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U. Schmid, M. Schneider:
"Piezoelectric MEMS: Materials, Devices and Applications";
Talk: 16th International Conference on Plasma Surface Engineering (PSE 2018), Garmisch-Partenkirchen, Deutschland (invited); 09-17-2018 - 09-21-2018; in: "16th International Conference on Plasma Surface Engineering (PSE 2018)", (2018), 1.

In a compact introduction, I will motivate the benefits of piezoelectric thin films for
MEMS and will give a short overview to state of art application scenarios on device
level. Next, I will highlight latest results on the electrical, mechanical and
piezoelectrical characterization of sputter-deposited aluminium nitride (AlN) including
the impact of sputter parameters, film thickness and substrate pre-conditioning [1,2]. I
will present the impact of doping of AlN with scandium, which leads to an increase of
the moderate piezoelectric coefficient of AlN up to a factor of four. In a next step,
these films are implemented into fabrication processes of cantilever-type MEMS
devices. In combination with a tailored electrode design, resonators are realized
featuring Q factors up to about 300 in liquids covering the frequency range of 1-2
MHz. This enables the precise determination of the viscosity and density of fluids up
to dynamic viscosity values of almost 300 mPas [3]. Besides this application, such
high Q factors are useful when targeting mass-sensitive sensors, thus paving the way
to e.g. particle detection even in highly viscous media. Given the low increase in
permittivity of ScAlN compared to AlN, another field of application for this material are
vibrational energy harvesters, where the benefit of ScAlN compared to pure AlN is
demonstrated [4]. Finally, I will present some selected results of ScAlN thin films
within SAW devices ranging from high temperature applications to droplet
manipulation in microfluidics [5].