How the first transistor worked
Dalia: Bienvenidos y bienvenidas a “Inglés para ingenieros”, un programa de IEEE sección Ecuador. En cada episodio podrás practicar inglés a tu propio ritmo, escuchando y leyendo artículos de revistas reconocidas en ciencia y tecnología. En cada capítulo, yo te acompañaré, para asegurarme de que entiendas todo.
En el otoño de 1947, John Bardeen y Walter Brattain construyeron en AT&T Bell Telephone Laboratories el primer transistor de contacto puntual utilizando germanio, plástico y láminas de oro. Este dispositivo se utilizó en dispositivos como audífonos, ruteadores telefónicos o televisores experimentales. A pesar de que el diseño de William Shockley del transistor bipolar de unión (BJT) reemplazó eventualmente al transistor de contacto puntual, este último siguió en producción hasta 1966 debido a su velocidad superior.
Este Podcast es realizado a partir del artículo How the first transistor worked de la revista IEEE Spectrum. Iniciamos.
Jenny: Physicists attempted to create a successor to the vacuum-tube triode, which had revolutionized long-distance telephony, movie sound, and commercial radio. Vacuum tubes were unreliable and required a lot of power. Scientists aimed to develop a three-terminal semiconductor device that could amplify low-current signals by controlling the flow of larger currents through it, using the field effect, which was already known in diodes and semiconductors research.
Dalia: Durante más de dos décadas, construir un dispositivo como un transistor fue un desafío para los físicos más destacados. Aunque las patentes de dispositivos similares a los transistores se presentaron en 1925, el primer transistor funcional se construyó en 1947 en los laboratorios Bell.
Jenny: But building such a device had proved an insurmountable challenge to some of the world’s top physicists for more than two decades. Patents for transistor-like devices had been filed starting in 1925, but the first recorded instance of a working transistor was the legendary point-contact device built at AT&T Bell Telephone Laboratories in the fall of 1947.
Dalia: John Bardeen y Walter Brattain desarrollaron un dispositivo de germanio, plástico y papel de aluminio, conocido como transistor de contacto puntual, para amplificar señales. Sin embargo, encontraron un problema con una capa superficial de electrones que impedía que la corriente fluyera.
Jenny: It was an ungainly looking assemblage of germanium, plastic, and gold foil, all topped by a squiggly spring. Its inventors were John Bardeen and Walter Brattain. Both were working under William Shockley, a relationship that would later prove contentious. In November 1947, Bardeen and Brattain were stymied by a simple problem. In the germanium semiconductor they were using, a surface layer of electrons seemed to be blocking an applied electric field, preventing it from penetrating the semiconductor and modulating the flow of current. No modulation, no signal amplification.
Dalia: En 1947, los inventores Bardeen y Brattain encontraron una solución para construir un transistor de punto de contacto utilizando láminas de oro y germanio tratado para producir una delgada capa superficial con carga positiva.
Jenny: Sometime late in 1947 they hit on a solution. It featured two pieces of barely separated gold foil gently pushed by that squiggly spring into the surface of a small slab of germanium. So it seems appropriate somehow that the most comprehensive explanation of the point-contact transistor.
Dalia: El transistor de punto de contacto fue construido con una pequeña pieza de germanio tipo n, que se trató para producir una capa de superficie muy delgada que tenía un exceso de cargas positivas, conocidas como “agujeros”. Se agregó un electrodo conectado a tierra a la base del transistor y dos tiras de papel de aluminio formaron los electrodos del emisor y el colector.
Jenny: The point-contact transistor was built around a thumb-size slab of n-type germanium, which has an excess of negatively charged electrons. This slab was treated to produce a very thin surface layer that was p-type, meaning it had an excess of positive charges. These positive charges are known as holes. They are actually localized deficiencies of electrons that move among the atoms of the semiconductor very much as a real particle would. An electrically grounded electrode was attached to the bottom of this slab, creating the base of the transistor. The two strips of gold foil touching the surface formed two more electrodes, known as the emitter and the collector.
Dalia: Esa es la configuración. Se aplica un pequeño voltaje positivo al emisor y un voltaje negativo mayor al colector en relación a la base conectada a tierra. La interfaz entre la capa p y el sustrato tipo n crea una barrera que permite que la corriente fluya en una sola dirección, lo que permite que la corriente fluya desde el emisor al colector, pero no al revés.
Jenny: That’s the setup. In operation, a small positive voltage—just a fraction of a volt—is applied to the emitter, while a much larger negative voltage—4 to 40 volts—is applied to the collector, all with reference to the grounded base. The interface between the p-type layer and the n-type slab created a junction just like the one found in a diode: Essentially, the junction is a barrier that allows current to flow easily in only one direction, toward lower voltage. So current could flow from the positive emitter across the barrier, while no current could flow across that barrier into the collector.
Dalia: El día decisivo fue el 16 de diciembre de 1947, cuando Brattain tuvo la idea de usar un triángulo de plástico sujeto por una tira de papel de aluminio, con una pequeña hendidura que separaba los contactos del emisor y el colector. Esta configuración proporcionó una ganancia de potencia fiable, y la pareja supo entonces que habían tenido éxito. En el coche compartido camino a casa esa noche, Brattain dijo a sus compañeros que acababa de hacer “el experimento más importante que haría en su vida” y les hizo jurar que guardaran el secreto.
Jenny: Ungainly and fragile though it was, it was a semiconductor amplifier, and its progeny would change the world. And its inventors knew it. The fateful day was 16 December 1947, when Brattain hit on the idea of using a plastic triangle belted by a strip of gold foil, with that tiny slit separating the emitter and collector contacts. This configuration gave reliable power gain, and the duo knew then that they had succeeded. In his carpool home that night, Brattain told his companions he’d just done “the most important experiment that I’d ever do in my life” and swore them to secrecy. The taciturn Bardeen, too, couldn’t resist sharing the news. As his wife, Jane, prepared dinner that night, he reportedly said, simply, “We discovered something today.” With their children scampering around the kitchen, she responded, “That’s nice, dear.”
Dalia: Los transistores de punto de contacto se utilizaron en audífonos, osciladores, equipos de enrutamiento telefónico, en un receptor de televisión experimental construido en RCA y en el Tradic, el primer computador digital a bordo.
Jenny: Point-contact transistors were used in hearing aids, oscillators, telephone-routing gear, in an experimental TV receiver built at RCA, and in the Tradic, the first airborne digital computer, among other systems. In fact, point-contact transistors remained in production until 1966, in part due to their superior speed compared with the alternatives.
Dalia: Por otra parte, el físico William Shockley diseñó en enero de 1948 un nuevo tipo de transistor, conocido como BJT, que reemplazaría eventualmente al transistor de punto de contacto y se mantendría como el transistor dominante hasta finales de la década de 1970. Esto se produjo después de que Shockley quedara insatisfecho con su papel en el equipo que había creado el transistor de punto de contacto y se fuera de los laboratorios Bell.
Jenny: At the end of December, barely two weeks after the initial success of the point-contact transistor, Shockley traveled to Chicago for the annual meeting of the American Physical Society. On New Year’s Eve, holed up in his hotel room and fueled by a potent mix of jealousy and indignation, he began designing a transistor of his own. In three days he scribbled some 30 pages of notes. By the end of the month, he had the basic design for what would become known as the bipolar junction transistor, or BJT, which would eventually supersede the point-contact transistor and reign as the dominant transistor until the late 1970s.
Dalia: Luego Shockley, se convirtió en profesor en Stanford. Además, Bardeen dejó Bell Labs en 1951 para convertirse en profesor en la Universidad de Illinois y ganó un segundo Premio Nobel de Física por una teoría de la superconductividad. Mientras que Brattain se quedó en Bell Labs hasta 1967 y luego se unió a la facultad de Whitman College en Washington.
Jenny: Later in his life, Shockley became a professor at Stanford and began promulgating ungrounded and unhinged theories about race, genetics, and intelligence. In 1951 Bardeen left Bell Labs to become a professor at the University of Illinois at Urbana-Champaign, where he won a second Nobel Prize for physics, for a theory of superconductivity. (He is the only person to have won two Nobel Prizes in physics.) Brattain stayed at Bell Labs until 1967, when he joined the faculty at Whitman College, in Walla Walla, Wash.
Dalia: Gracias por haber escuchado inglés para ingenieros. Un programa de IEEE sección Ecuador que tiene como objetivo mejorar las habilidades del idioma inglés en nuestros miembros y el público en general.
Este episodio fue producido por Ronny Cabrera, voluntario de IEEE que vive en Loja, Ecuador.
Thank you for listening!
