Silicon, Circuits, and the Digital Revolution

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Silicon, Circuits, and theDigital Revolution

• George Watson
• Department of Physics and Astronomy
• University of Delaware
• ghw_at_udel.edu
• June 1, 1999
• ALLSTEL

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Silicon, Circuits, and theDigital
Revolutionhttp//www.physics.udel.edu/watson/sce
n103/

• The Way it Was
• Technology on Campus
• 25 years ago
• Slide Show

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Silicon, Circuits, and theDigital Revolution

• Everything is made of something!
• Atoms are comprised of nuclei and electrons.

Mass is nuclear.
Size is electronic.
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Electron Energy Levels in Hydrogen
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The Visible Spectrum
Photon color Wavelength Energy (nm) (eV) blu
e 430 2.9 yellow 530 2.3 red 650 1.9
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Electron Energy Levels
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Electronic Band Structure in Solids
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Metals, Insulators, and Semiconductors
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Column 4 Silicon among the elements
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Band Gaps of Column 4 Elements

• Element Band Gap
• (eV)

Carbon (diamond) 5.5 Silicon 1.1 Germanium 0.7
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The Visible Spectrum
Photon color Wavelength Energy (nm) (eV) blu
e 430 2.9 yellow 530 2.3 red 650 1.9
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Metals, Insulators, and Semiconductors
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Concept Check Band Gaps

• You are admiring the color of a gemstone by
  looking through it to see a nearby lamp.
• Your physicist friend states that the band gap of
  that particular stone is about 2.4 eV.
• Does the stone appear to be

a. red b. blue c. black
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Band Gaps of Several Elements

• Element Band Gap
• (eV)
• Carbon (diamond) 5.5
• Silicon 1.1
• Germanium 0.7

Selenium 1.8
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Silicon, Circuits, and theDigital Revolution

• Principle of photoconductivity
• applied to photocopying
• xerography
• (dry writing)
• Slide Show

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Essentials of Xerography
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Pure silicon - 4 valence electrons
From sand?
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Column 5 one more valence electron
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Silicon doped with arsenic
n-type silicon
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Column 3 one fewer valence electron
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Silicon doped with gallium
p-type silicon
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Effect of doping on band structure
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Transistors are structured fromn-type and p-type
silicon.
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Concept Check doped silicon

• You physicist friend hands you a wafer of
  germanium and tells you it is doped with
  phosphorus.
• Is the semiconductor wafer

a. n-type b. p-type
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Silicon, Circuits, and theDigital Revolution

• Building Transistors on
• Integrated Circuits
• lithography
• (stone writing)
• Slide Show

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MOSFET inverter
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CMOS inverter
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CMOS fabrication
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CMOS NAND gate
4 transistors
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Adder circuit
38 transistors!
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Moores Law for Intel Microprocessors
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Penetration rates of major consumer products in
U.S. households