Novel Thin-Film Piezoelectric Materials for Ultrasound Applications

我们的项目探索了一种设计高频平面微声转换器的新方法。此类设备目前用于移动通信系统中的信号处理或用作微声传感器。常见的压电单晶体(SiO_2、LiNbO_3、LiTaO_3、AlN、…)的性能极限似乎已经达到了极限。已经联系上了。我们的项目采用了一种全新的方法来增强当前微声部件的性能。关键元件是一种由新型压电材料制成的功能薄膜，用于将高频电信号转换为声信号。我们的创新之处在于通过外延生长来控制功能材料的性能，以便根据特定的应用来优化这些性能。这一方面是通过故意以受控的方式使晶格应变，另一方面是通过在薄膜生长过程中故意引入缺陷来实现的。我们的薄膜是由K_xNa_(1-x)NbO_3(K_xNa_(1-x)NbO_3)制备的，这允许压电超声转换。其机电系数与铅基压电化合物相当。然而，当使用K_xNa_(1-x)NbO_3时，没有可持续性的问题。与目前的层状超声换能器相比，厚度小于100 nm的超薄薄膜是一种本质上的新奇。特别是，这使得通过应变和缺陷工程在大范围内定制功能特性成为可能。因此，结构材料特性为下一代超声部件的发展提供了新的自由度。该项目以合作者在KxNa{1-x}NbO_3薄膜生长、结构和功能表征以及微声元件技术开发方面的专业知识为基础。通过将基础材料科学和应用材料科学与系统设计工程相结合，我们能够结合创新的设计策略来探索这种新型材料的潜力。然而，开发特定的设备并不是项目目标。该项目的成功实施在于，与已知的单晶衬底相比，验证了这种新型材料系统在高频(5 GHz)下的优势。

Our project explores a novel approach for designing high frequency planar microacoustic converters. Such devices are currently used for signal processing in mobile communication systems or as microacoustic sensors. It appears as if the performance limits of common piezoelectric single crystals (SiO2, LiNbO3, LiTaO3, AlN, …) have been reached. Our project employs a radically new approach to enhance the performance of the current microacoustic components. A key element is a functional thin film made from a novel piezoelectric material which is used to convert high frequency electrical into acoustic signals. Our innovation consists in controlling the functional material properties through epitaxial growth in order to optimize these properties with respect to a specificapplication. This is achieved on the one hand by intentionally straining the crystal lattice in a controlled way and, on the other hand, by purposefully introducing defects during film growth. Our thin films are fabricated from potassium-sodium-niobate (K_xNa_{1-x}NbO_3), which allows for piezoelectric ultrasound conversion. The electromechanical coefficients are comparable to lead-based piezoelectric compounds. However, there are no concerns about sustainability when using K_xNa_{1-x}NbO_3. The extremely thin film thickness of less than 100 nm is an essential novelty in comparison with current layered ultrasound converters. In particular, this enables tailoring of functional properties over a large range via strain- and defect engineering. Thus, structural material properties provide a new degree of freedom for the development of next generation ultrasound components. This project builds on the expertise of the collaborators for thin film growth of piezoelectric K_xNa_{1-x}NbO_3, its structural and functional characterization and for technology development for microacoustic components. By combining fundamental and applied material science with system design engineering we are able to explore the potential of this novel material in conjunction with innovative design strategies. However, development of specific devices is not a project goal. The successful execution of the project consists rather in the validation of the advantages of the novel material system at high operation frequencies (> 5 GHz) in comparison with known single-crystal substrates.