chemical etchant. ... The chemical compound potassium hydroxide, (KOH) sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. ... TMAH Tetramethylammonium hydroxide (CH3)4NOH Anisotropic etchant of silicon ... 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 plasma of Nitrogen, Chlorine and Boron Trichloride) that dislodge portions of the material from the exposed surface. ... Electrical Discharge Machine 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. ... Micromachines are mechanical objects that are fabricated in the same general manner as integrated circuits. ...

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. The phrase research and development (also R and D or R&D) has a special commercial significance apart from its conventional coupling of research and technological development. ... A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition. ... MEMS sensor generations represent the progress made in micro sensor technology and can be categorized as follows: 1st Generation MEMS sensor element mostly based on a silicon structure, sometimes combined with analog amplification on a micro chip. ...

Common applications include:

• inkjet printers, which use piezoelectrics or bubble ejection to deposit ink on paper.
• accelerometers in modern cars for airbag deployment in collisions.
• MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g. to deploy a roll over bar or trigger dynamic stability control.
• pressure sensors e.g. car tire pressure sensors, and disposable blood pressure sensors.
• Displays e.g the DMD chip in a projector based on DLP technology has on its surface several hundred thousand micromirrors.
• Optical switching technology which is used for switching technology for data communications, and is part of the emerging technology of smartdust.

Finite element analysis is an important part of MEMS design. Ink jet printers are the most common type of computer printer; and industry and commerce also use them extensively for special-purpose applications. ... Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. ... A depiction of an accelerometer designed at Sandia National Laboratories. ... An automobile airbag, like this one in a crashed SEAT Ibiza car, deflates after 0. ... In science, a vibrating structure gyroscope is a type of gyroscope that functions much like the halteres of insects. ... Yaw or Yam is the name for the Levantine god of chaos and the power of the untamed sea as found in texts from the ancient city of Ugarit. ... Dyanmic Stability Control is another name for Electronic Stability Control (ESC). ... A pressure sensorBold textmeasures Bold textBold textthe pressure, typically of fluids, at a point in a fluid network. ... Firestone tire A tire or tyre (see spelling differences) is a device covering the circumference of a wheel. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Blood pressure is the pressure exerted by the blood on the walls of the blood vessels. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Only meanings of encyclopedic scope are listed here for disambiguation purposes. ... A Digital Micromirror Device, or DMD is an optical semiconductor that is the core of DLP projection technology, and was invented by Dr. Larry Hornbeck and Dr. William E. Ed Nelson of Texas Instruments (TI) in 1987. ... The DLP Logo Digital Light Processing (DLP) is a technology used in projectors and video projectors. ... Optical Switching is a technique where Input optical rays are directed to the output to complete a circuit kind of thing. ... A computer network is a system for communication among two or more computers. ... Smartdust is a network of tiny wireless microelectromechanical sensors (MEMS), robots, or devices, installed with wireless communications, that can detect anything from light and temperature, to vibrations, etc. ... Visualization of how a car deforms in an asymmetrical crash using finite element analysis. ...

MEMS Materials

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 almost all integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of highly accurate processing 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 lithography and then etching to produce the required shapes. General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... An integrated circuit (IC) is a thin chip consisting of at least two interconnected semiconductor devices, mainly transistors, as well as passive components like resistors. ... In physics, Hookes law of elasticity states that if a force (F) is applied to an elastic spring or prismatic rod (with length L and cross section A), its extension is linearly proportional to its tensile stress σ and modulus of elasticity (E): or It is named after the 17th... Hysteresis is a property of systems (usually physical systems) that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state: that is, systems whose states depend on their immediate history. ... In materials science, fatigue is the progressive, localized, and permanent structural damage that occurs when a material is subjected to cyclic or fluctuating strains at nominal stresses that have maximum values less than (often much less than) the static yield strength of the material. ... The word billion and its equivalents in other languages refer to either one million million or one thousand million, depending on whether the writer is using the long scale or the short scale. ... The numeral trillion refers to one of two number values, depending on the context of where and how it is being used. ... Deposition is a word used in many fields to describe different processes: In law, deposition is the taking of testimony outside of court. ... Negative litography stone and positive print of a map of Munich Lithography is a method for printing on a smooth surface. ...

Polymers

Even though the electronics industry provides an economy of scale for the silicon industry, crystaline 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 can be used to make plastic artificial flowers such as these. ... This article or section does not cite its references or sources. ... Stereolithography is one of the more commonly used rapid manufacturing and rapid prototyping technologies. ... Microfluidics deals with the behavior, precise control and manipulation of microliter and nanoliter volumes of fluids. ...

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 Processes

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 nanometer to about 100 micrometer. Commonly used deposition processes are: Electroplating, Sputtering, Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD). Electroplating is the coating of an electrically conductive item with a layer of metal using electrical current. ... Sputtering is a physical process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ... Physical vapor deposition (PVD) is a technique used to deposit thin films of various materials onto various surfaces (e. ... DC plasma (violet) enhances the growth of carbon nanotubes in this laboratory-scale PECVD apparatus. ...

Photolithography

Main article: Photolithography Photolithography is a process used in semiconductor device fabrication to transfer a pattern from a photomask (also called reticle) to the surface of a substrate. ...

Lithography in the MEMS context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light. A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. If we selectively expose a photosensitive material 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 deposition, wet and dry etching.

Etching Processes

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.

Wet Etching

Main article: Wet etching Wet etching is the removal of material by immersing the wafer in a liquid bath of chemical etchant. ...

This is the simplest etching technology. All it requires is a container with a liquid solution that will dissolve the material in question. Unfortunately, there are complications since usually a mask is desired to selectively etch the material. One must find a mask that will not dissolve or at least etches much slower than the material to be patterned. Secondly, some single crystal materials, such as silicon, exhibit anisotropic etching in certain chemicals. Anisotropic etching in contrast to isotropic etching means different etch rates in different directions in the material. The classic example of this is the <111> crystal plane sidewalls that appear when etching a hole in a <100> silicon wafer in a chemical such as potassium hydroxide (KOH). The result is a pyramid shaped hole instead of a hole with rounded sidewalls with an isotropic etchant. The principle of anisotropic and isotropic wet etching is illustrated in the figure below.

RIE etching

Main article: Reactive ion etching Reactive ion etching (RIE) is a technology using plasma to etch material deposited on wafers. ...

In reactive ion etching (RIE), the substrate is placed inside a reactor in which several gases are introduced. 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 reacts at, 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 schematic of a typical reactive ion etching system is shown in the figure below.

DRIE etching

Main article: Deep reactive ion etching Deep Reactive Ion Etching or DRIE is a highly anisotropic etch process developed in the semiconductor industry and used to create deep and high aspect ratio channels in materials such as silicon. ...

A special subclass of RIE which continues to grow rapidly in popularity is deep RIE (DRIE). 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. The first gas composition creates a polymer on the surface of the substrate, and the second gas composition 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 3-4 times higher than wet etching.

Bulk micromachining

Main article: Bulk micromachining Bulk micromachining is a process used to produce micromachinery or MEMS. Unlike surface micromachining, which uses a succession of thin film deposition and selective etching, bulk micromachining defines structures by selectively etching inside a substrate. ...

Bulk micromachining is similar to deep etching but uses a different process to remove silicon. Bulk micromachining typically uses alkaline liquid solvents, such as potassium hydroxide, to dissolve silicon which has been left exposed by the photolithography masking step. These alkali solvents dissolve the silicon in a highly anisotropic way, with some crystallographic orientations dissolving up to 1000 times faster than others. Such an approach is often used with very specific crystallographic orientations in the raw silicon to produce v-shaped grooves. The surface of these grooves can be atomically smooth if the etch is carried out correctly with dimensions and angles being extremely accurate. The chemical compound potassium hydroxide, (KOH) sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ...

Metals are also often used as masks for dry and wet etching other materials depending on the selectivity of the metal to the etchant.

See also

• [1] A History of Silicon MEMS Product Development Through 1990
• NEMS, Nanoelectromechanical systems are similar to MEMS but smaller
• MOEMS, Micro Opto-Electrical-Mechanical Systems, MEMS including optical elements
• IBM Millipede, a MEMS technology for non-volatile data storage of more than a terabit per square inch
• STMicroelectronics [2] for 2x and 3x accelerometers
• Texas Instruments pioneers of the DMD chip
• ADI one of the major early players in accelerometer development
• Lucent who developed highly advanced optical telecommunications switches
• Cantilever one of the most common forms of MEMS.
• Electrostatic motors used where coils are difficult to fabricate

NEMS or nanoelectromechanical systems are similar to MEMS but smaller. ... Cantilever array showing multiple probes Millipede is a MEMS based technology for non-volatile data storage, being researched by IBM. It promises a data density of more than 1 Terabit per square inch, in other words more than 1 Gigabit per square millimeter, which is 20 times more than the... STMicroelectronics is an international leading supplier of semiconductors. ... Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is a company based in Dallas, Texas, renowned for developing and commercializing semiconductor and computer technology. ... A Digital Micromirror Device, or DMD is an optical semiconductor that is the core of DLP projection technology, and was invented by Dr. Larry Hornbeck and Dr. William E. Ed Nelson of Texas Instruments (TI) in 1987. ... Analog Devices is an American multinational producer of semiconductor devices. ... In 1996, AT&T spun off its Systems and Technology units, along with the famous Bell Laboratories, to form a new company named Lucent Technologies (NYSE: LU). ... Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... The cantilevered beam (green) projects out into space from its supports (blue). ... An electrostatic motor or capacitor motor is a type of electric motor based on the attraction and repulsion of electric charge. ...

MEMS Laboratories and Vendors

• The MEMS and Nanotechnology Exchange - A US-based MEMS resource for fabrication and design
• Stanford Microsystems Laboratory
• University of Illinois Micro Actuators, Sensors, and Systems Group
• U. C. Berkeley Sensor and Actuator Center
• DALSA, Canada, MEMS and wafer fabrication and processing services
• MEMS laboratory at Carnegie-Mellon
• Sensirion Inc., MEMS sensor manufacturer
• Micralyne Inc., MEMS developer and manufacturer
• Honeywell, Offers MEMS services from single process steps to full product development, from design concept through volume production, test and packaging.
• IMTEK, Department of Microsystems Engineering, University of Freiburg, Germany, largest MEMS research fascillity in Germany
• University of Colorado at Boulder - Multidisciplinary Engineering Micro-Systems Group (CU MEMS)
• McGill University in Montreal - Institute for Advanced Materials

Popular MEMS Sites

• MEMS Net - Very popular portal for information about MEMS
• Small Times - Excellent News Site for MEMS and Nanotechnology
• Image Gallery of Microscopic MEMS Machines
• Movie Gallery of Functioning MEMS
• Tutorials on MEMS
• Interactive MEMS Tutorials
• Interviews with MEMS industry leaders
• Introduction and resources on MEMS and Microtechnology