Session: 5F

Longitudinal leaky (LL) waves on YZ-LiNbO3 substrates [1, 2] feature many properties which are unusual for SAW and remain unexplained. Recent demonstration [3] of wideband low-loss filters operating on LL waves in the 2.5–5 GHz frequency range, manufactured with optical lithography, makes these waves of primary practical importance. Filters based on LL waves may become competitors against the FBAR technology, all operating practically in the same frequency range. Synchronous test resonators employing the LL SAW mode have been fabricated on the YZ-cut LiNbO3 substrate to study the dependence of resonator behavior on the metallisation ratio, aperture, finger thickness and the number of fingers in the IDT. Experimental data accumulated at different frequencies (2.5, 2.8, and 5.2 GHz) are presented and compared with simulations. In all the cases, high Q factors are achieved with “magic” relative Al thickness value of about h/λ=7.8% to 8.0%. For experimental resonators operating in the 2.8 GHz frequency range, Q factors at resonance of 340 and relative resonanceantiresonance distance of 4.2% have been measured. The corresponding figures for resonators in the 5.2 GHz frequency range are 180 and 5.2%, respectively. The Q factor decreases with increasing aperture and, unexpectedly, also with increased length of the IDT. We present here systematic FEM/BEM modeling results for dependence of LL wave characteristics on the electrode geometry. For better agreement between the simulation and measurement, additional lumped elements are added to the resonator equivalent circuit and their electrical parameter values are obtained through a fitting procedure. We assume that the waves are not guided by the structure and that different kinds of side radiation may influence the resonator Q factors. [1] V. I. Grigorievski, Proc. 2000 IEEE Ultrasonics Symp., p. 259. [2] T. Makkonen, V. Plessky, V. I. Grigorievski, L. Kopp, M. Solal, W. Steichen, and M. M. Salomaa, Proc. 2002 IEEE Ultrasonics Symp., p. 305. [3] T. Makkonen, V. P. Plessky, W. Steichen, and M. M. Salomaa, Appl. Phys. Lett. 82, p. 3351 (2003). This research has been carried out in the framework of the French-Finnish Eureka project E! 2442 SUMO.