Copyright Mark P D Burgess 2008 and 2011
Innovation at General Electric in the field of semiconductors in the 1950s occurred at two main sites: Syracuse and Schenectady. It centres on the pioneering work of Harper North, Robert Hall and William Dunlap at Schenectady and that of John Saby at Syracuse in the period 1948-51. By the time the silicon controlled rectifier, the Diac and Triac were developed in the period 1957-1963 General Electric had assembled a significant team of researchers and engineers at Syracuse, Schenectady and the Clyde rectifier plant.
The Schenectady laboratories date back to 1900 when Willis Whitney, a chemist from MIT, was hired to be its foundation director. Its alumni include some famous names in science and technology such as William Coolidge who worked on medical X-ray technologies, the Nobel prize winning chemist Irving Langmuir and Albert Hull who developed the magnetron and other vacuum tubes. In 1950 the laboratory moved to the Schenectady suburb of Niskayuna.
At Syracuse, Electronics Park was the headquarters for electronics research, development and was General Electric’s main electronics manufacturing site (radio, radar, television and similar equipment). Construction began in 1946 on a park like site of 150 acres and phase one was completed early in 1948. The Electronics Laboratory moved there in February 1948.
The Schenectady laboratories were intended to investigate more basic research whereas the Syracuse laboratories were there to support production. But researchers at both sites all had considerable freedom to investigate new technologies and undertook novel developments. The culture of innovation was also strong at Clyde which was a manufacturing site.
The invention of the cavity magnetron in Britain and the potential for high resolution radar led to a large scale development programme managed by the Radiation Laboratory at MIT. This included the development of new crystal rectifiers: a redeployment of very old technology now revisited because vacuum tubes could not operate at the GHz frequencies being used. But to meet military standards the humble cat’s whisker crystal detector needed to become a reliable detector.
General Electric was a contractor in the programme and represented by Harper North in the more academic “crystal meetings” which were dominated by researchers from the Radiation Laboratory and the University of Pennsylvania. [Henriksen 1987]
The overall purpose of the General Electric contract was to investigate germanium as a possible improvement over silicon which was the dominant crystal in use. [North 1946]
At General Electric North made germanium from its oxide under hydrogen at 650 C and then fused it into a crystalline mass by heating it at 1015 C. The purity of the resulting germanium (as indicated by its resistivity) was crucially dependent on the quality of the oxide, processing conditions and control over the purity of the hydrogen.
Extensive work was undertaken on germanium dopants, antimony being preferred over phosphorous which was also investigated.
To produce detector cartridges a doped ingot was sliced into 0.02 inch wafers, polished and rhodium plated on one side diced into 0.07 inch squares. These were soldered to the cartridge stud and finally highly polished. Heat treatment and chemical etching were found to be undesirable for radar detectors.
North undertook an extensive investigation of welded point-contact diodes where the contact was welded to the germanium by passing a high current briefly through the unit. Due to their negative resistance characteristics these had high gain but were not used because of their high noise. Unlike conventional point-contact diodes, they were, however, excellent rectifiers. Using germanium with high levels of antimony doping, North obtained very low forward resistance at only 0.4 volts. [Torrey 1948]
North’s coaxial cartridge design followed the dimensional outline of the Sylvania silicon 1N26 but typically utilized antimony doped germanium. The assembly was sealed into silver plated steel tube with low-loss glass. Use of antimony doping (n-type germanium) gave reversed polarity compared to conventional silicon diodes. [Drawing from Torrey 1948]
General Electric 1N23A cartridge [Courtesy Jan de Groot]
The first diodes released by General Electric were based on the North wartime research and the subsequent development of Harper North and his team.
The first diodes released commercially by General Electric were the G5 series submitted for RMA registration in June 1948. They were general purpose small signal types and used North’s welded germanium technology. These were the G5A, G5B, G5C and G5D which corresponded to the series 1N49-1N51.
These were followed by the G5E (1N63) that December, G5G (1N65) and G5F (1N64) in 1950 [RMA Release 670]
In 1950 the package outlined changed to the newer format illustrated below. In addition the G5 series was extended to include hermetically sealed ceramic cases as the G5K, G5L and G5P (1N69, 1N70 and 1N81) from 1950. [RMA release 891B, 1951, RMA release 1016 1951]
The G range of welded germanium diodes was extended with the G6 and G7 series. The G6 diode was intended as a VHF detector and meter rectifier and the G7 series for UHF applications. A summary of the range is shown in the following data sheets (click on these thumbnails for full resolution). For the story of their manufacturing process see "Welded Germanium Diodes."
The G8 matched pairs and G9 bridge rectifiers completed the commercial G series. By now alloy junction rectifiers known then as “diffused junction rectifiers” were in development. The G10 rectifier made a brief appearance as noted below.
Robert Hall returned to General Electric Research Laboratories Schenectady just as Bell announced its point-contact transistor. Hall had just graduated PhD from Caltech and had previously worked at the laboratories on a range of projects including the Harper North Wartime radar diode project. Dr Albert Hull was Assistant Director of the Laboratory. He was known for his collegial management style with a relaxed approach to the research agenda of his staff members. Hall recalls that Hull came in with the reprint of the Physical Review letters that announced the transistor [Bardeen 1948] and said “Robert here’s an interesting development from Bell Laboratories. It looks like something pretty new and exciting. Would you like to look into it and see if there’s anything interesting there.” [Choi 2004]
General Electric had all the knowhow it needed to duplicate the Bell design quickly. North’s diode programme had diodes that could handle 100 volts back voltage which was state of the art at that time. (Purdue University produced the high back voltage germanium for the Bell point contact transistor.) North’s diode programme and related research ensured it had a manufacturing understanding of the key technologies:
High back voltage poly-crystalline germanium;
Point contact design;
Welding or forming; and
Assembly and encapsulation.
Its first designs were crude with two pins for the collector and emitter with the base connection through the case in the manner of the Bell Type A. No socket was available and users were recommended to use a 5 pin subminiature tube socket using positions 2 and 3 for the collector and emitter and to create a base connection by inserting phosphor-bronze strips in positions 1 and 4 and bending them so they contacted the transistor case.
The transistors were known as germanium triodes or germanium whisker transistors. Two types were produced evolving from prototype coding through the familiar “G” designation in use for its point-contact diodes and finally adopting RMA registration:
The prototype numbers appear in early data sheets and in a General Electric price list dated June 1st 1951 in which the new SX-4A and Z2 transistors were priced at a massive $29 each.
The two transistors had the same mechanical and electrical characteristics but the switching transistor was tested for “trigger action” or negative resistance. [General Electric 1950 courtesy Jack Ward]
From 1952 the transistors had 3 pins with the base connection being soldered to the outside of the transistor’s case.
Early General Electric G11 and G11A point-contact transistors.[Courtesy Jack Ward]
Production General Electric G11 point-contact transistor [Courtesy Jan de Groot]
Hall had the opportunity to take a more fundamental approach to support semiconductor development.erious impurity that turned out to be boron. This crystal was a rectifier which Hall called a “barrier-less” rectifier. “I realized sometime later that this was a very broad P-N
junction and obeyed the same laws that Bill Shockley had worked out for P-N junctions“ [Choi 2004]
Hall decided to make a more efficient rectifier by taking most of the germanium away and putting donor and acceptor impurities on opposite sides. Because they both have low melting
points indium (acceptor) and antimony (donor) are good candidates for an alloy diffusion experiment. Hall assembled a wafer of germanium with a drop of indium on the top and antimony on the bottom. This was situated on a metal plate and heated in an hydrogen atmosphere to obtain alloying. It rectified: “It was very leaky in the reverse direction but it had remarkably good forward characteristics. It would carry several amperes at only a volt or so.” [Choi 2004] Previous rectifiers had only been able to pass a few milliamps. Hall improved the reverse characteristics by etching (which removes excess dopant that has diffused across the surface of the germanium).
Hall began making large area rectifiers 5mm square by this process and used water cooling for improved power. He was able to make devices that could pass 100s of amperes in one direction and block a 100 volts in the other. “So I could handle many kilowatts of power with these rectifiers which were rather phenomenal.” [Choi 2004]
By 1949 the work was sufficiently advanced to be transferred to the Electronics Laboratory at Schenectady as a production development project while the more theoretical work continued at the Research Laboratory.
Hall assumed that he was doping his junctions through diffusion into germanium. Crawford Dunlap had already been working on impurity diffusion in germanium and when learning of Hall’s success proposed a joint paper on diffused rectifiers. “Dr. Dunlap became aware of the work I was doing, and he called me into his office and proposed that we produce a joint paper on diffused rectifiers. And I was rather taken aback by this, because as far as I can see, he hadn’t contributed anything to this. I did not make use of any of his work. I don’t know if he had any diffused results.” [Choi 2004]
In 1950 Hall and Dunlap published Hall’s work on P-N junctions made by diffusing donors and acceptors from opposite sides of a germanium wafer. They discussed their approach for optimizing both the forward current and reverse voltage and showed why the alloy junction approach pioneered at General Electric gave better dopant profiles across the junction compared to those achieved by melt solidification.
“The non-linear impurity distribution which is required may be obtained by thermal diffusion of the donor and acceptor impurities into opposite sides of a wafer of semiconductor. Germanium diodes have been prepared in this manner which will withstand inverse potentials of the order of 100 volts and which will pass 500 amp/cm2 at one volt in the forward direction.” [Hall 1950]
They noted that the I-V characteristics of their rectifiers were similar to those of selenium or copper oxide but that the current densities were 1000 times better.
This work was patented by Dunlap evidently because the General Electric’s attorneys considered Dunlap had made the inventive step. The application covered the preparation of single or multiple junction units for rectifiers, thermoelectric junctions, photoelectric junctions and transistors. Dunlap’s patent describes junction formation by
diffusing donor or acceptor impurities into a semi-conductor body already doped with impurities of opposite conductivity. The assembly is fired and by controlling the firing time and temperature the degree of penetration of the impurity is controlled. The penetrated area changes to the opposite conductivity and a PN junction is formed. Contacts are made by soldering wires or connectors to the surface dopant and the wafer. [Dunlap 1950] On the left is a schematic for the General Electric G-10 power rectifier. It features heating sinking through its base. Loads of several kilowatts could be handled by this design. [Hall 1952]
The G-10 was an early prototype that was offered in pilot scale quantities from October 1951 according to its advertising "The Truth about Transistors" in Tele-Tech for May 1952 and in a two page spread in Tele-Tech for January 1952 "These rectifiers are now in pilot production." But the G-10 was never commercialized. Finis Gentry recalls “The G10 Rectifier was a germanium rectifier about the size of a quarter and about 3/16' thick. The case was made of copper with the anode insulated from the cathode by a rubber O ring. This did not provide sufficient hermetic protection so it was replaced by the hermetically sealed 4JA2 germanium rectifier.” [Gentry 2009]
Pilot scale quantities of the G-10 Rectifier were offered in Tele-Tech January 1952
Hall carried out extensive characterization of the rectifiers he made from high purity germanium wafers doped on opposite faces with acceptor and donor impurities. These were known as PIN types implying intrinsic semiconductor at the barrier. Current flow in the high purity region is determined by the generation and recombination of holes and electrons and these structures enabled the study of these phenomena. Recombination was expected to be proportional to the square of the carrier concentration at high levels of injection but Hall found a linear dependence. His observations could be accounted for by assuming that recombination takes place largely through recombination centers distributed through the germanium [Hall 1952].
“So I was pretty well convinced that I had a new model of recombination which I discussed at a meeting of the Physical Society. Bill Shockley was there. After the meeting he quizzed me at length about this, and apparently was convinced the mechanism was quite important.“ [Choi 2004]
In 1952 Shockely and Read carried out an extensive analysis based on Hall’s hypothesis. They named the recombination sites “traps” that sat at energy levels mid-way between the conduction and valance bands. They agreed with Hall: “It should be noted that at high carrier densities the rate of recombination through traps is linear in the carrier density whereas any direct recombination would be quadratic. This is in agreement with the findings of R N Hall for P-N junctions operating with high injected densities in the region of recombination.” [Shockley 1952]
This form of recombination is now known as Shockley Read Hall recombination. The ideal trap energy level is half way between the valance and conduction bands. Hall found a value of 0.22 ev for the position of the traps above the valence band or below the conduction band. [Hall 1952]
Reflecting on Hall’s achievements (including his later development of the first semiconductor laser) Holonyak muses: “If I had been giving Nobel Prizes for semiconductors, after Bardeen, Brattain, and Shockley, the next guy who would have gotten the Nobel Prize would have been Bob Hall, my colleague, later, in Schenectady.” [Ashrafi 2005]
In 1949 Hall’s work on the rectifier was transferred to the Electronics Laboratory at Syracuse for the development of production processes.
General Electric had a diode programme since 1942 when Harper North began work on an improved radar diode. Both silicon and germanium had been considered but germanium proved best. This work was not unique to General Electric: Sylvania, Western Electric and Raytheon had also developed radar diodes. Following the war General Electric had a strong diode business.
Paul Jordan hired Addison Sheckler in March 1948 to work on nuclear instruments at Syracuse. In late 1948 production asked for help on purifying the germanium they were using. At the time Eagle Picher Co was their sole supplier and quality was variable. A chemist at Syracuse, Fred Pingert suggested this could be done by the Bridgeman method (progressive feezing). Sheckler developed the method using high purity General Electric carbon boats. Crystallisation gave excellent purity gains at a yield of 80% (20% had the impurities).
Sheckler writes “About the end of 1949 R.N. Hall and W. Crawford Dunlap of GE’s Research Laboratory came up with the alloy/diffused junction using antimony and indium for contacts. (The Hall-Dunlap patent). We at Electronics Laboratory picked this up immediately and started to make diodes. It very quickly became apparent that we were going to need single crystal germanium for a successful product.” [Sheckler 2004].
Thus the Laboratory assigned Sheckler to build a crystal pulling apparatus which Sheckler says he had operational in only five weeks. He notes that subsequently he discovered that Hall already had single crystal pulling working at Schenectady. Apparently the relations between the two laboratories were somewhat competitive.
Sheckler recalls that about this time the “Laboratory Management” told Jordan to get his team back to some “real work” or be fired. This meant tube electronics. Jordan went to the head of the Electronics Division, Dr W R G Baker and pitched the future of semiconductors and Baker bought it with sanction for $10,000 in continuing development. The $10,000 became $30,000 and secured the place of General Electric in semiconductors.
In 1950 everything to do with the new rectifier needed to be developed. There were no useful pre-existing processes. The interim can consisted of two copper cups one fitting inside the other insulated by a paper washer, sealed with an O-ring and crimped. 50,000 diodes made this way were sold for $5.00 each!
Demand was huge and General Electric opened a manufacturing facility at Clyde NY and started production of the 1N91-1N93 diode series in the now famous top hat outline.These were first registered at the end of 1952 [RTMA 1952 Release 1146]
Work on junction transistors was carried out by Hall at Schenectady (new forms of grown junction transistors) and Saby at Syracuse (the alloy junction transistor). Later Hall worked on power alloy junction transistors.
Commercially the alloy junction transistor became the workhorse device through the 1950s and were made by many semiconductor companies.
These developments reflect the cultures of the two sites. Hall’s grown junction work depended on an exquisite understanding of the kinetics of segregation of impurities between the semiconductor melt and the solid phase. His rate growing and meltback junction transistors could not be “discovered;” they were based on the segregation studies.
Saby worked in a production laboratory and adopted alloy diffusion processes that had been invented by Hall and Dunlap and developed for production of rectifiers at Syracuse and doped single crystal germanium wafers also used in rectifiers. This was a pragmatic approach which led him to useable transistors quite quickly.
Grown junction transistors are discussed in the companion article on this site Early Transistor Technologies.
Hall used the Czochralski method to grow single germanium crystals and used this to make grown junctions using the double doping method pioneered by Gordon Teal and Morgan Sparks at Bell [Shockley 1976]. In this method an NPN grown junction, for example, is made by commencing with an N-type semiconductor from which a single crystal is started. Then a P-type impurity is added to convert the melt to P-type and produce a P region in the crystal. Finally the melt is restored to N-type by adding a suitable quantity of N-type impurities.
As part of his studies on the purification of germanium, Hall measured the segregation constants of a range of impurities. P-type impurities have high segregation constants. Hall had discovered this early on when he tried to make N-type germanium by doping with arsenic: his germanium was contaminated with boron and this co-crystallized first creating P-type germanium. The arsenic followed creating N-type germanium forming Hall’s “barrier-less” rectifier. Other P-type impurities such as gallium and indium behave similarly and their segregation constants are relatively independent of crystallization rates. Incorporation of antimony, however, is strongly dependent on crystallization rate: more is incorporated at high growth rates. Thus Hall found he could pull a single crystal from a melt containing antimony and indium that was P-type when grown slowly and N-type when grown rapidly. By repeated cycling of the growth rates he could produce “more than a hundred uniformly spaced PN junctions.” [Hall 1952]
Double doping transistors had poor high frequency performance due to their thick base layer. The rate grown process gave greatly improved high frequency performance.
Rate-grown transistors were manufactured by General Electric at Syracuse using this process. Early examples were the 2N78 and 2N167. [Gottlieb 1959]
In September 1954, General Electric announced a new production facility for its rate grown transistors would soon be commissioned noting that “at present, GE is making a few hundred transistors a week on its pilot line in Syracuse. A rate grown ingot is being produced every ten days, which is currently enough to keep the line supplied for about ten days. The firm is presently mechanizing the fabrication process of attaching the leads to the transistor bars.” See Making a 2N78 Transistor
“The rate grown process, first announced a year ago, involves varying the heat and withdrawal rate controls cyclically during the crystal-growing process. As a result, as many as a hundred usable wafer-thin slices of germanium can be cut from a six-inch ingot. With other processes only one useful slice is formed per crystal. The disc shaped slices are then diced into thousandths of an inch long, with a junction layer through the center of each. The more cycles there are in the crystal-growing process, the more layers there are for slicing and dicing.” [Electronics 1954]
By April 1955 the 2N78 transistor was available in volume quantities:
Advertising for Mass Production of the 2N78 in Electronics April 1955
“The General Electric N_P_N transistor type 2N78 is designed for RF and IF amplification in broadcast receivers. It employs a new and revolutionary manufacturing technique – the exclusive GE rate-growing process. This process makes possible stable operation at junction temperatures up to 1—C. The 2N78 is hermetically sealed and rated for a collector dissipation of 50 mw in 30C free air.” [General Electric datasheet ECG-78]
This set of 2N78 are from mid 1955 representing some of the first from the new production line:
Early 2N78 and a 2N167
The melt-back process invented by Hall [Ward 2001] also exploited the stronger incorporation of P-type impurities in germanium at slow crystallization rates and can be used to make NPN transistors. In this case small bars of single crystal N-type germanium with a minority amount of P-type impurities are prepared. One end of the bar is melted and on solidification P-type germanium forms first followed by N-type thus converting a uniformly N-type bar into a NPN structure. The General Electric 2N1289 is an example of a melt-back transistor.
Relative high frequency performance of these types is shown in the table.
A variant that gives improved high frequency performance is the meltback-diffused process developed by Lesk and Gonzalez in 1957. They made experimental PNP transistors from a bar containing two P-type and one N-Type impurities. After meltback and crystalisation a PNP structure is formed in which one of the three dopants predominates in each region.
Both meltback grown junctions feature accelerating base fields. Lesk’s experimental transistors showed a gain of 15db at 60mhz. [Lesk 1957]
John Saby was hired by General Electric late in 1950 and started in February 1951 after first recovering from a bout of polio. His first assignment was to make a “control device” using General Electric’s technology for making PN junctions that was already being exploited in rectifier development. At the time, General Electric was already making point contact transistors (GE11/2N30 and GE11A/2N31).
There was little in the public domain that was helpful. Shockley’s book, Electrons and Holes in Semiconductors had been published in 1950 but Saby had been working at General Electric for some time before he read it. The Bell Laboratories work on the junction transistor was not published until 1951 [Shockley 1951] over a year after Teal and Sparks made the first crude grown junction transistor.
Saby decided that he needed a structure where the emitter-base-collector junctions were close together. “We also wanted the emitters [as] close to the collectors as possible, and the way to do that, I thought, was across the thickness of something. That’s really where the alloy transistor idea came from.” [Morton 2000]
Fortunately the key production technologies were already in place:
1) Hall had produced PIN rectifiers which had the geometry and construction of an alloy junction transistor (other than doping selection)
2) Syracuse could produce single crystal doped germanium wafers (intended for rectifiers)
Sheckler says Saby made his first transistor by March 11th 1951. This is remarkably fast but possible given that Saby did not have to develop any new technologies. Saby’s experimental transistors were PNP types with alloyed indium on either side of a thin N-type germanium wafer. The response at the Laboratory was skeptical: tubes were still King! But Richard Shea, leader of the Circuits Group was interested. He and his Group worked with Saby to characterize the new device and to make example practical circuits: a megaphone with a half watt class B output, a hearing aid and an audio amplifier.
Saby’s work attracted the attention of Lloyd DeVore during a visit to the Research Laboratories at Schenectady who thought the development was worth presenting to W R G Baker, Director over the Syracuse site. This was on Friday and over the weekend Saby made a dozen transistors “just to give him an idea how fast you could make them.” [Morton 2000]
Saby’s transistor was first disclosed at the IRE Electron Devices closed conference at Durham in June 1951. Both Saby and Sheckler note with some pleasure that their announcement of the junction transistor was made ahead of Bell who presented their grown junction transistor work at the same conference. The time taken by Bell to take Shockley’s concept (1949) to a viable transistor reflected the immense difficulties presented by the grown junction approach.
Saby published his work the following year after General Electric had filed a patent on the alloy junction transistor [Saby 1952]. His paper is clearly calculated not be of any value to competitors: no constructional details are included. He does make some general observations however:
A collector that is larger than the emitter is desirable to capture more of the injected carriers. However, symmetrical transistors (same sized emitter and collector dots) give good power gains.
His transistors had been operated up to 140C .
The alpha cut-off frequency ranged from 100KHz to several MHz
The transistors could operate with collector voltages of up to 150v. Junctions of 1mm2 had been constructed that could dissipate up to 8 watts with forced cooling and 3 watts continuous dissipation at 25C.
It was not initially clear if PN junctions were being formed by an indium-germanium alloying process or by diffusion of the indium into the N-type germanium wafer. When Hall and Dunlap published PN Junctions by Impurity Diffusion [Hall 1950] they made it clear that they thought the mechanism was “thermal diffusion.”
Albert English worked at General Electric, Lynn, Massachusetts most famous for aircraft jet engine developments from World War II. He wanted an improved alternative to copper oxide rectifiers for electric welders. He investigated one of Hall’s diodes, etched away the indium and observed a recrystallised region which he realised was a germanium-indium alloy. Hall’s diode patent recognised both mechanisms: diffusion and alloy but Hall notes “the recrystallization from the alloying process was one of the key ingredients to make these rectifiers work” [Choi 2004].
Conventional wisdom at General Electric was that diffusion was unlikely to be significant in the short time available during annealing and these transistors became known as alloy junction transistors. This meant that for a PNP transistor the PN junctions coincided with the line dividing the recrystallised P-type germanium and the unchanged N-type base.
Saby showed that this was incorrect [Saby 1953] and that at the temperatures used in annealing sufficient diffusion occurred to move the PN junction clear of the re-crystallized region. This had important consequences for the design and theory of alloy junctions: Diffusion would create a gradation at the junction likely to influence performance.
The first alloy junction transistors General Electric produced were the 2N43, 2N44 and 2N45 announced in September 1953. [Earliest documented reference from McGarrah 1953 Commercial Transistor Data Chart.]
Conrad Zierdt was the production engineer at Syracuse responsible for the encapsulation design. In 1954 he published a review on their development. He noted: “Transistors have been disappointing to many application engineers because of lack of stability with temperature and operating point variations, and degradation with time. Early units have also had wide ranges of characteristic variations, requiring “tailoring" of circuits to individual transistors. The 2N43, 2N44 and 2N45 transistors have been designed to eliminate the vagaries introduced by environment changes, and to delineate inherent variations in such form that design allowance may be made for them.” [Zierdt 1954]
Saby agreed: “The major practical problem was the degradation of the junctions, due to atmospheric moisture.” [Morton 2000]
Zierdt’s design had glass to metal sealed housing with all seams being welded. Moisture and other atmospheric contaminants were eliminated by evacuation down to levels used in vacuum tubes. Welding eliminated contamination by solder fluxes. There was no reliance on potting compounds so that any leaks were immediately apparent on evacuation.
The transistors came from the same production line and had similar characteristics. They were sorted by gain (the 2N43 was high gain and the 2N45 was low gain).
A product announcement in the November 1953 edition of Radio Electronics noted that:
“in a novel exhibit at the West Coast Electronics Show in San Francisco the transistor was operated at the heart of a miniature radio transmitter while frozen in a cake of ice which was then melted and turned into boiling water."
"This demonstrated the transistor’s ability to perform efficiently under extreme variations in temperature and humidity.” (Photo left from Electronics January 1954 advertising by General Electric "Vacuum Junction Transistors," right.)
Those that did not make the specification for this series became the 2N107 with highly down-rated specifications and sold into the hobby market from 1955. A military version, the 2N43A was the first transistor to be qualified for the USAF. [Ward 2002, McGarrah 1995]
Saby recalls that General Electric had reservations about patenting his transistor and suggests that they thought it was covered in the Dunlap PN junction patent. The record shows they were recklessly slow, filing on “Broad Area Transistors” on 14th June 1952 over a year after its invention. The patent does not disclose any further developments that might have taken place in that time: it is remarkably lacking in any details beyond the fundamental concept.
General Electric discovered that RCA had filed on the work of Jacques Pankove and his alloy junction transistor a day earlier. It is likely that both companies were filing in advance of the closed Electron Devices conference at Durham later the same month.
In order to assert its position General Electric had to argue that they were the first to invent which required proof that Saby did produce his transistor ahead of Pankov.
After nine years of litigation General Electric won and their patent issued on 5th September 1961. RCA obtained a patent on an improved alloy junction transistor: Their surviving claims covered the use of a collector of significantly greater diameter than the emitter in order to obtain improved collector efficiency and higher alpha. The data given shows that for emitters and collectors of the same diameter alpha ranges from 0.5-0.85. Where the collector is 8 times the diameter of the emitter then alphas of up to 0.98 are obtained. The RCA patent issued on 17th October 1961. Given the universal adoption of collectors of larger diameter than the associated emitter there was significant residual value in this patent. (see the RCA page on this site for additional information).
The UniJunction or Double Base diode was discovered by Jerry Suran in 1953. At the time Suran was working in the circuits group under Richard Shea evaluating experimental tetrode transistors made by John Saby’s group. The work was being
funded by a tri-services military contract and was intended to improved high frequency performance by applying a transverse field to the base via a second base electrode. The tetrodes were being made by Arnold Lesk and the first two tested by Suran showed that a transverse base field gave little improvement. Suran recalled “on the other hand, one of those tetrodes curiously had a hysteresis effect on the input, and when we put an oscilloscope on it we found that the thing was oscillating.” [Ward 2005] Investigation showed that there was no collector current and it was clear that the collector had become disconnected. This was unsurprising: these test transistors were simply enclosed in a glass vial filled with silicone oil and sealed with wax to stabilize the leads. Thus by accident an active device consisting of an emitter-base junction and two ohmic connections to the base had been made. It had a negative resistance characteristic and could be made to oscillate and act as a trigger. [Ward 2005; Aldrich 1954] It was patented by Lesk in 1953. [Lesk 1953]
The discovery work was done on germanium devices but commercialized as the silicon unijunction transistors (2N489-2N494). Their principal application was for use in SCR triggering circuits.
The SCR or Thyristor was based on work done at Bell Laboratories on PNPN switches and commercialized by General Electric. Some of the oral history references included in this section give most of the credit for the development to a single innovator. The person most clearly the champion of the SCR, Bill Gutzwiller gives credit to the entire development team at General Electric: “we just had a wonderful team.” The SCR was never patented as it was anticipated by the prior work at Bell and therefore, from a legal perspective, there is no inventor of record.
The PNPN switch was a major project at Bell Laboratories led by John Moll. Bell wanted a solid state replacement for the mechanical relay for use in communications. The project commenced in 1954. It was clear that to meet the specifications for a high “off” impedance the device would have to be based on silicon and this posed immense technology issues as silicon was in its infancy (the first silicon transistor was announced by Texas Instruments in 1954). Nick Holonyak and Carl Frosch were part of Moll’s team and worked on impurity diffusion. Morris Tanenbaum who was working on the silicon diffusion transistor was part of the team. In the course of this work silicon dioxide masking was discovered by Carl Frosch. Issues such as insufficient silicon purity and crystal defects resulting in inadequate minority carrier lifetime and inconsistent properties had to be solved. Metal thin film technologies for the emitters were developed (Goldey and Holonyak). [Moll 1997]
By 1956 silicon PNPN switches had been created and characterized [Moll 1956]. While the work had been directed to two terminal devices the authors noted “By making a third terminal connection to one of the base layers the PNPN can be turned on by a small amount of control power much in the manner of a gas tube thyratron. If the series resistance is close to zero the structure will conduct several amperes at one volt drop.” [Moll 1956]
In his oral history [Nebeker 1993] Holonyak recalls meeting Robert Hall at Bell and “digging out of Bob how you make alloy junctions.” Alloy junctions were used in the Bell PNPN switch and this early cooperation presaged their later collaboration when both worked at General Electric.
Holonyak arrived at General Electric in November 1957; too late to be part of the original development. [Holonyak 2001]
The PNPN technology was made available to Bell licensees and particularly to Shockley Laboratories where Shockley had made the PNPN diode his major development.
Gutzwiller started with General Electric in January 1955 in an engineering role at the rectifier manufacturing site at Clyde where Ray York was site director. His first assignment was to produce the sales specification for the new General Electric 5 ampere rectifier. Soon Gutzwiller was appointed as applications engineer for the Clyde rectifier product range and in this role he recognized the need for a controllable rectifier whereby the amount of power would be steplessly variable. “I was continually looking to our physicists and engineers for some way of developing semiconductor technology to produce what to me would be the holy grail: a controllable rectifier.” [Ward 2005]
When Bell Laboratories published their work on the PNPN switch in September 1956 [Moll 1956], Gordon Hall and his team of power engineers at Clyde recognized that here was the technology they had been looking for. Gutzwiller notes “In short order they produced a power version of the PNPN diode, but with a third lead to control the point in each A-C cycle when the device would switch on.” The work was done on a budget of only $1,000 provided by Ray York and the first two units were produced in July 1957. [Owen 2007]
Gutzwiller recalls Hall bringing him the first prototype SCR and asking him to do something with it: Gutzwiller bought an electric drill from the local hardware store in Clyde and used the SCR to control its speed. It worked and was the first semiconductor electric motor speed controller.
The project at Clyde to build an SCR had been low budget and carried out in spare time. Now their success was shared with management at Syracuse with the request that a major development project be undertaken to commercialise the SCR. General Electric went public with the new device in August 1957 and had prototype SCRs rated for 300 volts and 7 amperes available for $60 each. Its house publication the Monogram carried an article by Lyle Morton in January 1958 entitled New Semiconductor Horizons Seen as Success Marks Development Effort.
Significant technologies were needed to make a successful SCR. Good forward conduction depends on very high purity silicon to prevent recombination of minority carriers and consequently conduction losses. This was sourced by Hubbard Horn, a semiconductor materials specialist working at Robert Hall’s Schenectady laboratory. John Harden at the General Electric Engineering Laboratory, Schenectady supported the work after the end of 1957. [Owen 2007] Nick Holonyak at Syracuse provided theoretical support for the team.
Picture Right: Zone melting process for the production of high purity silicon is observed by Dr Hubbard Horn [Electronics 1955]
Production SCR were made from wafers of N-type silicon around 8.5 mils thick and inititially gallium diffused to a depth of 2.2 mils on both sides to form the anode and the base layer. The wafer was then masked on both sides by silicon dioxide and etched to permit formation of the cathode by phosphorus diffusion to a depth of around 1.1 mils. [Gentry 1963]
The SCR became a huge success for General Electric. It was reported in the business press by Business Week in their December 28th edition headlined New way to Change AC to DC. Commercial SCR were on the market in early 1958 [Ward 2005] and Gutzwiller was responsible for their technical and promotional support. The launch of the SCR coincided with his publication Solid-State Thyratron Switches Kilowatts Electronics March 28, 1958. A General Electric advertisement run in 1958 described it as “The revolutionary new controlled rectifier. Does the job of thyratron, a relay, a switch, a circuit breaker, a magnetic amplifier…its uses are limited only by the imagination.” The advertisement states that devices that will operate up to 300 volts and 16 amperes are available.
Gutzwiller writes: “I was besieged by phone calls from industrial businesses all over the country, even from outside the United States, asking for more detailed technical information. I started writing magazine articles for the technical journals and application notes on the SCR. I assembled a number of these original application notes and edited them into a 50 page GE publication which we called the SCR Manual”. [Ward 2005]
The first of many editions of the General Electric Controlled Rectifier Manual was published in 1960.
The SCR is a controlled half wave rectifier. To obtain full wave rectification two SCRs are needed with more complex gates control circuitry. It was clear that full wave rectification in a single package was desirable and potentially possible given even the modest state of development of masking technologies of the late 1950s. Such a device became known as the Triac enabling full wave rectification with power controlled with a single external gate connection.
The Triac evolved in three inventive steps:
(1) The shorted emitter design by Aldrich and Holonyak (1958)
(2) The remote gate by Gentry and Tuft (1963)
(3) The Triac by Gutzwiller (1963)
Holonyak recalls that in the Spring of 1958 at a meeting in Syracuse with Ray York, Richard Aldrich and Finis Gentry he and Aldrich were asked to develop a full wave controllable switch which could operate down to low forward voltages. After the meeting Holonyak and Aldrich stayed on and devised a solution. Their prototype was
made from a parent N-type wafer in a single diffusion step using gallium and phosphorus simultaneously. The N wafer was oxidized and then selectively etched as shown. Etch resistance was achieved crudely: Holonyak and Aldrich used Apiezon black wax pulled into threads, applied it to the oxide layer and etched off the oxide between the threads. On diffusion gallium penetrates the masking creating a P-type layer. Where there is no masking an N-P layer is formed due to the slower rate of diffusion of the phosphorus leading to a surface N-type region over a deeper P-type region. [Holonyak 2001]
In the subsequent patent numerous geometries with up to 3 control electrodes were proposed. The shorted emitter gave General Electric a pioneering position on the Diac and Triac.
But General Electric patent attorneys were slow to respond filing some 18 months after the original invention. [Aldrich 1959] The corporation was again faced with a patent interference action: this time by Fairchild claiming priority for work by Robert Noyce which Fairchild lost.
In summary: “Aldrich and Holonyak developed and described several bidirectional p-n-p-n devices having two, three, and more terminals. These devices utilized the “shorted emitter,” an innovation of theirs which not only made single-chip bidirectional p-n-p-n devices possible, but also led to improvements in the characteristics of unidirectional devices (such as SCR’s).” [Gentry 1965]
The original SCR design was triggered from an electrode on one of its internal bases. The remote gate put the trigger adjacent to the emitter on the surface. It was invented by Gentry and Tuft and patented in 1963. [Gentry 1963] Whereas an SCR of the design shown previously was turned on by a gate voltage positive with respect to the cathode, the structure shown here was turned on by a negative voltage with respect to the anode.
The Triac is a bidirectional device equivalent to two SCR connected in anti-parallel with connected gates. The Triac was invented by Gutzwiller:
“One late night, a combination of several of the new developments occurred to me as a possible answer: technically speaking, a five-layer NPNPN power semiconductor with shorted emitters and a remote gate. I brought my speculative sketch in to Finis [Gentry] the next day and explained it. He said, “You know, it just might work!” In a few days, his laboratory people had constructed a device using this fabrication. I took it back into my applications laboratory, hooked it up with a capacitor and a potentiometer, and it worked! Three components (later a fourth component, a trigger diac was added) controlled both halves of the A-C cycle from full-off to full-on. I promptly christened my new device the “Triac” (tri for three leads, and ac for alternating current).” [Ward 2005]
In his patent application Gutzwiller points out that conceptually his device can be split into two equal parts by a vertical line. The left hand side is a conventional SCR. The right hand side is the complementary remote gate SCR. Combined they exploit the shorted emitter structure with a conventional and remote gate. For a three terminal device shown here, the gates may be connected creating a further shorted junction. [Gutzwiller 1963]
The first commercial Triacs were the SC40 and SC45, rated 6 amperes and 10 amperes respectively. Gutzwiller recalls “Our first major customers for the Triac were manufacturers of theater lighting dimmers. Before that, the backstages had large off-curtain rheostats that took a lot of space and generated lots of heat. Other early Triac users made electrical heating controllers and home lamp dimmers.” [Gutzwiller 2008]
For his invention of the Triac and earlier work in semiconductors Gutzwiller was awarded the prestigious GE Cordiner Award “for outstanding contributions” to the Company.
“Why did Bell receive all the accolades and credit while GE received very little?” asks Sheckler from the perspective of 2004.
General Electric commercialized heavy duty germanium rectifiers when the rest of the world had only small signal devices. They commercialized the alloy junction transistor…the first really practical transistor. They put the silicon controlled rectifier on the map. And they developed the first visible light LED and the laser diode.
This history shows that while General Electric had some highly talented and committed researchers there was no corporate vision that drove their semiconductor research. In the absence of a strategy management did not recognise success. When General Electric considered a strategy it was more likely to be driven by major product innovation: they did not need to invest in components.
Bell had vision. Kelly launched the quest for the solid state switch in 1945. We can be sure that no one at Bell thought the point contact transistor was the solution but it was a well celebrated milestone. General Electric had the first practical transistor suited to mass production. But there are no public relations in coming second.
A direct answer to Sheckler is: “because General Electric did not seek the accolades and worse, did not act aggressively to protect its commercial position.” At the time, General Electric was not in a position to claim priority on the junction transistor because it was a day behind RCA. There were no Public Relations of the kind that Bell exploited on the discovery of the point contact transistor.
And General Electric has not changed its view of history notwithstanding the importance of semiconductors to modern technology. Their corporate website celebrates the diversified achievements of that corporation without a mention of semiconductors in the 1950s. General Electric had too much to celebrate and in the decade commencing 1946: they could claim two breakthroughs in jet engine technology, two new resins, new electric appliances and synthetic diamonds! One slot remains for that decade…and the winner is: a miniature relay. Not solid state but rugged and mechanical! In the following decade the laser diode is recognized. [General Electric 2008]
The author gratefully acknowledges the helpful comments and advice from Bill Gutzwiller and the work of Jack Ward, the IEEE and the American Institute of Physics for the recordings of the oral histories referenced below.
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