Presentation on theme: "ME 6405 Student Lecture: Transistors"— Presentation transcript:
1 ME 6405 Student Lecture: Transistors Chester Ong Ajeya Karajgikar Emanuel JonesThursday September 30, 2010 Georgia Institute of Technology
2 Presentation Outline Transistor Fundamentals 1Transistor FundamentalsChester Ong2Bipolar Junction TransistorsAjeya Karajgikar3Power TransistorsAjeya Karajgikar4But there are much more than these.Field Effect TransistorsEmanuel Jones5Applications of Transistor(covered by each speaker in respective topic)
3 Transistors BJT (PNP) Electrical Diagram Representation Transistors of various type & sizeYou’ve all seen the transistor before, but instead of regurgitation, provide student perspective….FET TransistorFirst Transistor Model, 1947Used in all modern electronicsBJT Transistor
4 Understanding Transistors (conceptually) 1. What is a Transistor?Basic Purpose of a TransistorRecognize Transistor Role in Modern ElectronicsUnderstand Reason(s) for its InventionComparison to its “predecessor,” the Vacuum Tube2. How are transistors made?“Doping” Manufacturing ProcessEffect of Doping on SemiconductorsCreation of a P-N Junction via Doping3. How do transistors work?Depletion Region of a P-N JunctionHow to Control Current through a Depletion RegionHow a P-N Junction can act as an Electrical SwitchCombination of P-N Junctions -> Transistorsto understand the transistor, conceptually, we must address the three questions:
5 What is a Transistor? Basic Purpose  To amplify signals  To electronically switch (no moving parts) a signal on or off (high/low)Role in Modern ElectronicsBasic building blocks for all modern electronicsMicroprocessors, Microcontrollers, Computers, Digital watches, Digital Logic Circuits, Cell Phones….ROADMAP OF BUILD TRANSISTOR -> PROPERTIESMotor ControllersMicroprocessorPC & Cell PhonesHeadphones
6 Reason for Transistor’s Invention: Early 20th century, vacuum tube was used for signal amplifier & switch.Use of vacuum tube* resulted in extremely large, fragile, energy inefficient, and expensive electronics.Evolution of electronics required device that was small, light weight, robust, reliable, cheap to manufacture, energy efficient:*Vacuum tube advantages: operation at higher voltages (10K region vs. 1K region of transistors); high power, high frequency operation (over-the-air TV broadcasting) better suited for vacuum tubes; and silicon transistors more vulnerable to electromagnetic pulses than vacuum tubesVacuum Tube RadiosENIAC : 17, 468 vacuum tubes
7 …and the TRANSISTOR was born! InventionIn 1947, John Bardeen, Walter Brattain, and William Schockly, researchers at Bell Lab, invented Transistor.They found Transistor Effect: “when electrical contacts were applied to a crystal of germanium, the output power was larger than the input.”Awarded the Nobel Prize in physics (1956)Transistoris a semiconductor device commonly used to amplify or switch electronic signals.John Bardeen, Walter Brattain, and William SchocklyFirst model of Transistor, 1947
8 Historical Development 1941, Vacuum Tube1948, the first (Germanium) TRJohn Bardeen, Walter Brattain, and William Schockly1954, Silicon TRAt TI Lab, Ease of processing, lower cost, greater power handling, more stable temperature characteristics1958, Integrated CircuitCircuits based on individual transistors became too large and too difficult to assemble.To make the circuits even faster, one needed to pack the transistors closer and closer together.In 1958 the integrated circuit was developed at Texas Instrument.Instead of making transistors one-by-one, several transistors could be made at the same time, on the same piece of semiconductor.Not only transistors, but other electric components such as resistors, capacitors and diodes could be made by the same process.For more than 30 years, since the 1960's, the number of transistors per unit area has been doubling every 1.5 years based on Moore's law.Latest technology is 2nm silicon wafer. Intel CEO Paul Otellini introduced it last Tuesday. This wafer can contain more than 2.9 billion TRs into an area of fingernail.Individual electronic components were soldered on to printed circuit boards.IC placed all components in one chip.Sep 2009, 22nm silicon wafermore than 2.9 billion transistors is packed into an area of fingernailIntel CEO Paul Otellini, Sep
9 Transistor Categories and Types Transistor are categorized bySemiconductor material: germanium, silicon, gallium arsenide, etc.Structure: BJT, FET, IGFET (MOSFET), IGBTPolarity: NPN, PNP (BJTs); N-channel, P-channel (FETs)Maximum power rating: low, medium, highMaximum operating frequency: low, medium, highApplication: switch, audio, high voltage, etc.Physical packaging: through hole, surface mount, ball grid array, etc.Amplification factorVarious Types of Transistor:Various Types of TransistorsBipolar Junction Transistor (BJT)Field Effect Transistors (FET)Power Transistors
10 Understanding Transistors (conceptually) 1. What is a Transistor?Basic Purpose of a TransistorRecognize Transistor Role in Modern ElectronicsUnderstand Reason(s) for its InventionComparison to its “predecessor,” the Vacuum Tube2. How are transistors made?“Doping” Manufacturing ProcessEffect of Doping on SemiconductorsCreation of a P-N Junction via Doping3. How do transistors work?Depletion Region of a P-N JunctionHow to Control Current through a Depletion RegionHow a P-N Junction can act as an Electrical SwitchCombination of P-N Junctions -> Transistorsto understand the transistor, conceptually, we must address the three questions:
11 Doping Manufacturing Process Doping: “Process of introducing impure elements (dopants) into semiconductor wafers to form regions of differing electrical conductivity.”Two Main Manufacturing Processes:  High-temperature furnace diffuse a solid layer of “dopant” onto wafer surface.  Ion implanter: gaseous dopants are ionized (stripped of electrons); accelerated using an electric field; and deposited in a silicon wafer.High-Temp Furnace“Pure” Wafers“Doped” WafersRead doping slowlyWafer RefinementIon Implanter
12 Effect of Doping on Semi-Conductors(1/3) General Characteristics of Semiconductors:Possesses an electrical conductivity somewhere betweeninsulators & conductorsTypical material composition is either silicon or germaniumSemiconductors are more “insulators” than “conductors,” since semiconductors possess few free electrons (as opposed to conductors, which have many free electrons)Doping impurities into a “pure”semiconductor will increase conductivity.Doping results in an “N-Type” or “P-Type” semiconductor.
13 Effect of Doping on Semi-Conductors(2/3) P-Type Semiconductors : Positively charged Semiconductor Dopant Material: Boron, Aluminum, Gallium Effect of Dopant:“takes away” weakly-bound outer orbit electrons from semiconductor atom.Semiconductor now has “missing” electron or “hole” in its lattice structure.Overall material is now positively charged , because material has fewer electrons but still wants to accept electrons to fill holes in its lattice structure
14 Effect of Doping on Semi-Conductors(3/3) N-Type Semiconductors : Negatively charged Semiconductor Dopant Material: Phosphorous, Arsenic, Antimony (Sb) Effect of Dopant:“adds” electrons to semiconductor atomSemiconductor is now negatively charged, because of electron abundanceOverall material (semiconductor + dopant) wants to donate “extra” electrons to make lattice structure at its lowest energy state
15 Creation of P-N Junction via Doping Remember: Doping introduces impurities into semiconductor materialRemember: Dopant is added to same piece of semiconductor materialResulting Material: Single, solid material called “P-N Junction”Example: Boron (P-Type) to side A and Antimony (N-Type) to side BPositively-charged P-type SideNegatively-charged N-type SideLattice structure wants electrons to fill “holes”Lattice structure has too many electronsWhat happens at the point of contact or “junction?
16 Understanding Transistors (conceptually) 1. What is a Transistor?Basic Purpose of a TransistorRecognize Transistor Role in Modern ElectronicsUnderstand Reason(s) for its InventionComparison to its “predecessor,” the Vacuum Tube2. How are transistors made?“Doping” Manufacturing ProcessEffect of Doping on SemiconductorsCreation of a P-N Junction via Doping3. How do transistors work?Depletion Region of a P-N JunctionHow to Control Current through a Depletion RegionHow a P-N Junction can act as an Electrical SwitchCombination of P-N Junctions -> Transistorsto understand the transistor, conceptually, we must address the three questions:
17 Depletion Region of P-N Junction At equilibrium with no external voltage, a thin and constant-thickness“depletion region” forms between P-type and N-type semiconductors.In depletion region, free electrons from N-type will “fill” the electronholes in the P-type until equilibrium.Negative and positive ions are subsequently created in depletion region.Ions exhibit a (Coulomb) force which inhibits further electron flow (i.e. current) across the P-N Junction unless a forward bias external voltage is applied.
18 Current through a Depletion Region Remember:Depletion region is created at equilibrium between P & N-type junction.Positive & negative ions are created in depletion region.Ions have a Coulomb force which impedes motion of electrons – essentially insulator property.Applying External Voltage……of Forward Biasing polarity facilitates motion of free electrons -> Coulomb force is overcome, electrons flow from N to P…of Reverse Biasing polarity impedes motion of free electrons -> No current flow because of Coulomb force in depletion region
19 Electrical Switching on P-N Junction Applying External Voltage……of Forward Biasing polarity facilitates motion of free electrons…of Reverse Biasing polarity impedes motion of free electronsForward BiasingReverse BiasingCircuit is “On”Current is FlowingCircuit is “Off”Current not Flowing
20 Finally – combining all concepts Semiconductor -> Doping -> P-N Junction -> Depletion Region-> Ions & Coulomb Force -> External Voltage -> Current on/offOne P-N Junction can control current flow via an external voltageTwo P-N junctions (bipolar junction transistor, BJT) can control current flow and amplify the current flow.Also, if a resistor is attached to the output, the resulting voltage output is much greater than the applied voltage, due to amplified current and I*R=V.
21 Presentation Outline Transistor Fundamentals 1Transistor FundamentalsChester Ong2Bipolar Junction TransistorsAjeya Karajgikar3Power TransistorsAjeya Karajgikar4But there are much more than these.Field Effect TransistorsEmanuel Jones5Applications of Transistor(covered by each speaker in respective topic)
23 BJT schematic NPN PNP NPN: BE forward biased BC reverse biased PNP: BE reverse biasedBC forward biased
24 BJT formulaeCurrent controlNPNSuggestion: state the qualitative definition behind these equations: when ib =0, when ib !=0, etc, what happens?β is the amplification factor and ranges from 20 to 200It is dependent on temperature and voltage
25 BJT formulae NPN Emitter is more heavily doped than the collector. Therefore,VC > VB > VEfor NPN transistorNPNWhy do more heavily doped (less electrons, more electrons) are of less/more voltage? Write it on the slide. Change the font. Change the background. b/c e is heavily doped…lower potential
26 BJT formulaeNPNα is the fraction of electrons that diffuse across the narrow base region1 – α is the fraction of electrons that recombine with holes in the base region to create base current
27 Common Emitter Transistor Circuit Emitter is grounded and input voltage is applied to BaseBase-Emitter starts to conduct when VBE is about 0.6V, iC flows withiC= β.iBAs iB further increases, VBE slowly increases to 0.7V, iC rises exponentiallyAs iC rises, voltage drop across RC increases and VCE drops toward ground (transistor in saturation, no more linear relation between iC and iB)
28 Common Emitter Characteristics Collector current controlled by the collector circuit (Switch behavior)In full saturation VCE=0.2VCollector current IC proportional to Base current IBNo current flows
29 BJT operating regions Operating Region Parameters Mode Cut Off VBE < Vcut-inVCE > VsupplyIB = IC = 0Switch OFFLinearVBE = Vcut-inVsat < VCE < VsupplyIC = β*IBAmplificationSaturatedVBE = Vcut-in,VCE < VsatIB > IC,max, IC,max > 0Switch ON
30 BJT as an amplifier I II I II Question: What is the minimum Vin that makes the transistor act as an amplifier?Given:RB = 10 kΩRC = 1 kΩβ = 100VSupply = 10 VVcut-in = 0.7 VVsat = 0.2 VVsupply – iC . RC – VCE = 0IiC = (Vsupply – VCE) / RCSet VCE = Vsat = 0.2ViC = (10 – 0.2) / 1000 = 9.8mAiC = β . iBVSupplyVinRBRCiB = iC / β = /100 = 0.098mAIIVin – iB . RB – VBE = 0Vin = iB . RB + VBEISet VBE = Vcut-in = 0.7VVin = (0.098) .(10-3).(10000 )+ 0.7VIIVin = 1.68V or greater.
31 BJT as a switchFromexercise 3Turns on/off coils digitally
32 Power Transistors Concerned with delivering high power Used in high voltage and high current applicationIn generalFabrication process different in order to:Dissipate more heatAvoid breakdownDifferent types: Power BJTs, power MOSFETS, etc.
33 Presentation Outline Transistor Fundamentals 1Transistor FundamentalsChester Ong2Bipolar Junction TransistorsAjeya Karajgikar3Power TransistorsAjeya Karajgikar4But there are much more than these.Field Effect TransistorsEmanuel Jones5Applications of Transistor(covered by each speaker in respective topic)
34 Field-Effect Transistor (FET) Presented by: Emanuel Jones
35 What is a Field-Effect Transistor (FET)? Semiconductor device that depends on electric field to control the currentPerforms same functions as a BJT; amplifier, switch, etc.Relies on PNP or NPN junctions to allow current flowHowever, mechanism that controls current is different from the BJTRemember the BJT is bipolar. The FET is sometimes called a unipolar transistorOne type of charge carrier
36 What makes a Field-Effect Transistor? FETs have three main partsDrainSourceGateThe body has contacts at the ends: the drain and sourceGate surrounds the body and can induce a channel to because of an electric fieldFETBJTInput voltage controls output currentInput current controls output currentGateBaseControls flow of currentDrainCollectorCurrent goes out hereSourceEmitterCurrent comes in here
37 How does a FET work? Simplified Notation No Voltage to Gate SourceDrainSourceDrainnnSimplified NotationMOSFET shown hereNo current flow“Short” allows current flow
38 Types of Field-Effect Transistors FunctionJunction Field-Effect Transistor (JFET)Uses reversed biased p-n junction to separate gate from bodyMetal-Oxide-Semiconductor FET (MOSFET)Uses insulator (usu. SiO2) between gate and bodyInsulated Gate Bipolar Transistor (IGBT)Similar to MOSFET, but different main channelOrganic Field-Effect Transistor (OFET)Uses organic semiconductor in its channelNanoparticle Organic Memory FET (NOMFET)Combines the organic transistor and gold nanoparticles“DNAFET”Uses a gate made of single-strand DNA moleculesMOSFETIGBT
39 JFETA single channel of single doped SC material with terminals at endGate surrounds channel with doping that is opposite of the channel, making the PNP or NPN typeUses reversed biased p-n junction to separate gate from bodyFlow of current is similar to water flow through a garden hosePinch the hose (decrease current channel width) to decrease flowOpen the hose (increase channel width) to increase flowAlso, the pressure differential from the front and back of the hose (synonymous with the voltage from drain to source) effects the flown-channelJFETp-channelJFET
40 JFET analysisI–V characteristics and output plot of a JFET n-channel transistor.
41 JFET analysis IDS : Drain current in saturation region VGS : Voltage at the gateVth : Threshold voltageVDS : Voltage from drain to sourceVP : Pinch-off voltage  - This "pinch-off voltage" varies considerably, even among devices of the same type. Forexample, VGS(off) for the Temic J201 device varies from -0.8V to -4V. Typical values vary from-0.3V to -10V.
42 MOSFET Similar to JFET – remember… A single channel of single doped SC material with terminals at endGate surrounds channel with doping that is opposite of the channel, making the PNP or NPN typeBUT, the MOSFET uses an insulator to separate gate from body, while JFET uses a reverse-bias p-n junctionp-channeln-channelMOSFET enhanced modeMOSFET depleted mode
43 FETs vary voltage to control current. This illustrates how that works MOSFETFETs vary voltage to control current. This illustrates how that worksMOSFET drain current vs. drain-to-source voltage for several values of VGS − Vth; the boundary between linear (Ohmic) and saturation (active) modes is indicated by the upward curving parabola.
44 MOSFET Triode Mode/Linear Region VGS > Vth and VDS < ( VGS - Vth )Saturation/Active ModeVGS > Vth and VDS > ( VGS - Vth )VGS : Voltage at the gateVth : Threshold voltageVDS : Voltage from drain to sourceμn: charge-carrier effective mobilityW: gate widthL: gate lengthCox : gate oxide capacitance per unit areaλ : channel-length modulation parameter
45 Characteristics and Applications of FETs JFETsSimplest type of FET – easy to makeHigh input resistanceLow CapacitanceHigh input impedanceSlower speed in switchingUses?Displacement sensorHigh input impedance amplifierLow-noise amplifierAnalog switchVoltage controlled resistor
46 Characteristics and Applications of FETs MOSFETsOxide layer prevents DC current from flowing through gateReduces power consumptionHigh input impedanceRapid switchingMore noise than JFETUses?Again, switches and amplifiers in generalThe MOSFET is used in digital CMOS logic, which uses p- and n-channel MOSFETs as building blocksTo aid in negating effects that cause discharge of batteriesUse of MOSFET in batteryprotection circuit
47 Presentation Summary Transistor Fundamentals Chester Ong 1Transistor Fundamentals Chester OngQualitative explanation of the what & how behind transistorsGeneral application and history of transistors“Physics” behind transistors : Doping Process, Effect on Semiconductors, & Formation of P-N Junction Electrical Properties of P-N Junction & using P-N to control / amplify current2Bipolar Junction Transistors Ajeya KarajgikarIntroduction & FormulaeExplain function and characteristics of common emitter transistorDescribe BJT operating regionsApplications of BJTs3Power Transistors Ajeya KarajgikarDefinition and Applications4Field Effect Transistor Emanuel JonesUse of electric field to change the output currentJFETs and MOSFETs are most common, and accomplish similar goals as BJTsUsed for switches, amplification, applications for protecting electronics5Applications of Transistor(covered by each speaker in respective topic)
48 References (32)really good video!- also really good explanation!
49 Questions?Thank you!But there are much more than these.