Dielectric and Piezoelectric Properties of Epitaxial Ferroelectric Bilayers

Alexei Y. Grigoriev, University of Tulsa, DMR 1057159

Thermodynamic theory of ferroelectrics provides important information on dielectric and piezoelectric properties of Pb(Zr,Ti)O3 (PZT) ferroelectric bilayers. This theory helped us to interpret experimental data and conclude that the electrostatic coupling between ~100-nm-thick PZT layers is weak. The weak coupling explains the stability of unusual tail-to-tail polarization domains observed in the bilayers (PRB, 2013, in preparation). It can also explain a very strong frequency dependence of the dielectric permittivity at a non-zero applied bias (JAP 113, 0747104 (2013)). The approach that combines thermodynamics-based calculations with experimental measurements will be very useful not only for interpreting experiments, but also for engineering new ferroelectric multilayer materials with enhanced dielectric and piezoelectric properties. Such new advanced materials are of great interest for applications in microelectronics, electromechanical devices, and sensors.

(a) The average relative dielectric permittivity of a PZT bilayer as a function of the epitaxial misfit strain and the strength of the electrostatic coupling. (b) Piezoelectric coefficients d33 as a function of the electrostatic coupling strength. (c) Relative dielectric permittivity as a function of the applied bias voltage for a PbZr0.6Ti0.4O3/PbZr0.2Ti0.8O3 bilayer capacitor at several ac signal frequencies. (d) Frequency dependence of the relative dielectric permittivity at several selected values of the applied bias. (c) and (d) are from JAP paper.

Improving Learning Experience of Undergraduate Students in Science and Technology

Alexei Y. Grigoriev, University of Tulsa, DMR 1057159

Undergraduate instrumentation lab at the University of Tulsa is used for testing new approaches to improving students understanding of physical principles of operation and engineering design concepts of analog and digital electronic circuits:• Origin data analysis and graphing software is integrated in the lab course. Students can now

analyze data and present results in a professional format. (see press release: http://www.originlab.com/index.aspx?go=Solutions%2FCaseStudies&pid=2023)

• Some examples of new students projects involve:• testing ferroelectric materials using professional equipment as well as developing

simple measurement circuits• using Lego Mindstorms based development kits to design and implement complex

systems involving sensors, actuators, and microcontrollers. For example, a Brewster angle measurement system (shown in the picture) is controlled by a combination of PIC and Lego NXT microcontrollers.

Undergraduate students participated in multiple research projects including theoretical modeling of ferroelectric multilayers and epitaxial growth of oxide thin films. Kirby Smithe, a student who was involved in research with our group on this NSF project and visited the Argonne National Lab, has received the NSF Graduate Research Fellowship.