the last revolution happened ~ 60 years ago, when vacuum tubes were replaced by semiconductor...

The last revolution happened ~ 60 years ago, when vacuum tubes were replaced by semiconductor devices

1918

1960s

Vacuum tubes show high performance but are too big

Vacuum tubes can survive a nearby nuclear explosion

What is a vacuum tube?

What vacuum tubes are for

_

+

gate

Diode: a valve for electrons

Triode: a switch or an amplifier

First digital computers

ENIAC (1946) weighed 30 tons, occupied 1800 square feet and had 17,468 vacuum tubes.It could make 5000 additions per second

First computer bug was a real bug Harvard Mark II computer, 1947

1954-1963: SAGE Air Defense Project

• 2 32-bit computers • Each contains 55,000 vacuum tubes, weighs 250 tons, and consumes 3 Megawatt• Tracks 300 flights• Total cost: $60 billion (double the price of Manhattan Project!)• Performance equivalent to $8 calculator built on transistors!

Dangers of forecasting

ENIAC (1946) weighed 30 tons, occupied 1800 square feet and had 17,468 vacuum tubes.It could make 5000 additions per second

Computers in the future may weigh no more than 1.5 tons. (Popular Mechanics, 1949)

1940's - IBM Chairman Thomas Watson predicts that "there is a world market for maybe five computers".

1950's - There are 10 computers in the U.S. in 1951. The first commercial magnetic hard-disk drive and the first microchip are introduced. Transistors are first used in radios.

1960's-70's - K. Olson, president, chairman and founder of DEC, maintains that "there is no reason why anyone would want a computer in their home." The first microprocessor, 'floppy' disks, and personal computers are all introduced. Integrated circuits are used in watches.

Semiconductor Revolution“One should not work on semiconductors, that is a filthy mess; who knows whether they really exist.”

Wofgang Pauli 1931

Transistor invention: 1947John Bardeen, Walter Brattain, and William Shockley AT&T Bell Labs

Nobel Prize in Physics 1956

energy

Conduction band

Valence band

Band gap

Semiconductor or dielectric

metal

The coolest thing about semiconductors: they can be doped

Even tiny fraction of impurities (0.00001) dramatically increases the ability to conduct current (conductivity)

Energy diagram of doped semiconductors

Free electrons are supplied to the empty conduction band Holes are left in the full valence band

Both electrons and holes can now conduct current!

Reverse bias

+_

P-type N-type

P-n junction

neutral neutral_ +Forward bias

+ _

Field-effect transistor

+_ +

Commons.wikimedia.org

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Voltage on gate controls the current of electrons from source to drain.

FET can be made very small using nanotechnology!

Current, Ohm’s Law, Etc.

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dQi

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VRLawsOhm

A

lR

Ej

jE

The Continuity Equation for Steady State Currents

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Currents and current densities are constant in time – steady state. The flux of out of any closed surface must be zero.

j

Drift velocity

nq

jv

For steady state situation

1.Kirchhoff’s junction rule: The algebraic sum of the currents into any junction is zero.

2.Kirchhoff’s loop rule: The algebraic sum of the potential differences in any loop must be zero.

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Resistors in parallel:

Resistors in series:

21 RRR

21

111

RRR

Circuit with capacitors

Joule’s Law

R

VRiViP

22

Why does a light bulb burn out when you switch the light on and never when you turn it off?

The amount of current drawn by a given device is determined by its power inputi

V

PiiVP

The current in a 100-W light bulb is

AV

W

V

Pi 83.0

120

100

14483.0

120

A

V

i

VR

A kitchen circuit

An 1800-W toaster, a 1.3-kW electric frying pan, and a 100-W lamp are plugged into the same 20-A, 120-V circuit.

a) What current is drawn by each device, and what is the resistance of each device?

b) Will this combination blow the fuse?

To prevent the fuse from blowing, you replace the fuse with one rated at 40 A.Is this a reasonable thing to do?

RiP 2

Wheatstone bridge

British scientist and inventor1802-1875

Charles Wheatstone

Samuel Hunter Christie, British scientist and mathematician

Wheatstone English concertina

Electromotive force

The Magnetic Field

The force on a charge q moving with a velocity F

v

)( BvEqF

The magnitude of the force

sinqvBF

sec)//(][ meterCoulombNewtonsB

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TGaussBEarth4101

left-hand ruleright-hand rule