**6. Conclusions**

The AlN and Al0.68Sc0.32N is was developed for the use at high electric fields up to 200 MV/m to increase the maximum electric energy the system can transform into a deflection. Additionally, the use of Al0.68Sc0.32N, in comparison to AlN, increased the static deflection per electric field by a factor of 3.5. This shows the impact of AlScN based transducer materials for piezoelectric microsystems. By using 2 µm thick Al0.68Sc0.32N with high electric breakdown voltage, the maximum actuation voltage was increased up to 400 V.

In Table 4 a comparison of the MOEMS Designs 1 and 2 with AlN and AlScN and the micromirror of Gu-Stoppel et al. [14] is presented. A figure of merit (FOM) is shown as a product of mirror diameter, respectively, mirror length, and scan angle. Another figure of merit considers the influence of the stiffness of the MOEMS by including the resonance frequency [1]. The presented MOEMS Design 1 and 2 with Al0.68Sc0.32N as transducer material have very high values for the FOMs. The FOM for the Design 2 MOEMS with Al0.68Sc0.32N is FOM = θ · e · fres = 116.8 m· ◦ ·Hz and therefore 3.2 times higher than the reference in literature. The reason therefore can be a 2 µm thick Al0.68Sc0.32N with high piezoelectric coefficients and the use of high voltages as well as optimized design parameter with a leverage effect. However, Gu-Stoppel et al. [14] were able to manufacture a 2D MOEMS on a very small footprint using vertical silicon integration technologies.

**Table 4.** Comparison of (quasi-)static driven micromirrors based on piezoelectric AlN and AlScN of current literature and this work.


<sup>1</sup> Limited by measurement setup. <sup>2</sup> Estimated chip size with frame.

In summary, two different MOEMS designs with AlN and Al0.68Sc0.32N as piezoelectric actuator materials are compared. AlN and Al0.68Sc0.32N driven MOEMS with static scan angles up to 55.6◦ were fabricated. The chip performances for different designs and transducer materials with focus on the static actuation were compared. The use of Al0.68Sc0.32N, larger actuators, softer springs, the increased thickness of the transducer, and a material with high electrical breakdown voltages enabled the increase of the performance. The resonant deflection per electric field increased by a factor of 12. The static deflection per electric field increases more than 10 times due to the optimization in design and transducer material. The development of high-performance transducer materials and optimized MOEMS designs will allow miniaturized and robust micro optics with large static scan angles.

**Author Contributions:** Conceptualization, C.S.; Data curation, K.M.; Formal analysis, C.S. and K.M.; Investigation, C.S., K.M., M.M. and A.Ž.; Methodology, C.S. and R.F.; Project administration, C.S., R.F., S.Z. and K.H.; Supervision, C.S.; Writing—original draft, C.S., K.M., M.M. and A.Ž.; Writing—review and editing, R.F., S.Z. and K.H.; Funding acquisition, C.S. and H.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the European Union (EU-ESF), the Sächsische Aufbaubank SAB, the free state of Saxony, the Fraunhofer Gesellschaft FhG and the Deutsche Forschungsgemeinschaft DFG ("E-PISA", FK: 100310500, "Wafer-Level Sensorstruktur zur Bestimmung von

Ionenenergie- und Ionenwinkelverteilungsfunktionen in Niederdruckplasmen", AOBJ: 636895). The publication of this article was funded by the Fraunhofer Gesellschaft.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
