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2.008-spring-2005 S.G. Kim 1
2.008 Design & Manufacturing II
Spring 2005Sang-Gook Kim
MEMS/Nano I
2.008-spring-2005 S.G. Kim 2
Nano/Micro in MEMy Office: 1-310, [email protected], MEMS/Nanomanufacturing
Small is not small enough?
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Nano/Micro in MEFluidics, heat transfer and energy conversion at the micro- and nanoscaleBio-micro-electromechanical systems (bio-MEMS)Optical-micro-electromechanical systems (optical-MEMS)Engineered nanomaterialsNano-Manufacturing
Course 2A (Nanotrack)Micro/Nano Group in MEhttp://web.mit.edu/nanomicro/Index.html
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Moore’s Law
Year of introduction Transistors
4004 1971 2,250
8008 1972 2,500
8080 1974 5,000
8086 1978 29,000
286 1982 120,000
386™ 1985 275,000
486™ DX 1989 1,180,000
Pentium® 1993 3,100,000
Pentium II 1997 7,500,000
Pentium III 1999 24,000,000
Pentium 4 2000 42,000,000
The number of transistors per chip doubles every 18 months.
– Moore’s Law
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Why shrink things?
Use less materials, energy, powerFaster response, better sensitivity, simpler, better accuracy reliabilityPerformance/$Minimally invasive..
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Why shrink things?
Shock and impactScale and form factorLoad carrying capability
Spider silk v.s. steel
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Frog, Water Strider, Gecko
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Learn from the nature, but never try to mimic the nature.
Biomimetic researches. K. Autumn, www.lclark.edu
DNA~2-1/2 nm diameter
Things Natural Things Manmade
MicroElectroMechanical devices10 -100 µm wide
Red blood cellsPollen grain
Fly ash~ 10-20 µm
Atoms of siliconspacing ~tenths of nm
Head of a pin1-2 mm
Quantum corral of 48 iron atoms on copper surfacepositioned one at a time with an STM tip
Corral diameter 14 nm
Human hair~ 10-50 µm wide
Red blood cellswith white cell
~ 2-5 µm
Ant~ 5 mm
The Scale of Things -- Nanometers and More
Dust mite
200 µm
ATP synthase
~10 nm diameter Nanotube electrode
Carbon nanotube~2 nm diameter
Nanotube transistor
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21st Century Challenge
Combine nanoscale building blocks to make novel functional devices, e.g., a photosynthetic reaction center with integral semiconductor storage
Th
e M
icro
wo
rld
0.1 nm
1 nanometer (nm)
0.01 µm10 nm
0.1 µm100 nm
1 micrometer (µm)
0.01 mm10 µm
0.1 mm100 µm
1 millimeter (mm)
1 cm10 mm
10-2 m
10-3 m
10-4 m
10-5 m
10-6 m
10-7 m
10-8 m
10-9 m
10-10 m
Visi
ble
Th
e N
ano
wo
rld
1,000 nanometers =
Infr
ared
Ultr
avio
let
Mic
row
ave
Soft
x-ra
y
1,000,000 nanometers =
Zone plate x-ray “lens”Outermost ring spacing
~35 nm
Office of Basic Energy SciencesOffice of Science, U.S. DOE
Version 03-05-02
DOE 2001
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Micro to Nano20th Century - Microelectronics and Information Technology
Semiconductors, computers, and telecommunication
21st Century - Limits of Microsystems Technology--- Nanotechnology
Moore’s lawHard disc drive
John Bardeen, Walter Brattain, and William Shockleyat Bell Laboratories, “First Transistor”
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Limit of Optical LithographyW = k λ/NA (Rayleigh Eqn.) In 1975, 405 nm (Hg H-line) at an NA of 0.32, a line width of 10 µm deep-UV (248-nm), 193 nm, 157nm
Table 1: Wavelength "Generations"Intel Road Map
Year Node Lithography1981 2000nm i/g-line Steppers1984 1500nm i/g-line Steppers1987 1000nm i/g-line Steppers1990 800nm i/g-line Steppers1993 500nm i/g-line Steppers1995 350nm i-line -> DUV1997 250nm DUV1999 180nm DUV2001 130nm DUV2003 90nm 193nm2005 65nm 193nm -> 157nm2007 45nm 157nm -> EUV2009 32nm and below EUV
193 nm immersionlithography
NanoimprintingSoft LithographyDip Pen LithographySPM-based patterning
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Immersion Lithography
substratephotoresist
UV Lightmask
Exposure
Developing
Air, n=1
Water, n=1.47
W = k λ/NA (Rayleigh Eqn.)
NA= n sin α
193nm, sin a ~0.93, k1~0.25
W in Air? Immersion?
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Aerial density, hard disk
Superparamagnetic Effect“a point where the data bearing particles are so small that random atomic level vibrations present in all materials at room temperature can cause the bits to spontaneously flip their magnetic orientation, effectively erasing the recorded data. “
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MEMS (Microelectromechanical Systems)
Intergrated systems of sensing, actuation, communication, control, power, and computingTiny,Cheaper,Less power, material..New functions!!! (chemical, bio, µ-fluidic, optical, …)
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MEMSMEMS MEMSTechnologiesOptical MEMSRF MEMSRF MEMSData StorageBio. MEMSPower MEMSMEMS for ConsumerElectronicsMEMS In Space
MEMS for Nano.
Courtesy: Sandia national laboratory
MaterialsProcessesSystems
http://www.memsnet.org/mems/what-is.html
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History of MEMS
Y.C.Tai, Caltech
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Tiny ProductsAirbag sensors: Mechanical vs. MEMSDLP (Digital Micromirror Array)DNA chipOptical MEMS
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Tiny ProductsAirbag sensors: Mechanical vs. MEMS
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Tiny ProductsDLP (Digital Micromirror Array)
DLP106 micromirrors, each 16µm2, ±10° tilt
(Hornbeck, Texas Instruments DMD, 1990)
TM
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Segway
-Tilt-Rotation
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Vibrating Gyroscope
By Charles Stark Draper LaboratoryBy Charles Stark Draper Laboratory
x
z
y
CoriolisAcceleration
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substrate
magnetic layer
EM coil
conductive substrate
conductive layer
insulator
substrate
patterned resistive layer
ForceForce
Force
ApplyCurrent
ApplyVoltage
Actuation of MEMS devices
Electrostatic actuation
Thermal Actuation
Electromagnetic force
ApplyCurrent
substrate
patterned resistive layer Force
Piezoelectric Actuation
ApplyCurrent
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Electrostatic Comb Drive/sensing
Paralle Plate CapacitorCapacitance=Q/V=ε A/dε Dielectric permittivity of air
Electrostatic Force = ½ ε (A/d2).V2
Pull-in point: 2/3 d
d
K
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Comb Drive
C= ε A/d = 2n ε l h/d∆C = 2n ε ∆l h/dElectrostatic force
Fel = ½ dC/dx V2 = n ε h/d V2
∆l
d
V
x
l
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Suspension mode failures
x
y
x
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Comb Drive Designs
DC Bias
AC Signal(180° phase shift)
AC Signal
Grating beamsFlexuresElectrostatic comb-drives
linear
rotational
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ADXL 50 accelerometer
Capacitive sensing
Comb drive
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Swing Analyzer withTri-axial accelerometer
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Begin with a bonded SOI wafer. Grow and etch a thin thermal oxide layer to act as a mask for the silicon etch.
Etch the silicon device layer to exposethe buried oxide layer.
Etch the buried oxide layer in buffered HF to release free-standing structures.
Si device layer, 20 µm thick
buried oxide layer
Si handle wafer
oxide mask layer
silicon
Thermal oxide
SOI (Silicon on insulator)
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Microfabrication process flow
Single-mask process
IC compatible
Negligible residual stress
Thermal budget
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Process Flow
Deposition Lithography Etch
Wafers DevicesPhoto resist coatingPattern transferPhoto resist removal
OxidationSputteringEvaporationCVDSol-gelEpitaxy
Wet isotropicWet anisotropicPlasmaRIEDRIE
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Micromachining processes•Bulk micromachining
•Surface micromachining
•Bonding
•LIGA
• x-ray lithography, electrodeposition and molding
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LIGA (lithographie galvanoformung abformtechnik)
x-rays
Mask
PMMA
Wafer
• X-ray on PMMA, electroplating metal and molding polymer• High aspect ratio >100:1, up to 1000 µm
Ni Molded Polymer
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LIGA parts
Sandia National Laboratory
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BondingSilicon Direct Bonding (Silicon Fusion Bonding)Anodic Bonding(Electrostatic Bonding, Field Assisted Thermal Bonding)Intermediate Layer Bonding
MIT Microturbine Project
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Bulk, Surface, DRIEBulk micromachining involves removal of the silicon wafer itself
Typically wet etchedInexpensive equipmentsIC compatibility is not good.
Surface micromachining leaves the wafer untouched, but adds/removes additional thin film layers above the wafer surface.
Typically dry etchedExpensive equipmentsIC compatibility, conditionally.
Polysilicon
“Anti-stiction” bumpp-Si
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Bulk machiningSquare nozzlePumping ink?
Piezoelectric ink jet
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Ink jet printer – A quasi-MEMS case
Thermal jet by HPSuperheat ink 250oCPeak pressure 1.4 MPa
Refills in 50µs
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Thermal ink jet
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Pressure sensor
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Surface MicromachiningDeposit sacrificial layer Pattern anchors
Deposit/pattern structural layer Etch sacrificial layer
Si
PSGBy HF
PolybyXeF2
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Surface micromachining
Structure sacrificial etchantPolysilicon Silicon dioxide HFSiNx PSG HFSilicon dioxide polysilicon XeF2SiNx polysilicon XeF2Aluminum photoresist oxygen plasma
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Residual stress gradients
More tensile on top
Less tensile on top
Just right!
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VGA640 X 480307,200 pixels
50 µm
Human Hair
XGA1024 X 768
786,432 pixels
Micromirror Arrays
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MaterialsMetals
Al, Au, ITO, W, Ni, Ti, TiNi,…Insulators
SiO2 - thermally grown above 800oC or vapor deposited (CVD), sputtered. Large intrinsic stress
SixNy – insulator, barrier for ion diffusion, high E, stress controllable
Polymers: PR, SU-8, PDMS
Glass, quartzSilicon
stronger than steel, lighter than aluminumsingle crystal, polycrystalline, or amorphous
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Silicon
Atomic mass average: 28.0855Boiling point: 2628KCoefficient of linear thermal expansion: 4.2. 10-6/°CDensity: 2.33g/ccYoung’s modulus: 47 GPaHardness scale: Mohs’ 6.5Melting point: 1683K Specific heat: 0.71 J/gK
Electronic grade silicon99.99999999% purity
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MaterialsSingle crystal silicon
Anisotropic crystalSemiconductor, great heat conductor
Polycrystalline silicon – polysiliconMostly isotropic materialSemiconductor
SemiconductorElectrical conductivity varies over ~8 orders of magnitude depending on impurity concentration (from ppb to ~1%)N-type and P-type dopants both give linear conduction.
Two different types of dopingElectrons (negative, N-type) --phosphorusHoles (positive, P-type) --boron
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Silicon Ingot
Czochralski (CZ) method
Float Zone (FZ) method.
1” to 12” diameterhttp://www.msil.ab.psiweb.com/english/msilhist4-e.html
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Miller indices
[100]
[010]
[001]
ab
c
[abc]
•[abc] in a cubic crystal is just a directional vector
•(abc) is any plane perpendicular to the [abc] vector
•(…)/[…] indicate a specific plane/direction
•{…}/<…> indicate equivalent set of planes/directions
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Crystallographic planes
[100]
[010]
[001]
(100)
{100}(001)
(010)
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Crystallographic planes
[100]
[010]
[001]
(110)(111)
(001)
54.74o
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Wafers of different cuts
(111) (100) (110) (111)
(100) (111)
Bulk Si
54.74o
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Anisotropic wet etching
When a (100) wafer with mask featuresOriented to <110> direction is placed in an anisotropic etchant.
A square <110> oriented mask feature results in a pyramidal pit.
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Pressure sensor