seminar report
TRANSCRIPT
MEMS Technology
Visvesvarya Technological University, Belgaum
A Seminar Report On
MEMS TECHNOLOGY
Submitted in fulfillment for the award of
Bachelor of Engineering In
Electronics and Communication Engineering
Madhura S M (1BM07EC054)
Under the guidance ofMr Dinesh
Lecturer, Dept. of E&C,BMSCE
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MEMS Technology
CERTIFICATE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
B.M.S COLLEGE OF ENGINEERING
BANGALORE – 560019
This is to certify that the seminar entitled MEMS Technology has been carried out by Madhura S M bearing USN 1BM07EC054 submitted in the fulfillment for the award of Bachelor of Engineering degree prescribed by the Visvesvaraya Technological University, Belgaum during academic year 2011 .
Seminar Guide Signature Signature of HOD
DATE:
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Contents
Sl No Section/Topic Page No
1. Introduction/overview 4
2. MEMS Description 7
3. MEMS Design Process 8
4. MEMS Fabrication Technologies 17
5. Key applications 19
6. Advantages & comparisons 20
7. Current Challenges 21
8. Future Developments 22
9. Conclusion 23
10. Refrences 24
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ABSTRACT
The technology, Micro-Electro-Mechanical-Systems (MEMS), emerged in the
late1980s which enables us to fabricate mechanical parts on the order of microns.
Micromachining technology is suitable for developing new transducers or improving
existing transducer designs. Due to the dramatic reduction in size, micro transducers
can outperform traditional ones by orders of magnitude. Furthermore, MEMS is a
fundamental technology which has the potential to influence advancements in many
fields. In the automobile, electronics, bio-medical and television industries, MEMS
products have already made appreciable impacts.
SECTION 1 INTRODUCTION
Microelectromechanical systems (MEMS) are small integrated devices
or systems that combine electrical and mechanical components. They range in size
from the sub micrometer level to the millimeter level and there can be any number,
from a few to millions, in a particular system. MEMS extend the fabrication
techniques developed for the integrated circuit industry to add mechanical elements
such as beams, gears, diaphragms, and springs to devices.
Examples of MEMS device applications include inkjet-printer cartridges,
accelerometer, miniature robots, microengines, locks inertial sensors
microtransmissions, micromirrors, micro actuator (Mechanisms for activating process
control equipment by use of pneumatic, hydraulic, or electronic signals) optical
scanners, fluid pumps, transducer, pressure and flow sensors. New applications are
emerging as the existing technology is applied to the miniaturization and integration
of conventional devices.
These systems can sense, control, and activate mechanical processes on the micro
scale, and function individually or in arrays to generate effects on the macro scale.
The micro fabrication technology enables fabrication of large arrays of devices, which
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individually perform simple tasks, but in combination can accomplish complicated
functions.
SECTION 1.1 WHAT IS MEMS TECHNOLOGY?
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical
elements, sensors, actuators, and electronics on a common silicon substrate through
microfabrication technology. While the electronics are fabricated using integrated
circuit (IC) process sequences, the micromechanical components are fabricated using
compatible "micromachining" processes that selectively etch away parts of the silicon
wafer or add new structural layers to form the mechanical and electromechanical
devices.
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 control the environment. Sensors gather information from
the environment through measuring mechanical, thermal, biological, chemical,
optical, and magnetic phenomena. The electronics then process the information
derived from the sensors and through some decision making capability direct the
actuators to respond by moving, positioning, regulating, pumping, and filtering,
thereby controlling the environment for some desired outcome or purpose. Because
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.
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SECTION 1.2 WHAT ARE MEMS / MICROSYSTEMS?
As the smallest commercially produced "machines", MEMS devices are
similar to traditional sensors and actuators although much, much smaller. E.g.
Complete systems are typically a few millimeters across, with individual features
devices of the order of 1-100 micrometers across.
MEMS devices are manufactured either using processes based on Integrated Circuit
fabrication techniques and materials, or using new emerging fabrication technologies
such as micro injection molding. These former processes involve building the device
up layer by layer, involving several material depositions and etch steps. A typical
MEMS fabrication technology may have a 5 step process. Due to the limitations of
this "traditional IC" manufacturing process MEMS devices are substantially planar,
having very low aspect ratios (typically 5 -10 micro meters thick). It is important to
note that there are several evolving fabrication techniques that allow higher aspect
ratios such as deep x-ray lithography, electrodeposition, and micro injection molding.
MEMS devices are typically fabricated onto a substrate (chip) that may also contain
the electronics required to interact with the MEMS device. Due to the small size and
mass of the devices, MEMS components can be actuated electrostatically
(piezoelectric and bimetallic effects can also be used). The position of MEMS
components can also be sensed capacitively. Hence the MEMS electronics include
electrostatic drive power supplies, capacitance charge comparators, and signal
conditioning circuitry. Connection with the macroscopic world is via wire bonding
and encapsulation into familiar BGA, MCM, surface mount, or leaded IC packages.
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A common MEMS actuator is the "linear comb drive" (shown above) which consists
of rows of interlocking teeth; half of the teeth are attached to a fixed "beam", the other
half attach to a movable beam assembly. Both assemblies are electrically insulated.
By applying the same polarity voltage to both parts the resultant electrostatic force
repels the movable beam away from the fixed. Conversely, by applying opposite
polarity the parts are attracted. In this manner the comb drive can be moved "in" or
"out" and either DC or AC voltages can be applied. The small size of the parts (low
inertial mass) indicates that the drive has a very fast response time compared to its
macroscopic counterpart. The magnitude of electrostatic force is multiplied by the
voltage or more commonly the surface area and number of teeth. Commercial comb
drives have several thousand teeth, each tooth approximately 10 micro meters long.
Drive voltages are CMOS levels.
The linear push / pull motion of a comb drive can be converted into
rotational motion by coupling the drive to push rod and pinion on a wheel. In this
manner the comb drive can rotate the wheel in the same way a steam engine
functions!
SECTION 2 MEMS DESCRIPTION
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
The economies of scale, ready availability of cheap high-quality materials and ability
to incorporate electronic functionality make silicon attractive for a wide variety of
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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. The basic techniques for producing all silicon based
MEMS devices are deposition of material layers, patterning of these layers by
photolithography and then etching to produce the required shapes.
POLYMERS
Even though the electronics industry provides an economy of scale for the silicon
industry, crystalline 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.
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.
SECTION 3 MEMS DESIGN PROCESS
There are three basic building blocks in MEMS technology - Deposition Process-the
ability to deposit thin films of material on a substrate, Lithography-to apply a
patterned mask on top of the films by photolithograpic imaging, and Etching-to etch
the films selectively to the mask. A MEMS process is usually a structured sequence of
these operations to form actual devices.
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SECTION 3.1 DEPOSITION PROCESSES
One of the basic building blocks in MEMS processing is the ability to deposit thin
films of material. MEMS deposition technology can be classified in two groups:
1. Depositions that happen because of a chemical reaction:
o Chemical Vapor Deposition (CVD)
o Electrodeposition
o Epitaxy
o Thermal oxidation
2. Depositions that happen because of a physical reaction:
o Physical Vapor Deposition (PVD)
o Casting
CHEMICAL VAPOR DEPOSITION (CVD)
In this process, the substrate is placed inside a reactor to which a number of gases are supplied. The fundamental principle of the process is that a chemical reaction takes place between the source gases. The product of that reaction is a solid material with condenses on all surfaces inside the reactor. The two most important CVD technologies in MEMS are the Low Pressure CVD (LPCVD) and Plasma Enhanced CVD (PECVD). The LPCVD process produces layers with excellent uniformity of thickness and material characteristics. The main problems with the process are the
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high deposition temperature (higher than 600°C) and the relatively slow deposition rate. The PECVD process can operate at lower temperatures (down to 300° C) thanks to the extra energy supplied to the gas molecules by the plasma in the reactor. However, the quality of the films tends to be inferior to processes running at higher temperatures.
Figure 1: Typical hot-wall LPCVD reactor.
ELECTRODEPOSITION
This process is also known as "electroplating" and is typically restricted
to electrically conductive materials. There are basically two technologies for plating:
Electroplating and Electro-less plating. In the electroplating process the substrate is
placed in a liquid solution(electrolyte). When an electrical potential is applied
between a conducting area on the substrate and a counter electrode (usually platinum)
in the liquid, a chemical redox process takes place resulting in the formation of a layer
of material on the substrate and usually some gas generation at the counter electrode.
In the electro-less plating process a more complex chemical solution is
used, in which deposition happens spontaneously on any surface which forms a
sufficiently high electrochemical potential with the solution. This process is desirable
since it does not require any external electrical potential and contact to the substrate
during processing. Unfortunately, it is also more difficult to control with regards to
film thickness and uniformity. A schematic diagram of a typical setup for
electroplating is shown in the figure below.
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EPITAXY
This technology is quite similar to what happens in CVD processes,
however, if the substrate is an ordered semiconductor crystal (i.e. 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. If an amorphous/polycrystalline substrate surface is used, the film will
also be amorphous or polycrystalline.
There are several technologies for creating the conditions inside a
reactor needed to support epitaxial growth, of which the most important is Vapor
Phase Epitaxy (VPE). In this process, a number of gases are introduced in an
induction heated reactor where only the substrate is heated. The temperature of the
substrate typically must be at least 50% of the melting point of the material to be
deposited. A schematic diagram of a typical vapor phase epitaxial reactor is shown in
the figure below.
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Figure 3: Typical cold-wall vapor phase epitaxial reactor.
THERMAL OXIDATION
This is one of the most basic deposition technologies. It is simply
oxidation of the substrate surface in an oxygen rich atmosphere. The temperature is
raised to 800° C-1100° C to speed up the process. This is also the only deposition
technology which actually consumes some of the substrate as it proceeds. The growth
of the film is spurned by diffusion of oxygen into the substrate, which means the film
growth is actually downwards into the substrate. As the thickness of the oxidized
layer increases, the diffusion of oxygen to the substrate becomes more difficult
leading to a parabolic relationship between film thickness and oxidation time for films
thicker than ~100nm. This process is naturally limited to materials that can be
oxidized, and it can only form films that are oxides of that material. This is the
classical process used to form silicon dioxide on a silicon substrate. A schematic
diagram of a typical wafer oxidation furnace is shown in the figure below.
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PHYSICAL VAPOR DEPOSITION (PVD)
PVD covers a number of deposition technologies in which material is
released from a source and transferred to the substrate. The two most important
technologies are evaporation and sputtering.
CASTING
In this process the material to be deposited is dissolved in liquid form in
a solvent. The material can be applied to the substrate by spraying or spinning. Once
the solvent is evaporated, a thin film of the material remains on the substrate. This is
particularly useful for polymer materials, which may be easily dissolved in organic
solvents, and it is the common method used to apply photoresist to substrates (in
photolithography). The thicknesses that can be cast on a substrate range all the way
from a single monolayer of molecules (adhesion promotion) to tens of micrometers.
SECTION 3.2 LITHOGRAPHY
PATTERN TRANSFER
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 differ (as shown in figure below).
Figure : Transfer of a pattern to a photosensitive material.
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THE LITHOGRAPHY MODULE
Typically lithography is performed as part of a well-characterized
module, which includes the wafer surface preparation, photoresist deposition,
alignment of the mask and wafer, exposure, develop and appropriate resist
conditioning. The lithography process steps need to be characterized as a sequence in
order to ensure that the remaining resist at the end of the modules is an optimal image
of the mask, and has the desired sidewall profile. A brief explanation of the standard
process steps included in a lithography module is (in sequence):
Dehydration bake - dehydrate the wafer to aid resist adhesion.
HMDS prime - coating of wafer surface with adhesion promoter.
Resist spin/spray - coating of the wafer with resist either by spinning or spraying.
Typically desire a uniform coat.
Soft bake - drive off some of the solvent in the resist, may result in a significant loss
of mass of resist (and thickness). Makes resist more viscous.
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Alignment - align pattern on mask to features on wafers.
Exposure - projection of mask image on resist causing selective chemical property
change.
Post exposure bake - baking of resist to drive off further solvent content.
Develop - selective removal of resist after exposure. Usually a wet process.
Hard bake - drive off most of the remaining solvent from the resist.
Descum - removal of thin layer of resist scum that may occlude open regions in
pattern helps to open up corners.
SECTION 3.3 ETCHING PROCESSES
In order to form a functional MEMS structure on a substrate, it is necessary to etch the thin
films previously deposited and/or the substrate itself. In general, there are two classes of
etching processes:
1. Wet etching where the material is dissolved when immersed in a chemical solution
2. Dry etching where the material is sputtered or dissolved using reactive ions or a vapor
phase etching.
WET ETCHING
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 etches 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 a isotropic etchant. The principle of anisotropic and isotropic wet etching is
illustrated in the figure below.
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DRY ETCHING
The dry etching technology can split in three separate classes called
reactive ion etching (RIE), sputter etching, and vapor phase etching.
In RIE, the substrate is placed inside a reactor in which several gases are
introduced. Plasma is struck in the gas mixture using an RF power source, breaking
the gas molecules into ions. The ion is 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
very complex tasks 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.
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Sputter etching is essentially RIE without reactive ions. The systems
used are very similar in principle to sputtering deposition systems. The big difference
is that substrate is now subjected to the ion bombardment instead of the material
target used in sputter deposition.
Vapor phase etching is another dry etching method, which can be done
with simpler equipment than what RIE requires. In this process the wafer to be etched
is placed inside a chamber, in which one or more gases are introduced. The material
to be etched is dissolved at the surface in a chemical reaction with the gas molecules.
The two most common vapor phase etching technologies are silicon dioxide etching
using hydrogen fluoride (HF) and silicon etching using xenon diflouride (XeF2), both
of which are isotropic in nature. Usually, care must be taken in the design of a vapor
phase process to not have bi-products form in the chemical reaction that condense on
the surface and interfere with the etching process.
SECTION 4 FABRICATION TECHNOLOGIES
The three characteristic features of MEMS fabrication technologies are
miniaturization, multiplicity, and microelectronics. Miniaturization enables the
production of compact, quick-response devices. Multiplicity refers to the batch
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fabrication inherent in semiconductor processing, which allows thousands or millions
of components to be easily and concurrently fabricated. Microelectronics provides the
intelligence to MEMS and allows the monolithic merger of sensors, actuators, and
logic to build closed-loop feedback components and systems. The successful
miniaturization and multiplicity of traditional electronics systems would not have
been possible without IC fabrication technology. Therefore, IC fabrication
technology, or microfabrication, has so far been the primary enabling technology for
the development of MEMS. Microfabrication provides a powerful tool for batch
processing and miniaturization of mechanical systems into a dimensional domain not
accessible by conventional techniques. Furthermore, microfabrication provides an
opportunity for integration of mechanical systems with electronics to develop high-
performance closed-loop-controlled MEMS.
SECTION 4.1 IC FABRICATION
Any discussion of MEMS requires a basic understanding of IC
fabrication technology, or microfabrication, the primary enabling technology for the
development of MEMS. The major steps in IC fabrication technology are:
Film growth: Usually, a polished Si wafer is used as the substrate, on which a
thin film is grown. The film, which may be epitaxial Si, SiO2, silicon nitride
(Si3N4), polycrystalline Si, or metal, is used to build both active or passive
components and interconnections between circuits.
Doping: To modulate the properties of the device layer, a low and controllable
level of an atomic impurity may be introduced into the layer by thermal
diffusion or ion implantation.
Lithography: A pattern on a mask is then transferred to the film by means of a
photosensitive (i.e., light sensitive) chemical known as a photoresist. The
process of pattern generation and transfer is called photolithography. A typical
mask consists of a glass plate coated with a patterned chromium (Cr) film.
Etching: Next is the selective removal of unwanted regions of a film or
substrate for pattern delineation. Wet chemical etching or dry etching may be
used. Etch-mask materials are used at various stages in the removal process to
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selectively prevent those portions of the material from being etched. These
materials include SiO2, Si3N4, and hard-baked photoresist.
Dicing: The finished wafer is sawed or machined into small squares, or dice,
from which electronic components can be made.
Packaging: The individual sections are then packaged, a process that involves
physically locating, connecting, and protecting a device or component. MEMS
design is strongly coupled to the packaging requirements, which in turn are
dictated by the application environment.
SECTION 4.2 BULK MICROMACHINING AND WAFER BONDING
Bulk micromachining is an extension of IC technology for the
fabrication of 3D structures. Bulk micromachining of Si uses wet- and dry-etching
techniques in conjunction with etch masks and etch stops to sculpt micromechanical
devices from the Si substrate. The two key capabilities that make bulk
micromachining a viable technology are:
Anisotropic etchants of Si, such as ethylene-diamine and pyrocatechol (EDP),
potassium hydroxide (KOH), and hydrazine (N2H4). These preferentially etch
single crystal Si along given crystal planes.
Etch masks and etch-stop techniques that can be used with Si anisotropic
etchants to selectively prevent regions of Si from being etched. Good etch
masks are provided by SiO2 and Si3N4, and some metallic thin films such as Cr
and Au (gold).
SECTION 4.3 SURFACE MICROMACHINING
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Surface micromachining enables the fabrication of complex
multicomponent integrated micromechanical structures that would not be possible
with traditional bulk micromachining. This technique encases specific structural parts
of a device in layers of a sacrificial material during the fabrication process. The
substrate wafer is used primarily as a mechanical support on which multiple
alternating layers of structural and sacrificial material are deposited and patterned to
realize micromechanical structures. The sacrificial material is then dissolved in a
chemical etchant that does not attack the structural parts. The most widely used
surface micromachining technique, polysilicon surface micromachining, uses SiO2 as
the sacrificial material and polysilicon as the structural material.
SECTION 5 APPLICATIONS
PRESSURE SENSORS
MEMS pressure microsensors typically have a flexible diaphragm that
deforms in the presence of a pressure difference. The deformation is converted to an
electrical signal appearing at the sensor output. A pressure sensor can be used to sense
the absolute air pressure within the intake manifold of an automobile engine, so that
the amount of fuel required for each engine cylinder can be computed.
ACCELEROMETERS
Accelerometers are acceleration sensors. An inertial mass suspended by
springs is acted upon by acceleration forces that cause the mass to be deflected from
its initial position. This deflection is converted to an electrical signal, which appears
at the sensor output. The application of MEMS technology to accelerometers is a
relatively new development.
Accelerometers are used in consumer electronics devices such as game
controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone ) and
a number of Digital Cameras. They are also used in PCs to park the hard disk head
when free-fall is detected, to prevent damage and data loss.
MICROENGINES
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A three-level polysilicon micromachining process has enabled the
fabrication of devices with increased degrees of complexity. The process includes
three movable levels of polysilicon, each separated by a sacrificial oxide layer, plus a
stationary level. Microengines can be used to drive the wheels of microcombination
locks. They can also be used in combination with a microtransmission to drive a pop-
up mirror out of a plane. This device is known as a micromirror.
SOME OTHER COMMERCIAL APPLICATIONS INCLUDE:
Inkjet printers, which use piezoelectrics or thermal bubble ejection to deposit ink on
paper.
Accelerometers in modern cars for a large number of purposes including 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.
Silicon 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 and alignment
for data communications.
Bio-MEMS applications in medical and health related technologies from Lab-On-
Chip to MicroTotalAnalysis (biosensor, chemosensor).
SECTION 6 ADVANTAGES OF MEMS
Minimize energy and materials use in manufacturing
Cost/performance advantages
Improved reproducibility
Improved accuracy and reliability
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Increased selectivity and sensitivity
Low interference with environment
COMPARISON
CONVENTIONAL MEMS – BASED
Bulky Miniaturised
High power consumption Low power consumption
Mechanical wear and tear Less moving parts
Highly accurate Lower accuracy
Expensive Low cost
SECTION 7 CURRENT CHALLENGES
MEMS and Nanotechnology is currently used in low- or medium-
volume applications. Some of the obstacles preventing its wider adoption are:
LIMITED OPTIONS
Most companies who wish to explore the potential of MEMS and
Nanotechnology have very limited options for prototyping or manufacturing devices,
and have no capability or expertise in microfabrication technology. Few companies
will build their own fabrication facilities because of the high cost. A mechanism
giving smaller organizations responsive and affordable access to MEMS and Nano
fabrication is essential.
PACKAGING
The packaging of MEMS devices and systems needs to improve
considerably from its current primitive state. MEMS packaging is more challenging
than IC packaging due to the diversity of MEMS devices and the requirement that
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many of these devices be in contact with their environment. Currently almost all
MEMS and Nano development efforts must develop a new and specialized package
for each new device. Most companies find that packaging is the single most expensive
and time consuming task in their overall product development program. As for the
components themselves, numerical modeling and simulation tools for MEMS
packaging are virtually non-existent. Approaches which allow designers to select
from a catalog of existing standardized packages for a new MEMS device without
compromising performance would be beneficial.
FABRICATION KNOWLEDGE REQUIRED
Currently the designer of a MEMS device requires a high level of
fabrication knowledge in order to create a successful design. Often the development
of even the most mundane MEMS device requires a dedicated research effort to find a
suitable process sequence for fabricating it. MEMS device design needs to be
separated from the complexities of the process sequence.
SECTION 8 FUTURE DEVELOPMENTS
Each of the three basic microsystems technology processes we have
seen, bulk micromachining, sacrificial surface micromachining, and
micromolding/LIGA, employs a different set of capital and intellectual resources.
MEMS manufacturing firms must choose which specific microsystems manufacturing
techniques to invest in.
MEMS technology has the potential to change our daily lives as much as
the computer has. However, the material needs of the MEMS field are at a
preliminary stage. A thorough understanding of the properties of existing MEMS
materials is just as important as the development of new MEMS materials.
Future MEMS applications will be driven by processes enabling greater
functionality through higher levels of electronic-mechanical integration and greater
numbers of mechanical components working alone or together to enable a complex
action. Future MEMS products will demand higher levels of electrical-mechanical
integration and more intimate interaction with the physical world. The high up-front
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investment costs for large-volume commercialization of MEMS will likely limit the
initial involvement to larger companies in the IC industry. Advancing from their
success as sensors, MEMS products will be embedded in larger non-MEMS systems,
such as printers, automobiles, and biomedical diagnostic equipment, and will enable
new and improved systems.
SECTION 9 CONCLUSION
The automotive industry, motivated by the need for more efficient safety
systems and the desire for enhanced performance, is the largest consumer of MEMS-
based technology. In addition to accelerometers and gyroscopes, micro-sized tire
pressure systems are now standard issues in new vehicles, putting MEMS pressure
sensors in high demand. Such micro-sized pressure sensors can be used by physicians
and surgeons in a telemetry system to measure blood pressure, allowing early
detection of hypertension and restenosis. Alternatively, the detection of bio molecules
can benefit most from MEMS-based biosensors. Medical applications include the
detection of DNA sequences and metabolites. MEMS biosensors can also monitor
several chemicals simultaneously, making them perfect for detecting toxins in the
environment.
Lastly, the dynamic range of MEMS based silicon ultrasonic sensors have many
advantages over existing piezoelectric sensors in non-destructive evaluation,
proximity sensing and gas flow measurement. Silicon ultrasonic sensors are also very
effective immersion sensors and provide improved performance in the areas of
medical imaging and liquid level detection.
The medical, wireless technology, biotechnology, computer, automotive and
aerospace industries are only a few that will benefit greatly from MEMS.
This enabling technology allowing the development of smart products,
augmenting the computational ability of microelectronics with the perception
and control capabilities of microsensors and microactuators and expanding the
space of possible designs and applications.
MEMS devices are manufactured for unprecedented levels of functionality,
reliability, and sophistication can be placed on a small silicon chip at a
relatively low cost.
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MEMS promises to revolutionize nearly every product category by bringing
together silicon-based microelectronics with micromachining technology,
making possible the realization of complete systems-on-a-chip.
MEMS will be the indispensable factor for advancing technology in the 21st
century and it promises to create entirely new categories of products.
SECTION 10 REFERENCES
Online Resources
IEEE Explore http://ieeexpl ore.ieee.org/Xplore/DynWel.jsp
Introduction to Microengineering http://www.dbanks.demon.co.uk/ueng/
MEMS Clearinghouse http://www.memsnet.org/
Journals
Journal of Microelectromechanical Systems (JMEMS)
MEMS : Introduction and Fundamentals ( Mohammed Gad-el-Hak)
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