Fabrication of an interdigitated sample holder for dielectric spectroscopy of thin films

Abstract

A planar interdigitated sample substrate has been designed to support a thin-film sample of a polymer while the frequency-dependent dielectric properties of the thin film are measured. Trenches for the electrodes were etched into a SiO2/Si wafer surface. Chromium was used as an adhesion layer prior to thermal evaporation of copper for the body of the electrode. The device was placed in a standard probe station and the dielectric character was recorded as a function of frequency with an impedance analyser. Devices with 20 to 70 fingers were measured and the results compared to analytical and finite element simulations. At 1 kHz, the total capacitance of a typical 20-finger device was 8 pF. The capacitive contribution of the thin film due to the fringing field in the polymer was about 2% of the total capacitance of the fabricated structures.