Integrated circuits
Last updated: September 16, 2009.
Have you ever heard of a 1940s computer
called the ENIAC? It was about the same length and weight as three to four double-decker buses and
contained 18,000 buzzing electronic switches known as vacuum tubes.
Despite its gargantuan size, it was thousands
of times less powerful than a
modern laptop—a machine about 100 times smaller.
If the history of computing sounds like a magic trick—squeezing more and more power
into less and less space—it is! What made it
possible was the invention of the integrated
circuit (IC) in 1958. It's a neat way of cramming hundreds, thousands, millions, or
even billions of electronic components
onto tiny chips of silicon no
bigger than a fingernail. Let's take a closer look at ICs and how
they work!
Photo: An integrated circuit from the outside. This is what an IC looks like when it's conveniently packaged inside a flash memory chip. Inside the black protective case, there's a tiny integrated circuit, with millions of transistors capable of storing millions of binary digits of information. You can see what the circuit itself looks like in the photograph below.
What is an integrated circuit?
Open up a television or a radio and you'll see it's built around a
printed circuit board (PCB): a bit like an electric street-map with
small electronic
components (such as resistors and capacitors)
in place of
the buildings and printed copper connections
linking them together
like miniature metal streets. Circuit boards are fine in small
appliances like this, but if you try to use the same technique to
build a complex electronic machine, such as a computer, you quickly
hit a snag. Even the simplest computer needs eight electronic
switches to store a single byte (character) of information. So if you
want to build a computer with just enough memory to store this
paragraph, you're looking at about 750 characters times 8 or about
6000 switches—for a single paragraph! If
you plump for
switches like they had in the ENIAC—vacuum tubes about the size of
an adult thumb—you soon end up with a whopping great big,
power-hungry machine that needs its own mini electricity
plant to
keep it running.
Photo: An integrated circuit from the inside. If you could lift the cover off a typical microchip like the one in the top photo (and you can't very easily—believe me, I've tried!), this is what you'd find inside. The integrated circuit is the tiny square in the center. Connections run out from it to the terminals (metal pins or legs) around the edge. When you hook up something to one of these terminals, you're actually connecting into the circuit itself. You can just about see the pattern of electronic components on the surface of the chip itself. Photo by courtesy of NASA Glenn Research Center (NASA-GRC).
When three American physicists invented transistors in 1947, things
improved somewhat. Transistors were a fraction the size of vacuum tubes and relays
(the electromagnetic switches that had started to replace vacuum tubes in
the mid-1940s), used much less power, and were far more reliable. But
there was still the problem of linking all those transistors
together in complex circuits. Even after transistors were invented,
computers were still a tangled mass of wires.
Photo: A typical modern transistor mounted on a printed circuit board. Imagine having to wire hundreds of millions of these things onto a PCB!
Integrated circuits changed all that. The basic idea was to take a
complete circuit, with all its many components and the connections between
them, and recreate the whole thing in microscopically tiny form on the surface of a
piece of silicon. It was an amazingly clever idea and it's made
possible all kinds of "microelectronic" gadgets we now take for
granted, from digital watches and
pocket calculators to Moon-landing
rockets and missiles with built-in satellite navigation.
How are integrated circuits made?
Doping semiconductors
If you've read our articles on diodes and
transistors, you'll be
familiar with the idea of semiconductors.
Traditionally,
people thought of materials fitting into two neat categories: those
that allow electricity to flow through
them quite readily
(conductors) and those that don't (insulators). In fact, things are
far more complex than that—especially when it comes to certain
elements in group 14 and 15 of the periodic table, notably silicon and
germanium. Normally insulators, these elements can be
made to behave more like conductors if we add small quantities of
impurities to them in a process known as doping.
If you add antimony to silicon, you give it slightly more electrons than it
would normally have—and the power to conduct electricity. Silicon
"doped" that way is called n-type. Add boron instead of antimony
and you remove some of silicon's electrons, leaving behind "holes"
that work as "negative electrons," carrying a positive electric
current in the opposite way. That kind of silicon is called p-type.
Putting areas of n-type and p-type silicon side by side creates
junctions where electrons behave in very interesting ways—and that's
how we create electronic, semiconductor-based components like diodes,
transistors, and memories.
Photo: A traditional printed circuit board (PCB) like this has tracks linking together the terminals (metal connecting legs) from different electronic components. Think of the tracks as "streets" making paths between "buildings" where useful things are done (the components themselves). There's a miniaturized version of a circuit board inside an integrated circuit: the tracks are created in microscopic form on the surface of a silicon wafer.
Inside a chip plant
The process of making an integrated circuit starts off with a big
single crystal of silicon, shaped like a long solid pipe, which is "salami sliced" into thin discs
(about the dimensions of a compact disc) called wafers.
The wafers are marked out into many identical square or rectangular areas, each
of which will make up a single silicon chip (sometimes called a
microchip). Thousands, millions, or billions of components are then
created on each chip by doping different areas of the surface to turn them into
n-type or p-type silicon. Doping is done by a variety of different
processes. In one of them, known as sputtering,
ions of the doping material are fired at the silicon wafer like bullets from a
gun. Another process called vapor deposition
involves introducing the doping material as a gas and letting it condense so
the impurity atoms create a thin film on the surface of the silicon
wafer. Molecular beam epitaxy
is a much more precise form of deposition.
Photo: A silicon wafer. Photo by courtesy of NASA Glenn Research Center (NASA-GRC).
Of course, making integrated circuits that pack hundreds, millions,
or billions of components onto a fingernail-sized chip of silicon is all
a bit more complex and involved than it sounds. Imagine the havoc
even a speck of dirt could cause when you're working at the
microscopic (or sometimes even the nanoscopic)
scale. That's why semiconductors are made in spotless laboratory environments called
clean rooms, where the air is meticulously
filtered and
workers have to pass in and out through airlocks wearing all kinds of
protective clothing.
Who invented the integrated circuit?
You've probably read in books that ICs were developed jointly by
Jack Kilby (1923–2005) and
Robert Noyce (1927–1990), as though these two men
happily collaborated on their brilliant invention! In fact, Kilby and Noyce
came up with the idea independently, at more or less exactly the same
time, prompting a furious battle for the rights to the invention that
was anything but happy.
Photo: Computer microchips like these—and all the appliances and gadgets
that use them—owe their existence to Jack Kilby and Robert Noyce.
Photo by Warren Gretz courtesy of
US Department of Energy/National Renewable Energy Laboratory (US DOE/NREL).
How could two people invent the same thing at exactly the same time? Easy:
integrated circuits were an idea waiting to happen. By the mid-1950s,
the world (and the military, in particular) had discovered the
amazing potential of electronic computers and it was blindingly
apparent to visionaries like Kilby and Noyce that there needed to be
a better way of building and connecting transistors in large
quantities. Kilby was working at Texas Instruments when he came upon
the idea he called the monolithic principle:
trying to build all the different parts of an electronic circuit on a silicon chip.
On September 12, 1958, he hand-built the world's first, crude integrated circuit
using a chip of germanium (a semiconducting element similar to
silicon) and Texas Instruments promptly applied for a patent on the
idea.
Meanwhile, at another company called Fairchild Semiconductor (formed by
transistor pioneer William Shockley and a small group of associates),
the equally brilliant Robert Noyce was experimenting with miniature
circuits of his own. In 1959, he used a series of photographic
and chemical techniques known as the planar process
(which had just been developed by a colleague, Jean Hoerni)
to produce the first, practical, integrated circuit, a method that Fairchild then tried to
patent.
There was considerable overlap between the two men's work and Texas
Instruments and Fairchild battled in the courts for much of the 1960s over who
had really developed the integrated circuit. Finally, in 1969, the
companies agreed to share the idea.
Kilby and Noyce are now rightly regarded as joint-inventors of
arguably the most important and far-reaching technology developed in the 20th
century. Both men were inducted into the National Inventors Hall of
Fame (Kilby in 1982, Noyce the following year) and Kilby's
breakthrough was also recognized with the award of a half-share in the
Nobel Prize in
Physics in 2000 (as Kilby very generously noted in his acceptance speech,
Noyce would surely have shared in the prize too had he not died of a heart attack a decade earlier).
While Kilby is remembered as a brilliant scientist, Noyce's legacy has an
added dimension. In 1968, he co-founded the Intel Electronics company
with Gordon Moore (1929–), which went on to develop the microprocessor
(single-chip computer) in 1974. With IBM, Microsoft, Apple, and other
pioneering companies, Intel is credited with helping to bring
affordable personal computers to our homes and workplaces. Thanks to Noyce and
Kilby, and brilliant engineers who subsequently built on their work, there are now something like two billion computers in use
throughout the world, many of them built into cellphones,
portable satellite navigation devices, and other electronic gadgets.
Further reading
- Interested in computer history? Find out much more in our detailed article on the
history of computers.
- Want to learn more about the pioneers? Look at the excellent archive on
Jack Kilby on the Texas Instruments website
or explore the Intel Museum
to find out about Robert Noyce, Gordon Moore, and their colleagues. Both sites have a superb collection of
photos of early integrated circuits.
