GPS/GLONASS filter using the Stoneley wave for high reliability applications

We developed a very small sized GPS/GLONASS filter for high reliability applications using boundary acoustic wave. Boundary acoustic wave devices have many advantages such as smaller size and higher reliability than surface acoustic wave devices, because they don´t need cavity. As a boundary acoustic wave, we adopted the Stoneley wave on 120° Y-X LiNbO₃ (LN). Although the conventional Stoneley wave has not been studied widely because of its too small electromechanical coupling coefficient (k²), the Stoneley wave on around 128° Y-X LN has larger k², which is enough to design narrow band applications such as GPS/GLONASS filters. Cut angle of LN is optimized so as to minimize the k² of the shear-horizontal type boundary acoustic wave which causes a spurious response. Additionally, we developed a new concept simple and high reliable package structure utilizing the features of boundary acoustic wave. Using this boundary acoustic wave mode and package structure, we fabricated a novel filter with very small size (1.3mm × 0.9mm × 0.5mm). The developed filter achieves good electrical characteristics for example small insertion loss and steep cut off. Moreover, several reliability tests such as humidity and thermal shock were carried out and it was confirmed that the developed filter realizes automotive class high reliability performances. These results show the applicability of the boundary acoustic wave devices to high reliability applications.