exam for Electronic Engineering
Jocelyn yang 
EE1301Session18-SemiconductorTechnology-Class.pdf
3/4/2018
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EE 1301: MODERN ELECTRONIC TECHNOLOGY
SESSION #18: SEMICONDUCTOR TECHNOLOGY
3/02/2018
Instructor: Joseph Cleveland, Ph.D. Email: [email protected]
Thought for the Day
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Semiconductor Chip Technology
Turning sand (SiO2) into technology that works for us!
Semiconductor Devices Pervasive
• We live in a world filled with diodes, transistors, integrated circuits and digital processors – Digital computers
– Cell phones
– HD TVs
– Digital Cameras
– Cars (50-100 digital microprocessors)
• All made from semiconductor materials
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Types of Materials
• Semiconductors – Some free electrons – Moderate resistance – Examples: silicon, germanium, diamond (carbon)
• Insulators – Very few free electrons to move around – Very high resistance – Examples: glass, plastic, rubber
• Conductors – Many, many free electrons – Very, very low resistance – Examples: all metals
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HOW DO WE TAKE A COMPONENT OF SAND AND MAKE USEFUL THINGS?
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Semiconductor Atomic Structure
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Each Silicon atom shares four electrons with its neighbor
Electrons tightly bound Seems like an insulator Few free electrons
Adding Impurities
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P has 5 electrons to share
Put in an impurity (like phosphorous):
Silicon has 4 electrons to share
“negative” or n-type silicon
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Adding Impurities
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“positive” or p-type silicon
Boron has 3 electrons to share
Missing electron: a “hole:
P-Type / N-Type Junction
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Depletion Region
P-Type N-Type
- electrons pushed from n-type
+ holes pushed from p-type
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Forward Biased PN Junction Diode
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electrons in n-region pulled toward anode (+)
holes in p-region pulled toward cathode (-)
IP N
Depletion region disappears
Reverse Biased PN Junction Diode
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holes in p-region pulled left
electrons in n- region pulled right
P NI0
Depletion region widens
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pn Silicon Combinbation …
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Reverse Biased Diode Forward Biased Diode
We have a much smaller, lower-cost, lower power device to replace a vacuum tube diode!!
Application: Reading a Bar Code
• Photodiode detects the light reflected from the white spaces
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Photons of light
p-type n-type Photons create hole-electron pairs
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Switches for Light Sensing
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1.25V
1.25V
1.25V
1.25V
R V
OPEN
CLOSE
~0 V
> 0.5 V
“0”
“1”
No Light
Light
Light
Dark
White
Light On Diode conducts (I) V = IR
Light Off Very Low Current V = IR 0
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Bipolar Junction Transistor
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Transistors
1947: At ATT Bell Laboratories in Murray Hill, New Jersey, William Shockley, John Bardeen and Walter Brattain invented the transistor
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Collector
Base
Emitter Forward Biased
Reverse Biased
They were awarded the Nobel Prize in Physics in 1956 for the transistor.
Transistors …
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Collector
Base
Emitter
The space between pn junctions is very thin so electrons pulled into the base spill into collector region
An npn transistor
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NPN Transistors …
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Electron flow
Current in the base controls the electron flow through the collector
FWD
REV
~0.7 V
collector
emitter
NPN Transistors …
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Actual fabrication in silicon
Collector bonded to a substrate to dissipate heat
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PNP Transistors
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e-
e- Ic
IeIb
• Reverse the two p-n sections – Note the battery
polarities
• Base-emitter
FWD bias
• Base-collector
REV bias
~0.7 V
End of Session
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