Dependence of threshold thickness of crystallization and film morphology on film processing conditions in poly(vinylidene fluoride-trifluoroethylene) copolymer thin films

In spin-cast films of poly(vinylidene fluoride-trifluoroethylene) on metalized silicon substrate, there exists a threshold thickness of crystallization d(th), below which the crystallinity drops precipitously. Due to the direct link between the crystallinity and functional properties in the polymer, there is a corresponding large change in the film ferroelectric properties, including the dielectric constant, the polarization level, and polarization switching speed, as the thickness is reduced to below d(th). Detail microstructure studies show that this threshold thickness is controlled by the stable crystal lamellar size along the film thickness direction. By varying the film processing condition to reduce the crystal lamellar size in the thickness direction, d(th) can be reduced markedly. As a result, better ferroelectric responses were obtained in ultrathin films. (C) 2002 American Institute of Physics.