High field poling of poly(vinylidene fluoride) films using a current limiting circuit

A high field room temperature poling technique has been developed for preparing poly(vinylidene fluoride), PVDF, films with high piezoelectric activity. The technique utilizes a resistor (typically 5 × 107 to 1011 Ω) which is inserted between the power supply and the polymer film to control the voltage buildup across the polymer film and to limit the current flow through the film in case of incipient breakdowns. Application of the technique to 25 μm-thick biaxially oriented films (with provision to prevent edge flashover) showed that the films could be poled without breakdown failure for a period of one to 105 s depending on the external resistance and the applied field. The piezoelectric e31 coefficients of the poled films were comparable to those obtained with the breakdown field poling method recently developed by Wang and West; however, the values obtained with the present method were in general more consistent and reproducible than the values obtained with the latter method. It is shown that physical process involved in poling by this technique can be modeled by a simple equivalent circuit. This hypothetical circuit involves a physical ''fiction'' but nevertheless gives results which correspond with experimental observations reasonably accurately; it has predictive value, therefore, for the choice of parameters to achieve control over the poling in device fabrication.