This document discusses MEMS (Micro Electro Mechanical Systems) technology. It begins by explaining that MEMS combines microelectronics and micromachining to create miniaturized systems on a chip. It then discusses some key fabrication techniques for MEMS like surface micromachining, bulk micromachining, and LIGA. Applications of MEMS discussed include communications, biotechnology, inertial sensors like accelerometers and gyroscopes, RF switches, and uses in consumer and industrial markets. Challenges for the future of MEMS include limited access to foundries for fabrication, challenges with design/simulation/modeling, and challenges with packaging and testing MEMS devices.

1. 1
21ST CENTURY’S REVOLUTION :MEMS
TECHNOLOGY
Kaneria Dhaval1, Ekata Mehul2
1
Pursuing M.Tech., Embedded System, U.V.Patel college of Engineering and Technology, Kherva, Mehsana, India
kaneriadhaval14@gmail.com,
2
Head eiTRA - eInfochips Training and Research Academy, Ahmedabad
ekata.mehul@eitra.org
Abstract— We are grateful in a revolution of microelectronics,
which has dramatically reduced the cost and increased the
capability of electronics. This has given much potential to
prosper in the area of micro mechanics encompassing MEMS
(Micro Electro Mechanical Systems). MEMS promises to
revolutionize nearly every product category by bringing
together silicon based microelectronics with micro machining
technology, making possible the realization of complete
systems on a chip. often referred to as micro systems
technology, are fabricated using modified silicon and nonsilicon fabrication technology. It reduces cost and increases
reliability of the system. MEMS is a process technology used
to create tiny integrated devices or systems that combine
mechanical and electrical componentsMEMS has been
identified as one of the most promising technologies for the
21st Century and has the potential to revolutionize both
industrial and consumer products by combining silicon based
microelectronics with micromachining technology. Its
techniques and microsystem based devices have the potential
to dramatically effect of all of our lives and the way we live.
If semiconductor micro fabrication was seen to be the first
micro manufacturing revolution, MEMS is the second
revolution.
IndexTerms—Technology,Febrication,Packeging,
Application in various field,future scope,revolution
reliability). Furthermore, it is clear that current MEMS
products are simply precursors to greater and more
pervasive applications to come, including genetic and
disease testing, guidance and navigation systems, power
generation, RF devices( especially for cell phone
technology), weapon systems, biological and chemical
agent detection, and data storage. Micro mirror based
optical switches have already proven their value; several
start-up companies specializing in their development have
already been sold to large network companies for hundreds
of millions of dollars. The promise of MEMS is
increasingly capturing the attention of new and old
industrises alike, as more and more of their challenges are
solved with MEMS.
After extensive development, todays commercial
MEMS – also known as Micro System Technologies
(MST), Micro Machines (MM) have proven to be more
manufacturable, reliable and accurate, dollar for dollar,
than their conventional counterparts. However the
technical hurdles to attain these accomplishments were
often costly and time- consuming, and current advances in
this technology introduce newer challenges still. Because
this field is till in its infancy, very little data on design,
manufacturing processes or liability are common or
shared.
II. FEBRICATION
I. INTRODUCTION
Micro electromechanical systems (MEMS) is a
technology of miniaturization that has been largely
adopted from the integrated circuit (IC) industry and
applied to the miniaturization of all systems not only
electrical systems but also mechanical, optical, fluid,
magnetic, etc.
Micro Electromechanical systems or MEMS,
represent an extraordinary technology that promises to
transform whole industries and drive the next
technological revolution. These devices can replace bulky
actuators and sensors with micron-scale equivalent that
can be produced in large quantities by fabrication
processes used in integrated circuits photolithography.
This reduces cost, bulk, weight and power consumption
while increasing performance, production volume, and
functionality by orders of magnitude. For example, one
well known MEMS device is the accelerometer (its now
being manufactured using mems low cost, small size, more
MEMS devices are fabricated using a number of
materials, depending on the application requirements. One
popular material is polycrystalline silicon, also called
“polysilicon” or “poly”. This material is sculpted with
techniques such as bulk or surface micro- machining, and
Deep Reactive Ion Etching (DRIE), proving to be fairly
durable for many mechanical operations. Another is
nickel, which can be shaped by PMMA (a form of
plexiglass) mask platng (LIGA), as well as by
conventional photolithographic techniques. Other
materials – such as diamond, aluminum, silicon carbide
and gallium arsenide – are currently being evaluated for
use in micro machines for their desirable properties; e.g.,
the hardness of diamond and silicon carbide. To create
moveable parts, several layers are needed for structural and
electrical interconnect (ground plane) purposes, with socalled “sacrificial” oxide layers in between. The current
manufacturing record is five layers, making possible a
variety of complex mechanical systems. These

2. 2
capabilities, developed over the last several years, are
beginning to unlock the almost unlimited possibilities of
MEMS applications.
The methods used to integrate multiple patterned
materials together to fabricate a completed MEMS device
are just as important as the individual processes and
materials themselves. Depending on the type of material
used fabrication techniques are classified as:
A. Silicon Micro fabrication:
The two most general methods of MEMS integration are:
Surface micro machining ,Bulk micro machining
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).
1.
Surface Micromachining
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.
Figure 2 Process flow of bulk micromachining
B. Non-Silicon Micro fabrication:
Figure 1 Process flow of surface micromachining
 Advantages of surface micro machining
a) Structures, especially thicknesses, can be smaller than
10 µm in size,
b) The micro machined device footprint can often be much
smaller than bulk wet-etched devices,
c)It is easier to integrate electronics below surface microstructures, and
d)Surface microstructures generally have superior
tolerance compared to bulk wet-etched devices.
The primary disadvantage is the fragility of surface
microstructures to handling, particulates and condensation
during manufacturing. Surface Micro machining is being
used in commercial products such as accelerometers to
trigger air bags in automobiles.
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 development of MEMS has contributed significantly
to the improvement of non-silicon micro fabrication
techniques. Two prominent examples are LIGA and plastic
molding from micro machined substrates.
1.
LIGA
LIGA is a German acronym standing for
lithographie, galvanoformung (plating), and abformung
(molding). However, in practice LIGA essentially stands
for a process that combines extremely thick-film resists
(often >1 mm) and x-ray lithography, which can pattern
thick resists with high fidelity and results in vertical
sidewalls. Although some applications may require only
the tall patterned resist structures themselves, other
applications benefit from using the thick resist structures
as plating molds (i.e., material can be quickly deposited
into the mold by electroplating). A drawback to LIGA is
the need for high-energy x-ray sources that are very
expensive and rare.

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IV. PACKAGING
Figure 3 Process flow of LIGA
The LIGA process exposes PMMA (poly methyl metha
crylate) plastic with synchrotron radiation through a
mask. This is shown at the top of the Figure 1. Exposed
PMMA is then washed away, leaving vertical wall
structures with spectacular accuracy. Structures a third of
a millimeter high and many millimeters on a side are
accurate to a few tenths of a micron. Metal is then plated
into the structure, replacing the PMMA that was washed
away. This metal piece can become the final part, or can
be used as an injection mold for parts made out of a variety
of plastics.
As with micromachining processes, many MEMS
sensor-packaging techniques are the same as, or derived
from, those used in the semiconductor industry. However,
the mechanical requirements for a sensor package are
typically much more stringent than for purely
microelectronic devices. Microelectronic packages are
often generic with plastic, ceramic, or metal packages
being suitable for the vast majority of IC applications. For
example, small stresses and strains transmitted to a
microelectronics die will be tolerable as long as they stay
within acceptable limits and do not affect reliability. In the
case of a MEMS physical sensor, however, such stresses
and strains and other undesirable influences must be
carefully controlled in order for the device to function
correctly. Failure to do so, even when employing
electronic compensation techniques, will reduce both the
sensor performance and long-term stability.
Standard IC Packages
 Ceramic Packages
 Plastic Packages
 Metal Packages
III. MEMS DESIGN PROCESS
There are three basic building blocks in MEMS
technology, which are,Deposition Process-the ability to
deposit thin films of material on a substrate, Lithographyto apply a patterned mask on top of the films by
photolithograpic imaging. Etching-to etch the films
selectively to the mask. A MEMS process is usually a
structured sequence of these operations to form actual
devices.
Figure 5 Standard IC packeges
A. MEMS Mechanical Sensor Packaging
A MEMS sensor packaging must meet several
requirements :
•
Protect the sensor from external influences and
environmental effects. Since MEMS inherently include
some microscale mechanical components, the integrity of
the device must be protected against physical damage
arising from mechanical shocks, vibrations, temperature
cycling, and particle contamination. The electrical aspects
of the device, such as the bond wires and the electrical
properties of the interconnects, must also be protected
against these external influences and environmental effects
•
Protect the environment from the presence of the
sensor. In addition protecting the sensor, the package must
prevent the presence of the MEMS from reacting with or
contaminating potentially sensitive environments. The
Figure 4 MEMS design flow starting to end

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classic examples of this are medical devices that contain
packaged sensors that can be implanted or used within the
body; these must be biocompatible, nontoxic, and able to
withstand sterilization.
•
Provide a controlled electrical, thermal,
mechanical, and/or optical interface between the sensor, its
associated components, and its environment. Not only
must the package protect both the sensor and its
environment, it must also provide a reliable and repeatable
interface for all the coupling requirements of a particular
application. In the case of mechanical sensors, the
interface is of fundamental importance since, by its nature,
specific mechanical coupling is essential but unwanted
effects must be prevented. A simple example would be a
pressure sensor where the device must be coupled in some
manner to the pressure but isolated from, for example,
thermally induced strains. The package must also provide
reliable heat transfer to enable any heat generated to be
transmitted away from the MEMS device to its
environment.
V.APPLICATIONS OF MEMS
A.Communications:
High frequency circuits will benefit considerably
from advent of the RF-MEMS technology. Electrical
components such as inductors and tunable capacitors can
be improved significantly compared to their integrated
counter parts if they are made using MEMS technology. If
the integration of such components, the performance of
communication circuits will improve, while the total
circuit area, power consumption and cost will be reduced.
In addition, the mechanical switch, as developed by
several research groups, is a key component with huge
potential in various micro wave circuits
B. Biotechnology:
MEMS enabling new discoveries in science and
engineering such as the polymerase chain Reaction (PCR)
Microsystems for DNA amplification and identification,
micro machined scanning Tunneling microscopes (STMs),
Biochips for detection of hazardous chemical and
biological agents, and Microsystems for high-throughput
drug screening and selection.
C. Inertial sensors:
Inertial sensors are mechanics sensors aiming at
measuring accelerations, in the mechanics science
definition. There are two categories of inertial sensors.
They are, accelerometers which measures variation of
rotational speed and gyroscopes which measures variation
of rotational speed.
D. Accelerometers:
Figure 6 Capacitive accelerometer’s working diagram(reference from
www.sensorsmag.com)
Figure 7 Schematic of micro accelerometer, ADXLseries, produced by
Analog Device.
Figure 8 Schematic of micro accelerometer with closerview
On these diagrams, we can see a micro accelerometer
device and the chip including associated electronics, made
by Analog Device. This is a two axis micro accelerometer.
This means it is able to measure accelerations in two
directions at a time (in the directions of the plane).
Micro accelerometers were the first MEMS
device to flood the market. Micro accelerometers measure
variation of translational speed. So acceleration,
deceleration, even very high deceleration, like…shock!
The sensor that detects a shock and launches the airbag is
a micro accelerometer combined with a electronic circuit
able to decide wether or not the shock was an accident or
just your car passing a pothole. There are lots of
applications, like navigation, micro accelerometers can
help in increasing precision. There are more and more to
say about micro accelerometers, they are still the
spearhead of MEMS industry.
E. Gyroscopes:
Micro gyroscopes are newer in the market
compared to micro accelerometers. Some devices have
appeared on the market for navigation application. The key
point in these devices is sensitivity.
F. RF switches:
RF switches have been under development for
years, but the commercial applications just begin to
appear. The reason is the difficulty to combine high
efficiency, reproducibility and reliability. RF switches will
be preferred to full electronic switches on applications
where security, integration capabilities, power
consumption and other parameters are critical.
G. Consumer Market:

5. 5
Sports
Training
Devices,omputer
Peripherals,
Car and Personal Navigation Devices,Active Subwoofers
etc
H. Industrial Market:
Earthquake Detection and Gas Shutoff,Machine
Health, Shock and Tilt Sensing etc.
I. Military:
Tanks,Planes,Equipment for Soldier etc.
Table I. Application of MEMS in various fields
VI. THE FUTURE OF MEMS TECHNOLOGY
A. Industry Challenges
Some of the major challenges facing the MEMS
industry include:
1. Access to Foundries.
MEMS companies today have very limited access
to MEMS fabrication facilities, or foundries, for prototype
and device manufacture. In addition, the majority of the
organizations expected to benefit from this technology
currently do not have the required capabilities and
competencies to support MEMS fabrication. For example,
telecommunication companies do not currently maintain
micromachining facilities for the fabrication of optical
switches. Affordable and receptive access to MEMS
fabrication facilities is crucial for the commercialization of
MEMS.
2. Design, Simulation and Modelling.
Due to the highly integrated and interdisciplinary
nature of MEMS, it is difficult to separate device design
from the complexities of fabrication. Consequently, a high
level of manufacturing and fabrication knowledge is
necessary to design a MEMS device. Furthermore,
considerable time and expense is spent during this
development and subsequent prototype stage. In order to
increase innovation and creativity, and reduce unnecessary
‘time-to-market’ costs, an interface should be created to
separate design and fabrication. As successful device
development also necessitates modelling and simulation, it
is important that MEMS designers have access to adequate
analytical tools.
3. Packaging and Testing.
The packaging and testing of devices is probably
the greatest challenge facing the MEMS industry. As
previously described, MEMS packaging presents unique
problems compared to traditional IC packaging in that a
MEMS package typically must provide protection from an
operating environment as well as enable access to it.
Currently, there is no generic MEMS packaging solution,
with each device requiring a specialized format.
Consequently, packaging is the most expensive fabrication
step and often makes up 90% (or more) of the final cost of
a MEMS device.
4. Standardization.
Due to the relatively low number of commercial
MEMS devices and the pace at which the current
technology is developing, standardization has been very
difficult. To date, high quality control and basic forms of
standardization are generally only found at multi-million
dollar (or billion dollar) investment facilities. However, in
2000, progress in industry communication and knowledge
sharing was made through the formation of a MEMS trade
organization. Based in Pittsburgh, USA, the MEMS
industry group (MEMS-IG) with founding members
including Xerox, Corning, Honeywell, Intel and JDS
Uniphase, grew out of study teams sponsored by DARPA
that identified a need for technology road mapping and a
source for objective statistics about the MEMS industry. In
addition, a MEMS industry roadmap, sponsored by the
Semiconductor Equipment and Materials International
organization (SEMI)
5. Education and Training.
The complexity and interdisciplinary nature of
MEMS require educated and well-trained scientists and
engineers from a diversity of fields and backgrounds. The
current numbers of qualified MEMS-specific personnel is
relatively small and certainly lower than present industry
demand. Education at graduate level is usually necessary
and although the number of universities offering MEMSbased degrees is increasing, gaining knowledge is an
expensive and time-consuming process. Therefore, in
order to match the projected need for these MEMS
scientists and engineers, an efficient and lower cost
VII. CONCLUSIONS
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-achip.Future Work.
MEMS will be the indispensable factor for
advancing technology in the 21st century and it promises
to create entirely new categories of products.
The automotive industry, motivated by the need
for more efficient safety systems and the desire for
enhanced performance, is the largest consumer of MEMSbased technology. In addition to accelerometers and

6. 6
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 at a stet, allowing early
detection of hypertension and restenosis. Alternatively, the
detection of bio molecules can benefit most from MEMSbased 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.
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