SUBJECT: Ph.D. Dissertation Defense
BY: Yaser Bastani
TIME: Monday, October 21, 2013, 12:00 p.m.
PLACE: MARC Building, 431
TITLE: Ferroelectric thin and ultrathin films for MEMS applications
COMMITTEE: Dr. Nazanin Bassiri-Gharb, Chair (ME)
Dr. Levent Degertekin (ME)
Dr. Kenneth Sandhage (MSE)
Dr. Hamid Garmestani (MSE)
Dr. Peter Hesketh (ME)
Dr. Todd Sulcheck (ME)


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 investigation 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. Three 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, and 3) the role of substrate clamping and effects of biaxial residual stresses on the films’ dielectric and piezoelectric responses via back-side etching of the Si substrate. The last approach was performed in view of application of ferroelectric thin films in freestanding MEMS structures and was conducted by continuous characterization of the films through partial removal of the Si substrate via back-side etching. These approached resulted in remarkable enhancement of the piezoelectric (and dielectric) response of the ferroelectric thin and ultrathin films.