Ferroelectric properties of vinylidene fluoride-trifluoroethylene copolymer thin films fabricated on amorphous alloy electrode

We have investigated the structure and ferroelectric properties of vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer thin films fabricated on amorphous alloy electrodes. Thin films of amorphous Pd-Cu-Si alloys with various compositions were successfully prepared by sputtering deposition. An atomically flat surface resulting from a fully amorphous structure of Pd-Cu-Si was obtained upon achieving a uniform surface of a spin-coated VDF-TrFE copolymer thin film. X-ray diffraction (XRD) measurements revealed that the crystalline structure of the VDF-TrFE copolymer thin films was of ferroelectric ß-phase, being independent of the composition and crystalline state of the Pd-Cu-Si alloy. The clearly observed D-E hysteresis loops showed a remanent polarization of 0.075C/m2 and a coercive field of 90MV/m at a measurement frequency of 10 Hz for a 50-nm-thick film, which is almost consistent with the results obtained with Pt electrode samples. We also observed the thinning-induced reduction of remanent polarization, which was explained by the depolarization field induced by the surface dead layer in VDF-TrFE copolymer rather than the oxidized layer in Pd-Cu-Si alloy electrode.