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

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 degreesC). 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 (beta and gamma relaxations). The gamma 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 degreesC). Temperature dependence of the dielectric constant is well described by a simple Debye model (linear variation of the dielectric constant with 1/T). The gamma relaxation is tentatively ascribed to C-F bonds (Nmu(2)=4x10(-32) C-2 m(-1)). The beta 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 degreesC. The high-frequency part of the beta loss peak decreases as omega(-0.35). Study of its temperature dependence leads to an activation energy of 0.66 eV. (C) 2002 American Institute of Physics.