Moems

MOEMS stands for micro-opto-electromechanical systems. MOEMS is a miniaturised system combining optics, micromechanics and microelectronics, depending upon the application and device type, fabricated by the use of the collective techniques of micro fabrication and micromachining (Fig. 2.10). MOEMS device technology requires a different set of rules for operation when compared with the normal MEMS devices. For example, tunable microlasers and optical switching based on MOEMS technology can improve the capability of wavelength division multiplexing (WDM) systems. MOEMS technology also manufactures structures in the micron to millimeter ranges.

Mostly, MOEMS have emerged to provide unparalleled functionality in telecommunication applications. Although the ultimate speed of these devices is unlikely to compete with solid-state electro-optic devices, the precision that can be achieved with MOEMS contributes to good performance and negligible signal degradation in the channels, thereby enabling a flexible all-optical system. System bandwidth and power consumption are the key issues. Using fiber links and optical methods, MOEMS technology demands precision interfaces and integrated components in order to achieve reliable and available quality of service (QoS). The advantages of MOEMS are:

• Miniaturisation

• Insensitivity to electromagnetic interference

• Can be used in harsh environments

• High sensitivity and selectivity

• Reasonably faster

• Reliability and availability

• Mass production capability hence low manufacturing costs

Fig. 2.10. Expression of hybrid systems

The applications of MOEMS are presented in Table 2.2. More detail is given below (http://www-leti.cea.fr/commun/europe/MOEMS/moems.htm),

• Arrays of micromirrors for digital image processing (projection and printing)

• Optical switches and routers, variable attenuators, shutters (optical communications)

• Tunable sources and filters, reflection modulators, spectral equalisers (optical communications, optical sensing, spectral analysis)

• Micro-scanners (image processing, bar code reading, obstacle detection)

• Deformable membranes for adaptive optics (astronomy, ophtalmology, FSO, defence)

• Free-space microoptics (diffractive and refractive microlenses)

• Guided optics devices

• Optical sources and photodetectors

Table 2.2. Applications of MOEMS

Broader applications

Specific applications

Communication applications

Biomedical Automotive

Industrial maintenance & control Domestics

Space and astronomy Environmental monitoring

Scanning

Projection

Display

Printing

Sensing

Data storage Motors Sensors Gyroscopes Optical scanner

Switches

Variable attenuators

Equalisers

Modulators

Dispersion compensators Deformable micro mirrors Optical chopper Digital or analog circuits Optical interconnect with micro-gratings

MOEMS devices are designed by adopting various manufacturing methods. All of these methods involve the deposition of layers of appropriate materials and etching away the sacrificial layers to produce the desired structures. One of the important combined methods used in developing the MOEMS devices is the LIGA process. LIGA is a German acronym for lithography, electroplating, and molding. The process states that each layer of the different material is deposited lithographically. These layers are different thicknesses and can overlap one another depending upon the MOEMS device being designed. One layer is usually used as a sacrificial layer to fill in and support a void area. The subsequent layer can be used to make a mold for the next layer. The succeeding layer will overlap the first and be molded into shape by the second (www.memsoptical.com/ techinfo/memstut1.htm). Then the first two layers can be removed. This in turn leaves a freestanding structure.

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