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!