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Fig. I. Germanium resistance thermometer as it appears wilk the ouler case removed.

Novel

THE usofulncss of semiconductor ma-tcrials, such as Silicon and germanium. in the field of transistors and diodes is well established. It might be reasoned that materials of such widc usefulness in one area could also find applications in other areas and we find this to be the case. Some of the properties of semiconductor materials, such as extreme stability, temperaturę sensitivity. and sensitivity to magnetic fields. have l>ecn exploited and several devices are now under active develop-ment in various laboratories.

Temperafure-Sensifive Resisfor

Singlc-crystal Silicon has a very high positive temperaturę coefficiont. that is. its resistance inereases very rapidly as its temperaturę rises. This character-istic has been applied by Texus Instruments, hic. in developing a device which has been tradenamed the ^,,Sen-sistor.” This device has a positive temperaturę coefTicient of resistance of 0.7# per degree C.. which means that the resistance inereases 0.7# for every degree the temperaturę rises.

“Sensistors” are asailable with 14-watt and %-watt ratings and a wide variety of resistances. For the sake of comparison and uniformity. the resistance is usually given at 25° C, which is normal room temperaturę. The actu-al resistance at any other temperaturę can then be computed from a chart similar to Fig. 5. which gives the resistance at a given temperaturę in terms of the value at 25°C multiplied by an appropriate factor.

As an example. suppose we have a nominał 100-ohm ‘Sensistor” and would like to know its resistance at 50°C. Looking at the 50° point on the chart, we find that the multiplying factor is about 1.18. Therefore, the resistance will be 100 x 1.18 or 118 ohms. Similarly, we can compute the resist-

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Some inłeresłing new and unusual semiconducłor producłs along

wiłh a few of łheir applicałions.

Fig. 2. Pair oi probe “Sensistors."

C« BAiOCEs

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Fig. 3. Cross-section drawing showing construction ol germanium resistance unit.

Fig. 4. Germanium resistance thermometer compared in site with common pin.

Devices / ^ harold s. renne

Fig. 5. Ambient temperaturę correction lactor curres lor the “Sensistors" shown. The lactor Irom this cunre multiplied by the resistance at a temperaturę ol 2S* C

will give the no-load resistance ol the units at the desired ambient temperaturę.

AMBIENT TEMPERATURĘ CORRECTION FACTOR TM 1/4 ANO TC 1/0

i _

i-. .

-60    -40    -20    0    20    40    60    80    100    120    140 IfO

AMBIENT TEMPERATURĘ-°C

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