Piezoelectric materials
for MEMS applications
Hiroshi Funakubo
Tokyo Institute of Technology
MEMS Engineer Forum
2016/5/11
11：50-12：15
Content
1. Introduction
2. Processing
3. Materials Matter
Content
1. Introduction
2. Processing
3. Materials Matter
Piezoelectric Materials
Dielectric
Materials
Direct Piezoelectric Effect
Stress-induced Electricity
Piezoelectricity
Pyroelectricity
Ferroelectricity
++++
---1880 P. Curie & J. Curie
Inverse Piezoelectric Effect
Nonsymmetrical Crystal Having
Ionic Displacement
Electric Field-induced Displacement
Spontaneous Polarization
Reversibility of Spontaneous Polarization
1881 Lippman
Energy Conversion Materials Between Electrical Energy and
Mechanical Energy
4
Application of Piezoelectric Property
Ink Jet Printer Head
Sensor Gyro
++++
---Fuel Injector
Sonogram
Piezoelectric Materials
Piezoelectric Materials
Dielectric
Materials
Piezoelectricity
Pyroelectricity
Quarts
ZnO, AlN, GaN, GaAs
Polarization Direction
Depend on Stack Direction of Charged Layer
Nonsymmetrical Crystal Having
Ionic Displacement
Spontaneous Polarization
Polarization
Direction
Ferroelectricity
http://phys.sci.hokudai.ac.jp/newHP/topics/ferro‐electro.htm
Reversibility of Spontaneous Polarization
Polarization Direction is
Determined by Deposition
Condition.
8
Piezoelectric Property
Intrinsic contribution
（following Devonshire[1] and Kay[2] ）
x  QP
P  Ps   0 r E
2
x : Strain
Q : Electrostrictive Coefficient
P : Polarization
Ps : Spontaneous Polarization
0 : Dielectric Constant in Vacuum
r : Relative Dielectric Constant
E : Electric Fields
E=0
E
Ps
+
Ps
Ps
x  QPs2  2Q 0 r Ps E  Q 02 r2 E 2
Piezoelectric Electrostrictive
Effect
Effect
180º Domain Contribution
Field Induced Strain （Dx） from E=0 to E
x  2Q 0 r Ps E  Q 02 r2 E 2
[1] A.
F. Devonshire, Adv. Phys. 3, 85 (1954).
[2]
H. F. Kay, Rep. Prog. Phys. 43, 230 9
(1955).
Piezoelectric Materials
Dielectric
Materials
Piezoelectricity
LiNbO3, LiTaO3
BaTiO3, Pb(Zr, Ti)O3
Pyroelectricity
Ferroelectricity
Nonsymmetrical Crystal Having
Ionic Displacement
Spontaneous Polarization
Reversibility of Spontaneous Polarization
10
Various Sensor Applications
Dielectric
Materials
Piezoelectricity
Pyroelectricity
Ferroelectricity
Nonsymmetrical Crystal Having
Ionic Displacement
Spontaneous Polarization
Tunable
Devices
Cooling
System
Pyrometer
Bolometer
Reversibility of Spontaneous Polarization
11
Spontaneous Polarization (Ps)
Origin of spontaneous polarization (Ps)
← Displacement of Ions Along Polar-axis Direction.
x = (c-a)/a = (c/a)-1
Pb
x
O
c
Ti (Zr)
a
The projection of the PZT
tetragonal perovskite unit cell
12
Feature of Ferroelectric Materials
• Ferroelectric materials have Critical Temperature (Tc : Curie
Temperature)by Phase Transition from Ferroelectric Phase to
Paraelectric Phase
Curie – Wise Law
Low Temperature Ferroelectric Phase
High Temperature Paraelectric Phase
13
Domain Formation by Phase Change
14
Piezoelectric Materials
Dielectric
Materials
Piezoelectricity
LiNbO3, LiTaO3, PVDF
BaTiO3, Pb(Zr, Ti)O3
Pyroelectricity
Ferroelectricity
Nonsymmetrical crystal Having
Ionic displacement
Spontaneous polarization
(Poling Treatment)
Reversibility of spontaneous polarization
15
Bipolar and Unipolar Response
＋E
Polarization Direction
－E
Ｘ０
①
②
③
④
⑥
②
①
Unipolar Measurement
Bipolar Measurement
P
⑤
P
④
②
③
①
②
E
E
⑥
①
Strain(%)
Strain(%)
⑤
S
S
⑥
④
②
③
Electric field ( kV/cm)
⑤
②
①
E
①
Electric field ( kV/cm)
E
16
Piezoelectric Materials
Dielectric
Materials
Piezoelectricity
LiNbO3, LiTaO3
BaTiO3, Pb(Zr, Ti)O3
Pyroelectricity
Ferroelectricity
Nonsymmetrical crystal Having
Ionic displacement
Spontaneous polarization
Reversibility of spontaneous polarization
17
Piezoelectric Materials
Pb(Zr, Ti)O3, Pb(Mg1/3Nb2/3)TiO3-PbTiO3
BaTiO3, (K, Na)NbO3, BaTiO3-(Bi1/2Na1/2)TiO3
Linear and Small Response with Electric Field (Voltage)
Non Linear and Large Response with Electric Field (Voltage)
18
Content
1. Introduction
2. Processing
3. Materials Matter
Sputtering Method
20
Solution Based Process
• Good Compatibility for
Multi Composition
System to Increase
Reliability.
• Low Density Strain
Introduction by Sintering
(Shrinkage).
Content
1. Introduction
2. Processing
3. Materials Matter
Pb(ZrxTi1-x)O3 (PZT)
 There is Morphotropic Phase Boundary (MPB) at x = 0.52 at Room
Temperature.
 Dielectric Constant and Electromechanical Coupling Factor Show the
Maximum around MPB.
Tetragonal MPB Rhombohedral
B. Jaffe et al., J. Res. Nat. Bur. Stand. 55, 239 (1955).
Origin of Large Piezoelectricity at MPB in Pb(Zr, Ti)O3
Phase Change Under Electric Filed
111
101
001
Polarization Rotation Model
B. Noheda et al., Phys. Rev. Lett. (2001)
Electric Filed
Bulk PZT
Tetragonal
Monoclinic
Rhombohedral
Potential Map
Near MPB
Noheda
al.,5568
Phys.(2003).
Rev. Lett. (2001)
D. J. Kim , J.B.
Appl.
Phys.et93,
Depression of Piezoelectricity in Pb(Zr, Ti)O3 Films
Phase Change Under Electric Filed
111
101
001
Polarization Rotation Model
• Depression of
Piezoelectric Response
by Substrate Clamping
D. J. Kim , J. Appl. Phys. 93, 5568 (2003).
Thin Films
Clamping Effect in Piezoelectric Film
Problem ： Smaller Piezoelectricity in Films Form
Field-induced-Strain (%)
Inverse
E
Piezoelectricity
E
0.8
0.6
Free standing
Bulk
0.4
E
0.2
Film
0
Film is In-plane Clamped
by Substrate
-0.2 Pb(Zr,Ti)O
3
-200
-100
0
100
Electric field (kV/cm)
V. Nagarajan et al, Appl. Phys. Lett., 81, 4215 (2002).
200
d 33 , film  d 33    d 31
Clamping Effect of Single Crystalline Pb(Zr, Ti)O3 Films
d33(expect.) = 150pm/V
PZT
d33(obs.) = 75pm/V
0
d33,( obs.)
0.1 0.2 0.3 0.4
Zr/(Zr+Ti) ratio
0.5
s13E
 d33,(expect.)  2d31 E E
s11  s12
d31: Real in plain in-plane d31
d33: Real out-of-plane d33
sijE: elastic compliance under constant E
※Nagarajan, et al., Appl. Phys. Lett. 81, 4215 (2002).
PZT
Substrate
d33、(obs.) < d33、(expect.)
For Single Crystal
Orientation Dependency
Polarization-electric field (P-E) & Strain-electric field (S-E) properties
MOCVD Samples
Rhombo.
100
Mixture
{100}
{110}
{111}
Tetra.
5Hz
Rhombo.
Tetra.
Mixture
50
0
0.4
{100}
-50
{110}
-100
{111}
-150
0.4
0.3
0.2
0.1
0
-0.1
-100
-50
0
50
100
Electric field (kV/cm)
-100
-50
0
50
100
Electric field (kV/cm)
-100
-50
0
50
100
Electric field (kV/cm)
Field-induced strain (%)
2
Field-induced strain (%) Polarization (µC/cm )
150
5Hz
0.3
{111}
0.2
{110}
0.1
0
0.2
{100}
0.3
0.4
0.5
0.6
0.7
0.8
PT content
 {111}PZT films consisting of mixed phase showed larger field-induced strain
than others.
 Piezoresponse property was enhanced for the film with mixed phase and
depended on crystal orientation.
J. Applied Physics 98, 094106 2005
Pb(Zr, Ti)O3 vs Pb(Mg1/3Nb2/3)TiO3-PbTiO3
{100} Pb(Mg1/3Nb2/3)TiO3PbTiO3
AFM cantilever
Field-induced strain,
x33 (%)
{100}Pb（Zr, Ti)O3
0.15
Rhombo.
Tet.
Mix.
[Epi. film]
0.1
[Epi. film]
0.05
|e31| (C/m )
Laser Doppler
2
PC
(Rhombo.)
Tet.
Mix.
MOCVD Samples
0
15
Mix.
Mix.
[Single crystal]
[Sintered body]
10
5
0
0
Ref. 1 [Sintered body]
0.2
0.4
0.6
PT content, x
1)
0.8
Ref. 2 [Single crystal]
1
0
0.2
0.4
0.6
PT content, x
H. Jaffe et al., Proc. IEEE 53, 1372 (1965).
2)
0.8
1
Similar to “Engineered domain” concept
H. Cao et al., J. Appl. Phys. 96, 3471 (2004).
Green Piezoelectric Films -Lead Free-
Pb‐based Materials
Strategy for Materials Survey
PbTiO3-Based
(Bi1/2K1/2)TiO3-Based
T
T
BaTiO3Based
R
R
PC
T
Pb(Mg1/3Nb2/3)O3 - PbTiO3
(Bi1/2K1/2)TiO3
-(Bi1/2Na1/2)TiO3-BaTiO3
BaTiO3
-Bi(Mg1/2T1/2)O3
Y. Hiruma et al., Jpn. J. Appl. Phys. 45, 7409 (2006).
S. Wada, J. Appl. Phys. 108, 194114 (2010).
R
T
Pb(Zn1/3Nb2/3)O3-PbTiO3
J. Zhao et al., Jpn. J. Appl. Phys. 34, 5658 (1995).
J. Kuwata et al., Ferrorlrctrics 37, 579 (1981).
• End Member of MPB Composition is
Ferroelectric Materials with
Tetragonal Symmetry.
Tetragonal Ferroelectric Compound
Conventional materials
1.00 1.01 1.02
Research area up to now
Poling Possible
Tetragonality
Pb2+
PbTiO3
(1950s)
(c/a)
＞1.2
*BiCoO3
PbVO3
**Bi(Zn1/2Ti1/2)O3
(2004)
(2006)
New area after 2000
Poling Impossible
PbTiO3
Ti4+
(c/a)
1.07
BaTiO3(Bi, K)TiO3
(1940s)(1960s)
O2-
Tetragonality
Growth:
Ambient
pressure
c/a = 1.06
Bi3+
O2(Zn2+Ti4+) Co3+
BiCoO3
Bi(Zn1/2Ti1/2)O3
Growth:
High pressure
c/a > 1.2
* A. A. Belik et al.,Chem. Mater., 18, (2006) 798 ** M. Suchomel et al., Chem. Mater. 18 (2006) 4987
(Bi1/2Na1/2)TiO3-BaTiO3 System
KNbO3-NaNbO3 System
State of Art of Piezoelectric Films
(Bi1/2Na1/2)TiO3-BaTiO3
(K0.5Na0.5)NbO3
Remarks
• Selection of Best Piezoelectric Materials
Depend on Required Properties (Application).
• Novel Materials are Under Developed for
Thin Films Applications.
• Piezo MEMs Design Must Think About
Origin of Piezoelectricity.
• Reliability Matters also Need to Understand
Origin of Piezoelectricity.