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.
Top Related