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THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



It can be accomplished, for example, by pyrolysis of a single compound 

 such as tripropylborane, or by use of a mixture of a boron hydride and a 

 hydrocarbon such as methane or benzene. Usually, however, boron tri- 

 chloride is employed as the source of boron and a suitable hydrocarbon as 

 the source of carbon. The films produced by codeposition of carbon and 

 boron are, in many respects, indistinguishable from carbon films of like 

 thickness. 



0.2 



0.3 0.4 0.6 0.8 1.0 2 3 4 5 6 8 10 



BORON CONTENT OF FILM IN PER CENT 



Fig. 21 — Dependence of the temperature coefficients of resistance of borocarbon films 

 on boron content and temperature of formation 



As the boron content of thick films increases from zero in films of like 

 thickness, however, the temperature coefficient of resistance, a, decreases 

 through a minimum value and then increases, as shown in Fig. 21. The po- 

 sition of the minimum value of a is essentially independent of the pyrolyzing 

 temperature, but the magnitude of a at the minimum decreases, as shown, 

 with increase in furnace temperature. It will be noted that, at its minimum, 

 the magnitude of a is less than 20 PPM deg C"^ when comparatively high 

 pyrolyzing temperatures are employed. 



The specific resistance of carbon films, except for the relatively smal' 

 variations shown previously in Fig. 13, is independent of the pyrolyzing 



