Dielectric characteristics of in-plane polarized lead zirconate titanate thin films on oxide layers

Sol-gel derived lead zirconate titanate (PZT) films have been prepared on STO-passivated silicon substrates. The STO buffer layer of thickness about 55 nm is prepared by rf-magnetron sputtering. XRD results reveal that the PZT film has well-crystallized perovskite phase, indicating that the thin STO layer can effectively prevent reaction and inter-diffusion between the PZT film and silicon substrate. Inter-digitated electrodes (IDEs) have then been deposited on the PZT film by magnetron sputtering and patterned using the standard photolithography. With the IDEs, the dielectric and ferroelectric properties of the PZT film under transverse or in-plane electric fields have been investigated. By assuming a uniform distribution of electric field (in-plane electric field model), the estimated relative permittivity of the PZT film is about 2100, while the dielectric loss is less than 1%. Good in-plane polarization hysteresis loop is observed, showing an observed remanent polarization value of 21 μC/cm2, which is comparable to that of a PZT film with both top and bottom electrodes. The in-plane polarized PZT/STO/SiO2/Si film can be used to fabricate d33-mode unimorph bending transducers, which will have much better performance than the conventional bending transducers driven electromechanically through the piezoelectric d31mode.