Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ EE 4345 - Semiconductor Electronics Design Project Spring 2002 - Lecture 07 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc/ L07 February 05

Lab schedule As announced last week, plan to attend your lab session (Tu or Th at 230 to 500 PM) this week for additional Cadence instruction. Topics to be covered schematic capture of a circuit making a symbol simulating a circuit L07 February 05

Bipolar junction transistor (BJT) General bias on a pnp transistor The BJT is a ‘silicon sandwich’ p+np- or n+pn- npn For. Active BJT action when VBE > 0 and VBC < 0 p n E B C VEB VCB Charge neutral Region Depletion Region L07 February 05

npn BJT currents (F A region, ©RLC) IC = JCAC IB=-(IE+IC ) JnE JnC IE = -JEAE JRB=JnE-JnC JpE JGC JRE JpC L07 February 05

Ebers-Moll (npn injection model) (common-emitter) E L07 February 05

E-M model equations L07 February 05

Ebers-Moll Model (npn bipolar jctn. tran. w/o inj.) aRIR aFIF E C (Common base) B L07 February 05

IC npn BJT (*Fig 9.2a) L07 February 05

npn BJT regions of operation VBC Reverse Active Saturation VBE Forward Active Cutoff L07 February 05

npn FA BJT minority carrier distribution (Fig 9.4*) L07 February 05

npn RA BJT minority carrier distribution (Fig 9.11a*) L07 February 05

npn cutoff BJT min carrier distribution (Fig 9.10a*) L07 February 05

npn sat BJT minority carrier distribution (Fig 9.10b*) L07 February 05

Defining currents in FA mode npn BJT (Fig 9.13*) L07 February 05

Non-ideal effects in BJTs 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 for NE --> density of states at cond. band. edge Junction breakdown at BC junction L07 February 05

npn Base-width modulation (Early Effect) Fig 9.15* L07 February 05

Base-width modulation (Early Effect, cont.) Fig 9.16* L07 February 05

Emitter current crowding in base Fig 9.21* L07 February 05

Interdigitated base fixes emitter crowding Fig 9.23* L07 February 05

Effect of HLI in npn base region Figs 9.18 and 9.19* L07 February 05

Ebers-Moll Model (Neglecting G-R curr) (Fig. 9.30*) L07 February 05

Hybrid-pi Circuit model Fig 9.33 Semiconductor Physics and Devices, 2nd ed., by Neamen, Irwin, Boston, 1997. L07 February 05

Hybrid-pi circuit model Adapted from inj. model version of E-M model with parasitic rb, rc, re, and CSubst C-E branch is linking current B-E branch is the reduced B-E diode with diffusion (for and rev) resistance and capacitance and junction cap. B-C branch is the reduced B-C diode with diffusion (for and rev) resistance and capacitance and junction cap. L07 February 05

References * Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997. L07 February 05