GOALI: Environmentally-Benign Lead-Free Piezoelectric Films for Flexible High Strain Transducers and Actuators

用于柔性高应变传感器和执行器的环保型无铅压电薄膜非技术说明：传感器和执行器在现代生活中扮演着关键角色，它们无缝集成到汽车、家庭、相机、声纳、打印机、医疗成像和诊断、智能可穿戴设备、电子系统控制等系统中。由于可以实现很高的机电转换效率，大多数这些应用中使用的主要压电材料系统是锆钛酸铅(PZT)系统。然而，铅的毒性导致全球努力寻找替代系统。该项目采用了一种新的致动器材料、设计和制造方法，并展示了具有坚固器件结构的高应变无铅致动器。它将提供对无铅换能器材料在高应变下运行的基本理解。该项目还表明，可以在可穿戴设备和移动应用的灵活电子设备中内置更多功能。该项目将是一个要求苛刻的研究培训工具，因为它要求研究的深度和广度，并涵盖多学科的主题，从环境友好型铁电和压电材料的基本性质，加工，器件结构和集成，以及柔性电子系统的设计元素。技术描述：传统上，小信号压电系数(D33)值被用来比较不同的压电材料。然而，对于执行器应用，在外加电场Emax时可实现的应变Smax是关键的品质因数，它们的比率Smax/Emax(归一化应变，大信号D33或D33*)是感兴趣的量。两者之间的区别非常重要，必须谨慎处理；在传统的“软”PZT中，由于对响应的贡献不同，小信号和大信号的应变响应可能相差2倍。对PZT材料的压电性有了基本的了解。然而，越来越清楚的是，非铅基材料在极化和应变的微观贡献、开关机制、电畴行为、非本征贡献等方面表现出相当不同的行为。此外，对于高应变驱动器至关重要的无铅压电材料的高场高应变特性还处于非常早期的研究阶段，因为大多数研究都集中在无铅材料的小信号特性上。施乐-布朗关于高场-高应变特性的合作项目以及对这些材料来源的基础研究将为专注于开发高应变无铅致动器的合作提供关键的支持和理解。这项合作将建立在布朗大学在加工和器件方面的创新以及施乐在高应变压电致动器和建模能力方面的经验的基础上。该项目将利用对环境友好的非铅基压电材料的行为的新兴集体理解，并将这种理解应用于我们正在开发的使用柔性金属箔衬底的多功能高应变致动器的新工艺方法。在此过程中，我们将更好地了解压电致动器的性能控制参数，并了解高场高应变效应的机制以及高质量压电器件可能的性能限制退化，包括但不限于高应变传感器和致动器。这项研究将为新出现的环境友好型高性能压电材料和器件的创新加工提供指导和平台，并将提供可与其他柔性电子设备集成的新型柔性压电传感器和执行器的设计概念。

Environmentally-Benign Lead-Free Piezoelectric Filmsfor Flexible High Strain Transducers and ActuatorsNon-technical Description: Sensors and actuators play a critical role in modern life, where they are seamlessly integrated into systems such as automobiles, homes, cameras, sonar, printers, medical imaging and diagnostics, smart wearable devices, electronic system controls, and so on. The dominant piezoelectric material system used for most of these applications is the lead zirconate titanate (PZT) system, due to the high electromechanical conversion efficiencies that can be achieved. However, the toxicity of lead (Pb), however, has led to global efforts to identify a replacement system. This project takes a novel approach to actuator materials, design and fabrication, and provides a demonstration of high strain lead-free actuators with robust device structures. It will provide fundamental understanding of the lead-free transducer materials operating at high strains. The project also demonstrates that greater functionality can be built into flexible electronics for wearable devices and mobile applications. The project will be a demanding research training vehicle, as it demands both research depth and breadth, and covers multidisciplinary topics ranging from fundamental properties of environmentally friendly ferroelectric and piezoelectric materials, processing, device structure and integration, and design elements of flexible electronic systems.Technical Description: Traditionally a small-signal piezoelectric coefficient (d33) value has been used to compare different piezoelectric materials. However, for the actuator applications the achievable strain Smax at the applied electric field Emax is the key figure of merit and their ratio Smax/Emax (normalized strain, large-signal d33, or d33*) is the quantity of interest. The difference between the two is very important and has to be carefully addressed; in traditional "soft" PZT small signal and large signal strain responses can differ by a factor of 2 due to different contributions to the response. The basic understanding of the piezoelectric behavior of the PZT materials is relatively well developed. However, it is becoming increasingly clear that the non-lead based materials display rather different behavior in terms of microscopic contributions to polarization and strain, switching mechanisms, domain behavior, extrinsic contributions, etc. In addition, the high-field high-strain properties of the lead-free piezoelectric materials, critical for high strain actuators, are only at very early stages of research, as most of the research has been focused on small signal properties of the lead-free materials. The Xerox-Brown collaborative project for high-field-high-strain properties and fundamental investigation of their origin on these materials will provide critical support and understanding for the collaboration that is focused on developing high strain lead-free actuators. The collaboration will build upon Brown University innovations in processing and devices and Xerox experience in high strain piezoelectric actuators and modeling capability. This project lies in the use of the emerging collective understanding of the behavior of environmentally-benign non-lead based piezoelectric materials and applying this understanding to a new process method that we are developing for multi-functional high strain actuators using flexible metal foil substrates. In doing so, we will develop an improved understanding of the property-control parameters of the piezoelectric actuators, and an understanding of the mechanisms of high-field high-strain effects and the possible performance-limiting degradation of high quality piezoelectric devices, including but not limited to high strain sensors and actuators. The research will provide guidance and a platform for the innovative processing of emerging environmentally benign piezoelectric materials and devices with high performance, and will deliver design concepts for a new class of flexible piezoelectric sensors and actuators that could be integrated with other flexible electronics.