Dielectric Properties of and Charge Transport in Columnar Microfibrous Thin Films of Parylene C

Parylene-C microfibrous thin films (μFTFs), 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 C μFTFs 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 the μFTFs. The dc leakage current in the μFTFs at temperatures not exceeding 100 °C (~373 K) was found to arise from Poole-Frenkel (PF) emission mechanism 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 the major responsible mechanism and confirming the low-κ characteristic of microfibrous Parylene C. The ac current transport in the μFTFs was found attributable to small-polaron-tunneling hopping conduction and characterized by the power law ω
^s
, with s ∈ [0.082,0.85] increasing with temperature. AC conduction in the μFTFs 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.