,^60 



BELL SYSTEM TECIIMCM. JOl RXAL 



The delay feature discussed in connection with I*"igs. 1 and 8 indicates 

 interesting possibihties of using germanium filaments as delay or storage 

 elements. 



5. 'I'lri-, 'rifi;()Kv OF iiik I'li. \.\ii;ntakv Tkansistok 



In Fig. 9 we show a transistor with a I'llamentary structure."* Modula- 

 tion is achieved in this case by injecting holes at the emitter point which 

 flow to the right and modulate the resistance in the outi)ut branch between 

 emitter and collector. Structures of this sort can be produced by the sand- 

 blasting technique discussed in Section 2. The enlarged ends, which give the 



U 



INPUT 

 A-C 



BASE, b 

 lb 



EMITTER, € 



,, COLLECTOR, C 



'^xx'xx-x -^ x-x'xVy -. 



Jl.I 



(a) FILAMENTARY TRANSISTOR 



EMITTER, f o 



Rb 

 3ASE , b 0—\f\J\, 



VOLTAGE 

 GENERATOR 



(b) EQUIVALENT CIRCUIT 



COLLECTOR, C 



Lc,Vc 



Fig. 9 — Filamentary transistor and equivalent circuit. 



unit a dumbbell appearance, decrease the problem of making contact to the 

 unit. The large area at the left side serves the additional purpose of reducing 

 unwanted hole emission from the metal electrode and affords an opportunity 

 for any emitted holes to recombine before they enter the narrow part of 

 the unit. 



The theory of this transistor is relatively simple and most of the features 

 we shall discuss in connection with it have counterj)arts in the theory of the 

 type-A transistor. We shall discuss the case for which the injected current 

 is a small fraction of the total current in the filament. Under these conditions 

 we can use a simple linear theory. We shall show that the behavior of the 

 transistor can be gi\-en for small a-c signals 1)\- the equivalent circuit in 



