Epitaxial growth of piezoelectric oxide films

氧化物电极的制备和表征是用单晶LGS压电衬底(La3Ga5SiO14)完成的。主要研究对象是外延沉积的LGS薄膜。由于掺杂，它们相对于衬底表现出更高的导电性，从而充当例如压电谐振器的电极。通常情况下，电极和衬底的电导率差很大，才能在电极之间形成均匀的电场。使用导电率较低的压电性衬底可以进一步增加导电性的差异。由于LGS系列的新的压电晶体，即CTGS晶体(Ca3TaGa3Si2O14)，在项目开始时就有足够的尺寸和质量，这些晶体也被用作衬底并包括在调查中。这些LGS同象只表现出略有不同的晶格常数。加入CTGs衬底是工作计划的延伸。总体而言，整体或几乎整体的电极可以在1000°C下运行，并在高温下导致品质因数的适度提高。然而，频率的意外温度响应尤其重要，因为它打开了新的研究视角。因此，该项目的重点从薄膜的开发转移到与电极导电性有关的声学性能上。因此，温度补偿谐振器代表了一个重要的应用相关方面。为了了解潜在的机制，必须确定振动的模式。此外，必须验证这一假设，即横向和横向振动的叠加可以通过电极的导电性来调整。问题是，与温度相关的谐振频率的最大值的位置和宽度是否可以调整，以便在特定温度范围内应用具有平坦温度分布的定制谐振器。为了充分利用电极的导电性，除了LGS外，还应该包括非外延氧化膜。需要解决的任务包括通过测量谐振器的横向和横向位移来确定振动模式。这是一个具有挑战性的方面，因为在高温下必须预期(亚)纳米范围的位移。此外，还需要对层和衬底系统的结构、化学、电气和机电特性进行详细的表征。

The preparation and characterization of oxide and thus oxidation-resistant electrodes is performed by using single crystalline piezoelectric LGS substrates (La3Ga5SiO14). The main object of investigation are epitaxially deposited LGS films. Due to doping, they exhibit increased electrical conductivity with respect to the substrate and thus act as electrodes for e. g. piezoelectric resonators. In general, a large difference in conductivity of electrode and substrate is required to form a homogeneous electric field between the electrodes. The difference in conductivity can be increased even more by using piezoelectric substrates with lower conductivity. Since new piezoelectric crystals of the LGS family, namely CTGS crystals (Ca3TaGa3Si2O14), are available in sufficient size and quality at the beginning of the project, these crystals are also used as substrates and included in the investigations. These LGS isomorphs exhibit only slightly different lattice constants. The incorporation of CTGS substrates represents an extension of the work program.Overall, it can be stated that monolithic or almost monolithic electrodes are operational at 1000 °C and result in a moderate improvement of the quality factor at high temperatures. However, the unexpected temperature response of the frequency is of particular importance as it opens new research perspectives. Therefore, the focus of the project is shifted from film development to acoustic properties in relation to electrode conductivity. Thereby, temperature-compensated resonators represent an important application relevant aspect. In order to understand the underlying mechanisms, the modes of vibration must be determined. Further, the hypothesis must be validated that a superposition of transverse and lateral vibrations can be adjusted by the conductivity of the electrodes. The question is, whether the position and the width of the maximum of the temperature-dependent resonant frequency can be adjusted so that tailored resonators with a flat temperature profile for certain temperature ranges can be applied. In order to take advantage of a wide range of electrode conductivity, non-epitaxial oxide films other than LGS should be included.The tasks to be solved include the determination of the vibration modes by measuring the lateral and transversal displacements of the resonators. It is a challenging aspect since displacements in the (sub)nanometer range have to be expected at high temperatures. Furthermore, a detailed structural, chemical, electrical and electromechanical characterization of the system of layer and substrate is required.