Polarization hysteresis and piezoelectricity in open-porous fluoropolymer sandwiches

Open-porous polymers form an attractive class of piezoelectric materials. Up to now it has been demonstrated that fibrous polyterafluoroethylene films after proper polarizing are responsible for the high piezoelectric response if confined between two electrically blocking polyfluoroethylene propylene layers. The sandwich structures reveal large quasistatic piezoelectric coefficients of up to 1500 pC/N. Here a theoretical model is proposed for a three-layer sandwich which quantitatively explains the experimentally obtainable polarization and its hysteresis behavior for different poling voltages. It will be reported that each sandwich structure exhibits a limit for the remanent polarization induced by polarization backswitching due to insufficient charge compensation. The correlation of the remanent polarization to the device geometry and the dielectric constants will be highlighted and suggestions for optimization will be given. It will be reported that the limitation of the remanent polarization also limits the obtainable piezoelectric coefficient of the sandwich structures.