Abstract The flexoelectric effect describes the electromechanical coupling of a strain gradient to a polarization and vice versa. This effect scales linearly with permittivity and strain gradients can get very high for dimensions on the micro and nanoscale. Even though the flexoelectric effect can be best exploited within micro or nanoelectromechanical systems (M/NEMS) applications, it has not been established in today`s M/NEMS device architectures as other transducer principles, like piezoelectricity. In this work, values of the converse flexoelectric coefficient for one of the most promising flexoelectric materials, titanium dioxide (TiO2) are provided. The experimental results are based on a carefull characterization of IrO2/TiO2/IrO2 cantilevers. Besides CMOS compatiblity TiO2 is selected as functional thin film material as it offers a very high permittivity and shows no hysteresis or saturation effects as it is neither ferro- nor paraelectric. Additionally, it guarantees a low cost, lead-free realization and can be directly integrated in a standard silicon MEMS fabrication process by sputter deposition. In order to correctly determine the flexoelectric coefficient, other electromechanical coupling effects are considered and assessed. The flexoelectric coefficient is shown to be µeff = 1.78 ± 0.16 nC m−1 at 10 kHz. The flexoelectric coupling constant with a value of 2.75 V is in good agreement with that theoretically predicted by Kogan`s estimate of 3.14 V.

中文翻译：

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多晶 TiO2 薄膜中的柔电性

摘要 挠电效应描述了应变梯度与极化的机电耦合，反之亦然。这种效应与介电常数呈线性关系，应变梯度对于微米和纳米尺度的尺寸会变得非常高。尽管可以在微或纳米机电系统 (M/NEMS) 应用中最好地利用挠曲电效应，但在当今的 M/NEMS 设备架构中，它还没有像压电等其他换能器原理那样建立。在这项工作中，提供了最有前途的挠电材料之一二氧化钛 (TiO2) 的逆挠曲电系数值。实验结果基于对 IrO2/TiO2/IrO2 悬臂的仔细表征。除了 CMOS 兼容性，TiO2 被选为功能性薄膜材料，因为它提供了非常高的介电常数，并且没有滞后或饱和效应，因为它既不是铁电也不是顺电。此外，它保证了低成本、无铅的实现，并且可以通过溅射沉积直接集成到标准的硅 MEMS 制造工艺中。为了正确确定挠电系数，需要考虑和评估其他机电耦合效应。弯曲电系数在 10 kHz 时显示为 µeff = 1.78 ± 0.16 nC m-1。值为 2.75 V 的挠曲电耦合常数与 Kogan 估计的 3.14 V 理论预测值非常一致。它保证了低成本、无铅的实现，并且可以通过溅射沉积直接集成到标准硅 MEMS 制造工艺中。为了正确确定挠电系数，需要考虑和评估其他机电耦合效应。弯曲电系数在 10 kHz 时显示为 µeff = 1.78 ± 0.16 nC m-1。值为 2.75 V 的挠曲电耦合常数与 Kogan 估计的 3.14 V 理论预测值非常一致。它保证了低成本、无铅的实现，并且可以通过溅射沉积直接集成到标准的硅 MEMS 制造工艺中。为了正确确定挠电系数，需要考虑和评估其他机电耦合效应。弯曲电系数在 10 kHz 时显示为 µeff = 1.78 ± 0.16 nC m-1。值为 2.75 V 的挠曲电耦合常数与 Kogan 估计的 3.14 V 理论预测值非常一致。