Characterization of a roof tile-shaped out-of-plane vibrational mode in aluminum-nitride-actuated self-sensing micro-resonators for liquid monitoring purposes

Abstract

This Letter reports on an advanced out-of-plane bending mode for aluminum-nitride (AlN)-actuated cantilevers. Devices of different thickness were fabricated and characterized by optical and electrical measurements in air and liquid media having viscosities up to 615 cP and compared to the classical out-of-plane bending and torsional modes. Finite element method eigenmode analyses were performed showing excellent agreement with the measured mode shapes and resonance frequencies. Quality factors (Q-factor) and the electrical behavior were evaluated as a function of the cantilever thickness. A very high Q-factor of about 197 was achieved in deionized water at a low resonance frequency of 336 kHz, being up to now, the highest quality factor reported for cantilever sensors in liquid media. Compared to the quality factor of the common fundamental out-of-plane bending mode, a 5 times higher Q-factor was achieved. Furthermore, the strain related conductance peak of the roof tile-shaped mode is superior. Compared to any out-of-plane bending mode, this combination of most beneficial properties is unique and make this mode superior for a large variety of resonator-based sensing applications.

Thickness dependence of Young's modulus and residual stress of sputtered aluminum nitride thin films

“…1 Given its piezoelectric properties, high thermal and electrical stability as well as its compatibility with standard CMOS technology, aluminum nitride thin films are frequently used as active layer in MEMS devices. [2][3][4][5] In addition, applications as passivation layers are possible due to high chemical resistance and heat conductivity and a good thermal match to silicon. 6 The design of aluminum nitride based devices typically requires analytical and finite element based simulations, thus presenting the need for accurate knowledge of mechanical material properties of AlN thin films, such as the residual stress and Young's modulus.…”

Precision density and viscosity measurement using two cantilevers with different widths

“…A general approach to separate viscosity and density effects experimentally is to relate quality factor changes with viscosity and resonant peak shifts with density [6][7][8][9]. This approach is also used with other types of MEMS structures like Suspended microchannel resonators (SMR) [11,12] and piezoelectric MEMS resonators [13][14][15][16] and suspended microcapillary resonators [17]. With this approach in order to attain high sensitivity in a broad dynamic range, frequency sweeps with high frequency resolution is necessary.…”

Piezoelectric MEMS resonators for density and viscosity sensing in engine oil with diesel fuel

“…They are actuated in the first extensional mode in the MHz range [3]. The second sensor is a cantilever microplate (2524x 1274x20 f.lm 3 ) resonating in a high order out-of-plane mode, designated as 14-mode according to the number of nodal lines in each direction, and working near 345 kHz [4].…”