Pyrolytic Film Resistors: Carbon and Borocarbon 



By R. O. GRISDALE, A. C. PFISTER, and W. van ROOSBROECK 



(Manuscript Received Jan. 10, 1951) 



1. Introduction 



AN IDEAL resistor would possess a resistance precisely adjusted to 

 -^ ^ value and constant with time, temperature, voltage and frequency 

 under all conditions of use in the application for which it is intended. Wire- 

 wound resistors, which early references to "resistance heHces" suggest were 

 the first to be employed, approach the ideal in a number of respects. The 

 advent, however, of appUcations requiring resistors with high values of 

 resistance, of smaller size, and of greater stabiHty over augmented ranges in 

 operating conditions soon made the realization of the ideal more difficult. 

 Moreover, despite great progress in the development of resistance alloys and 

 in the drawing of fine wires from them, the growth of the communications 

 and electronics industries necessitated the development of resistors smaller 

 and cheaper than can be produced from wire and possessing different char- 

 acteristics. Non-metallic resistive materials were accordingly introduced, 

 even though some of these possess electrical and mechanical properties which 

 are comparatively less stable. The industries now require resistors having 

 the advantages of the non-metallic types and which at the same time are 

 highly precise and stable. The problem, thus, is that of imparting precision 

 and stability to non-metallic resistive materials or of employing metallic 

 ones in new ways. 



Oxides, sulfides, nitrides, carbides and non-metallic elements such as 

 carbon, germanium, and siHcon are among the many materials which have 

 been employed in making resistors.^ While some of these can be fabricated 

 precisely as materials, it has become increasingly apparent that, to meet 

 the complex requirements of modern circuitry, these materials must further 

 be employed in specific geometrical forms. Thus, the trend towards use of 

 increasingly higher frequencies requires that the resistive material be em- 

 ployed in film form in order to avoid resistance instability resulting from 

 the "skin effect" or from excessive values of reactance. The fihn type of 

 resistor possesses particular advantages for high frequency apphcations,^' ^ 

 and great effort has therefore been expended in the development of films of 

 various resistive materials, including metals and alloys. 



Metal films, produced chemically or by high-vacuum evaporation, have 

 been studied extensively. Pure elemental metals have temperature coeffi- 



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