Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ 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 ©rlc L21-28Mar2011

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 L21-28Mar2011

npn Base-width mod. (Early Effect) Fig 9.15* ©rlc L21-28Mar2011

Base-width modulation (Early Effect, cont.) Fig 9.16* ©rlc L21-28Mar2011

Emitter current crowding in base Fig 9.21* ©rlc L21-28Mar2011

Interdigitated base fixes emitter crowding Fig 9.23* ©rlc L21-28Mar2011

Base region high- level injection (npn) ©rlc L21-28Mar2011

Effect of HLI in npn base region Fig 9.17* ©rlc L21-28Mar2011

Effect of HLI in npn base region (cont) ©rlc L21-28Mar2011

Effect of HLI in npn base region (cont) ©rlc L21-28Mar2011

Emitter region high- level injection (npn) ©rlc L21-28Mar2011

Effect of HLI in npn emitter region ©rlc L21-28Mar2011

Effect of HLI in npn base region Figs 9.18 and 9.19* ©rlc L21-28Mar2011

Bandgap narrowing effects Fig 9.20* Replaces ni2 throughout ©rlc L21-28Mar2011

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. ©rlc L21-28Mar2011

The npn Gummel-Poon Static Model RC ICC - IEC = IS(exp(vBE/NFVt - exp(vBC/NRVt)/QB B RBB ILC IBR B’ ILE IBF RE E ©rlc L21-28Mar2011

Gummel Poon npn Model Equations IBF = ISexpf(vBE/NFVt)/BF ILE = ISEexpf(vBE/NEVt) IBR = ISexpf(vBC/NRVt)/BR ILC = ISCexpf(vBC/NCVt) QB = (1 + vBC/VAF + vBE/VAR )  {½ + [¼ + (BFIBF/IKF + BRIBR/IKR)]1/2 } ©rlc L21-28Mar2011

Making a diode from the GP BJT model C RC ICC - IEC = IS(exp(vBE/NFVt - exp(vBC/NRVt)/QB B RBB ILC IBR B’ ILE IBF RE E ©rlc L21-28Mar2011

Making a complete diode with G-P BJT 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 ©rlc L21-28Mar2011

Charge components in the BJT **From Getreau, Modeling the Bipolar Transistor, Tektronix, Inc. ©rlc L21-28Mar2011

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 L21-28Mar2011