Modeling and Suppression of SiO2 Guided Mode on TC-SAW with a Cancelling Circuit

A TC-SAW (Temperature Compensated Surface Acoustic Wave) by LiNbO3 covered with a SiO2 film structure is proposed as a temperature compensation method. The TC-SAW with SiO2/LiNbO3 structure has satisfactory Q and TCF and moderate k(eff)(2). However, this structure contains various spurious responses in and out of the passband. Management of these spurious responses is necessary for TC-SAW filter design. One of the spurious responses observed well above the passband is the SiO2 guided mode. Suppression of this spurious mode is critical to achieving the attenuation required by Carrier Aggregation. This study discusses the SiO2 guided mode analysis and modeling method. Additionally, a design technique for suppression of the SiO2 guided mode by means of a cancelling circuit is discussed and applied to a ladder-type filter design.