Introduction to Microelectronics

Transcription

1 The iolar Juctio Trasistor Physical Structure of the iolar Trasistor Oeratio of the NPN Trasistor i the Active Mode Trasit Time ad Diffusio aacitace Ijectio fficiecy ad ase Trasort Factor The bers-moll Model of the JT The PNP Trasistor Grahical Reresetatio of the JT haracteristics The arly ffect Aedices: JT arameters for simulatio 1

2 Physical Structure of the JT i mitter-ase Juctio i i ollector-ase Juctio mitter ase + eitaxy + + ollector + mitter + Active ase Regio ollector Simlified cross-sectio of a trasistor with currets that occur durig ormal oeratio i + buried layer + i ase eitaxy + i Active Trasistor Regio + ross-sectio of a itegrated biolar juctio trasistor 2

3 JT of a high-voltage I rocess

4 Tyical imurity cocetratio for a moolithic trasistor i a high-voltage rocess

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6 Oeratio of the JT i the Active Mode SR SR: sace-charge regio (a) trasistor with base-emitter juctio forward biased, base-collector juctio reverse biased. (b) Potetial-eergy barriers for electros. 6

7 Oeratio of the JT i the Active Mode ( ) Illustratio of JT currets, usig the JT cross sectio (a) ad eergy-bad diagram (b). ( ) S. Dimitrijev, Uderstadig Semicoductor Devices, Oxford, New York,

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10 JT i the Active Mode urret flow i a trasistor biased to oerate i the active mode. The electro flux stream is greater tha the hole flux stream. lectros are sulied by the emitter cotact, ijected across the base-emitter SR ad diffuse across the base lectric field i the base-collector SR extracts electros ito the collector. Holes are sulied by the base cotact ad diffuse across the emitter. The reverse ijected holes recombie at the emitter ohmic cotact. 10

11 JT i the Active Mode QN emitter QN base QN coll. Hyotheses: juctio QN = quasi-eutral juctio Oe-dimesioal device Ohmic cotacts at,, ad 3 QN regios ad 2 deletio regios Low ijectio level High emitter efficiecy istei relatioshi oltzma statistics valid i the deletio regio W <<L egligible recombiatio i the base 11

12 The electro (collector) curret - trasistor Oe-dimesioal device + istei relatioshi d t J = qµ + qd = dx qµ dx d t J = qµ qd + = dx qµ dx I the QN base (1) becomes Low ijectio level High emitter efficiecy J J a φ φ N >> J >> J d d J D ( ) J J d = q D D dx ( ) d q (2) dx (1) For egligible recombiatio J costat. Itegratig (2) from 0 to W results i W W V V W 2 φt φt J dx qd d ( ) = qd = qd 0 i e e 0 0 oltzma statistics W W V V V V qadi φt φt φt φt a W S 0 a dx N dx I = AJ = e e = I e e N dx 12

13 0 W N P N Law of the juctio: (0) = o ex(v /φ t ) (W ) = o ex(v /φ t ) o = i2 / N a V > 0, V < 0 For costat imurity cocetratio i the base ad low ijectio level ( ) J d d J I N a q = = Diffusio curret D dx dx qd qad 0 t t t t 2 V V 2 V V i φ φ qadi φ φ qad I = e e = e e W NaW N dx a 13

14 JT i the Active Mode V > 0, V < 0 0 W 2 V i φt 0 = ; (0) = 0 ; ( ) = 0 Na e W e x ( x) (0) 1 W V φ t 14

15 Forward Trasit Time (0) Q = q Q τ F = = I (0)A 2 W 2D 2 W Q 0 W x If W = 10-4 cm ( = 1µm ), D = 12.5 cm 2 /s (=µ φ t ) cm = 2x12.5 cm τf 2 /s xcess miotity charge stored i the eutral base τ F = s Oeratig frequecy f 1 2πτ F 15

16 Diffusio aacitace ( D ) N P base N = D dq dv Q =τ F I (0,V +dv ) (0,V ) dq I = I S dq = dv e V φ t τ F di dv Q D = τ F I φ t 0 W x x: τ F = 4 x10-10 s, I = 1 ma D = 16 F 16

17 mitter efficiecy juctio of trasistor is a N + P juctio. lectros from the emitter are ijected ito the base, but holes from the base are also ijected ito the emitter. The ratio γ=j /J is desigated as emitter efficiecy. J dx D = J dx D Negligible recombiatio d mitter ase regio regio dx N dx; dx N dx a Let us, oce agai, use ( ) J J d = q D D dx (1) At the ohmic cotacts ad, 2 = i Itegratig (1) from to yields J γ = = J D D dx J dx γ = = D mitter regio Low-level ijectio d a ase regio N dx J D N dx 17

18 mitter efficiecy If the recombiatio curret is egligible, we have N dx a ase I D regio = = γ D Nddx << mitter regio I I I ase trasort factor -α T I 1 W α T = = I W L L cosh ( / ) 2 xamle: W L µ W = = m 1 αt µ m 2L 18

19 The base curret Forward-active mode I I = I + I + I + ( 1 α ) I + I γ T 3 The ase urret I 1 : holes ijected from the base regio ito the emitter regio I 2 : some electros that diffuse across the base do ot reach the collector, but o the way they recombie with holes. The missig holes must be relaced from the exteral circuit. I 3 : recombiatio curret i the juctio (imortat at low curret levels) Usually I 2 <<I 1 I I 1+ I 3 I = I + I I I I = α I F β F αf = 1 α F I I = β I F 19

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21 ase ad collector resistaces

22 The (bers-moll) Trasort Model of the NPN Trasistor i v ollector ollector () i i ase i ase () i = i + i v = v + v v mitter i mitter () (a) i (b) (a) (b) Idealized trasistor structure for a geeral bias coditio ircuit symbol for the trasistor 22

23 Forward Trasort urret i i F ollector i i v = i = I ex F S 1 φ t if IS = = ex v 1 β β φ t F F v i i F β F i i F β F i F NPN trasistor with V >0 ad V = 0. ase mitter 20 β F 500 ( tyically ) β F : forward commo-emitter curret gai + 1 F i = i + i = i = β F β i α α F : forward commo-base curret gai F 23

24 Reverse Trasort urret v i i i R β R ollector ase i i v = i = I ex R S 1 φ t ir IS v = = ex 1 β β φ t R R 0.02 β R 20 i R mitter i = i α R = βr + 1 i β R i Trasistor with V >0 ad V = 0. 24

25 The Trasort Model of the NPN Trasistor i i ( ) if = IS ex v / φt 1 i i R β R I S β R ( ) ir = IS ex v / φt 1 i i i T = i F I S β F β F i ( ) ( ) i = I ex v / φ ex v / φ T S t t i - i F R i F i = + βf i = i T T i β i β i = i + i β R R R R F F Trasort model equivalet circuit for the trasistor 25

26 The lateral PNP trasistor Lateral structure Miority carrier flow i the lateral trasistor 26

27 The substrate PNP trasistor Substrate structure Miority carrier flow i the substrate trasistor 27

28 Oeratig regios of the JT juctio INVRS RGION (TTL logic) forward bias SATURATION RGION (losed Switch) reverse bias forward bias juctio UTOFF RGION (Oe Switch) reverse bias NORMAL, ATIV RGION (Good Amlifier) 28

29 Grahical Reresetatio of the JT haracteristics i i v v i v 1st quadrat ircuits for determiig the commo-emitter outut characteristics i R / β R i F / β F i F - i R i = I β S F ex v I v 1 S ex + φ t β φ t R 1 I 29

30 Grahical Reresetatio of the JT haracteristics o l l e c t o r u r r e t 3.0mA 2.0mA 1.0mA Saturatio Regio Forward-Active Regio I = 100 ua I = 80 ua I = 60 ua I = 40 ua I = 20 ua 0.0mA I = 0 ua utoff -1.0mA Reverse-Active Regio Saturatio Regio β = 25 β = 5 F R -5V 0V 5V 10V V ommom-emitter outut characteristics for the JT 30

31 Grahical Reresetatio of the JT haracteristics i -v v i o l l e c t o r 1.0mA 0.5mA I = 1.0 ma I = 0.8 ma I = 0.6 ma v V ircuit to determie commo-base outut characteristics u r r e t 0.0mA Forward-Active Regio I = 0.4 ma I = 0.2 ma I = 0 β = 25 β = 5 F R V i R / β R -2V 0V 2V 4V 6V 8V 10V v or v i F / β F i T = i F - i R ommo-base outut characteristics for the JT ( i vs. v for JT or i vs. v for the JT I -V 31

32 Grahical Reresetatio of the JT haracteristics I V = I S ex 1 φ t v = V I ollector urret Ic (A) mv/decade log (Ic) ase-mitter Voltage (V) JT trasfer characteristic i the forward-active regio V T I 2 mv/ Deedet of I 32

33 The arly ffect mitter N ase Sace harge Regio Widths P W' W ollector v 1 ase-width modulatio or arly effect N I S v 2 > v 1 Active mode ( ) i = I ex v / φ S t qad qad = = W 0 N 2 2 i i ; I S NaW adx Modulated by V (or V ) Uiform base doig Usig liear aroximatio for W yields W (1 / ) = W0 v VA ISO v v i = ex I ex 1 + v / V ( 1 v / VA ) φt φt ( ) SO A v / V A <<1 V A : arly voltage 33

34 The arly Voltage o l l e c t o r u r r e t 4.0mA 2.0mA 0A I = 100 ua I = 80 ua I = 60 ua I = 40 ua I = 20 ua -V A -15V -10V -5V 0V 5V 10V 15V ollector-mitter Voltage Trasistor outut characteristics idetifyig the arly voltage V A 34

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36 Refereces L 7061 Itroductory lectroics htt:// I. Getreu, Modelig the iolar Trasistor, IG Associates, Portlad,2009. P. R. Gray, P. J. Hurst, S. H. Lewis, ad R. G. Meyer, Aalysis ad Desig of Aalog Itegrated ircuits, Fourth ditio, Joh Wiley & Sos, New York, Richard Jaeger, Microelectroic ircuit Desig, McGraw-Hill, A. Sedra ad K. Smith, Microelectroic ircuits, 5 th ed., Oxford, 2004 harles Sodii, Microelectroic Devices ad ircuits, OeourseWarehtt://ocw.mit.edu Sze & Ng, Physics of semicoductor devices, 3rd ed., Wiley Pierret, Semicoductor device fudametals, Addiso-Wesley 36

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