Geometry optimization of uncoated silicon microcantilever-based gas density sensors

Abstract

Abstract:In the absence of coating, the only way to improve the sensitivity of silicon microcantilever-based density sensors is to optimize the device geometry. Based on this idea, several microcantilevers with different shapes (rectangular-, U-and T-shaped microstructures) and dimensions have been fabricated and tested in the presence of hydrogen/ nitrogen mixtures (H2/N2) of various concentrations ranging from 0.2% to 2%. In fact, it is demonstrated that wide and short rectangular cantilevers are more sensitive to gas density changes than U-and T-shaped devices of the same overall dimensions, and that the thickness doesn't affect the sensitivity despite the fact that it affects the resonant frequency. Moreover, because of the phase linearization method used for the natural frequency estimation, detection of a gas mass density change of 2 mg/l has been achieved with all three microstructures. In addition, noise measurements have been used to estimate a limit of detection of 0.11 mg/l for the gas mass density variation (corresponding to a concentration of 100 ppm of H2 in N2), which is much smaller than the current state of the art for uncoated mechanical resonators.

Young’s modulus of multi-layer microcantilevers

“…[10][11][12][13][14][15][16][17] As the critical issues of mechanical performance of microcantilevers, Young's modulus [18][19][20][21][22][23] and resonant frequency [24][25][26][27][28][29][30][31] have been studied by various characterizations. In this research, atomic force microscopy (AFM) measurement is conducted to characterize resonant frequency of multi-layer microcantilevers, and a theoretical model is proposed and discussed including the impact of coating on both Young's modulus and resonant frequency.…”

A MEMS Resonant Sensor to Measure Fluid Density and Viscosity under Flexural and Torsional Vibrating Modes

“…The design dimensions of the two different microcantilevers were a length of 1500 μm, width of 2500 μm, thickness of 20 μm, and the free end width of the trapezoidal micro-cantilever was 1000 μm. It is proven that a microcantilever with a larger width could help to improve the sensitivity [ 16 ] and quality factor [ 28 ] of a microcantilever, and in particular it could improve the Re (Re = ρ f fw /4 η f ), where f is the resonant frequency of the microcantilever) [ 23 ]. If The Re is much larger than 1, it means the viscosity equation and the density equation could be decoupled when the fluid density and viscosity are measured simultaneously.…”

“…The quality factor of a rectangular microcantilever was significantly reduced with the increase of fluid viscosity due to the increase of resonator energy dissipation, so this type of sensor could not be used to measure high viscosity fluids. Boudjiet [ 16 ] studied the effects of microcantilever shape and geometrical dimensions on the density sensitivity. This study showed that a wide and short cantilever was more sensitive to the density variation, the highest sensitivity was 228 Hz/(kg·m −3 ) and the measurement accuracy ranged from 0.4% to 0.6%.…”

Role of surface morphology on desorption kinetics of water molecules from uncoated silicon microcantilever

“…Moreover, the limited long term stability of the viscoelastic coatings and the resulting aging also affect the reliability of the sensor [6]. Taking these aspects into consideration, recently there are attempts to use uncoated MCs for various sensing applications [6][7][8][9][10].…”