Takai Tsutomu, Iwamoto Hideki, Takamine Yuichi, Fuyutsume Toshiyuki, Nakao Takeshi, Hiramoto Masahiro, Toi Takanori, Koshino Masayoshi
IEEE Trans Ultrason Ferroelectr Freq Control. 2019 May;66(5):1006-1013. doi: 10.1109/TUFFC.2019.2898046. Epub 2019 Feb 7.
In response to the increased mobile data traffic, there is a growing need for more low-loss RF band filters with steep frequency characteristics, and high-quality ( Q )-factor and low-temperature coefficient of frequency (TCF) resonators are required to achieve this. We previously reported that for a surface acoustic wave (SAW) resonator on a three-layer structure, which is composed of a thin LiTaO (LT) plate whose orientation is 50° rotated YX propagation, SiO layer, and AlN layer on a Si substrate, a Q-factor several times higher than that of an SAW resonator on a standard 42° rotated YX propagation LiTaO (42YX-LT) substrate could be obtained. In this study, we investigated this layer structure and found that a two-layer structure, in which the AlN layer is removed, achieves a high Q -factor. Numerical analyses using a finite element method showed that the acoustic wave energy can be confined to the surface of the two-layer substrate, and the TCF and electromechanical coupling coefficient ( k ) were improved by optimizing the thickness of each layer. We fabricated and evaluated prototype one-port resonators with the two-layer structure and the standard 42YX-LT SAW substrate with resonant frequencies from 0.95 to 3.6 GHz. An improvement of the Q-factor of 3 to 4 times compared with that of the resonator with standard 42YX-LT substrate was observed for the two-layer structure, which means that a reduction of complexity of the layer structure could be obtained without performance loss. The two-layer structure was applied to a 2.4-GHz band Wi-Fi filter to achieve high performances such as low-loss, better steepness, and high attenuation.
随着移动数据流量的增加，对具有陡峭频率特性的更多低损耗射频带通滤波器的需求日益增长，为此需要高品质因数（Q）和低频率温度系数（TCF）的谐振器。我们之前报道过，对于由在Si衬底上取向为50°旋转YX传播的薄钽酸锂（LT）板、SiO层和AlN层组成的三层结构上的表面声波（SAW）谐振器，可以获得比标准42°旋转YX传播钽酸锂（42YX-LT）衬底上的SAW谐振器高出几倍的Q因数。在本研究中，我们对该层结构进行了研究，发现去除AlN层的两层结构可实现高Q因数。使用有限元方法进行的数值分析表明，声波能量可以限制在两层衬底的表面，并且通过优化各层的厚度提高了TCF和机电耦合系数（k）。我们制作并评估了具有两层结构的原型单端口谐振器以及谐振频率为0.95至3.6 GHz的标准42YX-LT SAW衬底。对于两层结构，观察到与具有标准42YX-LT衬底的谐振器相比，Q因数提高了3至4倍，这意味着在不损失性能的情况下可以降低层结构的复杂性。两层结构被应用于2.4 GHz频段的Wi-Fi滤波器，以实现低损耗、更好的陡度和高衰减等高性能。
