Analyses on thin film between contacts by using third harmonic distortion

This paper describes a graphic method to evaluate the effective physical parameters (potential barrier height and film thickness) of a thin insulating film for the tunnel current. The theoretical third harmonic distortion (THD) of the terminal contact current due to the tunnel effect is expressed as a function of the tunnel resistivity and illustrated in a graph, which makes it possible to determine the physical parameters. Experimental results, using Au vs. Au 0.5%Co alloy contacts at very small contact loads (<1 mN), show that the THD and the contact resistance are very high when the contacts are contaminated with an organic vapor from practical soldering. By making use of these results, the effective potential barrier height for electron emission from the contact metal into the organic film is evaluated at voltages of less than 0.3 eV and film thicknesses of 0.5-0.7 nm. It is possible to estimate the large THD using the voltage-tunnel resistance characteristics without measuring the third harmonic. The electric current due to the field emission through the film is theoretically evaluated to be much less than the tunnel current at low applied voltages.