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MEMS AN OVERVIEW OF THE TECHNOLOGY

By Bryan King,2014-09-23 03:28
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MEMS AN OVERVIEW OF THE TECHNOLOGY

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    MEMS

    (AN OVERVIEW OF THE TECHNOLOGY)

    ABSTRACT

     Using the basic fundamental process namely Deposition process, lithography, and etching process the fabrication of micro mechanical components in various fields is lucidly present in this paper. Overall Micro-Electro-Mechanical-Systems (MEMS) is the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate through micro fabrication technology. MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits unprecedented levels of functionality, reliability and sophistication can be placed on a small silicon chip at a relatively low cost.

     The main objective of this paper is to improvise and bring down the size of the equipment using the MEMS technology along with the Nanotechnology. The main advantage of MEMS is that the high performance of MEMS based fabricated equipment and to bring out at low prices. It is widely used along with nanotechnology in various fields like Biotechnology, Communications and Accelerometers.

CONTENTS:

    1. Introduction

    2. MEMS processing

     a) Deposition process

     b) Lithography

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     c) Etching process

     3. Deposition process

     a) Chemical Vapor Deposition (CVD)

     b) Physical Vapor Deposition (PVD)

    4. Advantages of MEMS

    5. Applications in

     a) Biotechnology

     b) Communications

     c) Accelerometer

    6. Conclusion

    7. Reference

    Introduction to MEMS

    Technology:

    MEMS revolutionize silicon based micro Micro-Electro-Mechanical-Systems

    electronics with micro machining (MEMS) is the integration of mechanical

    technology, making possible the elements, sensors, actuators &

    realization of complete System-on-a electronics on a Common silicon

    chip. MEMS is an enabling technology substrate through microfabrication

    allowing the development of smart technology. While the integrated circuit

    products, augmenting the computational (IC) process sequences (e.g., CMOS,

    ability of microelectronics with the Bipolar or BICMOS processes), the

    perception and control capabilities of micro mechanical components are

    microsensors and microactuators and fabricated using compatible

    expanding the space of possible designs “micromachining” processes that

    and applications. selectively etch away parts of the silicon

     Microelectronic integrated wafer or add new structural layers to

    circuits can be thought of as the “brains” form the mechanical and

    of a system and MEMS augments this electromechanical devices.

    decision making capability with eyes

    and arms to allow Microsystems to sense

    and control the environment. Sensors

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    gather information from the environment filtering, there by controlling the through measuring mechanical, thermal, environment for some desired outcome biological, chemical, optical and or purpose. Because MEMS devices are magnetic phenomena. The electronics manufactured using batch fabrication then process the information derived techniques similar to those used for from the sensors and through some integrated circuits unprecedented levels decision making capability direct the of functionality, reliability and actuators to respond by moving, sophistication can be placed on a small positioning, regulating, pumping and silicon chip at a relatively low cost.

    materials on a substrate, to apply a MEMS Processing

    patterned mask on the top of the films by Micro Electro Mechanical

    photolithographic imaging and to etch Systems Technology is based on a

    the films selectively to the mask. A number of tools and methodologies,

    MEMS process is usually a structured which are used to form small structures

    sequence of these operations to form with dimensions in micrometer scale

    actual devices. (one millionth of a meter). Significant

    1. Deposition process parts of the technology have been

    2. Lithography adopted from integrated circuit (IC)

    3. Etching process technology.

    Deposition Process Almost all devices are built of

    silicon which are realized in thin films of Ability to deposit thin films of materials and are patterned using materials is one of the basic building photolithographic methods like IC’s. blocks in MEMS process. Here we There are several processors that are not assume a thin film to have a thickness derived from IC technology and as the any where between a few nanometers technology continues the gap with IC about 100 micrometers. This film is technology also grows. locally etched using process described in

     There are three basic building lithography and etching sections. blocks in MEMS technology, which are MEMS deposition technology the ability to deposit thin films of can be classified into two groups.

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    1. Chemical Vapor Deposition 300 ?c). The PECVD deposit the

    (CVD) material on one side of the wafers on 1

    2. Physical Vapor Deposition (PVD) to 4 wafers at a time where as LPCVD

     systems deposit films on both sides of at

    least 25 wafers at a time. Chemical Vapor Deposition

    (CVD)

     This process exploits the creation of solid materials directly from chemical reactions in gas and/or liquid compositions or with substrate materials. The solid material is usually not the only product formed by the reaction.

    Byproducts can include gases, liquids

    and even other solids.

     In this process, the substrate is

    placed inside a reactor to which a

    number of gases are supplied. The Fig: typical hot-wall LPCVD reactor. principle is that a chemical reaction

    takes place between the source gases.

    The product of that reaction is a solid

    Electrodeposition material with condenses on all surface

     This process is also known as inside the reactor.

    “Electroplating” and is restricted to The two important CVD

    electrically conductive materials. There technologies in MEMS are Low Pressure

    are electroplating and electroless plating CVD (LPCVD) and Plasma Enhanced

    technologies. In the electro plating CVD (PECVD). The LPCVD process

    process the substrate is placed in a liquid produces layers with uniformly thickness

    solution (electrolyte). When an electrical and material characteristics, and the

    potential is applied between a problem is high deposition temperature

    conducting area on the substrate and a (>600 ?c) and also lower temperature (<

    counter electrode (usually platinum) in

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    In any process, the surface of the the liquid, a chemical redox process

    takes place resulting in the formation of substrate must have an electrically a layer of material on the substrate and conducting coating before the deposition usually some gas generation at the can be done.

    counter electrode. Epitaxy

     This technology is quite similar to

    that of CVD process. If the substrate is

    an ordered semiconductor crystal like

    silicon, gallium arsenide it is possible

    with this process to continue building on

    the substrate with the same

    crystallographic orientation with the

    substrate acting as a seed for the

    deposition.

     There are several technologies

    for creating the conditions inside a Fig: Typical setup for Electrodeposition.reactor needed to support epitaxial

     In the electroless plating process a growth of which the most important is more complex chemical solution is used, Vapor Phase Epitaxy (VPE).

    in which deposition happens In this process a number of gases are spontaneously on any surface which introduced in an induction heater reactor forms a sufficiently high electrochemical where only the substrate is heated. The potential with the solution. This process temperature of the substrate typically is desirable since it doesn’t require any must be atleast 50% of the melting point external electrical potential contact to of the material to be deposited. the substrate during processing.The advantage of this process is it allows

     The Electrodeposition process is the formation of films with considerable suited to make films (=1μm > 100μm) of thickness (>100μm). It is widely used metals such as copper, gold and nickel. for producing silicon on insulator (SOI) The deposition is best controlled when substrates and also for depositing silicon. used with an external electrical potential.

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    A schematic diagram of a typical vapor

    phase epitaxial reactor is shown in figure.

    Fig: Typical wafer oxidation furnace

    Fig: Typical cold-wall vapor phase

    epitaxial reactor It is typically used to form films

     This process can be used to that are used for electrical insulation. form films of silicon with thicknesses of Physical Vapor Deposition (PVD)

    (1μm to > 100μm). In this PVD there is no Thermal oxidation chemical reaction which forms the

     This is a basic deposition material on the substrate. This is not process. It is oxidation of the substrate completely correct for casting processors, surface an oxygen rich atmosphere. This though it is more convenient to think of is also the only deposition technology them that way.

    that consumes some of the substrate as it It covers deposition technologies proceeds. The growth of the film is in which material is released from source spurned by diffusion of oxygen in to the and transferred to the substrate. The two substrate. As the thickness of the most important technologies are oxidized layer increases the diffusion of evaporation and sputtering. PVD oxygen in to substrate becomes more comprises the standard technologies for difficult leading to a parabolic deposition of metals.

    relationship between film thickness and Evaporation

    oxidation time for films thicker than Here the substrate is placed 100nm. As it is a simple process it can inside a vacuum chamber in which a be used whenever we want. block of the material to be deposited is

     also located .the source material is then

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    heated to boiling point. The vacuum is Sputtering

    required to allow the molecules to It is a technology in which the evaporate freely in the chamber and then material is released from the source at condense on all surfaces. There are two much lower temperature than

    popular evaporation technologies which evaporation. The substrate is placed in are e-beam evaporation and resistive the vacuum chamber with the source evaporation. In e-beam evaporation an material named a target and an inert gas electron beam is aimed at the source (argon) is introduced at lower pressure. material causing local heating and Glass plasma is struck using an RF evaporation. In resistive evaporation a power source causing the gas to become tungsten boat containing the source ionized.

    material is heated electrically with a high The ions are accelerated towards current to make the material evaporate. the surface of the target causing atoms of A schematic diagram of a typical system the source material to break of from the for e-beam evaporation is shown in the target in vapor form and condense on all figure below. surfaces including the substrate. The

    differences typically relate to the manor

    in which the ion bombardment of the

    target is realized. A schematic diagram

    of a typical RF sputtering system is

    shown in the figure below.

    Fig: Typical system for e-beam

    evaporation of materials

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    Fig: Typical RF sputtering system Advantages of MEMS and Nano Casting Manufacturing

    In this process the material to be First MEMS and

    deposited is dissolved in liquid form is a Nanotechnology are extremely diverse solvent. The material can be applied to technologies that could significantly the substrate by spraying or spinning. affect every category of commercial and Once the solvent is evaporated a thin military products.

    film is evaporated a thin film of the MEMS and Nanotechnology are material remains on the substrate. This is already used for tasks ranging from in-particularly used for polymer materials dwelling blood pressure monitoring to which may be easily dissolved in organic active suspension system for solvents and is the common method used automobiles.

    to apply photoresist to substrates. The nature of MEMS and

     It is a simple technology Nanotechnology and its diversity of used for a variety of materials .some of useful applications make it potentially a the materials such as polyimide and far more pervasive technology than even spin-on-glass is applied on casting. integrated circuit microchips.

     MEMS and Nanotechnology

    allows complex electromechanical

    systems to be manufactured using batch

    fabrication techniques, decreasing cost

    and increasing the reliability of the

    sensors and actuators to equal those of

    integrated circuits. Even though the

    performance of MEMS and Nano

    devices is expected to be superior to

    macro scale components and systems, Fig: The spin casting process as used for the price is predicted to be much lower.

    photoresist in photolithography

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     High frequency circuits will MEMS and Nanotechnology

    benefit considerably from the advent of Applications

    the RF-MEMS technology. Electrical

    components such as inductors and There are numerous possible

    tunable capacitors can be improved applications for MEMS and

    significantly compared to their Nanotechnology. As a breakthrough

    integrated counterparts if they are made technology, allowing unparalleled

    using MEMS and Nanotechnology. With synergy between unrelated fields such as

    the integration of such components, the biology and microelectronics, many new

    performance of communication circuits MEMS and Nanotechnology

    will improve, while the total circuit area, applications will merge, expanding

    power consumption and cost will be beyond that which is currently identified

    reduced. In addition, the mechanical or known. Here are few applications of

    switch, as developed by several research current interest:

    groups, is a key component with huge ; Biotechnology

    potential in various microwave circuits. ; Communications

    The demonstrated samples of ; Accelerometer

    mechanical switches have quality factors 1) BIOTECHNOLOGY

    much higher than anything previously

     MEMS and Nanotechnology is

    available.

    enabling new discoveries in science and

     Reliability and packing of RF-

    engineering such as the Polymerase

    MEMS components seem to be the two Chain Reaction (PCR) Microsystems for

    critical issues that need to be solved

    DNA amplification and identification.

    before they receive wider acceptance by

     Micro machined Scanning

    the market.

    Tunneling Microscopes (STMs),

    3) ACCELEROMETERS biochips for detection of hazardous

     MEMS accelerometers are quickly chemical and biological agents and

    replacing conventional accelerometers Microsystems for high-throughput drug

    for crash air-bag deployment systems in screening and selection.

    automobiles. The conventional approach 2) COMMUNICATIONS

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    reliable and are produced for a fraction uses several bulky accelerometers made

    of discrete components mounted in the of the cost of the conventional macro

    front of the car with separate electronics scale accelerometer elements.

    near the air-bag (cost around $50).

    MEMS and Nanotechnology has made it

    possible to integrate the accelerometer

    and electronics onto a single silicon chip

     (at a cost between $5 to $10). These

     MEMS accelerometers are such smaller,

    more functional, lighter, and more

    Conclusion:

     Hence, MEMS revolutionize silicon based micro electronics with micro machining technology, making possible the realization of complete System-on-a chip.

    Micro Electro Mechanical Systems Technology is based on a number of tools and methodologies, which are used to form small structures with dimensions in micrometer scale (one millionth of a meter).

     MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of micro sensors and micro actuators and expanding the space of possible designs and applications.

     Microelectronic integrated circuits can be thought of as the “brains” of a system and MEMS augments this decision making capability with eyes and arms to allow Microsystems to sense and controls the environment

     In the present world, the technological revolution increasing at a rapid speed, hence the demand for manufacturing the goods to an improvised size at an effective performance is expected using the MEMS technology.

References:

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