Download Integrated Circuits

Integrated Circuits
Our world is full of integrated circuits. You find several of them in computers. For example,
most people have probably heard about the microprocessor. The microprocessor is an
integrated circuit that processes all information in the computer. It keeps track of what keys
are pressed and if the mouse has been moved. It counts numbers and runs programs, games
and the operating system. Integrated circuits are also found in almost every modern electrical
device such as cars, television sets, CD players, cellular phones, etc. But what is an integrated
circuit and what is the history behind it?
Electric Circuits
The integrated circuit is nothing more than a very advanced electric circuit. An electric circuit
is made from different electrical components such as transistors, resistors, capacitors and
diodes, that are connected to each other in different ways. These components have different
behaviors.
The transistor acts like a switch. It can turn electricity on or off, or it can amplify current. It is
used for example in computers to store information, or in stereo amplifiers to make the sound
signal stronger.
The resistor limits the flow of electricity and gives us the possibility to control the amount of
current that is allowed to pass. Resistors are used, among other things, to control the volume
in television sets or radios.
The capacitor collects electricity and releases it all in one quick burst; like for instance in
cameras where a tiny battery can provide enough energy to fire the flashbulb.
The diode stops electricity under some conditions and allows it to pass only when these
conditions change. This is used in, for example, photocells where a light beam that is broken
triggers the diode to stop electricity from flowing through it.
These components are like the building blocks in an electrical construction kit. Depending on
how the components are put together when building the circuit, everything from a burglar
alarm to a computer microprocessor can be constructed.
components are put together when building the circuit, everything from a burglar alarm to a
computer microprocessor can be constructed.
The Transistor vs. the Vacuum Tube
Of the components mentioned above, the transistor is the most important one for the
development of modern computers. Before the transistor, engineers had to use vacuum tubes.
Just as the transistor, the vacuum tube can switch electricity on or off, or amplify a current. So
why was the vacuum tube replaced by the transistor? There are several reasons.
The vacuum tube looks and behaves very much like a light bulb; it generates a lot of heat and
has a tendency to burn out. Also, compared to the transistor it is slow, big and bulky.
When engineers tried to build complex circuits using the vacuum tube, they quickly became
aware of its limitations. The first digital computer ENIAC, for example, was a huge monster
that weighed over thirty tons, and consumed 200 kilowatts of electrical power. It had around
18,000 vacuum tubes that constantly burned out, making it very unreliable.
When the transistor was invented in 1947 it was considered a revolution. Small, fast, reliable
and effective, it quickly replaced the vacuum tube. Freed from the limitations of the vacuum
tube, engineers finally could begin to realize the electrical constructions of their dreams, or
could they?
The vacuum tube and
the transistor.
Photo: Nobelprize.org
ENIAC-The first
digital computer
Photo: U.S Army
.
Then
Advanced circuits contained so many components and connections that they were virtually
impossible to build. In the summer of 1958 Jack Kilby at Texas Instruments found a solution
to this problem. In September 1958, he had his first integrated circuit ready. It was tested and
it worked perfectly!
Chip Production Today - in Short
Chip production today is based on photolithography. In photolithography a high energy UVlight is shone through a mask onto a slice of silicon covered with a photosensitive film. The
mask describes the parts of the chip and the UV-light will only hit the areas not covered by
the mask. When the film is developed, the areas hit by light are removed. Now the chip has
unprotected and protected areas forming a pattern that is the first step to the final components
of the chip.
Next, the unprotected areas are processed so their electrical properties change. A new layer of
material is added, and the entire process is then repeated to build the circuit, layer by layer.
When all the components have been made and the circuit is complete a layer of metal is
added. Just as before, a layer of photosensitive film is applied and exposed through a mask.
However, this time the mask used describes the layout of the wires connecting all the parts of
the chip. The film is developed and the unexposed parts are removed. Next, the metal not
protected with film is removed to form the wires. Finally, the chip is tested and packaged.
When making chips today, a process called "stepping" is often used. On a big wafer of silicon
the chips are made one next to the other. The silicon wafer is moved in steps under the mask
and the UV-light to expose the wafer. In this way, chip after chip can be made using the same
mask each time.
The integrated circuit has come a long way since Jack Kilby's first prototype. His idea
founded a new industry and is the key element behind our computerized society. Today the
most advanced circuits contain several hundred millions of components on an area no larger
than a fingernail. The transistors on these chips are around 90 nm, that is 0.00009
millimeters*, which means that you could fit hundreds of these transistors inside a red blood
cell.
Each year computer chips become more powerful yet cheaper than the year before. Gordon
Moore, one of the early integrated circuit pioneers and founders of Intel once said, "If the auto
industry advanced as rapidly as the semiconductor industry, a Rolls Royce would get a half a
million miles per gallon, and it would be cheaper to throw it away than to park it."**