Comparison of the k_t²Extraction Methods of Piezoelectric Films in Film/Substrate Structure and Self-Standing Film Structure

Electromechanical coupling coefficient kt2 of piezoelectric layer strongly affects the performance of BAW devices. The resonance-antiresonance method, which is standard for kt2 evaluation, requires self-standing film structure (FBAR). On the other hand, the conversion loss (CL) makes it possible to estimate the kt2 value from film/substrate structure (HBAR). Last year, we proposed new CL methods using electromagnetic signal or acoustic loss subtraction to eliminate the underestimation in the conventional CL method. In this study, we compared conventional and new CL methods with resonance-antiresonance method at the same point on the same ScAlN films. As a result, extracted kt2 values of new CL methods agree well with the that of resonance-antiresonance method.