Alloy transistor

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The term alloy transistor denotes a form of manufacture of a flat transistor , a special form of the bipolar transistor . It was in 1952 by General Electric as an improvement of the drawn transistor (Engl. Grown junction transistor ) developed.

Manufacturing

Scheme of a pnp alloy transistor made of germanium

A pnp alloy transistor is manufactured in three steps. In the first step, a pill (small ball) made of trivalent metal is applied to one side of an n-doped semiconductor wafer (the substrate, usually germanium ). In the second step, the substrate with the emitter and collector pills applied is exposed to a temperature above the melting temperature of the metal but below that of the semiconductor. An alloy forms at the interface between substrate and metal . The size of this alloy layer increases with the process time and that of the transistor base between them decreases with time. The temperature process is ended when the base is thin enough, that is, the transistor has the desired electrical characteristics. The basic contact is established in the last production step.

This technique was mainly used in the manufacture of discrete germanium transistors. Among other things, indium was used as an alloy material. In addition, alloy transistors were made from the less common semiconductor material silicon and aluminum as pill material. Production was more complicated due to the vastly different expansion coefficients .

The alloy principle can also be used to manufacture npn transistors. The doping material used here is pentavalent materials such as arsenic or antimony, which are incorporated into a “neutral” pill material such as lead. The doping with a pentavalent material causes the tetravalent semiconductors germanium and silicon to form n-doped regions in an originally p-doped semiconductor substrate.


Similar transistor types

Further developments of the alloy transistor are the surface barrier transistor , e.g. For example, the micro-alloying diffusion transistor (engl. Micro-alloy diffused transistor , MADT), and the diffusion transistor , z. B. the PAD transistor (English. Post-alloy diffused transistor , PADT).

The manufacturing principle of the alloy transistors can also be used for semiconductor substrates with a gradient doping concentration. The transistors produced in this way are called drift transistors .

With the introduction of the planar transistor , in which diffusion or implantation processes are used to produce the emitter and collector regions, alloy transistors disappeared relatively quickly in the early 1960s. The main reasons for this were the possibility of mass production, i.e. several transistors on one substrate, which led to the development of integrated circuits (ICs), the associated lower production costs and the rapid improvement in electrical properties.

Individual evidence

  1. ↑ Martin Kulp: Tube and transistor circuits: transistor technology . Vandenhoeck & Ruprecht, 1970, p. 454 .
  2. ^ Ernest Braun: Revolution in Miniature: The History and Impact of Semiconductor Electronics . Cambridge University Press, 1982, ISBN 0-521-28903-3 , pp. 1955 .
  3. ↑ a b c d e S. W. Amos, Mike James: Principles of Transistor Circuits . 9th edition. Newnes, 2000, ISBN 0-08-052320-X , pp. 371-373 .
  4. ^ SW Amos, Roger Amos: Newnes Dictionary of Electronics . Newnes, 2002, ISBN 0-08-052405-2 , pp. 296 .
  5. ↑ Werner Bindmann: German Dictionary of Microelectronics: English-German, German-English . Psychology Press, 1999, ISBN 0-415-17340-X .