Magazine article Science News

Raising a Crop of Transistors

Magazine article Science News

Raising a Crop of Transistors

Article excerpt

Raising a crop of transistors

The latest development in theworld of miscroelectronics is almost as magical as pulling a rabbit out of a hat and potentially a lot more useful. A team of researchers at GTE Laboratories in Waltham, Mass., has succeeded in "growing' the basic components of a transistor. In effect, they let nature do the work of creating a silicon structure that can easily be turned into an electronic device. The technique circumvents much of the costly, delicate, fault-prone processing normally used to construct integrated circuits on the surfaces of silicon wafers. And, as a bonus, it produces transistors that can survive large electrical currents.

The GTE process, developed by Brian M. Ditchek, starts witha mixture of molten silicon and tantalum metal. In the liquid state, both ingredients mix completely, with tantalum spread evenly throughout the silicon. However, when the mixture is cooled and starts to solidify, it separates into two components. Each component seeks its own kind, and patches of the compound tantalum disilicide form within a silicon matrix.

To capture this structure in a useful crystal form, theresearchers lower a silicon "seed' rod into the molten mixture just before it begins to solidify. When this rod is slowly drawn out of the liquid, solidification occurs at the interface between the rod and the liquid. Tantalum disilicide appears as numerous microscopic threads that run the length of the resulting crystal. The rest of the material has the orderly structure of a single crystal of silicon. The tantalum threads, about 1 micron in diameter, are, on the average, 6 microns apart.

The cylindrical crystal is then sliced into wafers, about 25millimeters in diameter and 1 millimeter thick. Each wafer is converted into an array of transistors by laying down a set of target-shaped electrical contacts on the wafer's surface (see photograph). …

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