Research of Super-High Electromechanical Coupling Surface Acoustic Wave Substrates

• Published in: Japanese Journal of Applied Physics Vol. 40; no. 5S; p. 3726
• Main Authors: Yamanouchi, Kazuhiko, Odagawa, Hiroyuki
• Format: Journal Article
• Language: English
• Published: 01-05-2001
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.40.3726

The properties of surface acoustic wave (SAW) devices mainly depend on the choice of piezoelectric substrate materials. The important properties required for SAW substrates are a large electromechanical coupling coefficient (
k
2
), small temperature coefficient of delay (TCD), and low propagation loss, etc. Especially, super-high coupling substrates are very important for obtaining wide-band SAW filters, wide-band voltage controll oscilater (VCO) and delay lines with small insertion loss. KNbO
3
single crystal has an extremely large electromechanical coupling coefficient (
k
2
=53%) and zero TCD at approximately room temperature. Large-scale single-crystal growth technologies are now under investigation. In this study, the propagation characteristics of SAW in PZNT and KTP substrates are investigated experimentally in order to obtain higher coupling substrates than those of KNbO
3
. The experimental results show that the substrates have large
k
2
. Also, theoretical SAW propagation characteristics with a
k
2
of about 100% are analyzed and their physical phenomena are discussed.