Spurious mode suppression in multiple layer HfO2/Simax acoustical mirror structure for ILAW on 15°-YX LiNbO3

Cavityless wafer level packaging and TCF improvement are possible with isolated layer acoustic wave (ILAW) with an acoustical mirror structure. Meanwhile orientations of LiNbO₃ with high coupling factor that are needed for wideband SAW filters are known to possess spurious modes in the working frequency range. Several attempts with useful outcome have been published for orientations around 15°-YX LiNbO₃, the cut angle was also optimized for reduction of the spurious mode coupling factor. This paper investigates the possibility to use the ILAW supporting structure for suppression of spurious modes by exploiting the difference in propagation properties of the waves with different displacement polarization. The results show that the mirror structure with ILAW that is aimed for cavityless wafer level packaging and TCF improvement can simultaneously be used for suppression of the spurious mode in wideband filters.