In Situ Synchrotron XRD Characterization of Piezoelectric Al(1−x)Sc(x)N Thin Films for MEMS Applications

Aluminum scandium nitride (Al(1−x)Sc(x)N) film has drawn considerable attention owing to its enhanced piezoelectric response for micro-electromechanical system (MEMS) applications. Understanding the fundamentals of piezoelectricity would require a precise characterization of the piezoelectric coefficient, which is also crucial for MEMS device design. In this study, we proposed an in situ method based on a synchrotron X-ray diffraction (XRD) system to characterize the longitudinal piezoelectric constant d(33) of Al(1−x)Sc(x)N film. The measurement results quantitatively demonstrated the piezoelectric effect of Al(1−x)Sc(x)N films by lattice spacing variation upon applied external voltage. The as-extracted d(33) had a reasonable accuracy compared with the conventional high over-tone bulk acoustic resonators (HBAR) devices and Berlincourt methods. It was also found that the substrate clamping effect, leading to underestimation of d(33) from in situ synchrotron XRD measurement while overestimation using Berlincourt method, should be thoroughly corrected in the data extraction process. The d(33) of AlN and Al(0.9)Sc(0.1)N obtained by synchronous XRD method were 4.76 pC/N and 7.79 pC/N, respectively, matching well with traditional HBAR and Berlincourt methods. Our findings prove the in situ synchrotron XRD measurement as an effective method for precise piezoelectric coefficient d(33) characterization.