Transistors’s history
Dr. John Bardeen(left), Dr. Walter
Brattain(right), and Dr. William Shockley(center) discovered the transistor
effect and developed the first device in December, 1947, while the three were
members of the technical staff at Bell Laboratories in Murray Hill, NJ. They
were awarded the Nobel Prize in physics in 1956.
The PN Junction:
What the Bell Labs scientists
discovered was that silicon was comprised of two distinct regions differentiated
by the way in which they favored current flow. The area that favored positive
current flow they named “P” and the area that favored negative current flow they
named “N.” More importantly, they determined the impurities that caused these
tendencies in the “P” and “N” regions and could reproduce them at will. With the
discovery of the P-N junction and the ability to control its properties, the
fundamental ground work was laid for the invention of the transistor. This Bell
Labs discovery was instrumental in the development of all semiconductor devices
to come.
The 1st Silicon Transistor:
It was late afternoon in 1954 at a conference for
the Institute of Radio Engineers. Many people giving talks had complained about
the current germanium transistors–they had a bad habit of not working at high
temperatures. Silicon, since it’s right above germanium on the periodic table
and has similar properties, might make a better gadget. But, they said, no one
should expect a silicon transistor for years.Then Gordon Teal of Texas
Instruments stood up to give his talk. He pulled three small objects out of his
pocket and announced: “Contrary to what my colleagues have told you about the
bleak prospects for silicon transistors, I happen to have a few of them here in
my pocket.”That moment catapulted TI from a small start-up electronics
company into a major player. They were the first company to produce silicon
transistors — and consequently the first company to produce a truly consistent
mass-produced transistor. Scientists knew about the problems with
germanium transistors. Germanium worked, but it had its mood swings. When the
germanium heated up–a natural outcome of being part of an electrical
circuit–the transistor would have too many free electrons. Since a transistor
only works because it has a specific, limited amount of electrons running
around, high heat could stop a transistor from working altogether.While
still working at Bell Labs in 1950, Teal began growing silicon crystals to see
if they might work better. But just as it had taken years to produce pure enough
germanium, it took several years to produce pure enough silicon. By the time he
succeeded, Teal was working at Texas Instruments. Luring someone as
knowledgeable about crystals as Teal away from Bell proved to be one of the most
important things TI ever did.On April 14, 1954, Gordon Teal showed TI’s
Vice President, Pat Haggerty, a working silicon transistor. Haggerty knew if
they could be the first to sell these new transistors, they’d have it made. The
company jumped into action — four weeks later when Teal told his colleagues
about the silicon transistors in his pocket, TI had already started
production.The Invention of the First
Transistor Nov 17 – Dec 23, 1947.
Getting ‘Wet’:On November 17, 1947,
Walter Brattain dumped his whole experiment into a thermos of water. The silicon
contraption he’d built was supposed to help him study how electrons acted on the
surface of a semiconductor — and why whatever they were doing made it
impossible to build an amplifier. But condensation kept forming on the silicon
and messing up the experiment. To get rid of that condensation, Brattain
probably should have put the silicon in a vacuum, but he decided that would take
too long. Instead he just dumped the whole experiment under water — it
certainly got rid of the condensation!Out of the blue, the wet device
created the largest amplification he’d seen so far. He and another scientist,
Robert Gibney, stared at the experiment, stunned. They began fiddling with
different knobs and buttons: by turning on a positive voltage they increased the
effect even more; turning it to negative could get rid of it completely. It
seemed that whatever those electrons had been doing on the surface to block
amplification had somehow been canceled out by the water–the greatest obstacle
to building an amplifier had been overcome.Putting the Idea to Use. When John Bardeen was told what had happened he thought of a new way
to make an amplifier. On November 21, Bardeen suggested pushing a metal point
into the silicon surrounded by distilled water. The water would eliminate that
exasperating electron problem just under the point as it had in the thermos. The
tough part was that the contact point couldn’t touch the water, it must only
touch the silicon. But as always, Brattain was a genius in the lab. He could
build anything. And when this amplifier was built, it worked. Of course, there
was only a tiny bit of amplification–but it worked.Big
Amplification. Once they’d gotten slight amplification with that tiny
drop of water, Bardeen and Brattain figured they were on the road to something
worthwhile. Using different materials and different setups and different
electrolytes in place of the water, the two men tried to get an even bigger
increase in current. Then on December 8, Bardeen suggested they replace the
silicon with germanium. They got a current jump, all right–an amplification of
some 330 times–but in the exact opposite direction they’d expected. Instead of
moving the electrons along, the electrolyte was getting the holes moving. But
amplification is amplification — it was a start.Brattain Makes a
Mistake =”#000000″>Unfortunately this giant jump in amplification only worked for
certain types of current — ones with very low frequencies. That wouldn’t work
for a phone line, which has to handle all the complex frequencies of a person’s
voice. So the next step was to get it to work at all kinds of
frequencies.
Bardeen and Brattain thought it might be the liquid which
was the problem. So they replaced it with germanium dioxide — which is
essentially a little bit of germanium rust. Gibney prepared a special slab of
germanium with a shimmering green oxide layer on one side. On December 12,
Brattain began to insert the point contacts.
Nothing happened:
In fact the device worked as if there was no oxide layer at
all. And as Brattain poked the gold contact in again and again, he realized
that’s because there wasn’t an oxide layer. He had washed it off by accident.
Brattain was furious with himself, but decided to fiddle with the point contact
anyway. To his surprise, he actually got some voltage amplification — and more
importantly he could get it at all frequencies! The gold contact was putting
holes into the germanium and these holes canceled out the effect of the
electrons at the surface, the same way the water had. But this was much better
than the version that used water, because now, the device was increasing the
current at all frequencies.
Bringing it All Together:
In the past month, Bardeen and Brattain had managed
to get a large amplification at some frequencies and they’d gotten a small
amplification for all frequencies — now they just had to combine the two. They
knew that the key components were a slab of germanium and two gold point
contacts just fractions of a millimeter apart. Walter Brattain put a ribbon of
gold foil around a plastic triangle, and sliced it through at one of the points.
By putting the point of the triangle gently down on the germanium, they saw a
fantastic effect — signal came in through one gold contact and increased as as
it raced out the other. The first point-contact transistor had been
made.
Telling the Brass:
For a week,
the scientists kept their success a secret. Shockley asked Bardeen and Brattain
to show off their little plastic triangle at a group meeting to the lab and the
higher-ups on December 23. After the rest of the lab had a chance to look it
over and conduct a few tests, it was official — this tiny bit of germanium,
plastic and gold was the first working solid state
amplifier.
—————
Shockley Invents the Junction
Transistor
January and February, 1948
A Solitary New Year’s
Eve
William Shockley spent New Year’s Eve alone in a hotel in Chicago. He
was there for a Physical Society meeting, but he was most excited about having
some time to himself to concentrate on his work. There may have been a party
going on downstairs, but Shockley wanted nothing to do with it. He had more
important things to think about. He spent that night and the next two days
working on some of his ideas for a new transistor-one that would improve on
Bardeen and Brattain’s ideas.
Scratching page after page into his
notebook, one of Shockley’s ideas was to build a semiconductor “sandwich.” Three
layers of semiconductors all piled together, he thought, just might work like a
vacuum tube-with the middle layer turning current on and off at will. After some
30 pages of notes, the concept hadn’t quite come together so Shockley set it
aside to do other work.
The Idea Comes
Together
Shockley’s January was pretty dismal. He thought he
should get sole credit for inventing the transistor–the initial research ideas,
after all, had been his own. The Bell Labs attorneys didn’t agree. They refused
to even put him on the patent. The only thing to do, Shockley decided, was to
build a better mouse trap.
As the rest of the group worked merrily away
on improving Brattain and Bardeen’s point-junction transistor. Shockley
concentrated on his own ideas — never letting anyone else in the lab know what
he was up to.
On January 23, unable to sleep, Shockley was sitting at the
kitchen table bright and early in the morning. He suddenly had a revelation.
Building on the “sandwich” device he’d come up with on New Year’s Eve, he
thought he had an idea for an improved transistor. This would be three-layered
sandwich. The outermost pieces would be semiconductors with too many electrons,
while the bit in the middle would have too few electrons. The middle layer would
act like a faucet–as the voltage on that part was adjusted up and down, it
could turn current in the sandwich on and off at will.
Shockley told no
one about his idea. The physics behind this amplifier was very different from
Bardeen’s and Brattain’s, since it involved current flowing directly through the
chunks of semiconductors, not along the surface. No one was sure if current even
could flow right through a semiconductor and possibly Shockley wanted to test it
before discussing it. Or possibly he felt that Bardeen and Brattain had “taken”
ideas of his for the point-contact transistor and he didn’t want to risk that
happening again.
The Eureka Moment
Then, on February 18, Shockley
learned it could work. Two members of the group, Joseph Becker and John Shive,
were working on a separate experiment. Their results could only be explained if
the electrons did in fact travel right through the bulk of a semiconductor. When
they presented their findings to the group, Shockley knew he had the proof he
needed. He jumped up and for the first time shared his concept of a sandwich
transistor to the rest of his team.
Bardeen and Brattain were stunned
that they hadn’t been filled in before now. It was clear that Shockley had been
keeping this secret for weeks. It added still more space to the ever-widening
gap that was growing between them.
—————
Telling the
Military
June 23, 1949
They had no way of knowing all that
the transistor could do, but the administrators at Bell Labs still knew they
were on to something big. They were about to hold a huge press conference to
announce what they’d invented — but before telling the public they had to check
with the military. At the very least, the transistor could revolutionize
communications and radio signals, something that would give the US Army an
advantage if the invention was kept a secret from other countries. Bell’s
president, Mervin Kelly, hoped the army wouldn’t want to classify this research,
but he knew it just might happen.
On June 23, Ralph Bown gave a
presentation to a group of military officers. He showed the way the tiny bit of
crystal and wire could amplify an electrical signal much more efficiently than a
bulky vacuum tube could. He also told them this was the same demonstration he
was preparing to give to the press the next week. What he didn’t do was ask
permission. Bown and Kelly didn’t want to make it easy for the military to
classify the transistor. If they wanted to keep it a secret, the army would have
to bring up the subject itself.
The armed services went home to their
various offices and discussed whether to classify Bell’s work. There were
certainly those who thought that, at the very least, it should be kept secret
until it was better understood just what the transistor could do. But in the
end, nobody said a word. Bell Labs went on to its big press conference without a
hitch.
—————
A Working Junction
Transistor
1948-1951
There was no doubt about it,
point-contact transistors were fidgety. The transistors being made by Bell just
didn’t work the same way twice, and on top of that, they were noisy. While one
lab at Bell was trying to improve those first type-A transistors, William
Shockley was working on a whole different design that would eventually get rid
of these problems.
Early in 1948, Shockley conceived of a transistor
that looked like a sandwich, with two layers of one type of semiconductor
surrounding a second kind. This was a completely different setup which didn’t
have the shaky wires that made the point-contact transistors so hard to
control.
Not Just on the Surface
A working
sandwich transistor would require that electricity travel straight across a
crystal instead of around the surface. But Bardeen’s theory about how the
point-contact transistor worked said that electricity could only travel around
the outside of a semiconductor crystal. In February of 1948, some tentative
results in the Shockley lab suggested this might not be true. So the first thing
Shockley had to do was determine just what was going on.
Careful
experiments led by a physicist in the group, Richard Haynes, helped. Haynes put
electrodes on both sides of a thin germanium crystal and took very sensitive
measurements of the size and speed of the current. Electricity definitely flowed
straight through the crystal. That meant Shockley’s vision of a new kind of
transistor was theoretically possible.
Growing
Crystals
But Haynes also discovered that the layer in the middle
of the sandwich had to be very thin and very pure.
The man who paved the
way for growing the best crystals was Gordon Teal. He didn’t work in Shockley’s
group, but he kept tabs on what was going on. He’d even been asked to provide
crystals for the Solid State team upon occasion. Teal thought transistors should
be built from a single crystal-as opposed to cutting a sliver from a larger
ingot of many crystals. The boundaries between all the little crystals caused
ruts that scattered the current, and Teal had heard of a way to build a large
single crystal which wouldn’t have all those crags. The method was to take a
tiny seed crystal and dip it into the melted germanium. This was then pulled out
ever so slowly, as a crystal formed like an icicle below the seed.
Teal
knew how to do it, but no one was interested. A number of institutions at the
time, Bell included, had a bad habit of not trusting techniques that hadn’t been
devised at home. Shockley didn’t think these single crystals were necessary at
all. Jack Morton, head of the transistor-production group, said Teal should go
ahead with the research, but didn’t throw much support his way.
Luckily,
Teal did continue the research, working with engineer John Little. Three months
later, in March of 1949, Shockley had to admit he’d been wrong. Current flowing
across Teal’s semiconductors could last up to one hundred times longer than it
had in the old cut crystals.
Growing Even Better
Crystals
Nice crystals are all well and good, but a sandwich
transistor needed a sandwich crystal. The outer layers had to be a semiconductor
with either too many electrons (known as N-type) or too few (known as P-type),
while the inner layer was the opposite. Under Shockley’s prodding, Teal and
Morgan Sparks began adding impurities to the melt while they pulled the crystal
out of the melt. Adding impurities is known as “doping,” and it’s how one turns
a semiconductor into N- or P-type.
As they pulled the seed crystal out
of an N-type germanium melt, they quickly added some gallium to turn the melt
into P-type. As a layer of P-type formed on the ever-lengthening crystal, they
added antimony, which compensated for the gallium and turned the melt back into
N-type. Once the process was done, there was a single, thin crystal formed into
a perfect sandwich.
By etching away the surface of the outside layers,
Sparks and Teal left a tiny bit of P-type crystal protruding. To this they
attached a fine electrode-creating a circuit the way Shockley had envisioned. On
April 12, 1950, they tested what they had built. Without a doubt, more current
came out of the sandwich than went in. It was a working
amplifier.
The First Junction Transistor
The
first junction transistor had been born.
But It Wasn’t a Very Good One .
. . Yet
This transistor could amplify electrical signals, but not
particularly complicated ones. If the signal changed rapidly, as a voice coming
over a phone line does, the transistor couldn’t keep up and would garble the
output. The problem lay in the middle of the sandwich: it was too easy for
electric current to spread out and become unfocused as it crossed the P-type
layer. To solve the problem, the layer had to be even thinner.
In
January of 1951, Morgan Sparks figured out a way to accomplish that. By pulling
the crystal out more slowly than ever, while constantly stirring the melt, he
managed to get the middle layer of the sandwich thinner than a sheet of
paper.
This new, improved sandwich did all that the researchers hoped.
They still weren’t up to the point-contact transistor’s ability to handle
signals that fluctuated extremely rapidly, but in every other way they were
superior. They were much more efficient, used very little power to work, and
they were so much quieter that they could handle weaker signals than the type-A
transistors ever could.
In July of 1951, Bell held another press
conference — this time announcing the invention of a working and efficient
junction transistor.
—————
Sharing the Technology:
Bell Hosts Transistor Symposia
1951-1952
Bell Labs had an
important realization: development of the transistor was going to move a lot
more quickly if they opened up the field to other companies. So in September
1951, Bell Labs hosted a symposium to spread the gospel about what the
transistor could do.
Attending the conference were some 300 scientists
and engineers. The attendees all went home to their respective companies with a
great sense of what the transistor could do — but little idea of how to build
one. For that knowledge, Bell announced, a company would have to pay a licensing
fee of $25,000. Twenty-six companies, from both the US and abroad, signed up for
the privilege. The companies were both big, such as IBM and General Electric,
and small, such as then-unknowns like Texas Instruments.
Over one
hundred registrants from the select companies returned for the Transistor
Technology Symposium in April of 1952. For eight days Bell Labs worked the
attendees day and night — but at the end, they were equipped to go off and
build transistors for themselves.
Bell took all the information from the
meeting and bound it into a two volume book set called “Transistor Technology.”
The book became fondly known as “Mother Bell’s Cookbook.”
—————-
William Shockley Moves to
California
1956
William Shockley had gone as far as he was
going to go at Bell Labs. He had watched the people underneath him get promoted
above him — and with good reason. Too many top quality scientists hadn’t been
able to work with him . A genius he may have been, but a good manager he was
not.
Shockley decided he needed a big change. The first thing to go was
the car — he traded in the fancy MG for a Jaguar convertible. Next: the job. He
spent a semester at Caltech and then a year working for the Weapons Systems
Evaluation Group in Washington DC., but nothing completely satisfied him. Eager
to be able to run things his own way, he finally decided to strike out on his
own — get some funding and start his own company.
In August of 1955,
Shockley flew to LA to spend a week with his new friend Arnold Beckman, a
California chemist and businessman. Shockley shared his dream of starting a
company to build cutting edge semiconductor devices. Beckman was sold on the
idea and agreed to underwrite the venture.
Shockley was lured to the Palo
Alto area by Stanford’s provost, Fred Terman who thought that a solid research
institution in the area would benefit Stanford. With a location picked out,
Shockley just had to find the people. He wanted to staff his company with only
the best and the brightest. He first sought to employ his colleagues from Bell
Labs, but they wouldn’t make the jump to the west coast — or perhaps they
couldn’t make the jump to working with Shockley again. So Shockley began
traveling all over the country recruiting young scientists.
At a lavish
luncheon in February of 1956, Shockley and Beckman announced the formation of
their brand new lab. They only had four employees at the time, but Shockley
Semiconductor Laboratory had officially opened for business. Shockley’s was the
first company of its kind to settle in the Palo Alto area, but over the years
more and more semiconductor labs — and the computer industries they initiated
– flocked to the area. It wasn’t long before the region had earned a new name:
Silicon Valley.
—————
The Future of
Transistors
The first announcement of the invention of the
transistor met with almost no fanfare. The integrated circuit was originally
thought to be useful only in military applications. The microprocessor’s
investors pulled out before it was built, thinking it was a waste of money. The
transistor and its offspring have consistently been under valued — yet turned
out to do more than anyone predicted.
Today’s predictions also say that there
is a limit to just how much the transistor can do. This time around, the
predictions are that transistors can’t get substantially smaller than they
currently are. Then again, in 1961, scientists predicted that no transistor on a
chip could ever be smaller than 10 millionth of a meter — and on a modern Intel
Pentium chip they are 100 times smaller than that.
With hindsight, such
predictions seem ridiculous, and it’s easy to think that current predictions
will sound just as silly thirty years from now. But modern predictions of the
size limit are based on some very fundamental physics — the size of the atom
and the electron. Since transistors run on electric current, they must always,
no matter what, be at least big enough to allow electrons through.
On the
other hand, all that’s really needed is a single electron at a time. A
transistor small enough to operate with only one electron would be phenomenally
small, yet it is theoretically possible. The transistors of the future could
make modern chips seem as big and bulky as vacuum tubes seem to us today. The
problem is that once devices become that tiny, everything moves according to the
laws of quantum mechanics — and quantum mechanics allows electrons to do some
weird things. In a transistor that small, the electron would act more like a
wave than a single particle. As a wave it would smear out in space, and could
even tunnel its way through the transistor without truly acting on
it.
Researchers are nevertheless currently working on innovative ways to
build such tiny devices — abandoning silicon, abandoning all of today’s
manufacturing methods. Such transistors are known, not surprisingly, as single
electron transistors, and they’d be considered “on” or “off” depending on
whether they were holding an electron. (Transistors at this level would be
solely used as switches for binary coding, not as amplifiers.) In fact, such a
tiny device might make use of the quantum weirdness of the ultra-small. The
electron could be coded to have three positions — instead of simply “on” or
“off” it could also have “somewhere between on and off. This would open up doors
for entirely new kinds of computers. At the moment, however, there are no
effective single electron transistors.
Even without new technologies,
there’s room for miniaturization. By improving on current building techniques,
it’s likely that current transistors will be at least twice as small by 2010.
With nearly a billion transistors on Intel’s latest processor that would mean
four times as many transistors on a chip are theoretically possible. Chips like
this would allow computers to be much “smarter” than they currently are.
