Mechanical and electromechanical properties of PZT sol-gel thin films measured by nanoindentation

Microelectromechanical systems (MEMS) with ferroelectric thin films as the actuating element are currently under development. Micromotors, microcantilevers for atomic force microscopy, and microwave switches are three examples of MEMS that have been demonstrated. The potential commercialisation of MEMS rests on addressing design and reliability issues. Their design requires knowledge of the elastic coefficients of the ferroelectric film, as well as the other materials in the system. Understanding their reliability requires the determination of stress thresholds for depolarisation. Lead zirconate titanate (PZT) compositions are preferred for actuation applications. We present here the mechanical properties of PZT films with Zr/Ti ratios of 30/70 and 50/50, prepared by sol-gel processing. Nanoindentation with spherical tipped indenters was used to obtain the elastic stiffness coefficient of the films. Electromechanical measurements were also performed with the nanoindentation system. Films were poled by using the spherical tipped indenter as the top electrode. Current intensity transients were recorded during subsequent indentation of poled areas.