Micro Electro Mechanical System:Micro Electro Mechanical System:MEMS

Shuji TanakaTohoku University, Sendai, JapanTohoku University, Sendai, Japan

MEMS Used in Our Daily Life

MEMS for motion detection and controlAccelerometer usedin airbag systems(Analog Devices)

Yaw rate (gyro) sensor usedfor car stability control (Toyota)

3-axis accelerometer used in Nintendo“Wii” (STMicroelectronics)

MEMS Used in Our Daily Life

MEMS for imagingNEC Weight: 1 kgNEC g g

nch

1 i

Printing head

Digital Micromirror DeviceDigital Micromirror Device(DMD) used in imageprojectors Thermal ink jet printer head (Fuji Xerox)

Manufacturing Process of MEMS

MEMS is produced by wafer-level batch process based on semiconductor fabrication technology

Repeated

Si waferDepositionPhotolithographyEtching

Wafer-level test DicingWiring Packaging Final testChip

MEMS Fabrication Technology

X-ray exposure Resist removalHigh-aspect-ratio structuring

110 µm Development Injection molding

170 µm

Electroplating Demolding

515 µm

p g Demolding

SF6 C4F8 SF6 C4F8

Etching Passivation Etching Passivation

LIGA (Lithographie, Galvanoformung，Abformung)

Deep reactive ion etching: DRIE(Bosch process)

MEMS Fabrication Technology

1. Deposition and patterning 2. Deposition and pattering

Sacrificial layer etching and lifting-up processg

4. Sacrificial etching3. Electrode fabrication

50 µm

Electrostatic motor(UB Berkeley)SiO sacrificialPoly Si Poly Si

Poly 1OxidePoly 2

(UB Berkeley)SiO2 sacrificial layer

Poly-Si structure

Poly-Si structure

Sacrificial layer etching and lifting-up

Micro optical bench fabricated by lifting-up technology (UCLA)

MEMS Fabrication Technology

1 Si micromachining

Use of variety of materials (e.g. quartz, SiC, CNT)

1. Si micromachining

2. SiC deposition

3 P li hi3. Polishing

4. SiC-SiC bonding SiC micro-mold f l30 µm

5. Si etching

C b

for glass press molding

CNT Carbon source

CNT

1 mm

Si

Catalyst

Electric field

CNT

Si

Quartz tuning fork fabricated by DRIE CNT grown at the tip of Si probe

CatalystSi

MEMS Fabrication Technology

5 µm

3D and nano fabrication

5 µm

ø1

mm

ProbeAnodic oxidation

Silicon

Oxide

3-axis accelerometer on

Probe lithography

Silicon 3 axis accelerometer on ø 1mm Si sphere(Ball Semiconductor)

Applications: Information & Communication

Ball lens

ShutterShutter

Optical fiber

Actuator

1 mm

Moritex & Multi-channel variable optical attenuator (VOA)

Recording

Tohoku Univ.

gprobe

100 µmR di 30

0 μm

Pressure sensor Si clock oscillator (SiTime)Multi-probe data storage

Recording media

3

Applications: Highly-Sensitive Sensors

Sample (CNT)Electrostatic levitation

Silicon cantilever

(CNT)Electrostatic levitationand rotation of ø 4mm or 1 mm ring

with several tennm thickness

Resonating Si cantilever

Rotating ring gyro sensor (Tokimec)

Resonating Si cantileversensor for highly-sensitivemass and force detection

Applications: Energy and Power

Actuator メタノール＋空気MeOH/H2 + Air20 mm

改質ガス

メタノール水溶液MeOH + H2OReformed

gas

Pressure balance mechanism

6 m

m

排気ガス

1 cmBoss

Exhaust gas

Microvalvefor portable Mi f l f

25 mm5.61 cm

for portable fuel cells

Micro fuel reformer(Panasonic EW & Tohoku Univ.)

10 mm

Pressure sensorMicro gas turbine (Tohoku Univ. & IHI)

Application: Medical Tools

ReserverMicrovalve

Microchannel

Optical fiber Sensor

Connector

Reserver

Micropump

Medicine screening chip (µTAS)Optical fiber pressure sensor

SensorMicropump

Shape memory alloy actuator Ion sensitive

FET (ISFET)Pressure sensorActive catheter and bloodpressure sensor Pylori germ sensor (Nihon Koden)

FET (ISFET)

Applications: Aerospace

Micro tribo-coating system for ball bearing(Courtesy of Prof. Adachi, Tohoku Univ.)

Solid propellant

Ignition heater

Circuit

Nozzle

Ignition heater

ø 0 8 mm

Micro solid rocket array thruster (Tohoku Univ. & ISAS/JAXA)Thrust ø 0.8 mm

Inertia Sensors (Analog Devices)

Safety steel ball sensor

Detection circuit

ADXRS150 2-axis gyroG sensor

125 μm

1.3 μm

ADXL202 accelerometer used for airbags

2 μm

Integrated Accelerometer (Analog Devices)

Circuit(NPN NMOS)

Poly Si sensor structure

On-CMOS structureA tiny capacitance changecorresponding to 1 6×10-4

Judy et al., Hilton Head Island WS 2004, 27

(NPN, NMOS) corresponding to 1.6×10 4

Å displacement (gyro) isdetectable by embeddedi t t d i it

Poly-Si sensor structure on 3 µm-ruled, W-metalized BiCMOSPoly Si annealing at 1100 °C for 30 min Impossible to fabricate in LSI foundry

integrated circuit.

Poly-Si annealing at 1100 C for 30 min, Impossible to fabricate in LSI foundrySOI MEMS structureSensor structure release Trench isolationfrom this trench Sensor structure Circuit

SOI

Single crystal Si sensor structure beside 0.6 μm-ruled, Al-metalized CMOSCompatible with advanced LSI from LSI foundry, Low space efficiency

Digital Micromirror Device (TI)

Hornbeck, IEDM 2007, 17-24

• 10~16 μm square micromirrors• ~2 μs response time• 8.5 V driving voltage• ±12 ° tilt angle• 848×600 = 508800 pixels for SVGA p

~ 1280×1024 = 1310720 pixels for SXGA

Metal Surface Micromachining for DMD (TI)

0.8 µm CMOS

AlResist

ResistCMOS

address circuit

(SRAM) Al SiO2

1. Sacrificial resist layer

5. Sacrificial resist layer and Al mirrory

SiO2 Al

2. Al and SiO2 mask for hinges

6. Sacrificial resist etching

3 Al and SiO mask for beams

g

Kessel et al.,

3. Al and SiO2 mask for beams

Proc. IEEE, 86 (1998) 1687 4. Al etching for beams and hinges Hornbeck, IEDM 2007, 17-24

Memory Effect of Metal HingesA. B. Southeimer, IEEE 40th Annual International Reliability Physics Symposium, Dallas, TX, 2002

e s

Test duration Mirrors exhibiting hinge memory

volta

gefm

irror

sde

hinge memory

ofbi

asa

half

ofhe

left

si

hift

(%)

twhi

cha

ndon

th

50 % / 50% 5 % / 95%

Sh

at la

Duty cycle in accelerating test

Simulating random image Simulating static image

Corrosion Cracking of Single Crystal SiliconPierron and Muhlstein, J. MEMS 15 (2006) 111

z)

30 °C, 50 %R.H.

z)

30 °C, 50 %R.H.

uenc

y (H

z σa = 1.5 GPaf0 = 40 kHz

uenc

y (H

z σa = 2.55 GPaf0 = 40 kHz

tura

l fre

qu

tura

l fre

qu

Test interruptedFractured

4 Hz

0 1 4×109

Nat

0 2×109

Nat

Number of Cycles0 1.4×10 0 2×10

Natural frequency change during fatigue testNumber of Cycles

Corrosion Cracking of Single Crystal SiliconPierron and Muhlstein, J. MEMS 15 (2006) 111

cy (H

z)

per

)

1000 030 °C

l fre

quen

c

ease

in f 0

pcl

es (H

z)

mid

ity (%

)

σa = 2.85 GPaf0 = 40 kHz

in n

atur

al

rage

dec

rebi

llion

cyc

lativ

e hu

m

50

Dec

reas

e

Aver b

Rel

2×10100-12

0 3 5-3.5

D

Number of Cycles Stress amplitude (GPa)2×100 0 3.5

Decrease in natural frequency during Average decrease in naturalcycling at constant stress amplitude frequency per billion cycles as a

function of stress amplitude fordifferent environments

Si is almost fatigue-free in dry environment at low temperature.

RF MEMS Switch for LSI Tester

Y. Liu et al., MEMS ’01

80 mW driving up to 3 kHzMetal pad

Feedthrough Heater Microspring contact

SiO2 Al Metal padON resistance: 0.2~0.5 Ω107 cycles (< 0.3 Ω)

LSI tester (Advantest)

Anodically-bondable LTCC (Nikko)

Low temperature cofired ceramic (LTCC) substrate anodicallybondable with silicon• Wafer-level hermetic packaging of MEMS• Interposer between MEMS and LSI• Embedded passive components

Si

• Embedded passive components

IC Component ~400 °C

3 5

4n C

500~1000 V

2

2.5

3

3.5

Si

LTCC

CapacitorInductorVia Thermal viaConductor

expa

nsio

nt, p

pm/°

C

LTCC

Si

0.5

1

1.5

2 LTCC

Ther

mal

eco

effic

ien

0

0 100 200 300 400 500

T c

Temperature, °C

Plastic Deformation of Si at High TemperatureSilicon plastically shaped at 1374 °CNakajima et al., Nature Mater. 4 (2005)

Pa)

800

600 No plastic

stre

ss (M

P 600

400

deformation

Frac

ture

200

00 200 0

Temperat re (°C)400 600 800 1000 1200

Temperature (°C)

Fracture stress of Si as a function of temperature

Fractured with plastic deformation

High temperature tensile test apparatus

Fracture stress of Si as a function of temperature

Si does not plastically deform below 600 °CSylwestrowicz, Phil. Mag. 7 (1962) 1825

SiC as a Material of MEMS

s (M

Pa) CVD SiC

eld

stre

s

Epstein, J. Eng. Gas Turbine & P 126 (2004) 205 226 Te

nsile

yi

Si

Power, 126 (2004) 205-226Mehregany et al., Proc. IEEE, 86, 8 (1998) 1595-1610

T

Temperature (K)

Deep RIE of SiC Ceramic

Tanaka et al., J. Vac. Sci. Technol. B, 19 (2001) 2173-2176

in)

ctiv

ity

te (µ

m/m

i

hing

sele

c

Etch

rat

iC/N

i etc

h

Lab.-made reactive ion etcher

Effect on etch rate and SiC/Ni

S

O2 mixture ratio (%)

• Electroplated Ni mask

Effect on etch rate and SiC/Niselectivity of O2 addition

• SF6 etching gas with 5 % oxygen• Over 200 µm depth• 0.4~0.5 µm/min etch rate100 µm µ• ~30 : 1 selectivity to the electroplated

Ni maskCross section of etched SiC

µ

SiC Surface Micromachining

Hatakeyama et al., Sensor Symposium 20081. SiO2 sacrificial layer patterning

SiC surface micromachining

2. SiN layer patterning

SiC surface micromachiningbased on selective SiC CVDon SiN, SiO2 and Si

SiC成長後：図1 (a) 4) SiO2除去後：図1 (a) 5)3 SiO2 etching

After SiCdeposition (step 4)

After SiO2 etching (step 5)

3. SiO2 etching

4. Selective SiC growth

5. Sacrificial layer etching and SiC lift off

200 µm

SiC Resonant Strain Sensor (UC Berkeley)

Azevedo et al., IEEE Sensors J. (2007), Prof. Pisano’s Lab.

z)ue

ncy

(Hz

100 Hz

nant

freq

uR

eson 1 µɛ

Resonant frequency vs. applied strainApplied stain (µɛ)

SiC Reaction-Sintering Using Si Micromolds

(1) Fabrication of Si mold Tanaka et al., J. MEMS, 10 (2001) 55-61

(2) Material powder packing and bonding

Si moldAlignment hole

Adh i h l i

Material powder (α-SiC, C andphenol resin with isopropanol) Micromachined Si mold ø 5 mm SiC microrotor

(3) Glass-encapsulation and reaction-sintering

Adhesive phenol resin

.)

: graphite

: α-SiC : Si

: β-SiC

Micromachined Si mold ø 5 mm SiC microrotor

P nten

sity

(a.u

(a)

HeatPressure

BN powderGlass tube

(4) Sample release by wet etching

In

(b)

Etchant (HF + HNO3)

20 30 40 50 60 70

2θ (degree)

XRD pattern (a) before/(b) after reaction-sintering

SiC Mold for Micro Glass Press Molding

1. Fabrication of a Si master

Min et al., MEMS 2005

2 SiC CVD → Polishing2. SiC CVD → Polishing

Si molds

3. Bonding with a SiC ceramic plate

Ni

4. Si etching (Si lost molding)Ra 1 nm

4. Si etching (Si lost molding)

SiC molds

50 µm100 µm

SiC Mold for Micro Glass Press Molding

Min et al., MEMS 2005

1 4T ()1st press(820 °C)

600

800

re(

)

0 811.21.4

MPa

)

Tempeature()Pressure(MPa)

(820 C)

2nd press(560 °C)

200

400

Tem

pera

tur

0.40.60.8

Pres

sure

(M(560 C)

00:00 0:28 0:57 1:26 1:55 2:24

T

00.2

Time(h:m)

Press molding of Pyrex glass #7740Press molding of Pyrex glass #7740• 1st press at 820 °C (Softening point)• 2nd press at 560 °C (Glass transient

point above which thermal expansionpoint, above which thermal expansioncoefficient increases)

MEMS for Aerospace Applications

Micro Solid Rocket Array Thruster

Control circuitSolder ball

Ignition signal

Solid propellantElectric feedthrough

Si top layer

Glass middle layer

N lDiaphragmMicro-ignition heaterSi bottom layer

NozzleThrust

LUNAR-A

IC

Penetrator

LUNAR-A with Penetratorsplanned by ISAS/JAXA

↑ NozzlesIgnition heaters →

Movie of Operation in Air and Vacuum

Test in vacuum

Test in air

B/Ti Multilayer Reactive Igniter

2B + Ti → TiB2 + 1320 cal/gHigh temp plasma

Ti/B/Ti/B/Ti/B/Ti/B/Ti multilayer(Ti: 250 nm B: 220 nm)

High temp. plasma

(Ti: 250 nm, B: 220 nm)Au/Pt/Ti electrical line

(300/30/20 nm)( )

++ Si di h

SiO2 insulation layer (600 nm)p++ Si diaphragm(5 µm)

(a) Before ignition

Bridge SiO2

(b) After ignitionBefore ignition After ignition

Ti/B/Ti/B/Ti/B/Ti/B/Ti Tanaka et al., MEMS 2007

Micro Evaporator for Tribo-Coating

Ball bearingBall bearing

Senor for friction d t ti

Adhesion layer Au connector

Pt heater

Lubricant (In)

detection

Micro indium evaporator for tribo-coating

Membrane area

SiO2

Si wafer

300 µmCourtesy of Prof. K. Adachi, Tohoku University

Electrostatic-Actuated Capacitive Shunt Switch

Ni bridgeDielectric layer(SiO2)On state

Ground200 µm

Yuki et al., Sensor Symposium 2007

Signal

Ground

Off state

Actuation pad Ground

0

5

10

15

20

-0 2

-0.15

-0.1

-0.05

0

Insert lossn

(dB

)

ss (d

B)

Notches for close contactDriving voltage: 38 V

25

-20

-15

-10

-5

0

0 45

-0.4

-0.35

-0.3

-0.25

0.2

IsolationIsol

atio

n

Inse

rtion

los

Sacrificial PR (3.5 µm)

Sacrificial PR (1.5 µm)

-30

-25

1 3 5 7Freqency（GHｚ）

-0.5

-0.45

Frequency (GHz)

I

GND GNDSignal

Phase Shifter Using RF MEMS Switches

Z0 Z0

Reflection typeSwitching line type

Z1

C iti Z2Capacitive shunt SW

Capacitive shunt SW

SW downReflect here

0°

90°

22.5°45°

Reflect here

SW up

90180°

Reflection-type phase shifter SW upReflect here

Reflection-type phase shifter using RF MEMS switch

(Taiko Denki & Tohoku Univ.)

Single Crystal RF MEMS Switch on LSI

Metal anchor

Signal line 200 μm

35

Actuation electrodeSingle crystal Si cantilever

20

25

30

35

t [μm

]

30

20(μm

)

5

10

15

Hig

ht

0

10

Hei

ght (

200 μm

00 100 200 300 400 500 600 700 800

Scan length [μm]Scan length (μm)0 100 200 300 400 500 600 700 800

0RF MEMS switches on a

dummy LSI wafer

Wafer Bonding-based MEMS-LSI Integration

1. Fabrication of metal padson a (dummy) LSI wafer

4. Patterning of metalelectrodes

7. Removal of thephotoresist molds

2 Bonding a SOI wafer on

LSI wafer

2. Bonding a SOI wafer onthe LSI wafer usingpolymer interlayer

5. Shape formation of thedevice by reactive ionetching

8. Sacrificial polymer etchingby O2 ashing to releasethe devicethe device

SOI wafer

3 Etching of the handle and

6. Cu electroplating usingphotoresist molds for

Polymer

3. Etching of the handle andBOX layers

electrical connection Cu

Photoresist mold

Summary

• MEMS is “a great bunch of trivial technologies”, and hasdiverse applicationsdiverse applications.

• Silicon is almost fatigue-free and reliable on moderategconditions.

Sili bid i it bl t i l f MEMS d i h h• Silicon carbide is a suitable material of MEMS used in harshenvironments.

• MEMS is also useful for aerospace applications.