SAW Filter Bank with Low Insertion Loss and High Power Handling Capability Employing Multi Layered Sapphire Substrate

In this study, we succeeded to realize low loss and high power capable multi-layered SAW (Surface Acoustic Wave) technologies and demonstrated a filter bank in a single die for mid to high band systems. Firstly, we clarified the dependence of cut angle of LiTaO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and electrode thickness on SAW resonator characteristics comparing to Leaky SAW (L-SAW) and multi-layered SAW employing sapphire substrate. The admittance ratio of L-SAW strongly depends on the cut angle of LiTaO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and electrode thickness. In contrast, the admittance ratio of multi-layered SAW depends less on both cut angle of LiTaO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> from 30°Y-X to 56°Y-X and electrode thickness per wavelength from 0.07 to 0.11. Therefore, the cut angle of LiTaO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and the electrode thickness can be selected according to the filter requirements of each band by multi-layered SAW structure. Next, we investigated the power handling performance. Due to good heat radiation of SAW substrate and direct mount type package, power handling more than 35dBm was confirmed. Finally, we fabricated a n34/n39/n40/n41 TDD filter bank in a single die with the same electrode thickness. The minimum insertion loss in the pass band of all filters was achieved at less than 1dB. The results realized mid to high band filter bank integration of lower insertion loss. Furthermore, mid to high band FDD filter bank (duplexer bank) was demonstrated.