Hot Plate Annealing at a Low Temperature of a Thin Ferroelectric P(VDF-TrFE) Film with an Improved Crystalline Structure for Sensors and Actuators

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 degrees C). It was found that an annealing temperature of 100 degrees C (slightly above the Curie temperature, Tc) has induced a highly crystalline beta phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, P-r = 94 mC/m(2), and pyroelectric constant, p = 24 mu C/m(2)K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 degrees C by annealing the thin film with a simple and cheap method.