ME 6405 Student Lecture: Transistors Chester Ong Ajeya
ME 6405 Student Lecture: Transistors Chester Ong Ajeya Karajgikar Emanuel Jones Thursday September 30, 2010 Georgia Institute of Technology Presentation Outline 1 Transistor Fundamentals 2 Bipolar Junction Transistors 3 Power Transistors
4 Field Effect Transistors 5 Applications of Transistor Chester Ong Ajeya Karajgikar Ajeya Karajgikar Emanuel Jones (covered by each speaker in respective topic) Transistors Transistors of various type & size
First Transistor Model, 1947 BJT (PNP) Electrical Diagram Representation Used in all modern FET Transistor BJT Transistor electronics Understanding Transistors (conceptually) 1. What is a Transistor? 2.
Basic Purpose of a Transistor Recognize Transistor Role in Modern Electronics Understand Reason(s) for its Invention Comparison to its predecessor, the Vacuum Tube How are transistors made? 3. Doping Manufacturing Process Effect of Doping on Semiconductors Creation of a P-N Junction via Doping How do transistors work?
Depletion Region of a P-N Junction How to Control Current through a Depletion Region How a P-N Junction can act as an Electrical Switch Combination of P-N Junctions -> Transistors 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 Electronics Basic building blocks for all modern electronics Microprocessors, Microcontrollers, Motor Digital Logic Computers, Digital watches, PC & Cell Controllers Microprocesso Headphones Circuits,
Cell Phones. Phones r Reason for Transistors Early 20 century, vacuum tube was used for signal Invention: th amplifier & switch. Vacuum Tube Radios vacuum tube* ENIAC : 17, 468 vacuum tubes large, fragile, resulted in extremely
Use of 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 tubes and the TRANSISTOR was Invention born! In 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. John Bardeen, Walter Brattain, and William Schockly Awarded the Nobel Prize in physics (1956) Transistor is a semiconductor device commonly used to amplify or First model of Transistor, 1947 Historical Development 1941, Vacuum Tube 1948, the first (Germanium) TR John Bardeen, Walter Brattain, and William Schockly
1954, Silicon TR At TI Lab, Ease of processing, lower cost, greater power handling, more stable temperature characteristics 1958, Integrated Circuit Individual electronic components were soldered on to printed circuit boards. Sep 2009, 22nm silicon wafer Intel CEO Paul Otellini, Sep 23 2009 more than 2.9 billion transistors is packed into an area of fingernail IC placed all components in one chip.
Transistor Categories and Types Transistor are categorized by Semiconductor material: germanium, silicon, gallium arsenide, etc. Structure: BJT, FET, IGFET (MOSFET), IGBT Polarity: NPN, PNP (BJTs); N-channel, P-channel (FETs) Maximum power rating: low, medium, high Maximum operating frequency: low, medium, high Application: switch, audio, high voltage, etc. Physical packaging: through hole, surface mount, ball grid array, etc. Amplification factor Various Types of Transistor: http://en.wikipedia.org/wiki/Category:Transistor_typ es Various Types of Transistors Bipolar Junction Transistor (BJT) Field Effect Transistors (FET) Power Transistors Understanding Transistors
(conceptually) 1. What is a Transistor? 2. Basic Purpose of a Transistor Recognize Transistor Role in Modern Electronics Understand Reason(s) for its Invention Comparison to its predecessor, the Vacuum Tube How are transistors made? 3.
Doping Manufacturing Process Effect of Doping on Semiconductors Creation of a P-N Junction via Doping How do transistors work? Depletion Region of a P-N Junction How to Control Current through a Depletion Region How a P-N Junction can act as an Electrical Switch Combination of P-N Junctions -> Transistors Doping Manufacturing Doping: Process of introducing impure elements (dopants) into Process 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 anHigh-Temp electric field; and deposited in a silicon wafer. Furnace Pure Wafers Ion Implanter Wafer Refineme nt Doped Wafers Effect of Doping on SemiGeneral Conductors (1/3) of Semiconductors: Characteristics Possesses an electrical conductivity somewhere between insulators & conductors
Typical material composition is either silicon or germanium Semiconductors are more insulators than conductors, since semiconductors possess few free electrons (as opposed to conductors, which have many free electrons) Doping impurities into a puresemiconductor will increase conductivity. Doping results in an N-Type or P-Type semiconductor. Effect of Doping on SemiP-TypeConductors Semiconductors(2/3) : 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
Effect of Doping on SemiN-Type Semiconductors : Negatively charged Semiconductor Conductors (3/3) Dopant Material: Phosphorous, Arsenic, Antimony (Sb) Effect of Dopant: adds electrons to semiconductor atom Semiconductor is now negatively charged, because of electron abundance Overall material (semiconductor + dopant) wants to donate extra electrons to make lattice structure at its lowest energy state Creation of P-N Junction via Remember: Doping Doping introduces impurities into semiconductor material Remember: Dopant is added to same piece of
semiconductor material Resulting Material: Single, solid material called P-N Negatively-charged Positively-charged Junction N-type Side P-type Side Example: Boron (P-Type) to side A and Antimony (N-Type) to side B structure Lattice Lattice structure has wants electrons to fill holes too many electrons What happens at the point of contact or junction? Understanding
Transistors (conceptually) 1. What is a Transistor? 2. Basic Purpose of a Transistor Recognize Transistor Role in Modern Electronics Understand Reason(s) for its Invention Comparison to its predecessor, the Vacuum Tube How are transistors made? 3.
Doping Manufacturing Process Effect of Doping on Semiconductors Creation of a P-N Junction via Doping How do transistors work? Depletion Region of a P-N Junction How to Control Current through a Depletion Region How a P-N Junction can act as an Electrical Switch Combination of P-N Junctions -> Transistors Depletion Region of P-N Junction At equilibrium with no external voltage, a thin and constantthickness depletion region forms between P-type and N-type semiconductors. In depletion region, free electrons from N-type will fill the electron
holes in the P-type until equilibrium. Negative and positive ions are subsequently created in depletion region. Current through a Depletion Region Remember: Depletion region is created at equilibrium between P & Ntype 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 Electrical Switching on P-N Applying
Junction External Voltage of Forward Biasing polarity facilitates motion of free electrons of Reverse Biasing polarity impedes motion of free electrons Forward Biasing Circuit is On Current is Flowing Reverse Biasing Circuit is Off Current not Flowing Finally combining all concepts Semiconductor -> Doping -> P-N Junction -> Depletion Region -> Ions & Coulomb Force -> External Voltage -> Current on/off One P-N Junction can control current flow via an external
voltage Two 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. Presentation Outline 1 Transistor Fundamentals 2 Bipolar Junction Transistors 3 Power Transistors 4 Field Effect Transistors
5 Applications of Transistor Chester Ong Ajeya Karajgikar Ajeya Karajgikar Emanuel Jones (covered by each speaker in respective topic) BJT introduction BJT = Bipolar Junction Transistor
3 Terminals Base (B) Collector (C) Emitter (E) BJT schematic NPN: BE forward biased BC reverse biased NPN PNP
PNP: BE reverse biased BC forward biased BJT formulae NPN Current control i E iC i B i C i B V V E V CE V C V
E BE V is the amplification factor and ranges from 20 to 200 It is dependent on temperature and voltage B BJT formulae NPN Emitter is more heavily doped than the collector. Therefore, VC > VB > VE for NPN transistor BJT formulae NPN
iC iE iB (1 )iE iC iB 1 is the fraction of electrons that diffuse across the narrow base region 1 is the fraction of electrons that recombine with holes in the base region to create base current Common Emitter Transistor Circuit Emitter is grounded and input voltage is applied to Base Base-Emitter starts to conduct when VBE is about 0.6V, iC flows with iC= .iiB As iB further increases, VBE slowly increases to 0.7V, iC rises exponentially As iC rises, voltage drop across RC increases and VCE drops toward ground (transistor in saturation, no more linear relation between iC and iB) 27
Common Emitter Characteristics Collector current controlled by the collector circuit (Switch behavior) Collector current IC proportional to Base current IB In full saturation VCE=0.2V No current 28 BJT operating regions
Operating Region Cut Off Parameters VBE < Vcut-in VCE > Vsupply IB = IC = 0 Mode Switch OFF Linear VBE = Vcut-in Vsat < VCE < Vsupply IC = *IB Amplification Saturated
VBE = Vcut-in, VCE < Vsat IB > IC,max, IC,max > 0 Switch ON BJT as an amplifier Question: What is the minimum Vin that makes the transistor act as an amplifier? Given: RB = 10 k RC = 1 k = 100 VSupply = 10 V Vcut-in = 0.7 V Vsat = 0.2 V
I II VSupply I RB II iC = (Vsupply VCE) / RC Set VCE = Vsat = 0.i2V iC = (10 0.2) / 1000 = 9.8mA iC = .i iB iB = iC / = 0.0098/100 = 0.098mA RC Vin Vsupply iC . RC VCE = 0
Vin iB .i RB VBE = 0 Vin = iB .i RB + VBE Set VBE = Vcut-in = 0.i7V Vin = (0.i098) .i(10-3).i(10000 )+ 0.i7V Vin = 1.68V or greater. BJT as a switch From exercise 3 Turns on/off coils digitally Power Transistors Concerned with delivering high power Used in high voltage and high current application In general Fabrication process different in order to: Dissipate more heat Avoid breakdown Different types: Power BJTs, power MOSFETS, etc.
Presentation Outline 1 Transistor Fundamentals 2 Bipolar Junction Transistors 3 Power Transistors 4 Field Effect Transistors 5 Applications of Transistor Chester Ong
Ajeya Karajgikar Ajeya Karajgikar Emanuel Jones (covered by each speaker in respective topic) Field-Effect Transistor (FET) Presented by: Emanuel Jones What is a Field-Effect Transistor (FET)? Semiconductor device that depends on electric field to control the current Performs same functions as a BJT; amplifier, switch, etc. Relies on PNP or NPN junctions to allow current flow However, mechanism that controls
current is different from the BJT Remember the BJT is bipolar. The FET is sometimes called a unipolar transistor One type of charge carrier What makes a Field-Effect Transistor? FETs have three main parts Drain Source Gate The body has contacts at the ends: the drain and source Gate surrounds the body and can induce a channel to because of an electric field FET Input voltage controls output
current Gate Drain Source BJT Input current controls output current Base Collector Emitter Controls flow of current Current goes out here Current comes in here How does a FET work? No Voltage to Gate Source Voltage to Gate
Drain Source Drain n n MOSFET shown here No current flow Simplified Notation Short allows current flow Types of Field-Effect Transistors Type Function Junction Field-Effect Transistor
(JFET) Metal-Oxide-Semiconductor FET (MOSFET) Insulated Gate Bipolar Transistor (IGBT) Similar to MOSFET, but different main channel Organic Field-Effect Transistor (OFET) Uses organic semiconductor in its channel Nanoparticle Organic Memory FET (NOMFET) DNAFET Uses reversed biased p-n junction to separate gate from body
Uses insulator (usu. SiO2) between gate and body Combines the organic transistor and gold nanoparticles Uses a gate made of single-strand DNA molecules MOSFET IGBT JFET A single channel of single doped SC material with terminals at end Gate surrounds channel with doping that is opposite of the channel, making the PNP or NPN type n-channel Uses reversed biased p-n junction to separate JFET gate from body Flow of current is similar to water flow through a garden hose Pinch the hose (decrease current channel
width) to decrease flow Open the hose (increase channel width) to increase flow Also, the pressure differential from the front and back of the hose (synonymous with the voltage from drain to source) effects the flow p-channel JFET JFET analysis IV characteristics and output plot of a JFET n-channel transistor. JFET analysis IDS : Drain current in saturation region VGS : Voltage at the gate Vth : Threshold voltage VDS : Voltage from drain to source VP : Pinch-off voltage   - This "pinch-off voltage" varies considerably, even among devices of the same type. For
example, VGS(off) for the Temic J201 device varies from -0.8V to -4V. Typical values vary from -0.3V to -10V. MOSFET Similar to JFET remember p-channel A single channel of single doped SC material with terminals at end Gate surrounds channel with doping that is opposite of the channel, making the PNP or NPN type BUT, the MOSFET uses an insulator to separate gate from body, while JFET uses a reversebias p-n junction n-channel MOSFET
enhanced mode MOSFET depleted mode MOSFET FETs vary voltage to control current. This illustrates how that works MOSFET 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. MOSFET Triode Mode/Linear Region Saturation/Active Mode VGS > Vth and VDS < ( VGS - Vth ) VGS > Vth and VDS > ( VGS - Vth ) VGS : Voltage at the gate
Vth : Threshold voltage VDS : Voltage from drain to source n: charge-carrier effective mobility W: gate width L: gate length Cox : gate oxide capacitance per unit area : channel-length modulation Characteristics and Applications of FETs JFETs Simplest type of FET easy to make High input resistance Low Capacitance High input impedance Slower speed in switching Uses? Displacement sensor High input impedance amplifier Low-noise amplifier Analog switch
Characteristics and Applications of FETs MOSFETs Oxide layer prevents DC current from flowing through gate Reduces power consumption High input impedance Rapid switching More noise than JFET Uses? Again, switches and amplifiers in general The MOSFET is used in digital CMOS logic, which uses p- and n-channel MOSFETs as building blocks To aid in negating effects that
cause discharge of batteries Use of MOSFET in battery protection circuit Presentation Summary 1 Transistor Fundamentals 2 Bipolar Junction Transistors 3 Power Transistors 4 5 Chester Ong
Qualitative explanation of the what & how behind transistors General application and history of transistors Physics behind transistors : Doping Process, Effect on Semiconductors, & Formation of P-N Jun Electrical Properties of P-N Junction & using P-N to control / ampli Ajeya Karajgikar Introduction & Formulae Explain function and characteristics of common emitter transistor Describe BJT operating regions Applications of BJTs Ajeya Karajgikar Definition and Applications Field Effect Transistor Emanuel Jones Use of electric field to change the output current JFETs and MOSFETs are most common, and accomplish similar goals Used for switches, amplification, applications for protecting electroni
Applications of Transistor (covered by each speaker in respective topic) References (32) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
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