Investigation on Thickness Effect of Ultrathin Vinylidene Fluoride/Trifluoroethylene Copolymer Films

We investigated the thickness effect on ferroelectric properties of vinylidene fluoride (VDF)/trifluoroethylene (TrFE) copolymer films in the region of 9.7–230 nm. Film thickness was estimated from cross-sectional transmission electron microscope (TEM) images. Relative permittivity calculated using precise thickness measurements decreased from 10 to 5.3 with decreasing thickness. Remnant polarization gradually decreased from 80 to 34 mC/m2 with decreasing thickness, whereas maximum polarization was almost constant. These results suggested the existence of a dead layer with a low permittivity at the interface between the VDF/TrFE copolymer films and electrodes. Finally, the thickness of the dead layer was estimated to be 4.1 nm by assuming the existence of two layers with different permittivities.