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ME 6405 Student Lecture:
Transistors
Chester OngAjeya KarajgikarEmanuel Jones
Thursday September 30, 2010Georgia Institute of Technology
Transistor FundamentalsChester Ong
Power TransistorsAjeya Karajgikar
Field Effect TransistorsEmanuel Jones
1
3
4
Applications of Transistor(covered by each speaker in respective topic)
5
Bipolar Junction TransistorsAjeya Karajgikar
2
Presentation Outline
Transistors
First Transistor Model, 1947 FET Transistor BJT Transistor
Transistors of various type & size
Used in all modern electronics
BJT (PNP) Electrical Diagram Representation
1. What is a Transistor?• Basic Purpose of a Transistor• Recognize Transistor Role in Modern Electronics• Understand Reason(s) for its Invention• Comparison to its “predecessor,” the Vacuum Tube
2. How are transistors made?• “Doping” Manufacturing Process• Effect of Doping on Semiconductors• Creation of a P-N Junction via Doping
3. 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
Understanding Transistors (conceptually)
Basic Purpose[1] To amplify signals[2] 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,
Computers, Digital watches, Digital Logic Circuits, Cell Phones….
What is a Transistor?
Microprocessor
PC & Cell Phones
Motor Controllers Headphones
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 tubes
Reason for Transistor’s Invention:
Vacuum Tube Radios
ENIAC : 17, 468 vacuum tubes
Invention 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.”
Awarded the Nobel Prize in physics (1956)
Transistor is a semiconductor device
commonly used to amplify or switch electronic signals.
John Bardeen, Walter Brattain, and William
Schockly
First model of Transistor, 1947
…and the TRANSISTOR was born!
more than 2.9 billion transistors is packed into an area of
fingernail
1941, Vacuum Tube
1948, the first (Germanium) TR
1954, Silicon TR
1958, Integrated Circuit
Sep 2009, 22nm silicon wafer
John Bardeen, Walter Brattain, and William Schockly
At TI Lab, Ease of processing, lower cost, greater power handling, more stable temperature characteristics
Intel CEO Paul Otellini, Sep 23 2009
Individual electronic components were soldered on to printed circuit boards.
IC placed all components in one
chip.
Historical Development
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_types
Various Types of Transistors• Bipolar Junction Transistor (BJT)• Field Effect Transistors (FET)• Power Transistors
Transistor Categories and Types
1. What is a Transistor?• Basic Purpose of a Transistor• Recognize Transistor Role in Modern Electronics• Understand Reason(s) for its Invention• Comparison to its “predecessor,” the Vacuum Tube
2. How are transistors made?• “Doping” Manufacturing Process• Effect of Doping on Semiconductors• Creation of a P-N Junction via Doping
3. 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
Understanding Transistors (conceptually)
Doping Manufacturing ProcessDoping: “Process of introducing impure elements (dopants) into
semiconductor wafers to form regions of differing electrical conductivity.”
Two Main Manufacturing Processes:[1] High-temperature furnace diffuse a solid layer of “dopant” onto wafer surface.[2] Ion implanter: gaseous dopants are ionized (stripped of electrons); accelerated using an electric field; and deposited in a silicon wafer.
Ion Implanter Wafer Refinement
High-Temp Furnace
“Pure” Wafers
“Doped” Wafers
Effect of Doping on Semi-Conductors(1/3)General Characteristics of Semiconductors:
• 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 “pure”semiconductorwill increase conductivity.
Doping results in an “N-Type” or “P-Type” semiconductor.
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
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 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 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 B
Positively-charged P-type Side
Lattice structure wants electrons to fill
“holes”
What happens at the point of contact or
“junction?
Lattice structure has too many electrons
Negatively-charged N-type Side
1. What is a Transistor?• Basic Purpose of a Transistor• Recognize Transistor Role in Modern Electronics• Understand Reason(s) for its Invention• Comparison to its “predecessor,” the Vacuum Tube
2. How are transistors made?• “Doping” Manufacturing Process• Effect of Doping on Semiconductors• Creation of a P-N Junction via Doping
3. 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
Understanding Transistors (conceptually)
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 electron holes 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.
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
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 electrons
Reverse Biasing
Forward Biasing •Circuit is “Off”
•Current not Flowing
•Circuit is “On”•Current is 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.
Transistor FundamentalsChester Ong
Power TransistorsAjeya Karajgikar
Field Effect TransistorsEmanuel Jones
1
3
4
Applications of Transistor(covered by each speaker in respective topic)
5
Bipolar Junction TransistorsAjeya Karajgikar
2
Presentation Outline
BJT introduction BJT = Bipolar Junction
Transistor
3 Terminals Base (B) Collector (C) Emitter (E)
NPN
PNP
NPN: BE forward
biased BC reverse
biased
PNP: BE reverse
biased BC forward
biased
BJT schematic
BJT formulae
ECCE
EBBE
BC
BCE
VVV
VVV
ii
iii
NPN
Current control
β is the amplification factor and ranges from 20 to 200It is dependent on temperature and voltage
BJT formulaeNPN
Emitter is more heavily doped than the collector.
Therefore,
VC > VB > VE
for NPN transistor
BJT formulaeNPN
α is the fraction of electrons that diffuse across the narrow base region
1 – α is the fraction of electrons that recombine with holes in the base region to create base current
1
)1(
B
C
EB
EC
i
i
ii
ii
27
Common Emitter Transistor CircuitEmitter is grounded and input voltage is applied to BaseBase-Emitter starts to conduct when VBE is about 0.6V, iC flows with
iC= β.iB
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)
Common Emitter Characteristics
28No current flows
Collector current controlled by the collector circuit (Switch behavior)
In full saturation VCE=0.2V
Collector current IC proportional to Base current
IB
BJT operating regions
Operating Region
Parameters Mode
Cut OffVBE < Vcut-in VCE > Vsupply
IB = IC = 0Switch OFF
LinearVBE = Vcut-in
Vsat < VCE < Vsupply
IC = β*IB
Amplification
Saturated
VBE = Vcut-in,VCE < Vsat
IB > IC,max, IC,max > 0
Switch ON
VSupplyVin
RB
RC
BJT as an amplifier Question: What is the minimum Vin that makes the transistor act as an amplifier?
Given:• RB = 10 kΩ• RC = 1 kΩ • β = 100• VSupply = 10 V• Vcut-in = 0.7 V• Vsat = 0.2 V
iB = iC / β = 0.0098/100 = 0.098mA
Vin – iB . RB – VBE = 0
Vsupply – iC . RC – VCE = 0
iC = (Vsupply – VCE) / RC
Set VCE = Vsat = 0.2V iC = (10 – 0.2) / 1000 = 9.8mA
iC = β . iB
Vin = iB . RB + VBE
Set VBE = Vcut-in = 0.7V
Vin = (0.098) .(10-3).(10000 )+ 0.7V
Vin = 1.68V or greater.
I
II
II
I
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 generalFabrication process different in order to: Dissipate more heat Avoid breakdown
Different types: Power BJTs, power MOSFETS, etc.
Transistor FundamentalsChester Ong
Power TransistorsAjeya Karajgikar
Field Effect TransistorsEmanuel Jones
1
3
4
Applications of Transistor(covered by each speaker in respective topic)
5
Bipolar Junction TransistorsAjeya Karajgikar
2
Presentation Outline
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 BJT Input voltage controls output
current
Input current controls output
currentGate Base Controls flow of currentDrain Collector Current goes out here
Source Emitter Current comes in here
How does a FET work?
Simplified Notation
No current flow “Short” allows current flow
No Voltage to Gate Voltage to Gate
MOSFET shown here
Source Source DrainDrain
n n
Types of Field-Effect Transistors
MOSFET IGBT
Type Function Junction Field-Effect Transistor (JFET) Uses reversed biased p-n junction to separate gate from body
Metal-Oxide-Semiconductor FET (MOSFET) Uses insulator (usu. SiO2) between gate and body
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) Combines the organic transistor and gold nanoparticles
“DNAFET” Uses a gate made of single-strand DNA molecules
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 type
Uses reversed biased p-n junction to separate gate from body
Flow 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 flow
n-channelJFET
p-channelJFET
JFET analysis
I–V characteristics and output plot of a JFET n-channel transistor.
JFET analysis
IDS : Drain current in saturation regionVGS : Voltage at the gateVth : Threshold voltageVDS : Voltage from drain to sourceVP : Pinch-off voltage [1]
[1] - 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.
MOSFETSimilar to JFET –
remember…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 reverse-bias p-n junction
p-channel
n-channel
MOSFETenhanced mode
MOSFETdepleted mode
MOSFETFETs 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.
MOSFETTriode Mode/Linear Region VGS > Vth and VDS < ( VGS - Vth )
VGS : Voltage at the gateVth : Threshold voltageVDS : Voltage from drain to sourceμn: charge-carrier effective mobilityW: gate width L: gate length Cox : gate oxide capacitance per unit areaλ : channel-length modulation parameter
Saturation/Active Mode
VGS > Vth and VDS > ( VGS - Vth )
Characteristics and Applications of FETsJFETs
• 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– Voltage controlled resistor
Characteristics and Applications of FETsMOSFETs
• 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
Transistor Fundamentals Chester Ong
Power Transistors Ajeya Karajgikar
Field Effect Transistor Emanuel Jones
1
3
4
Applications of Transistor(covered by each speaker in respective topic)
5
Bipolar Junction Transistors Ajeya Karajgikar2
Presentation Summary
• Use of electric field to change the output current• JFETs and MOSFETs are most common, and accomplish similar goals as BJTs• Used for switches, amplification, applications for protecting electronics
•Definition and Applications
•Introduction & Formulae•Explain function and characteristics of common emitter transistor•Describe BJT operating regions•Applications of BJTs
•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 Junction Electrical Properties of P-N Junction & using P-N to control / amplify current
References (32)1. http://www.utdallas.edu/research/cleanroom/TystarFurnace.htm2. http://www.osha.gov/SLTC/semiconductors/definitions.html3. http://www.products.cvdequipment.com/applications/diffusion/1/4. http://amath.colorado.edu/index.php?page=an-immersed-interface-method-for-modeling-semiconductor-d
evices5. http://www.extremetech.com/article2/0,2845,1938467,00.asp6. http://macao.communications.museum/eng/Exhibition/secondfloor/moreinfo/2_10_3_HowTransistorWorks.
html7. http://fourier.eng.hmc.edu/e84/lectures/ch4/node3.html8. http://www.appliedmaterials.com/htmat/animated.html really good video!9. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c310. http://www.tpub.com/neets/book7/25.htm11. http://esminfo.prenhall.com/engineering/wakerlyinfo/samples/BJT.pdf12. http://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdf13. http://www.me.gatech.edu/mechatronics_course/transistors_F09.ppt14. http://en.wikipedia.org/wiki/Bipolar_junction_transistor15. http://en.wikipedia.org/wiki/Common_emitter16. http://en.wikipedia.org/wiki/Diode17. http://www.kpsec.freeuk.com/trancirc.htm18. http://en.wikipedia.org/wiki/Field-effect_transistor19. http://en.wikipedia.org/wiki/JFET20. http://en.wikipedia.org/wiki/MOSFET21. http://www.slideshare.net/guest3b5d8a/fets22. http://www.rhopointcomponents.com/images/jfetapps.pdf23. http://cnx.org/content/m1030/latest/24. http://www.play-hookey.com/semiconductors/enhancement_mode_mosfet.html25. http://www.youtube.com/watch?v=-aHnmHwa_6I&feature=related26. http://www.youtube.com/watch?v=v7J_snw0Eng&feature=related27. http://info.tuwien.ac.at/theochem/si-srtio3_interface/si-srtio3.html28. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c429. http://inventors.about.com/library/inventors/blsolar5.htm30. http://thalia.spec.gmu.edu/~pparis/classes/notes_101/node100.html31. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html#c332. http://science.jrank.org/pages/6925/Transistor.html - also really good explanation!
Questions?Thank you!