To obtain a bonded structure with low attenuation for longitudinal leaky surface acoustic waves (LLSAWs), the propagation and resonance properties on a LiTaO3 (LT) or LiNbO3 thin plate bonded to an X-cut quartz substrate were theoretically analyzed. The attenuation of an X-cut 31°Y-propagating LT (X31°Y-LT)/X32°Y-quartz (X32°Y-Q) was calculated to be 0.0005 dB/λ 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-Q. Using a finite element method, for the X31°Y-LT/X32°Y-Q, the admittance ratio and Q factor were improved to 120 dB and 53 400 from 62 dB and 1000 for the X31°Y-LT/AT45°X-Q, respectively. Then, 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 280 from 1.8% and 32 for the single LT, respectively. The temperature coefficient of frequency of the LLSAW was measured to be −26.2 ppm °C−1.

Recently, bonded structures comprising a quartz substrate and a LiNbO3 (LN) or LiTaO3 thin-plate have been attracting attention as a means of obtaining enhanced properties for surface acoustic wave (SAW) devices. It was reported that the bonding strength was extremely improved by utilizing an amorphous thin film as a middle layer. In this research, the propagation and resonance characteristics of longitudinal leaky SAWs on an amorphous layer inserted to the boundary between an X-cut 36°Y-propagating LN (X36°Y-LN) and X35°Y-quartz were investigated. For the metallized surface of an X36°Y-LN/Al2O3/X35°Y-quartz structure, an attenuation of 0.0001 dB /λ was obtained at an LT thin-plate thickness of 0.072λ (λ: wavelength), which was better than that of an X36°Y-LN/X35°Y-quartz structure. Utilizing a finite element method, we found that the admittance ratio and Q factor for the X36°Y-LN/Al2O3/X35°Y-quartz model were improved owing to the reduction of the leakage due to the shear-vertical particle displacement.

The enhancement of high-order surface acoustic wave (SAW) harmonics by increasing the metallization ratio was theoretically and experimentally investigated in high-performance bonded dissimilar-material structures. The simulation using a finite element method for 36°Y-cut X-propagating LiTaO3 (36°YX-LT)/AT-cut 90°X-propagating quartz (AT90°X-quartz) and 27°YX-LiNbO3/AT90°X-quartz was performed by setting the metallization ratio of the interdigital transducer to a/p = 0.8 (a: electrode width, p: pitch), and the LT and LN thin-plate thicknesses to h/λ = 0.05 (λ: wavelength) and 0.1, respectively. The fractional bandwidths for 36°YX-LT/AT90°X-quartz and 27°YX-LN/AT90°X-quartz were obtained to be 1.6% and 4.0%, respectively, which were larger than those for single LT and LN. For a leaky SAW (LSAW) resonator with a/p = 0.8 fabricated on 36°YX-LT/AT0°X-quartz, the resonance properties and temperature coefficient of frequency of LSAW fundamental waves and harmonics were measured. The measured fractional bandwidth increased from 0.8% to 1.4% for single LT.

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