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Lecture 4.0Lecture 4.0
Properties of Metals
Importance to Silicon ChipsImportance to Silicon Chips
Metal Delamination– Thermal expansion failures
Chip Cooling- Device Density– Heat Capacity– Thermal Conductivity
Chip Speed – Resistance in RC interconnects
Electrical CurrentElectrical Current
Flow of Charged Particles due to applied voltage– Solids• Ions/holes are large and slow• electrons are small and fast
– Electrons are often responsible for conduction
Ohm's LawOhm's Law
Current density, J=I/A==/ =electric field[V/cm] =Conductivity, [=1/] =Resistivity =ne, =mobility, e=electron charge,
n=#/vol.
Resistance, R= L/AV=IR
Metal ConductionMetal Conduction
Drude’s theory– electron scattering
by lattice
Mobility, e/me = average time
between collisions of electron with ions
Bloch’s Quantum theory– no electron scattering
in perfect lattice only in a imperfect lattice
Scattering– lattice vibrations– impurities– dislocations
Remember Molecular OrbitalsRemember Molecular Orbitals
New Energy– Bonding– Anti Bonding
•• •
•1s 1s
Energy BandsEnergy Bands
Energy BandsEnergy Bands
Partially Filled
Distribution of Electrons in BandDistribution of Electrons in Band
Fermi-Dirac distributionProbability, – F(E)=1/(exp{[E-Ef]/kBT}+1)
– Ef is the Fermi Energy
Fermi EnergyFermi EnergyMetal Ef(eV)
Na 3.22
Cu 7.00
Ag 5.46
Au 5.49
Mg 7.05
Zn 9.38
Al 11.58
Sn 9.99
Work FunctionWork Function
Fermi-Dirac Probability Fermi-Dirac Probability DistributionDistribution
Density of States-Density of States-3D Schrodinger Eq.3D Schrodinger Eq.
3/222
2/12/3
22
0
3
2
2
2)(
)(
V
N
mE
EmV
Eg
dEEgN
ef
e
E f
ElectronElectronFilling inFilling inBand-Band-density of density of occupied occupied statesstates
Eletrical ConductivityEletrical Conductivity
=ne =mobility, e=electron charge, n=#/vol.
=(N/V) F(E)G(E) e2/me,
Thermal Properties - Chapter 7Thermal Properties - Chapter 7
Thermal ConductivityThermal ExpansionHeat CapacityThermoelectric effect– thermocouple
Thermal Properties - Chapter 7Thermal Properties - Chapter 7
Thermal Vibrations-phonons– Displacement, xmax=(3kBT/Yao)1/2
– Y ao
is the spring constant
Thermal Expansion (l/lo)(1/T), also volume->(V/Vo)(1/T)
Heat Capacity– Cp=1/2 kBT per degree of freedom– 6 degrees of freedom per ion, Cp=3R
• kinetic and potential
Variation of Conductivity with Temp. d /dT
Thermal Thermal ExpansionExpansion
Heat CapacityHeat Capacity-Effect of Phonons/electrons-Effect of Phonons/electrons
Einstein Model
Debye Model
Electrons– density of occupied
statesElectronsValenceofNumbertotalN
NE
TkC
TkkNC
Tk
Tk
TkkNC
f
Bp
BBAp
B
B
BBAp
2
3
max
4
2
2
2
9
5
12
)1)(exp(
)exp(
3
En=(n+1/2)h<E>= h/(exp(h/kBT)-1)
g()= 2V/(22v3)
T
dTk
g
T
UC Bp
]
1)/exp()(
3[max
0
Heat Capacity of ElectronsHeat Capacity of Electrons
ElectronsValenceofNumbertotalN
NE
TkC
f
Bp
2
2
9
Heat CapacityHeat Capacity
Thermal ConductionThermal Conduction
Transport of Phonons (vibrations)kthermal/(T)=constant
– thermal conductivity scales with electrical conductivity
kthermal=kelectrons + kphonons
ConductivitiesConductivities
Thermal Conductivity-PhononThermal Conductivity-Phonon
kphonons= Ne Cp ph Vph/3
– Ne number e-/volume,
– Cp=heat capacity of atoms =3kB
ph =mean free path,
– Vph=velocity
Thermal Conductivity - ElectronThermal Conductivity - Electron
ke= Ne Ce e Ve/3
– Ne number e-/volume,
– Ce=heat capacity of electrons
e =mean free path,
– Ve=velocity
ElectronsValenceofNumbertotalN
NE
TkC
f
Bp
2
2
9
Thermal ConductivityThermal Conductivity
Phonon InteractionsPhonon Interactions
With other phononsWith impurities– depends upon phonon wavelength
With imperfections in Crystal– depends upon phonon wavelength
Phonons travel at speed of sound
Phonon InteractionsPhonon Interactions