Longitudinal Leaky Surface Acoustic Wave Research Articles

Surface acoustic waves in semi-insulating Fe-doped GaN films grown by hydride vapor phase epitaxy

The propagation properties of surface acoustic waves (SAWs) in semi-insulating Fe-doped GaN films grown on sapphire substrates by hydride vapor phase epitaxy are investigated. Compared with native n-type GaN, Fe-doped GaN exhibits a higher electromechanical coupling coefficient due to its high electrical resistivity. In addition, guided longitudinal leaky surface acoustic wave (LLSAW) was observed experimentally with a very high phase velocity (about 7890 m/s), and this mode was verified by numerical simulations. The small propagation attenuation of LLSAW along liquid/solid interfaces was demonstrated in glycerol solutions, which implies the potential applications in high-frequency chemical sensing.

Finite element modeling of electrode mass loading effects in longitudinal leaky SAW resonators

AbstractA finite element (FE) model is developed for investigating effects of metal electrode mass loading in longitudinal leaky surface acoustic wave (SAW) resonators on YZ‐LiNbO3. Variation of resonator admittance with electrode height and electrode metallization ratio is observed. FE modeling is promising for the prediction and optimization of LLSAW performance, especially sensitive to electrode mass loading effects. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 390–395, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24042

Longitudinal leaky SAW resonators and filters on YZ-LiNbO/sub 3/

The high-phase velocity (above 6100 m/s in an aluminum (Al) grating on lithium niobate (LiNbOs)) of the longitudinal leaky surface acoustic wave (SAW) (LLSAW) mode makes it attractive for application in high-frequency SAW ladder filters in the 2-5 GHz range. We investigate the dependence of one-port synchronous LLSAW resonator performance on YZ-LiNbO3 on the metallization thickness and metallization ratio, both experimentally and theoretically. Our results indicate a strong dependence of the Q factor and resonance frequency on the aluminum thickness, with the optimal thickness that produces the highest Q values being about 8%. The optimal thickness increases with the metallization ratio. The observed behavior is interpreted with the help of simulations using a combined finite element method (FEM)/boundary element method (BEM) technique. As an application, bandpass filters have been fabricated in the 2.8 GHz frequency regime, based on LLSAWs. The synchronous resonators constituting the ladder filters operate in the fundamental mode. The filters feature low insertion losses below 3 dB and wide relative passbands of 4.5-5%.

Investigation of new‐mode‐type SAWs by procedures combined with finite‐element and analytical method, and their applications for devices used in mobile communications

AbstractSimulations using a combination of the finite‐element method and the analytical method as well as experiments are used to study new‐mode‐type SAWs. First, in 171°YZé‐LiNbO3, it is found that there exists a longitudinal leaky SAW with a high acoustic velocity and a high Q in a grating structure with an Al film thickness of 0.084 wavelength. The acoustic velocity is 6100 to 6500 m/s and the Q values are more than 4000 (computed) at both the resonance and antiresonance points. These excellent properties are suitable for high‐frequency SAW devices. Next, in 15°YX‐LiNbO3, it is found that there exists a grating mode SAW of a transverse wave type in a grating structure with an Al film thickness of 0.125 wavelength. In this case, k2 has an extremely large value of 28.5% and hence the mode is suitable for a SAW resonator for use in a voltage‐controlled oscillator. By means of this SAW, SAW‐VCOs at 400 and 170 MHz for mobile communication are fabricated. At 400 MHz, the frequency variable width is 54 MHz (3.2%/V) and the phase noise is less than –115 dBc/Hz at 25 kHz; the corresponding values at 170 MHz are 24 MHz (3.4%/V) and < –12 dBc/Hz at 25 kHz. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(4): 49–58, 2001

Propagation characteristics of longitudinal leaky SAW in Al-grating structure

New orientations for longitudinal leaky SAW with small propagation losses and high velocities in lithium niobate (LN) and lithium tantalate (LT) have been found. Their velocities are 6100 to 6500 m/s in LN and 5200 to 5800 m/s in LT. Their propagation losses are almost negligible only in the case of an Al-grating structure. For example, the Al thickness relative to the SAW wavelength must be 8.4% for 171 degrees YZ'-LN; for 133 degrees YZ'-LT, the value must be 9.2%. These propagation properties were obtained by using a simulator that combined both finite-element and analytical methods. These results were also well confirmed by measuring the impedance responses of one-port SAW resonators.

Saw properties of Li2B4O7 crystals and their applications to acousto-optic waveguide modulators

Theoretical and experimental results have shown the potential usefulness of Li2B4O7 crystals for leaky SAW and acousto-optic applications. The shear leaky SAW has excited at (45°,90°,70°), whose SAW properties are vp of 3680m/s, k2 of 2.3% and TCD of 0. Further, k2 of the Rayleigh SAW was zero at this cut substrate, which gives no spurious response for the temperature compensated shear leaky SAW. The longitudinal leaky SAW with the fast vp of 6825m/s has been also observed at the (0°,45°,90°). Several amorphous thin films were successfully fabricated on the (110) LBO substrates by sputtering. Among them, the borate glass film has been a suitable material for acousto-optic applications because it has lower velocity and relatively larger index than those of LBO substrates