Impact of SAW Slowness Shape on Anti-Resonance Quality Factor of RF SAW Resonators

This letter investigates impact of the surface acoustic wave (SAW) slowness curvature on anti-resonance quality factor (
${Q}_{\text {a}}$
) of RF SAW resonators. First, variation of SAW resonance characteristics with aperture width
${W}$
is studied using periodic three dimensional finite-element method for three structures with different slowness curvature. It is shown that the slowness shape affects the frequency (
${f}$
) dependence of Bode
${Q}$
, and smaller slowness curvature makes the Bode
${Q}$
less sensitive to both
${f}$
and
${W}$
. This means that when the curvature is small, SAWs propagate like parallel beams on the substrate surface and are scarcely influenced by discontinuities at side boundaries such as electrode tips. Since loss mechanisms in the aperture region mainly contribute to the Bode
${Q}$
reduction, high
${Q}_{\text {a}}$
and maximum Bode
${Q}$
are achievable. Finally, series of I.H.P. SAW resonators using 42°YX-LiTaO3 are fabricated, and it is verified that the Bode
${Q}$
is not sensitive to
${W}$
when the electrode ohmic loss is ignored.