Single crystal growth of KNbO3 and application to surface acoustic wave devices

Potassium niobate (KNbO3) has large piezoelectric constants. The surface acoustic wave (SAW) substrates with high couplings are very important for wide-band SAW filters and SAW devices. Therefore, the large size KNbO3 single crystals are required for SAW device applications. In this paper, the techniques of a large size of KNbO3 using the top seeded solution growth techniques (TSSG) with large size of crucible of 60 mmφ platinum are described. The results show that 50×50×15 mm3 single crystals are obtained. Also, the poling techniques of KNbO3 crystal are investigated by using the nonlinear scanning dielectric microscope. The propagation characteristics of SAW and piezoelectric leaky surface waves in KNbO3 single crystal were investigated theoretically. The results show that the electro-mechanical coupling coefficient of the surface wave propagating along the X-axis of the rotated Y-cut plane is extremely large: K2=0.53, compared to K2 of 0.055 for LiNbO3. The experimental results of the above KNbO3 substrates agree with the theoretical ones. Also the KNbO3 substrates showed experimentally the zero temperature coefficients of frequency (TCF) around 20 °C.