High piezoelectric activity in nonpoled thin films prepared by vapor deposition polymerization

The piezoelectric constant of 50 pmV(-1) and pyroelectric constant of 20 mu Cm(-2) K(-1) were obtained for polyurea thin films (similar to 300 nm) prepared by vapor deposition polymerization from methane diisocyanate and diaminofluorene. The pyroelectric signal and the infrared spectrum indicate that the dipoles of urea groups in the polymer were highly oriented normal to the surface of the aluminum Substrate to induce remanent polarization without it conventional poling process. The piezoelectricity observed for the film is due to the coupling effect of the remanent polarization and electrostriction. No ferroelectric polarization reversal was observed for the film up to 390 K.