Regensburg 2007 – scientific programme
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DF: Fachverband Dielektrische Festkörper
DF 10: Dielectric and Ferroelectric Thin Films and Nanostructures III
DF 10.9: Talk
Thursday, March 29, 2007, 17:10–17:30, H48
Thin-film piezodevices based on expanded PTFE with improved thermal stability — •Torsten Finnberg1, Sergej Zhukov2, Bernd-Joachim Jungnickel1, and Heinz von Seggern2 — 1Deutsches Kunststoffinstitut, Schlossgartenstrasse 6, Darmstadt, Deutschland — 2Fachbereich Material- und Geowissenschaften, TU Darmstadt, Petersenstrasse 23, Darmstadt, Deutschland
Piezoelectric sensors and actors are important devices in a large number of applications ranging from the entertainment to the automotive industry. Present research is focused on a new class of piezoelectric materials based on cellular polymer films. The inherent flexibility and easy processability of these materials opens new fields of applications. High quasistatic piezocoefficients of up to 300 pC/N have already been demonstrated in the usually used polypropylene. A lasting challenge concerns the thermal stability of the piezocoefficient in that material. The use of expanded polytetrafluorethylene (PTFE) could solve that problem. However, this material exhibits open pores, necessitating multilayer systems by sandwiching it between solid PTFE films. It is shown by measurements of the dynamic inverse piezocoefficient in the acoustic frequency range, that such multilayer systems have a similar performance as commercially available cellular piezoelectric polypropylene. It is shown by measurements of thermally stimulated currents, that the poling temperature strongly influences the thermal stability of the polarisation. By poling at elevated temperatures, a significant increase of the thermal stability of the piezocoefficent can be achieved, as demonstrated by forced cyclic ageing at 80 °C.