Electronics Chapter Three

1. Electronics Chapter Three Seventh, ninth weeks 1- 19/2/ 1440 هـ أ / سمر السلمي

2. Time of Periodic Exams • The first periodic exam in / 2 / 1440 هـ12 – 14 every student in her group • The second periodic exam in / 3 / 1440 هـ10 – 12 every student in her group The third homework I put the third homework in my website in the university homework Due Wednesday 22/ 2/ 1440 هـ in classroom in Faculty of Physics Department , I will not accept any homework after that , but if you could not come to university you should sent it to me by email in the same day

3. Chapter Three: Transistor • Brief its history • The discovery of the transistor in year 1947 in Bell Lab’s in United States of America. Since then, this discovery is one of the most important discoveries and that the performance of a global revolution in technology. • the first transistorin 1947 Now

4. Transistor • In the second chapter we studied and we focused on two types of contacts : • PN Junction: ( semiconductor of n-type & p-type) which enters in the structure of bipolar junctiontransistor (BJT) and Junction gate field-effect transistor (JFET) • MOS contact: (Metal, Oxide, Semiconductor of n-type or p-type) which enters in the structure of metal–oxide–semiconductor field-effect transistor (MOSFET) • Concept of transistor • It is a piece of three parts and as PN Junction this parts contain extrinsic semiconductor N-type&p-type • Transistor mission • 1. Works as amplifier in electrical signals2. works as switch in integrated circuits =

5. Transistor’s types • The most important types of transistor two types are: • Bipolar junction transistor (BJT): • Will be studied in detail in this chapter (Chapter There) • Field-effect transistor (FET) : • Will be studied in detail in (Chapter four) • Diffusion transistor • Unijunction transistors • Single-electron transistors • Nanofluidic transistor,

6. Transistor’s types • There are special types classified within provirus types which • Within bipolar junction transistor • Heterojunction bipolar transistor Schottky transistor • Avalanche transistorDarlington transistors. • Insulated-gate bipolarPhoto transistor • Multiple-emitter transistorMultiple-base transistor • Within field effect transistor • Carbon nanotube field-effect transistor (CNFET) • Junction gate field-effect transistor (JFET) • metal–semiconductor field-effect transistor (MESFET( • metal–oxide–semiconductor field-effect transistor (MOSFET) • metal–Insulator–semiconductor field-effect transistor (MISFET) • Organic field-effect transistor • Ballistic transistor • Floating-gate transistor etc… =

7. Bipolarjunction transistor • BJT structure • The Bipolar junction transistor contains • of npn or pnp • Which is distributed in three parts • Emitter, Base & Collector • emitter and collector contain from the • same semiconductor type either n-type • or p-type; but often emitter has more • Impurities than base and collector. • Therefore n+p n or p+n p =

8. Bipolarjunction transistor • BJT structure =

9. Bipolarjunction transistor • BJT structure =

10. Contact methods for BJT’s Circuits • The electronic circuits often have a signal or voltage inside and another outside, and here in a BJT part of the three parts involved in each of the entrance and exit thus • common emitter configuration • basecommon configuration • common collector configuration • The figure for (npn) type, however for the other type (pnp) just reverse the arrow =

11. Currents and voltage and symbols in circles BJT • IB Base currentIEEmitter current ICCollector current • Always gather those three by relationship IE = IB + IC • VBEvoltage between base & emitter VBC voltage between base & collector • VCEvoltage between emitter & collector • Distribution in the two typesnpn&pnp • W1 The length of the first depletion region between base and emitter • W2 The length of the second depletion region between base and collector • WB The length of the base region =

12. Currents and voltage and symbols in circles BJT • IB Base currentIEEmitter current ICCollector current • Always gather those three by relationship IE = IB + IC • VBEvoltage between base & emitter VBC voltage between base & collector • VCEvoltage between emitter & collector • Distribution in the two typesnpn و pnp • In electronic circuits for system method for contact transistor we need to know • Vin Input voltage VoutOutput voltage • RinInput resistance RoutOutput resistance (often called load resistance RL ) =

13. Band Energy Description of BJT at equilibrium Conditions to npn & pnp • In the first figure • in equilibrium condition for npn, • the second figure for pnp • In two figures, we notice • Fermi level stability along • across emitter, base & • collector. • It must be recalled that the contact • potential between emitter and basejunction higher than the contact • potential between , base and • collector junction .This is because impurities in emitter higher than impurities in base • and collector. = P Ec Ef n+ n Ev B E C P+ P n

14. Band Energy Description of BJT at non equilibrium Conditions to npn & pnp • In the first figure in non • equilibrium condition • for npn, the second • figure for pnp • In two figures, we notice • Fermi level variable along • across emitter, base & • Collector duo to forward • and reverse bias. • We will see in detail what is • happening in the diffusion of electrons • and holes and also the recombination • process in BJT in the next topics. = Ef P Ec n+ n B E Ev C forward bias reverse bias P P+ n

15. Modes of Operation for BJT • We saw that in equilibrium condition there will be two case of the forward and reverse bias. thus there will be four modes of operation BJT (we will only mention now) • Active mode : • The forward bias in base & emitter junction. The reverse bias in base & collector junction.( which often we will take about) • Saturation mode : • The forward bias in two junctions. the transistor in this case be a maximum connection status and operates as if it is closed switch in a circle • Cut – off mode : • The reverse bias in two junctions. the transistor in this case only leaking current passes in circle and operates as if it is open switch in a circle • Inverted mode : • The reverse bias in base & emitter junction. The forward bias in base & collector junction

16. Bipolarjunction transistor • What happens inside transistor • At the beginning, we deal with Active mode and basecommon configuration to npn. We notice that in forward bias between base & emitter junction, the length of the depletion region W1 is small unlike the length of the depletion region between base & collector junction W2is big. Also, we care about the thickness of base WBis small. • At base & emitter junction (np), the diffusion of electrons from emitter to base and opposite for the diffusion of hole from base to emitter. If the thickness of base WBis small, the diffusion of electrons from emitter to base complete its way to collector = - + W1 W2

17. What happens inside transistor • At the beginning ,electrons inject in emitter then diffuse to base and part of electrons recombine with holes. In return, holes inject in base then diffuse to emitter which know base current. However, we must remember that the emitter and base junction n+p has more impurities in emitter therefore most junction current in forward bias will be from electrons (electronic current). As we mentioned earlier, if the thickness of base is small, electronic current will not be able to recombine with all majority carrier (holes) in base. =

18. What happens inside transistor • Thus, most electronic current will withdraw or diffused to base and collector junction pn (also, reverse voltage effects in diffusion process which lead to the fall of electrons in energy well). This is followed by the appearance of equivalent region inside base as we move away from two junctions region toward the center, if concentration of impurities’ injection regular, the base region will be free of electronic field and charge carrier will be driven by diffusion power. • Also, base current IB creates from recombination some of electrons which inject with holes in base region (IB considers of most important current). In addition, there are small weak currents such as reverse leakage current Icp of thoes in base and collector junction . =

19. what happen inside transistor • Also, from the figure we should know • IEnTotal electronic current emit from emitter • ICnResidual part of total electronic current emit from emitter and collect in collector • IEn- IcnResidual part of total electronic current emit from emitter and flow in base as recombination current • IEphole current at base current and it creates from holes inject in base to emitter • Icphole current as reverse leakage current direction from collector to base =

20. Transistor parameters • Previously we mentioned that WBthe thickness of base plays very important role in efficiency transistor ( two possibilities) • 1- WB ≈ LnorLp(The diffusion length of electron and hole depending on the type of transistor npn or pnp, respectively ) is small, as we mentioned early, so a few amount of charge carrier recombine with other type of carrier . Thus, efficiency transistor increases, in addition to injection of emitter from a number of charge carrier to base so it requires(high doping of emitter as n+or p+) =

21. Transistor parameters 2 - WB >>LnorLp(The diffusion length of electron and hole depending on the type of transistor npn or pnp, respectively ), the thickness of base is big. Therefore, any charge carrier which inject from emitter to base will recombine with other type of carrier in base before going to collector . Thus, the only current in base and collector junction is reverse leakage current or reverse saturation current ICBO and no passing of other current in base and collector junction and become two open circles

22. How amplification occurs in the transistor • Here also, we deal with npn type and active mode but we now use emitter common configuration . When hole current enters from base, potential reduce between emitter and base (forward bias). If WB the thickness of base is small, we will assume that % 1 of electronic current recombine with hole current in base and 99% of electronic current go toward collector • Therefore, output current from collector IC • almost 99% higher from base current IB • Thus, we can say when a small amount of • current enters of IB , it will create high • current of IE also of IC because most • electronic current go from emitter to • collector. We can say IE ≈ IC =

23. Calculation gain coefficientβandα • Gain coefficient α when basecommon configuration & gain coefficient β when common emitter configuration. • We start with gain coefficient β when common emitter configuration, so when we discussed about amplification in this configuration, we mentioned how base current effect on emitter current. thus, gain coefficient β is ratio between collector current &base current • When we assume that few recombination in base duo to its small thickness soIE ≈ IC • Here emitter current proportional with emitter doping and base current proportional with base doping. therefore, gain coefficient β equal to is ratio between collector doping & base doping • Here also efficiency transistor depend on gain coefficient , so when gain coefficient is big , the efficiency transistor is increases

24. Calculation gain coefficientβandα • Gain coefficient α when basecommon configuration & gain coefficient β when common emitter configuration. • However, the Gain coefficient α when basecommon configuration equal to is ratio between collector current & emitter current • We can find relation between gain coefficient β & gain coefficient α • Or

25. Calculation gain coefficientβ • In the diode, we derive diffusioncurrent density for excess of minority - carriers of electrons and holes • Since transistor is as two diodes, diode’s calculation will be the same for transistor’s calculation . current density equal to current per area (the area is the same for 3 part) therefore, for npn • And when assume base thickness is small (WB≈Ln) also from previously relation • By substitute ingain coefficient • this relation is approximately =

26. Calculation gain coefficientβ • Final approximately relation for gain coefficient β in npn is • Where is time of minority – carriers life in base • And is time of transit electrons to base =

27. CalculationEmitter Efficiency coefficientγ • It know as ratio between electronic current (npn) which injection from emitter and total current • Since total current is , therefore: • In transistor of n+p n type , so IEp< IEn . therefore =

28. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits • Previously, we discussed about gain coefficient α and β to two of common base configuration& common emitter configuration, respectively. In two cases the equation was • Here, we will calculate voltage, current and power gains Av,Ai&Aprespectively for the three common configurationsin addition to the characteristics of their circuits. • In the three circuits, we will focus at active mode . Aslo, we must remember the equation • IE = IB + IC =

29. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits • emitter common configuration • This circuit is the most important and used in • amplifiers for transistor • input current is base current & output • current is collector current • input voltage is Vin & output voltage is Vout. • theoutput signal opposite to input signal ,mean Out of phase with 180o, so it is Inverting Amplifiercircuit • input resistance Rin is lower duo to forward bias & output resistance RL is higher duo to reverse bias • Current gain is • Voltage gain is • The gain in this circuit less than basecommon configuration • power gain is

30. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits • basecommon configuration • input current is emitter current & output • current is collector current • input voltage is Vin & output voltage is Vout. • theoutput signal the same to input signal ,mean In of phase , so it is non inverting Amplifiercircuit • the ratio between output resistance RL &input resistance Rinis higher • Current gain is • In most case approximate value is one and IB is small, thus IE ≈ IC • Voltage gain is • power gain is

31. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits • collector common configuration • input current is base current & output • current is emitter current • input voltage is Vin & output voltage is Vout. • theoutput signal the same to input signal ,mean In of phase , so it is non inverting Amplifiercircuit • input resistance Rin is higher & output resistance RL is lower • in the circuit input voltage contact direct to base while output voltage is taken from load resistance • Current gain is • Voltage gain is • Always is less than one duo to • power gain is

32. The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits

33. I – V Characteristic of BJT • In chapter two, we study I – V Characteristic of diode in lecture and Lab, so we know about proportional relation in addition to load line. Also, in this chapter we will study I – V Characteristic of BJTand its calculationand duo to different contact methods, there will be different curves , however, the relation always proportional • I – V Characteristic emitter common I – V Characteristic base common

34. I – V Characteristic of BJT in emitter common configuration and load line • we will deal with emitter common configuration to see • relation between IC& VCE • 1- we notice that IC increases rapidly by change VCE • at beginning in region called Saturation Region. Than, • The increase becomes very slow unnoticed which • consider as constant in region called • Amplification Region or Active Region. • 2- when we change IB , IC will also change • duo to input voltage (means that IC • control by IB) • 3- the third region called Cut OffRegion • which is region under current value IB =0

35. I – V Characteristic of BJT in emitter common configuration and load line • 4 - load line will cut y- axis at Saturation point (S –point) and x- axis at cut off point (C –point) • 5- at operation point (Q- point) cut of load linewith I – V Characteristic • load line equation • 6- from equation and figure, we notice • cut off point when IB =0 &IC =0 thus • VCE = VCC • Saturation point when VCE =0 thus • The mean operation point is )

36. I – V Characteristic of BJT and his job as Switch • we can describe job’s BJT as switch • 1- Saturation Region: • which represent an close switch (Fully-ON) • input voltage and base contact with VCC • VBE > 0.7V • the maxim value of collector current • The two junction at forward bias • ideal Saturation at VCE =0

37. I – V Characteristic of BJT and his job as Switch • we can describe job’s BJT as switch • 2- Cut OffRegion : • which represent an open switch (Fully-OFF) • input voltage and base contact with • grounded 0V • VBE < 0.7V • The two junction at reverse bias • There no current flow to collector • IC = 0

38. Finding minority carrier distributions & terminal currents in BJT • we deal with active mode and basecommon configuration to npn . At the beginning and to make calculationease, we assume the following : • 1- the thickness of base WBis small, therefore, the diffusion here for electronic current from emitter to collector . In addition, we neglects drift current at base. • 2- emitter efficiency γ ≈ 1because emitter current is only electronic current • 3- reverse leakage current or reverse saturation current is neglected • 4- the action part in base and two • junctions have regular section area • and electronic current move in one • direction or one dimension which is x • 5- all currents and voltages are stable VEB VCB A n n p ΔnC ΔnE xp 0 WB

39. First: the solution of diffusion equation in the base region in BJT • we deal with active mode and basecommon configuration to npn . Previously, we study about a excess of minority -carriers of electrons concentration in p-type in base region. • Electronic current enter to base from emitter, also come out from base to collector. • To calculate excess of electrons to two end-sides of base at two depletion regions from emitter side and collector side to obtain : • excess of electrons concentration from • end-side depletion regions of emitter • excess of electrons concentration from • end-side depletion regions of collector VEB VCB A n n p ΔnC ΔnE xp 0 WB

40. First: the solution of diffusion equation in the base region in BJT • If we assume that emitter & base junction has strong forward bias which means • and base & collector junction has strong reverse bias which means • , we will obtain • We mentioned before of minority carrier diffusion equations which is quadratic equation, hence the solution are • Where Lnthe diffusion length of minority • carrier electron . We must remember that • thickness of base is small which means that • WB≤Ln to move all electronic current from • emitter to collector. VEB VCB A n n p ΔnC ΔnE xp 0 WB

41. First: the solution of diffusion equation in the base region in BJT • Finding constants C with boundary conditions at the two end-sides of base • When multiply the first equation with , we obtain • And collected with second equation to obtain C1 • bysubstituting in the first equation to obtain C2

42. First: the solution of diffusion equation in the base region in BJT • bysubstituting with constants C in • we mentioned that high reverse voltage to obtain • We can write equation in this from • where

43. First: the solution of diffusion equation in the base region in BJT • the figure shows the distribution of minority carriers in the base also in the emitter and collector • where M1ΔnE ΔnE M2ΔnE δn

44. Second: Evaluation Values of Terminal Currentsin BJT • We will find current by known current density to two end-sides of base • At driven excess of electron in base reign in p-type respect of xp • This driven at borders of depletion region from emitter • Therefore, electronic emitter current • by substituting in constants • since the • So emitter current

45. Second: Evaluation Values of Terminal Currentsin BJT • This derivation at the bordersof the depletion region from collector side • Therefore, collector current is • By substituting in constants

46. Second: Evaluation Values of Terminal Currentsin BJT • Finally, we can find base current from emitter and collector currents • When taking into consideration , we obtain threse approximate value

47. minority carrier distributions for modes of operation for BJT for npn • Active mode: the figure shows the distribution of minority carriers in the base also in the emitter and collector in active mode

48. minority carrier distributions for modes of operation for BJT for npn • Saturation mode: the figure shows the distribution of minority carriers in the base also in the emitter and collector in saturation mode

49. minority carrier distributions for modes of operation for BJT for npn • Cut - off mode the figure shows the distribution of minority carriers in the base also in the emitter and collector in cut off mode

50. minority carrier distributions for modes of operation for BJT for npn • Inverted mode :the figure shows the distribution of minority carriers in the base also in the emitter and collector in inverted mode