Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

Abstract

Ultrathin films of poly(vinylidene fluoride-trifluoroethylene) copolymer [P(VDF-TrFE), with a content (mol %) ratio of 50/50 VDF/TrFE] were fabricated on silicon wafers covered with platinum by a spin-coating technique, ranging in thickness from 20 nm to 1 m. The effect of thickness on dielectric properties and polarization behavior was investigated. A critical thickness was found to be about 0.1 m. An abrupt drop of dielectric constant was observed, although there is no significant change in dielectric loss at this thickness. Square and symmetric hysteresis loops were obtained in films thicker than 0.1 m. However, for films thinner than 0.1 m, fewer square hysteresis loops were observed. SEM and X-ray results demonstrate that the effect of thickness on dielectric and ferroelectric properties could be explained by the changes of crystal structure in these films. In addition, the effects of irradiation on dielectric property and polarization response for ultrathin P(VDF-TrFE) films were also presented.

Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures

“…Secondly, an increase of the coercive field E c from 48 MV m, for film thicknesses of 3.5 µm and 1 µm, towards 65 MV m for the 0.1 µm thick P(VDF-TrFE) film. Such a decrease of P r and increase of E c for ultra thin films has been reported by Xu et al 138 and Naber et al 77 Both authors relate this thickness dependency of P r and E c mainly to the decrease of crystallinity with film thickness. The hysteresis curves suggest that the spin coated films with thicknesses down to 0.1 µm can be remanently polarized.…”

“…The remanent polarization and the coercive field may further be influenced when the thickness of the P(VDF-TrFE) film is decreased below 0.5 µm. Several authors 77,[136][137][138] have shown that the decrease of film thickness leads also to a decrease of remanent polarization, however, increases the coercive field. This behavior is strongly amplified for film thicknesses below a critical thickness of around 0.15µm.…”

“…3.7 on page 38). 33,77,136,138 This macroscopic effect of remanent polarization is attributed to the large net dipole moment of the β-conformation on one side and the fact that the molecular dipoles can maintain the orientation on the other side. When the coercive field is exceeded, the molecules start to rotate around their axis and align therewith their molecular dipoles along the field lines, as illustrated in Fig.…”

Micro FTIR Mapping of Nanometer Ferroelectric Polymer Films

“…[13,14] The 80 nm film was more uniform than the 35 nm film and the relative amount of the amorphous phase in the 35 nm film was almost twice than that in the 80 nm film. The observed changes in dielectric properties and ferroelectric behaviors originated from the change of crystallinity in the films.…”

“…The change of dielectric properties around 100 nm has been observed in earlier studies with SEM and X-ray diffraction. [13,14] The exact critical thickness, however, was dependent on solvent and processing conditions. Figure 2 demonstrated that the observed changes in dielectric properties and ferroelectric behaviors originated from the change of crystallinity in the film.…”