Ferroelectric zirconium oxide for piezo- and pyroelectric devices

Prof. Dr. rer. nat. Alfred Kersch
Department Applied Sciences and Mechatronics

The DFG project takes place in cooperation with Namlab (TU Dresden) and RWTH Aachen. The aim is to transfer the large piezoelectric effect in ZrO2 and HfO2, which previously could only be realized in layers of a few 100 nm, to thicknesses of 1000-2000 nm.

With the piezoelectric effect, mechanical tension leads to an electric field, or conversely, an electric field leads to mechanical expansion. This transducer property is of enormous importance in engineering. Applications can be found in actuators, motors, oscillators, but also in sensors and energy harvesting. Frequency filters based on thin-film piezoelectrics are an application for the general public in mobile communications. The best known piezoelectric materials are lead zirconium titanate (PZT) for actuators and aluminium nitride (AlN) for thin-film sound wave resonators. Due to environmental standards, people have been working on lead-free materials for years. At the same time, the requirements placed on the piezo coefficient have increased, especially in microelectronic applications as frequency filters. The ferroelectric properties of zirconium and hafnium oxide were discovered about 10 years ago. The piezoelectric properties are so great that there is the hope of using this material for lead-free frequency filters. The pyroelectric properties are another issue.

However, layers thicker than a few 100 nm tend to lose the required ferroelectric and piezoelectric properties. This is where the project starts. Solving the problem requires a fundamental understanding of thin film material properties. These are obtained with the help of experimental data and simulations based on density functional theory. The Munich University of Applied Sciences is responsible for the simulations. One possibility to achieve the desired properties is specific doping, where the choice of the dopant is done with the help of the simulations.