A method to estimate kt2 of piezoelectric films from the change of lattice strain by XRD without removing substrate

Electromechanical coupling coefficient k
_t
²
is one of the important parameters to estimate performance of BAW filters. The resonance-antiresonance method according to IEEE standard is common method to determine k
_t
²
. However, this method requires a self-standing film structure (FBAR). In this study, we propose the k
_t
²
estimation method for a film/substrate structure (HBAR). This method allows us to estimate k
_t
²
for as grown wafers without removing substrates. The lattice strains of piezoelectric crystals are induced when electric field are applied. The strains can be measured by X-ray diffraction (XRD). Therefore, the k
_t
²
of the film is expected to be indirectly determined by the use of piezoelectric equations. The values of k
_t
²
determined by this method were compared with the resonance-antiresonance method and the conversion loss method.