Potentialities of LiTaO3 for Bulk Acoustic Wave Filters

In the present work, Film Bulk Acoustic Resonators (FBAR) based on 700 nm-thick LiTaO
₃
films have been fabricated and characterized. Two orientations of single crystal LiTaO
₃
thin films have been investigated: (i)
$\mathrm{Y}+42^{\circ}$
-cut, in which the longitudinal wave exhibits an electromechanical coupling factor similar to the one of the longitudinal wave in c-axis AlScN; and (ii) X-cut, in which the fast shear wave displays a larger electromechanical coupling coefficient and a lower Temperature Coefficient of Frequency (TCF) than for
$\mathrm{Y}+42^{\circ}$
-cut. In both cases, we have demonstrated resonators in the 1–3 GHz range, with electromechanical coupling factors close to respectively 6.6 and 17.4% and quality factors of 230 and 400. Moreover, the X-cut LiTaO
₃
FBAR displays lower TCF values than those previously reported for LiNbO
₃
FBAR, with measured temperature coefficients of the resonance and antiresonance frequency of +16 (± 3) and −42 (± 2) ppm/K, respectively. LiTaO
₃
appears therefore as an appealing candidate for the next generation of wide bandwidth RF filters.