Theoretical and experimental study of surface acoustic wave substrates with super high couplings

The properties of SAW device mainly depend on the choice of piezoelectric substrate materials. The important properties required for SAW substrates are large electromechanical coupling coefficient (k² ), small temperature coefficient of delay (TCD), low propagation loss, etc. Especially, super high coupling substrates are very important for fabricating the wideband SAW filters, wideband VCO and delay lines with small insertion loss. KNbO₃ single crystal has extremely large electromechanical coupling coefficient (K²=53%) and zero TCD around room temperature and single crystal growth technologies with a large size are now investigating. In this paper, the propagation characteristics of surface acoustic waves (SAW) in PZNT and KTP substrates are investigated experimentally in order to obtain the higher coupling substrates than those of the KNbO₃. The experimental results show that the substrates have the large k². Also, theoretical SAW propagation characteristics with the k² of about 100% will be analyzed and the physical phenomena of those will be discussed