Enhanced thermo-electro-mechanical characteristics of purified P(VDF-TrFE) films for ultrasonic transducers

In this study, the fabrication process of a piezoelectric poly[(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] film was optimized to maximize its crystallinity and piezoelectric properties and to improve its thermal stability. The effect of purification of P(VDF-TrFE) solution dissolved in methyl ethyl ketone [MEK] and uniaxial stretching on the properties and performance of P(VDF-TrFE) film was studied. In the purification process, the solution was filtered with a syringe filter with 2.7 μm pores. X-ray diffraction measurements showed that the stretching and purification processes increased the crystallinity of the P(VDF-TrFE) films by approximately 16.2% and 2.2%, respectively. A high-temperature storage test showed that the unstretched P(VDF-TrFE) films lose most of their polarization after 1-h storage at 70 °C. The stretching process greatly increased the thermal stability of the films so that the purified and stretched P(VDF-TrFE) films exhibited a small variation within 6% in the piezoelectric strain constant (d33) for 96 h at 70 °C. Ultrasonic transducers (UTs) were also fabricated with the purified and stretched P(VDF-TrFE) films. The pulse-echo measurement showed that the sensitivity and bandwidth of the UTs increased by 4.5 dB and decreased by 24.3%, respectively, compared to UTs fabricated with the purified P(VDF-TrFE) film without stretching.