1. ME 6405 Student Lecture: Transistors
Chester Ong Ajeya Karajgikar Emanuel Jones
Thursday September 30, 2010 Georgia Institute of Technology

2. Presentation Outline Transistor Fundamentals1
Transistor Fundamentals
Chester Ong 2
Bipolar Junction Transistors
Ajeya Karajgikar 3
Power Transistors
Ajeya Karajgikar 4
But there are much more than these.
Field Effect Transistors
Emanuel Jones 5
Applications of Transistor
(covered by each speaker in respective topic)

3. Transistors BJT (PNP) Electrical Diagram Representation
Transistors of various type & size
You’ve all seen the transistor before, but instead of regurgitation, provide student perspective….
FET Transistor
First Transistor Model, 1947
Used in all modern electronics
BJT Transistor

4. Understanding Transistors (conceptually)
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
to understand the transistor, conceptually, we must address the three questions:

5. What is a Transistor? 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….
ROADMAP OF BUILD TRANSISTOR -> PROPERTIES
Motor Controllers
Microprocessor
PC & Cell Phones
Headphones

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 tubes
Vacuum Tube Radios
ENIAC : 17, 468 vacuum tubes

7. …and the TRANSISTOR was born!
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

8. 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
Circuits 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 wafer
more than 2.9 billion transistors is packed into an area of fingernail
Intel CEO Paul Otellini, Sep

9. 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:
Various Types of Transistors
Bipolar Junction Transistor (BJT)
Field Effect Transistors (FET)
Power Transistors

10. Understanding Transistors (conceptually)
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
to 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: [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.
High-Temp Furnace
“Pure” Wafers
“Doped” Wafers
Read doping slowly
Wafer Refinement
Ion Implanter

12. 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”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 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

15. Creation of P-N Junction via Doping
Remember: Doping introduces impurities into semiconductor material
Remember: Dopant is added to same piece of semiconductor material
Resulting 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
Negatively-charged N-type Side
Lattice structure wants electrons to fill “holes”
Lattice structure has too many electrons
What happens at the point of contact or “junction?

16. Understanding Transistors (conceptually)
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
to 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 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.

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 electrons
Forward Biasing
Reverse Biasing
Circuit is “On”
Current is Flowing
Circuit is “Off”
Current not Flowing

20. 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.

21. Presentation Outline Transistor Fundamentals1
Transistor Fundamentals
Chester Ong 2
Bipolar Junction Transistors
Ajeya Karajgikar 3
Power Transistors
Ajeya Karajgikar 4
But there are much more than these.
Field Effect Transistors
Emanuel Jones 5
Applications of Transistor
(covered by each speaker in respective topic)

22. BJT introduction BJT = Bipolar Junction Transistor 3 Terminals
Base (B)
Collector (C)
Emitter (E)

23. BJT schematic NPN PNP NPN: BE forward biased BC reverse biased PNP:
BE reverse biased
BC forward biased

24. BJT formulae
Current control
NPN
Suggestion: 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 200
It is dependent on temperature and voltage

25. BJT formulae NPN Emitter is more heavily doped than the collector.
Therefore,
VC > VB > VE
for NPN transistor
NPN
Why 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 formulae
NPN
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

27. 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= 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)

28. Common Emitter Characteristics
Collector current controlled by the collector circuit (Switch behavior)
In full saturation VCE=0.2V
Collector current IC proportional to Base current IB
No current flows

29. BJT operating regions Operating Region Parameters Mode Cut Off
VBE < Vcut-in
VCE > Vsupply
IB = IC = 0
Switch OFF
Linear
VBE = Vcut-in
Vsat < VCE < Vsupply
IC = β*IB
Amplification
Saturated
VBE = Vcut-in,
VCE < Vsat
IB > IC,max, IC,max > 0
Switch 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 kΩ
RC = 1 kΩ
β = 100
VSupply = 10 V
Vcut-in = 0.7 V
Vsat = 0.2 V
Vsupply – iC . RC – VCE = 0 I
iC = (Vsupply – VCE) / RC
Set VCE = Vsat = 0.2V
iC = (10 – 0.2) / 1000 = 9.8mA
iC = β . iB
VSupply
Vin RB RC
iB = iC / β = /100 = 0.098mA II
Vin – iB . RB – VBE = 0
Vin = iB . RB + VBE I
Set VBE = Vcut-in = 0.7V
Vin = (0.098) .(10-3).(10000 )+ 0.7V II
Vin = 1.68V or greater.

31. BJT as a switch
From
exercise 3
Turns on/off coils digitally

32. 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.

33. Presentation Outline Transistor Fundamentals1
Transistor Fundamentals
Chester Ong 2
Bipolar Junction Transistors
Ajeya Karajgikar 3
Power Transistors
Ajeya Karajgikar 4
But there are much more than these.
Field Effect Transistors
Emanuel Jones 5
Applications 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 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

36. 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 current
Gate
Base
Controls flow of current
Drain
Collector
Current goes out here
Source
Emitter
Current comes in here

37. How does a FET work? Simplified Notation No Voltage to Gate
Source
Drain
Source
Drain n n
Simplified Notation
MOSFET shown here
No current flow
“Short” allows current flow

38. Types of Field-Effect Transistors
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
MOSFET
IGBT

39. 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
Uses reversed biased p-n junction to separate 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
n-channel
JFET
p-channel
JFET

40. JFET analysis
I–V characteristics and output plot of a JFET n-channel transistor.

41. 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 [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.

42. MOSFET Similar 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
MOSFET enhanced mode
MOSFET depleted mode

43. FETs vary voltage to control current. This illustrates how that works
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.

44. MOSFET Triode Mode/Linear Region
VGS > Vth and VDS < ( VGS - Vth )
Saturation/Active Mode
VGS > Vth and VDS > ( VGS - Vth )
VGS : Voltage at the gate
Vth : Threshold voltage
VDS : Voltage from drain to source
μn: charge-carrier effective mobility
W: gate width
L: gate length
Cox : gate oxide capacitance per unit area
λ : channel-length modulation parameter

45. 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
Voltage controlled resistor

46. 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

47. Presentation Summary Transistor Fundamentals Chester Ong1
Transistor Fundamentals 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 Junction Electrical Properties of P-N Junction & using P-N to control / amplify current 2
Bipolar Junction Transistors Ajeya Karajgikar
Introduction & Formulae
Explain function and characteristics of common emitter transistor
Describe BJT operating regions
Applications of BJTs 3
Power Transistors Ajeya Karajgikar
Definition and Applications 4
Field Effect Transistor Emanuel Jones
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 5
Applications 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.