(Invited) A New Approach to Multifunctional Piezoelectric Thin Films for Flexible Device Applications

Abstract

The objective of this research is to demonstrate the novel concept of enhancing the sensing capability and the long-term reliability of thin film piezoelectric devices via a low cost and simple MEMS-less processed flexible structure with our unique ultra-thin conductive metal foil substrate. The flexible thin metal foil substrate can act as a substrate and electrode without any process temperature limitation up to 750 oC. Piezoelectric films (PZT-based and environmentally friendly lead (Pb)-free KNN-based systems) constructed on ultra-thin flexible substrate enhance the piezoelectric performance because of the contributions resulting from the biaxial strain imposed by the substrate. These films show further improved output voltage and sensing capacity due to increased flexure of the device in comparison with piezoelectric devices integrated with more rigid substrates. Moreover, this flexible piezoelectric structure has a high degree of freedom with no shape limitation and is easy to laminate on any substrates including PCBs if necessary. In this research, we also suggest the key solutions for solving the current degradation mechanisms such as depolarization, temperature, voltage, and stress limitations, and other aging effects by systematic investigation from materials to structure designs. The prediction and the solution for degradation mechanism and failure mode will be explained in simple and clear terms. Our experimental results for piezoelectric materials and flexible devices propose to achieve the robust piezoelectric sensors and actuators that overcome the limitations of current state-of-the-art devices. Our suggested concept is envisioned as a commercially viable structure since the devices can be constructed by simple and mass-producible process.