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From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
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instructors if the 3rd Edition
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course. Permission is given to
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edition with CD-!"
Electronic "aterials and
Devices to use these slides in
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provided that the boo$ title#
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From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Definition of Capacitance
C o = capacitance of a parallel plate capacitor in free
space
Qo = charge on the plates
V = voltage
C o =
Qo
V
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Fig 7.1
!a* Parallel plate capacitor $ith free space +et$een the plates.
!+* s a sla+ of ins-lating material is inserted +et$een the plates, there is an eternal c-rrent
flo$ indicating that more charge is stored on the plates.
!c* The capacitance has +een increased d-e to the insertion of a medi-m +et$een the plates.
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Fig 7.6 From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Polari/ation charge densit0 on the s-rface of a polari/ed medi-m is related to the normal
component of the polari/ation vector.
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Fig 7.9 From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* a2l chain in the a2l cr0stal $itho-t an applied field. verage or net dipole
moment per ion is /ero.
!+* 3n the presence of an applied field the ions +ecome slightl0 displaced $hich leads to
a net average dipole moment per ion.
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Fig 7.! From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* n ac field is applied to a dipolar medi-m. The polari/ation P ! P = Np* is o-t of phase $ith
the ac field.
!+* The relative permittivit0 is a comple n-m+er $ith real !ε r 4* and imaginar0 !ε r 44*
parts that ehi+it fre5-enc0 dependence.
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Fig 7.7 From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Cole-Cole plots
Cole-Cole plot is a plot of ε ″ r vs. ε ′r as a f-nction of fre5-enc0, ω . s the
fre5-enc0 is changed from lo$ to high fre5-encies, the plot traces o-t a
circle if De+0e e5-ations are o+e0ed.
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Fig 7.2
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* 6o-ndar0 conditions +et$een dielectrics
!+* The case for Et 1 = Et '.
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Fig 7.2"
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
Time to +reado$n and the field at +reado$n, E+r, are interrelated and depend on the mechanism that ca-ses
the ins-lation +reado$n. Eternal discharges have +een ecl-ded !+ased on 8.. Dissado and 9.2. Fothergill,
Electrical Degradation and 6reado$n in Pol0mers, Peter Peregrin-s 8td. for 3EE, :, " 1;;', p.
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Fig 7.!"
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The pie/oelectric effect.
!a* pie/oelectric cr0stal $ith no applied stress or field.
!+* The cr0stal is strained +0 an applied force that ind-ces polari/ation in the cr0stal and generates s-rface charges.
!c* n applied field ca-ses the cr0stal to +ecome strained. 3n this case the field compresses the cr0stal.
!d* The strain changes direction $ith the applied field and no$ the cr0stal is etended.
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Fig 7.#2
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The pie/oelectric spar generator.
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Fig 7.#7
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The p0roelectric detector. >adiation is a+sor+ed in the detecting element, , $hich generatesa p0roelectric voltage that is meas-red +0 the amplifier. The second element, 6, has a reflecting
electrode and does not a+sor+ the radiation. 3t is a d-mm0 element that compensates for the
pie/oelectric effects. Pie/oelectric effects generate e5-al voltages in +oth and 6 $hich across
a and + !the inp-t of the amplifier* cancel each other.
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Fig 7.#"
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* Parallel plate capacitor $ith free space +et$een plates $hich has +een charged to avoltage V o. There is no +atter0 to maintain the voltage constant across the capacitor. The
electrometer meas-res the voltage difference across the plates and, in principle, does no
affect the meas-rement. !+* fter the insertion of the dielectric, the voltage difference is
V , less than V o and the field in the dielectric is E less than E o.
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Fig 7.#9
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
2onsider a #a-ss s-rface ?-st aro-nd the right plate and $ithin the dielectric
encompassing +oth @Qfree and −Q P . ! E is the electric field.*
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Fig 7.5
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* Polari/ation and the depolari/ing field in a spherical shaped dielectric placed
in an applied field E o
!+* Depolari/ation field in a thin rod placed in an applied field is nearl0 /ero.
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Fig 7.52
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
!a* The macroscopic field E is determined +0 the applied field E o and the depolari/ation field d-e
to P . !+* 2alc-lation of the local field involves maing a h0pothetical spherical cavit0S inside the
dielectric. This prod-ces polari/ation s-rface charges on the inside s-rfaceS of the cavit0. The
effects of the dipoles inside the cavit0 are treated individ-all0.
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Fig 7.56
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
The 8angevin f-nction.
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Fig 7.5"
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
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Fig 7.59
From Principles of Electronic Materials and Devices, Third Edition, S.O. Kasap (© McGraw-Hill, 2005)
&eterogeneo-s dielectric media eamples
!a* Dispersed dielectric spheres in a dielectric matri.!+* heterogeneo-s medi-m $ith t$o distinct phases 3 and 33.
!c* Series mit-re r-le.
!d* Parallel mit-re r-le.