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M. Schneider, U. Schmid:
"Piezoelectric MEMS Devices: from Material Aspects to Low-Power Applications";
Talk: 22nd International Conference on Advanced Materials and Simulation, Rom, Italien (invited); 12-10-2018 - 12-12-2018; in: "22nd International Conference on Advanced Materials and Simulation", (2018), ISSN: 2471-9838; 41 - 42.

Electromechanical transducers based on the
piezoelectric effect are continuously finding
their way into micro-electromechanical
systems (MEMS), typically in the form of
thin films. Piezoelectric transducers feature a
linear voltage response, no snap-in behaviour
and can provide both attractive and repulsive
forces. This removes inherent physical
limitations present in the commonly used
electrostatic transducer approach while
maintaining beneficial properties such as
low-power operation. Furthermore,
piezoelectric materials can serve for both
actuation and sensing purposes, thus enabling
pure electrical excitation and read-out of the
transducer element in combination with a
compact design. Based on these outstanding
features, piezoelectric transducers are
operated most beneficially in a large variety
of different application scenarios, ranging
from resonators in liquid environment,
advanced acoustic devices to sensors in harsh
environments. In order to exploit the full
potential of piezoelectric MEMS in the
future, interdisciplinary research efforts are
needed ranging from investigations of
advanced piezoelectric materials over the
design of novel piezoelectric MEMS sensor
and actuator devices, to the integration of
PiezoMEMS devices into full low-power
systems.
In this talk, we 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]. We 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. We will also present first
results on the piezoelectric co-polymer
PVDF-TrFE.
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 in liquids Q-factors up to
about 300 in 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 functional material class
are vibrational energy harvesters, where the
benefit of ScAlN compared to pure AlN is
demonstrated [4].
Finally, we will present some selected results
of ScAlN thin films within SAW devices
ranging from high temperature applications to
droplet manipulation in microfluidics [5].

http://dx.doi.org/10.21767/2471-9838-C7-027