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

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.