Transcript Electroceramics - Universiti Sains Malaysia

Introduction to
Electroceramics
EBB 443
Seramik Teknikal
Ceramic Materials
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Ceramic materials can now be broadly
considered to be all inorganic non-metallic
materials.
However, it is more useful to classify them as
polycrystalline non-metallic materials.
The inherent physical properties of ceramics has
made them desirable for use in wide range of
industries, with their first applications in the
electronics sector.
Introduction to Ceramics: Concept
Evolution of Materials and Ceramics
Pottery and Electroceramics
Electroceramics
What are electroceramics?
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The term Electroceramic is used to describe ceramic materials
that have been specially formulated for specific electrical,
magnetic, or optical properties.
Their properties can be tailored to operation as insulators,
ferroelectric materials, highly conductive ceramics, electrodes as
well as sensors and actuators.
The performance of electroceramic materials and devices depends
on the
 complex interplay between processing,
 chemistry,
 structure at many levels and
 device physics.
What are electroceramics?
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The applications of ceramics in the electronics
industry can be divided into two groups:
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the use of materials for interconnection and packaging of
semiconductor circuits, and
the use of ceramics in circuit components which perform a
function in their own right, such as capacitors and sensors.
The former application forms a large market and has
been well reviewed elsewhere.
The latter is particularly interesting because the
materials which are used for a very wide range of
applications are in many cases closely related in
crystal structure.
Common Applications for Electroceramics
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Insulator
Resistor
High dielectric constant capacitors
Piezoelectric sonar transducers
Ultrasonic transducers
Radio & communication filters
Medical diagnostic transducers
Ultrasonic motors
Electro-optic light valves
Thin-film capacitors
Ferroelectric thin-film memories
Ceramic insulators
Bulk Ceramic Varistors
(VDR-voltage dependent
resistors)
Bulk Ceramic Thermistors
Bulk ceramic resistors
Cellular Telephone
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Portable communication devices such
as cordless, portable, and car
telephone have become popular
worlwide.
Do you know what kind of
dielectric and ferroelectric
components are used in a cellular
phone?
Cellular Telephone
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Chip Monolithic ceramic
capacitors
Microwave Oscillators
Microwave Filters
Ceramic Resonators
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High Frequency SAW
Filter
Ceramic Filters
Piezoelectric Receivers
Piezoelectric Speakers
Johanson Dielectrics
Capacitor Products:
Ceramic SMT and
Leaded High Voltage
and High
Temperature, Dual
and Multi Capacitor
Arrays, Low
Inductance, X2Y,
Switchmode.
Capacitors
Capacitors
Capacitors
C = "capacitance"
= q /DV
Units: Coulomb/Volt
= Farad (F)
----------------------------The capacitance of a
capacitor is constant;
if q increases, DV
increases proportionately.
Michael Faraday
(1791-1867)
C   r o
A
Q   r o
AV
d
d
Q = CV
Q: charge (Coulomb)
C: capacitance (Farad)
V: potential difference (Volt)
d: separation/thickness (meter)
o: permitivity of vacuum =
8.854x10-12 C2/m2 or F/m
r: dielectric constant
Dielectric Materials and Devices
Multilayer Ceramic Capacitor
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The demands for miniaturization largely preclude
an increase in the face area A.
One exception is the multilayer ceramic capacitor
(MLCC), in which case:
C   r o
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A ( N  1)
d
where N is the number of stacked plates.
Ideally, the dielectric should have a low electrical
conductivity so that the leakage current is not too
large.
Multilayer Ceramic Capacitor
Cut-away view of multilayer
ceramic capacitor.
Surface-Mount Ceramic
Capacitors
Military electronics
Surface-Mount Capacitors
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Ceramic surface-mount capacitors are used in
every type of electronic equipment including
computers, telecommunication, automotive
electronics, military electronics, medical
electronics and consumer electronics.
High voltage and high temperature ceramic
capacitors are serve military, aerospace, oil
service, oil exploration and other markets
including medical imaging, power generation,
and high voltage power supply.
Temperature Sensitive Resistor
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There are
numerous uses for
resistors with high
valuea of the
temperature
coefficient of
resistance (TCR)
and they may be
negative (NTC) or
positive (PTC).
Voltage-dependent Resistors (Varistors)
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There are a number of situations in which it is valuable to have a
resistor which offers a high resistance at low voltages and a low
resistance at high voltages.
Such a devices can be used to protect a circuit from high-voltage
transients by providing a path across the power suply that
 takes only a small current under normal conditions but takes
large current if the voltage rises abnormally,
 thus preventing high-voltage pulses from reaching the circuit.
Schematic use of a VDR to protect a circuit against transients,
Source
VDR
Circuit to be
protected
Schematic representation of
varistor-capacitor device
construction and its
equivalent circuit.
High-K Dielectric Materials
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The discovery of materials with unusually high-dielectric
constants (r > 2000-100000), and their ferroelectric nature,
led to an explosion in ceramic use.
The first employed in high-k capacitors is BaTiO3 based, and
later developed into
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piezoelectric transducers,
positive temperature coefficient (PTC) devices, and
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electro-optic light valves.
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Recent developments in the field of ferroelectric ceramics is
their use in
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medical ultrasonic composites,
high displacement piezoelectric actuators, and
photoresistors.
Piezoelectric
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Piezoelectricity was discovered in 1880 by J & P Curie
during studies into the effect of pressure on the generation
of electrical charge by crystals (such as quartz).
Described as the generation of electricity as a result of
mechanical pressure, or
"electrical polarisation produced by mechanical strain
in crystals belonging to certain classes".
The phenomenon can be attributed to a lack of centre of
symmetry in the crystallographic unit cell - or the unit cell is
described as non-centrosymmetric.
Piezoelectric
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For Piezoelectricity  the effect is linear and reversible,
 the magnitude of the polarisation is dependant
on the magnitude of the stress,
 the sign of the charge produced is dependant on
the type of stress (tensile or compressive).
Piezoelectric Ceramics
Piezoelectric Microactuator Devices
Schematic draw of optical scanning device
with double layered PZT layer (a) and the
fabricated device, (b) Mirror plate: 300×300
(µm2, DPZT beam: 800 × 230 µm2).
Micropump using screen-printed PZT
actuator on silicon membrane. (Courtesy
of Neil White, Univ. of Southampton,
UK.)
Schematic drawing of self-actuation
cantilever with an integrated
piezoresistor.
Ferroelectric ceramics
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This kind of material has perovskite structure, with
general formula ABO3, in which
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A is a large divalent metal ion such as Pb2+ or Ba2+,
B is a small tetravalent metal ion, such as Ti4+ or Zr4+,
octahedrally coordinating with oxygen.
Ferroelectricity occurs due to the displacement of
positive ions B4+ and negative ions O2- in opposite
directions.
Ferroelectric Ceramics
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This displacement causes spontaneous
polarisation which is the origin of many other
properties such as
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extremely high dielectric constant,
hysteresis loop (non-linear dependence of polarisation with
applied field),
piezoelectricity (the ability to change the dimension with
applied field and to produce the current with applied
mechanical stress).
Ferroelectric ceramics: PZT
(PbZrTiO3) structure
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Ferroelectric ceramics are widely used in
modern technology with various applications
(sensors, actuators, generators, transducers to
very recent IC for RAM).
They can be used for DRAM (dynamic random
access memory), and high remanent
polarisation and low coercive field for being
used as NVRAM (non-volatile random access
memory).
Examples of piezoelectric microsensors on silicon: (a) microphone
and (b) accelerometer. (OPA N.V., Taylor and Francis Ltd.)
Microwave Dielectrics
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The Microwave materials including of dielectric and
coaxial resonators to meet the demands of microwave
applications for high performance, low cost devices in
small, medium and large quantities.
Applications
Patch antennas
Resonators/inductors
Substrates
C-band resonator-mobile
Filters
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Photograph of split post dielectric resonators
operating at frequencies: 1.4, 3.2 and 33 GHz.
Jerzy Krupka, Journal of the European Ceramic Society 23 (2003) 2607–2610
EM Spectrum
Mobile phones operate in two main frequency ranges:
In
US - the older systems ~850 MHz & the newer ~1900 MHz.
In
European - near 900 MHz & 1800 MHz (GSM).
Magnetic Ceramics
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There are various types of magnetic material
classified by their magnetic susceptibilities:
diamagnetic, paramagnetic and ferromagnetic.
Diamagnetic, have very small negative
susceptibilities (about 10-6).
Example: inert gases, hydrogen, many metals, most
non-metals and many organic compounds.
Paramagnetics are those materials in which the
atoms have a permanent magnetic moment arising
from spinning and orbiting electrons.
The susceptibilities are therefore positive but again
small (in range 10-3 – 10-6).
Transformer
Magnetic Ceramics- cont.
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Ferromagnetic materials are spontaneously
magnetized below the Curie point.
The spontaneous magnetization is not apparent in
materials which have not been exposed to an
external field because of the formation of small
volumes (domains) of materials each having its own
direction of magnetization.
Spontaneous magnetization is due to the alignment of
uncompensated electron spin by the strong quantum
mechanical exchange forces.
Giant Magnetoresistance (GMR)
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The GMR is the change in electrical resistance of some
materials in response to an applied magnetic field.
GMR effect was discovered in 1988 by two European
scientists working independently:
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Peter Gruenberg of the KFA research institute in Julich, Germany, and
Albert Fert of the University of Paris-Sud .
They saw very large resistance changes - 6 percent and 50
percent, respectively - in materials comprised of alternating
very thin layers of various metallic elements.
These experiments were performed at low temperatures and
in the presence of very high magnetic fields.
Intrinsic Magnetoresistance
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SrRuO3
Tl2Mn2O7
CrO2
La0.7(Ca1-ySry)0.3MnO3
Fe3O4
CaCu3Mn4O12 (CCMO)
Applications of GMR
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The largest technological application of GMR is in the
data storage industry.
IBM were first to market with hard disks based on GMR
technology although today all disk drives make use of
this technology.
On-chip GMR sensors are available commercially from
Non-Volatile Electronics.
Other applications are as diverse as solid-state
compasses, automotive sensors, non-volatile magnetic
memory and the detection of landmines.
Applications of GMR
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Read sensors that employ the GMR effect available for
detecting the fields from tiny regions of magnetization.
These tiny sensors can be made in such a way that a very
small magnetic field causes a detectable change in their
resistivity; such changes in the resistivity produce electrical
signals corresponding to the data on the disk.
It is expected that the GMR effect will allow disk drive
manufacturers to continue increasing density at least until
disk capacity reaches 10 Gb per square inch.
At this density, 120 billion bits could be stored on a typical
3.5-inch disk drive, or the equivalent of about a thousand
30-volume encyclopedias.