Silicon Toady
Essay by 24 • October 29, 2010 • 1,293 Words (6 Pages) • 1,278 Views
circuit (IC) fabrication. It is the second most abundant
substance on the earth. It is extracted from rocks and
common beach sand and put through an exhaustive
purification process. In this form, silicon is the purist
industrial substance that man produces, with impurities
comprising less than one part in a billion. That is the
equivalent of one tennis ball in a string of golf balls
stretching from the earth to the moon.
Semiconductors are usually materials which have energy-band
gaps smaller than 2eV. An important property of
semiconductors is the ability to change their resistivity
over several orders of magnitude by doping. Semiconductors
have electrical resistivities between 10-5 and 107 ohms.
Semiconductors can be crystalline or amorphous. Elemental
semiconductors are simple-element semiconductor materials
such as silicon or germanium.
Silicon is the most common semiconductor material used
today. It is used for diodes, transistors, integrated
circuits, memories, infrared detection and lenses,
light-emitting diodes (LED), photosensors, strain gages,
solar cells, charge transfer devices, radiation detectors
and a variety of other devices. Silicon belongs to the
group IV in the periodic table. It is a grey brittle
material with a diamond cubic structure. Silicon is
conventionally doped with Phosphorus, Arsenic and Antimony
and Boron, Aluminum, and Gallium acceptors. The energy gap
of silicon is 1.1 eV. This value permits the operation of
silicon semiconductors devices at higher temperatures than
germanium.
Now I will give you some brief history of the evolution of
electronics which will help you understand more about
semiconductors and the silicon chip. In the early 1900's
before integrated circuits and silicon chips were invented,
computers and radios were made with vacuum tubes. The
vacuum tube was invented in 1906 by Dr.Lee DeForest.
Throughout the first half of the 20th century, vacuum tubes
were used to conduct, modulate and amplify electrical
signals. They made possible a variety of new products
including the radio and the computer. However vacuum tubes
had some inherent problems. They were bulky, delicate and
expensive, consumed a great deal of power, took time to
warm up, got very hot, and eventually burned out. The first
digital computer contained 18,000 vacuum tubes, weighed 50
tins, and required 140 kilowatts of power.
By the 1930's, researchers at the Bell Telephone
Laboratories were looking for a replacement for the vacuum
tube. They began studying the electrical properties of
semiconductors which are non-metallic substances, such as
silicon, that are neither conductors of electricity, like
metal, nor insulators like wood, but whose electrical
properties lie between these extremes. By 1947 the
transistor was invented. The Bell Labs research team sought
a way of directly altering the electrical properties of
semiconductor material. They learned they could change and
control these properties by "doping" the semiconductor, or
infusing it with selected elements, heated to a gaseous
phase. When the semiconductor was also heated, atoms from
the gases would seep into it and modify its pure, crystal
structure by displacing some atoms. Because these dopant
atoms had different amount of electrons than the
semiconductor atoms, they formed conductive paths. If the
dopant atoms had more electrons than the semiconductor
atoms, the doped regions were called n-type to signify and
excess of negative charge. Less electrons, or an excess of
positive charge, created p-type regions. By allowing this
dopant to take place in carefully delineated areas on the
surface of the semiconductor, p-type regions could be
created within n-type regions, and vice-versa. The
transistor was much smaller than the vacuum tube, did not
get very hot, and did not require a headed filament that
would eventually burn out.
Finally in 1958, integrated circuits were invented. By the
mid 1950's, the first commercial transistors were being
shipped. However research continued. The scientist began to
think that if one transistor
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