Preparation of composition-modulated ALN/Al_2O_3 structure and its application to acoustic wave devices

该项目旨在合成成分调制压电材料并将其应用于声波器件。成分调制材料是指两种以上不同种类的材料在空间上排列而成的材料，结果表明，当空间排列的周期性小于约1/5声波波长时，成分调制材料可视为均匀材料。然而，对于增加的周期性（或减小的声波波长），高阶模式传播并且成分调制材料的行为变得复杂。除了这些事实，它表明，复杂的安排，其组成材料给成分调制材料的新特性，不在于其组成材料之间。在实验上，我们尝试了在N_2或N_2+Ar气氛中用直流反应磁控溅射法制备AlN压电薄膜。最后，在GaAs衬底上制备了ZnO和AlN结构，开发了单片声表面波器件。正如理论分析所预期的那样，该结构表现出很大的压电耦合。然而，人们发现，需要一种技术来制备小于0.5的非常薄的压电AlN薄膜<micrn>，以开发由薄的多层组成的成分调制结构。

The project is aimed at synthesising composition-modulated piezoelectric materials and applying them to acoustic wave devices. The composition-modulated materials are those which are realised by spacially arranging more than two materials of different kind.The result has shown that the composition-modulated material can be regarded as a homogeneous material when the periodicity for the spacial arrangement is less than about 1/5 acoustic wavelengths. However, for an increased periodicity (or a decreased acoustic wavelength), higher order modes propagate and the behaviour of the composition-modulated material becomes complicated. Added to these facts, it is shown that sophisticated arrangements of its constituent materials give the composition-modulated material new properties which do not lie between those of its constituent materials. Experimentally, preparation of piezoelectric AlN films by reactive DC magnetron sputtering in an N_2 or N_2+Ar atmosphere has been attempted. Finally, a ZnO and AlN structure was prepared on a GaAs substrate to develop a monolithic surface acoustic wave device. As was expected from the theoretical analysis, the structure exhibited a large piezoelectric coupling. However, it was found that a technique to prepare very thin piezoelectric AlN fims of less than 0.5<micrn> is needed to develop a composition-modulated structure consisting of thin multi-layers.