20-09-2009, 03:46 PM
APPLICATION OF MEMS TECHNOLOGY
ABSTRACT
MEMS (Micro-electro mechanical system) devices combines the merits of both electronic and mechanical systems [1].The MEMS technology has seen expansion in broad range from mechanical to chemical ,optical to bio-tech and many other fields .It is the integration of mechanical elements ,sensors ,actuators and electronics components on a single silicon substrate through micro fabrication technology .In this paper ,different MEMS devices are demonstrated like nanosatellite ,MEMS optical devices and bio-tech products .This technology not only provides better integration ,light weight and compactness but, also provides low power cost.
KEYWORDS
Nano-satellite , Optical MEMS devices and Bio-MEMS .
1. INTRODUCTION
MEMS has been undergoing rapid development over the past decade .The devices using this technology are manufactured using similar fabrication techniques as that of Integrated circuits .MEMS are referred to as micro machines (in Japan)and micro system technology MST (in Europe) .The components manufactured using this technology have sizes of approximately 10 to 100 micro meters .MEMS technology is used for a wide variety of application .It is used to build nano or even pico-satellites components which has low weight ,small size and which are less power hungry .It is also used to manufacture optical devices like WDM\DWDM ,add-drop multiplexer ,optical crossconnect etc,[3]. Biological application includes biosensors , immuno-isolation and injectable MEMS. All these MEMS devices are manufactured using fabrication techniques likemolding ,plating ,wet-etching and electro discharge machining[2].
2. NANOSATELLITE
To fabricate a larger satellite ,scientists used to work on it for several years .MEMS devices for satellites have enabled much lighter and smaller nanosatellites with higher performance and longer lifetime. Smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in multiples [1].They can also be launched Ëœpiggybackâ„¢, using excess capacity on larger launch vehicles .NS-1 is a nano-satellite launched on 18 April,2004 for scientific exploration and to test the reliability .Huge scientific data and images were collected with this satellite. The characteristics of NS-1 are:
ÂÂÅ“ Weighs less than 25kg
ÂÂÅ“ Consists of components -1 MIMU,3 micro CMOS
cameras,1 sun sensor,3 momentum wheels and 1 micro magnetic sensor. With these MEMS devices nano-satellite are successfully manufactured and integrated. MEMS devices can be easily destroyed after use ,due to their smaller dimensions.
2.1. Reliability : The outer space rays and particles can damage MEMS devices in orbit so ,before a satellite is launched to particular orbit its components must be tested for reliability[1].
3. MEMS OPTICAL DEVICES
MEMS devices have application in the optical field of telecommunication. The objective is to provide high performance, low cost, solution for optical switching, WDM and other application[3].
3.1. OPTICAL CROSS CONNECT (OXC):
An optical cross-connect (OXC) is a device used by telecommunication carriers to switch high-speed optical signals in a fiber optics network. It is a wavelength and protocol insensitive device for optical switching, which replaces conventional optical-
electrical-optical (OEO) switching .In conventional OEO ,optical signal is converted to electrical ,this electrical signal is processed and then conversion of electrical to optical takes place .This is known as an OEO (Optical Electrical-Optical) design .A MEMS OXC ,typically consists of micro-mirrors made of either poly-silicon or crystalline silicon coated with metal for reflectivity .The actuation can be electrostatic ,magnetic or a combination both. - of
Application
: MEMS Add/Drop 2×2 Optical Switches the the Add ewed as spe ed function of data e lly moveble m r MEMS devices for optical network pplic )
. BIO-MEMS
are two position devices that are commonly used in Optical Add/Drop Multiplexers. In the Bypass state, Input and Output ports are connected to each other. In the Inserted state, the Input and Drop ports are connected to each other, while at the same time and Output ports are connected to each other.
3.2. OPTICAL ADD-DROP MULTIPLEXER (OADM):
An optical add-drop multiplexer can be vi a cial case of an OXC. In optical WDM system, a data channel can be dropped to a local network or add from the local network .MEMS provides a simple and elegant solution in optical add-drop multiplexer(OADM)[4].This add-drop channels is obtained by inserting the channel blocker between an optical splitter and an optical coupler .Her ,each channel can be individually controlled .This has advantage of wavelength selectivity and offers flexibility to add or drop new data channels The MEMS chip consists of an electrica a irror on a silicon support. A voltage applied to the MEMS chip causes the mirror to rotate, which changes the coupling of light between two input fibers and two output fibers. The othe a ations include variable optical attenuators(VOA and polarization mode dispersion(PMD) compensator.
4
MEMS devices are often moving components that allow physical or analytical functions to be performed by the device[2] .Interest for MEMS in biological applications is increasing rapidly with MEMS devices such as biosensors ,pacemakers , immuno-isolation capsule etc,.
4.1. BIO-SENSORS:
Bio-sensors are the MEMS devices which are used in vivo diagnostics . Bacteria can be detected using biosensors. A biosensor is a device that detects, records, and transmits information regarding a physiological change or the presence of various chemical or biological materials in the environment. Technically, a biosensor is a device that integrates a biological component, such as a whole bacterium or a biological product (e.g., an enzyme or antibody) with an electronic component to yield a measurable signal. Biosensors, which come in a large variety of sizes and shapes, are used to monitor changes in environmental conditions. They can detect and measure concentrations of specific bacteria or hazardous chemicals; they can measure acidity levels (pH),analytes and pressure in blood ,tissue and body fluids and so on ,thus biosensors can use bacteria and detect them, too.
4.2. INJECTABLE MEMS:
Injectable MEMS are being investigated for vivo applications .The research in injectable MEMS is mainly in : 1.Micro-needles for drug delivery system. 2.Injectable micro modules for neuro-muscular stimulation or sensing application.
4.2.1. MICRO-NEEDLES:
Micro-needles are devices that permit drug delivery into the skin with minimal or no damage ,pain or irritation to the tissues [2].They are used to induce drugs into human system by using needles of smaller size of few microns .This is the painless injection .The smaller sizes are obtained through micro fabrication processes .micro needles can be used to deliver compounds to cells in culture or into localized region of tissue inside the body .The fabrication materials used are silicon ,glass and metal.
4.2.2. INJECTABLE MICRO MODULES:
Injectable micro modules are the MEMS devices which are injected into human system so that, they can co-ordinate in the neuro-muscular stimulation or other sensing applications. Micro module system are small enough to be implanted by using micro needles .Thus, eliminating the need for surgical implantations .The principle of injectible micro needles is same as that of radio frequency identification devices . The RFID tag is miniature glass capsule containing a solenoidal coil and an integrated circuit ,which forms a inductive page link to power and communicate with the device .
4.3. IMMUNO-ISOLATION DEVICES:
Immuno-isolation capsules are used to overcome polymer-based capsules that suffer from inadequate mechanical strength and broad pore size distribution .These factors can cause failure of the mechanical system due to diffusion of antibodies and complement components through membrane .Semi-permeable immuno-isolation capsules that are induced into human system eg., to isolate implanted cell from surrounding biological environment ,while at the same time allowing cells to secrete insulin for treatment of diabetes. In spite ,of MEMS being aseptically fabricated and hermetically sealed bio-compatibility of these devices is a major issue for MEMS in vivo[2].
5. CONCLUSION
MEMS devices has many characteristics that make them appealing for applications from physics to biology and optical .It has potential to provide future telecommunication , bio-tech products of better performance ,low cost and higher miniaturization.
6. REFERENCES
1. You Zheng Li Bin Yu Shijie Zhang Gaofei
Applications of MEMS devices in nanosatellite,June
2005
2. GRAYSON, A.C.R. SHAWGO, R.S. JOHNSON, A.M.
FLYNN, N.T. YAWEN LI CIMA, M.J. LANGER, R. A
BioMEMS review: MEMS technology for physiologically
integrated devices , Volume: 92 , Issue: 1, Jan 2004
3. Liu, A.Q. Zhang Photonic MEMS: From Laser
Physics to Cell Biology, June 2007
4. Chorng-Ping Chang Optical MEMS technology for
telecommunication, VOLUME 3, Oct. 2004
