Thickness dependence of ferroelectric polarization switching in poly(vinylidene fluoride–trifluoroethylene) spin cast films

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Abstract
In poly(vinylidene fluoride–trifluoroethylene) copolymer spin cast films, it has been observed that the polarization switching time increases as the film thickness is reduced to below 1 μm. We will show that this change with film thickness can be divided into two thickness regimes, i.e., those above 120–150 nm and those below that thickness. For films thicker than 120–150 nm, the change in the switching behavior is due to interface effects that can be modeled by an effective interface layer with lower dielectric constant that is in series with the film. For films below 120–150 nm thickness, there is an additional and very large increase of the switching time with reduced film thickness. This additional effect is caused by the precipitous drop of the crystallinity in films at this thickness range.