1. Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/
Semiconductor Device Modeling and Characterization – EE5342 Lecture 17 – Spring 2011
Professor Ronald L. Carter

2. Bipolar junction transistor (BJT)E B C
VEB
VCB
Charge neutral Region
Depletion Region
The BJT is a “Si sandwich” Pnp (P=p+,p=p-) or Npn (N=n+, n=n-)
BJT action: npn Forward Active when VBE > 0 and VBC < 0
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3. BJT coordinate systemsz
x”c x” WB
WB+WC
-WE xB x
x’E x’
Charge neutral Region
Depletion Region
Base
Collector
Emitter
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4. BJT boundary and injection cond (npn)
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5. BJT boundary and injection cond (npn)
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6. IC npn BJT (*Fig 9.2a)
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7. npn BJT bands in FA region
q(VbiE-VBE )
q(VbiC-VBC )
qVBE
qVBC
injection
high field
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8. Coordinate system - prototype npn BJT (Fig 9.8*)
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9. Notation for npn & pnp BJTs
NE, NB, NC E, B, and C doping (maj)
xE, xB, xC E, B, and C CNR widths
DE, DB, DC Dminority for E, B, and C
LE, LB, LC Lminority for E, B, and C (L2min = Dmin tmin)
The minority carrier lifetimes in the E, B, and C regions are tE0, tB0, & tC0
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10. Notation for npn BJTs only
pEO, nBO, pCO: E, B, and C thermal equilibrium minority carrier conc
pE(x’), nB(x), pC(x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations
The excess carrier concentrations dpE(x’), dnB(x), dpC(x’’) are the positional mathematical functions in the E, B, and C
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11. Notation for pnp BJTs only
nEO, pBO, nCO: E, B, and C thermal equilibrium minority carrier conc
nE(x’), pB(x), nC (x’’): positional mathe- matical function for the E, B, and C total minority carrier concentrations
dnE(x’), dpB(x), dnC(x’’): positional ma- thematical function for the excess minority carriers in the E, B, and C
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12. npn BJT boundary conditions
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13. Emitter solution in npn BJT
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14. Base solution in npn BJT
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15. Collector solution in npn BJT
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16. Hyperbolic sine function
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17. npn BJT regions of operation
VBC
Reverse Active
Saturation
VBE
Forward Active
Cutoff
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18. npn FA BJT minority carrier distribution (Fig 9.4*)
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19. npn RA BJT minority carrier distribution (Fig 9.11a*)
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20. npn cutoff BJT min carrier distribution (Fig 9.10a*)
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21. npn sat BJT minority carrier distribution (Fig 9.10b*)
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22. Defining currents in FA mode npn BJT (Fig 9.13*)
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23. npn BJT currents (F A region, ©RLC)
IC = JCAC
IB=-(IE+IC )
JnE
JnC
IE =
-JEAE
JRB=JnE-JnC
JpE
JGC
JRE
JpC
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24. Common base current gain, aF (cont.)
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25. Common emitter current gain, bF
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26. Ebers-Moll Model (Neglecting G-R curr)
(Fig. 9.30*)
-JEAE=IE
JCAC=IC
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27. Source of Ebers-Moll Equations (E)
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28. Source of Ebers-Moll Equations (C)
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29. E-M model equations
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30. Ebers-Moll Model (Neglecting G-R curr)
(Fig. 9.30*)
-JEAE=IE
JCAC=IC
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31. Linking current E-M circuit model
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32. Linking current version of E-M model
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33. Linking current E-M model (cont)
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34. References
1 OrCAD PSpice A/D Manual, Version 9.1, November, 1999, OrCAD, Inc.
2 Semiconductor Device Modeling with SPICE, 2nd ed., by Massobrio and Antognetti, McGraw Hill, NY, 1993.
* Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997.
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