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 Invention of the First Transistor
November 17 - December 23, 1947
The First 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.
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
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.
Ricardo A Monroy B
C.I 17646658
EES
No hay comentarios:
Publicar un comentario