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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



course, larger than for lower resistance films; but in the very high resistance 

 range made accessible through use of borocarbon films, the temperature 

 coefficient of resistance is relatively less important. 



The data of Fig. 24 and Fig. 25 suggest that the maximum usable film 

 resistance for a given material of constant specific resistance may be deter- 



-10 -20 -40-60-100-200-400 -1000 -4000-10,000 



TEMPERATURE COEFFICIENT OF RESISTANCE IN PARTS 



PER MILLION PER DEGREE CENTIGRADE 



Fig. 25 — Dependence of the temperature coefficients of pyrolytic films of carbon and 

 borocarbon on film resistance. 



mined by purely geometrical factors. Films which are thinner than a given 

 limiting value become increasingly less coherent, or less continuous and 

 uniform in thickness. The result of this may be that contacts between 

 "patches" of the conducting material become increasingly important, the 

 spreading resistance at these contacts being more temperature sensitive 

 and giving rise to the observed increase in temperature coefficient of re- 



