Super high electromechanical coupling and zero-temperature characteristics of KNbO3 and its applications for low-loss wide band filters

This paper describes a super high electromechanical coupling SAW propagating on potassium niobate (KNbO₃) substrate and its applications for low-loss, wide band and temperature stable SAW filters. KNbO₃ has large piezoelectric constants. We obtained the electromechanical coupling coefficient (K²) of 0.53 for SAW in Y-cut X-propagating substrate theoretically and experimentally. It is about 10 times as large as that in LiNbO₃. Moreover, we obtained the zero temperature characteristics around room temperature in rotated Y cut substrate. Experimental results of wide band SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20% and insertion losses are less than 2~6 dB. Simulation result of ladder type filter using Y-cut KNbO₃, shows the bandwidth of 40%