Review of scaling effects on physical properties and practicalities of cantilever sensors

Abstract

Reducing sensor dimension is a good way to increase system sensitivity and response. However the advantages gained must be weighed against other effects which also became significant during the scaling process. In this paper, the scaling effect of cantilever sensors from micrometer to nanometer regimes is reviewed. Changes in the physical properties such as Q-factor, Young’s modulus, noise and nonlinear deflections, as well as effects on practical sensor applications such as sensor response and sensor readouts, are presented. Since cantilever is an elemental transducer and device building block, its scaling effects can be further extrapolated to other sensing systems and applications.

Nanomechanical Modeling of the Bending Response of Silicon Nanowires

“…1,13 For example, the quality factor of Sibased nanoresonators is reduced due to surface loss mechanisms such as adsorption, surface stress, surface oxidation/reconstruction, and surface defects. 1,12,15 The fracture strength is also shown to be strongly correlated to surface-related defects. 13,16 Therefore, a wide range of experimental and computational attempts have been performed to explore Si NW mechanical behavior.…”

“…25 Although there are complicated experimental aspects of bending tests mainly related to nanometrology, 13,17,21,26 the interpretation of test results proved to be the most challenging task, as without a reliable nanomechanical model, the quantification of even the most basic properties such as stiffness and strength becomes an enormous task. 21,23,27−33 The lack of such a sound modeling approach is in fact reflected by a series of conflicting observations including broad range of estimations for elastic and strength properties 1,12 and significant differences between experimental and computational findings. 1,12,18,19,19,20,34,35 Models usually suffer from a poor description of surfacerelated phenomena 18,20,36 and inconsistent use of constitutive surface models as well as nonlinear elasticity.…”

“…21,23,27−33 The lack of such a sound modeling approach is in fact reflected by a series of conflicting observations including broad range of estimations for elastic and strength properties 1,12 and significant differences between experimental and computational findings. 1,12,18,19,19,20,34,35 Models usually suffer from a poor description of surfacerelated phenomena 18,20,36 and inconsistent use of constitutive surface models as well as nonlinear elasticity. 1,18,36 In this context, an effective model should involve the implementation of the following three sets of parameters:…”

“…The resulting load–displacement data have then to be interpreted through appropriate models . Although there are complicated experimental aspects of bending tests mainly related to nanometrology, ,,, the interpretation of test results proved to be the most challenging task, as without a reliable nanomechanical model, the quantification of even the most basic properties such as stiffness and strength becomes an enormous task. ,,− The lack of such a sound modeling approach is in fact reflected by a series of conflicting observations including broad range of estimations for elastic and strength properties , and significant differences between experimental and computational findings. ,,,,,,, Models usually suffer from a poor description of surface-related phenomena ,, and inconsistent use of constitutive surface models as well as nonlinear elasticity. ,, In this context, an effective model should involve the implementation of the following three sets of parameters: Native oxide, essentially amorphous silicon dioxide (aSiO 2 ), is an indispensable part of the Si NW surface ,,, and thus affects the NW structure by introducing defects or other interfaces. , Although usually overlooked, a recent study has revealed tensile intrinsic stresses in Si NWs upon native oxide formation under ambient conditions . Atomistic simulations also exhibit a reduction in the modulus of elasticity of Si NWs to be as much as 40% due to native oxide surface condition while compared to the pristine surface state. ,, Similar reduction in the ultimate strength is estimated to be up to 20%. ,, Appropriate interatomic potentials for atomistic simulations of surface stress and surface elasticity have to be introduced. ,, In this regard, surface stress is defined as the reversible work per unit area needed to elastically stretch a pre-existing surface. , Surface elastic constants represent the variation in bulk elastic constants due to the formation of a surface. …”

“…Silicon (Si) nanowires (NWs) are essential building blocks in nanoelectromechanical systems (NEMS) and nanoelectronics. , Because of their compatibility with semiconductor manufacturing, Si NWs bear potential for improving existing technologies or generating new approaches regarding mass spectroscopy, , electromechanical/biochemical sensors, , field effect transistors (FETs), − energy conversion, and harvesting and storage media . The operation of these nanodevices, especially NEMS, relies significantly on their high surface-to-volume ratios leading to remarkable size-dependent mechanical properties. ,− The surface contribution to the overall mechanical behavior increases with decreasing size, thereby resulting in significant size dependence in NW properties. , For example, the quality factor of Si-based nanoresonators is reduced due to surface loss mechanisms such as adsorption, surface stress, surface oxidation/reconstruction, and surface defects. ,, The fracture strength is also shown to be strongly correlated to surface-related defects. , Therefore, a wide range of experimental and computational attempts have been performed to explore Si NW mechanical behavior. ,,− …”