Finite Element Modelling of Micro-cantilevers Used as Chemical Sensors

TL;DR

This paper uses finite element modeling to accurately predict the resonant frequencies and sensitivities of complex-shaped silicon micro-cantilevers used as chemical sensors, validating the approach with experimental data.

Contribution

It introduces a FEM-based method for modeling complex micro-cantilever geometries and coatings, improving the prediction of their resonant frequencies and sensitivities.

Findings

FEM accurately predicts resonant frequencies of micro-cantilevers.

Sensitivity depends on geometrical and mechanical parameters.

Validation shows good agreement with experimental measurements.

Abstract

Nowadays, silicon micro-cantilevers with different geometrical shapes are widely used as micro-electro-mechanical systems and, more recently, as force sensor probes in atomic force microscopy (AFM). During the last ten years, several applications, which include these AFM micrometer-sized cantilevers as mass probes in microbalances or as chemical sensors in chemical micro-system devices, were developed. In the case of complex shapes of cantilevers, where the cross-section is not constant along the cantilever length (case of ?V-shaped? micro-cantilevers), their resonant frequencies can not be analytically calculated. Firstly, in order to validate the accuracy of our FEM approach, we carried out a comparison between analytical, experimental and FEM-computed values of the resonant frequencies for homogenous rectangular shaped micro-cantilevers. Then, we performed a modeling of silicon beams coated with a thin sensitive layer (50 nm of Gold). To precisely calculate the resonant frequencies of these multilayer-cantilevers, the influence of the mesh parameters on the calculated frequencies was strongly investigated. Secondly, the sensitivity of different ?V-shaped? silicon cantilevers was estimated, as a function of their geometrical dimensions and of their mechanical parameters (Young modulus, density). The resonant frequencies of uncoated cantilevers were calculated and compared with the values experimentally determined. Then, a similar approach was employed to predict the sensitivities of such cantilevers recovered with a sensitive layer.