Super high electromechanical coupling and zero-temperature characteristics of KNbO/sub 3/ and its applications for low-loss wide band filters

Abstract

This paper describes a super high electromechanical coupling SAW propagating on potassium niobate (KNbO/sub 3/) substrate and its applications for low-loss, wide band and temperature stable SAW filters. KNbO/sub 3/ has large piezoelectric constants. We obtained the electromechanical coupling coefficient (K/sup 2/) of 0.53 for SAW in Y-cut X-propagating substrate theoretically and experimentally. It is about 10 times as large as that in LiNbO/sub 3/. 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/spl sim/6 dB. Simulation result of ladder type filter using Y-cut KNbO/sub 3/, shows the bandwidth of 40%.