Electronic Design

Switching, Frequency Barriers Fall

Solid-state devices for faster switching or higher frequency operation were prominent among developments unveiled at the Electron Devices Meeting in Washington, Oct. 26-28. New advances in microwave, data-handling, and energy-source devices also were introduced to the industry.

Some of the more important developments for the design engineer were:

  • Producible planar-silicon (Si) transistors, capable of operating to over 2 Gc, and of switching with less than 2-nsec propagation-delay time.
  • Mesa-type switching transistors for switching rates up to 100 mc in saturated circuits.
  • Gallium-arsenide (GaAs) solar cells with efficiencies up to 13% \[see photo\].
  • A multiposition core driver using electron-beam-switched Si diodes in place of transistors.
  • A new type of 1.5-megawatt magnetron said to have four times the frequency stability of present types.
  • A microspot CRT capable of displaying 92 million picture elements on a 5-in. face.
  • Gallium-antimonide (GaSb) tunnel diodes with fmax up to 10 Gc, said to have half the shot noise constant of equivalent germanium devices.
  • Cryosistor—a three-terminal field-effect-controlled fast germanium switch for operation at liquid-helium temperatures.

Gigacycle Si transistors, reported by Fairchild Semiconductor Corp., are designed so that areas where lead can be attached are larger than the actual active areas. This is said to make production simpler and is expected to result in devices cheaper than many existing types that have poorer characteristics. Measurements at 1 Gc with 625 mW into one of these devices showed 50 mW out, according to Fairchild. The 2-msec time was obtained by dividing total delay time through an 11-stage ring counter by 11, Fairchild reported.

Germanium epitaxial maser-type switches, reported by Texas Instruments Inc., are said to have a unity-gain frequency of 1.5 to 4 Gc.

GaAs solar cells, developed by RCA's Semiconductor Div., are said to have considerably higher radiation tolerance than Si cells. Efficiency is said to decrease less with temperature for GaAs than for Si types. An in-flight comparison of these devices with Si cells will be made next year on the Relay communications satellite, which will be orbited in the Van Allen radiation belts. The chief disadvantages of these devices at present is the expense in obtaining gallium and the difficulty in producing suitable crystals, according to an RCA spokesman.

High-speed driving of memory core arrays has been achieved using an array of Si-diode junctions by switching with an electron beam, Dr. A.V. Brown of IBM Corp. reported. Higher output currents and shorter switching times than those obtained with present transistors drivers were achieved, he said.

A new type of magnetron using an improved anode structure, reported by S-F-D Laboratories Inc., was said to have achieved X-band operation at over 50% efficiency, delivering 1.5-megawatt peak and 750-W average power. The device is called the CEM Coaxial Magnetron. (Electronic Design Nov. 8, 1961, p. 4)

See associated figure

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