A piezoresistive microcantilever array for surface stress measurement: curvature model and fabrication

Abstract

This paper presents a procedure for the fabrication of a piezoresistive microcantilever array for surface-stress-based chemical and biochemical sensing applications. All existing microcantilever surface stress sensors that are based on single-crystal silicon use p-doped piezoresistors. In this work, the advantages of using n-doped silicon piezoresistors for surface stress sensing have been demonstrated. Further, a new model for surface-stress-sensitive cantilevers, based on classical laminated plate theory, is presented. This model allows for the estimation of the deformation and piezoresistive response of a multilayered microcantilever to surface stresses during analyte measurement and residual stresses in the structural layers due to fabrication processes. Also, the model accounts for bending–stretching coupling in the microcantilever response to the stresses. The utility of the model as a design tool for control of cantilever curvature during the fabrication process has been demonstrated.

On accuracy of sensitivity relations for piezoresistive microcantilevers used in surface stress studies

“…3,4 In contrast, there are few models for calculating the surface stress sensitivity of piezoresistive microcantilevers when used in surface stress studies. The models presented by Choudhury et al 20 and Yang and Yin 21 used laminated plate bending equations for the piezoresistive microcantilever, and therefore are not very convenient to implement in practice. Kassegne et al 22 has given a simple model using beam bending equations.…”

Design and characterization of MEMS-based flow-rate and flow-direction microsensor

“…Such systems possess many advantages compared to their traditional large-scale counterparts, including amongst other things lower power consumption, a higher precision, a more rapid response, an improved portability, and a lower manufacturing cost. Importantly, the functionality and reliability of these micro-sensors can be enhanced through their integration with mature logic IC technology or with other micro-scale devices (Yamazoe 2005;Velanki and Ji 2006;Korotcenkov 2007;Choudhury et al 2007;Tuomas et al 2008;Chen et al 2008;Wang et al 2008).…”

A theoretical model for surface-stress piezoresistive microcantilever biosensors with discontinuous layers

“…Yang et al [26,27] presented a two-dimensional model to analyze a four-layer piezoresistive microcantilever applied with surface stress. Choudhury et al [28] developed a model for surface stress microcantilevers using classical laminated plate theory, and showed the benefit of ntype piezoresistors for sensitivity. Besides theoretical methods, finite-element-method (FEM) was also employed to analyze microcantilever sensors [29,30].…”

“…Therefore, due to the discontinuous piezoresistors, the thickness of the microcantilever is nonuniform and there exists at least one layer consisting of both silicon and silicon dioxide. For such a case, the theoretical models [27,28], which require a precondition of continuous layers and uniform thickness through the width of the microcantilevers, are not applicable. Since the Young's modulus of silicon is more than 2 times that of silicon dioxide, when the thickness of the silicon piezoresistors are comparable to that of the BOX microcantilever, it is improper to use a constant Young's modulus for the whole layer that consists of different materials.…”