Attenuation Of Leaky Surface Acoustic Waves Research Articles

Propagation properties of leaky surface acoustic wave on reverse‐proton‐exchanged 10° Y‐X LiNbO3

AbstractIn this study, to reduce leaky surface acoustic wave (LSAW) attenuation, a layered structure of air/bulk LiNbO3 (LN) layer/elastically softened LN substrate which can be fabricated by a reverse proton exchange (RPE) process was applied to 10° Y‐X LN with a larger coupling factor. First, the LSAW attenuation on a structure of air/bulk LN/modified LN was calculated with all material constants of the buried proton exchange (PE) layer taken into consideration. It was found that a condition under which the attenuation decreases as compared with the bulk value exists for the free and metallized surfaces. Next, the LSAW propagation properties were measured using IDT pairs with a 3.6‐μm wavelength on 10° Y‐X LN with the RPE layer and the buried PE layer. The propagation loss PL for the metallized surface was decreased by carrying out the RPE process from 0.44 dB/λ of a virgin wafer to 0.01 dB/λ. The decrease in PL for the shorted grating was also observed. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(3): 19–27, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10412

Leaky-Surface-Acoustic-Wave Properties on Reverse-Proton-Exchanged LiNbO3

A proton-exchanged (PE) layer with an elastically soft property can be buried into a substrate by a reverse proton exchange (RPE) process. It is expected that an RPE layer with a property similar to that of bulk LiNbO3 will prevent the degradation of coupling factor, and that the buried PE layer will change the anisotropy of the substrate effectively and reduce the leaky surface acoustic wave (LSAW) attenuation as compared with bulk LN. In this study, first, a layered structure of air/bulk LN/softened LN was assumed for rotated Y–X LN and LSAW attenuation was calculated. By controlling the elastic constant of the softened LN, the rotation angle from the Y-axis giving zero attenuation shifted from 64 to 5° for a metallized surface, and the rotation angle at which the attenuation decreases as compared with bulk LN was drastically changed for a free surface. Next, the LSAW propagation loss PL was measured on 41° Y–X LN. The PL for the metallized surface was decreased by carrying out the RPE process from 0.036 dB/λ of a virgin sample to 0.015 dB/λ. The decrease in PL for the free surface was also observed.

Acoustic microscopy measurement of elastic constants and mass density

A method is presented to determine the elastic constants and the mass density of isotropic and anisotropic solids and anisotropic thin films. The velocity and attenuation of leaky surface acoustic waves (SAWs) have been obtained for specified propagation directions from V(z) curves measured by line-focus acoustic microscopy (LFAM). The experimentally obtained velocities have been compared to velocities obtained from a measurement model for the V(z) curve which simulates the experiment. Since the measured and simulated V(z) curves have the same systemic errors, the material constants are free of such errors. For an isotropic solid, Young's modulus E, the shear modulus G and the mass density /spl rho/ have been determined from the leaky Rayleigh wave velocity and attenuation, measured by LFAM, and a longitudinal wave velocity measured by a pulse-echo transit-time technique. For a cubic-crystalline solid, the ratios of the elastic constants to the mass density (c/sub 11///spl rho/, c/sub 12///spl rho/, c/sub 44///spl rho/) have been determined from the directional variation of measured SAW velocities, using a preliminary estimate of /spl rho/. The mass density /spl rho/ has subsequently been determined by additionally using the attenuation of leaky SAWs in crystal symmetry directions. For a cubic-crystalline thin film deposited on a substrate, the elastic constants and the mass density (c/sub 11/, c/sub 12/, c/sub 44/, /spl rho/) of the film have been determined from the directional variation of the measured SAW velocities, and a comparison of the corresponding attenuation coefficient with the measured attenuation coefficient has been used to verify the results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Anisotropy detection in hot-pressed silicon nitride by acoustic microscopy using the line-focus beam

Anisotropy in velocity and attenuation of leaky surface-acoustic waves (leaky SAWs) on hot-pressed silicon nitride was measured by acoustic microscopy using the line-focus beam. On the surface normal to the pressing direction the velocity was 5651 m/s for all propagation directions, whereas on the surface parallel to the pressing direction the velocities varied markedly, depending on the wave propagation direction—typically 5726 m/s along the direction normal to the pressing axis and 5642 m/s along the direction parallel to the pressing axis. Because the fracture toughness KIC, measured by the Vickers indentation technique, also showed an anisotropy on the surface normal to the pressing direction, the anisotropic velocity measurement of the leaky SAWs proved to be useful in the NDE of anisotropic mechanical properties of ceramics products made by hot-pressing.