Electrical Properities (1)
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Transcript of Electrical Properities (1)
Chapter 18 - 1
ISSUES TO ADDRESS...
• How are electrical conductance and resistance characterized?
• What are the physical phenomena that distinguish conductors, semiconductors, and insulators?
• For metals, how is conductivity affected by imperfections, temperature, and deformation?
• For semiconductors, how is conductivity affected by impurities (doping) and temperature?
Chapter 18: Electrical Properties
Chapter 18 - 2
Electrical Conduction• Ohm's Law: V = I R
voltage drop (volts = J/C) C = Coulomb
resistance (Ohms)current (amps = C/s)
1
• Conductivity, s
• Resistivity, r: -- a material property that is independent of sample size and geometry
RA
l
surface area of current flow
current flow path length
Chapter 18 - 3
Electrical Properties
• Which will have the greater resistance?
• Analogous to flow of water in a pipe• Resistance depends on sample geometry and
size.
D
2D
R1 2
D
2
2
8D2
2
R2
2D2
2
D2
R1
8
Chapter 18 - 4
Measurement of R
Chapter 18 - 5
Definitions
Further definitions
J = <= another way to state Ohm’s law
J current density
electric field potential = V/
flux a like area surface
current
A
I
Electron flux conductivity voltage gradient
J = (V/ )
Chapter 18 - 6
DefinitionsElectric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.
http://www.mysearch.org.uk/website1/html/479.Fieldlines.html
Chapter 18 - 7
• Room temperature values (Ohm-m)-1 = ( - m)-1
Selected values from Tables 18.1, 18.3, and 18.4, Callister & Rethwisch 8e.
Conductivity: Comparison
Silver 6.8 x 10 7
Copper 6.0 x 10 7
Iron 1.0 x 10 7
METALS conductors
Silicon 4 x 10-4
Germanium 2 x 10 0
GaAs 10 -6
SEMICONDUCTORS
semiconductors
Polystyrene <10-14
Polyethylene 10-15-10-17
Soda-lime glass 10
Concrete 10-9
Aluminum oxide <10-13
CERAMICS
POLYMERS
insulators
-10-10-11
Chapter 18 - 8
What is the minimum diameter (D) of the wire so that V < 1.5 V?
Example: Conductivity Problem
Cu wire I = 2.5 A- +
V
Solve to get D > 1.87 mm
< 1.5 V
2.5 A
6.07 x 107 (Ohm-m)-1
100 m
I
V
AR
4
2D
100 m
Chapter 18 - 9
Electron Conductivity
• The magnitude of the conductivity depends on the number of electrons available to participate in the conduction process
• Not all electrons in every atom will accelerate in the presence of an electric field
• It depends on the arrangement of electron states or levels w.r.t energy and the manners in which these states are occupied by electrons.
Chapter 18 -10
Electron Energy Band Structures
Adapted from Fig. 18.2, Callister & Rethwisch 8e.
Chapter 18 -11
Band Structure Representation
Adapted from Fig. 18.3, Callister & Rethwisch 8e.
Chapter 18 -12
Band Structures in Solids at 0K
Outermost band is partially filled Ex. Copper has one electron in 4s
Overlap between an empty and filled band Ex. Magnesium has one two 3s electrons. Then 3s and 3p bands overlap
Valence band i.e. completely filled is separated from an empty band and an energy band gap lies between them. Difference depends on the magnitude of the energy gap. Insulators: gap is relatively wide. Semiconductors: gap is narrow
Femi Energy
Chapter 18 -13
Conduction & Electron Transport• Metals (Conductors):-- for metals empty energy states are adjacent to filled states.
-- two types of band structures for metals
-- thermal energy excites electrons into empty higher energy states.
- partially filled band - empty band that overlaps filled band
filled band
Energy
partly filled band
empty band
GAP
fille
d st
ates
Partially filled band
Energy
filled band
filled band
empty band
fille
d st
ates
Overlapping bands
Chapter 18 -14
Energy Band Structures: Insulators & Semiconductors
• Insulators: -- wide band gap (> 2 eV) -- few electrons excited across band gap
Energy
filled band
filled valence band
fille
d st
ates
GAP
empty
bandconduction
• Semiconductors: -- narrow band gap (< 2 eV) -- more electrons excited across band gap
Energy
filled band
filled valence band
fille
d st
ates
GAP?
empty
bandconduction
Chapter 18 -15
Conduction In Metals• For an electron to become free, it must be excited or promoted
into one of the empty and available energy states above Ef
Chapter 18 -16
Charge Carriers in Insulators and Semiconductors
Two types of electronic charge carriers:
Free Electron – negative charge – in conduction band
Hole – positive charge
– vacant electron state in the valence band
Adapted from Fig. 18.6(b), Callister & Rethwisch 8e.
Move at different speeds - drift velocities
Chapter 18 -17
Electron Mobility• Free Electrons accelerates when
electric field is applied. • The acceleration direction is
opposite to the applied field.• Free electrons should accelerate
as long as the field is applied!! • But! We know that the current
reaches a constant value the instant that field applied.
• Thus frictional forces exists, which counter this acceleration from the field.
Why?
Scattering of electrons by imperfections in the crystal lattice
It is the resistance to the passage of an electric current Parameters
mobilityDrift velocity
v
Chapter 18 -18
EXAMPLE
At room temperature the electrical conductivity and the electron mobility for copper are 6.0 107 (W-m)-1 and 0.0030 m2/V-s, respectively. (a) Compute the number of free electrons per cubic meter for copper at room temperature. (b) What is the number of free electrons per copper atom? Assume a density of 8.9 g/cm3.
Chapter 18 -19
Metals: Influence of Temperature and Impurities on Resistivity
• Presence of imperfections increases resistivity -- grain boundaries -- dislocations -- impurity atoms -- vacancies
These act to scatterelectrons so that theytake a less direct path.
• Resistivity increases with:
=
deformed Cu + 1.12 at%Ni
Adapted from Fig. 18.8, Callister & Rethwisch 8e. (Fig. 18.8 adapted from J.O. Linde, Ann. Physik 5, p. 219 (1932); and C.A. Wert and R.M. Thomson, Physics of Solids, 2nd ed., McGraw-Hill Book Company, New York, 1970.)
T (ºC)-200 -100 0
1
2
3
4
5
6
Res
istiv
ity,
r
(10
-8 O
hm
-m)
0
Cu + 1.12 at%Ni
“Pure” Cu
d -- %CW
+ deformation
i
-- wt% impurity
+ impurity
t
-- temperature
thermal
Cu + 3.32 at%Ni
Chapter 18 -20
Estimating Conductivity
Adapted from Fig. 7.16(b), Callister & Rethwisch 8e.
• Question:-- Estimate the electrical conductivity of a Cu-Ni alloy that has a yield strength of 125 MPa.
mOhm10 x 30 8
16 )mOhm(10 x 3.31
Yie
ld s
tre
ngt
h (
MP
a)
wt% Ni, (Concentration C)0 10 20 30 40 50
6080
100120140160180
21 wt% Ni
Adapted from Fig. 18.9, Callister & Rethwisch 8e.
wt% Ni, (Concentration C)R
esi
stiv
ity,
r
(10
-8 O
hm
-m)
10 20 30 40 500
10203040
50
0
125
CNi = 21 wt% Ni
From step 1:
30
Chapter 18 -21
What is a semiconductor?
• Low resistivity => “conductor”• High resistivity => “insulator”• Intermediate resistivity => “semiconductor”
– conductivity lies between that of conductors and insulators
– generally crystalline in structure for IC devices• In recent years, however, non-crystalline
semiconductors have become commercially very important
polycrystalline amorphous crystalline
Chapter 18 -22
Semiconductor Materials
Chapter 18 -23
Intrinsic Semiconductors
• Pure material semiconductors: e.g., silicon & germanium– Group IVA materials
• Compound semiconductors – III-V compounds
• Ex: GaAs & InSb
– II-VI compounds• Ex: CdS & ZnTe
– The wider the electronegativity difference between the elements the wider the energy gap.
Chapter 18 -24
Band Gap of SemiconductorsMaterial Band Gap
Si 1.11
Ge 0.67
GaP 2.25
GaAs 1.42
InSb 0.17
CdS 2.4
ZnTe 2.26
Chapter 18 -25
Silicon
• Atomic density: 5 x 1022 atoms/cm3
• Si has four valence electrons. Therefore, it can form covalent bonds with four of its nearest neighbors.
• When temperature goes up, electrons can become free to move about the Si lattice.
Chapter 18 -26
Intrinsic Semiconduction in Terms of Electron and Hole Migration
Adapted from Fig. 18.11, Callister & Rethwisch 8e.
electric field electric field electric field
• Electrical Conductivity given by:
# electrons/m3 electron mobility
# holes/m3
hole mobilityhe epen
• Concept of electrons and holes:
+-
electron hole pair creation
+-
no applied applied
valence electron Si atom
applied
electron hole pair migration
Chapter 18 -27
Number of Charge Carriers
Intrinsic Conductivity
)s/Vm 45.085.0)(C10x6.1(
m)(10219
16
hei e
n
For GaAs ni = 4.8 x 1024 m-3
For Si ni = 1.3 x 1016 m-3
• Ex: GaAs
he epen
• for intrinsic semiconductor n = p = ni = ni|e|(e + h)
Chapter 18 -28
Intrinsic Semiconductors: Conductivity vs T
• Data for Pure Silicon: -- s increases with T -- opposite to metals
Adapted from Fig. 18.16, Callister & Rethwisch 8e.
material Si Ge GaP CdS
band gap (eV) 1.11 0.67 2.25 2.40
Selected values from Table 18.3, Callister & Rethwisch 8e.
ni e Egap / kT
ni e e h
Chapter 18 -29
Intrinsic Semiconductors: Conductivity vs T
material Si Ge GaP CdS
band gap (eV) 1.11 0.67 2.25 2.40
Selected values from Table 18.3, Callister & Rethwisch 8e.
ni e Egap / kT
ni e e h
Chapter 18 -30
Example• At room temperature the electrical conductivity of PbTe is
500 (Ω-m)–1, whereas the electron and hole mobilities are 0.16 and 0.075 m2/V-s, respectively. Compute the intrinsic carrier concentration for PbTe at room temperature.
Chapter 18 -31
• Intrinsic: -- case for pure Si -- # electrons = # holes (n = p)
• Extrinsic: -- electrical behavior is determined by presence of impurities that introduce excess electrons or holes -- n ≠ p
Intrinsic vs Extrinsic Conduction
3+
• p-type Extrinsic: (p >> n)
no applied electric field
Boron atom
4+ 4+ 4+ 4+
4+
4+4+4+4+
4+ 4+ hep
hole
• n-type Extrinsic: (n >> p)
no applied electric field
5+
4+ 4+ 4+ 4+
4+
4+4+4+4+
4+ 4+
Phosphorus atom
valence electron
Si atom
conductionelectron
een
Adapted from Figs. 18.12(a) & 18.14(a), Callister & Rethwisch 8e.
Chapter 18 -32
Extrinsic Semiconductors
N-type(a) Without field(b) With field
P-type(a) Without field(b) With field
Chapter 18 -33
Extrinsic Semiconductors: Conductivity vs. Temperature
• Data for Doped Silicon: -- s increases doping -- reason: imperfection sites lower the activation energy to produce mobile electrons.
• Comparison: intrinsic vs extrinsic conduction... -- extrinsic doping level: 1021/m3 of a n-type donor impurity (such as P). -- for T < 100 K: "freeze-out“, thermal energy insufficient to excite electrons. -- for 150 K < T < 450 K: "extrinsic" -- for T >> 450 K: "intrinsic"
Adapted from Fig. 18.17, Callister & Rethwisch 8e. (Fig. 18.17 from S.M. Sze, Semiconductor Devices, Physics, and Technology, Bell Telephone Laboratories, Inc., 1985.)
Co
nd
uct
ion
ele
ctro
n
con
cen
tra
tion
(1
021/m
3 )T (K)6004002000
0
1
2
3
fre
eze
-ou
t
ext
rin
sic
intr
insi
c
doped
undoped
Chapter 18 -34
Numerical Example• An extrinsic p-type silicon material is desired having a
room-temperature conductivity of 50 (ohm.m)-1. Specify an acceptor impurity type that may be used as well as its concentration in atom percent to yield these electrical characteristics.
Chapter 18 -35
Summary of Charge Carriers
Chapter 18 -36
• Allows flow of electrons in one direction only (e.g., useful to convert alternating current to direct current).• Processing: diffuse P into one side of a B-doped crystal.
-- No applied potential: no net current flow.
-- Forward bias: carriers flow through p-type and n-type regions; holes and electrons recombine at p-n junction; current flows.
-- Reverse bias: carriers flow away from p-n junction; junction region depleted of carriers; little current flow.
p-n Rectifying Junction
++
++
+- ---
-p-type n-type
+ -
++ +
++
--
--
-
p-type n-typeAdapted from Fig. 18.21 Callister & Rethwisch 8e.
+++
+
+
---
--
p-type n-type- +
Chapter 18 -37
Properties of Rectifying Junction
Fig. 18.22, Callister & Rethwisch 8e. Fig. 18.23, Callister & Rethwisch 8e.
Chapter 18 -38
Properties of Diodes• The transconductance curve on the previous slide is characterized by the following
equation:
ID = IS(eVD/VT – 1)• As described in the last slide, ID is the current through the diode, IS is the saturation
current and VD is the applied biasing voltage.
• VT is the thermal equivalent voltage and is approximately 26 mV at room temperature. The equation to find VT at various temperatures is:
VT = kT q
k = 1.38 x 10-23 J/K T = temperature in Kelvin q = 1.6 x 10-19 C
• is the emission coefficient for the diode. It is determined by the way the diode is constructed. It somewhat varies with diode current. For a silicon diode is around 2 for low currents and goes down to about 1 at higher currents
Chapter 18 -39
Diode Circuit ModelThe Ideal Diode Model The diode is designed to allow current to flow in only one
direction. The perfect diode would be a perfect conductor in one direction (forward bias) and a perfect insulator in the other direction (reverse bias). In many situations, using the ideal diode approximation is acceptable.
Example: Assume the diode in the circuit below is ideal. Determine the value of ID if a) VA = 5 volts (forward bias) and b) VA = -5 volts (reverse bias)
+
_VA
ID
RS = 50 a) With VA > 0 the diode is in forward bias and is acting like a perfect conductor so:
ID = VA/RS = 5 V / 50 = 100 mA
b) With VA < 0 the diode is in reverse bias and is acting like a perfect insulator, therefore no current can flow and ID = 0.
Chapter 18 -40
Diode Circuit ModelsThe Ideal Diode with Barrier Potential This model is more accurate than the simple ideal
diode model because it includes the approximate barrier potential voltage. Remember the barrier potential voltage is the voltage at which appreciable current starts to flow.
Example: To be more accurate than just using the ideal diode model include the barrier potential. Assume V = 0.3 volts (typical for a germanium diode) Determine the value of ID if VA = 5 volts (forward bias).
+
_VA
ID
RS = 50 With VA > 0 the diode is in forward bias and is acting like a perfect conductor so write a KVL equation to find ID:
0 = VA – IDRS - V
ID = VA - V = 4.7 V = 94 mA RS 50
V
+
V
+
Chapter 18 -41
Types of DiodesPN Junction Diodes:
Are used to allow current to flow in one direction while blocking current flow in the opposite direction. The pn junction diode is the typical diode that has been used in the previous circuits.
A K
Schematic Symbol for a PN Junction Diode
P n
Representative Structure for a PN Junction Diode
Zener Diodes: Are specifically designed to operate under reverse breakdown conditions. These diodes have a very accurate and specific reverse breakdown voltage.
A K
Schematic Symbol for a Zener Diode
Chapter 18 -42
Types of DiodesLight-Emitting Diodes (LED):
Light-emitting diodes are designed with a very large bandgap so movement of carriers across their depletion region emits photons of light energy. Lower band gap LEDs (Light-Emitting Diodes) emit infrared radiation, while LEDs with higher band gap energy emit visible light. Many stop lights are now starting to use LEDs because they are extremely bright and last longer than regular bulbs for a relatively low cost.
A K
Schematic Symbol for a Light-Emitting Diode
The arrows in the LED representation indicate emitted light.
Chapter 18 -43
Types of DiodesPhotodiodes:
While LEDs emit light, Photodiodes are sensitive to received light. They are constructed so their pn junction can be exposed to the outside through a clear window or lens.In Photoconductive mode the saturation current increases in proportion to the intensity of the received light. This type of diode is used in CD players.In Photovoltaic mode, when the pn junction is exposed to a certain wavelength of light, the diode generates voltage and can be used as an energy source. This type of diode is used in the production of solar power.
A K
A K
Schematic Symbols for Photodiodes
Chapter 18 -44
PhotoVoltaic
+
+
++-
--
-
Photo Voltaic cell
Electrode
P-Type Semiconductor
N-Type Semiconductor
Reflect-Proof Film
Electrode
Solar Energy
Load
Ele
ctri
c C
urre
nt
The solar cell is composed of a P-type semiconductor and an N-type semiconductor. Solar light hitting the cell produces two types of electrons, negatively and positively charged electrons in the semiconductors.Negatively charged (-) electrons gather around the N-type semiconductor while positively charged (+) electrons gather around the P-type semiconductor. When you connect loads such as a light bulb, electric current flows between the two electrodes.
Chapter 18 -45
PhotoVoltaic• Direction of current inside PV cell
P
N
Current appears to be in the
reverse direction ?
• Inside current of PV cell looks like “Reverse direction.” Why?
?
• By Solar Energy, current is pumped up from N-pole to P-pole.
• In generation, current appears reverse. It is the same as for battery.
P
N
Looks like
reverse
Chapter 18 -46
Photovoltaic• Voltage and Current of PV cell ( I-V Curve )
(V)
(A)
Voltage(V)
Cur
rent
(I)
P
N
A
Short Circuit
Open Circuit
P
N
V
about 0.5V (Silicon)
High insolation
•Voltage on normal operation point0.5V (in case of Silicon PV)
•Current depend on- Intensity of insolation- Size of cell
•Voltage on normal operation point0.5V (in case of Silicon PV)
•Current depend on- Intensity of insolation- Size of cell
Low insolation
Normal operation point(Maximum Power point)
I x V = W
Chapter 18 -47
PhotoVoltaic• I / V curve and P-Max control
P
N
A
V
• To obtain maximum power, current control (or voltage control) is very important.
(V)
(A)
Voltage(V)
Cur
rent
(I)
I x V = W
P2
PMAX
P1
Vpmax
IpmaxI/V curve
P- Max controlP- Max control
• “Power conditioner” (mentioned later) will adjusts to be most suitable voltage and current automatically.
Power curve
Chapter 18 -48
PhotoVoltaic• Estimate obtained power by I / V curve
(V)
(A)
Voltage(V)
Cur
rent
(I)
12
10
8
6
4
2
0
0 0.1 0.2 0.3 0.4 0.5 0.6
P
N
A
)(05.0 R
PV character( I/V curve )
If the load has 0.05 ohm resistance, cross point of resistance character and PV-Character will be following point.Then power is 10x0.5=5 W
)(05.0 R
Resista
nce chara
cter
05.0/VI R
VI
Ohm’s law
Chapter 18 -49
PhotoVoltaic• Temperature and efficiency
4
6
8
10
12
14
0 10 20 30 40 50 60 70 80 90 100Module Temperature (deg.C)
Eff
icie
ncy
(%)
Crystalline cell
Amorphous cell
0.25 (%/deg)
Typical(25C)
Summer timeon roof top
(65C)
2%down 0.4 – 0.5 (%/deg)
• When module temperature rises up, efficiency decreases.• The module must be cooled by natural ventilation, etc.
Chapter 18 -50
PhotoVoltaic
CrystallineCrystalline
Non-crystallineNon-crystalline
Single crystalSingle crystal
Poly crystallinePoly crystalline
AmorphousAmorphous
Gallium Arsenide (GaAs)Gallium Arsenide (GaAs)
Conversion Efficiency of ModuleConversion Efficiency of Module
10 - 17%10 - 17%
10 - 13%10 - 13%
7 - 10%7 - 10%
18 - 30%18 - 30%
Conversion Efficiency =Electric Energy Output
Energy of Insolation on cellx 100%
Dye-sensitized TypeDye-sensitized Type
Organic Thin Layer TypeOrganic Thin Layer Type
7 - 8%7 - 8%
2 - 3%2 - 3%
• Types and Conversion Efficiency of Solar Cell
Silicon SemiconductorSilicon Semiconductor
CompoundSemiconductorCompoundSemiconductor
Solar CellSolar Cell
OrganicSemiconductorOrganicSemiconductor
Chapter 18 -
PhotoVoltaic
51
• Crystal cell (Single crystal and Poly crystalline Silicon)
Formed by melting high purity silicon like as Integrated Circuit
For mass production, cell is sliced from roughly crystallized ingot.
Single crystal Poly crystalline
Chapter 18 -52
PhotoVoltaic• Surface of PV cell
Front Surface(N-Type side)
• Aluminum Electrode (Silver colored wire)
• To avoid shading, electrode is very fine.
Anti reflection film(Blue colored film)
• Back surface is P-type.
• All back surface is aluminum electrode with full reflection.
Example of Poly Crystalline PV
Chapter 18 -53
PhotoVoltaic
Single crystal Poly crystalline
120W(25.7V , 4.7A)
1200mm
800mm800mm
1200mm
• PV Module (Single crystal, Poly crystalline Silicon)
(3.93ft)
( 2.62ft )
( 3.93ft)
(2.62ft)
128W(26.5V , 4.8A)
Efficiency is higher Efficiency is lower
Same size
Chapter 18 -54
PhotoVoltaic• Hierarchy of PV
2 – 3 W
100 - 200 W
10 - 50 kW
Cell
Array
Module,Panel
Volt Ampere Watt SizeCell 0.5V 5-6A 2-3W about 10cmModule 20-30V 5-6A 100-200W about 1mArray 200-300V 50A-200A 10-50kW about 30m
6x9=54 (cells) 100-300 (modules)
Chapter 18 -55
PhotoVoltaic• Roughly size of PV Power Station.
How much PV can we install in this conference room?
1 kw PV need 10 m21 kw PV need 10 m2 Please remember
10m(33feet)
20m
(66f
eet)
ConferenceRoom
(We are now)
Our room has about 200 m2
We can install about20 kW PV in this room
(108 feet2)
(2,178 feet2)
Chapter 18 -56
PhotoVoltaic• Roof top of residence ( Grid connected )
Most popular installation style in Japan.(Almost 85% PV in Japan )
Owner can sell excess power to power utility.
Chapter 18 -57
PhotoVoltaic• Distant and independent power supply ( Off grid )
Relay station on top of mountain
Advertising sign beside highway
Chapter 18 -58
Junction Transistor
Fig. 18.24, Callister & Rethwisch 8e.
Chapter 18 -59
MOSFET Transistor Integrated Circuit Device
• Integrated circuits - state of the art ca. 50 nm line width– ~ 1,000,000,000 components on chip– chips formed one layer at a time
Fig. 18.26, Callister & Rethwisch 8e.
• MOSFET (metal oxide semiconductor field effect transistor)
Chapter 18 -60
Dielectric Behavior• Dielectric material is non-
conducting and it exhibit an electric dipole. i.e. separation between a positive and negative electric charge
• Electric dipole moment: a vector directed from –q to +q, p=qd
• When a field is applied (vector), a force or torque will come to bear on an electric dipole to orient it with the field. Known as Polarization
Chapter 18 -61
Capacitance• When a voltage is applied across a
capacitor, one plate becomes positively charged, the other negatively charged. The capacitance C is related to the quantity of charge stored on either plate Q by:
• C=Q/V
• If a vacuum exists between the two plates; C can be computed from
• • If a dielectric material is inserted into the
region within the plates then:
• ,
Chapter 18 -62
Dielectric Displacement• The surface charge density D in case of
vacuum is:
• If a dielectric material is inserted into the region within the plates then:
• =+P
(-1)
Chapter 18 -63
Numerical Problems
• Consider a parallel-plate capacitor having an area of 6.45x10-3 m (0.08 in) across which a potential of 10 V is applied. If a material having a dielectric constant of 6.0 is positioned within the region between the plates, compute the following:
• (a) The capacitance• (b) The magnitude of the charge stored on each
plate• The dielectric displacement D• The polarization.
Chapter 18 -64
Ferroelectric Ceramics
• Experience spontaneous polarization
Fig. 18.35, Callister & Rethwisch 8e.
BaTiO3 -- ferroelectric below its Curie temperature (120ºC)
Chapter 18 -65
Piezoelectric Materials
stress-free with applied stress
Adapted from Fig. 18.36, Callister & Rethwisch 8e. (Fig. 18.36 from Van Vlack, Lawrence H., Elements of Materials Science and Engineering, 1989, p.482, Adapted by permission of Pearson Education, Inc., Upper Saddle River, New Jersey.)
Piezoelectricity – application of stress induces voltage – application of voltage induces dimensional change
Chapter 18 -66
• Electrical conductivity and resistivity are: -- material parameters -- geometry independent• Conductors, semiconductors, and insulators... -- differ in range of conductivity values -- differ in availability of electron excitation states• For metals, resistivity is increased by -- increasing temperature -- addition of imperfections -- plastic deformation• For pure semiconductors, conductivity is increased by -- increasing temperature -- doping [e.g., adding B to Si (p-type) or P to Si (n-type)]• Other electrical characteristics -- ferroelectricity -- piezoelectricity
Summary