Contact current distortion due to the tunnel effect

Harmonic analyses and measurements of the tunneling currents through a thin insulating film between two electrodes have been conducted. The equation for tunneling current derived by J.G. Simmons was analyzed by Fourier expansion, and a numerical evaluation of the third harmonic ratio was performed. The theoretical third harmonic ratio was determined to be a function of s/spl psi//sub 0//sup 1/2/ (s is film thickness, /spl psi//sub 0/ is work function) and to fall between -40 and -83 dB when s was in the range of practical importance (0.4 to 2.0 nm) and /spl psi//sub 0/ was between 1 and 4 eV. Experiments on practical contacts (95Au-5Ni) indicated an actual third harmonic ratio between -50 and -130 dB. Contact resistance was measured for copper contacts with a thin insulating film. A small temperature coefficient for resistivity proved that the tunnel effect was contributing to the measurements. It was shown that the harmonic measurement could clearly detect the film, which could further deteriorate the contact performance by corrosion.