Fabrication of planar interdigitated electrodes for dielectric spectroscopy of thin films

Abstract

The dielectric properties of polymeric thin films (100-200 nm) are hard to measure with the standard approaches as the samples aren't free standing necessitating a supporting substrate. Consequently, a planar interdigitated sample holder has been designed to hold the thin film where the polymeric capacitance was derived from the passing fringing fields. The electrodes were fabricated by creating 120 nm trenches in a SiO2/Si wafer; 20 nm Cr was deposited as an adhesion layer prior to the deposition of Cu by thermal evaporation. The electrical measurements were implemented using HP 4294A and a probe station. Devices of 20 to 70 fingers were measured and the results were compared to the analytical and finite element simulation. At 10 KHz, the total measured capacitance of a 20-finger device was about 8 pF with 3 % represented the polymeric contribution. The measurements differed from the calculations or finite modeling results by about 12%.