Electronic Design

Ultra-Fast Epitaxials In Production

Epitaxial silicon transistors, offering such advantages as faster switching speed, saturation resistance relatively independent of temperature, and low collector capacitance compared to conventionally fabricated devices, are now available off-the-shelf in unlimited quantities. Housed in TO-18 packages, the 2N743 and 2N744 types, announced by Texas Instruments Incorporated, Dallas, have been optimized for switching applications.

Compared with a conventional-type 2N706 silicon switching transistor, the epitaxial 2N743 is more than twice as fast at 10 ma and four times faster at 100 ma; cost-wise the 2N743 is about ten percent higher than the 2N706. In a saturated mode, total switching time (typical) for the 2N743 is 26 nsec at 10 ma and 24 nsec at 100 ma; maximum switching time is 40 nsec at 10 ma and 52 nsec at 100 ma. For the 2N744, typical switching time is 27 nsec at 10 ma and 29 nsec at 100 ma; maximum switching time is 40 nsec at 10 ma and 57 nsec at 100 ma. Storage time is 14 nsec (max) for the 2N743 and 18 nsec (max) for the 2N744.

The maximum saturation voltage of the 2N743 is essentially constant at 1 V from -55° to +170°C. VCE of the 2N706 at 100 ma varies from 2.2 V at 25°C to 4 V at 170°C. The low saturation resistance of the epitaxial devices makes them suitable for switching tasks previously requiring medium-power transistors of conventional structure.

The forward current ratio, hFE, for the 2N743 is specified as 10 (min) at 1 and 100 ma and 20 (min) to 60 (max) at 10 ma. Values for the 2N744 are 20 (min) at 1 and 100 ma and 40 (min) to 120 (max) at 10 ma. Typical capacitance values for both types are 3.5 pf at 5 V and ft (typical) is rated at 400 mc. In quantities of 100 to 999, the 2N743 is priced at $13.95, the 2N744 at $15.35. (Electronic Design, Feb. 15, 1961, p. 74)

With epitaxial transistors coming on strong, this announcement from Texas Instruments (TI) merited the magazine's cover article. Moreover, the epitaxial process was a step forward in producing transistors with consistent characteristics. Although the prices quoted, $13.95 and $15.35, might seem high by today's standards, volume manufacturing soon took care of those types of problems. The next step was the learning-curve effect, which TI perfected to a tee. Prices declined steadily, and usually steeply, as the number of produced devices increased over time.

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