Nondestructive measurements of the resistivity of thin conductive films and the dielectric constant of thin substrates using an open-ended coaxial line

Abstract

This paper presents a modified theory for the measurement of the surface resistivity of thin films, deposited on either thin or thick dielectric substrates; in addition the formulations for the measurements of thin dielectric substrates is derived. The reflection coefficient of a probe in contact with the surface is used to calculate the surface resistivity of the film or else the dielectric constant of the dielectric substrate. The expression giving the reflection coefficient in terms of the surface resistivity of a film on a thin substrate is developed by matching the electromagnetic fields at the aperture of the coaxial line. Experimental results of conductive thin films on thin substrates (indium tin-oxide thin film deposited on polyethylene substrates) and dielectric substrates without films are reported from DC to 4 GHz. The experimental results calculated with the derived expressions and the measured reflection coefficients are in agreement with surface resistivity values quoted by the manufacturer of the various test samples used.