Ferroelectric materials are used to couple electrical and mechanical energy and store information. Therefore, they are used pervasively as sensors, actuators, and energy and memory storage components in microelectronics, ultrasonic devices, and consumer products. The properties of ferroelectric materials can change significantly as their size is reduced. In ferroelectric thin films, it is now widely recognized that significant size effects are observed at film thicknesses between 10 nm and 1 um. At these thicknesses, the effectiveness of these materials at storing and transducing energy is dramatically reduced - in some cases being suppressed to <20% of the values seen in their larger counterparts. Using state-of-the-art experimental approaches offered by a collaborative team of investigators, this project elucidates the atomistic origins of these size effects in ferroelectric thin films. This understanding enables the design and realization of next-generation devices at substantially smaller length scales with superior performance and functionality. Examples of devices impacted by this research include piezoelectric microelectromechanical systems and scaled capacitors.
TECHNICAL DETAILS: The goal of the project is to develop a universal physical understanding of the fundamental structure-property-processing relationships that govern extrinsic size effects in ferroelectric thin films. The specific objectives include proving the extrinsic mechanism(s) affecting the size effects in ferroelectric thin films, quantifying the relative contributions from intrinsic and extrinsic mechanisms to properties, and establishing new fundamental structure-property-processing relationships. To accomplish these objectives, the Trolier-McKinstry group at Penn State synthesizes high-quality thin films and analyzes property measurements using Rayleigh and Preisach models. The Jones group at North Carolina State University uses in situ X-ray diffraction while applying voltage to quantify the intrinsic and extrinsic contributions under equivalent electrical loading conditions. The integrated results provide a quantitative understanding of contributions of intrinsic and extrinsic effects to the dielectric and piezoelectric coefficients in ferroelectric thin films as a function of film thickness and other key variables. The fundamental nature of the mechanisms and the results in the present work will be applicable to many ferroelectric thin film compositions including those being developed for high-temperature and lead(Pb)-free applications. Graduate students gain additional exposure to facilities and scientists through conducting experiments at the Advanced Photon Source at Argonne National Laboratory. The educational outreach program includes participation by the project participants at workshops and camps directed at elementary, middle school, and high school students. Students from underrepresented groups will be engaged in the project through targeted recruitment and outreach activities.
