1. MICRO- ELECTRO-MECHANICAL STSTEM
Author1- AbhishekMahajan
Line 1 – Electronics and Communication
Line 2 – Shreejee Institute of Technology and
Management
Line 3 – Khargone
Line 4 – Abhishekmahajan6991@gmail.com
I Introduction
Micro-electro-mechanical system, also written
as MEMS is the technology of very small
devices; it merges at the Nano-scale into
nanoelectromechnical system (NEMS) and
nanotechnology. MEMS are separate and
distinct from the hypothetical vision of
molecular nanotechnology or molecular
electronics. MEMS are made up of components
between 1 to 100 micro meters in size and
MEMS devices generally range in size from 20
micrometers to a millimeter. They usually
consist of a central unit that processes data (the
microprocessor) and several components that
interact with the surroundings such as micro
sensors. At these size scales, the standard
constructs of classical physics are not always
useful. Because of the large surface area to
volume ratio of MEMS, surface effects such as
electrostatics and wetting dominate over
volume effects such as inertia or thermal mass.
MEMS became practical once they could be
fabricated using modified semiconductor device
fabrication technologies, normally used to make
electronics. These include molding and plating,
wet etching and dry etching, electro discharge
machining (EDM), and other technologies
capable of manufacturing small devices. An
early example of a MEMS device is the
resonistor – an electromechanical monolithic
resonator.
II History of MEMS:-
The physicist Richard Feynman delivered a talk
at Caltech in December 1959 with the title
“There’s Plenty of Roomat the Bottom.” “What
I want to talk about,” said Feynman “is the
problem of manipulating and controlling things
on a small scale.”
In one sense, a real sense Feynman laid the
roots for today’s MEMS industry.
From those very early days and origins, MEMS
has enjoyed classic hockey stick growth: i.e.
dramatic increases in sales revenue or unit
shipment growth over time that started at a
normal, linear pace from the 1960s through to
the 1990s, hit an inflection point and took off in
the 2000s and sustained its considerable
momentum into the 2010s, fueled by such
MEMS-enabled killer apps as the Nintendo
Wii, the Apple iPhone, Bosch airbag systems,
Epson ink jet print heads, microphones from
Knowles Electronics, and blood pressure
sensors fromAcuity, Merit sensor, and others.
III Material used for MEMS
manufacturing:-
The fabrication of MEMS evolved from the
process technology in semiconductor device
fabrication, i.e. the basic techniques are
deposition of material layers, pattering by
photolithography and etching to produce the
required shapes.
a) Silicon: - Silicon is the material used to
create most integrated circuits used in consumer
electronics in the modern industry. The
economics of scale ready availability of
inexpensive high-quality materials, and ability
to incorporate electronic functionality make
silicon attractive for a wide variety of 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 fixed there is virtually no hysteresis
and hence almost no energy dissipation. As well
as making for highly repeatable motion, this
also makes silicon very reliable as it suffers
very little fatigue and can have service lifetime
in the range of billions to trillions of cycle
without breaking.
b) 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 be
produced. Polymers on the other hand can be
2. produced in huge volumes, with a great variety
of material characteristics. MEMS devices can
be made from polymers by processes such as
injection molding, embossing or stereo
lithography and are especially well suited to
microfluidic applications such as disposable
blood testing cartridges.
c) 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. Commonly used metals
include gold, nickel, aluminum, copper, chromi
um, titanium, tungsten, platinum, and silver.
d) Ceramic: - The nitrides of silicon, aluminum
and titanium as well as silicon carbide and
other ceramics are increasingly applied in
MEMS fabrication due to advantageous
combinations of material
properties. AiN crystallizes in the wurtzite
structure and thus shows pyroelectric
and piezoelectric properties enabling sensors,
for instance, with sensitivity to normal and
shear forces. TiN, on the other hand, exhibits a
high electrical conductivities and large elastic
modulas allowing realizing electrostatic MEMS
actuation schemes with ultrathin
membranes. Moreover, the high resistance of
TiN against bio corrosion qualifies the material
for applications in biogenic environments and
in biosensors.
IV MEMS basic processes:-
a) Deposition processes: - One of the basic
building blocks in MEMS processing is the
ability to deposit thin films of material with a
thickness anywhere between a few nanometers
to about 100 micrometers. There are two types
of deposition processes, as follows
i) Physical deposition: - Physical vapor
deposition ("PVD") consists of a process in
which a material is removed from a target, and
deposited on a surface. Techniques to do this
include the process of sputtering, in which an
ion beam liberates atoms from a target,
allowing them to move through the intervening
space and deposit on the desired substrate,
and evaporation, in which a material is
evaporated from a target using either heat
(thermal evaporation) or an electron beam (e-
beam evaporation) in a vacuumsystem.
ii) Chemical deposition: - Chemical deposition
techniques include chemical vapor deposition
("CVD"), in which a stream of source gas reacts
on the substrate to grow the material desired.
This can be further divided into categories
depending on the details of the technique, for
example, LPCVD (Low Pressure chemical
vapor deposition) and PECVD (Plasma
Enhanced chemical vapor deposition).
Oxide films can also be grown by the technique
of thermal oxidation, in which the (typically
silicon) wafer is exposed to oxygen and/or
steam, to grow a thin surface layer of silicon
dioxide.
b) Patterning: - Patterning in MEMS is the
transfer of a pattern into a material.
i) Lithography
ii) Electron beam lithography
iii) Ion beam lithography
iv) Ion track technology
v) X-ray lithography
vi) Diamond patterning
c) Die preparation: - After preparing a large
number of MEMS devices on a silicon wafer,
individual dies have to be separated, which is
called die preparation in semiconductor
technology. For some applications, the
separation is preceded by wafer back
grinding in order to reduce the wafer
thickness. Wafer dicing may then be performed
either by sawing using a cooling liquid or a dry
laser process called stealth dicing.
V Applications:-
Some common commercial applications of
MEMS include:
Inkjet printers, which use piezoelectric or
thermal bubble ejection to deposit ink on
paper.
Accelerometers in modern cars for a large
number of purposes
including airbag deployment and electronic
stability control.
Accelerometers and MEMS gyroscopes in
remote controlled, or autonomous,
helicopters, planes and multirotors (also
known as drones), used for automatically
sensing and balancing flying
characteristics of roll, pitch and yaw.
3. Accelerometers in consumer electronics
devices such as game controllers
(Nintendo Wii), personal media players /
cell phones (Apple iPhone, various Nokia
mobile) phone models, various HTC PDA
models and a number of Digital Cameras
(various Canon Digital IXUS models).
Also used in PCs to park the hard disk
head when free-fall is detected, to prevent
damage and data loss.
MEMS gyroscopes used in modern cars
and other applications to detect yaw; e.g.,
to deploy a roll over bar or
trigger electronic stability control
MEMS microphones in portable devices,
e.g., mobile phones, head sets and laptops.
Silicon pressure sensors e.g.,
car tire pressure sensors, and
disposable blood pressure sensors
Displays e.g., the digital micro mirror
device (DMD) chip in a projector based
on DLP technology, which has a surface
with several hundred thousand micro
mirrors or single micro-scanning-mirrors
also called micro scanners
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, chemo sensor), or embedded in
medical devices e.g. stents.
Interferometric modulator display (IMOD)
applications in consumer electronics
(primarily displays for mobile devices),
used to create interferometric modulation −
reflective display technology as found in
mirasol displays
Fluid acceleration such as for micro-
cooling
Micro-scale energy harvesting including
piezoelectric, electrostatic and
electromagnetic micro harvesters.
Micro machined ultrasound transducers.
VI Current Challenges:-
Some of the obstacles facing organizations in
the development of MEMS and
Nanotechnology devices include
a) Access to fabrication: - Most organizations
who wish to explore the potential of MEMS
and Nanotechnology have little or no internal
resources for designing, prototyping, or
manufacturing devices, as well as little to no
expertise among their staff in developing these
technologies. Few organizations will build their
own fabrication facilities or establish technical
development teams because of the prohibitive
cost. Therefore, these organizations will benefit
greatly from the availability of MNX’s
fabrication services, which offers its customers
affordable access to the best MEMS and Nano
fabrication technologies available.
b) Packaging:- MEMS packaging is more
challenging than IC packaging due to the
diversity of MEMS devices and the requirement
that many of these devices need to be
simultaneously in contact with their
environment as well as protected from the
environment. Frequently, many MEMS and
Nano device development efforts must develop
a new and specialized package for the device to
meet the application requirements. As a result,
packaging can often be one of the single most
expensive and time consuming tasks in an
overall product development program. The
MNX staffs are experts in packaging solutions
for devices for any application.
c) Fabrication Knowledge Required: - MEMS
device developers must have a high level of
fabrication knowledge and practical experience
coupled with a significant amount of innovative
engineering skill in order to create and
implement successful device designs. Often the
development of even the most mundane MEMS
device requires very specialized skills. Without
this expertise and knowledge, at best device
development projects can cost far more and
take much longer. At worst, they can result in
failure. The MNX has more expertise and
knowledge in device design and fabrication
than anyone in the world.
4. VII Future of the MEMS:-
The future of MEMS is rich with commercial
possibilities, including the trillions of MEMS
sensors envisioned to be used as the eyes and
ears of the Internet of Things (IoT); the future
of MEMS also includes local MEMS-based
environmental monitoring devices;
deployments in the MEMS-enabled quantified
self movement and in personalized medicine
applications; MEMS-containing wearables; and
MEMS-reliant drones and other small personal
robots.
