Chater 6 Bipolar Junction Transistor (BJT)

Transcription

1 hater 6 iolar Juctio Trasistor (JT) Xiula heg/shirla heg -5-

2 vetio asic about JT veted i 948 by ardee, rattai ad Shockley i ell ab (First Trasistor) iolar oth tyes of carriers (electro ad hole) lay imortat roles i oeratio of JT Field ffect Trasistor (FT) is uiolar miority device. Alicatio liear amlifier circuits (liear meas that the outut is roortioal to iut). switch ( for examle, logic circuits).

3 Mai alicatios Alicatio of JT Uiqueess of JT: high curret drivability er iut caacitace fastexcellet for aalog ad froted commuicatios alicatios. Power alicatio ad aalog alicatio due to high curret drive caability ad erfect aalog erformace. High seed ad RF alicatio (e.g., mitter coule logic, ) imos: combie the best of MOSFT ad JT most alicatio areas, JT is gradually substituted by istead of MOSFT.

4 asic structure JT Structure A semicoductor device costructed with three doed regios which form two back-to-back - juctios i the same block of semicoductor material (silico). lose eough that miority carriers iteract (egligible recombiatio i base) For aart eough that deletio regios do t iteract (o uchthrough ) Three regios: emitter (), base () ad collector () regios mitter: heavy doig, ~ 9 /cm 3 ase: arrow ad little heavy doig, ~ 7 /cm 3; ollector: light doig,, ~ 5 /cm 3 asic is very thi comared to the diffusio legth of miority carriers (. f the base is much larger, the this will behave like back-to-back diodes.

5 Doig

6 Structure of JT

7 JT Structures ad Symbols

8 Pricile JT Oeratio Pricile The majority of curret eters collector, crosses the base regio ad exits through the emitter. A small curret also eters the base termial, crosses the base-emitter juctio ad exits through the emitter. arrier trasort i the active base regio directly beeath the heavily doed (+) emitter domiates the i-v characteristics of the JT. Oeratio deeds o the bias coditio

9 JT cofiguratios () ommo emitter is the most commo cofiguratio () ommo base is occassioally used. (3) ommo collector is barely used. 663

10

11 ias Modes of JT ias Mode - Juctio - Juctio Saturatio Forward Forward Active Forward Reverse verted Reverse Forward utoff Reverse Reverse

12 JT Fabricatio JT i Discrete JT 663

13 lectrostatic roerties ()

14 PNP Trasistor Active ias Mode --Active bias mode: V >( ositive bias), V >( egative bias) --Majority holes iject ito ase from mitter( ) ad electros iject ito mitter from ase ( ) --if ase width W<<, most of holes ijected (miority i ase) diffuse i ase ad the swee ito ollector by electrical filed of ( ). -- mitter: emittig carrier ito ase as source. --ollector: collectig carrier from ase as drai. --ase: rovidig a ath of carrier, Miority distributio

15 663 JT Oeratio Pricile D 3 cotrollig u scalig creasig, : gai D ad curret hole is small very ad curret electro is mode ( mitter commo for ricile Amlyfig ase i curret ombiatio - (small) curret bias reverse juctio -, ) ( R

16 JT Parameters (PNP) gai curret JT high,, as curret ollector gai D ase ommo : gai D ase (3) ommo gai. curret JT high, JT) ( : ase of oefficiet () Trasort gai. curret JT high, JT) ( : efficiecy () mittig D T T T T T T T α α α α, ) ( as curret ollector - gai D mitter ommo : gai D mitter ommo (4) β β β β For trasistor, similar aalysis ca be carried ou However, the emitter curret is maily carried by electros. etc., T

17 Detailed Quatitative Aalysis

18 Assumtios ad Diffusio quatios Assumtios trasistor, steady state, low-level ijectio. Oly drift ad diffusio, o exteral geeratios Oe dimesioal etc. Geeral aroach is to solve miority carrier diffusio equatios for each of the three regios: G x D t G x D t For steady state ad whe G =, ad for ase of x D t

19 Review: Oeratioal Parameters R R jectio fficiecy : /( ) ase trasort factor : T = / ollector to emitter curret gai: = T ollector to base curret gai: = / ( ) These arameters ca be related to device arameters such as doig, lifetimes, diffusio legths, etc.

20 urret i a Forward PN Juctio kt qv qad kt qv qad kt qv qad kt qv qad qad qad qad dx d qad qad dx d qad ex ex ex ex () () : urret Total (), ()

21 ollector urret kt qv W qad kt qv W qad W qad W qad dx d qad ex ex () () juctio - biased reverse of curret saturatio reverse small the eglect we if curret hole oly : urret ollector

22 mitter urret kt qv D qa kt qv D qa kt qv W qa kt qv W D qa qaw R ex ex ex ex ()

23 3 ase urret kt qv D qa kt qv W qa ex ex emitter. to ijectio for electros sulies - base i recombiatio for electros sulies - urret, ase

24 4 JT Parameters T : gai D ase ommo ase i doig -, N mitter i doig -, N where / / : efficiecy ijectio mitter ex ex ex : factor trasort ase i i T W N D N W D N N N D N W D D W D W D D W kt qv qaw kt qv W qad kt qv W qad : gai D mitter ommo W N D N W D

25 Deviatio from deal JT

26 Deviatios from the ideal The measured characteristics deviates slightly from the ideal characteristics discussed. ase-width modulatio Puch-through Avalache multilicatio ad breakdow Others base resistace, deletio regio recombiatio-geeral

27 arly ffect ase Width Modulatio Whe the reverse bias alied to the - juctio icreases, the - deletio width icreases ad W decreases. the collector curret, icrease,but uchaged. Reverse arly ffect imact of V o W : icrease V W icrease smaller, uchaged. V x W smaller tha ideal, F uchaged qad () W qad W e qv kt

28 ase With Modulatio--arly ffect

29 ause Reaso Puch-through ca be viewed as base width modulatio carried to the extreme, i.e., uch-through occurs whe W. For - voltage beyod uch-through, the - barrier lowers ad results i large icrease i carrier ijectio from emitter to collector. arge icrease i collector currets at high V occurs due to two reasos: uchthrough or avalache multilicatio. Puch Through

30 High jectio ffect V icreasesase ijected miority carrier cocetratio may aroach, or eve become large tha the majority carrier cocetratio.lowerig the emittig efficiecy

31 High ollector urret ffect t As, electro velocity i collector, ad aroaches a limit v sat, c aroaches.qa N V sat

32 urret rowdig

33 reakdow ffect Sudde rise i for large reverse V.

34 iolar ssues i MOS: atch-u atch u teractio of two hidde JT s iside a MOS air. ricile, o roblem because i both JTs, V =.

35 ut there are also two arasitic resistors: Suose for some reaso: Miority carrier ijectio ito substrate by trasiet forward bias o juctios (tyically i /O circuits); hotogeeratio by ioizig radiatio; or imact ioizatio by hot carriers urret flows through R X goes ito FAR () voltage dro i R W goes ito FAR () more voltage dro i R X POSTV FDAK OOP ca cause device destructio.

36 Avoidig of atch u Reduce R X ad R W Reduce ad Methods Heavily doed substrate (eed lower doig ei layer o to for devices) Sufficiet trasistor sacig Guard rigs at sesitive locatios SO wafer

37 Guard rig: reverse-biased juctio that collects ijected holes.

38 Other ffect ase series resistace Recombiatio-geeratio curret : 38

39 Homework Pierret ook: P76:.,.6 P3:.(b),.8,.9,.7