[Back]


Books and Book Editorships:

M. Kucera:
"Performance of Cantilever-based Piezoelectric MEMS Resonators in Liquid Environment";
TUVerlag an der Technischen Universität Wien, Wien, 2017, ISBN: 9783903024533; 204 pages.



English abstract:
In this work, piezoelectric-actuated MEMS (micro electromechanical systems) resonators are presented to study and optimise
different mechanical vibration modes and their specific properties for monitoring the viscosity and density of liquid media. For
this purpose, the mechanics of cantilevers as well as plate-type devices is introduced. They are fabricated using silicon
micromachining in combination with sputter-deposited aluminium nitride.
The functional thinfilm material serves both for excitation of the specific vibration mode and for sensing purposes to determine
the resonance frequency and the damping (Q-factor) by measuring the piezoelectrically generated charges as a change in the
impedance spectrum.
The MEMS resonators are characterised predominantly in their fundamental in-plane vibration mode, as, in contrast to any
out-of-plane mode, shear forces are transferred to a higher extend to the surrounding liquid media, thus favouring this mode for
viscosity and density sensing. Especially the knowledge about the mode shape and the corresponding local distribution of the
generated polarisation charges are of utmost importance for an optimised device operation. Basically, it turned out that a
minimal mechanically strained surface area of the vibrating structure has to be covered with the piezoelectric layer to generate a
technically exploitable measurement signal. In addition, a new class of vibration modes is investigated, showing a superior
performance in the Q-factor and the level of the electrical output signal compared to commonly used vibration modes (e.g.
out-of-plane, in-plane or torsional modes).
To evaluate the MEMS resonators under close to real life operation conditions a specific test setup is realised to control the
liquid temperature up to 100°C. Furthermore, an electronic feedback circuit is realised allowing to enhance the Q-factor up to
about a factor of 20 in air and up to about a factor of nine in ethanol, respectively.
The novel vibration modes and the design guidelines presented within the scope of this doctoral thesis will allow in the future to
realise piezoelectric-actuated MEMS resonators based on cantilever or plate-type structures for measuring the viscosity and
density in a widespread range of liquid media with a high sensitivity.

German abstract:
In this work, piezoelectric-actuated MEMS (micro electromechanical systems) resonators are presented to study and optimise
different mechanical vibration modes and their specific properties for monitoring the viscosity and density of liquid media. For
this purpose, the mechanics of cantilevers as well as plate-type devices is introduced. They are fabricated using silicon
micromachining in combination with sputter-deposited aluminium nitride.
The functional thinfilm material serves both for excitation of the specific vibration mode and for sensing purposes to determine
the resonance frequency and the damping (Q-factor) by measuring the piezoelectrically generated charges as a change in the
impedance spectrum.
The MEMS resonators are characterised predominantly in their fundamental in-plane vibration mode, as, in contrast to any
out-of-plane mode, shear forces are transferred to a higher extend to the surrounding liquid media, thus favouring this mode for
viscosity and density sensing. Especially the knowledge about the mode shape and the corresponding local distribution of the
generated polarisation charges are of utmost importance for an optimised device operation. Basically, it turned out that a
minimal mechanically strained surface area of the vibrating structure has to be covered with the piezoelectric layer to generate a
technically exploitable measurement signal. In addition, a new class of vibration modes is investigated, showing a superior
performance in the Q-factor and the level of the electrical output signal compared to commonly used vibration modes (e.g.
out-of-plane, in-plane or torsional modes).
To evaluate the MEMS resonators under close to real life operation conditions a specific test setup is realised to control the
liquid temperature up to 100°C. Furthermore, an electronic feedback circuit is realised allowing to enhance the Q-factor up to
about a factor of 20 in air and up to about a factor of nine in ethanol, respectively.
The novel vibration modes and the design guidelines presented within the scope of this doctoral thesis will allow in the future to
realise piezoelectric-actuated MEMS resonators based on cantilever or plate-type structures for measuring the viscosity and
density in a widespread range of liquid media with a high sensitivity.

Created from the Publication Database of the Vienna University of Technology.