Transistors & Semiconductors

Transistor Amplifying Switch – Current to base enables current from emitter to collector – Base requires small amount of current relative to emitter

Silicon SI = Element 14 – 4 electrons in outer shell – 8 would be full

Silicon Silicon crystal – Stable diamond like structure – Thermal noise occasionally bumps electrons, but settle back rapidly

Doping Doped silicon has impurities – N type : Extra electrons Phosphorus – P type : Short an electron Boron

Doped Conductors Doped silicon: – Free roaming electrons or holes – Phosphorus/Boron ions

N + P Sandwich N&P sandwich forms neutral area : Depletion layer – Insulation against flow

N + P Sandwich N&P sandwich forms : Depletion layer – Electrons/holes merge – Ions present barrier to more movement

N + P Sandwich = Diode Current flow into N closes depletion layer Current flow into P increases depletion layer

Transistor = Diode Sandwich Transistor is 3 layers: – NPN or PNP Default is to insulate

Transistor = Diode Sandwich Positive current at base removes spare negatives – Shrink P  N depletion layer Relatively small current at base er_embedded&v=9CrcRabTQ0s# er_embedded&v=9CrcRabTQ0s#

MOS MOS – Metal Oxide – "Metal" conductor – Oxide insulator Charge to conductor produces conductive layer in silicon via field effect

MOSFET Metal Oxide Field Effect Transistor – NPN regions of silicon – Conductor used to create channel Channel requires no current!!!

CMOS CMOS : Complementary MOSFETS – NPN and PNP used together Always high or low signal ?v=QO5FgM7MLGg&list=FL8JW MIsIgFMX3tv2BU-K4Uw (Jump to 3:00) ?v=QO5FgM7MLGg&list=FL8JW MIsIgFMX3tv2BU-K4Uw

Fabrication Circuits "printed" with photo reactive chemicals light u74&list=FL8JWMIsIgFMX3tv2BU-K4Uw u74&list=FL8JWMIsIgFMX3tv2BU-K4Uw – Minute 2