Unformatted text preview:

EE 5340 Semiconductor Device Theory Lecture 21 Spring 2011 Professor Ronald L Carter ronc uta edu http www uta edu ronc Test 2 Tuesday 05Apr11 11 AM Room 129 ERB Covering Lectures 11 to19 Open book 1 legal text or ref only You may write notes in your book Calculator allowed A cover sheet will be included with full instructions For examples see http www uta edu ronc 5340 tests rlc L2107Apr2011 2 npn BJT currents in the forward active region RLC JnC JnE JRB JnE JnC IE JEAE IC JCAC JGC JpE rlc L2107Apr2011 JRE IB IE IC JpC 3 E M linking current model I EC IS VBC expf R R Vt I B C B I B E C I C E I CT I CC I EC E I CC I S VBE expf F F Vt rlc L2107Apr2011 4 E M linking current model cont In terms of I S the E M eqns become IS VBC VBE I S expf I C expf R Vt Vt IS VBE VBC I S expf I E expf F Vt Vt The current that links the C E branch VBE VBC exp I C E I S exp Vt Vt rlc L2107Apr2011 5 E M linking current model cont Similarly I B C R IS VBC expf with R R 1 R Vt F IS VBE I B E expf with F F 1 F Vt still give the same values for the E M eqns with definitions I C I C E I B C and I E I C E I B E rlc L2107Apr2011 6 More non ideal effects in BJTs a Base width modulation FA xB changes with changes in VBC a 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 rlc L2107Apr2011 edge 7 npn Base width mod Fig 9 15 Early Effect np n J n qDn x Q j VBC CjC xB qNBA VBC J J xB xB J J xB VBC xB VBC rlc L2107Apr2011 8 Base width modulation Early Effect cont xB I J A VCB xB VBC Fig 9 16 J CjC xB qNBA CjC I I VCE QB VCE VA rlc L2107Apr2011 9 Emitter current crowding in base Fig 9 21 rlc L2107Apr2011 10 Interdigitated base fixes emitter crowding Fig 9 23 rlc L2107Apr2011 11 Base region highlevel injection npn Law of the Junction DR edges 2 VBE Vt pEnE x 0 ni e pBnB x 0 NB Base HLI when VBE 2Vt ln ni VBE 2Vt when pB 0 nB 0 nie NB 2 VBE Vt Note pBnB 0 ni e in HLI rlc L2107Apr2011 12 Effect of HLI in npn base region Fig 9 17 pB nB rlc L2107Apr2011 13 Effect of HLI in npn base region cont Consequent ly the electron current at x 0 J nE qDBnB0 expf VBE Vt expf VBC Vt LB tanh xB LB sinh xB LB must be rewritten in the HLI region as J nE qDB ni exp VBE 2Vt nB0 expf VBC Vt LB tanh xB LB sinh xB LB causing J nE J nE J markedly notice J rlc L2107Apr2011 pE pE factor to change changes for E HLI 14 Effect of HLI in npn base region cont Furthermore the electron current at x xB qDBnB0 expf VBE Vt expf VBC Vt J nC LB sinh xB LB tanh xB LB must be rewritten in the HLI region as qDB ni exp VBE 2Vt nB0 expf VBC Vt J nC LB sinh xB LB tanh xB LB causingthe factor T J nC J nE to changemarkedly rlc L2107Apr2011 15 Emitter region highlevel injection npn Law of the Junction DR edges 2 VBE Vt pEnE x 0 ni e pBnB x 0 NE Emitter HLI when VBE 2Vt ln ni so pE 0 nE 0 nie VBE 2Vt NE 2 VBE Vt Note pEnE 0 ni e in HLI rlc L2107Apr2011 16 Effect of HLI in npn emitter region Consequent ly the hole current at x 0 qDEpE0 VBE exp 1 J pE LE tanh xE LE Vt must be rewritten for VBE Vtln NE ni qDEni VBE exp as J pE LE tanh xE LE 2Vt causing J nE J nE J pE factor to change in addition to the changes for B HLI rlc L2107Apr2011 17 Effect of HLI in npn base region Figs 9 18 and 9 19 rlc L2107Apr2011 18 Bandgap narrowing effects Fig 9 20 Eg Eg Nd 0 Eg Nd Eg 10mV 2e17 Eg 2 2 niE ni exp kT 1 slope 2 rlc L2107Apr2011 Replaces ni2 throughout 19 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 L2107Apr2011 20 Hybrid pi circuit model Adapted from linking current version of E M model with parasitic Rs and CSubstr 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 rlc L2121 07Apr2011 and capacitance and junction cap Hybrid pi Circuit model Fig 9 33 rlc L2107Apr2011 22 Gummel Poon Static npn Circuit Model C RC B RBB B ILC IBR ILE IBF ICC IEC IS exp vBE NFVt exp vBC NRVt QB RE rlc L2107Apr2011 E 23 Gummel Poon Static npn Circuit Model C Intrinsic Transistor RC B RBB B ILC IBR ILE IBF ICC IEC IS QB exp vBE NFVt exp vBC NRVt RE rlc L2107Apr2011 E 24 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 rlc L2107Apr2011 BF IBF IKF 1 2 25 BR IBR IKR Charge components From Getreau in the BJT Modeling the Bipolar Transistor Tektronix Inc rlc L2107Apr2011 26 Gummel Poon Base Resistance If IRB 0 RBB RBM RB RBM QB If IRB 0 RB RBM 3 RB RBM tan z z ztan2 z 1 144iB p2IRB 1 2 1 z 24 p2 iB IRB 1 2 From An Accurate Mathematical Model for the Intrinsic Base Resistance of Bipolar Transistors by Ciubotaru and Carter Sol St Electr 41 pp 655 658 1997 RBB Rbmin Rbmax 1 iB IRB aRB rlc L2107Apr2011 27 BJT Characterization Forward Gummel vBCx 0 vBC iBRB iCRC vBEx vBE iBRB iB iC RE iB IBF ILE IS expf vBE NFVt BF ISE expf vBE NEVt L21i rlc C bFIBF QB 07Apr2011 iC iB vBEx RB RC vBC vBE RE 28 BJ T I A vs Vbe V for the G P model Forward Gummel configuration Vbcx 0 1 E 02 1 E 03 1 E 04 1 E 05 Ideal F G Data 1 E 06 1 E 07 1 E 08 1 E 09 iC and iB A 1 E 10 vs vBE V 1 E 11 1 E …


View Full Document

UT Arlington EE 5340 - EE 5340 Lecture 21

Download EE 5340 Lecture 21
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view EE 5340 Lecture 21 and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view EE 5340 Lecture 21 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?