Crystalline structures, surface morphology, and ferroelectric response in ultrathin film of vinylidene fluoride and trifluoroethylene copolymer

Abstract

This paper presents crystalline structures, surface morphology, and improved ferroelectric response in ultrathin film of 70 mol % vinylidene fluoride and 30 mol % trifluoroethylene copolymer with 22 nm thickness. Remanent polarization (Pr) of 45 mC∕m2 was obtained at maximum applied voltage of 11 V (500 MV/m) for the ultrathin film annealed at 142 °C. This Pr value is twice as high than that previously reported. We ascribed higher Pr to both smoothness of sample surface and no significant reduction of crystallinity and crystallite size when film thickness is down to 22 nm. Thermal annealing at the temperature above 135 °C induced the growth of flat-on lamella crystals with smoothed uniform surface morphology, and further thermal annealing at temperature of 142 °C led the realignment of crystal c axis in flat-on lamella parallel to the substrate.

Facile preparation of ferroelectric poly(vinylidene fluoride-co -trifluoroethylene) thick films by solution casting

“…Polar phases were maximally created at the annealing temperature of 130°C. This coincides with most previous studies reporting that the annealing temperature would be between 120°C and 140°C . Interestingly, this temperature is between the Curie and melting temperatures of P(VDF‐TrFE) 75:25 mol% copolymers (i.e., melting temperature of 150°C, the Curie transition temperature in the cooling process of 57–79°C and the Curie transition temperature in the heating process of 124°C) .…”

Towards nonvolatile memory devices based on ferroelectric polymers

“…Furthermore, we have already shown that crystallinity of P(VDF-TrFE) (70/30) was not changed down to 22 nm thickness. 18 As the probe chip of AFM is conductive, one can imagine that ferroelectric switching could be measured upon direct probing by an AFM probe chip. We have tried to measure the direct switching using a conductive AFM probe chip attached to the surface of the sample film without assistance of electrode.…”

Nanoscale piezoresponse of 70 nm poly(vinylidene fluoride‐trifluoro‐ethylene) films annealed at different temperatures

“…Accordingly, special attention has been paid for achieving ultrathin P(VDF‐TrFE) films with good ferroelectric properties. Spin coating is a commonly used method for preparing the P(VDF‐TrFE) films on inorganic and organic substrates over a large area although several process parameters, such as initial polymer concentration, spin speed and annealing temperature, affect their ferroelectric properties 1–3, 8–10. Recently, spin‐coated films down to 20 nm thickness have been demonstrated with measurable ferroelectric properties for the low voltage operation 9, 10.…”

“…Spin coating is a commonly used method for preparing the P(VDF‐TrFE) films on inorganic and organic substrates over a large area although several process parameters, such as initial polymer concentration, spin speed and annealing temperature, affect their ferroelectric properties 1–3, 8–10. Recently, spin‐coated films down to 20 nm thickness have been demonstrated with measurable ferroelectric properties for the low voltage operation 9, 10. Meantime, piezoresponse force microscopy (PFM) has been developed to investigate the structure and dynamics of ferroelectric domains and to understand polarization related processes in ferroelectric thin films 11, 12.…”