Electronic 1 Dr. M.H.Moradi

Transcription

1 1 ه دی زیک ایБR قد Electronic 1 Dr. M.H.Moradi 2

2 . ه دها حا ل ی یانا ل رونو ه ند. : P-N 3 د لوه ه دها ) (

3 وا د عا ق دیو ه دی. ). (...( E G ) ( ) 5 5/ Ω.cm K.... 6

4 Element Properties Conductor Easily can conduct electrical current Least electron valence on the atom-loosely bounded Insulator Does not conduct electrical current under normal condition Most are compounds Lots of electron exist on the valence shell-tightly bounded Semiconductor Element that is neither a conductor nor an insulator but lies between the two element A material that is between conductors and insulators in its ability to conduct electrical current Easily affected by temperature and light energy Most of them have 4 electron valence on the valence shells-bounded in intermediate strength A semiconductor is a material whose resistance depends strongly on the applied voltage and temperature. σ Conductivity : σ metals ~10 10 /Ω-cm S/C σ insulators ~ /Ω-cm The conductivity (σ) of a semiconductor (S/C) lies between these two extreme cases.

5 9 Elemental: C, Si and Ge Binary: GaAs, InP, SiC, ZnO, etc. Ternary: AlGaAs, InGaAs, etc.

6 Semiconductor 3 most used semiconductors: carbon (C), silicon (Si) and germanium (Ge) Carbon Silicon Germanium يي ون ی.. Figure 3.40 Two-dimensional representation of the silicon crystal. The circles represent the inner core of silicon atoms, with +4 indicating its positive charge of +4q, which is neutralized by the charge of the four valence electrons. Observe how the covalent bonds are formed by sharing of the valence electrons. At 0 K, all bonds are intact and no free electrons are available for current conduction..

7 Energy band diagram for a pure (intrinsic) silicon crystal with unexcited atoms. There are no electrons in the conduction band (at 0 Kelvin). Silicon energy gaps and levels. 1.8 ev 0.7 ev = 1.1 ev 14

8 Covalent bonds Figure 3.41 At room temperature, some of the covalent bonds are broken by thermal ionization. Each broken bond gives rise to a free electron and a hole, both of which become available for current conduction. هوا ل رون ( )....!...

9 Creation of electron-hole pair At room temperature. Creation of electron-hole pair Electron-hole pairs in a silicon crystal. Free electrons are being generated continuously while some recombine with holes.

10 Hole current in intrinsic silicon. 20

11 ويدوТR ب. : : n i : 1cm 3 of silicon weighs 2.3 gram and so contains : = atoms Resistance - temperature relationship for a conductor and a semiconductor 22

12 23 ش( Drift ) )ورا Diffusion ار( ی دیده : :(Diffusion) ()...

13 ثا ی از دیده وذ.. x : q بار الکتريکی الکترون Dp مقداری است ثابت Jpدانسيته جريان رابطه مشابه برای جريان الکترون Figure 3.42 A bar of intrinsic silicon (a) in which the hole concentration profile shown in (b) has been created along the x-axis by some unspecified mechanism. ش( drift ) دیدهرا... E µ p..

14 یانرا ش p E n. : : اودن خا ی ه دی.. p-type n-type. n. 5 E.g. Phosphorus (P), Arsenic (As), Antimony (Sb)

15 Figure 3.43 A silicon crystal doped by a pentavalent element. Each dopant atom donates a free electron and is thus called a donor. The doped semiconductor becomes n type. اودن خا ی ه دی n. (Doner) ND : Commonly used doping elements Trivalent Impurities (p-type) Aluminum (Al) Gallium (Ga) Boron (B) Indium (In) Pentavalent Impurities (n-type) Phosphorus (P) Arsenic (As) Antimony (Sb) Bismuth (Bi) (Acceptor impurities) (Donor impurities) 30

16 : :. Conductivity of n-type material is increased due to more free-electrons. E.g: B, Al, Ga, In وعp ه دی Figure 3.44 A silicon crystal doped with a trivalent impurity. Each dopant atom gives rise to a hole, and the semiconductor becomes p type : :

17 p-type material and its energy diagram. Conductivity of p-type material is increased due to more holes in valence band. 33 Doping Density 1 impurity atom per 10 5 to 10 8 Si atoms and about Si atoms/cm to impurity atom/cm 3 (much more than heatrupture electrons) Advantages of doped semiconductors: Able to tune conductivity by choice of doping fraction At the rate 1 donor atom per 10 8 Si atoms, the conductivity at 30 C is multiplied by a factor of 24,100. Conductivity in doping semiconductor is less dependent on temperature. Able to choose majority carrier (electron or hole) Able to vary doping fraction and/ or majority carrier within piece of semiconductor 34

18 زیکد ود pn. n p. Figure 3.39 Simplified physical structure of the junction diode. (Actual geometries are given in Appendix A.) pnد حا دار باز Figure 3.45 (a) The pn junction with no applied voltage (open-circuited terminals). (b) The potential distribution along an axis perpendicular to the junction. n p n p p. n p n.. I D

19 pn-junction initial energy levels. Energy Energy (a) (b) 37 The forming of the depletion layer. Energy Energy 38

20 Depletion Layer Charges. Electric field Total (+) = 21 Total (-) = 20 Net charge = +1 Total (+) = 19 Total (-) = 20 Net charge = PN Junction

21 ه خه n p.... n p. Figure 3.45 (a) The pn junction with no applied voltage (open-circuited terminals). (b) The potential. distribution along an axis perpendicular to the junction. Energy diagrams illustrating the formation of the pn junction and depletion region.

22 قداروتاژه خه : (). Rضه خه A. :

23 م ش ا pnد. p n. (barier). Figure 3.49 The pn junction excited by a constant-current source supplying a current I in the forward direction. The depletion layer narrows and the barrier voltage decreases by V volts, which appears as an external voltage in the forward direction. A forward-biased diode showing the flow of majority carriers and the voltage due to the barrier potential across the depletion region. The depletion region narrows and a voltage drop is produced across the pn junction when the diode is forward-biased.

24 The effect of forward bias. (a) An unbiased pn junction (b) Charge motion at the moment SW1 is closed (c) Conduction increases as the depletion layer becomes narrower (d) Bulk resistance 47 وز حامهای ТЗر ق ده Is.. Figure 3.50 Minority-carrier distribution in a forward-biased pn junction. It is assumed that the p region is more heavily doped than the n region; N A N D.

25 راه یانووتاژد ود. : Forward-bias measurements show general changes in V F and I F as V BIAS is increased.

26 V-I characteristic curve for forward bias. Part (b) illustrates how the dynamic resistance r d decreases as you move up the curve (r d =?V F I F?I F ). kvd T ID = Is e K Is I S =reverse saturation current k=11,600/η (η=1 for Ge and η=2 for Si) T K =T C +273 هدیpn تو تاژ ع وس Is n n. p. p Figure 3.46 The pn junction excited by a constant-current source I in the reverse direction. To avoid breakdown, I is kept smaller than I S. Note that the depletion layer widens and the barrier voltage increases by V R volts, which appears between the terminals as a reverse voltage..

27 The effect of reverse bias. (a) A conducting pn junction (b) A depletion layer forms when there is no current (c) When the bias is reversed, the depletion layer widens as charge carriers move away from the junction 53 Diode capacitance. Insulator Conductor Conductor n p Insulator V R 54

28 دpnه ش ت Is Figure 3.48 The pn junction excited by a reverse-current source I, where I > I S. The junction breaks down, and a voltage V Z, with the polarity indicated, develops across the junction

29 V-I characteristic curve for reverse-biased diode. The complete V-I characteristic curve for a diode.

30 صاتد ودوا ی : 3 - Figure 3.8 The diode i v relationship with some scales expanded and others compressed in order to reveal details. Diode Equation (Accurate Model) VD VT ID = IS e η 1 where ID = diode current, A VD = diode voltage, V (positive, for forward bias) IS = saturation current, A η = emission coefficient kt T VT = thermal voltage = = q 11, where k (Boltzmann constant) = J/ K ( ) ( 1 η 2depending on the material) T (Kelvin) = 273+ T C ;C (degrees Celcius) q (charge of an electron) = C; C (Coulombs) The equation is not valid in the reverse breakdown region. 60

31 ش م ا ه : : ش ع وس ا ه. :.. Is ه ش ت....

32 Actual Diode Characteristics Note the regions for No Bias, Reverse Bias, and Forward Bias conditions. Look closely at the scale for each of these conditions! 63 Comparison of Si and Ge semiconductor diodes Zener region Note that Reverse saturation current is in order of 10nA(10x10-9 ) for Si diode and 1µA(10-6 ) for Ge diode Is temperature effecting this VI characteristics? 64

33 Temperature effects on diode operation. I F (ma) C 25 C 8 6 V 2 I 2 V 1 4 V R T = 25 C I R = 5 A 2 5 I V F (V) T = 35 C I R = 10 A T = 45 C I R = 20 A 20 I R 65 Diode structure and schematic symbol.

34 Forward-bias and reverse-bias connections showing the diode symbol. د ود ایده ا ل : () ().. Figure 3.1 The ideal diode: (a) diode circuit symbol; (b) i v characteristic; (c) equivalent circuit in the reverse direction; (d) equivalent circuit in the forward direction.

35 The ideal model of a diode. The practical model of a diode.

36 ی-ت ه ای هد ود Typical diode packages with terminal identification.

37 DMM diode test on a properly functioning diode. Testing a defective diode.

38 حا ت ازد ود. Figure 3.2 The two modes of operation of ideal diodes and the use of an external circuit to limit the forward current (a) and the reverse voltage (b). چون جريان قطع است کل ولتاژ 10 ولت روی ديود می افتد. Diode part number Peak reverse voltage 1N N N N N N N Diode Maximum ratings. Rating Peak repetitve reverse voltage, V RRM Discussion Maximum allowable reverse voltage. Nonrepetitive peak reverse voltage, V RSM RMS reverse voltage, V R(rms) Maximum allowable value of a single event reverse voltage. (V RSM > V RRM ) V R(rms) = V RRM Average rectified forward current, I 0 Maximum average diode current. Nonrepetitive peak surge current, I FSM Operating and storage junction temperature, T J or T stg Maximum allowable value of forward current surge. (30A for 1N400X) Temperature that diode can withstand. 76

39 Diode electrical characteristics. Maximum forward voltage drop, V F Maximum full-cycle average forward voltage drop, V F(AV) Maximum reverse current, I R Maximum value that V F will ever reach. Maximum average forward voltage. Usually given at various temperature. The rating is valid for all reverse dc voltage below V RRM. Maximum full-cycle average Maximum average value of I R. reverse current, I R(AV) 77 Mathematical expression of a Diode kv D kv D T = K T I K D IS e IS IS e Assume I S = 10 fa = 10 x Amp ( f = femto = ) and that at room temperature (see page 21 ) ( T K / k ) = 26 mv Then forward curve of the diode can be written as V D = 26mV I I 10fA e V = 26mVlog D D D e 10fA Diode drop V D

40 ( ) [ ] D D D d D D D D k D D d k k S D D k S D k S k S k S D D D d D D d S D I mv I. I. r di dv I. I T k dv di r ), ( equation From., T k T e, temperatur room at Si) and Ge both for (,, k ) ( I I I T k I I T k I T k e I T k e I dv d I dv d r di dv r curve diode of Slope e I I T k kv D T k kv D T k kv D = = = = = = = = = = + = = η = η = >> + = + = = = = = Diode resistance r d Resistance levels of a Diode

41 Diode characteristic Ι d Q pt Tangent line v D 81 Average AC Resistance r av Vd = (point to point) Id AC resistance can be determined by picking 2 points on the characteristic curve developed for a particular circuit. 82

42 دل ينال وچک dc. ac Ĥ. Figure 3.17 Development of the diode small-signal model. Note that the numerical values shown are for a diode with n = 2.

43 ا ز داراتد ودی: ا زد ق VDD. : در اين دومعادله دو مجهول وجود دارد که به دوطريق گرافيکی و تکراری قابل حل است. ا ز ا ي ی دلما ی. -. محل تلاقی نقطه کار ناميده ميشود و خط رسم شده خط بار ناميده ميشود. Figure 3.11 Graphical analysis of the circuit in Fig using the exponential diode model.

44 9/14/2010 Load Line Analysis Determine ID, VD & VR E = VD + VR = VD + I D R For VD = 0, E = 0 + I D R Circuit for load line analysis =8 = ma R 0.33k I D = 0, E = VD + (0) R ID = E For VD = E = 8 V The load-line analysis becomes: From the analysis: VDQ = VD H 0.9 V IDQ = ID H 21.5 ma V R = I D R = (21.5 m )(0.33 k ) = V

45 ل روش ت ار. : R=1K E= V DD =5v 1mA 0.7. VD ID 0.1v پا خ : Vd=0.7 : : :

46 Example: Calculate V D and I D in the following figure Hint:- use iteration method with the diode equation I V (mv) 26mVln D D = 10fA I V 26mVlog D D = e (1) 10fA 20 V I D D= (2) 0.5k andsolving equation(1) and (2)byiterationmethodwehave 1. Take V D =0.7V use eqn(2) find I D =38.6mA 2. substitute I D =38.6mA in eqn(1) find V D =0.753V V D (V) I D (ma) Take V D =0.753V use eqn(2) find I D =38.494mA 4. substitute I D =38.494mA in eqn(1) find V D =0.753V 5. Take V D =0.753V use eqn(2) find I D =38.494mA Converge at V D =0.753V and I D =38.494mA Answer 91 ا ز ر... 1/r D.

47 ی هد ود : : Figure 3.13 Piecewise-linear model of the diode forward characteristic and its equivalent circuit representation. ثال. : Figure 3.14 The circuit of Fig with the diode replaced with its piecewise-linear model of Fig

48 وتاژ دلا :. V=0.7. Figure 3.15 Development of the constant-voltage-drop model of the diode forward characteristics. A vertical straight line (B) is used to approximate the fast-rising exponential. Observe that this simple model predicts V D to within ±0.1 V over the current range of 0.1 ma to 10 ma. ثال. Figure 3.16 The constant-voltage-drop model of the diode forward characteristics and its equivalent-circuit representation.

49 Example: Use approximate method to solve V D and I D for the given diode circuit, (a) if it is a Si diode, (b) if it is a Ge diode, (c) if it is an ideal diode (a) Si diode VD = 0.7V 10 V I D D= = = = 9.3mA Ans 1k 1k 1k (b) Ge diode VD = 0.3V 10 V I D D= = = = 9.7mA Ans 1k 1k 1k (c) Ideal diode VD = 0V 10 V 10 0 I D D= = = 10mA Ans 1k 1k 97 Example: Find V o and I R for the given diode circuits = I R 5.6k I R = = 1.96mA 5.6k V o = I R 5.6k = 1.96mA 5.6k = 10.97V orv o = = 11V D 2 isreverse -biased I R = 0mA ThenV o = I R 5.6k = 0 5.6k = 0V 12 = V D1 + V D2 + V o = 0 + V D2 + 0 V D2 = 12V Ans Because there is no current through the diode, voltage drop of the diode D 1 is zero

50 خلا : : : n= nv. T. r = -6 d I D 99 ivه ن یکدار : ( E). v i. v i 10 0

51 ... ( ) ivه یک با نا ن دار... iv.. کم شيب مشخصه iبرحسب v معادل زياد شدن مقاومت ورودي است: 10 2

52 اضافه شدن شدن شيب مشخصه iبرحسب v معادل کم شدن مقاومت ورودي است: ترآيب سري منبع مقاومت و ديود ). (. ). ( اواعدود. (LED ). 10 4

53 د ود زR... Common Zener Voltages: 1.8V to 200V Figure 3.20 Circuit symbol for a zener diode. Figure 3.21 The diode i v characteristic with the breakdown region shown in some detail. د وده ش ت - Izk mA..

54 دلد ود زRه ش ت : rz. Vz...Vz Vzo. Figure 3.22 Model for the zener diode. Complete-model diode curve. V RZ = I R R Forward operating region Reverse operating region (also called the reverse breakdown region) VF RB = I F 10 8

55 ثال Figure 3.23 (a) Circuit for Example Vo line Regulation. load Regulation 1mA.. 2K, 0.5K Vo Rl پا خ : : : +-1V : Figure 3.23 (b) The circuit with the zener diode replaced with its equivalent circuit model.

56 1mA. 2k : Figure 3.23 (b) The circuit with the zener diode replaced with its equivalent circuit model. : mA R. :. Vzk=6.7 Iz=0.2 R :

57 د ود وردنده( LED ) PN LED. bandgap ) (. LED. In a forward-biased p-n junction, recombination of the holes and electrons requires energy possessed by the unbound free electrons In Si and Ge, most of the energy is dissipated in the form of heat and photons But in other material such as GaAs, the energy generate light but it is invisible for the eye to see (infrared) Other materials that emit light during forward-bias operation Color Construction Forward Voltage Amber Blue Green Orange Red White Yellow AlInGaP GaN GaP GaAsP GaAsP GaN AlInGaP

58 Relative response of the human eye to various colors 10 0 Relative eye response GaN ZnSe GaP:N GaAs.14 p 86 GaAs.35 p 65 GaAs p violet blue green yellow orange red Wavelength in nanometers The materials which are used for important light emitting diodes (LEDs) for each of the different spectral regions. Color Name Wavelength (Nanometers) Semiconductor Composition Infrared 880 GaAlAs/GaAs Ultra Red 660 GaAlAs/GaAlAs Super Red 633 AlGaInP Super Orange 612 AlGaInP Orange 605 GaAsP/GaP Yellow 585 GaAsP/GaP Incandescent White Pale White Cool White 4500K (CT) 6500K (CT) 8000K (CT) InGaN/SiC InGaN/SiC InGaN/SiC Pure Green 555 GaP/GaP Super Blue 470 GaN/SiC Blue Violet 430 GaN/SiC Ultraviolet 395 InGaN/SiC

59 Material Wavelength (µm) Material Wavelength (µm) ZnS ZnO Gan ZnSe CdS ZnTe GaSe CdSe CdTe GaAs InP GaSb InAs Te PbS InSb PbTe PbSe د ود وری( photodiode )......

60 ا وو پ LED..... LED دود خاز ی..... (VCO))

61 دودو ن ی. -.. دودشا ت ی n n P. P

62 .. ( ) n.. Low forward voltage ( V) Suitable for digital switching applications Capable of operating at freq. of 20 GHz and more در ولتاژهاي بالا توان آم مصرف می کند Other Diodes Constant-Current Diodes PIN diodes Current controlled resistance (in forward operation) Used as switches or modulators in UHF and microwave applications Step-recovery diodes Low-picosecond switching time

63 Any Questions?? 12 5