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, sangkim@mit.edu, MEMS/Nanomanufacturing

Small is not small enough?

2.008-spring-2005 S.G. Kim 3

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

O O

O

OO

O OO O OO OO

O

S

O

S

O

S

O

S

O

S

O

S

O

S

O

S

PO

O

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

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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