Piezoelectric properties of thin films of aromatic polyurea prepared by vapor deposition polymerization

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Abstract
Aromatic polyurea films of a few hundred nanometer thickness were prepared by vapor deposition polymerization of the monomers 4,4’‐diaminodiphenylmethane and 4,4’‐diphenylmethane‐diisocyanate. Piezoelectric activity was observed after poling the films under an electric field of 100 MV/m at 210 °C for 10 min. The piezoelectric stress constant (polarization/strain) remains constant at about 15 mC/m2 over the temperature range from −50 to 200 °C. The multilayer film produced by the alternate deposition of polyurea layers and aluminum electrodes exhibited a response proportional to the number of layers. The residual polarization caused by alignment of the dipoles of the urea bond is believed to be the origin of the effect.