Other articles in the series:
- History of the relay
- History of electronic computers
- History of the transistor
- Internet history
The crucible of war set the stage for the advent of the transistor. From 1939 to 1945, the technical knowledge of semiconductors expanded enormously. And there was one simple reason for that: radar. The most important technology of warfare, examples of which include: air raid detection, submarine search, night air raids on targets, air defense and naval guns. Engineers have even learned how to stuff tiny radars into artillery shells so that they explode when they pass close to the target - . However, the source of this powerful new military technology was a more peaceful area: the study of the upper atmosphere for scientific purposes.
Radar
In 1901, the Marconi Wireless Telegraph Company successfully transmitted a wireless message across the Atlantic, from Cornwall to Newfoundland. This fact has thrown modern science into confusion. If radio transmissions travel in a straight line (as they should), such transmission should be impossible. There is no direct line of sight between England and Canada that does not cross the Earth, so Marconi's message must have flown into space. The American engineer Arthur Kennelly and the British physicist Oliver Heaviside simultaneously and independently suggested that the explanation for this phenomenon must be due to a layer of ionized gas in the upper atmosphere, capable of reflecting radio waves back to the Earth (Marconi himself believed that radio waves follow the curvature of the Earth's surface, however, physicists did not support him).
By the 1920s, scientists had developed new equipment to first prove the existence of the ionosphere and then study its structure. They used vacuum tubes to generate shortwave radio pulses, directional antennas to send them up into the atmosphere and record echoes, and to show results. The longer the echo return delay, the further away the ionosphere must be. This technology was called atmospheric sensing, and it provided the basic technical infrastructure for the creation of radar (the term "radar", from RAdio Detection And Ranging, did not appear until the 1940s in the US Navy).
It was only a matter of time before people with the right knowledge, resources, and motivation realized the potential for terrestrial applications of such equipment (thus, the history of the radar is the opposite of that of the telescope, which was first intended for terrestrial use). And the likelihood of such an insight increased as the radio spread more and more around the planet, and more and more people noticed interference from nearby ships, aircraft and other large objects. Knowledge of upper atmospheric sounding technologies spread during the second (1932-1933), when scientists made a map of the ionosphere from different Arctic stations. Shortly thereafter, teams in Britain, the US, Germany, Italy, the USSR and other countries developed their simplest radar systems.
with his 1935 radar
Then came the war, and the importance of radar to countriesβand the resources to develop themβincreased dramatically. In the US, these resources have gathered around a new organization founded in 1940 at MIT known as (It was named so on purpose to mislead foreign spies and give the impression that radioactivity was being studied in the laboratory - then few people believed in atomic bombs). The Rad Lab project, which has not become as famous as the Manhattan project, nevertheless got into its ranks equally outstanding and talented physicists from all over the United States. Five of the first employees of the laboratory (including ΠΈ ) subsequently won the Nobel Prize. By the end of the war, about 500 doctors of sciences, scientists and engineers worked in the laboratory, and a total of 4000 people worked. Half a million dollars - which is comparable to the full budget for the creation of ENIAC - was spent only on the publication of the Radiation Laboratory Series, twenty-seven volumes, which described all the knowledge gained in the laboratory during the war (while the US government's spending on radar technology was not limited to the Rad Lab budget ; during the war, the government bought three billion dollars worth of radars).
MIT Building 20, where Rad Lab was located
One of Rad Lab's main areas of research was high frequency radar. Early radars used wavelengths measured in meters. But higher frequency beams measured in centimetersβmicrowavesβallowed for smaller antennas and less scattering over long distances, promising greater range and accuracy advantages. Microwave radars could fit in the nose of an aircraft and detect objects the size of a submarine's periscope.
The first to solve this problem was a team of British physicists from the University of Birmingham. In 1940 they developed "", which worked like an electromagnetic "whistle", converting a random pulse of electricity into a powerful and finely tuned beam of microwaves. This microwave transmitter was a thousand times more powerful than its closest competitor; he paved the way for practical high-frequency radar transmitters. However, he needed a companion, a receiver capable of picking up high frequencies. And at this point we return to the history of semiconductors.
Magnetron in section
The second coming of the cat's whisker
It turned out that vacuum tubes were not at all adapted to receive microwave radar signals. The gap between the hot cathode and the cold anode creates a capacitance, which is why the circuit refuses to work at high frequencies. The best technology available for high-frequency radar was the old-fashioned ""- a small piece of wire pressed against a semiconductor crystal. This was discovered independently by several people, but what is closest to our story is what happened in New Jersey.
In 1938, Bell Laboratories awarded the Navy a contract to develop a fire-control radar in the 40 cm range, which was much shorter, and therefore more frequent, than existing radars in the pre-resonant magnetron era. The main research work went to the Holmdel Laboratories, south of Staten Island. It didn't take long for the researchers to figure out what they would need for a high-frequency receiver, and soon engineer George Southworth was scouring radio stores in Manhattan for old "cat's whisker" detectors. As expected, it worked much better than the lamp detector, but it was unstable. So Southworth sought out an electrochemist named Russell Ohl and asked him to try to improve the uniformity of response of a single-point crystal detector.
Ol was a rather idiosyncratic person who considered the development of technology his destiny, and talked about periodic insights with visions of the future. For example, he stated that back in 1939 he knew about the future invention of a silicon amplifier, but that fate was destined to invent it to another person. After studying dozens of options, he settled on silicon as the best material for Southworth's receivers. The problem was being able to control the contents of the material in order to control its electrical properties. At that time, industrial silicon ingots were widespread, they were used in steel mills, but in such production no one was bothered, for example, by the content of 1% phosphorus in silicon. Enlisting the help of a couple of metallurgists, Ol set out to get much cleaner blanks than he had previously managed.
As they worked, they discovered that some of their crystals rectified current in one direction and others in the other. They called them "n-type" and "p-type". Further analysis showed that different types of impurities were responsible for these types. Silicon is in the fourth column of the periodic table, meaning it has four electrons in its outer shell. In a blank of the purest silicon, each of these electrons would unite with its neighbor. Impurities from the third column, say boron, which has one electron less, created a "hole", additional space for the current to flow in the crystal. The result was a p-type semiconductor (with an excess of positive charges). Elements from the fifth column, such as phosphorus, provided additional free electrons to carry current, and an n-type semiconductor was obtained.
Crystal structure of silicon
All of these studies were very interesting, but by 1940, Southworth and Ohl were no closer to creating a working prototype of a high-frequency radar. The British government at the same time demanded immediate practical results because of the impending threat from the Luftwaffe, which had already created ready-to-manufacture microwave detectors paired with magnetron transmitters.
However, the balance of technological advances will soon tip to the western side of the Atlantic. Churchill decided to reveal all the technical secrets of Britain to the Americans even before he really entered the war (because, as he assumed, it had to happen anyway). He believed that it was worth the risk of leaking information, since then all the industrial capabilities of the United States would be thrown into solving problems such as atomic weapons and radars. British Science and Technology Mission (better known as ) arrived in Washington in September 1940 and brought a gift in the form of technical miracles in her luggage.
The discovery of the incredible power of the resonant magnetron and the effectiveness of British crystal detectors in picking up its signal revived American research into semiconductors as the basis of high frequency radar. There was a lot of work to be done, especially in the field of materials science. To meet demand, semiconductor chips βneeded to be produced in the millions, far more than was previously possible. It was necessary to improve rectification, reduce shock sensitivity and burnout, and minimize the difference between different batches of crystals.β
Silicon point contact rectifier
Rad Lab has opened new research departments to study the properties of semiconductor chips and how they can be modified to maximize valuable properties as a receiver. The most promising materials were silicon and germanium, so Rad Lab decided to play it safe and launched parallel programs to study both: silicon at the University of Pennsylvania and germanium at Purdue. Industrial giants such as Bell, Westinghouse, Du Pont and Sylvania started their own semiconductor research programs and began developing new manufacturing facilities for crystal detectors.
Together, the purity of silicon and germanium crystals was raised from 99% at the beginning to 99,999% - that is, to one impurity particle per 100 atoms. In the process, the staff of scientists and engineers became closely acquainted with the abstract properties of germanium and silicon and applied technologies for controlling them: melting, growing crystals, adding the right impurities (such as boron, which increased conductivity).
And then the war ended. The demand for radar disappeared, but the knowledge and skills gained during the war did not disappear, and the dream of a solid-state amplifier was not forgotten. Now the race was to create such an amplifier. And at least three teams were in a good position to receive this prize.
West Lafayette
The first was a group at Purdue University led by an Austrian-born physicist named Carl Lark-Horowitz. He single-handedly brought the university's physics department out of obscurity through talent and influence and influenced the Rad Lab's decision to entrust its germanium research lab.
Carl Lark-Horowitz in 1947, center, with a pipe
By the early 1940s, silicon was considered the best material for radar rectifiers, but the material just below it on the periodic table also looked worthy of further study. Germanium had the practical advantage of having a lower melting point that made it easier to work with: about 940 degrees, compared to silicon's 1400 degrees (almost like steel). Due to the high melting point, it was extremely difficult to make a blank that would not flow into the molten silicon, contaminating it.
Therefore, Lark-Horowitz and his colleagues spent the entire war studying the chemical, electrical, and physical properties of germanium. The most important obstacle was "reverse voltage": germanium rectifiers at a very low voltage stopped rectifying the current and allowed it to flow in the opposite direction. The reverse current pulse burned the rest of the radar components. One of Lark-Horowitz's graduate students, Seymour Benzer, studied this problem for over a year, and finally developed a tin-based additive that stopped reverse pulses at voltages up to hundreds of volts. Shortly thereafter, Western Electric, the manufacturing arm of Bell Labs, began issuing Benzer rectifiers for the war effort.
The study of germanium at Purdue continued after the war. In June 1947, Benzer, already a professor, reported an unusual anomaly: in some experiments, high-frequency vibrations appeared in germanium crystals. And his colleague Ralph Bray continued to study "volumetric resistance" on a project begun during the war. Bulk resistance described how electricity flows in a germanium crystal at the contact point of a rectifier. Bray found that high voltage pulses significantly reduced the n-type germanium's resistance to these currents. Without knowing it, he witnessed the so-called. "minority" charge carriers. In n-type semiconductors, excess negative charge serves as the majority charge carrier, but positive "holes" can also carry current, and in this case, high-voltage pulses created holes in the germanium structure, which created minor charge carriers.
Bray and Benzer came seductively close to the germanium amplifier without realizing it. Benzer caught Walter Brattain, a Bell Labs scientist, at a conference in January 1948 to discuss volume resistivity. He suggested to Brattain that they place another point contact next to the first one that could conduct current, and then they might be able to understand what was happening under the surface. Brattain quietly agreed to this proposal, and left. As we shall see, he knew only too well what such an experiment might reveal.
One-sous-Bois
The Purdue group had both the technology and the theoretical foundations to make the leap towards the transistor. But they could only stumble upon it by accident. They were interested in the physical properties of the material, and not in the search for a new type of device. A completely different situation prevailed in Aunais-sous-Bois (France), where two former radar researchers from Germany, Heinrich Welker and Herbert Matare, led a team whose goal was to create industrial semiconductor devices.
Welker first studied and then taught physics at the University of Munich, run by the famous theorist Arnold Sommerfeld. From 1940, he left the purely theoretical path and began working on a radar for the Luftwaffe. Mathare (of Belgian origin) grew up in Aachen where he studied physics. He joined the research department of the German radio giant Telefunken in 1939. During the war, he moved his work from Berlin to the east to the abbey in Silesia to avoid the air raids of the Anti-Hitler coalition, and then back to the west to avoid the advancing Red Army, and eventually fell into the hands of the American army.
Like their anti-Hitler rivals, the Germans knew by the early 1940s that crystal detectors were ideal radar receivers, and that silicon and germanium were the most promising materials for their construction. Matare and Welker tried during the war to improve the efficient use of these materials in rectifiers. After the war, both were subjected to periodic interrogations regarding their military work, and eventually received an invitation from a French intelligence officer to Paris in 1946.
Compagnie des Freins & Signaux ("brake and signal company"), the French division of Westinghouse, received a contract from the French telephone company to build solid-state rectifiers and was looking for German scientists to help them. Such an alliance of recent enemies may seem strange, but this arrangement turned out to be quite favorable for both sides. The French, defeated in 1940, did not have the opportunity to gain knowledge in the field of semiconductors, and they desperately needed the skills of the Germans. The Germans could not develop in any high-tech areas in an occupied and war-torn country, so they jumped at the opportunity to continue working.
Welker and Mathare set up headquarters in a two-story house in the Parisian suburb of Aunay-sous-Bois, and with the help of a team of technicians, successfully produced germanium rectifiers by the end of 1947. Then they turned to more serious prizes: Welker returned to superconductors that interested him, and Mathare to amplifiers.
Herbert Matare in 1950
During the war, Matare experimented with rectifiers with two point contacts - "duodiodes" - in an attempt to reduce noise in the circuit. He resumed experiments and soon discovered that the second "cat's whisker", located 1/100 million of a meter from the first, could sometimes modulate the current through the first whisker. He created a solid state amplifier, albeit a rather useless one. To achieve more reliable work, he turned to Welker, who had gained extensive experience with germanium crystals during the war. Welker's team grew larger, purer samples of germanium crystals, and with the improvement in material quality, by June 1948 Matare's point-contact amplifiers were reliable.
X-ray of a "transistron" based on the Mathare circuit, which has two points of contact with germanium
Matare even had a theoretical model of what was happening: he believed that the second contact makes holes in germanium, speeding up the passage of current through the first contact, supplying minority charge carriers. Welker did not agree with him, and believed that what was happening depended on some kind of field effect. However, before they could work out the device or theory, they learned that a group of Americans had developed exactly the same concept - a germanium amplifier with two point contacts - six months earlier.
Murray Hill
At the end of the war, Mervyn Kelly reformed the Bell Labs semiconductor research group headed by Bill Shockley. The project has grown, received more funding, and moved from the original laboratory building in Manhattan to an expanding campus in Murray Hill, New Jersey.
Campus at Murray Hill, ca. 1960
In the spring of 1945, Shockley visited Russell Ohl's laboratory in Holmdel to reacquaint himself with advanced semiconductors (after having been in operations research during the war). Ol spent the war years working on silicon and wasted no time. He showed Shockley a crude amplifier of his own design, which he called the Desister. He took a point-contact silicon rectifier and ran current through it from the battery. Apparently, the heat from the battery reduced the resistance across the contact point, and turned the rectifier into an amplifier capable of passing incoming radio signals into a circuit powerful enough to power a speaker.
The effect was crude and unreliable, unsuitable for commercialization. However, it was enough to confirm Shockley's opinion about the possibility of creating a semiconductor amplifier, and that this should be made a priority for research in the field of solid state electronics. Also, this meeting with Ohl's team convinced Shockley that silicon and germanium needed to be studied first. They exhibited attractive electrical properties, and in addition, Ohl's colleagues, metallurgists Jack Scaff and Henry Terer, achieved amazing success in growing, refining, and doping these crystals during the war, surpassing all the technology available for other semiconductor materials. Shockley's group was no longer going to waste time on pre-war copper oxide amplifiers.
With Kelly's help, Shockley began putting together a new team. Among the key players were Walter Brettain, who helped Shockley with his first attempt at a semiconductor amplifier (in 1940), and John Bardeen, a young physicist and new employee at Bell Labs. Bardeen probably had the most extensive knowledge of solid state physics of all the members of the team - his dissertation described the energy levels of electrons in the structure of metallic sodium. He was also another protΓ©gΓ© of John Hasbrouck Van Vleck, like Atanasoff and Brettain.
And, like Atanasoff's, Bardeen's and Shockley's dissertations required the most complex calculations. They had to use the quantum mechanical theory of semiconductors, defined by Alan Wilson, to calculate the energy structure of materials using Monroe's desktop calculator. By helping to create the transistor, they, in fact, contributed to the deliverance of future graduate students from such labor.
Shockley's first approach to the solid state amplifier relied on what was later called "". He suspended a metal plate over an n-type semiconductor (with an excess of negative charges). The application of a positive charge to the plate pulled the excess electrons to the surface of the crystal, creating a river of negative charges through which an electric current could easily flow. The amplified signal (represented by the level of charge on the plate) in this way could modulate the main circuit (passing along the surface of the semiconductor). The efficiency of this scheme was suggested to him by his theoretical knowledge in physics. But, despite many experiments and experiments, the scheme did not work.
By March 1946, Bardeen had come up with a well-developed theory explaining the reason for this: the surface of a semiconductor behaves differently at the quantum level than its interior. Negative charges drawn to the surface become trapped in "surface states" and block the electric field from the plate from penetrating the material. The rest of the team found this analysis compelling, and launched a new research program in three ways:
- Prove the existence of surface states.
- Study their properties.
- Figure out how to defeat them and make it work .
After a year and a half of research and experimentation, on November 17, 1947, Brettain made a breakthrough. He discovered that if you place an ion-filled liquid, such as water, between a plate and a semiconductor, the electric field from the plate will push the ions toward the semiconductor, where they will neutralize the charges trapped in the surface states. Now he could control the electrical behavior of a piece of silicon by changing the charge on the wafer. This success gave Bardeen the idea for a new approach to building an amplifier: surround the contact point of the rectifier with electrolyte water, and then use a second wire in the water to control surface conditions, and in this way control the conduction level of the main contact. So Bardeen and Brettain reached the finish line.
Bardeen's idea worked, but the amplification was weak and worked at very low frequencies, inaccessible to the human ear - so it was useless as a telephone or radio amplifier. Bardeen suggested switching to Purdue's reverse-voltage resistant germanium, believing that fewer charges would collect on its surface. Suddenly, they received a powerful boost, but in the opposite direction from what they expected. They discovered the effect of minority carriers - instead of the expected electrons, the current through germanium was amplified by holes coming from the electrolyte. The current on the wire in the electrolyte created a p-type layer (a region of excess positive charges) on the surface of the n-type germanium.
Subsequent experiments showed that no electrolyte was needed at all: simply by placing two contact points close together on the germanium surface, one could modulate the current from one of them to the current on the other. To bring them as close as possible, Brattain wrapped a piece of gold foil around a triangular piece of plastic, and then carefully cut the foil at the end. Then, with the help of a spring, he pressed the triangle against germanium, as a result of which the two edges of the cut touched its surface at a distance of 0,05 mm. This gave Bell Labs' transistor prototype its distinctive look:
Brettain and Bardeen's prototype transistor
Like the device of Mathare and Welker, it was, in principle, a classic "cat's whisker", just with two points of contact instead of one. On December 16, it delivered a significant boost in power and voltage, and a frequency of 1000 Hz in the audible range. A week later, after some minor improvements, Bardeen and Brattain got 100 times the voltage and 40 times the power, and demonstrated to the Bell directors that their device could reproduce audible speech. John Pierce, another member of the solid state design team, coined the term "transistor" after the name of the Bell copper oxide rectifier, the varistor.
For the next six months, the lab kept the new creation a secret. Management wanted to make sure they had a head start in commercializing the transistor before anyone else got it. The press conference was scheduled for June 30, 1948, just in time to shatter all of Welker and Mathare's dreams of immortality. Meanwhile, the semiconductor research group quietly fell apart. Upon hearing of Bardeen and Brattain's accomplishments, their boss, Bill Shockley, began working to claim all the glory for himself. Although he played only an observational role, Shockley received equal if not more publicity in the public presentation - as can be seen from this published image, where he is in the thick of things, and right at the laboratory table:
1948 publicity photo - Bardeen, Shockley and Brettain
However, equal fame was not enough for Shockley. And before anyone outside Bell Labs even knew about the transistor, he was busy reinventing it to claim it for himself. And this was only the first of many such re-inventions.
What else to read
- Robert Buderi, The Invention That Changed the World (1996)
- Michael Riordan, βHow Europe Missed the Transistor,β IEEE Spectrum (Nov. 1, 2005)
- Michael Riordan and Lillian Hoddeson, Crystal Fire (1997)
- Armand Van Dormael, βThe 'French' Transistor,β (1994)
Source: habr.com