principles of semiconductor devices-l27
TRANSCRIPT
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www.nanohub.org
NCN
Lecture27:IntroductiontoBipolarTransistors
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Background
E C
PointcontactGermanium transistor(your HW problem!)
2
.
TransistorresearchwasalsoinadvancedstagesinEurope(radar).
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ShockleysBipolarTransistors
Double pbasencollector
n+
DiffusedBJT n+
n+ p n n+
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ModernBipolarJunctionTransistors(BJTs)
CollectorEmitterBase
N+
SiGeintrinsicbase Dielectric trench
N+P+
N
P
Transistor speed increases
as the electron's travel
distance is reduced
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SiGe Layer
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SymbolsandConvention
SymbolsE
Lowdo edbase
N+
P
NPN PNP
Collector CollectorB
CollectordopingN
Base Base
optimizationEmitter Emitter
C
IC+IB+IE=0
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VEB
+VBC
+VCE
=0
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Outline
1 E uilibriumandforwardbanddia ram
2) Currentsinbipolarjunctiontransistors
4) Conclusions
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TopicMap
signal
SignalDiode
Schottky
BJT/HBT
MOS
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BandDiagramatEquilibrium
( )D AD q p n N N +
= + 1n
Equilibrium
N N N r g
t q= +
J = + n E D n DC dn dt=0
1P P P
pr g
t
= +
J
Smallsignaldn/dt~jtnTransient Chargecontrolmodel
P P Pqp E qD p= J
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BandDiagramatEquilibrium
BaseEmitter Collector
Vacuum
level 2EC
EF
1 3
EV
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ElectrostaticsinEquilibrium
( )0
,
2 s E p BE bi
B E B
k Nx V
q N N N =
+
( )0
,
2s C
p BC bi
B C B
k Nx V
q N N N =
+
02 s Bk Nx V=
2k N
,
E B E q N N N + ( ),n C bi
C C B
xq N N N
=+
BaseEmitter Collector
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Outline
1) Equilibriumandforwardbanddiagram
2) Currentsinbipolarjunctiontransistors
3) EbersMollmodel
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TopicMap
signal
SignalDiode
Schottky
BJT/HBT
MOS
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BandDiagramwithBias
( )D AD q p n N N +
= + 1n
Nonequilibrium
N N N r g
t q= +
J = + n E D n DC dn dt=0
1P P P
pr g
= +J
Smallsignaldn/dt~jtnTransient Chargecontrolmodel
P P Pqp E qD p= J
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ElectrostaticsinEquilibrium
( )( )0,
2 s E p BE bi EB
B E B
k N x V V
q N N N
=
+ ( )( )0,
2s C
p BC bi CB
B C B
k N x V V
q N N N
=
+
02 s Bk N x V V
= 02 s Bk N= ,
E B E q N N N + ( ),n C i CB
C C Bq N N N +
BaseEmitter Collector
VEBCB
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CurrentflowwithBias
ECFn,EV
ECFn,C
p,B V
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CoordinatesandConvention
BaseEmitter Collector
N+
P N
0 W
, , , E D E B A B C A C N N N N N N = = =
0 0 0 0 0 0
E P B N C N
E p B n C nn n p p n n= = =
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CarrierDistributioninBasex x
2
,
2
,BE BCi B qV Bi qVx xn n =
B BW W DC
2n 2
B B B BW WN N
, BE
B
n eN
= ( ),( ) 1BCi B qVBB
n x W eN
= =
VCB
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CollectorandEmitterElectronCurrent
( ) ( )2
,
2
,1) 1( 1BE BC
i B qV
B
B
B
i qV
B B
x xn x
W W
ne
ne
N N
= +
( ) ( )2
,
,
2
, 1 1BBE
B
Ci B qVn i B qn C
Vn
BB
n
BW B
nqD eW
dn J qDdx
nqD eW NN
= = +
VBE
, p E p
dp J qD
dx=
VBE
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( )2
1BEp qVi
n D
D ne
W N
=
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CurrentVoltageCharacteristics
Normal,ActiveRegion ( ) ( )2 2
, ,
,1 1BCBE
i B i B qVqVn nn C
B B B B
n nqD qD J e e
W N W N = +
J log J Highlevelinjection
BC: Reversebiased
seriesresistance,etc.
IB
VBE
> m ec.
19Have you seen this figure before?
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Outline
1 E uilibriumandforwardbanddia ram
2) Currentsinbipolarjunctiontransistors
4) Conclusions
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EbersMollModel Holediffusionincollector
( ) ( )2 2 2
, , ,1 1BCBE
pi B i B i C qVqVn n
B B B B C C
VV
C
qDn n nqD qDI A e A e
W N W N W N
= + +
C= c,n+ c,p0 0F F Re e
F
E C
R
IE=IE,n+IE,p
( )0 1BE
BC
qV
F F
qV
I I e
= IE
I
IC
B
FIFRIR
0R R
( ) ( )2 2 2
, , ,1 1BCBE
p i E i B i B qVqVn nE
qD n n nqD qD A e A eI
= + +
21( ) ( )0 01 1BCBE
E E B B E B
qVqV
F R R
I e I e
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CommonBaseConfiguration
E C
F
E C
R
E CVEB(in)
CB
(out) IE ICR R F F
IBCBE CBC
HowwouldthemodelchangeifthiswasaSchottkybarrierBJT?
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CommonEmitterConfiguration
EIE
C
R RBE
B
IB F FIF F R R
I I C
IR
P+
N
PB
VEB
VEC(out)
ICIB
FIFCBC
IR
I I
F
E E
in
IC
1
F F BFF
F
= = =
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This is a practice problem
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Conclusion
ThephysicsofBJTismosteasilyunderstoodwith
.
Theequationscanbeencapsulatedinsimple
equivalentcircuitappropriatefordc,ac,andlarge
si nala lications.
Designoftransistorsisfarmorecomplicatedthan
ss mp emo e sugges s. Foraterrificandinterestinghistoryofinventionof
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bipolartransistor,readthebookCrystalFire.