Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ Semiconductor Device Modeling and Characterization – EE5342 Lecture 20 – Spring 2011 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/

IC npn BJT (*Fig 9.2a) ©rlc L20-25Mar2011

npn BJT currents (F A region, ©RLC) IC = JCAC IB=-(IE+IC ) JnE JnC IE = -JEAE JRB=JnE-JnC JpE JGC JRE JpC ©rlc L20-25Mar2011

Defining currents in FA mode npn BJT (Fig 9.13*) ©rlc L20-25Mar2011

Common base current gain, aF (cont.) ©rlc L20-25Mar2011

Common emitter current gain, bF ©rlc L20-25Mar2011

Ebers-Moll Model (Neglecting G-R curr) (Fig. 9.30*) -JEAE=IE JCAC=IC ©rlc L20-25Mar2011

Source of Ebers-Moll Equations (E) ©rlc L20-25Mar2011

Source of Ebers-Moll Equations (C) ©rlc L20-25Mar2011

E-M model equations ©rlc L20-25Mar2011

Ebers-Moll Model (Neglecting G-R curr) (Fig. 9.30*) -JEAE=IE JCAC=IC ©rlc L20-25Mar2011

Linking current E-M circuit model ©rlc L20-25Mar2011

Linking current version of E-M model ©rlc L20-25Mar2011

Linking current E-M model (cont) ©rlc L20-25Mar2011

Non-ideal effects in BJTs Recombination/Generation effects Base-width modulation (FA: xB changes with changes in VBC) Current crowding in 2-dim base High-level injection (minority carriers g.t. dopant - especially in the base). Emitter Bandgap narrowing (NE ~ density of states at cond. band. edge) Junction breakdown at BC junction ©rlc L20-25Mar2011

Recombination/Gen Currents (FA) ©rlc L20-25Mar2011

npn Base-width mod. (Early Effect) Fig 9.15* ©rlc L20-25Mar2011

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. ** Modeling the Bipolar Transistor, by Ian Getreau, Tektronix, Inc., (out of print). ©rlc L20-25Mar2011