Soumen Das sou@smst.iitkgp.ernet.in School of Medical Science and Technology Indian Institute of Technology Kharagpur

1. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
School of Medical Science and Technology
Indian Institute of Technology Kharagpur
EXPLORING MEMS AS TRANSDUCERS
and
ELECTROPHYSIOLOGICAL CHARACTERISATION
OF CELLS IN HEALTHCARE APPLlCATIONS
Soumen Das
sou@smst.iitkgp.ernet.in

2. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
OUTLINE OF THE TALK
Evolution of microelectronics
Introduction to MEMS
Lithography
Why silicon
Critical issues in Microsystem technology
Scaling laws
Conclusions

3. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
EVOLUTION OF MICROELECTRONICS
Device (Transistor) (1947)
Silicon Planar Technology (1954)
Integrated Circuits (1958)
VLSI Micromachining / SOP / SOC
MEMS (1970)
ULSI / Nano CMOS NEMS
MARKET DEMANDS…..Present to Future
 Higher speed
 Low power consumption
 Multi to Mega function
 Functional convergence (digital + analog + RF + optical)
System in package: Convergence of computing,
communication, consumer & Biomedical
Transceive voice+ massive data
(e-mails, Internet, Camera)
MEMS micro gear-train by
Sandia National Laboratories
DRAM chip: 200 M transistors,
Wiring length 8–10 m, feature
size 35 nm, Supply < 1V

4. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Transistor (Bipolar/MOS) to
Integrated Circuits, VLSI/ULSI/SOC
 PCB based circuits
 Photolithography and silicon planar technology
 Linear bipolar ICs
 Bipolar digital ICs, TTL, ECL, IIL
 PMOS, NMOS, CMOS LSI / VLSI chips
 Device size shrinking, chip size increasing, speed and power
dissipation improving
 Microprocessors, microcomputers
 DSP chips
 On-chip analog-digital functions , SOC
 Nanoscale ICs

5. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Moore’s Law
Gordon Moore of Intel predicted in 1965 that “the number of
transistors per chip would double every 2 years”.
Moore’s law led to the development of NanoCMOS approaching
20 nm minimum feature with about a billion transistors per
chip.
But conventional CMOS cannot go beyond 0.5 nm gate oxide.
Moore’s law is steadily loosing validity in traditional IC
technology.
“Cramming More Components Onto Integrated Circuits” by G. Moore
Publication: Electronics, April 1965
2X transistors every 2 years
Traditional Scaling Era
40+ Years of Moore’s Law
at INTEL: From Few to
Billions of Transistors
END OF TRADITIONAL
SCALING ERA ~ 2003

6. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Nano CMOS Technology
Technology nodes ( min. feature size / gate length)
scaling down as : 350 nm, 250 nm, 180 nm, 150 nm, 130
nm, 90 nm, 65 nm, 45 nm, 30 nm, 22 nm.
Effective gate oxide thickness (EOT) shrinking from
80 nm to 1 nm (10 A)/ 4 to 5 atomic layers.
Subthreshold leakage current and GATE DIRECT
TUNNELING CURRENT increase significantly. GDTC
was not considered in previous designs.
Metal and polySi interconnect line width shrink
below 100 nm. Contact holes and vias approach 100-
200 nm. Interconnect resistance and RC delay
increase appreciably.
Copper metallisation, CoSi / NiSi and chemical-
mechanical polishing/planarisation (CMP) help in
reducing resistance and RC value. But it reaches a
limit.

7. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Feynman’s Vision (1959)
“There is plenty of room at the bottom”
“The entire encyclopedia could be written
on the head of a pin”
“ ……fabricate a motor with a volume less
than 1/64 of an inch on a side”

8. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Advantages:
 Size reduction
 Cost effective
 Improved sensitivity
 Integration with signal conditioning circuit
 Low power consumption
Due to the miniature size and complex geometry of the 3-D
mechanical structures, fabrication of MEMS devices is clearly
beyond the means of traditional machine tools.
Evolved from silicon planar integrated circuit technology
MEMS (Micro Electro Mechanical Systems) is the integration of
mechanical and electrical components on a common substrate
to produce a system of miniature dimensions through the use of
microfabrication technology. Operate in different energy
domains (thermal, mechanical, chemical, magnetic, electrical,
optical, biological energy domains) to produce/actuate electrical
signal.

9. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MEMS – Tiny Transducers
Accelerometers,
Gyroscopes,
Pressure sensors,
Position Sensors,
Micro Gears,
Micro Hinges,
Drug delivery,
Microgrippers,
Microfluidics,
Lab on a Chip,
Gas Sensors,
Bio-MEMS
Fluxgates,
Hall Effect sensors,
MAGNETIC SENSORS
MOEMS
Micro mirrors,
Micro Lens,
RF-MEMS
Tunable Inductors,
RF Switches.
Flow sensors,
Micro heaters,
Micro Reactor,
Mechanical
Biological/
Chemical
Magnetic Optical
Communication
Thermal
Untreated

10. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MEMS are interdisciplinary in their design, fabrication,
and operation. They encompass many aspects of
Engineering
 Mechanical (structures and phenomena: bending, deflecting, oscillations,
vibrating; fluid dynamics…)
 Electrical (electrical signals: detected, generated, processed;
optoelectronics; Integrated circuits and devices…)
 Chemical and Biochemical (reactions, processes, and kinetics… of many
systems including living organisms)
Science
 Physics and Biophysics (external world vs. materials/properties including
living organisms at macro and nano scale)
 Chemistry, biochemistry, and physical chemistry (step more from
corresponding engineering disciplines towards basic answers)
 Biology (macro and nano effects in plants, animals, and humans observed
by smart transducers)
Technology
 Macro ex. Fluidics and large mechanical structures
 Micro ex. µm scale dimension of transducers, and
 Nano ex.nanodevices CNT, nanoprobes ….)

11. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Integration of Various Science and Engineering Fields
Very powerful performance possible but difficulty in
realization comes due to the interdisciplinary character of
MEMS

12. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Building Blocks
Major components in MEMS systems include
Design
 Much more difficult than IC designs due to the interdisciplinary
character of MEMS
 Design includes packaging
 Packaging is one of the most challenging step both in design and realization
 Transducers must be integrated with electronics
 Integration with ICs is another challenge for MEMS due to difficult issues of
process compatibility
Fabrication
 Silicon technology is widely used in MEMS with new step added
 Dimensions are usually much larger than those in ICs even for nano-
transducers. To feel NANO you do not need to be in the nano-scale size!
 Other materials are included to perform required functions of transducers
 MEMS are frequently integrated with fluidics (polymers, glass…)
Materials
 Materials that can perform required functions (thermo, piezo-,
magneto-resististance…)
 Interaction with fluidics (half-cell potential, corrosion…)

13. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MICROMACHINING
Micromachining is defined to be a process technology for
shaping silicon or other material to realize 3-D MEMS
structure by chemical etching technique
 Evolved from silicon planar integrated circuit technology
 Completely different from conventional machining process
Micromachining has become a dominant and fundamental
technology in the fabrication of microsensors,
microactuators and microstructures
MEMS devices are fabricated by Micromachining
process.

14. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
ADVANTAGES of MEMS

15. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MICROCHIP AND MEMS DEVELOPMENT

16. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MICROFABRICATION PROCESS

17. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Basics of Lithography
Lithography is used to describe as, a process in which a layer of
material, sensitive to photons, electrons or ions, is selectively
exposed following a particular pattern/image to transfer that pattern
to the wafer.
“Lithos” (stone) + “graphein” (write) = Lithography ,
which means “ writing a pattern on stone”
 Why lithography?
 Device miniaturization to achieve the technology goals.
 Flexible technique.
 Enhanced properties, i.e. transport phenomenon,
 Fantastic characteristics, quantum confinement effect.

18. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Standard Photolithography:
Photolithography
apply resist
mask alignment/
exposure
develop
etching
resist removal
• Spin coat radiation
sensitive polymer -
Resist
• Expose layer (through
mask or direct write)
• Develop
• Etch away or deposit
material
Basics of Lithography

19. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Resolution Limit:
Contact Lithography,
Projection
Lithography: directly
dependent on
wavelength
Decreasing feature
sizes require the use of
shorter λ.Can’t go farther: From this point we
need EBL.
Why e-beam lithography?
Optical effect: Diffraction
Intensity profile produced by a
spatially coherent beam as it passes
through a slit

20. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Nanolithography
Conventional EB and Ion Beam Direct Writing / X-
ray Lithography are highly capital intensive, not
suitable for batch processing
Alternate lithography techniques for batch
fabrication :
Nanoimprint Lithography : Stamp-and-Repeat /
Stamp-and-Flash
Microcontact Printing Lithography
Scanning Electron Probe Nanofabrication

21. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
electronic
interface
computer
Expose:
The E-beam is turned on/off and
directed in a prearranged pattern over
the surface of the resist.
There are two types of scanning
system:
(1)Raster scan,
(2) vector scan.
Basic process for EBL cont..

22. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Basic process for EBL
Surface preparation E-resist coating
Soft bake Expose
Develop
Hard bake
Inspection
Metal deposition/Etch Resist Strip Final Inspection
Typical operations cycle of EBL

23. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Proximity effect
 Backscattering causes the
electron beam to broaden and
expose a large volume of resist
then expected.
 The proximity effect places a
limit on the minimum spacing
between pattern feature. This is
a limiting factor of high
resolution lithography.
 Depends on the pattern density
and the substrate material, as
well as parameters of the EBL
exposure.
 Acceleration voltage
 Electron dose
Parametric effect cont..

24. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Why Silicon for MEMS ?
 The largest silicon micromachining applications to
date, pressure and acceleration sensors, have
been enabled primarily by two factors:
 Excellent mechanical performance of silicon
enabling it effectively to replace a majority of all
other sensing technologies
 The existing infrastructure of the mainstream IC
industry, enabling development of products
offering an unmatched price-to-performance ratio.

25. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Mechanical performance of silicon
Silicon and its derivatives (SiO2, Si3N4) are some of the best
electrically characterized materials in the world.
Based on known characterization of silicon, it can be classified
as the best material for mechanical sensors. Silicon mechanical
strength is comparable to (even higher than) steel, but at a
lower density and better thermal conductivity.
Parameter Steel Silicon Units
Yield strength 4.2 (max) 7.0 1010
dyne cm-2
Young’s modules 2.1 1.9 1012
dyne cm-2
Density 7.9 2.3 G cm-2
Thermal
conductivity
0.97 1.57 W cm-10
C-1

26. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Why Silicon for Microsensors ?
 Lack of mechanical and thermal hysteresis, and long-term drift: For all
mechanical sensors the measure of excellence and performance limit is
defined by the achievable mechanical and thermal hysteresis, and long-
term stability. Silicon delivers good performance on each low-cost wafer,
thanks to its extremely pure, defect-free crystalline structure.
 High sensitivity to stress: The piezoresistive effect in silicon has a stress
sensitivity two orders of magnitude larger than that of metal strain
gauge, which enables fabrication of the high output devices with simple
electronics
 Batch manufacturability: The capability of manufacturing completed
mechanical structures simultaneously on multiple wafers, each carrying
multiple devices, forms the revolutionary aspect of the silicon
micromachining technology - batch manufacturability.
Besides the excellent performance, silicon brings significant support
from the established mainstream electronic industry, specifically:
Access to ultra-pure material
Access to advanced semiconductor processes
Availability of the high volume packaging technologies
Access to high volume manufacturing equipment
An available base of educated silicon processing technologists

27. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Unique Processes for MEMS
In addition to that
Double Sided Alignment and Lithography
Etch – Stop Processes
Deep Reactive Ion Etching (DRIE)
Sacrificial Layer Etching
Wafer Bonding
Deposition of Special Films
LIGA / Micromolding / NIL / MCP
Special Packaging Techniques
Virtually all micro fabrication processes used for ICs are used for silicon-
based MEMS and microsystems
 Photolithography / Electron Beam Lithography
 Diffusion / Implantation/ Oxidation
 CVD / LPCVD / PECVD
 Vacuum Deposition / DC-RF Sputtering
 Wet Chemical Etching – Isotropic / Anisotropic
 Dry Etching – Plasma, RIE, RIBE

28. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
 Bulk Micromachining
 Surface Micromachining
 Wafer Bonding
 LIGA/SLIGA and LIGA-Like
 Others
i) 3-D Lithography
ii) Laser Micromachining
MEMS Technologies

29. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Silicon Micromachining
Bulk Micromachining:
Using single crystalline silicon wafer, the bulk material
of the substrate along thickness direction is dissolved /
etched by wet chemical etchant to realize various 3-D
micromechanical structures
 Device thickness is controlled by etching/ diffusion
 Mechanical properties of bulk silicon is preserved
 Alignment required for top and bottom side of wafer
 Require etch stop mechanism
Micromachining
Bulk micromachining
Surface micromachining

30. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Bulk Micromachining
Bulk micromachining along crystallographic
planes

31. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
This technology is based on depositing and etching
structural and sacrificial films. After deposition of
thin film, sacrificial layer is etched away, leaving a
completely assembled microstructure
 Maximum possible thickness of the microstructure is limited to
that of the deposited film
Surface Micromachining

32. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Surface Micromachining

33. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
MICROSYSTEMS

34. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Integrated Microsystems
Miniature Mechanical Systems with Micron Feature Size
Batch Fabricated – No Assembly
Exploits Microelectronics Infrastructure
Common Technology Base for Sensors, Actuators and Electronics

35. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Integrated Microsystems

36. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Microsystems Technology
Motivation :
Quality factor → improvement in quality X reduction in costs
(per element)
≈ 107
(for microelectronics), 102
(technology in steel product
Thus “technology leap” given to microelectronics
Questions ?
Would it not be possible the implementation of
microelectronics in industrial scale to non-electric problems
as well ( mechanical, optical or fluidic structures)?
Would it not be possible to develop the analog of the
microprocessor, i.e. the “micro-systems”?
Would it not be possible to have this systems attain the
maximum level of performance?

37. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Major Problems
Interface - a great number of possible forms of energy
and information transmissions have to be coped with.
A great deal of novel technique has to be developed in
micro systems technology in order to handle information
transmission by electric, acoustic, optical, thermal, fluidic
or other means into the systems and out of the systems.
When the systems is applied in medical engineering, e.g.
as a minimally invasive therapeutic system, drugs or
biological substances must be handled by the system.
These requirements mean a great challenge to the
packaging and connection techniques in micro systems
technology.

38. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Implantable wireless microsystems
 Incorporates MEMS based transducers
 Have on-board power supply or powered from outside by
inductive coupling
 Communicate bi-directionally through RF interface
 Have on-board signal processing capability
 Constructed using biocompatible materials
 Use advanced packaging techniques
MICROSYSTEM COMPONENTS
Transducers are interfaces between tissue and readout circuitry and
their performance is critical to the success of overall microsystem.
Long term stability is an issue.
Transducers suffer poor S/N ratio, thus, requires on-board interface
electronics. Post or integrated CMOS processing or hybrid processing
technique is used for fabrication of the microsystem. Power
consumption is a major consideration particularly for implantable
devices, thus DSP is done outside the body.

39. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Packaging and encapsulation is a challenging task. It must
accomplish to 1) product electronics from harsh environment while
providing access window for transducer to interact with the desired
measurand, 2) Protect body from hazardous materials in
microsystem. The degree of protection required for implantable
systems depends on required life time of the device. Conventional
packaging technique may not be suitable like glass-metal sealing is
not batch scale technique, titanium encapsulation is not suitable for
data transmission.
Choice of power source depends on implant life time, system power
consumption, mode of operation (continuous or intermittent) and
size. Battery is used for low power system with limited lifetime.
Inductive powering is an alternative approach for large power
requirement. Fuel cell and thin film batteries are being explored.
Bidirectional wireless communication is essential for implantable
microsystem. Various modulation (AM, FM, and other pulse
modulation) methods are used for inward and outward data
transmission. The choice of transmission frequency is a trade off
between adequate miniaturisation and tissue loss.
MICROSYSTEM COMPONENTS

40. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Resonance shift due to single Cell
A gold dot, 50 nm fused to the end of a
cantilevered oscillator. A one-molecule-
thick layer of a chemicaldeposited on the
gold adds a mass of about 6 attograms,
which is measurable.
Silicon neural probe arrays
Kewley et al, Sensors
Actuators 58, 1997
Cell-based biosensor with
microelectrode array
Electrostatic micromotor
Fan Long-Sen et. al, Sensors
Actuators 20, 41- 47
Silicon micro-needle
Choi et al, Biomed. Microdev.,
2007
www.hgc.cornell.edu/biomems.html
Glimpse of BioMEMS

41. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
BioMEMS Activity @ IIT Kharagpur
Prof-In-Charge: Dr. Soumen Das, Associate ProfessorProf-In-Charge: Dr. Soumen Das, Associate Professor
School of Medical Science & Technology, I. I. T. Kharagpur, INDIA 721302School of Medical Science & Technology, I. I. T. Kharagpur, INDIA 721302
E-mail: sou@smst.iitkgp.ernet.inE-mail: sou@smst.iitkgp.ernet.in
Present R & D focusPresent R & D focus Flexible device/electronic forFlexible device/electronic for
biomedical app.biomedical app.
Label-free Separation of BiologicalLabel-free Separation of Biological
CellsCells
Funding/Collaboration:
NPMASS, Govt. of India; ISRO, India; TI India,
Bangalore
The real world dealing more with chemical, biological,
mechanical rather than electrical domain only necessitates
biomedical sensors involving 3D bio-microelectromechanical
(BioMEMS) systems for transforming sensible bio-signals into a
measurable output.
MEMS flow sensor
Ni-Cr resistor
on polymer
Technology for fluid flow at low power
Micro-thruster for generation of thrust by the phase change of
fluid
Silicon MEMS sensor for healthcare monitoring
Accelerometer
Microfluidic system for cell manipulation
Microfluidic chip
Flexible electronics
Micro-structuring of polymer -Array of micropillars on SU-8, PDMS
Deposition and patterning of Al, Au
and NiCr thin films on flexible
polymer
for BioMEMS applications
Development of MEMS Based Flexible Flow Sensor for Health Care
Monitoring
Heater
Substrate
Catheter
Artery (Aorta)
Catheter with sensor
against blood flow
direction
Flexible device concept / sensor bending
Wrapped Sensor
Thermocouple
Electric
Probes
Microheater
Fabricated sensor
Flow Measurements
Simulated temp. distribution
Sensor Test Setup
Cells are separated based on their electrical property
which changes with disease progressions, viability of cells
Electrical Characterization of
Cells
Applications:
•Cellular behavior
•Disease detection
•Cytotoxicity effect
•Cell signal
transduction
IEEE Trans Biomed Eng 2013. DOI:10.1109/TBME.2013.2265
319
IEEE J of MEMS, 2013. DOI 10.1109/JMEMS.20
IOP, JMM, 19, 2009;Microsystem technology,15, 2009

42. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
In this era of “think small,” one would intuitively simply scale
down the size of all components to a device to make it small.
Unfortunately, the reality does not work out that way.
It is true that nothing is there to stop one from down sizing the
device components to make the device small. There are,
however, serious physical consequences of scaling down
many physical quantities.
Scaling laws that will make engineers aware of both positive
and negative physical consequences of scaling down
machines and devices.
At very large scale physical problems are handled using relativity,
where as at very small scale it is handled by quantum mechanics.
Relative magnitude of different forces changes with the
characteristic size of a system.
Effect of miniaturisation: Scaling Laws

43. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
WHY SCALING LAWS?
Miniaturizing machines and physical systems is an ongoing effort in
human civilization that comes from our market demands for: Intelligent,
Robust, Multi-functional and Low cost consumer products has become
more stronger than ever.
The only solution to produce these consumer products is to package
many components into the product –
making it necessary to miniaturize each individual components.
Miniaturization of physical systems is a lot more than just scaling down
Device components in sizes.
Some physical systems either cannot be scaled down favorably, or cannot
be scaled down at all!
Scaling might favor smaller devices ( e.g., faster, less power, etc) but it
might also disfavor miniaturization (e.g., smaller power sources last less
long and small actuators exert less force).
Scaling laws thus become the very first thing that any engineer would do
in the design of MEMS and microsystems.
It is of two types: 1. Scaling in Geometry: Scaling of physical size of objects
2. Scaling of Phenomenological Behavior: Scaling of both size & material
characterizations

44. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Effect of miniaturisation: Scaling Laws
Scaling laws are rules used to predict how a system will behave as it changes its
size. Scaling laws deal with the structural and functional
consequences of changes in size or scale among otherwise similar
structures.The three parameters that can be changed when the
size of a structure is increased/decreased are:
Dimensions (e.g., thicker walls)
Materials (e.g., from brick to steel)
Design (e.g., from compression to tension elements)
Scaling in Geometry:
Volume (V) and surface (S) are two physical parameters that are frequently
involved in machine design.
Volume leads to the mass and weight of device components.
Volume relates to both mechanical and thermal inertia. Thermal inertia
is a measure on how fast we can heat or cool a solid. It is an
important
parameter in the design of a thermally actuated devices
Surface is related to pressure and the buoyant forces in fluid mechanics.
For instance, surface pumping by using piezoelectric means is a practical
way for driving fluids flow in capillary conduits.
When the physical quantity is to be miniaturized, the design engineer must
weigh the magnitudes of the possible consequences from the reduction on

45. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Volume of body increased, its surface area does not increase in same
proportion, but in proportion to 2/3 power of volume
If linear dimension is decreased by 10 times, its area (S) is decreased
by 100 times and volume (V) is decreased by 1000 times. S ~ V2/3
,
Thus smaller bodies have, relative to their volume larger surface area
than larger bodies of same shape.
For elephant S/V ~ .0001/mm, butterfly 0.1/mm. It requires little
energy and power, and thus low consumption of food to fly, whereas
elephant has huge appetite for food to generate sufficient energy for
even small movement.
Linear extrapolation of length comes easy to us, but we are quickly at a
loss when considering the implications that shrinking of length has on
surface area to volume ratios (S/V) and on the relative strength of
external forces (actuator mechanisms) e.g. capillary tubes: weight scales
as l3
and surface tension as l.

46. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
Scaling laws:
Time – l0
Mass – l3
Gravitational force - l3
Friction - l2
Surface tension - l1
Velocity - l1
Diffusion - l1/2
Thermal loss - l2
Cantilever deflection
δ
ρ
δ 2
2
4
/
)(2
)(3
s
st
slg
==
Assuming all dimensions are equally scaled down,
2
4
2
3
t
lgρ
δ =
Deflection shrinks faster than device dimension
Mechanical Resonance
1
0
31
0
,
2
1
−
∝
∝∝
=
Lf
LmLk
m
kf
π
1
0
53
0
,
2
1
−
∝
∝∝
=
Lf
LILk
I
kf
π
Cantilever Beam Torsional resonator

47. School of Medical Science and Technology, Indian Institute of Technology -Kharagpur
 MEMS and microsystems fields will lead to mature products in
a number of industrial applications as well as provide
inspiration for research in unexplored areas.
 Diverse set of materials used in microsystems is steadily
expanding to take advantage of properties ranging far beyond
those found in silicon alone.
 Critical issues associated with fabrication and packaging
needs to be examined in depth to achieve high throughput and
yield.
 Both fabrication flows and unit processes still involve
considerable innovation.
 MEMS packaging is also more difficult than in
microelectronics because many sensors must directly contact
the environment they are trying to measure, and for many
devices, packaging at the wafer level is essential both for
fabrication yield and for operating performance.
Conclusions