Tailored piezoelectric thin films for energy harvester

Abstract

Piezoelectric materials are excellent materials to transfer mechanical energy into electrical energy, which can be stored and used to power other devices. PiezoMEMS is a good way to combine silicon wafer processing and piezoelectric thin film technology and lead to a variety of miniaturized and premium devices. In this thesis, energy harvesters are made, based on epitaxial PZT thin films with enhanced material properties. These vibration energy-harvesting devices consists of a bulk mass attached to a cantilever. In order to increase the performance of energy harvesters, both intrinsic and extrinsic properties in the thin film play a role. For increasing the power output of the devices, we need to seek for piezoelectric thin film with both enhanced piezoelectric coefficient and a lower dielectric constant. Material with a high figure-of-merit (FOM) will be used for energy harvester fabrication. In this work, two ways are used to modify the PZT thin films. First of all, different properties are studied by changing the ratios of Zr and Ti. Secondly, the introduction of additional dopants make the properties of piezoelectric thin film change significantly. After the fundamental study, the epitaxial vibration-harvesting devices are fabricated, which are able to generate energy at microWatt scale with low vibration state. Furthermore, after power normalization, a comparison is made between different vibration harvester. It is concluded that the epitaxial PZT thin film harvester devices outperform the textured PZT and AlN thin film harvesters. To conclude, epitaxial PZT thin film based vibration energy harvesting devices were successfully designed and fabricated. From the material point of view, the crystallographic structure and functional properties of the epitaxial PZT thin films were investigated thoroughly. The physical mechanisms are discussed in each case. Those studies enabled the device specific optimization of the epitaxial PZT thin films. From the application point of view, vibration energy harvester devices with epitaxial piezoelectric thin films were investigated. The strong piezoelectric activity and the outstanding power output in these epitaxial harvesters open the possibility for industrial applications.