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Semiconductor Device Modeling and Characterization – EE5342 Lecture 21 – Spring 2011

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

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  1. Semiconductor Device Modeling and Characterization – EE5342 Lecture 21 – Spring 2011 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/

  2. Linking current E-M circuit model

  3. 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

  4. npn Base-width mod.(Early Effect) Fig 9.15*

  5. Base-width modulation(Early Effect, cont.) Fig 9.16*

  6. Emitter currentcrowding in base Fig 9.21*

  7. Interdigitated basefixes emitter crowding Fig 9.23*

  8. Base region high-level injection (npn)

  9. Effect of HLI innpn base region Fig 9.17*

  10. Effect of HLI in npnbase region (cont)

  11. Effect of HLI in npnbase region (cont)

  12. Emitter region high-level injection (npn)

  13. Effect of HLI innpn emitter region

  14. Figs 9.18 and 9.19* Effect of HLI innpn base region

  15. Fig 9.20* Replaces ni2 throughout Bandgap narrowing effects

  16. 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.

  17. 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

  18. 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 } Gummel Poon npnModel Equations

  19. 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

  20. 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

  21. Charge componentsin the BJT **From Getreau, Modeling the Bipolar Transistor, Tektronix, Inc.

  22. 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).

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