1. Capacitor ~high permittivity devices~ …APPLICATIONS OF PIEZOELECTRICS Gas igniter Pressure...
Transcript of 1. Capacitor ~high permittivity devices~ …APPLICATIONS OF PIEZOELECTRICS Gas igniter Pressure...
ELECTRONICS DEVICES AND MATERIALS
Atsunori KAMEGAWA
���� �� ������
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FERROELECTRIC DEVICES�
1. Capacitor ~high permittivity devices~ 2. Piezoelectric Devices 3. Pyroelectric Devices 4. Ferroelectric Memory Devices 5. Electrooptic Devices
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VARIOUS EFFECTS IN MATERIALS�
Charge Current�
Magnet-ization� Strain�
Temper-ature� Light�
Electric Field�
Permittivity Conductivity�
Elect.-Mag. efficient�
Converse piezo-effect�
Elec. Caloric effect�
Elec.-optic effect�
Magnetic Field�
Mgg.-elect. effect� Permeability� Magneto-
striction�Mag.caloric
effect�Mag.optic
effect�
Stress� Piezoelectric effect�
Piezomag. effect�
Elastic constant�
Photoelastic effect�
Heat� Pyroelectric effect�
Thermal expansion� Specific heat�
Light� Photovoltaic effect� Photostriction� Refractive
index�
Permittivity Conductivity
Mgg.-elect. effect
Piezoelectric effect
Pyroelectric effect
Photovoltaic effect
Converse piezo-effect
Magneto-striction
Elastic constant
Thermal expansion
Photostriction
Sensor� Actuator�
Input�Output�
Input� Material Device� Output�
4-3�CERAMIC CAPACITORS ~HIGH PERMITTIVITY DIELECTRICS~�
The basic Specifications required for capacitors: �! Small size, large capacitance
Materials with a large dielectric constant are desired.
! High frequency characteristics Ferroelectrics with a high dielectric constant are sometimes associated with dielectric dispersion, which must be taken into account for practical applications.
! Temperature characteristics We need to design materials to stabilize the temperature characteristics.�
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MULTILAYER CERAMIC CAPACITOR (MLCC)�
C=ε0εr =nε0εr A d
S L/n
External Electrode� Internal Electrode� Dielectric�
Dielectric Layer Thickness (µm)�
Number of Layers�
Die
lect
ric L
ayer
Thi
ckne
ss (µ
m)�
Num
ber o
f Lay
ers�
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TEMPERATURE CHARACTERISTICS�
Categories of dielectrics �thermal compensation type (TiO2) �high frequency, filtering, amplifier cir. �high permittivity type (BaTi03) �coupling or decoupling circuite�
-100
-80
-60
-40
-20
0
20
140120100806040200-20-40-60
Al-Electrolytic�
Ta-Electrolytic�
Ceramic(TiO2)
Ceramic(BaTiO3)
Temperature / �
Cha
nge
rate
of C
apac
itanc
e(%
)
BaTiO3
Shifter additive (decreasor: Sr, elevator: Pb� Depressor additive �MgTiO3, CaTiO3 ��
PMN
Combination of ferroelectrics with deferent composition (deferent Curie Temp.)�
Some approach to improve Temp. Characteristics�
Sr
MT
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PIEZOELECTRIC DEVICES�
Ps � ��
���
Piezoelectric Figures of Merit�Piezoelectric Strain Constant: d
x=dE External electric field: E, magnitude of he induced strain �x
Piezoelectric voltage constant: g
External stress: X, induced electric field: E
E=gX
Therfore� g= d ε0εr
An important figure of merit for actuator applications�
An important figure of merit for sensor applications�
Relationship of polarization and piezoelectric strain�
P=ε0ε(X) E
E= = P ε0ε(X)
dX ε0ε(X)
Fundamental Piezoelectric equations:�
x=c(E)X+dE P=dX+ε0ε(X)E
external E=0 P=dX
4-7�OTHER IMPORTANT FIGURE OF MERIT FOR PIEZOELECTRIC APPLICATIONS�
Electromechanical Coupling Factor: k
k2= Stored mechanical energy Input electrical energy�
Conversion rate between electrical energy and mechanical energy �
Mechanical Quality : Qm
Qm= ω0 2Δω ω0:resonance frequency�
The inverse of mechanical loss�
Acoustic Impedance : Z Evaluating the acoustic energy transfer between two materials �
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APPLICATIONS OF PIEZOELECTRICS�
Gas igniter Pressure sensor, Accelerometer,�
Piezoelectric transformer�
Piezo-actuator�Ultorasonic Motor�
Stress → Internal electrical field �
External electrical field →Stress
→ Internal electrical field �
External electrical field →Stress �
E1 E2
ω
Mass�
Acceleration�
Basic structure of an accelerometer�
Basic structure of a piezoelectric transformer�
4-9� PZT’S COMPOSITION AS PIEZOELECTRIC DEVICES�
PbZrO3 PbZrO3 [mol%] PbTiO3
Tem
pera
ture
/�
d15
d33
-d31
PbZrO3 [mol%]
Morphotropic phase
boudary
Dependence of several d constants on composition near morphotropic phase boundary in the PZT system�
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CERAMIC ACTUATOR MATERIALS ~PIEZOELECTRIC, ELECTROSTRICTIVE
AND PHASE CHANGE MATERIAL ~�
Piezoelectric material, (Pb, La)(Zr, Ti)O3, Ba(Sn, Ti)O3
Electrostrictive material, Pb(Mg1/3Nb2/3, Ti)O3
Phase change material, Pb (Zr, Sn, Ti)O3
Electrostriction �ΔyEy
2
Piezoelectric �ΔxEx
Field� Field� Field�
Field� Field�
stra
in�
stra
in�
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PYROELECTRIC DEVICES�
Ps
Principle of pyroelectric sensor�
Cur
rent�
Infrared irradiation�
A temperature increase due to the infrared irradiations (such as human body) �� Spontaneous polarization decrease ��� Variation in electric charge (or current)
Types of Infrared-sensors � semiconductor type ��Imaging and its processing � pyroelectric type (Pyrosensor) ��Infrared light sensors, ��Temperature sensors The merits of pyrosensors � wide range of response frequency � use at room temperature � quick response in comparison with other temperature sensors � low costs�
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PYROELECTRIC RESPONSE�
Light Intensity�
Temperature rise�
Pyroelectric current�
Time�
Time�
Time�
Pyroelectric response to chopped IR irradiation�
Current responsivity�ri
ri= ηp ρCph
η: transmittance of incident radiation p�pyroelectric coefficient ρ: density of pyro-material Cp :specific heat of detector h :thickness of detector�
Example of pyro-material for IR detector: �
(Ba, Sr)TiO3�
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FERROELECTRIC MEMORY DEVICES�
FeRAM (FRAM)
1
0
E
P
Ferroelectric for memory-cell (FeRAM)
1
0 E
P
Paraelectrics for memory-cell (DRAM)
Word Line�
Plate Line�
Bit Liine�
Ferroelectric cell�
Non-volatile memory device �(cf. MRAM, PRAM)
Pr
-Pr
When External Field is Zero, memorized information is non-volatile!�
-Pr
1 1
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EQUIVALENT CIRCUITS AND SCHEMATIC STRUCTURES OF TYPICAL MEMORY DEVICES �
Equivalent Circuit�
Memory State�
1
0
Word Line�
Bit Line�
Word Line�
Bit Line�
Word Line�
Plate Line�
Bit
Line�
Sou
rce�
Word Line�
Dra
in�Floating Gate�
Bit
Line�
Word Line�
Plate Line�
Crystalline�
Amorphous�
Insulator�Electrode�
Electrode�
+ + + +
- - - -
Control Gate�
Si substrate�Floating Gate�
- - - -
Electrode�
Electrode�
Ferroelectric Film�
+ + + + - - - -
+ + + + - - - -
Insulator�
Ferromagnetic Films�
DRAM Flash EEPROM FeRAM MRAM PRAM
4-15� PROBLEMS OF FERROELECTRICS FOR FERAM APPLICATIONS�
Leak-current� Dielectric breakdown�
Fatigue�
E
Q
Imprint�
E
Q
Retention�
E
Q
E
I
t
Q
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FERROELECTRIC MATERIALS FOR FERAM�
PZT (Pb(Zr,Ti)O3) SBT (SrBi2Ta2O9) Large Pr Relatively easy fabrication Relatively large Ec Large Fatigue Preparation conditions �Pb-composition� La addition → leakage & Ec Ca, Sr additions
→ Imprint and Retention Oxide Electrode, Buffer �����→ Fatigue Properties Film Orientation → Pr, Fatigue �����reduction of thickness�
Low Ec�low operation Voltage� Good tolerance for Fatigue Low Pr Difficult preparation conditions �High Temp., Bi-composion� Nb addition → Increment of Pr SBT-BT composite
→ dielectric properties�
Material
Merits
Demerits
Improvement Approach
Ramtron, Fujitsu, … Symetrix, Panasonic, NEC, …
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ELECTROOPTIC DEVICES�
Fundamental Construction of an electrooptic light shutter�
Δn=- Rn3E2 1 2
Second-order electrooptic effect (Kerr effect)�
Birefringence: Δn
R: quadratic electrooptic coefficient n: original refractive index (E=0) E: electric field�
L
-45��45��
Polarizer� Analyzer�
PLZT
Electric Field: E
Light Shutter, Light Switch, Waveguide Modulator�Typical Application of Electrooptic Devices�
First-order electrooptic effect (Pockels effect)
○ high speed, high contrast, gradation × high cost, high operation voltage�
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Birefringence�
RELATION BETWEEN PLZT COMPOSITION AND STRUCTURE AND ELECTROOPTIC APPLICATION�
PbZrO3 PbZrO3 [mol%] PbTiO3
La [m
ol%
]
Rhombohedral, Ferro� Tetragonal , Ferroelectric Phase�
Antiferroelectric�
Cubic, Parraelectric�
1st EO effect�Memory�
PLZT:(Pb1-xLax)(Zr1-yTiy)1-x/4O3�
4-19�POLARIZATION AND BIREFRINGENCE AS A FUNCTION OF ELECTRIC FIELD FOR PLZT�
Polarization P and Birefringence ∆n as a Function of Electric Field E for some PLZT ceramics�
PLZT 9/65/35 PLZT 7/38/62
2nd order EO effect� 1st order EO effect�P
-E
Δn-
E
Field E[kV/cm]
Field E[kV/cm]
Δn(
x10-
3 )
P P
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DIELECTRIC MATERIALS OF ELECTROOPIC DEVICES�
Pockels (1st) and Kerr (2nd) electrooptic coefficients for various materials�
Material�
Primary electrooptic coefficient�
Secondary electrooptic coefficient�
4-21� REQUIRED PROPERTIES FOR ELECTROOPTOIC DEVICES�
Required Properties for electrooptoic devices � high electrooptic coefficient � good mechanical properties�especially high toughness� � high transmittance � Δn close to zero, when external electric field is zero � low porosity, high sintered density�
(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3�
Tran
dmitt
ance
(%)
Ref
ract
ive
Inde
x n
Ele
ctro
optic
coe
ffici
ent
R/x
10-1
6 m2 V
2
Composition x
(1-x)PMN-xPT
Composition x Composition x
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