FERROELECTRIC CERAMICS: properties, processing and applications

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FERROELECTRIC CERAMICSproperties, processing
and applications

• Ignacio Martin-Fabiani, Dai Peng, Fang Yeyu and
  Sohaib Afzal
• Tuesday, 17 October 2006

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Introduction

• A ferroelectric ceramic mixes the smartness of a
  ferroelectric material and the tailoring
  possibilities of ceramics.
• Since both kind of materials exhibit many
  interesting properties, the mixture should be
  good

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Ferroelectrics ferroelectric domains

• Ferroelectric domains are generated by coupling
  between dipole moments of atoms.
• When subjected to electric field, the domains
  pointing towards its direction start to grow over
  its neighbouring domains.

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Ferroelectrics hysteresis loop

• Saturation and remanent polarization
• Coercive field
• Possibility to reverse the polarization
• Smart material it keeps information (remanent
  poalrization)

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Ferroelectrics phase transition

• Ferroelectricity is a phase transition (Curie
  point)
• Ferroelectric phase has always lower symmetry
• Example BaTiO3 (cubic changes into tetragonal)

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Ferroelectrics summary

• Present spontanous polarization
• Polarization can be inversed
• Ferroelectric domains
• Hysteresis loop
• Ferroelectricity is a phase transition
• Piezoelectric and pyroelectric effect

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Ceramics is a wide term

• The term ceramics covers all inorganic
  non-metallic materials whose formation is due to
  the action of heat.
• So you could think something like this

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but we are dealing with ADVANCED ceramics!
We can control, modify and optimize its
properties by tailoring the material!
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Properties of ceramics

• Mechanical poor toughness (under study)
• Electrical semiconductors, superconductors,
  piezoelectrics, pyroelectrics, ferroelectrics
  (BaTiO3, PZT)
• High resistance to abrasion
• Excellent hot strength
• Chemical inertness
• We can tailor properties for specific
  applications

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Why are ferroelectric ceramics so important?

• FERROELECTRICS
• High permittivities
• Spontaneus polarization
• Electric conducticity can be controlled
• Piezoelectric and pyroelectric effect
• Optical anisotropy, electrooptic an
  photorefractive deffect

• CERAMICS
• Broad range of chemical composition
• Control of grain size, porosity
• Possibility of varying its shape and size.
• High resistance to abrasion
• Excellent hot strength
• Chemical inertness

All this properties lead to a lot of potential
applications!
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2.Processing of Ferroelectric ceramics
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1. General Procedure of Processing

• Raw
• Materials

• Mixing

• Calcining

• Character
• -ization

• Milling

• Poling

• Sintering

• Binder
• Burnout

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1. raw materials

• Weighing the raw materials according to the
  stoichiometric formula of the ferroelectric
  ceramic desired .

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2. Mixing

• Mixing the powders either mechanically or
  chemically

• Mechanical mixing is usually done by either ball
  milling or attrition milling for a short time.
• Chemical mixing on the other hand is more
  homogeneous as
• it is done by precipitating the precursors
  in the same container.

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3.Calcination

• The solid phase reaction takes place between
  the constituents giving the ferroelectric phase
  during the calcination step

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4. Milling

• The lumps are ground by milling after
  calcining.

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5. binder burnout

• After shaping, the green bodies are heated
  very slowly to between 500-600 C in order to
  remove any binder present.

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6.Sintering

• After the binder burnout is over, the samples are
  taken to a higher temperature for sintering to
  take place.

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7.Poling

• it does not show any piezoelectricity when the
  ferroelectric ceramic is cooled after sintering .
  Piezoelectric behavior can be induced in a
  ferroelectric ceramic by a process called
  "poling" .
• In this process a direct current (dc) electric
  field with a strength larger than the coercive
  field strength is applied to the ferroelectric
  ceramic at a high temperature, but below the
  Curie point.

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8.Characterization

• On the application of the external dc field
  the spontaneous polarization within each grain
  gets orientated towards the direction of the
  applied field. This leads to a net polarization
  in the poling direction

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• Two special important methods widely uses in the
  labs .
• Metal Organic Decomposition (MOD)
• (2)hot-pressed solid-state sintering method

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1. MOD

• MOD Metal Organic Decomposition

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Desired thickness of the film is achieved

• spin-coat the solution on a bulk Si wafer at
  4000 rpm, 20 seconds .
• the film is baked on hot plate at 150 for 10
  minutes to remove the solvent .
• then the film is given a pyrolysis heat
  treatment in a furnace at 470 ?for 30 minutes to
  remove the residual organics
• and promote chemical reaction

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Ferroelectric BST-thick film ceramic on
analumina substrate
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2. hot-pressed solid-state sintering method

• SEM micrograph of a cross section of PLZT
  transparent ferroelectric ceramics.

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hot-pressed solid-state sintering method

• PbO, La2O3, ZnO, Nb2O5, ZrO2, and TiO2 with
  purity of 99.499.8 and micrometer particle size
  were used as starting materials. The
  stoichiometric mixture was ballmilled in a
  plastic container with zirconia grinding media in
  alcohol solution, then dried and ground. The
  ground mixture powders were pressed under 80
  kg/pressure into a cylindrical bar of 60 mm in
  diameter and 60 mm in height.

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hot-pressed solid-state sintering method

• During a sintering process, an oxygen flow of 3
  L/min was passed through the oven. The sintering
  temperature was elevated to 950 C at a rate of
  200 C/h and kept for 1/2 h, then pressure was
  gradually applied to the sample until 480 kg/
  while the oven temperature was increased to 1200
  C at the same time.

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hot-pressed solid-state sintering method

• The temperature and pressure were kept for 6 h
  before the pressure was released. Subsequently,
  the temperature was continuously increased to
  1250 C in 1/2 h and kept for 10 h. After
  sintering, the oven was cooled down to 950 C at
  a rate of 140 C/h and then cooled naturally
  until room temperature. The sintered specimen was
  cut and polished to obtain the required size for
  different measurements.

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Applications of Ferroelectric Ceramics ( general
overview )
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background

• Ferroelectric ceramics are used in a very broad
  range of functional ceramics and form the
  materials base for the majority of electronic
  applications. These electronic applicators
  account for more than 60 of the total high
  technology ceramics market worldwide

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Capacitors

• Basic principle
• 'C' is the capacitance, is the permittivity of
  free space, is the relative dielectric
  permittivity, 't' is the distance between the
  electrodes, 'A' is the area of the electrodes.

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multilayer ceramic (MLC)

• The volumetric efficiency can be further enhanced
  .
• consists of alternate layers of dielectric and
  electrode material.

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Ferroelectric Memories

• FRAM (Ferroelectric Random Access Memory) is a
  non-volatile memory combining both ROM and RAM
  advantages in addition to non-volatility
  features. It has higher speed in write mode,
  lower power consumption and higher endurance

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Overview of FRAM
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Advantages over EEPROM

• Transaction Time
• - 30,000 times faster than EEROM

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Energy Consumption

• 200 times lower power consumption compare to
  EEPROM
• 1 FRAM Cycle is just Reading
• 1 EEPROM Cycle consists of erasing , writing and
  reading

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Endurance

• 100,000 times higher endurance over EEPROM and
  the energy consumption is at 64Byte every write
  cycle

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 Electro-optic Applications

•  Ferroelectric Thin Film Waveguides. An optical
  waveguide controls the propagation of light in a
  transparent material (ferroelectric thin film)
  along a certain path
•  Ferroelectric Thin Film Optical Memory Displays
  .

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Other Ferroelectric Thin Film Applications

• Pyroelectric Detectors Pyroelectric detectors
  are current sources with an output proportional
  to the rate of change of its temperature

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Surface Acoustic Wave Substrates

• An elastic wave generated at the input
  interdigital transducer (IDT) travels along the
  surface of the piezoelectric substrate and it is
  detected by the output interdigital transducer.
  These devices are mainly used for delay lines and
  filters in television and microwave communication
  applications

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• Most Common Commercial
• Ferroelectric Ceramic

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Lead Zirconate Titanate (PZT)

• Chemical formula Pb Zrx Ti1-x O3
• Perovskite ABO3
• A and B are different in size
• A cation is at centre
• B cation is at the corner
• O atom are at centre of unit cell faces.

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Lead Zirconate Titanate (PZT)

• generates a voltage when some mechanical stress
  is applied piezoelectric effect
• useful for sensor and actuator application
• Doping
• Acceptor doping internal friction losses
  piezoelectric constant
• Donor doping internal friction
  losses piezoelectric constant

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Lead Zirconate Titanate (PZT)

• Poling
• High Temperature
• High Voltage
• Repeat to achieve high piezoelectric constant

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PZT Thin Films

• Used in number of devices
• Thickness of 90nm
• low crystallization temperature
• good surface morphology
• high remnant polarization

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Application of PZT

• Acoustic Device for underwater Application

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Acoustic Device for underwater Application

• Ultrasonic Sensors
• Commercial sound waves generating devices use PZT
  thin films
• Bulky ferroelectric ceramic sensors

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Acoustic Device for underwater Application

• Hence
• Thin films are used
• Low fabrication cost
• Film deposition techniques
• Electron beam evaporation 1
• Rf diode sputtering 2
• Ion beam deposition 3
• RF planar magnetron sputtering
  4
• MOCVD 5
• ECR 6
• laser ablation 7

and sol-gel 8
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Fabrication

• 0.25µm oxide layer
• 0.3µm Pt. electrode
• PZT thin film deposition for 2 hours at 350C
• Annealing at 650C for 20 minutes
• Cooled to room temperature

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Fabrication

• SEM patterns of deposited PZT thin film
• PZT thin film annealed at 850C for 5 minutes

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Fabrication

• Lithography used to form a window in silicone
  substrate
• Oxide layer is removed
• 100µm diaphragm was created by etching
• Successive layers of Pt, PZT and Pt deposited
• poling under an electric field of 10kV per cm at
  a temperature of 130C

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Results

• Improved ferroelectric property
• Improved accuracy
• Economical sensor
• Very small and light weight
• Can be used for application underwater

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Results

• Senstivity

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Applications

• Ultra Sonic Cleaners
• SODAR
• SONAR
• Medical Diagnostics
• Printer Heads
• Gas Lighters
• Micro Positioners
• Actuators
• Annunciators
• Sensors
• Capacitors
• FRAM
• Ceramic resonators
• Memory devices in thin film form

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• References of all material and
• diagrams are given in report

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Thankyou for your kind attention !!