Measurement and analysis of temperature-dependent rf impedance of discontinuous metal films on glass substrates

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Abstract
The electrical impedance of evaporated films of Mo, Pt, Al, and Cu was measured as a function of frequency from 0.5 to 30 MHz at temperatures in the range 100–450 K. The films were evaporated onto glass substrates held at various temperatures and had final thicknesses such that they were discontinuous. The impedance of such films is frequency dependent but may be represented by an equivalent circuit of frequency‐independent resistance and capacitance parameters, Rb, Rg, and Cg. Rb is associated with conduction within the grains of the film and was observed in most cases to be metallic, i.e., to possess a positive temperature coefficient of resistance (TCR). Rg and Cg are associated with intergranular conductivity, and Rg was observed to have a negative TCR and is assumed to be the result of an activated process, i.e., Rg(T) =Rg(∞) exp(Ea/kT). The behavior of the various films is discussed in terms of the relationship among values of Rb, Rg, Rg(∞), and Ea. A scheme to classify film‐substrate systems according to relative activation energies and relative interangular barriers is proposed.