1,720,962 research outputs found
Uncertainty quantification of microstructure-governed properties of polysilicon MEMS
Full text linkIn this paper, we investigate the stochastic effects of the microstructure of polysilicon films on the overall response of microelectromechanical systems (MEMS). A device for on-chip testing has been purposely designed so as to maximize, in compliance with the production process, its sensitivity to fluctuations of the microstructural properties; as a side effect, its sensitivity to geometrical imperfections linked to the etching process has also been enhanced. A reduced-order, coupled electromechanical model of the device is developed and an identification procedure, based on a genetic algorithm, is finally adopted to tune the parameters ruling microstructural and geometrical uncertainties. Besides an initial geometrical imperfection that can be considered specimen-dependent due to its scattering, the proposed procedure has allowed identifying an average value of the effective polysilicon Young's modulus amounting to 140 GPa, and of the over-etch depth with respect to the target geometry layout amounting to O = -0.09 μm. The procedure has been therefore shown to be able to assess how the studied stochastic effects are linked to the scattering of the measured input-output transfer function of the device under standard working conditions. With a continuous trend in miniaturization induced by the mass production of MEMS, this study can provide information on how to handle the foreseen growth of such scattering
Assessment of micromechanically-induced uncertainties in the electromechanical response of MEMS devices
Full text linkMicroelectromechanical systems (MEMS) have been already successfully commercialized
for around 20 years. The design of novel MEMS sensors currently targets two important features:
smaller dimensions and higher reliability. As the characteristic size of the mechanical components
of the devices decreases, uncertainties in the mechanical and geometrical properties induced
by the microfabrication process become more and more important. To address these issues,
an on-chip testing device has been proposed to avoid any visual inspection for the read-out.
The electromechanical responses of ten nominally identical specimens have been recorded, and
experimental data have shown a significant scattering due to the presence of relevant uncertainty
sources. To interpret the response of the device, an analytical reduced-order model of the whole
device has been developed. A genetic algorithm has then been adopted to identify features of the
mechanical and geometrical uncertainties in the batch of test structures
On-chip testing: A miniaturized lab to assess sub-micron uncertainties in polysilicon MEMS
No full textAn increasing impact of micromechanically governed uncertainties is nowadays foreseen due to the trend of progressively reducing the footprint of MEMS (Microelectromechanical Systems) devices. For polysilicon MEMS, the two major sources of uncertainties, as resulting from the microfabrication process, are linked to the polycrystalline morphology and to the etching. In this review, we summarize some of our recent results related to the statistical assessment of the aforementioned sources, on the basis of experimental data acquired via an on-chip testing device specifically designed to enhance such effects. Through standard electrostatic actuation and readout, the scattering in the response of a series of nominally identical cantilever structures is analyzed to determine characteristic features of etching defects, and of the overall stiffness of the polysilicon film constituting the movable parts of the tested devices
Modeling of fluid damping in resonant micro-mirrors with out-of-plane comb-drive actuation
Full text linkComb-drive micromirrors are becoming of interest for a broad range of light
manipulation applications. Due to technical reasons, some of these applications require
packaging of the micromirror’s optical module in ambient air. Furthermore, micromirrors
for picoprojectors application are required to function at high frequencies in order to
achieve high resolution images. Accordingly, a study of the energy dissipated due to the
interaction between the moving parts of the micromirror and the surrounding air, leading to
fluid damping, is an important issue. Even if air damping has been thoroughly studied, an
extension to large air domain distortion linked to large tilting angles of torsional
micromirrors is still partially missing. In such situations, the flow formation turns out to be
far more complex than that assumed in analytical models. This task is here accomplished
by adopting three-dimensional computational fluid dynamics models; specifically, two
models, holding at different length scales, are adopted to attack the problem through an
automated dynamic remeshing method. The time evolution of the torque required to
compensate for the fluid damping term is computed for a-specific micromirror geometry
Assessment of overetch and polysilicon film properties through on-chip tests
No full textDue to the increasing demand of miniaturization of MEMS devices, the
characteristic size (e.g. the width) of some mechanical components may become
comparable to that of a silicon grain. Therefore, the relevant effective mechanical
properties can vary significantly from one device to another. In this work, through on-chip
tests we investigate the behavior of polysilicon films using standard electrostatic
actuation/sensing. The outcomes of the experimental campaign are then compared to those
obtained with an analytical reduced-order model of the moving structure, and to coupled
electro-mechanical simulations accounting for the polycrystalline morphology of the
silicon film. These two models are adopted to bilaterally bound the experimental data up to
pull-in, and to assess the scattering induced by the random orientation of the crystal lattice
of each grain in slender parts of the devices
Statistical Investigation of the Mechanical and Geometrical Properties of Polysilicon Films through On-Chip Tests
Full text linkIn this work, we provide a numerical/experimental investigation of the micromechanics-induced scattered response of a polysilicon on-chip MEMS testing device, whose moving structure is constituted by a slender cantilever supporting a massive perforated plate. The geometry of the cantilever was specifically designed to emphasize the micromechanical effects, in compliance with the process constraints. To assess the effects of the variability of polysilicon morphology and of geometrical imperfections on the experimentally observed nonlinear sensor response, we adopt statistical Monte Carlo analyses resting on a coupled electromechanical finite element model of the device. For each analysis, the polysilicon morphology was digitally built through a Voronoi tessellation of the moving structure, whose geometry was in turn varied by sampling out of a uniform probability density function the value of the over-etch, considered as the main source of geometrical imperfections. The comparison between the statistics of numerical and experimental results is adopted to assess the relative significance of the uncertainties linked to variations in the micro-fabrication process, and the mechanical film properties due to the polysilicon morphology
Mechanical Characterization of Polysilicon MEMS: A Hybrid TMCMC/POD-Kriging Approach
Full text linkMicroscale uncertainties related to the geometry and morphology of polycrystalline silicon films, constituting the movable structures of micro electro-mechanical systems (MEMS), were investigated through a joint numerical/experimental approach. An on-chip testing device was designed and fabricated to deform a compliant polysilicon beam. In previous studies, we showed that the scattering in the input–output characteristics of the device can be properly described only if statistical features related to the morphology of the columnar polysilicon film and to the etching process adopted to release the movable structure are taken into account. In this work, a high fidelity finite element model of the device was used to feed a transitional Markov chain Monte Carlo (TMCMC) algorithm for the estimation of the unknown parameters governing the aforementioned statistical features. To reduce the computational cost of the stochastic analysis, a synergy of proper orthogonal decomposition (POD) and kriging interpolation was adopted. Results are reported for a batch of nominally identical tested devices, in terms of measurement error-affected probability distributions of the overall Young’s modulus of the polysilicon film and of the overetch depth
Micromechanical characterization of polysilicon films through on-chip tests
Full text linkWhen the dimensions of polycrystalline structures become comparable to the average grain size, some reliability issues can be reported for the moving parts of inertial microelectromechanical systems (MEMS). Not only the overall behavior of the device turns out to be affected by a large scattering, but also the sensitivity to imperfections gets enhanced. In this work, through on-chip tests, we experimentally investigate the behavior of thin polysilicon samples using standard electrostatic actuation/sensing. The discrepancy between the target and actual responses of each sample has then been exploited to identify: (i) the overall stiffness of the film and, according to standard continuum elasticity, a morphology-based value of its Young’s modulus; (ii) the relevant over-etch induced by the fabrication process. To properly account for the aforementioned stochastic features at the micro-scale, the identification procedure has been based on particle filtering. A simple analytical reduced-order model of the moving structure has been also developed to account for the nonlinearities in the electrical field, up to pull-in. Results are reported for a set of ten film samples of constant slenderness, and the effects of different actuation mechanisms on the identified micromechanical features are thoroughly discussed
Fluid damping in compliant, comb-actuated torsional micromirrors
No full textFluid damping is studied for resonant torsional micromirrors, electrostatically actuated by comb fingers. A three-dimensional computational fluid dynamics (CFD) model of the air flow around the moving parts of the mirror is developed, coping with dynamic remeshing procedures to properly account for the large displacement setting required by the motion of the compliant structure. The time evolution of the damping torque contributions, due to shear at comb fingers and to drag over the surfaces of the micromirror plate, are computed. The relevant numerical estimation of the overall quality factor of the system is shown to compare well with available experimental results
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