Pulled transistor

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A solid transistor , and transistor with drawn pn junction (engl. Grown-junction transistor ) or rarely growth transistor called a is bipolar transistor in which the differently doped regions already during the manufacture of semiconductor crystal (the " crystal pulling be defined"). The drawn transistor is the original shape of a flat transistor and, after the tip transistor, one of the first practically implemented variants of a bipolar transistor.

Manufacturing

Drawn transistor ST2010, production year 1961

The following describes the production of an npn transistor according to the method proposed by Shockley in 1949 and first implemented by Morgan Sparks in 1950. It is based on the Czochralski process for the production of single crystals , but deliberately uses different impurities in the melt to create the n- and p-conducting areas required for the transistor .

In the first step, an n-doping impurity such as phosphorus is added to the melt of a semiconductor such as germanium . This foreign substance is built into the semiconductor crystal during the crystal pulling process and, in a corresponding amount, causes n-doping with the necessary / desired electrical resistance for the later collector area. After the crystal has reached a sufficient length, a p-doping substance such as boron is added to the melt . In a corresponding amount, the doping can be changed from n-conducting to p-conducting. Since the base width must be relatively small for the transistor to function, the crystal only grows very slightly in this step (approx. 30 µm). In the third step, the n-doped emitter region is drawn. To this end, a sufficient amount of a foreign substance is again added to the melt, which causes n-doping.

The ingot drawn in this way is then placed in an etchant with a doping-dependent etching rate. The different etching rates in the collector and emitter area create a "hump" and the npn area can be easily determined optically. This area is now cut out of the cylindrical ingot as a disk perpendicular to the direction of drawing and then into pins parallel to the direction of drawing (approx. 3-5 mm edge length). In this way, with ingot diameters of 1 to 2 inches, which were common at the time, several hundred transistors could be obtained from one ingot. The head ends of these pins are now coated with metal in order to contact the emitter and collector areas. Contacting the narrow transistor base is less easy because it is not visible. Their position can, however, be easily determined using an electrical measurement and contacted using a micromanipulator by wire bonding .

properties

The doping profile of a drawn transistor does not have any sharp transitions between the n and p regions. The reasons for this are the simultaneous processes of segregation and diffusion during production , which cannot be prevented. Nevertheless, its electrical properties (especially usable amperage and higher signal-to-noise ratio) were significantly better than those of the tip transistor, even if the frequency behavior was initially worse due to the rather large base width.

Application and meaning

The invention of the drawn transistor is an important milestone in the history of semiconductor electronics. This technology made it possible for the first time to manufacture larger quantities of transistors with reproducible electrical properties. This enabled serial use in electronic circuits, including for on-board devices in military aircraft, which at that time mainly used larger, heavier and less reliable electron tubes .

The first drawn transistors used germanium as a semiconductor and were marketed on a large scale in 1952 by Western Electric (M-1752 and A-1858). Drawn silicon transistors were available from Texas Instruments beginning in 1954 .

literature

  • Peter Robin Morris: A History of the World Semiconductor Industry . IET, 1990, ISBN 0-86341-227-0 , pp. 31-35 .
  • Bo Lojek: History of Semiconductor Engineering . Springer, Berlin 2007, ISBN 978-3-540-34257-1 , Grown Junction and Diffused Transistors , pp. 41 ff .

Individual evidence

  1. ↑ a b SW Amos, Mike James: Principles of Transistor Circuits . 9th edition. Newnes, 2000, ISBN 0-08-052320-X , pp. 371-373 .
  2. ^ A b c Peter Robin Morris: A History of the World Semiconductor Industry . IET, 1990, ISBN 0-86341-227-0 , pp. 31-35 .
  3. ^ W. Shockley, M. Sparks, GK Teal: pn Junction Transistors . In: Physical Review . tape 83 , no. 1 , July 1951, p. 151–162 , doi : 10.1103 / PhysRev.83.151 .
  4. ^ A b Bo Lojek: History of Semiconductor Engineering . Springer, Berlin 2007, ISBN 978-3-540-34257-1 , Grown Junction and Diffused Transistors , pp. 41 ff .