ReferencesGad-el-Hak, M. MEMS, Design and Fabrication, Second
Edition. (2005) Lyshevski, S., MEMS and NEMS, CRC Press LLC. (2002)
Maluf, N. and Williams, K., An Introduction to Micromechanical
Systems Engineering, Second Edition, Artechouse, Inc.
(2004)Microsytems, Same-Tec 2005 Preconference Workshop, July 25
&26, 2005.Taylor and Francis, MEMS Introductory Course, Sandia
National Laboratories, June 13-15, 2006.What is MEMS technology?
MEMS and Nanotechnology Clearinghouse.
http://www.memsnet.org/mems/what-is.html.
www.nanotechworkforce.comMEMS AND NEMSLast updated: February 6,
2008.
Biography of Dr. Arunachala Nagarajan:Arunachala (Raj) Nagarjan
received his Bachelors and Masters degree in Electronics from the
University of Madras, India and later his M.S. and PH.D degrees
from Carnegie Mellon University in Pittsburgh, Pennsylvania. After
his graduation he worked for IBM for almost 30 years in different
aspects of semiconductor chip and packaging technologies in both
technical and management positions. He then was Vice President for
SRM Systems and Technology, Boston. Presently he is teaching
semiconductor technology at Austin Community College. He holds
almost 30 patents and an equal number of publications.Last updated:
February 6, 2008www.nanotechworkforce.comObjective.*Last updated:
February 6, 2008www.nanotechworkforce.comTopics.Last updated:
February 6,
2008www.nanotechworkforce.comIntroduction:Micro-ElectroMechanical
Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS) rely on
technologies of miniaturization. Watch makers have practiced the
art of miniaturization since the 13th century. With the invention
of the compound microscope in the 1600s and later use to observe
microbes, plant and animal cells and modern day, atomic force and
electron microscopes that allow for observation at the molecular
and atomic scale, there has been an interest to manipulate matter
at a smaller and smaller scale. One success story has been the
miniaturization of the modern eras transistor which has allowed for
the development of ever smaller and more powerful gadgets and
machines. The transistor in todays integrated circuits has a size
of 0.18 micron in production and approaches 10 nanometers in
research laboratories.
MEMS and NEMS represent a fundamental breakthrough in the way
materials, devices, and systems are understood, designed, and
manufactured. Utilizing a combination of microelectronics processes
developed within the semiconductor industry and available bulk
microfabrication techniques, mechanical elements such as sensors,
cantilevers and actuators used to sense and manipulate the
environment are combined with the needed electronic circuitry to
control the miniature device. MEMS usually combine electrical
properties with mechanical structural components at the micrometer
scale to produce devices capable of performing tasks impossible
using conventional technologies. For NEMS, the unique properties
and behaviors of matter displayed at the nanometer scale have yet
to be fully understood or exploited.
References:MicroFabrica. Microfabrica is a manufacturer of
micrometer- and millimeter-scale metal components, subsystems, and
devices with features measured in microns. Their website illustrate
several related products and processes currently in MEMS
production. See http://www.microfabrica.com.MEMS Introduction. In
Department of Engineering, Cambridge University. Retrieved February
5, 2008, from
http://www.eng.cam.ac.uk/~yf229/MEMS%20Introduction.htm.
Fig. 5.1 - http://mems.sandia.gov/scripts/images.asp. Courtesy
of Sandia National Laboratories, SUMMiTTM Technologies,
www.mems.sandia.gov.
*Last updated: February 6,
2008www.nanotechworkforce.comIntroduction, Continued:
The Scale of Things:Todays semiconductor technology aims at the
45 nanometer scale for circuit devices, several thousand times
smaller than the diameter of human hair.
Another way of looking at micro and nano technology is from the
perspective of processing. The micro world is all top down
fabrication using micro-miniaturization technologies and bulk
processing while the nano world is bottom up fabrication and uses
self assembly processes.
Fig. 5.2 -
http://www.nano.gov/html/facts/The_scale_of_things.html.
*Last updated: February 6,
2008www.nanotechworkforce.comIntroduction, Continued:
Definition and Terms:Unlike the European term MST, the U.S. term
MEMS applies to systems which include a moving part and some form
of electronics.
Alternately, MEMS, also known as Microelectronic Mechanical
Systems, can be described as the integration of mechanical
elements, sensors, actuators and electronics on a common silicon
substrate through micro fabrication technology. While the
electronics portion is manufactured using integrated circuits (IC)
process sequences, the micro mechanical components are fabricated
using compatible micromachining processes that selectively etch
away parts of silicon wafer or add new structural layers to form
the mechanical and electromechanical device.
The broadest requirement for these very small devices is ability
to sense the environment, to collect necessary data and to create a
signal or action to make desired changes to the environment.
References:Same-Tec 2007. Southwest Center for Microsystems
Education. Regional Advanced Technology Education Center.
http://www.scme-nm.org/.
*Last updated: February 6,
2008www.nanotechworkforce.comIntroduction, Continued:
The image shown provides an example of the scale of
micromachines created with MEMS technology. Visit Sandia National
Laboratories website on Micromachines at http://mems.sandia.gov/
for additional images and information on the technology and areas
of focus.
Fig. 5.3 - http://mems.sandia.gov/scripts/images.asp. Courtesy
of Sandia National Laboratories, SUMMiTTM Technologies,
www.mems.sandia.gov.
*Last updated: February 6, 2008www.nanotechworkforce.comBrief
History:
Dr. Richard Feynman, a Nobel Laureate physicist, is considered
the father of todays MEMS and NEMS based on his inspirational
lecture, There is Plenty of Room at the Bottom given in 1959 in
which he stated that miniaturization techniques would eventually be
capable of writing an entire Encyclopedia Brittanica to be written
on the head of a pin. He also noted that new applications would
emerge because the behavior of matter is different at the atomic
scale compared to conventional bulk scale. Despite Feynmans doubts
about the usefulness of small machines, micro- and nano-sized
electromechanical devices are finding a variety of applications in
industry with a potential market value in the billions of dollars
worldwide.
A combination of solid state physics research, the invention of
the transistor, the rapid miniaturization of devices consistent
with Moores Law and clearly evident in the consumer electronics
industry, the discovery of piezoelectricity in semiconductors, and
the discovery of silicon as a viable material for micromachining
have truly led to the serious development of microelectromechanical
devices.
References: Schottky diode. (2008, February 3). In Wikipedia,
The Free Encyclopedia. Retrieved 15:59, February 6, 2008, from
http://en.wikipedia.org/w/index.php?title=Schottky_diode&oldid=188700638.Richard
Feynman. (2008, February 5). In Wikipedia, The Free Encyclopedia.
Retrieved 16:01, February 6, 2008, from
http://en.wikipedia.org/w/index.php?title=Richard_Feynman&oldid=189155474
.Theres Plenty of Room at the Bottom. In Nanotechnology created by
Dr. Ralph Merkle and hosted by Zyvex. Retrieved February 6, 2008
from http://www.zyvex.com/nanotech/feynman.html.*Last updated:
February 6, 2008www.nanotechworkforce.comElectromechanical
Systems:
Functional Block Diagram:Electromechanical systems fall into
three groups - the conventional electromechanical systems, micro
electromechanical systems (MEMS) and Nanoelectromechanical systems
(NEMS). In the first two systems the behavior can be analyzed by
fundamental theory of electromechanics (classical mechanics and
electromagnetism). For nanoelectromechanical systems (NEMS),
quantum physics is needed to describe the operational parameters of
the devices.
Fig. 5.4 - ACC Instructional Development Services.*Last updated:
February 6, 2008www.nanotechworkforce.comMEMS:Microstructure
Fabrication:Traditionally MEMS have relied upon silicon and silicon
based materials, though other materials like silicon dioxide,
silicon nitride, and silicon on insulators (SOI), gallium arsenide,
quartz, glass, and diamond have also been explored. Silicon,
polysilicon, and amorphous silicon are the most common materials
currently used in MEMS commercial production.In silicon-based MEMS
processing, many of the features of integrated circuit processing
along with micromachining techniques are used. Silicon has very
valuable properties which lend itself well to micromachining.
Because of its natural abundance and versatility, it is also an
economically desirable element in commercial applications.
Crystallography is the study of crystal structure which affects the
electrical, mechanical, and optical properties of materials. The
crystal planes indicated by Miller indices affect the etching rates
and thus help to create different structural forms. Wet etching of
silicon crystals allows the creation of micro-channels, micro
nozzles, micro chambers, and alignment targets. There are different
forms of silicon: Amorphous - No predictable long range atomic
order; no clear or well defined band gap, electronic properties
affected.Polycrystalline - Long range order; solid consists of many
small crystals stuck together; distinct band gap.Crystalline -
Extremely long term order with few defects; little difference in
the placement of the atoms throughout solid; well-defined band gap,
a sharp transition from valence band to conduction band with no
tailing.Miller Planesare represented by (x, y, z) where the {x, y,
z} planes are perpendicular to the corresponding vectors. Miller
inices affect etching rates and help to create different structural
forms. The common orientations are indicated in the diagram.
Anisotopic wet etching of silicon crystals allows for the creation
of micro-channels, micro-nozzles, micro chambers and the alignment
targets needed for micro devices.
Fig. 5.5 -
http://en.wikipedia.org/wiki/Image:Indices_miller_direction_exemples.png.*Last
updated: February 6, 2008www.nanotechworkforce.comMEMS,
Continued:
Microstructure Fabrication, Continued:The basic operations for
building microstructures are pattern definition, deposition and the
removal of unwanted material. Micromachining techniques are used to
produce wells or channels in a prepared substrate by means of
selective etching.
The bulk micromachining manufacture of micro devices generally
uses top-down fabrication techniques of etching deep into prepared
silicon wafers to create three-dimensional MEMS components. These
techniques utilize etchants like KOH that etch different
crystallographic directions at different rates. This helps to make
vee grooves, pyramids and channels suited for production of
microsensors and accelerometers. The structures are formed using
orientation-independent isotropic etching and orientation-dependent
anisotropic etching (KOH & DRIE).
Fig. 5.6 - ACC Instructional Development Services.*Last updated:
February 6, 2008www.nanotechworkforce.comMEMS, Continued:
Microstructure Fabrication, Continued:
Processing Techniques:Deep Reactive Ion Etching (DRIE) is used
make deep grooves into the silicon and etch high aspect ratio
trenches into silicon. Surface micromachining builds structures by
adding materials layer by layer on top of a silicon substrate. As
each layer is formed the desired device structures, such as
cantilevers and gears are formed by the selective oxide removal of
SiO2 layers by etching. The LIGA process (a German acronym for
lithography electroplating - molding) utilizes radiation (initially
x-rays) to deep etch structures. A synchrotron light source is
required for the process. This process is important for creating
taller (versus wider) structures.The SUMMIT process developed by
SANDIA is a more complicated process requiring 5 masking steps. It
involves a polycrystalline silicon surface micromachining process
consisting of five layers: one ground plane/electrical interconnect
layer and four mechanical layers.
References:LIGA. (2007, December 9). In Wikipedia, The Free
Encyclopedia. Retrieved 16:15, February 6, 2008, from
http://en.wikipedia.org/w/index.php?title=LIGA&oldid=176843744.Southwest
Center for Microsystems Education. Regional Advanced Technology
Education Center. http://www.scme-nm.org/.SUMMiT V Overview. Sandia
National Laboratories.
http://mems.sandia.gov/tech-info/summit-v.html*Last updated:
February 6, 2008www.nanotechworkforce.comMEMS, Continued:
MEMS Advantages.*Last updated: February 6,
2008www.nanotechworkforce.comMEMS, Continued:
MEMS Economy:MEMS are one of the fastest growing technology
areas. In 2005, the global market for MEMS devices and production
equipment was worth an estimated $5 billion and is projected to
grow to $12.5 billion through 2010, with an average annual growth
rate of more than 20%. The Small Tech Business DirectoryTM Guide
published by Small Times lists more than 700
manufacturers/fabricators of microsystems and technologies. High
volume production with attractive sales figures has been achieved
by several companies making devices such as accelerometers for
automobiles, analog devices, micro-mirrors for digital projection
displays, and pressure sensors for the automotive and medical
industries.
References:McWilliams, Andrew. Microelectromechanical Systems
(MEMS) Technology: Current And Future Markets. Research Report #
GB-SMC051B (February 2006).
(http://www.electronics.ca/reports/mems/technology.html).
Fig. 5.7 - ACC Instructional Development Services.
*Last updated: February 6, 2008www.nanotechworkforce.comCurrent
Applications:
Microsensors have proven to be of great commercial value.
Examples include pressure sensors, strain gauges, accelerometers,
and gyroscopes. MEMS accelerometers are quickly replacing
conventional accelerometers for crash air bag deployment systems in
automobiles. MEMS accelerometers are much smaller, more functional,
lighter, and more reliable and are produced for a tenth of the cost
of the conventional macro-scale accelerometer elements.Optical MEMS
devices range from bar code readers to fiber optic
telecommunication and use a range of wide band-gap materials,
nonlinear electro-optic polymers, and ceramics. A well established
commercial example of an optical MEMS device is the Digital Light
Processor (DLP) by Texas Instruments used for projection displays.
Deformable mirrors are used for image enhancement systems including
imaging the retina of the eye.Computer hard drives have a MEMS
device accelerometer that senses rapid motion and parks the head to
avoid damaging the surface during a fall, the iPhone uses one to
automatically rotate the display as the phone is rotated by the
user.*Last updated: February 6,
2008www.nanotechworkforce.comCurrent Applications:
Biomedical:This is where rapid strides of development are
happening in MEMS device applications. The key areas of
applications are biomedical instruments and analysis and implants
and drug delivery. MEMS have special applications in these
activities because of smaller size, reduced cost, less intrusive
surgical procedures, reduction of the amount of test samples
needed, speed of diagnosis, and patient recovery time. MEMS pumps
can trigger subcutaneous infusion of insulin for diabetes patients
and the device is small enough to be worn directly on the skin for
real time glucose monitoring. Other applications include DNA
testing, drug delivery, and blood testing. Miniaturized implants
for the replacement of the retina and the ear drum are also on the
market.Purdue researchers created a device that detects the mass of
a single virus particle. The device naturally vibrates at a
specific frequency. When a virus particle weighing about one
trillionth as much as a grain of rice lands on the cantilever it
vibrates at a different frequency. The next step is to coat a
cantilever with the antibodies for a specific virus that attracts
certain viruses that could make it possible to create detectors to
specific pathogens. *Last updated: February 6,
2008www.nanotechworkforce.comCurrent Applications, Continued:
Detection systems.
*Last updated: February 6, 2008www.nanotechworkforce.comNEMS and
Nanotechnology:
A nanometer is a billionth of a meter. The prefix nano is Greek
for dwarf. The diameter of human hair is approximately 100,000
nanometers. A red blood cell is approximately 10,000 nanometers.
Nanotechnology is the manipulation of matter at the nanometer
(10-9m) scale. It involves the control of molecules at an atomic
level to create materials with unique properties. The mechanical
strength and electronic and optical properties of many materials
can be altered at this scale.Carbon, which is in the same periodic
column as silicon, is an important element in nanotechnology.
Carbon is known for forming stable and strong covalent bonds. In
short chains it has the properties of gas, in medium chains, a
liquid, and in long chains it can be a solid like plastic. In
diamond carbon atoms are stacked in a three dimensional array or
lattice structure.The carbon nanotube is a sheet of carbon chains
rolled with a seamed edge. These are self assembled carbon nano
structures and can be either single walled or multi-walled. Carbon
nanotubes have very high tensile strength - 100 times greater than
steel. They are elastic, light weight, and display thermal
conductivity (10 times silver). Carbon nanotubes can occur
naturally (as soot). They possess metallic and semiconducting
electronic behavior depending on chirality or handedness of the
atomic arrangment. The structural density of carbon-based
integrated circuits exceeds the density of integrated circuits
developed using conventional silicon based technologies by a
thousand-fold.
Fig. 5.8 -
http://en.wikipedia.org/wiki/Image:Eight_Allotropes_of_Carbon.png.
*Last updated: February 6,
2008www.nanotechworkforce.comNEMS:Quantum dots, Quantum wires, and
Quantum Films:As the size of structures becomes smaller and
smaller, matter at the nanoscale exhibits novel electrical and
structural characteristics due to the dominance of quantum effects
and to the confinement of electrons and holes in these small
dimensions. The number of directions free of confinement is used to
classify structures, thus 2D confinement is a quantum film, 1D
confinement is a quantum wire, and 0D of confinement is a quantum
dot.Quantum Dots are particularly significant in optical
applications; electronically they act like single-electron
transistors and display the Coulomb blockade effect. Nanowires,
also known as quantum wires, could be used to link tiny components,
including chemical compounds, into extremely small circuits. There
are many different types of nanowires - metallic (e.g., Ni, Pt,
Au), semiconducting (e.g., Si, InP, GaN, etc.), and insulating
(e.g., SiO2,TiO2). Repeating organic (e.g. DNA) or inorganic (e.g.
Mo6S9-xIx) units make up molecular nanowires. Depending on the
material composition, there are several methods available to make
nanowires, the most common being Vapor-Liquid-Solid (VLS).
References: Nanowire. (2008, January 27). In Wikipedia, The Free
Encyclopedia. Retrieved 04:36, February 5, 2008, from
http://en.wikipedia.org/w/index.php?title=Nanowire&oldid=187143934.
Fig. 5.9 - ACC Instructional Development Services.
*Last updated: February 6, 2008www.nanotechworkforce.comNEMS and
Nanotechnology, ContinuedNano Fabrication:Electrostatic
manipulation The Scanning Tunnel Microscope (STM) can be used to
make atoms slide over a surface in order to move them into a
desired arrangement by electrostatic forces. Resolution is
effectively the size of a single atom but the process is
exceptionally time consuming and requires special conditions to
prevent movement of atoms out of place. STM can also be made to
write on a chemically charged electron beam resist.Pattern Electron
Beam Lithography - Surface micromachining can be conducted at the
nanoscale using electron beam lithography to create free standing
or suspended mechanical objects. An electron beam is for scanning a
desired pattern in the resist.Dip pen lithography uses an atomic
force microscope (AFM) probe tip to deposit a layer of material
onto a surface, much as a pen writes on paper. A pattern can be
drawn on a surface using a wide range of inks such as thiols,
silanes, metals, and biological micromolecules. This technology can
be used in biosensor fabrication.Self Assembly - The self-assembly
of molecules is a favored mechanism at the nanoscale as it relies
on natural forces to create highly perfect assemblies. Snow flakes,
salt crystals and soap bubbles are all examples of self assembly.
Simply controlling environmental conditions and molecular
components may provide for a very cost efficient manufacturing
scheme.*Last updated: February 6, 2008www.nanotechworkforce.comNEMS
and Nanotechnology, Continued:
Merging of technologies:NEMS technology is still in its infancy
with global research and development actively under way. Many of
the NEMS device technologies use MEMS as a bridge to the
nano-world. We are already dealing with matter on the nanoscale in
a technology that most of us take for granted, hard disc drives.
The biosensor is a unique blend of the ability for biology to
identify individual types of molecules in complex mixtures with the
speed, convenience, and low cost of microelectronics. MEMS will
provide a bridge to enable the applications of nanotechnology as
illustrated in the cantilever sensor.
*Last updated: February 6, 2008www.nanotechworkforce.comNEMS
(Nanotechnology meets MEMS)A typical example is the cantilever
sensors used to detect a single E. Coli cell or the detection of a
single DNA strand. The atomic force microscope used in this
technique has a tip made of silicon using a typical MEMS device
process and is of micron dimensions. Cantilever sensors recognize
resonant frequency shifts with the addition of mass thereby
indicating the presence or absence of specific compounds in the
environment tested. These type of sensors have been used to detect
the presence of a single E. coli organism and a single DNA
strand.
References:Waldrop, M.M. and Lippel, P. The Sensor Revolution A
Special Report. (March 22, 2005) The National Science Foundation.
http://www.nsf.gov/news/special_reports/sensor/overview.jsp.
Fig. 5.10 ACC Instructional Development Services.*Last updated:
February 6, 2008www.nanotechworkforce.comImpact of
Miniaturization:
The impact of MEMS and NEMS on our future lives will be
tremendous. These emerging technologies open up entirely new job
opportunities both in semiconductor and biological applications.
MEMS and nano manufacturing is a logical transition from todays
semiconducting manufacturing methods and will lead to numerous
teaching and manufacturing jobs. The biological and optical
applications of MEMS and NEMS will open up applications,
development, and research. There is an incentive for research in
several universities and many government and privately-funded
initiatives are in place to create better products with
nanotechnology. MEMS and NEMS will likely greatly improve the
construction and transportation industries as vehicles and building
materials become lighter, stronger and more durable and incorporate
greater fuel efficiencies.Unfortunately the effects of MEMS and
NEMS on our environment are not currently well understood. Carbon
based NEMS may be more toxic than conventional systems. Some of the
NEMS may contain heavy metals and may be small enough to avoid
detection by the bodys immune system , causing damage against which
there is no defense. The NEMS constituent materials may be
extremely toxic to living organisms potentially hindering DNA
mechanics and protein synthesis. They may also be non-biodegradable
which would result in chronic toxicity. Nanomaterials may be
inadvertently introduced into the environment and make their way
into the food chain. Self replicating nano robots may cause serious
problems. It is important to invest more time and money to research
the potential dangers of nanotechnology.Just like semiconductors
changed the lives in the 20th century, MEMS and NEMS have the
potential to change human lives in the 21st century. *Last updated:
February 6, 2008www.nanotechworkforce.comChallenges and
Possibilities:
The level of activity in MEMS and NEMS is rapidly expanding.
There was only one program in the 1960s, now there are at least 40
centers in the U.S. and a hundred centers worldwide devoted to
micro- and nanotechnological advancements. In 2007, there were at
least 15 firms worth over $100 million in the industry. There are
at least 10,000 MEMS-related patents. Microsystems serve almost all
industries like aerospace, information technology, automotive
industry, defense industry, medical industry, the data projection
industry, telecommunications, chemical, oil, gas and many others.
The complexity of phenomenon and effects in MEMS and NEMS
processing requires new fundamental and applied science as well as
engineering and technological developments. High fidelity modeling
will most likely be required. Developing high-yield, low-cost
fabrication techniques will be essential. To fabricate nanoscale
structures, device and systems molecular manufacturing methods and
technologies must be developed and enhanced. The challenges in MEMS
and NEMS will be the reliability of the products and packaging.
Computational models need to be developed to design, test and
predict the behavior of MEMS and NEMS as they work together. The
packaging of MEMS and NEMS pose unique problems and lot of work has
to be done to understand the reliability exposures and to develop
the appropriate corrective procedures in product development and
manufacturing. Finally, bottoms-up self-assembly techniques are
still in their infancy . Concentrated efforts should be undertaken
to make it a more viable manufacturing technique as it holds the
greatest promise in our nanoscaled futures. *Last updated: February
6, 2008www.nanotechworkforce.comReferences:
Gad-el-Hak, M. MEMS, Design and Fabrication, Second Edition.
(2005) Lyshevski, S., MEMS and NEMS, CRC Press LLC. (2002) Maluf,
N. and Williams, K., An Introduction to Micromechanical Systems
Engineering, Second Edition, Artechouse, Inc. (2004)Microsytems,
Same-Tec 2005 Preconference Workshop,, July 25 &26, 2005.Taylor
and Francis, MEMS Introductory Course, Sandia National
Laboratories, June 13-15, 2006.What is MEMS technology? MEMS and
Nanotechnology Clearinghouse.
http://www.memsnet.org/mems/what-is.html.
Last updated: February 6, 2008
