Measurements of the bulk, C-axis electromechanical couplingconstant as a function of AlN film quality

摘要

Piezoelectric thin film AlN has great potential for on-chipndevices such as thin-film resonator (TFR)-based bandpass filters. ThenAlN electromechanical coupling constant, K2, is an importantnmaterial parameter that determines the maximum possible bandwidth fornbandpass filters. Using a previously published extraction technique, thenbulk c-axis electromechanical coupling constant was measured as anfunction of the AlN X-ray diffraction rocking curve [full width at halfnmaximum (FWHM)]. For FWHM values of less than approximately 4°, Kn2 saturates at approximately 6.5%, equivalent to the valuenfor epitaxial AlN. For FWHM values >4°, K2 graduallyndecreases to approximately 2.5% at a FWHM of 7.5°. These resultsnindicate that the maximum possible bandwidth for TFR-based bandpassnfilters using polycrystalline AlN is approximately 80 MHz and that, forn60-MHz bandwidth PCS applications, an AlN film quality of >5.5°nFWHM is required