1. Ferroelectricity

2. OUTLINE Introduction Polarization, Capacitance, Dielectric Properties
Spontaneous Polarization
Dielectric Response
Pyroelectricity
Electrostriction and Piezoelectricity
Switching of Polarization via an Electric Field
Structural Aspects of the Ferroelectric Phase Transformation
Applications

3. Polarization, Capacitance, Dielectric Properties
Capacitance of a parallel plate capacitor
Relative Dielectric Constant

4. Polarization, Capacitance, Dielectric Properties

5. Polarization, Capacitance, Dielectric Properties
Materials already possesing permanent dipoles, H2O, BaTiO3, oils, waxes, amorphous polymers,…
Displacement of ions with respect to each other due to external bias, only in ionic materials
Electric Dipole Moment
Polarization
displacement of the e- cloud with respect to the core due to external bias, occurs in ALL dielectric materials

6. Why Ferroelectrics? 1 Filters Oscillators Wireless CommunicationsP
Filters
Oscillators
Lead
Oxygen
Titanium
+PE
+PR 1 EC E
-PR
Wireless Communications
Ferroelectric Memories or
-PE

7. Typical Perovskite Ferroelectrics
Perovskite Structure
Typical Perovskite Ferroelectrics
Pb(Zr,Ti)O3-PZT
Ba(Sr,Ti)O3-BST
KNbO3 and LiNbO3
Pb(Ca,Ti)O3 -PCT
Pb(Sr,Ti)O3 –PST
Pb(Mg1/3Nb2/3)O3-PbTiO3
Properties
Spontaneous polarization in the absence applied electrical field.
Extremely high dielectric constant (~500-15,000).
Strong non-linear dielectric response to an applied electrical field.
High strain response to applied electrical field  piezoelectricity
Strong variation in polarization with temperature  pyroelectricity

8. Typical Ferroelectric Materials

9. Some Important Definitions
D: electrical displacement
: dielectric constant
E: electrical field
Ec: coercive field
dijk: piezoelectric coefficient (third rank tensor)
p: pyroelectric coefficient
Qijkl: electrostrictive coefficient (fourth rank tensor)

10. Spontaneous Polarization and the Hysteresis

11. Dielectric Constant: Slope of the P vs. E curve
Paraelectric
Ferroelectric
Field dependence of dielectric permittivity  TUNABILITY

12. Temperature Dependence of Spontaneous Polarization
PYROELECTRICITY

13. Exceptional Pyroelectric Response
Why Ferroelectrics?
Polarization Tc
Exceptional Pyroelectric Response
Temperature
Volts
PYROELECTRICITY

14. Electrostriction: Coupling between Polarization
and Self-Strain
 for BaTiO3 and PbTiO3, Q12<Q11 and Q12<0.

15. Piezoelectric effect: Strain due to an applied electric field
Strain due to combined Electrostrictive and Piezoelectric effect
Under non-zero external stress

16. Polarization Switching by an Electric Field
E≈EC

17. Polarization Switching by an Electric Field
Applied field E and switching current I versus time for a BaTiO3 crystal. The curve marked A is the switching pulse when the applied field is anti-parallel to the polarization, and the curve B is obtained when the field is parallel to the polarization and no switching occurs.

18. Polarization Switching by an Electric Field
Electrical (or 1800-domains) to minimize depolarization.

19. Polarization Switching by an Electric Field
Switching via Reversible Domain Wall Motion: Nucleation and Growth

20. Structural Aspects of Ferroelectric Phase Transformations

21. Applications of Ferroelectrics
Non-Volatile RAMs (memory)
Dynamic RAMs (capacitors)
Tunable Microwave Devices
Pyroelectric Detectors/Sensors
Optical Waveguides
Piezoelectric Sensors/Actuators, MEMS

22. Non-Volatile RAMs (memory)

23. Non-Volatile RAMs (memory)
Smart cards use ferroelectric memories. They can hold relatively large amounts of information and do not wear out from use, as magnetic strips do, because they use contactless radio frequency input/output. These cards are the size and shape of credit cards but contain ferroelectric memory that can carry substantial information, such as its bearer's medical history for use by doctors, pharmacists and even paramedics in an emergency. Current smart cards carry about 250 kilobytes of memory.

24. Dynamic RAMs (capacitors)
High dielectric constant near phase transformation from the cubic to the tetragonal phase (500~15,000)
Tetragonal
Cubic
Proximity of the Curie temperature to the room temperature yields large dielectric constant in BaxSr1-xTiO3 (x= ).

25. Tunable Microwave Devices / Optical Waveguides
(E=0)
Filters
Phase shifters
Delay lines
Oscillators

26. Pyroelectric Detectors/Sensors

27. Piezoelectric Sensors/Actuators, MEMS

28. Piezoelectric Sensors/Actuators, MEMS

29. Piezoelectric Sensors/Actuators, MEMS