Experimental measurements of propagation, attenuation, reflection and scattering of leaky waves in Al electrode gratings on 41°, 52° and 64°-LiNbO3

Abstract

A five transducer test structure, previously used for measuring COM model parameters of Rayleigh type SAWs has been applied to experimental measurement of leaky SAW COM parameters. Measurements have been made for Al electrodes of varying mark to period ratios and varying thicknesses on 41d, 52d and 64d rotated Y-cut, X-propagation LiNbO3. Accurate determination of COM model parameters often proved to be difficult due to the complicated nature of leaky SAWs. However, it was found that many of the desired model parameters could be determined based solely on the measured input admittance of a one port resonator (which forms the center portion of this particular five transducer test structure). Frequency dependence of the admittance clearly shows the edges of the stopband, which allows to determine the SAW velocity and the reflectivity of the electrodes, the magnitude of the admittance is proportional to the electro-mechanical transduction coefficient and the wave attenuation is related to Q-factors of the resonance peaks. Also, the static capacitance and parasitic series resistance can be determined from this admittance. This measured admittance is remarkably free of spurious bulk, reflected, scattered and other parasitic responses. In addition to measuring the COM parameters others interesting effects were observed. First, the interaction of leaky SAWs with Rayleigh type SAWs inside the electrode grating is clearly observed. This interaction was predicted earlier. Also, secondary propagation paths were experimentally observed which result from leakage into slow shear waves which reflect at the bottom surface of the substrate and then leak back into a leaky SAW