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Transistors & Semiconductors
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Transistor
• Amplifying Switch– Current to base enables current from emitter to
collector– Base requires small amount of
current relative to emitter
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Silicon
• SI = Element 14– 4 electrons in outer shell – 8 would be full
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Silicon
• Silicon crystal– Stable diamond like structure– Thermal noise occasionally
bumps electrons, but settleback rapidly
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Doping
• Doped silicon has impurities– N type :• Extra electrons• Phosphorus
– P type :• Short an electron• Boron
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Doped Conductors
• Doped silicon:– Free roaming electrons
or holes– Phosphorus/Boron ions
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N + P Sandwich
• N&P sandwich forms : Depletion layer– Electrons/holes merge– Ions present barrier to more movement
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N + P Sandwich = Diode
• Current flow into N closes depletion layer• Current flow into P increases depletion layer
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Transistor = Diode Sandwich
• Transistor is 3 layers:– NPN or PNP
• Default is to insulate
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Transistor = Diode Sandwich
• Positive current at base removes spare negatives– Shrink PN depletion layer
• Relatively small current at base
• http://www.youtube.com/watch?feature=player_embedded&v=9CrcRabTQ0s#
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MOS
• MOS – Metal Oxide– "Metal" conductor– Oxide insulator
• Charge to conductor produces conductive layer in silicon via field effect
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MOSFET
• Metal Oxide Field Effect Transistor– NPN regions of silicon– Conductor used to create channel• Channel requires no current!!!
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CMOS
• CMOS : Complementary MOSFETS– NPN and PNP used together• Always high or low signal
• http://www.youtube.com/watch?v=QO5FgM7MLGg&list=FL8JWMIsIgFMX3tv2BU-K4Uw
(Jump to 3:00)
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Fabrication
• Circuits "printed" with photo reactive chemicals light
http://www.youtube.com/watch?v=35jWSQXku74&list=FL8JWMIsIgFMX3tv2BU-K4Uw– Minute 2