Dielectric properties of and charge transport in columnar microfibrous thin films of Parylene C

Parylene-C microfibrous thin films (μ FTFs), grown using oblique-angle physicochemical vapor deposition, were examined for potential use as low-relative-permittivity (i.e., low- κ ) interlayer dielectrics in integrated circuits and, more importantly, flexible electronics. These films were characterized using capacitance-voltage-temperature (CVT) and current-voltage-temperature experiments at different temperatures (ranging from 298 to 420 K) and frequencies (ranging from 1 kHz to 1 MHz). Field emission scanning electron microscopy revealed the Parylene Cμ FTFs to be highly porous. Consequently, their κ values are at least 20% lower than those of bulk Parylene C. The dependences of κ on frequency and temperature suggest that molecular dipole oscillations are responsible for charge polarization in theμ FTFs. The dc leakage current in theμ FTFs at temperatures not exceeding 100 °C (373 K) was found to arise from Poole-Frenkel (PF) emissionmechanism with a barrier energy of about 0.77 eV. Moreover, when fitted to the PF model, the experimental data yielded high-frequency values κ∞ of κ in agreement with those obtained from CVT experiments, thus confirming our identification of PF as themajor responsiblemechanism and confirming the low- κ characteristic of microfibrous Parylene C. The ac current transport in theμ FTFs was found attributable to small-polaron-tunneling hopping conduction and characterized by the power law ω^s, with s ϵ [0.082,0.85] increasing with temperature. AC conduction in theμ FTFs is temperature-activated with an activation energy that decreases from 0.020 to 0.012 eV as frequency increases from 1 kHz to 1 MHz.