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Semiconductor Device Modeling and Characterization – EE5342 Lecture 21 – Spring 2011. Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/. Linking current E-M circuit model. Non-ideal effects in BJTs. Recombination/Generation effects
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Semiconductor Device Modeling and Characterization – EE5342 Lecture 21 – Spring 2011 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/
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
npn Base-width mod.(Early Effect) Fig 9.15*
Emitter currentcrowding in base Fig 9.21*
Effect of HLI innpn base region Fig 9.17*
Figs 9.18 and 9.19* Effect of HLI innpn base region
Fig 9.20* Replaces ni2 throughout Bandgap narrowing effects
Junction breakdown at BC junction • Reach-through or punch-through when WCB and/or WEB become large enough to reduce xB to zero • Avalanche breakdown when Emax at EB junction or CB junction reaches Ecrit.
The npn Gummel-Poon Static Model C RC ICC -IEC = IS(exp(vBE/NFVt - exp(vBC/NRVt)/QB IBR B RBB ILC B’ IBF ILE RE E
IBF = ISexpf(vBE/NFVt)/BF ILE = ISEexpf(vBE/NEVt) IBR = ISexpf(vBC/NRVt)/BR ILC = ISCexpf(vBC/NCVt) QB = (1 + vBC/VAF + vBE/VAR ) {½ + [¼ + (BFIBF/IKF + BRIBR/IKR)]1/2 } Gummel Poon npnModel Equations
Making a diode from the GP BJT model C RC ICC -IEC = IS(exp(vBE/NFVt - exp(vBC/NRVt)/QB IBR B RBB ILC B’ IBF ILE RE E
RB = RC = 0 Set RE to the desired RS value Set ILE and NE to ISR and NR so this is the rec. current Set BR=BF>>1, ~1e8 so IBR, IBF are neglibigle Set ISC = 0 so ILC is = 0 Set IS to IS for diode so ICC-IEC is the injection curr. Set VAR = VAF = 0 IKF gives the desired high level injection, set IKR = 0 Making a completediode with G-P BJT
Charge componentsin the BJT **From Getreau, Modeling the Bipolar Transistor, Tektronix, Inc.
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).