[Reddy, 2(9): September, 2013] ISSN: 2277-9655

Impact Factor: 1.852

IJESRT
INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH
TECHNOLOGY
Study on MEMS Fabrication Techniques and Applications
S. Madhava Reddy*1 and A. Anudeep Kumar2
*1
Associate Professor, Dept. of Mechanical Engineering, Mahatma Gandhi Institute of Technology,
Hyderabad., India
2
M.Tech(Mechatronics), Dept. of Mechanical Engineering, Mahatma Gandhi Institute of Technology,
Hyderabad., India
smrmech@gmail.com
Abstract
MEMS is the acronym for Micro Electro Mechanical Systems. Micromachining has potential applications
for large area image sensors and displays, but conventional MEMS technology, based on crystalline silicon wafers
cannot be used. Instead, large area devices use deposited films on glass substrates. This presents many challenges
for MEMS, both as regards materials for micro-machined structures and the integration with large area electronic
devices. A new single crystal silicon Micro Electro Mechanical Systems (MEMS) fabrication process is proposed
using proton-implantation smart-cut technique. Compared to conventional silicon on insulator (SOI) wafer
fabrication processes for MEMS applications. The fabrication of free-standing high-carbon microstructures by soft
lithographic techniques; these structures ranged in complexity from simple beams to complex, suspended deflectors.
MEMS products are highly used in various fields like telecommunications, communications satellites, automotive,
healthcare, in electronic devices and in many general applications.

Keywords: MEMS, Micromachining, Lithography, MOEMS, Nanotechnology.

Introduction
MEMS is the acronym for Micro Electrical It defines mechanical structures fabricated with
Mechanical Systems.The beginning of MEMS IC processing on (most often) silicon wafers.It is a highly
technology dates back to the discovery of miniaturized device or an array of devices combining
semiconductors at Bell Laboratories in the early1950s. electrical and mechanical components that is fabricated
Many consider their 1954 paper, announcing the using integrated circuit (IC) batch processing techniques
discovery of piezoresistive effect in silicon and and can range in size from micrometers to millimetres
germanium, as the birth date of MEMS. A related (1mm=1000m)
acronym MOEMS stands for Micro OptoElectro Micro-Electro-Mechanical Systems (MEMS) is
Mechanical Systems and defines a subset of MEMS, that the integration of a number of microcomponents on a
is, devices performing optical functions. single chip which allows themicrosystem to both sense
In Europe, MEMS is labeled Microsystems and control the environment.
Technology (MST) and in Japan it is labelled The components typically include microelectronic integr
Micromachines. The term MEMS evolved in the United ated circuits (the “brains”), sensors (the “senses” and
States in the 1990s. Prior to that period the technology “nervous system”), and actuators (the “hands” and
was labelled silicon micromachining. Micro Electro “arms”). MEMS defines the Technology; not specific
Mechanical Systems, the tiny mechanical devices that products.This technology encompasses a collection of a
are built variety of processes enabling three-dimensional shaping
onto semiconductorchips and are measured in of wafers or stacks of wafers. While most of the
micrometers. In the research labs since the 1980s, applications use silicon wafers, many other materials
MEMS devices began to materialize as commercial have been used, including glass and quartz wafers.
products in the mid-1990s. They are used to make As a result of batch manufacturing
pressure, temperature, chemical and vibration sensors, technology (using multiple devices photolithographically
light reflectors and switches, as well as accelerometers defined on a wafer), the cost of the single device depends
for vehicle airbags, smartphones, tablets and on its size; wafer processing cost is fixed for a given
games. process. The cost difference between a 1 × 1mm device
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and a 10 × 10mm device is 100 times, as the first device to accept CAD files as input, turning customer designs
would yield about 16000devices on a 6-in diameter into micromachines much faster than traditional methods
wafer, and the larger devicewould yield only about 160 as shown in fig.2. EFAB Microfabrica's EFAB system
devices on the same wafer. was the first MEMS foundry process builds the devices
one metal layer at a time. In this image, the square at the
MEMS and MOEMS top is a microfluidics device with internal passageways
When optical components are included in used for a "lab on a chip." The multi-arm device (center)
a MEMS device, it is called a micro-opto-electro is a fuel injection nozzle. Bottom left is an
mechanical system (MOEMS). For example, adding a accelerometer,and bottom right is an inductor used in RF
photonic sensor to a silicon chip constitutes a MOEMS circuits.
device. Seemicromachine, MEMS mirror, DLP and
optical switch.
MEMS Vs. Nanotechnology:
Sometimes MEMS and nanotechnology are
terms that are used interchangeably, because they both
deal with microminiaturized objects. However, they are
vastly different. MEMS deals with creating devices that
are measured in micrometers, whereas nano technology
deals with manipulating atoms at the nano meter level.

Fig. 3 MEMS-Based Accelerometer

MEMSIC's dual-axis thermal accelerator is

a MEMS based semiconductor device that like air bubble
in work conceptually a construction level as shown in
fig.3. The square in the middle of the chip is a resistor
that heats up a gas bubble. The next larger squares
contain thermal couples that sense the location of the
Fig.1 MEMS-based Optical Switch heated bubble as the device is tilted or accelerated.
In an all-optical switch,(Fig.1) MEMS mirrors A high level of interest in MEMS technology results
reflect the input signal to an output port without regard to from both business and technical factors.
line speed or protocol. This technology is expected to be Factors on the business side are given below:
the dominant method for building photonic switches. • Multiple emerging markets for MEMS devices
promise large financial gains. The cumulative
venture capital industry investments into
MEMS-based companies are estimated at over
$1 billion as of 2003.
• In 1999, Business Week selected MEMS as one
of the three technologies expected to fuel the
growth of the economy in the twenty-first
century. The other two were
information technology and biotechnology.
• The IC industry created a solid
technology infrastructure immediately availa
ble for MEMS.
Fig. 2 Sample Micromachines

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On the technical side, some of the multiple factors that Bacteria ～5 um Virus ～0.1 um
contributed to making MEMS attractive are as follows: IC elements ～0.2 um SARS: 0.01 ～0.05 um
• Potential for integration of devices with IC Year 2010 IC production rule～0.07 um
circuitry, to create integrated systems on a chip. Atomic spacing in solids～0.0003 um
• Excellent mechanical properties resulting
from extremely pure crystalline structure with a (3) Size of MEMS/micromachines:
silicon content of 99.999% or better, resulted in
1 ～1000 um
no material fatigue or mechanical hysteresis.
This makes silicon almost a perfect material
for sensors. The mechanical properties are
comparable to steel, see Table 1.
• Batch wafer processing technology, enabling
lowcost, high volume production.
• Excellent lateral dimension control to
submicron level.
• Available cutting edge IC processing
equipment, offering easy transition to volume
production.
• Available ultrapure (no mechanical fatigue)
low-cost materials.
• Available sophisticated diagnostic and test
equipment.
• Available design and simulation tools
(software).
• Available high-volume IC packaging
technologies. Fig.4 components of MEMS
• Available pool of educated silicon processing
technologists MEMS Manufacturing Process
Another aspect of MEMS that adds to its MEMS is a manufacturing technology, that is a
attractiveness is its synergy with new way of making complex Electro mechanical
nanotechnology, which receives a high level of systems. This new manufacturing technology has several
government funding worldwide. In many cases, MEMS distinct advantages. First, MEMS is an extremely diverse
can be used as a packaging vehicle for nano devices. technology that potentially could significantly impact
Fig.4 shows MEMS is the integration of every category of commercial and military products.
mechanical elements, sensors actuators and electronics Second, it blurs the distinction between complex
on a single common silicon substrate through mechanical systems and integrated circuit electronics.
microfabrication technology . These systems can sense, MEMS manufacturing involves the repetitive process of
control and actuate on the microscale and function designing, fabrication, packaging and testing, as shown
individually or in arrays to generate effects on in Fig.5
microscale.
Size of mems components
(1) Size definition
1 micro =1 um =1/10-3 mm =1/10-6 m
1 nanometer =1 nm =1/10-3 um =1/10-9 m
1 Angstrom =1/10 nm =1/10-10 m

(2) Size comparison

Human hair ～100 um
Paper thickness ～100 um
Red blood cell, capillaries ～8um Fig. 5 MEMS manufacturing process
Visible light～0.5 um
Tobacco smoke ～0.5 um

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[Reddy, 2(9): September, 2013] ISSN: 2277-9655
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(A) Design: (B) Surface Micromachining:

There are software packages available for the It starts with wafer of material ,but unlike Bulk
design and simulation of MEMS devices. Micromachining where the wafer itself serves as the
(B) Fabrication: stock from which material is removed to define
The micromechanical components are mechanical structures, in surface micromachining is the
fabricated using compatible “micromacihing” substrate—the working surface—on which multiple,
process.MEMS promises revolutionize nearly every alternating layers of structural and sacrificial layers are
product category by bringing together silicon-based deposited and etched. Because of the laminated structural
microelectronics with micromachining technology. This and sacrificial material layers the etching of material
makes possible of realization of complete systems –on-a- done by a process that is insensitive
chip. to crystalline structure, surface micromachining enables
(C) Packaging: the fabrication of free-form complex and multi-
MEMS packaging is an application-specific component integrated electro mechanical structures,
task. It accounts for the largest fraction of the cost of the liberating the MEMS designer to envision and build
MEMS device. Packaging should avoid transferring devices and systems that are impossible to realize with
mechanical strain, heat, pressure, etc. to the device in the bulk process. More than any other factor, it is surface
package. MEMS introduce new interfaces, processes and micromachining that has ignited and is at the heart of
materials foreign to the current scientific and commercial scientific activity
the IC packaging industry. in MEMS.
(D) Testing: The components are typically integrated on a
The testing of MEMS devices is more complex single chip using microfabrication technologies. The
than that of ICs because of the integratedelectronic and electronics, mechanical and electromechanical
mechanical character of MEMS. Since MEMS devices components are fabricated using technologies borrowed
are manufactured using batch fabrication techniques, heavily, but not exclusively, from integrated circuit
similar to ICs, unprecedented levels of functionality, fabrication technology.
reliability and sophistication can be placed on a small There are three principal steps:
silicon chip at a relatively low cost.
Deposition processes - thin films of material are
placed on a substrate.
Fabrication of MEMS
Lithography - a patterned mask is applied on top
Micro engineering refers to the technologies and of the films
practice of making three dimensional structures and
Etching processes - the films are etched
devices with dimensions in the order of micrometers. selectively to provide relief following the mask
The two constructional technologies of micro outlines.
engineering are microelectronics and The fabrication of free-standing high-carbon
micromachining. Microelectronics, producing electronic microstructures by softlithographic techniques; these
circuitry on silicon chips, is a very well developed structures ranged in complexity from simple beams to
technology. Micromachining is the name for the complex, suspended deflectors. Microstructures of
techniques used to produce the structures polymeric precursors (copolymers of furfuryl alcohol-
and moving parts of micro engineered devices. phenol) to high-carbon solids were fabricated using
One of the main goals of Micro engineering is polydimethylsiloxane (PDMS) molds. Carbonization of
to be able to integrate microelectronic circuitry into these microstructures under argon resulted in mass loss
micro machined structures, to produce completely (up to 45%) and shrinkage (up to 20% linearly); the
integrated systems (Microsystems). Such systems could density increased to reach a plateau value of_1.5 g/cm3 at
have the same advantages of low cost, reliability and _900°C. Microstructures pyrolyzed at 900°C were
small size as silicon chips produced in the electrically conductive, with a conductivity of _10-2Ωcm.
microelectronics industry Elementary microelectromechanical functions
(A) Bulk Micromachining: were demonstrated in these microstructures: electrostatic
It is applied to a variety of etching procedures actuation induced deflection or vibrations of suspended
that selectively remove material, typically with a structures. The measurement of the frequency of
chemical enchants whose etching properties are resonance of highcarbon
dependent on the crystallographic structure of bulk cantilevered beams allowed the determination of
material. Young’s modulus for the solid: typical values were _15-
20 GPa. The microelectromechanical properties of more

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[Reddy, 2(9): September, 2013] ISSN: 2277-9655
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complex structures (microresonators, light deflectors) Communications Satellites

were also determined. MEMS offer significant benefits for future
Single crystal silicon MEMS fabrication based on satellite systems since they can realize various electrical
smart-cut technique and mechanical functions in a fraction of the size,
A new single crystal silicon weight, and power consumption of corresponding
MicroElectroMechanical Systems (MEMS) fabrication traditional “macro” systems. This makes these devices
process is proposed using proton-implantation smart-cut quite attractive in space applications, especially in
technique. Compared to conventional silicon on insulator commercial communications satellites, which are
(SOI) wafer fabrication processes for MEMS constantly drivenby increased capabilities, high levels of
applications, this technology can potentially result in a integration, miniaturization and cost reductions. Several
significant substrate and processing cost reduction. A applications of MEMS in satellite platforms are
silicon layer with 1.79_m thickness has beenachieved presently under consideration. This includes micro
over an oxidized 4-in silicon substrate using the proposed sensors, micro actuators, micro heat pipes for thermal
technique. TEM analyses of the silicon thin film reveal management, propulsion, active conformable surfaces,
single crystal characteristics, which is attractive for etc. Applications of MEMS technology in microwave
potential integration of MEMS devices with components and subsystems ore growing very rapidly.
microelectronics in the same structural layer. Implant- Automotive
induced defect density in the silicon can be substantially For the past six years, the automotive industry
reduced to a negligible level through high temperature has used MEMS to sense and control a car’s relationship
annealing. Prototypesingle crystal silicon MEMS to its environment, most notably to sense acceleration.
structures, such as cantilever beams and clamped– Healthcare
clamped micro-bridges with a typical length of a few Micro fabricated silicon pressure sensors for
hundreds of micrometers, have been successfully blood pressure monitoring, Respirators, Kidney dialysis
fabricated as demonstration vehicles for future micro- equipment are some of the applications of MEMS in this
systems implementation field.
Fabrication of Free-Standing Metallic General Applications:
Pyramidal Shells Pressure, temperature, chemical and vibration
A technique for fabricating sensors, Light reflectors Switches Accelerometers (for
three dimensional , metallic , pyramidalmicrostructure airbags, pacemakers) , Micro actuators for data storage
s with base dimensions of 1-2 µm, wall thicknesses of and read/write heads. All-optical switches
_100-200 nm, and tip-curvature radius of _50 nm. The storage devices etc are general applications of MEMS
procedure begins with the fabrication of pyramidal pits in devices.
the surface of an n-doped silicon substrate. An
electrically insulating surface layer of SiO2 covers the Conclusion
regions outside the pits. These pits are patterned
A single crystal silicon MEMS fabrication
using either conventional photolithography or soft technology has been demonstrated using proton-
lithography and formed by selective anisotropic etching. implantation smart-cut technique.
The resulting topographically patterned silicon serves as
The proposed technology, compared to
the cathode for the selective electrodeposition of metal in conventional SOI wafer fabrication processes
the pyramidal pits. Removing the silicon template by for MEMS applications, can potentially result in
etching generates free-standing, pyramidal, metallic a significant substrate and processing cost
microstructures. reduction.

Prototype cantilever beams and clamped–
Applications of MEMS clamped micro-bridges have been successfully
Telecommunications fabricated as demonstration vehicles for future
Telecommunications has a broad array of micro-system implementations. Material
applications, from micro relays for line card applications analyses show that the transferred silicon layer
to complex multi frequency tunable systems for wireless reveals single crystal characteristics and exhibits
communications. The integrated circuit industry is a negligible defect density after high
heading toward system on a chip (SOC), which seeks to temperature annealing.
integrate complete functionality on a single silicon
These characteristics are critical for realizing
substrate. high-performance MEMS sensors, actuators,

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and potential system integration with [10] N.P Mahalik, MEMS, TMH Publishers, 2012
microelectronics in the same structural layer. [11] Tai Ran Hsu, MEMS and microsystem Design,

The less expensive softlithographic techniques TMH, 2011
that we have developed: a key element in these
techniques is the availability of convenient,
inexpensive methods for the preparation of
polydimethysiloxane (PDMS) molds that are
used throughout these techniques, and the use of
these PDMS molds to generate microstructures
in polymeric materials that are precursors to
carbon solids.

The PDMS molds were prepared as described
previously, by casting PDMS on a
photographically generated master.

Free-standing metallic pyramidal
shellsprocedure provides a route to fabricate
metallic shells with a pyramidal structure, the
tips of whichhave a radius of curvature of _50
nm.

The uniformity of the template fabricated by
photolithography or soft lithography
ensures the uniformity in shape and size of the
pyramidal shells.

Pyramid-shaped microobjects are potentially
useful for exploring bottom-up self-assembly.

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