Investigation of ferroelectric thin film using piezoresponse force microscopy

Ferroelectric materials have found a wide range of applications in data storage devices, sensors and actuators, capacitors, oscillators and filters, among others thanks to fabrication methods that allow integration into semiconductor devices at micro and nanoscales. As many of these materials also exhibit ferroelasticity, the interplay between ferroelectric and ferroelastic phenomena is a subject of intensive research. In earlier work on this topic, resonance enhanced piezoresponse force microscopy was introduced and theoretical models were developed to support quantitative imaging with PFM. The resonant PFM mechanism was thoroughly investigated, and functional materials including tetragonal polycrystalline PbZr0.3Ti0.7O3 and epitaxial PbZr0.2Ti0.8O3 thin films were studied at different length scales using resonant PFM. This technique was also used to study the ferroelectric/ferroelastic domains and their dynamics. In the current work, the interplay between ferroelectric and ferroelastic domains is investigated in both polycrystalline and epitaxial thin films, during which a type of unexpected controllable defects was proposed. It is shown that certain defects are controllable via an external electrical excitation and the strain associated with the defect can also be controlled. Lastly, ways to modify the thin film geometry with focused ion beam milling and broad beam milling and its impact on domain configurations is studied. The resulting changing geometry and the ferroelectric/ferroelectric domain modification has been compared.