Ferroelectrics, as thin-films or heterostructures, are of critical importance in a wide variety of applications including microelectronics, nonlinear optics, sensors and actuators, and biotechnology or multi-functional combinations of each application. It also provides us with a wealth of interesting physics. How are the structure and electronic properties of a class of the electroceramic materials relevant to correlated electron systems? How do thin films interact with and modify the structure and properties of an interface of adjacent metals? How do the multi-layered heterostructures yield new functions and phenomena beyond the normal physical properties? We will focus on three case studies: the fatigue-free La-substituted bismuth titanate for non-volatile memory devices, domain switching physics probed by scanning force microscopy, and fabrication of piezoelectric cantilevers with state-of-the-art microelectromechanical systems (MEMS) technologies.
We will describe a new fatigue mechanism on oxygen stability in the octahedra of ferroelectric perovskites. From the comparative studies of strontium bismuth tantalate and bismuth titanate, it is found that chemical bond strength between bismuth and oxygen atoms in the octahedra is critical for polarization reversal characteristics. La-substituted bismuth titanate exhibits an excellent fatigue endurance property. Furthermore, it shows a good retention, resistance to hydrogen deterioration, and low-temperature processing temperature, indicating that this material is suitable for high-density ferroelectric random access memory applications. Owing to newly developed scanning probe microscopy, it is possible to study domain switching of ferroelectric thin films at nanometer scale. Retention and imprint behaviors have been studied by a normal and a reverse-poling scheme. Micromachining of silicon and related materials envisions new microstructures and devices. We are able to fabricate a variety of piezoelectric cantilevers, which are promising for high speed scanning probes, large density storage, or optical switch micromirrors.
Professor William Jo is a candidate for the ATOP-funded Assistant Professor position in the Department.