SUMMARY

Due to their strong dielectric, piezoelectric and pyroelectric properties, ferroelectric thin films are used in a variety of applications, such as Microelectromechanical System (MEMS) sensors and actuators, ferroelectric random access memories (FeRAM), multilayer ceramic capacitors and pyroelectric sensors. Dielectric and piezoelectric properties of ferroelectric materials are influenced by their composition, crystallographic orientation, microstructure (including crystalline quality and local and global chemical homogeneity), as well as the physical size. This proposal reports on current efforts and future directions in the science and engineering aspects of these parameters in ferroelectric thin and ultrathin films. Size effects and their sources on the dielectric and piezoelectric response of ferroelectric ultrathin films have been studied. Two strategies for increasing the piezoelectric response of ferroelectric thin films are also reported: 1) modification of cation gradient profiles through the film thickness, resulting in highly-textured, superlattice-like PbZr0.53Ti0.47O3 (PZT) thin films; 2) synthesis of highly textured, large-grained Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) thin films. Additionally, in view of application of ferroelectric thin films in freestanding MEMS structures, the role of substrate clamping and effects of biaxial residual stresses on the films’ dielectric and piezoelectric responses will be studied. This task will be accomplished by continuous characterization of the films through partial removal of the Si substrate via back-side etching. Lastly, as a proof of concept, ferroelectric thin films with optimized piezoelectric response will be integrated in a basic MEMS actuator device, with membrane or bridge configuration, in order to verify their superior piezoelectric performance.