Properties of LLSAW on YZ-cut LiNbO3: modeling and experiment

Synchronous test resonators employing the longitudinal leaky SAW mode have been fabricated on YZ-cut LiNbO₃ substrate to study the dependence of resonator behavior on the metallization ratio, aperture, finger thickness and the number of fingers in the IDT. Software based on a Green´s function method and the finite element method is used to simulate the effects of electrode geometry on the resonator characteristics. Simulated Q values and resonance frequencies are compared with experiment. Ladder filters for the 2.45, 2.8 and 5.2 GHz frequency regimes utilizing the longitudinal leaky SAW mode have been designed, fabricated and characterized. The one-port synchronous resonators constituting the ladder filters operate in the fundamental mode. The smallest finger width at 5.2 GHz is 0.29 μm, which allows conventional optical lithography to be used in the fabrication. The experimental filter with center frequency as high as 5.20 GHz features a minimum insertion loss of 3.3 dB, a 3 dB fractional bandwidth of 6.3%, corresponding to the absolute bandwidth of 327 MHz, and a selectivity of over 25 dB.