Radio age research, manufacturing, communications, broadcasting, television (1941)

Developmental junction-type transistor before and after embedment in plastic container, shown here in com- parison with pencil point. applications, however, the junction transistor promises to be as important as the point-contact type. In com- parison with point-contact transistors, the junction types have lower noise, liigher power gain, greater efficiency, and higher power-handling capabilities, but presently are more limited in frequency re.sponse. At first, the frequency response of the point-contact transistor appeared to be limited to frequencies in the neighborhood of 4 or 5 megacycles. Recently such transistors have been made to oscillate as high as 300 megacycles. Currently, the simple junction transistor has been made to amplify up to several megacycles and the limits are being rapidly raised. The power capabilities of either the point-cont.ict or the junction transistors depend largely on the rate at which heat can be removed from the active portion. There are no basic limitations imposed by the electronic principles of transistor devices which will prevent the attainment of high powers. With relatively simple special cooling means, particularly with the junction types, it is possible to design units with outputs up to a watt or more. The life expectancy of transistors is largely dependent on electrical and physical considerations. Realization of tens of thousands of hours does not .seem unlikely in normal operation. Transistors can be physically rugged. They can be made practically impervious to moisture and the elements. Resin-embedded units have withstood impact acceleration of 1,900 times gravity and centrif- ugal acceleration of 31,000 times gravity. Transistors have been immersed in water for several months, with practically no effect on their characteristics. Although high ambient temperature is now a limita- tion, developments indicate progress in lowering this barrier. No damage occurs to the transistor during storage from minus 94° F to 212° F. Operation over the wide ambient range of minus 94° F to 122° F is practical and higher ambient temperatures will be feasible if proper attention is given to heat dissipation. Vnijortnity of Characteristics Uniformity of characteristics comparable to that of the electron tube seems possible. The art of crystal growing is rapidly progressing and the uniformity of germanium has progressed to the point where various transistor characteristics such as current amplification, power gain, feedback resistance, and input and output resistance have been controlled within ± 25^7-. At present, the characteristics of high gain, low noise, greater stability, higher efficiency and higher power capabilities indicate that the junction transistor will be used principally as oscillators and amplifiers at lower frequencies. Another feature of the junction transistor is its ability to oscillate with power inputs around a millionth of a watt. It is anticipated that further development will increase the frequency limits and broaden circuit usefulness. On the other hand, the point-contact transistot may be applied to very-high-frequency ciraiits wherever noise is not a limiting factor. Another feature of the point-contact transistor is the negative resistance properties which are especially useful in counter and similar circuits. Negative resistance means that an increase in current flow decreases rather than increases the drop in voltage. Coiiniiercial Use Appears Near Estimates of the time when transistors will be avail- able in quantity for production of salable products must be somewhat speculative. Engineering of some types of transistors has reached an advanced stage. The problem of providing adequate supplies of processed germanium with proper char- acteristics at reasonable costs remains to be worked out. Also, quantity manufacturing processes, machinerj' and other facilities are yet to be developed. Limited application in special devices where cost .ind quantity are not major factors is close at hand. Wider use in quantity production, such as consumer home instruments, is dependent on the availability of processed germanium and production facilities. 8 RADIO AGE