High-coupling leaky surface acoustic waves on LiNbO₃or LiTaO₃thin plate bonded to high-velocity substrate

Abstract

The propagation properties of leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) on a LiNbO3 (LN) or LiTaO3 (LT) thin plate bonded to an AT-cut quartz or c-plane sapphire (c-Al2O3) substrate with a high phase velocity were investigated. It was theoretically revealed that when the LN or LT thin-plate thickness is less than one wavelength, the particle displacement of LLSAWs was concentrated in the thin plate and the electromechanical coupling factor (K2) was increased to two to three times that in the single substrate. Furthermore, for 36° Y-cut X-propagating LT/c-Al2O3 with an LT thin-plate thickness of 0.35 λ and X-cut 36° Y-propagating LN/c-Al2O3 with an LN thin-plate thickness of 0.19 λ, the values of K2 for an LSAW and an LLSAW were experimentally found to increase from 5.6 and 10.4% in the single substrate to 11.5 and 19.7% in the thin-plate bonded structure, respectively.

High coupling and highly stable leaky surface acoustic waves on LiTaO3 thin plate bonded to quartz substrate

“…[24][25][26] In addition, to obtain a substrate structure with a large K 2 , the propagation properties of LSAWs and LLSAWs on a LiNbO 3 (LN) or LT thin plate bonded to a high-velocity substrate were investigated theoretically and experimentally. 27) In that study, K 2 larger than that of a single LT substrate was obtained theoretically when 36°Y-cut X-propagating LT (36°YX-LT)= AT-cut 90°X-propagating quartz (AT90°X-quartz) for an LSAW and X-cut 31°Y-propagating LT (X31°Y-LT)=AT-cut 45°X-propagating quartz (AT45°X-quartz) for an LLSAW were employed. The increase in K 2 is due to the fact that the particle displacements of LSAWs concentrate in the thin plate.…”

“…4 shows those of the LLSAW with the calculated results. 27) Hereafter, for the color of lines and plots in the figures, green, red, and blue correspond to 36°YX-LT=AT0°X-quartz, 36°YX-LT= AT90°X-quartz, and X31°Y-LT=AT45°X-quartz, respectively. For the LSAWs, as shown in Figs.…”

“…The propagation direction of the AT-cut quartz was set to 90°X-propagating for the LSAW and 45°X-propagating for the LLSAW because a large K 2 was estimated in the theoretical calculation. 27) Moreover, the AT-cut quartz was also set to 0°X-propagating (AT0°X-quartz) to compare its characteristics with that to 90°X-propagating. These wafers were bonded by surface-activated room-temperature bonding (SAB).…”

“…This peculiar phenomenon is considered to be caused by a strong effect of the concentration of the particle displacement on the bonded structure. 27) Furthermore, the K 2 values of the LSAW and LLSAW were determined from the admittance properties of IDTs (N = 10 or 15). The K 2 values were determined from the relationship K 2 = (πG a =4NB) × 100%, 28) where G a and B are the radiation conductance and susceptance at a center frequency, respectively.…”

Properties of engine oil measured using a surface acoustic wave sensor

“…An SAW device is mainly used as a high-frequency electronic device such as a filter. [5][6][7][8][9] SAW devices have been applied to sensors and actuators. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] As the SH-SAW can propagate at a liquid=solid interface, a liquid sensor is realized with an SH-SAW sensor.…”