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

非技术描述压电材料将机械力转换为电压，反之亦然。这些材料用于精密传感器、光学、声学发射器和接收器以及能量采集设备。大多数高性能的压电材料都含有铅。据估计，全球含铅压电材料的年产量在1250吨至4000吨之间。这些材料中所含的铅代表着整个价值链上的环境风险，从采矿到终端设备处置，越来越多地受到健康、安全和环境立法的制约。该项目将开发一种对环境无害的压电换能器的替代品。这项新技术将基于在包括硅在内的半导体材料中新观察到的一种现象。在这个项目中，研究团队将制造可以取代含铅压电材料的纳米结构硅器件。除了创造含铅压电材料的替代品外，这项新技术的研究还将加强科学界对固体材料中更广泛的机电相互作用的理解。这些新发明的器件将对传感、驱动和能量采集应用产生革命性的影响。技术描述钛酸铅(PZT)或其他含铅压电材料广泛应用于精密传感器、光学致动器、声发射器和接收器、能量采集器和精密定位设备。尽管存在严重的环境问题，但PZT仍然没有很好的替代品。在这个项目中，我们将利用一种新观察到的现象--空间电荷感应挠曲电来创造一种高性能的替代PZT换能器的方法。挠性电是指电介质材料在应变梯度下的电极化。最近观察到，包括硅在内的具有绝缘界面的半导体材料(即空间电荷材料)表现出增强的挠曲电性。在这个项目中，研究团队将制造纳米结构硅金字塔阵列，以创建和研究空间电荷感应型挠曲电换能器。在制造工作的同时，研究人员将创建一个计算框架，用于模拟应变梯度、电场和移动电荷载流子扩散之间的相互作用。这一计算框架将使我们能够详细研究驱动空间电荷挠曲电性的机制，并允许优化换能器。这种换能器的有效压电系数可能比最先进的微尺度压电材料高一个数量级。考虑到它们是由硅制成的，它们填补了对高性能压电换能器的无毒、环保替代品的需求。空间电荷感应式挠曲电传感器将对智能材料的广泛应用产生革命性的影响。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.