The surface-barrier transistor is a type of transistor developed by Philco in 1953 as an improvement to the alloy-junction transistor and the earlier point-contact transistor. Like the modern Schottky transistor, it offered much higher speed than earlier transistors and used Metal-semiconductor junctions (instead of semiconductor–semiconductor junctions), but unlike the schottky transistor, both junctions were metal–semiconductor junctions.
Philco used a patented process of applying two tiny electrochemical jet streams of liquid indium sulfate (electrolyte solution) on opposite sides of a thin strip of N-type germanium base material. This process would etch away and form circular well depressions on each side of the N-type germanium base material, until the germanium base material was ultra thin and having a thickness of approximately a few ten-thousandths of an inch. After the etching process was finished, the polarity applied to the electrolyte was reversed, resulting in metallic indium being electroplated into these etched circular well depressions, forming the transistor's emitter and collector electrodes. The Philco surface-barrier transistor was the world's first high-frequency transistor to be developed and was capable of obtaining frequencies up to 60 MHz.
The world's first all-transistor car radio, was developed and produced by Chrysler and Philco in 1955. Chrysler offered this all-transistor car radio, Mopar model 914HR, available as an "option" in the fall of 1955, for its new line of 1956 Chrysler and Imperial cars. Philco was the manufacturer of these all-transistor car radios for the Chrysler Corporation and had also used its surface-barrier transistors in the radio's circuitry design.
Commercial Manufacturing License Agreements
Starting in 1955, Philco had decided to sell commercial manufacturing license agreements with other large electronic semiconductor companies, which allowed them the right to produce and sell its high-frequency surface-barrier transistors. Sprague Electric Company was one of the first companies to purchase a license agreement from Philco in late 1955 and started to manufacture the surface-barrier transistors under its Sprague name, in early 1956. Another company to purchase a license agreement from Philco in early 1957, was Semiconductors Limited, a division of the British-based Plessey Company.
In 1956, Philco had developed a "improved" higher-speed version of its original surface-barrier transistor, which was used in military applications and was called the surface-barrier diffused-base transistor (SBDT). Philco had used surface diffusion of a gaseous form of phosphorus atom particles, to penetrate the surface of the intrinsic semiconductor base material. The Philco SBDT transistor was capable of operating in the UHF range. Philco's SBDT improved surface-barrier transistor, was used in the early prototype design of the 10-milliwatt Minitrack satellite transistorized (radio beacon) transmitter, for the United States Navy Vanguard I satellite project program.
On January 31, 1958, the United States first artificial Earth satellite was launched at Cape Canaveral in Florida, which was called Explorer 1, and was developed by the California Institute of Technology Jet Propulsion Laboratory (JPL). The Explorer 1 satellite's payload, consisted of a low-power Microlock transistorized (radio beacon) 108.00 MHz transmitter, which was used for tracking and telemetry, and had consisted of a Philco high-frequency surface-barrier transistor in its original circuitry designs.
The Philco high-frequency surface-barrier transistor was also the first transistor that was suitable for high-speed computers. Philco developed and produced a miniature transistorized computer brain called the "Transac" (models C-1000 and C-1100), for the Navy's jet fighter planes in 1955. "Transac" stood for "Transistor Automatic Computer." They used Philco's high-frequency surface-barriers transistors. 
In 1955, MIT's Lincoln Laboratory researchers started to design and build the first transistorized general purpose programmable 18-bit computer, called the "TX-0." It was an experimental computer, used to test transistor logic circuitry and large capacity magnetic-core memory, and was completed and operational in April 1956. The TX-0 computer's circuitry consisted of 3600 transistors and used the Philco high-frequency L-5122 surface-barrier transistor in its design. MIT's Lincoln Laboratory commenced the design and construction of a large-scale transistorized programmable 36-bit general purpose computer in 1957, which was called the "TX-2." It was operational in 1958, and utilized 22,000 transistors that included Philco high-frequency surface-barrier transistors. 
In June 1955, Philco was awarded a contract with the National Security Agency to build a transistorized scientific computer, which was named the "SOLO" and used high-frequency surface-barrier transistors. The SOLO transistorized computer was the world's first completely transistorized computer, and was later commercially marketed by Philco as the Transac S-1000 scientific computer model. Also, later in 1955, Philco contracted with the United States Navy David Taylor Basin Research Unit to build a larger-scale fully transistorized computer using its high-frequency surface-barrier transistor technology, named the CPXQ model. It was later commercially marketed by Philco as the Transac S-2000 electronic data processing computer model.
During 1955-56, Ferranti-Canada was in charge of miniaturizing the Royal Canadian Navy's DATAR (Digital Automatic Tracking and Resolving) seaborne tactical data defense computer. Ferranti-Canada had used Philco's SB-100 surface barrier transistors in its experimental transistorized prototype circuitry designs.
In late 1956, Ferranti-Canada had built the world's first experimental transistorized computer mail-sorting system (Route Reference Computer). It was delivered to the Canadian Postal System in January 1957 and was capable of sorting 36,000 letters an hour. This experimental computerized mail-sorter had used the Philco surface-barrier (SB-100) transistors in its circuitry design.
Philco's Transac models S-1000 scientific computer and S-2000 electronic data processing computer were the world's first commercially produced large-scale all-transistor computers, which were introduced in 1957 and used these high-frequency surface-barrier transistors in its circuitry designs.
In June 1957, the Burroughs Corporation transistorized ground guidance computer (AN/GSQ-33) was built and installed at Cape Canaveral missile test range, for the United States Air Force's Atlas intercontinental ballistic missile defense system (ICBM). This transistorized ground guidance Atlas computer system was designed by Burroughs engineer Issac Auerbach and used Philco's high-frequency surface-barrier transistors in its circuitry design.
In 1956-57, Remington Rand St. Paul Univac-division of Sperry Rand Corporation, had designed and built a transistorized "test" computer for the United States Air Force, which was called "TRANSTEC". It was designed by Univac's St. Paul engineer Seymour Cray, and used the Philco's high-frequency surface-barrier transistors in its computer's circuitry design. This was Univac's first computer designed with transistors and was used to test transistor logic circuits and also its speed and reliability, compared to magnetic amplifier (MAGSTEC) and vacuum tube circuit computers. After Univac had demonstrated the TRANSTEC computer to the United States Air Force, it was awarded a contract to build a transistorized ground guidance (Athena) ICBM defense computer.
In 1957, Remington Rand St. Paul Univac-division of Sperry Rand Corporation, had built a transistorized ground guidance Athena computer, for the United States Air Force's Titan 1 intercontinental ballistic missile defense system (ICBM). It was designed by Univac's St. Paul engineer Seymour Cray, and used the Philco's high-frequency surface-barrier transistors in its computer's circuitry design.
In March 1958, Remington Rand St. Paul Univac-division of Sperry Rand Corporation, had built and delivered a transistorized 30-bit AN/USQ-17 computer, for the United States Navy Tactical Data System (NTDS). It was designed by Univac's St. Paul engineer Seymour Cray starting on January 1957, and used the Philco's high-frequency surface-barrier transistors in its computer's circuitry design. 
Philco's high-frequency surface-barrier transistors was also used in the circuitry design of the first transistorized supercomputer. It was called the UNIVAC LARC (Livermore Advanced Research Computer) that was built by Remington Rand Philadelphia Univac-division of Sperry Rand Corporation and was delivered to the Atomic Energy Commission-University of California's Lawrence Radiation Laboratory in May 1960. A second Univac LARC transistorized supercomputer, using Philco's surface-barrier transistor technology, was contracted and delivered in October 1960 to the United States Navy-David Taylor Basin Research Unit.
The surface-barrier transistor became obsolete in the early 1960s with the development of the planar diffusion transistor.
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