Superhigh Electromechanical Coupling and Zero-Temperature Characteristics of KNbO 3 and Wide Band Filter Applications

• Published in: Japanese Journal of Applied Physics Vol. 37; no. 5S; p. 2929
• Main Authors: Hiroyuki Odagawa, Hiroyuki Odagawa, Kazuhiko Yamanouchi, Kazuhiko Yamanouchi
• Format: Journal Article
• Language: English
• Published: 01.05.1998
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.37.2929

In this paper, a superhigh electromechanical coupling surface acoustic wave (SAW) propagating on a potassium niobate (KNbO 3 ) substrate is described and its applications for low-loss, wide band and temperature stable SAW filters are investigated. KNbO 3 has large piezoelectric constants. We obtained the electromechanical coupling coefficient ( K 2 ) of 0.53 for SAW in a Y-cut X-propagating substrate, theoretically and experimentally. It is observed to be about 10 times as large as that in LiNbO 3 . Moreover, we obtained the zero temperature characteristics around room temperature, in a rotated Y cut substrate. The experimental results of the wide band SAW filters show low loss and stable temperature characteristics. The bandwidth is about 20% and the insertion losses are less than 2–6 dB. The simulation results of a ladder-type filter using the Y-cut KNbO 3 show a bandwidth of 40%.