Theoretical and experimental characterisation of a SAW delay line through its Y-matrix.

Surface acoustic wave (SAW) delay lines are commonly used devices, and it is important to characterise them to find the causes of deviations between the experimental and theoretical behaviour in order to consider them during design. The authors present the theoretical characteristics and the characterisation of a SAW delay line through X-ray diffraction, energy dispersive X-ray fluorescence, scanning electron microscopy, atomic force microscopy and the measurement of S-parameters. Using the S-parameters, the Y-parameters were calculated and comparing them with those obtained theoretically, they found disagreement in their magnitudes and also that the experimental SAW velocity was 2.8% larger than the theoretical one. The magnitude of experimental Y11 is smaller than that obtained theoretically because of the ill-defined profile and the metallisation ratio of the electrodes is not ideal due to inherent limitations in the fabrication process, and besides Y21 is smaller than expected because the attenuation of the SAW when it propagates through the delay line. When the electrode defects, the experimental SAW velocity and the attenuation coefficient of SAW in this material are considered in the theoretical calculations, agreement is found between theoretical and experimental results. This procedure is based in the comparison between experimental and theoretical Y-parameters and could be used to estimate attenuation, electrode capacitance and SAW velocity.