Integrated circuit

An integrated circuit (IC) is a microelectronic semiconductor device
consisting of many interconnected transistors and other components.

SEM image

ICs are constructed ("fabricated") on a small rectangle, called a "die", cut
from a silicon (or for special applications, silicon on sapphire or gallium
arsenide) wafer. This is known as the "substrate". Photolithography is used
to mark different areas of the substrate to be doped or to have polysilicon
or aluminium tracks laid down in them. (See also semiconductor.) The die is
then connected into a package using gold or aluminum wires which are welded
to "pads", usually found around the edge of the die.

Integrated circuits can be classified into analog, digital and mixed signal
(both analog and digital on the same chip). Digital integrated circuits can
contain anything from one to millions of logic gates, flip-flops,
multiplexers, etc. in a few square millimeters. The small size of these
circuits allows high speed, low power dissipation, and reduced manufacturing
cost compared with board-level integration.

The growth of complexity of integrated circuits follows a trend called
"Moore's Law", first observed by Gordon Moore of Intel. Moore's Law states
that the number of transistors in an integrated circuit doubles every two
years. By the year 2000 the largest integrated circuits contained hundreds
of millions of transistors, and the trend shows no signs of slowing down.

The integrated circuit is one of the most important inventions of the last
century. Modern computing, communications, manufacturing, and transportation
systems, including the Internet, all depend on its existence.

History

The concept for the integrated circuit was first published by Geoffrey W.A.
Dummer on May 7, 1952. The first integrated circuits were developed
independently by two scientists: Jack Kilby of Texas Instruments filed a
patent for a "Solid Circuit" on February 6, 1958, and Robert Noyce of
Fairchild Semiconductor was awarded a patent for a more complex "unitary
circuit" on April 25, 1961.

   * Noyce credited Kurt Lehovec of Sprague Electric for the principle of
     dielectric isolation caused by the action of a p-n junction (the diode)
     as a key concept behind the IC.

SSI

The first integrated circuits contained only a few transistors. Called
"Small-Scale Integration" (SSI), they used circuits containing transistors
numbering in the tens.

SSI circuits were crucial to early aerospace projects, and vice-versa. Both
the Minuteman missile and Apollo program needed lightweight digital
computers for their inertially-guided flight computers; the Apollo flight
computer led and motivated the integrated-circuit technology, while the
Minuteman missile forced it into mass-production.

These programs purchased almost all of the available integrated circuits
from 1960 through 1963, and almost alone provided the demand that funded the
production improvements to get the production costs from $1000/circuit (in
1960 dollars) to merely $25/circuit (in 1963 dollars).

MSI

The next step in the development of integrated circuits, taken in the late
1960s, introduced devices which contained hundreds of transistors on each
chip, called "Medium-Scale Integration" (MSI).

They were attractive economically because while they cost little more to
produce than SSI devices, they allowed more complex systems to be produced
using smaller circuit boards, less assembly work (because of fewer separate
components), and a number of other advantages.

LSI

Further development, driven by the same economic factors, led to
"Large-Scale Integration" (LSI) in the mid 1970s, with tens of thousands of
transistors per chip.

LSI circuits began to be produced in large quantities around 1970, for
computer main memories and pocket calculators.

VLSI

The final step in the development process, starting in the 1980s and
continuing on, was "Very Large-Scale Integration" (VLSI), with hundreds of
thousands of transistors, and beyond (well past several million in the
latest stages). The largest chips are sometimes called "Ultra Large-Scale
Integration" (ULSI).

For the first time it became possible to fabricate a CPU or even an entire
microprocessor on a single integrated circuit. In 1986 the first one
megabyte RAM was introduced, which contained more than one million
transistors. Microprocessor chips produced in 1994 contained more than three
million transistors.

This step was largely made possible by the codification ( see: Carver Mead
and Lynn Conway) of "design rules" for the CMOS technology used in VLSI
chips, which made production of working devices much more of a systematic
endeavour.

Further Developments

The most extreme integration technique is wafer-scale integration (WSI),
which uses whole uncut wafers containing entire computers (processors as
well as memory). Attempts to take this step commercially in the 1980s (e.g.
by Gene Amdahl) failed, and it does not now seem to be a high priority for industry.

In the 1980s programmable integrated circuits were developed. These devices
contain circuits whose logical function and connectivity can be programmed
by the user, rather than being fixed by the integrated circuit manufacturer.
This allows a single chip to be programmed to implement different LSI-type
functions such as logic gates, adders and registers. Current devices named
FPGAs (Field Programmable Gate Arrays) can now implement tens of thousands
of LSI circuits in parallel and operate at over 100 MHz.

Notable Integrated Circuits

   * 555 common multivibrator subcircuit
   * 741 operational amplifier
   * 4000 series CMOS logic building blocks
   * 7400 series TTL logic building blocks
   * Intel 4004 the first microprocessor
   * 6502 microprocessor - one of the most popular designs