The Electrical Conductivity and Current Noise of Carbon Resistors

Abstract

The variation of resistance with temperature, pressure and magnetic field in several types of carbon resistor has been measured down to helium temperatures. Temperature variation is interpreted on the basis of an assembly of contacts with two different ranges of barrier height. A resistance decrease with pressure of approximately 0.1% per atmosphere is found in carbon compound resistors, and a small size effect variation with magnetic field in the case of carbon film resistors. Noise measurements have been made which show that the 1/f law holds at all temperatures. The temperature dependence of the noise is not in agreement with Macfarlane's theory in terms of a single activation energy. Measured noise power is found to be closely proportional to I2, while the ambient temperature noise level at 10-5 A for small resistors is expressible as δR2/R2 10-11 δf/f.