Silicon, Circuits, and theDigital Revolution

George WatsonDepartment of Physics and Astronomy

University of Delaware

ghw@udel.edu

June 1, 1999

ALLSTEL

Silicon, Circuits, and theDigital Revolution

http://www.physics.udel.edu/~watson/scen103/

The Way it Was:

Technology on Campus

25 years ago

Slide Show

Silicon, Circuits, and theDigital Revolution

Everything is made of something!

Atoms are comprised of nuclei and electrons.

Mass is nuclear.

Size is electronic.

Electron Energy Levels in Hydrogen

The Visible Spectrum

Photon “color” Wavelength Energy

(nm) (eV)

blue 430 2.9

yellow 530 2.3

red 650 1.9

Electron Energy Levels

Electronic Band Structure in Solids

Metals, Insulators, and Semiconductors

Column 4: Silicon among the elements

Band Gaps of Column 4 Elements

Element Band Gap

(eV)

Carbon (diamond) 5.5Silicon 1.1Germanium 0.7

The Visible Spectrum

Photon “color” Wavelength Energy

(nm) (eV)

blue 430 2.9

yellow 530 2.3

red 650 1.9

Metals, Insulators, and Semiconductors

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. redb. bluec. black

Band Gaps of Several Elements

Element Band Gap

(eV)

Carbon (diamond) 5.5

Silicon 1.1

Germanium 0.7

Selenium 1.8

Silicon, Circuits, and theDigital Revolution

Principle of photoconductivity

applied to photocopying:

xerography

(dry writing)

Slide Show

Essentials of Xerography

Pure silicon - 4 valence electrons

From sand?

Column 5: one more valence electron

Silicon doped with arsenic

n-type silicon

Column 3: one fewer valence electron

Silicon doped with gallium

p-type silicon

Effect of doping on band structure

Transistors are structured fromn-type and p-type silicon.

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-typeb. p-type

Silicon, Circuits, and theDigital Revolution

Building Transistors on

Integrated Circuits:

lithography

(stone writing)

Slide Show

MOSFET inverter

CMOS inverter

CMOS fabrication

CMOS NAND gate

4 transistors

Adder circuit

38 transistors!

Moore’s Law for Intel Microprocessors

Penetration rates of major consumer products in U.S. households