Ferroelectric switching in Langmuir-Blodgett and spin-coated thin films of poly(vinylidene fluoride/trifluoroethylene) copolymers

Ferroelectric behaviour of poly(vinylidene fluoride/trifluoroethylene) copolymer thin films has been investigated through polarization switching measurements. Samples prepared by Langmuir-Blodgett (LB) deposition in the range of 37-139 nm and samples prepared by spin coating in the range of 53-327 nm exhibit almost the same switching behaviour. Reducing the sample thickness, the hysteresis loops tend to slant and the switching transients become broader. The coercive field increases with decreasing sample thickness, whereas the remanent polarization is nearly independent of film thickness. The switching time decreases with increasing field and it is almost independent of thickness down to 69 nm in LB films and 71 nm in spun films. Slower switching is observed for a thickness below 60 nm in both LB films and spun films. This could be due to the depolarization field induced by the surface oxidation layers of Al electrodes which becomes the more pronounced the thinner the sample is. Furthermore, retention properties and fatigue endurance of both kinds of films are studied which show a similar decay tendency. The above results suggest thin films in the range of 60-100 nm are promising candidates for technical applications.