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M. Kucera, E Wistrela, G. Pfusterschmied, V Ruiz-Díez, J.L. Sànchez-Rojas, J. Schalko, A. Bittner, U. Schmid:
"Characterisation of multi roof tile-shaped out-of-plane vibrational modes in aluminiumnitride- actuated self-sensing micro-resonators in liquid media";
Applied Physics Letters, 107 (2015).

This letter reports on higher orders of an advanced out-of-plane bending mode in aluminiumnitride
(AlN)-actuated cantilever plates achieving the highest quality factors (Q-factor) of
cantilever-based MEMS (micro electromechanical system) resonators in liquids up to now.
Devices based on a 20 lm thick silicon cantilever were fabricated and characterised by optical and
electrical measurements in air and in different liquids. Furthermore, finite element method eigenmode
analyses were performed, showing an excellent agreement with the measured mode shape
and the electrical characteristics. The highest Q-factor was achieved in deionised water with
Q¼366, operated at the 10th order mode at a resonance frequency less than 4 MHz. This is the
highest value ever measured in liquid media with a cantilever-based MEMS resonator up to now
and exceeds the Q-factors of state of the art resonators in liquids in the given resonance frequency
range by a factor of about 4. Furthermore, the strain related conductance peak of the multi roof tileshaped
modes is superior, showing great potential for further electrode design optimisation.
Compared to common out-of-plane bending modes, this combination of most beneficial properties
is unique, making this type of vibration mode the first choice for a large variety of resonator-based
liquid-phase sensing applications.

This letter reports on higher orders of an advanced out-of-plane bending mode in aluminiumnitride
(AlN)-actuated cantilever plates achieving the highest quality factors (Q-factor) of
cantilever-based MEMS (micro electromechanical system) resonators in liquids up to now.
Devices based on a 20 lm thick silicon cantilever were fabricated and characterised by optical and
electrical measurements in air and in different liquids. Furthermore, finite element method eigenmode
analyses were performed, showing an excellent agreement with the measured mode shape
and the electrical characteristics. The highest Q-factor was achieved in deionised water with
Q¼366, operated at the 10th order mode at a resonance frequency less than 4 MHz. This is the
highest value ever measured in liquid media with a cantilever-based MEMS resonator up to now
and exceeds the Q-factors of state of the art resonators in liquids in the given resonance frequency
range by a factor of about 4. Furthermore, the strain related conductance peak of the multi roof tileshaped
modes is superior, showing great potential for further electrode design optimisation.
Compared to common out-of-plane bending modes, this combination of most beneficial properties
is unique, making this type of vibration mode the first choice for a large variety of resonator-based
liquid-phase sensing applications.

http://dx.doi.org/10.1063/1.4928429