Piezoelectric Properties of Sputtered AlN Thin Films and Their Applications

In this study, aluminum nitride (AlN) thin films reactively sputter deposited from an aluminium target are characterized both under material related aspects as well as on device level for resonantly driven gyroscopes. The first topic comprises a qualitative evaluation of the c-axis orientation by applying a wet chemical etching procedure in phosphoric acid to specimens synthesized under varying sputter deposition conditions. Samples with a high c-axis orientation show a low etch rate and smooth surface characteristics on the etched areas and vice versa. Furthermore, a quantitative determination of the piezoelectric coefficients is presented including the impact of the silicon substrate on the change in AlN film thickness under excitation. With this advanced approach, the d(33) and the d(31) coefficients are gained simultaneously with high accuracy comparing FEM simulations and interferometric measurements. Finally, AlN are applied to bulk-micromachined gyroscopes to stimulate the drive mode. Parasitic effects oil the performance generated by the microactuator elements are identified and potential improvements are proposed.