The Dielectric Properties of P(VDF-TrFE) Copolymer Thin Films by Physical Vapor Deposition

초록

The copolymer thin films of poly(vinylidene fluoride-trifluoroethylene), which shows excellent piezoelectricity and pyroelectricity, were fabricated by physical vapor deposition method in the compositions 70/30 and 80/20 mol%. The effect of the substrate temperature and the mol% rates on the molecular structure, the dielectric and piezoelectric properties was investigated. In deposition process, the substrate temperature(Ts) was varied from 30℃ to the curie transition temperature(Tc). From the results of deposition rate, molecular and crystal structure of the films, it was found that 300℃ was the optimal evaporation temperature in the process. The β-from characteristic peaks increased with increasing the substrate temperature on account of the phase transition from the ferroelectric crystal phase to the paraelectric crystal phase. From this results, the copolymer films were fabricated from 30℃ to 90℃ substrate temperature. The relative dielectric constant decreased as a from of anomalous dispersion with increasing measurement frequency. With increasing Ts, the relative dielectric constant increased from 3.643 to 5.29 on the 70/30 mol% films, and from 4.367 to 10.77 on the 80/20 mol% films, respectively. The α relaxation by interfacial polarization and the β relaxation by dipole orientation polarization were observed in low and high frequency region, respectively. The α relaxation decreased and the β relaxation increased with increasing Ts. From the results, it is suggested that the crystallinity of the films increased with increasing Ts. The effect of increasing Ts on the piezoelectric properties will also be discussed in detail.