Bipolar Junction Transistor

Transcription

1 53: Smconductor vc hory nstructor: ragca aslska partmnt of lctrcal ngnrng Arzona Stat Unvrsty polar Juncton ransstor 53: Smconductor vc hory

2 Outln. ntroducton. haractrstcs of a J 3. rakdown n J 4. Gomtry ffcts n J 53: Smconductor vc hory

3 . ntroducton Orgnal pont-contact transstor (947 Frst grown transstor (950 nvntors of th transstor: llam Shockly, John ardn and altr rattan 53: Smconductor vc hory

4 (A rmnology and symbols PP - transstor P - transstor p + n p + + n + p n oth, pnp and npn transstors can b thought as two vry closly spacd pn-junctons. h bas must b small to allow ntracton btwn th two pn-junctons. 53: Smconductor vc hory + +

5 hr ar four rgons of opraton of a J transstor (xampl for a pnp J: Snc t has thr lads, thr ar thr possbl amplfr typs: Forward actv rgon (mttr-bas F, collctor-bas R utoff rgon (both junctons rvrs basd p + n p 53: Smconductor vc hory Saturaton rgon (both junctons forward basd nvrtd actv rgon (mttr-bas R, collctor-bas F p n p + (a ommon-bas (b ommon-mttr (c ommon-collctor p + n p

6 F ( Qualtatv dscrpton of transstor opraton p + n p p { n p n 3 p cn n p 53: Smconductor vc hory mttr dopng s much largr than bas dopng as dopng largr than collctor dopng urrnt componnts: p p n n 3 = currnt from lctrons bng back njctd nto th forward-basd mtr-bas juncton = currnt du to lctrons that rplac th rcombnd lctrons n th bas 3 = collctor currnt du to thrmally-gnratd lctrons n th collctor that go n th bas

7 ( rcut dfntons as transport factor : mttr njcton ffcncy : Alpha-: ta-: p p p p p p p p n n dally t would b qual to unty (rcombnaton n th bas rducs ts valu p Approachs unty f mttr dopng s much largr than bas dopng p n urrnt gan s larg whn approachs unty 53: Smconductor vc hory

8 ollctor-rvrs saturaton currnt: 0 n p n 0 ollctor currnt n common-mttr confguraton: arg currnt gan capablty: 0 Small bas currnt forcs th - juncton to b forward basd and njct larg numbr of hols whch travl through th bas to th collctor : Smconductor vc hory

9 ( yps of transstors scrt (doubl-dffusd p + np transstor 5 m mttr as 00 m ollctor ntgratd-crcut n + pn transstor 6 m 00 m 53: Smconductor vc hory

10 . -haractrstcs of a J (A Gnral onsdratons Approxmatons mad for drvaton of th dal -charactrstcs of a J: ( no rcombnaton n th bas quas-nutral rgon ( no gnraton-rcombnaton n th - and - dplton rgons (3 on-dmnsonal currnt flow (4 no xtrnal sourcs otaton: p + n p A = n = n = n p0 = n 0 n = = p = p = p n0 = p 0 p = A = n = n = n p0 = n 0 n = 53: Smconductor vc hory

11 h carrr concntraton varaton for varous rgons of opraton s shown blow: - - x n 0 n (x n (0 p (0 Forward actv p0 saturaton p (x p ( p ( 0 0 ut-off 0 n (0 n (x Assumng long mttr and collctor rgons, th solutons of th mnorty lctrons contnuty quaton n th mttr and collctor ar of th form: n n ( x" ( x' n n 0 0 x" x' n 0 x 53: Smconductor vc hory

12 53: Smconductor vc hory For th bas rgon, th stady-stat soluton of th contnuty quaton for mnorty hols, of th form: usng th boundary condtons: s gvn by: ot: h prsnc of th snh( trms mans that rcombnaton n th bas quas-nutral rgon s allowd. 0 p dx p d (, (0 0 0 p p p p snh snh snh ( snh ( 0 0 x p x p x p

13 Onc w hav th varaton of n (x, p (x and n (x, w can calculat th corrspondng dffuson currnt componnts: = n (0 + p (0 n (x x n (0 - p (0 p (x = p (0- p ( as rcombnaton currnt xprssons for varous dffuson currnt componnts: dn dn n (0" Aq, n (0' Aq dx" dx' p (0 Aq dp dx x0 p 53: Smconductor vc hory x" 0", ( - p ( Aq = n (0 + p ( n (0 dp dx x n (x x' 0' x

14 53: Smconductor vc hory Fnal rsults for th mttr, bas and collctor currnts: snh( coth( snh( coth( coth( snh( snh( coth(

15 53: Smconductor vc hory For short-bas dods, for whch <<, w hav: hrfor, for short-bas dods, th bas currnt smplfs to: As 0 (or, th rcombnaton bas currnt 0. snh( coth( ; snh( ; cosh( x x x x x x x - 3

16 53: Smconductor vc hory ( urrnt xprssons for dffrnt basng rgms Forward-actv rgon: - juncton s forward basd, - juncton s rvrsbasd: snh( cosh( snh( cosh( snh( coth( p p n hs trms vansh f thr s no rcombnaton n th bas

17 Graphcal dscrpton of varous currnt componnts: p + n p { } p p n { n 3 h mttr njcton ffcncy s gvn by: p p n coth( coth( 53: Smconductor vc hory Rcombnaton n th bas s gnord n ths dagram. short bas

18 h bas transport factor s gvn by: p cosh( short p bas ommon-mttr currnt gan: coth( coth( snh For a mor gnral cas of a non-unform dopng n th bas, th Gumml numbr s gvn by: G 0 53: Smconductor vc hory ( ( x dx ypcal valus of G : short bas G = (Gumml numbr

19 53: Smconductor vc hory Saturaton rgon: - and - junctons ar both forward basd: p n p p' p n - ' coth( snh( coth( coth( n 3 as currnt much largr than n forward-actv rgm

20 Graphcal dscrpton of varous currnt componnts: p + n p { p } p } p p { n { n Rcombnaton n th bas 3 s gnord n ths dagram. mportant not: As bcoms mor postv, th numbr of hols njctd from th collctor nto th bas and aftrwards n th mttr ncrass. h collctor hol flux s oppost to th flux of hols arrvng from th mttr, and th two currnts subtract, whch lads to a rducton of th mttr as wll as th collctor currnts. 53: Smconductor vc hory

21 utoff rgon: - and - junctons ar both rvrs basd. For shortbas dod wth no rcombnaton n th bas, ths lads to: n, p + n p n n n 3 Rcombnaton n th bas s gnord n ths dagram. 53: Smconductor vc hory

22 ( Form of th nput and output charactrstcs ommon-bas confguraton: <-3 =0 saturaton Forward actv 0 cutoff 0 =0 ommon-mttr confguraton: = 0 = 0 saturaton Forward actv 0 > 3 53: Smconductor vc hory 0 cutoff =0

23 ot on th collctor-bas rvrs saturaton currnt: n >0 = 0 Mnorty lctrons n th collctor that ar wthn from th - juncton ar collctd by th hgh lctrc fld nto th bas. 53: Smconductor vc hory

24 hy s 0 much largr than 0? n n p =0 p > 0 0 n p 0 = 0 p 53: Smconductor vc hory 0, h lctrons njctd from th collctor nto th bas and thn nto th mttr forward bas th - juncton. hs lads to larg hol njcton from th mttr nto th bas and thn nto th collctor. n summary, rlatvly small numbr of lctrons nto th mttr forcs njcton of larg numbr of hols nto th bas (transstor acton whch gvs 0 >> 0. p n

25 ( brs-moll quatons h smplst larg-sgnal quvalnt crcut of an dal (ntrnsc J conssts of two dods and two currnt-controlld currnt sourcs: F R R R F F 0 R R0 F F Usng th rsults for and, w can calculat varous coffcnt: F 0 F R R0 F 0 h rcprocty rlaton for a two-port ntwork rqurs that: F 0 R R0 53: Smconductor vc hory F R0

26 ( arly ffct n drvng th -charactrstcs of a J, w hav assumd that,, 0 and 0 to b constant and ndpndnt of th appld voltag. f w consdr a J n th forward actv mod, whn th rvrs bas of th - juncton ncrass, th wdth of th - dplton rgon ncrass, whch maks th wdth of th bas quas-nutral rgon ff to ras: ff (mtallurgcal h common-mttr currnt gan, takng nto account th ffctv wdth of th bas quas-nutral rgon (assumng = s thn gvn by: ff h common-mttr currnt gan can b approxmatd wth: 53: Smconductor vc hory x db ff x b

27 Graphcal llustraton of th arly (bas-wdth modulaton ffct: ff ff f w approxmat th collctor currnt wth th hol currnt: w fnd: p o ( x dx n( G Snc <0, w hav that > 0,.. ncrass. A G ( arly voltag 53: Smconductor vc hory

28 mprcally, t s found that a lnar ntrpolaton of th collctor currnt dpndnc on s adquat n most cass: 0 A 0 whr th arly voltag s gvn by: Graphcal llustraton of th arly ffct: - A 53: Smconductor vc hory A k A qg k s 0 Anothr ffct contrbutng to th slop s du to gnraton currnts n th - juncton: Gnratd hols drft to th collctor. Gnratd lctrons drft nto th bas and thn th mttr, thus forcng much largr hol njcton (transstor acton. A

29 (F vatons from th dal modl: hr ar svral factors that lad to dvaton from th dal modl prtons: rakdown ffcts Gomtry ffcts Gnraton-rcombnaton n th dplton rgons 3. rakdown n J s hr ar two mportant mchansms for brakdown n J s: ( punch-through brakdown ( avalanch brakdown (smlar to th on n pnjunctons 53: Smconductor vc hory

30 h punch-through brakdown occurs whn th rvrs-bas - voltag s so larg that th - and th - dplton rgons mrg. h mttr-bas barrr hght for hols s affctd by,.. small ncras n s ndd for larg ncras n. p + n p ncrasng ot: Punch-through voltag s usually much largr than th avalanch brakdown voltag. h mchansm of avalanch brakdown n J s dpnd on th crcut confguraton (common-mttr or commonbas confguraton. 53: Smconductor vc hory

31 For a common-bas confguraton, th avalanch brakdown n th - juncton (opn mttr s obtand va th maxmum (brakdown lctrc fld F R (~300 kcm for S and 400 kcm for GaAs: k s 0FR ks0 q h ncras n currnt for voltags hghr than s rflctd va th multplcaton factor n th currnt xprsson. t quals on undr normal opratng condtons, and xcds unty whn avalanch brakdown occurs. hn th mttr s opn, th multplcaton factor for th - juncton s: M 53: Smconductor vc hory m b F q R

32 For a common-mttr confguraton, th collctor-mttr brakdown voltag s rlatd to : M M M Opn bas confguraton M ( 0 M 0 M m b M 0 Multplcaton factor M 0 40 M Much smallr than du to transstor acton. Rvrs voltag 53: Smconductor vc hory

33 0 0 ommon-bas output charactrstcs ommon-mttr output charactrstcs 53: Smconductor vc hory

34 4. Gomtry ffcts h gomtry ffcts nclud: ( ulk and contact rsstanc ffcts ( urrnt crowdng ffct p + n + p + p as contacts n n + collctor mttr contacts as currnt flows n th drcton paralll to th - juncton, whch gvs rs to bas spradng rsstanc. hn s much largr than, most of th mttr currnt s concntratd nar th dgs of th - juncton. 53: Smconductor vc hory

35 Gnraton-rcombnaton n th dplton rgon ln( ln( g-r currnt modfcaton: ow-currnt lvls rcombnaton currnt larg currnt lvls hgh-lvl njcton and srs rsstanc urrnt crowdng, hgh-lvl njcton srs rsstnc 53: Smconductor vc hory Rvrs-basd - juncton adds a gnraton currnt to. Forward-basd - juncton has rcombnaton currnt. s not affctd by th rcombnaton n th - juncton. g-r urrnt crowdng or r ln(