Longitudinal Leaky Surface Acoustic Wave with Low Attenuation on LiTaO3 Thin Plate Bonded to Quartz Substrate

To obtain a bonded structure with low attenuation for longitudinal leaky surface acoustic waves (LLSAWs), the propagation and resonance properties on a LiTaO3 (LT) thin plate bonded to an X-cut quartz substrate were theoretically analyzed. The attenuation on the metallized surface of an X-cut 31°Y-propagating LT (X31°Y-LT)/X32°Y-quartz structure was calculated to be 0.0005 dB/1 at the normalized LT thin-plate thickness h/λ=0.062 (λ: wavelength) and was lower than that on an X31°Y-LT/AT45°X-quartz structure. Using a finite element method (FEM) system, for the X31°Y-LT/X32°Y-Q model, the admittance ratio and $Q$ factor were improved to 117 dB and 57,000 from 63 dB and 1,100 for the X31°Y-LT/AT45°X-Q model, respectively. On the basis of these results, several bonded samples were fabricated, and the propagation and resonance properties were measured. For the X31°Y-LT/X32°Y-Q, the measured electromechanical coupling factor (K²) and $Q$ factor increased to 5.6% and 282 from 1.8% and 32 for the single LT, respectively. The temperature coefficient of frequency (TCF) of the LLSAW was measured to be −26.2 ppm/°C.