Dielectric properties of fluorocarbon thin films deposited by radio frequency sputtering of polytetrafluoroethylene

Abstract

We investigate the dielectric properties of fluorocarbon thin films deposited by radio-frequency magnetron sputtering of polytetrafluroethylene. The dielectric constant and the loss factor are studied as a function of frequency (0.1 Hz-1 MHz, infrared frequencies) and temperature (room temperature to 100 °C). The value of the dielectric constant is 1.8 at optical frequencies, and around 2.3 in the 0.1 Hz–1 MHz range. The background loss factor is around 0.8% in these samples. Two different polarization mechanisms are identified (β and γ relaxations). The γ process dominates the dielectric constant from 0.1 to 1 MHz. In this frequency range the dielectric constant decreases with temperature (about –4% from room temperature to 100 °C). Temperature dependence of the dielectric constant is well described by a simple Debye model (linear variation of the dielectric constant with 1/T). The γ relaxation is tentatively ascribed to C−F bonds (Nμ2=4×10−32 C2 m−1). The β relaxation has a loss peak located at very low frequencies (<0.1 Hz). It leads to an increase of loss below 10 Hz when temperature is increased above 75 °C. The high-frequency part of the β loss peak decreases as ω−0.35. Study of its temperature dependence leads to an activation energy of 0.66 eV.