PRESENT STATUS OF TRANSISTOR DEVELOPMENT 



415 



Fig. 3 — The M1689 point-contact transistor is typical of those used iu minia- 

 ture packaged circuit functions. 



emitter region into the n-type material. These holes are swept along to 

 the collector under the influence of the field initially set up by the 

 original collector electron current — thus adding a controlled increment 

 of collector current. Because of their positive charge these holes can 

 lower the potential barrier to electron flow from collector to base and 

 thus allow several electrons to flow in the collector circuit for every 

 hole entering the collector barrier region. This ratio of collector current 

 change to emitter current change for fixed collector voltage is called 

 alpha, the current gain. In point-contact transistors alpha may be 

 larger than unit3^ Since the collector current flows through a high im- 

 pedance when the emitter current is injected through a low impedance, 

 voltage amplification is obtained as well. 



Some of the new transistors are point-contact transistors similar in 

 physical appearance to the type A. However, their electrical character- 

 istics will be shown to be significantly improved not over the old type A 

 only insofar as reproducibility and reliability are concerned, but also 

 as to range of performance. 



For use in miniature packaged circuit functions, the point contact 

 transistor has been miniaturized to contain only its bare essentials. Fig. 

 3 is a photograph of a so-called "bead" transistor (compared to a paper 

 clip for size) and several of the current development types are being 

 made in this form. 



In Fig. 4 is shown the family of static characteristics representative 

 of the Ml 689 bead type transistor. Note in particular the collector 



