Collaborative Research: Space Charge Induced Flexoelectric (SCIF) Transducers: A New Technology to Eliminate the Environmental Cost of Leaded Piezoelectric Transducers

Non-technical descriptionPiezoelectric materials convert mechanical force to electrical voltage and vice-versa. These materials are used in precision sensors, optics, acoustic transmitters and receivers, and energy harvesting devices. Most high-performance piezoelectric materials contain lead. It is estimated that the annual worldwide production of lead-containing piezoelectric materials is between 1250 and 4000 tons. The lead contained in these materials represents an environmental risk all along the value chain, from mining to end device disposal, and is increasingly subject to health, safety, and environmental legislation. This project will develop an environmentally benign replacement for piezoelectric transducers. This new technology will be based on a newly observed phenomenon in semiconducting materials including silicon. In this project, the team of researchers will fabricate nano-structured silicon devices that can replace lead-containing piezoelectric materials. In addition to creating a replacement for lead-containing piezoelectrics, the study of this new technology will enhance the scientific community’s understanding of electrical-mechanical interaction in solid materials more generally. The newly created devices will be transformative for sensing, actuation, and energy harvesting applications.Technical descriptionLead zirconate titanate (PZT), or other lead-containing piezoelectrics, are widely used in precision sensors, actuators for optics, acoustic transmitters and receivers, energy harvesters, and precision positioning devices. Despite the significant environmental concerns, there is still no good replacement for PZT. In this project we will make use of a newly observed phenomenon, space charge induced flexoelectricity, to create a high-performance alternative to PZT transducers. Flexoelectricity refers to electrical polarization of a dielectric material in response to strain gradient. It has recently been observed that semiconducting materials, including silicon, with insulating interfaces (i.e., space charge materials) exhibit enhanced flexoelectricity. In this project the team of researchers will fabricate arrays of nano-structured silicon pyramids to create and study space charge induced flexoelectric transducers. In tandem with the fabrication work, the investigators will create a computational framework for simulating the interaction between the strain gradient, the electric field, and the diffusion of mobile charge carriers. This computational framework will enable a detailed investigation into the mechanisms driving space charge flexoelectricity and allow optimization of transducers. Such transducers could have effective piezoelectric coefficients an order of magnitude higher than state-of-the-art micro-scale piezoelectric materials. Given that they are made from silicon, they fill the need for a non-toxic, environmentally benign replacement to high performance piezoelectric transducers. Space charge induced flexoelectric transducers will be transformative for a broad range of smart materials applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.