Transcript Information technology - People @ TAMU Physics

From Physics to
Optoelectronics Technology
Alexey Belyanin
TAMU-Physics
Physics in the Information Age
Transistor
Laser
Computer
World Wide Web
… Are all invented by physicists
History of the WWW
History of the WWW
• First proposal: Tim Berners-Lee (CERN)
in 1989
• 1991: First WWW system released by CERN
to physics community; first Web server in the US (SLAC)
• 1993: University of Illinois releases user-friendly
Mozaic server
• Currently: WWW is one of the most popular Internet
applications; 60 million users in the US alone
Invention of Computer
• The first digital electronic computer was invented by
Theoretical Physics Prof. John Vincent Atanasoff
in 1937. It was built by Atanasoff and his graduate
student Clifford Berry at Iowa State College
in 1939 ($650 research grant).
Basement of the Physics Dept. building
where the Atanasoff-Berry Computer
(ABC) was built.
ABC
•Used base-two numbers (the binary system) - all
other experimental systems at the time used base-ten
•Used electricity and electronics as it's principal media
•Used condensers for memory and used a regenerative
process to avoid lapses that could occur from
leakage of power
•Computed by direct logical action rather than by the
enumeration methods used in analog calculators
Implemented principles of modern computers
Only material base has been changed.
From ABC to ENIAC
• 1940s: J. Mauchly and J. Eckert build ENIAC
(Electronic Numerical Integrator And Computer). All
basic concepts and principles of ENIAC are
“borrowed” from Atanasoff’s papers.
• 1972: U.S. Court voids the Honeywell’s patent on the
computing principles and ENIAC, saying that it had
been “derived” from Atanasoff’s invention.
• 1990: Atanasoff receives the U.S. National Medal of
Technology. He dies in 1995 at the age of 91.
ABC Replica
Berry with the ABC
Card punch and reader
The drum – the only surviving fragment of ABC. It
holds 30 numbers of 50 bits each. They are
operated on in parallel. It is the first use of the idea
we now call "DRAM" -- use of capacitors to store
0s and 1s, refreshing their state periodically.
From ENIAC to …
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.
ENIAC (1946) weighed 30 tons,
occupied 1800 square feet and
had 19,000 vacuum tubes.
It could make 5000 additions per
second
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.
Intel Pentium 4 Processor Extreme Edition
(Nov. 3, 2003)
Clock speed: 3.20 GHz
Mfg. Process: 0.13-micron
Number of transistors: 178 million
2 MB L3 cache; 512 KB L2 cache
Bus speed: 800 MHz
The electronics and semiconductor industries
account for around 6.5% of the gross domestic
product, representing over $400 billion and 2.6
million jobs.
The telecommunications industry earns $1.5
trillion each year and employs 360,000
Americans.
Smaller, Denser, Cheaper
Moore’s Law (1965): every 2 years
the number of transistors on a chip is
doubled
Pushing Fundamental Limits:
Challenges and Bottlenecks
 Semiconductors: how small the transistor can be?
 Memory and data storage: limits on writing density?
 Communications: limits on data rate?
• Limit on the transistor size
• Limit on the manufacturing
technology
Before transistors: vacuum tubes
1954-1963: SAGE Air Defense Project
• 23 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!
Diode: one-way valve for electrons
Triode: controllable valve
Semiconductor Diodes and Transistors
“One should not work on semiconductors,
that is a filthy mess; who knows whether
they really exist.”
Wofgang Pauli 1931
Transistor invention: 1947
John Bardeen, Walter Brattain, and William Shockley
Nobel Prize in Physics 1956
Background: Semiconductors
Metals
Current flows, but no control
Conduction Band
Valence Band
• Electron energies
are grouped in bands
Semiconductors
Conduction Band
E
g
Just right!
Valence Band
Insulators
Conduction Band
E
No current at all
g
Valence Band
• Exclusion Principle:
Only one electron per
state allowed
Doping
N-type
hole
P-type
P-N junction and diode effect
Forward bias:
Current flows
Reverse bias:
No current
Bipolar junction transistors
FET: Field-Effect Transistor
Metal-Oxide-Semiconductor Field-Effect Transistor
(MOSFET)
MOSFET: the workhorse of Integrated Circuits
Jack Kilby:
Nobel Prize in Physics 2000
How thin can be the gate oxide?
Fabrication Limits
Photolithography
Rayleigh Resolution Limit
Best spatial resolution is of the order of
one wavelength of light
Telecommunications
Voltage variations repeat sound wave variations
Analog system: high-quality sound, but limited speed and apps
Binary code is transmitted
Digital system: any signal, high speed, but sound quality is lower
Remember Atanasoff!
Analog-to-digital conversion
Time
Time
Analog radio broadcasting:
Low-frequency audio signal modulates the amplitude
of high-frequency carrier wave
Sin(2f t)
1 kHz = 1/ms
Sound waves: 30 Hz-20 kHz
Amplitude Modulation (AM)
AM Station frequencies (in kHz): f = 1050, 1120,1240, 1280,…
Stations broadcast at different carrier frequencies to avoid cross-talk
Spectral window (Bandwidth) needs to be at least 30 kHz
for each station
Modulating a carrier wave with
digital data pulses
Time
How large is data rate?
It is limited by bandwidth!
Synthesizing digital data packet
4 sin(220t) + sin(219t)- cos(219t)+ (1/3) sin(217t)-(1/3) cos(217t)+…
Data rate = 1/1ms = 1kHz =
Distance between side-bands!
Time, ms
Bandwidth B = 4 kHz
Pulse duration ~ 1/B
Frequency, kHz
Max Data rate = one pulse per 0.25 ms
= 4 kHz = 4000 bit/s
Time, ms
Shannon-Nyquist Theorem
In a communication channel with bandwidth B,
the data rate (number of bits per second) can
never exceed 2B
Number of channels = Total bandwidth of the medium/B
Sharing the
bandwidth
(multiplexing)
Faster, faster, faster
Higher carrier frequencies
Wider bandwidth
Higher data rate
Using optical frequencies?! 1000 THz !!!
What kind of medium can carry
optical frequencies?
Air? Only within line of sight;
High absorption and scattering
Optical waveguides are necessary!
Copper coaxial cable? High absorption,
narrow bandwidth 300 MHz
Glass? Window glass absorbs 90% of light after 1 m.
Only 1% transmission after 2 meters.
Extra-purity silica glass?!
Loss per km
Loss in silica glasses
Maximum tolerable loss
Wavelength, nm
Transmisson 95.5% of power after 1 km
P = P(0) (0.995)N after N km
P = 0.01 P(0) after 100 km
Total bandwidth = 400 THz!!
How to confine light with
transparent material??
n > n’
Total internal reflection!
Dielectric waveguides
n > n’
Optical fiber!
1970: Corning Corp. and Bell Labs
Fibers open the flood gate
Bandwidth 400 THz would allow 400
million channels with 2Mbits/sec
download speed!
Each person in the U.S. could have his
own carrier frequency, e.g.,
185,674,991,235,657 Hz.
Limits and bottlenecks
Present-day WDM systems: bandwidth 400 GHz,
Data rate 10 GBits/sec
What’s Wrong?
Modulation speed of semiconductor lasers
is limited to several Gbits/sec
Electric-to-optical conversion is slow and expensive
All-optical switches
Micro-Electro-Mechanical Systems (MEMS)
256 micro-mirrors (Lucent 2000)
Conclusions
 Microelectronics is approaching its fundamental limit.
Revolutionary ideas are needed!
- Organic semiconductors?
- Single-molecule transistors?
 Communication: how to increase data rate?
- Novel lasers?
- All-optical network?
 New principles of computing??