MEMS

MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts.

[1] They usually consist of a central unit that processes data (an integrated circuit chip such as microprocessor) and several components that interact with the surroundings (such as microsensors).

[2] Because of the large surface area to volume ratio of MEMS, forces produced by ambient electromagnetism (e.g., electrostatic charges and magnetic moments), and fluid dynamics (e.g., surface tension and viscosity) are more important design considerations than with larger scale mechanical devices.

The potential of very small machines was appreciated before the technology existed that could make them (see, for example, Richard Feynman's famous 1959 lecture There's Plenty of Room at the Bottom).

An early example of a MEMS device is the resonant-gate transistor, an adaptation of the MOSFET, developed by Robert A. Wickstrom for Harvey C. Nathanson in 1965.

[5][6] During the 1970s to early 1980s, a number of MOSFET microsensors were developed for measuring physical, chemical, biological and environmental parameters.

Grace, titled "SCOFSS: A Small Cantilevered Optical Fiber Servo System", in the IEEE Proceedings Micro Robots and Teleoperators Workshop, Hyannis, MA Nov. 9–11, 1987.

Lithography in a MEMS context is typically the transfer of a pattern into a photosensitive material by selective exposure to a radiation source such as light.

The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching.

The primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer range.

This form of maskless lithography has found wide usage in photomask-making used in photolithography, low-volume production of semiconductor components, and research & development.

The key limitation of electron beam lithography is throughput, i.e., the very long time it takes to expose an entire silicon wafer or glass substrate.

Ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers.

X-ray lithography is a process used in the electronic industry to selectively remove parts of a thin film.

It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist", on the substrate.

[19][20] Wet chemical etching consists of the selective removal of material by dipping a substrate into a solution that dissolves it.

Isotropic wet etchant etch in all directions of the crystalline silicon at approximately equal rates.

The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate.

Some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate.

Xenon difluoride (XeF2) is a dry vapor phase isotropic etch for silicon originally applied for MEMS in 1995 at University of California, Los Angeles.

Models of the etching action are available,[23] and university laboratories and various commercial tools offer solutions using this approach.

The plasma produces energetic free radicals, neutrally charged, that react at the surface of the wafer.

It bombards the wafer with energetic ions of noble gases, often Ar+, which knock atoms from the substrate by transferring momentum.

Because the etching is performed by ions, which approach the wafer approximately from one direction, this process is highly anisotropic.

[citation needed] In reactive-ion etching (RIE), the substrate is placed inside a reactor, and several gases are introduced.

Analog Devices has pioneered the industrialization of surface micromachining and has realized the co-integration of MEMS and integrated circuits.

Both bulk and surface silicon micromachining are used in the industrial production of sensors, ink-jet nozzles, and other devices.

Larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics.

Smaller firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins.

Materials demand is driven by substrates, making up over 70 percent of the market, packaging coatings and increasing use of chemical mechanical planarization (CMP).