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DF: Fachverband Dielektrische Festkörper

DF 13: Thin Films and Nanostructures I

DF 13.3: Talk

Wednesday, March 25, 2009, 15:20–15:40, WIL B321

Humidity effects on electrical properties and thickness of P(VDF-TrFE) films. — •Gennady Vizdrik, Björn Martin, and Herbert Kliem — Saarland University, Germany

By the Langmuir-Blodgett technique films of P(VDF-TrFE) with 30 and 50 transfers are deposited onto a glass substrate. The films with ellipsometrically determined thicknesses of 56 nm and 75 nm absorb water. Between 10% and 100% relative humidity (r.h.) of the atmosphere the thickness change is less than 2% in accordance with [1]. Using DC measurements at capacitor structures with aluminum electrodes of the area of 1x1 mm square it turns out that water desorption from the saturated state to the dry state takes place in less than 1000 sec. The electrical properties are changed drastically by the absorbed water. In dry samples we find true ferroelectric hysteresis loops, whereas in samples exposed to 100% r.h. a space charge polarization prevails. The remanent polarization is increased by a frequency dependent factor of up to 10. Measurements of the complex permittivity are carried out in the range 0.01 Hz < f < 1 MHz. The imaginary part and the real part increase towards low frequencies. This increase is the more pronounced the higher the r.h. of the atmosphere is. A quantitative comparison of the measured DC conductivity with the permittivity confirms that a space charge polarization effect is responsible for the increase of the permittivity at low frequencies.

[1] P. A. Jacobson et al., App. Phys. Lett., 84, 88, 2004