Date of Completion

11-11-2016

Embargo Period

11-11-2016

Keywords

Ferroelectric, AFM, PFM, Piezoelectric property, Switching dynamics

Major Advisor

Bryan D. Huey

Associate Advisor

Pamir Alpay

Associate Advisor

Serge Nakhmanson

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The domain configurations and piezoelectric coefficient of ferroelectric materials such as PZT and PMN-PT thin films can have a significant effect on the optimization of future electronic devices. Piezo Force Microscopy (PFM) is an ideal tool based on Atomic Force Microscopy that allows unique investigations of such nanoscale effects, and can further be implemented to monitor domain switching dynamics. Utilizing PFM, the domain orientations as well as switching dynamics can be tracked in-situ. As the lateral dimension plays an important role in ferroelectric properties since it influences in-plane strain, both normal and lateral domain orientations are uniquely mapped simultaneously. Leveraging a new method for fabricating ferroelectric mesas down to the nanoscale, coercive fields and switching kinetics have thereby been investigated for continuous strained films as well as geometrically strain-relieved samples. A piezoelectric enhancement at edges of engineered nano islands is directly observed, while switching activation energies have been calculated and related to the strain-relief behavior. Piezoelectric coefficients in the surface normal direction were precisely measured on 2 μm, 1 μm and 0.75 μm wide PMN-PT microfabricated structures. These revealed piezoelectric enhancements up to 500 nm from feature edges for 2 μm or wider structures, and an increasing overall enhancement throughout smaller 1 μm and 0.75 μm structures as the strain relief becomes more complete. These results are corroborated by X-RAY diffraction and dielectric measurements from collaborators. The enhancement of dielectric and piezoelectric properties for geometrically strain relieved structures should furthermore be applicable to in-plane piezoactuation. Accordingly, lateral piezoactuation for PMN-PT microstructures is recorded for 4 μm and 2 μm features revealing xiv direction-dependent edge enhancement as hypothesized. Such insights are crucial for ferroelectric strain engineering efforts, the development of new device mechanisms, and their ultimate performance.

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