Single crystal PZT thin film membrane with highly conductive electrodes

Piezoelectric membrane based on single crystalline Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film on (001) Si substrate is reported in this paper. To obtain epitaxial single crystalline PZT thin film, SrTiO₃ (STO) buffer layer was grown by Molecular Beam Epitaxy on Si substrate, which has been proven as an effective way to increase the crystalline quality. 70nm-thick PZT thin film was deposited on STO-buffered Si substrate by the sol-gel method. 100nm-thick Ru top electrode was patterned by wet etching and subsequently 200nm-thick SiO₂ elastic layer was deposited on the top of the stack in order to mechanically strengthen the final membrane. Deep reactive ion etching was therefore used to release the membrane from the backside. Finally, 100nm-thick Au bottom electrode was deposited on the backside of the membrane. Two types of membrane structures were realized, i.e. piezoelectric actuator and resonator. The resonances were studied by an impedance meter and the hysteresis loop of the electromechanical response was characterized by a Wyko profilometer.