Abstract

Layered fluoroethylenepropylene (FEP) ferroelectret films with cross-tunnel structure were fabricated from sheets of FEP films by template-patterning followed by a fusion-bonding process and contact charging. The typical piezoelectric d₃₃ coefficients, measured by a quasi-static method of samples not annealed, are in the range of 1000-3700 pC/N. The resonance behavior of the samples is analyzed by dielectric spectroscopy which also yields Young’s modulus. Microphones built with such films exhibit a somewhat decreasing frequency response up to 1 kHz, an increase of the responses due to diffraction effects at higher frequencies, and eventually a peak probably due to a thickness resonance at about 40 kHz. Annealing at 125 °C indicates that the sensitivity stabilizes at about 40 percent of the original value. From this data, stable dynamic d₃₃ coefficients of up to 300 pC/N can be calculated. A micro energy harvesting generator utilizing these films and based on the excitation of thickness vibrations is also described. With an active area of 4.3 cm² and a seismic mass of 69.5 g, power up to 0.5 μW referred to an acceleration of 1g can be generated at a frequency of 120 Hz.

by Xiaoqing Zhang,   Gerhard M. Sessler, and Yujie Wang

Journal of Applied Physics  116, (2014)074109