epitaxial piezoelectric heterostructures for …...cross sectional tem images of pmn-pt on silicon...
TRANSCRIPT
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Seung-Hyub Baek
Center for Electronic Materials
Korea Institute of Science and Technology (KIST)
15th Korea-U.S. Forum on Nanotechnology
Epitaxial piezoelectric heterostructures
for ultrasound micro-transducers
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• Personal information • Banking
Security issue for mobile electronics
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Voice
Face
Iris
Vein
Fingerprint
• Highly secured
• Convenient
Fingervein
Biometrics-based authentication systems
Fingerprint
• Easy to hack
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Similar to medical imaging
Not affected by sweat or dirt
Convenient
Small, low-power consumption
3 dimensional recognition
Fingerprint/vein/blood flow
Ultrasonic transducer array
Ultrasound-based fingerprint/vein recognition
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Ultrasound Probe
Human
Body
Ultrasonic
Beam
Reflected
Signal
Principle of ultrasound imaging
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2D Transducer Array !
Beam-forming for 3D imaging
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Wiring issue
Not scalable
Issues on 2D array with bulk piezoelectric materials
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Electrodes Membrane
Insulation
Cavity
Si substrate Deflection
Vac+Vdc
Electrodes Piezoelectric layer
SiO2
Cavity
Si substrate Deflection
Vac
cMUT pMUT
Electrostatically-driven Piezoelectrically-driven
• Hard to fabricate
• High DC-field (electric shock!)
• Electrical charging
• Non-linear behavior
• Relatively easy to fabricate
• No DC-field necessary
• Stable
• Linear behavior
Micro-Machined Transducer (MUT)
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Vein recognition without gel !
vs.
pMUT-based fingerprint/vein imaging system
Ultrasonic transducer array
Air Air
Dermis
vs.
vein
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• Giant piezoelectric material.
PMN-PT Single crystal is 10 times
higher than PZT ceramic.
(d33= ~2000 pC/N, k33= ~0.92)
Giant piezoelectric relaxor-ferroelectrics
Pb(Mg1/3Nb2/3)O3 - PbTiO3 Single Crystals
S-E. Park, T.R. Shrout , J. Appl. Phys. 82, 1804 (1997).
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S-E. Park, T.R. Shrout , J. Appl. Phys. 82, 1804 (1997).
> 1.7% strain Field-Induced Phase Transition in (001) PZN-8% PT Single Crystal
Giant piezoelectric relaxor-ferroelectrics
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• Anisotropic piezo-property: d33 [001] > d33 [111]
Polycrystalline (001) Epitaxial
Giant piezoelectric relaxor-ferroelectrics
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Epitaxial PMN-PT thin films on Si
Si substrate Diamond Cubic structure Lattice parameter: 5.4302 Å
Conducting oxide Perovskite structure ~3.930 Å
Piezoelectric material Perovskite structure ~4.02 Å
Insulating oxide Perovskite structure 3.905 Å
MBE
Sputter
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Off-Axis Sputtering for high-quality films
Heater Block
Sputtering gun Energetic particles
Diffused particles
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Challenge for PMN-PT film growth
Voltage (V)
Pola
riza
tion (
µC/c
m2)
-40 -30 -20 -10 0 10 20 30 40
-60
-40
-20
0
20
40
60
Leaky!
Volatile PbO
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Miscut substrate to fix volatile PbO
Step as a preferential nucleation site
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X-ray diffraction with 2D area detector for
PMN-PT /SrRuO3/Si
Exact (001) Si 4o miscut (001) Si
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SrRuO3
PMN-PT
2 nm Si
SrRuO3
PMN-PT
100 nm
SrTiO3
Rocking Curve
FWHM
0.23o
0.58o
Cross Sectional TEM images of PMN-PT on silicon
TEM by X.Q. Pan, Michigan 0.32o (bulk PMN-PT single crystal)
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-600 -400 -200 0 200 400 600 -60
-40
-20
0
20
40
60
Po
lariza
tio
n (
µC
/cm
2)
Electrical field (kV/cm)
3000
0
1000
2000
0
0.1
0.2
0.3
-100 0 100
Electrical field (kV/cm)
Die
lectr
ic c
on
sta
nt
Lo
ss ta
ng
en
t
Strong Imprint- Unipolar Operation
• Highly insulating (>600 kV/cm)
• Strong imprint: unipolar operation
• Reduced dielectric constant for better detection
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Piezoelectric and energy harvesting FOM
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MEMS performance
• Simulations match experimental data using
bulk PMN-PT parameters.
• PMN-PT piezoelectric properties unaffected
by processing.
100 101 102
0.0
0.2
0.4
0.6
0.8
Tip
dis
pla
cem
ent
(µm
)
Voltage (V)
Modeled electrostatic cantilever
Modeled PMN-PT cantilever
Actual PMN-PT cantilever
0 0.02 0.04 -0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
Hei
ght
(µm
)
Length (mm)
0V
2.8V
Cantilever clamping point
Length:35µm
0.375 µm / V deflection
0.0 1.5 3.0 0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
∆Z
(μm
)
S.H. Baek et al. Science 334, 958 (2011)
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Development of relaxor-ferroelectrics
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1. Mn: Pb(Mg1/3Nb2/3)O3-Pb(Zr,Ti)O3
• Giant piezoelectricity &
• high temperature field stability
2. All sputtering process
PMN-PZT heterostructure on SOI
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-40 -20 0 20 40
-40
-20
0
20
40
Pola
rization (C
/cm
2)
Drive Voltage (V)
20 30 40 50 60 7010
0
101
102
103
104
105
106
107
Inte
nsity (
cps)
2
YSZ (
002)
YSZ (
004)
Si (004)
CeO
2 (
002)
CeO
2 (
004)
LSM
O (
001)
LSM
O (
002)
PM
N-P
ZT (
001)
PM
N-P
ZT (
002)
XRD P – E Curve
1 μm PMN-PZT/LSMO/CeO2/YSZ/Si
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Summary • We have fabricated epitaxial PMN-PT piezoelectric heterostructures on silicon with unparalleled piezoelectric properties. (d33: 1200 pm/V and e31: -29 C/m
2) (2-3 times better than best piezoelectric films ever reported and
on Si !)
• High strain piezoelectric heterostructures on silicon can be used
for integrated MEMS devices for actuation, sensing and imaging • High frequency ultrasound transducer 2-D arrays • Hyper-Active NEMS • High frequency filters • Energy Harvesting
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Buffer layer for epitaxial Oxide on Si
Si 5.43 Å
CeO2 5.41 Å
YSZ 5.15 Å
SRO, LSMO, PZT 3.86~3.93 Å
Si substrate
Perovskite oxides
Buffer Layers
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Doppler effect for blood flow imaging
Principle of ultrasound imaging
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(1960)
(2003) Ceramic PZT transducer array At 1 MHz
20x20 first 2-D array (currently 256x256 = 65,536 subdiced elements)
S.W. Smith, Duke Univ.
GE Medical