Extraction Of Material Properties Research Articles

Modeling of multiple cracking and decohesion of a thin film on a polymer substrate

Thin brittle films on polymer substrates are finding increasing use as gas barriers for example in the medical and food packaging industries and also for the next generation of ultra-light displays based on flexible polymer substrates. In order to determine the durability of the barrier under thermal and mechanical loads, test procedures and corresponding data reduction methods are needed to feed the analysis models. One of the tests frequently employed for this kind of multi-layer material systems is the fragmentation test, whose designation comes from the progressively denser pattern of parallel cracks developing when the specimen is loaded under uniaxial tension. From the crack-density versus strain data obtained, a critical strain for crack growth and an assessment of the adhesion of the coating to substrate can be obtained. However, no accepted data reduction methods exist to extract material properties from the test or inversely, successfully predict the crack density as a function of a set of material properties without fitting parameters. In an earlier paper, the authors presented a finite element based analysis methodology to determine the fracture toughness of both the coating and the interface from the fragmentation data. In the simulations, the plastic constitutive behavior of the substrate and the debonding of the coating from the substrate were explicitly included, the latter by use of a cohesive zone model. In this paper an extension of this methodology is presented that enables crack-density evolution with strain to be predicted. The results presented comprise comparisons with experiments to validate the methodology and the influence of (i) coating toughness, (ii) interface toughness and (iii) coating thickness on crack density versus strain.

Estimation of model parameters in nonlocal damage theories by inverse analysis techniques

The parameters identification problem of the gradient-enhanced continuum damage model is examined by means of an inverse analysis. Different related issues are analyzed: (i) the investigation of the limits of applicability and predictability of the adopted numerical model and (ii) the problem of objectively extracting material properties from a structural response. A necessary condition for an adequate identification of the model parameters is the well-posedness of the inverse problem. The results show that this requirement is obtained only if additional averaged local experimental information is involved in the inverse procedure, in addition to the global structural force–deformation response. Moreover, the adopted numerical model reveals limitations in predicting the entire size effect curve of tensile tests on dog-bone-shaped concrete specimens.

Experimental and numerical investigations of the deformation of soft materials under tangential loading

The surface ‘tensile test’, in which tangential loads are applied through surface mounted adhesive tapes, is a viable method for the assessment of mechanical properties of soft materials, particularly biological soft materials in vivo. In the present work the deformation pattern and force–displacement relationship in the surface tensile test were experimentally investigated using surface displacement analysis (SDA) and numerically simulated using finite element modelling. The experimental and FE results showed close agreement using silicone rubber as a model material. The force–displacement relationship was found to be dependent on the tape separations. SDA measurements and FE simulation showed that the displacement and strain fields were not uniform and the distribution pattern varies with tape separation. A combined experimental–numerical approach to inversely extract material properties using multiple tests with different length scales is proposed and assessed using a model material.

Theory of Pulsed Photothermal Radiometry for Transmission and Lateral Geometries

Pulsed photothermal radiometry (PPTR) employs a pulsed laser excitation to heat a sample and the resulting change in emitted IR radiation is detected remotely, which gives rise to the PPTR signal. A theory for analysing experimental data is considered for transmission geometry where excitation and detection are on opposite sides of the sample, and lateral geometry where excitation and detection are on the same side, but laterally displaced. For transmission geometry it is shown in detail how absorption coefficients at the excitation and detection wavelengths, α and β respectively, appear in a symmetrical way in this theory. In doing this an alternative way of calculating PPTR signals is introduced using a Laplace transform technique. For lateral geometry a similar symmetry for disc excitation and detection areas, with radii r1 and r0, is also demonstrated. The Laplace transform technique is also used to give signal expressions for transmission geometry which converge quickly for small values of time. Furthermore, ways of applying the theory to experimental data in order to extract material properties α, β and thermal diffusivity D are developed.

Torsion of viscoelastic spheres in contact

The theory of elastic contact between two spherical bodies is used as a basis for an extension to include the contribution of the viscous effects to the total stress for viscoelastic spheres subjected to twisting moments. Expressions relating twisting moment to penetration of slip and penetration of slip to twist angle are derived. Two term power series truncations of the relations are then used to derive approximate expressions for torsional compliance of the bodies. Validation experiments for the extended model were performed by use of a rheometer device. Applications for the model in post-harvest agriculture include extraction of material properties for use in Discrete Element Modelling of mechanical interactions of fruits and other regular shaped produce during machine handling. A specific application is performed involving the use of a rheometer to measure the coefficient of friction for fruit-fruit contact.

Polycrystalline silicon-carbide surface-micromachined vertical resonators-part I: growth study and device fabrication

This manuscript is the first of a two-part series describing the fabrication and testing of MHz frequency, polycrystalline silicon-carbide (poly-SiC) micromechanical resonators made from films deposited by atmospheric-pressure chemical-vapor deposition (APCVD). In Part I, the development of deposition and patterning techniques suitable for the fabrication of vertically actuated, clamped-clamped beam resonant structures is detailed. Recipe development involved film deposition and material analysis on both planar and patterned substrates. We found that a carbonization-based deposition process modeled after epitaxial growth of 3C-SiC on Si produced the highest quality poly-SiC films for use with sub-micron thick polysilicon sacrificial layers, regardless of topology. Devices utilizing beam thicknesses up to 1 /spl mu/m were fabricated and successfully released. Details about the testing of the released structures are presented in Part 2 of this series (see Wiser, Tabib-Azar, Mehregan, and Zorman, Polycrystalline silicon-carbide surface-micromachined vertical resonators-Part II: Electrical testing and material property extraction, J. Microelectromech. Syst., vol. 14, no. 3, Jun. 2005).

An analytical model for pull-in voltage of clamped–clamped multilayer beams

This paper develops an analytical model for the deflection of clamped–clamped multilayer beams as a function of applied voltage by the energy method. The normalized displacement of the center of the beams and the pull-in voltage have been obtained, the model is also suitable to clamped–clamped beams with compressive stress. The model results are compared with FEM simulations, provided by the CosolveEM module in Coventorware, showing excellent agreement. This provides an approach of extracting material properties for the multilayer beams.

Electronically probed measurements of MEMS geometries

Measurement of microelectromechanical systems (MEMS) geometry is critical for device design and simulation, material property extraction, and post-fabrication trimming. In this paper electrostatically driven laterally resonant comb-drive test structures with prescribed changes in spring width are used to ascertain systematic variations in process offsets (edge biases) and sidewall angles. The technique is both in situ and nondestructive. An analytical model for the resonant frequency, tuned with three-dimensional (3-D) simulations using MEMCAD, includes effects of a distributed mass, residual stress, and compliant supports. The model is corroborated by 3-D numerical simulations to validate the extraction approach. Fits of this model to experimental data determine the offset and sidewall angle of polysilicon devices fabricated by the Multi-User MEMS Processes of the Microelectronics Center of North Carolina, Research Triangle Park, NC.

Application of system identification to ultrasonic waveforms

In the context of NonDestructive Evaluation (NDE), system identification is a process that can be used to extract sample properties from ultrasonic waveforms. Usually, system identification is applied directly to time series data. We describe a novel application of system identification. The process is applied to ultrasonic data in the frequency domain. Some investigators have pointed out that useful information can be obtained from the cepstral analysis of frequency domain data. Our approach further generalizes this practice, to the point that frequency domain data are identically mapped to a linear system, with frequency playing the role of time. We believe that our approach can be used to extract material properties, provide sensitive measures to flaws, return detailed information about flaws, extrapolate the bandwidth of ultrasonic measurements, and provide avenues for data compression.

Characterization of contact electromechanics through capacitance-voltage measurements and simulations

Electrostatically actuated polysilicon beams fabricated in the multiuser MEMS process (MUMPs) are studied, with an emphasis on the behavior when the beam is in contact with an underlying silicon nitride dielectric layer. Detailed two-dimensional (2-D) electromechanical simulations, including the mechanical effects of stepups, stress-stiffening and contact, as well as the electrical effects of fringing fields and finite beam thickness, are performed. Comparisons are made to quasi-2-D and three-dimensional simulations. Pull-in voltage and capacitance-voltage measurements together with 2-D simulations are used to extract material properties. The electromechanical system is used to monitor charge buildup in the nitride which is modeled by a charge trapping model. Surface effects are included in the simulation using a compressible-contact-surface model. Monte Carlo simulations reveal the limits of simulation accuracy due to the limited resolution of input parameters.

M-TEST: A test chip for MEMS material property measurement using electrostatically actuated test structures

A set of electrostatically actuated microelectromechanical test structures is presented that meets the emerging need for microelectromechanical systems (MEMS) process monitoring and material property measurement at the wafer level during both process development and manufacturing. When implemented as a test chip or drop-in pattern for MEMS processes, M-Test becomes analogous to the electrical MOSFET test structures (often called E-Test) used for extraction of MOS device parameters. The principle of M-Test is the electrostatic pull-in of three sets of test structures [cantilever beams (CB's), fixed-fixed beams (FB's), and clamped circular diaphragms (CD's)] followed by the extraction of two intermediate quantities (the S and B parameters) that depend on the product of material properties and test structure geometry. The S and B parameters give a direct measure of the process uniformity across an individual wafer and process repeatability between wafers and lots. The extraction of material properties (e.g., Young's modulus, plate modulus, and residual stress) from these S and B parameters is then accomplished using geometric metrology data. Experimental demonstration of M-Test is presented using results from MIT's dielectrically isolated wafer-bonded silicon process. This yielded silicon plate modulus results which agreed with literature values to within /spl plusmn/4%. Guidelines for adapting the method to other MEMS process technologies are presented.

Thin film characterization by acoustic microscopy

In this paper a brief review of the recent applications of acoustic microscopes for material property determination of thin films is given. Acoustic microscopes generate Rayleigh waves near the surface (up to one or two wave length depth) of the specimen under inspection. Since the Rayleigh wave speed is sensitive to thin film properties such as Young's modulus, Poission's ratio, longitudinal and shear wave speeds, elastic wave attenuation coefficient and density, these properties, in principle, can be extracted from the acoustic microscope generated signals. In this paper it is discussed how one can extract these properties from the V(z) curve generated by an acoustic microscope using the simplex algorithm. V(z) curve is obtained by vertically moving the microscope lens from the specimen surface, thus varying the distance (z) between the focal point of the lens and the reflecting surface of the specimen and recording the corresponding variation of the voltage (V) with z. Extraction of material properties of a thin film specimen from its V(z) curve requires solving the inversion problem, that has not been done by many investigators. The author does it by the simplex algorithm technique which is an optimization technique for solving one or more unknowns in linear or nonlinear equations. Some theoretical and experimental results involving thin (a few micron thick) metal films on a substrate and thin biological cells are also presented in this paper.

Effects of diffraction and experimental geometry on acoustic beam reflection from a fluid-loaded plate: a 3-D analysis

This article presents an accurate, approximate analysis for the receiver voltage in a geometry with bounded acoustic beams reflected from fluid-loaded structures. The relationship between reflection coefficient poles and transducer voltage minima is calculated and discussed. A series of precision experiments on a uniform, homogeneous plate is shown to validate the calculation. These results have significance for material property extraction from reflection measurements on fluid-loaded structures.

Precision ultrasonic reflection studies in fluid-coupled plates

An approximate, but highly accurate, analysis is presented for the reflection of bounded acoustic beams—and their detection by finite receivers—from fluid-loaded structures, demonstrating the relationship between the plane-wave reflection coefficient and the transducer voltage. The correspondence of the reflection coefficient zeros, in both angle and frequency, with the observed voltage minima is found to depend critically on the experimental geometry, especially the lateral transducer placement. In measurements with two identical transducers, the beam shape, its sidelobes, and far-field or near-field conditions are found to play a relatively minor role in the receiver voltage. Instead, the size of the transducers and their relative lateral positioning with respect to the sample are the major geometrical factors determining the appearance, width, and depth of reflection minima. A series of precision, swept-frequency experiments on a uniform, homogeneous plate to validate the calculation and expose any possible limitations is also reported here. In general, excellent detailed agreement between the efficient approximate calculation and the results of the experiments has been obtained. An expression is derived to predict the optimal transducer positioning for accurate estimation of reflection coefficient zeros from voltage measurements. These results have significance for material property extraction from reflection measurements on fluid-loaded structures.

Analytical treatment of MOSFET source—Drain resistance

Series resistance in the metal-oxide-semiconductor field-effect transistor becomes increasingly important as design rules shrink. Material properties associated with the interconnect metal, the semiconductor, and the interface separating the two regions thus assume greater importance. An analytical formulation of the resistance in terms of these material properties is thus quite desirable. We formulate and solve a two-dimensional model of current flow by the method of matched asymptotic expansions. The major utility of this solution is provided by higher order corrections to the standard transmission line model of current flow in the ohmic contact region. We find that present methods for the extraction of material properties from experimental measurements with a transmission line model analysis would be enhanced by the inclusion of higher order terms we present here.

New angle on ultrasonic cleaning: Metalworking Production (31st January 1968) p50

Transmission-line scattering parameters becomes unpractical to calculate as one includes more interfaces. Thus, to get an analytical expression, approximations are required. In this paper, an approximation methodology for the calculation of scattering parameters of transmission-line transducers is presented. The transducer cell is partitioned at each interface and the partial scattering equations are calculated, considering two interfaces at a time. Next, standard techniques are applied to solve the signal-flow diagrams to obtain the full scattering equations. Transmission-line transducers are used for the measurement of power absorption and reflection of different materials, such as: liquids, granular medium, and ground, in the RF/microwave range. Such measurements are used to extract materials properties. The proposed methodology has been applied to a coaxial transducer cell filled with different low-loss liquids. The results have been validated with computer simulations and experimental measurements. Measurements and simulations were carried out in the 300 kHz to 3 GHz frequency range.

Ultrasonics for Industry exhibition: Wire Industry, Vol 34, No 408 (December 1967) p1268

Transmission-line scattering parameters becomes unpractical to calculate as one includes more interfaces. Thus, to get an analytical expression, approximations are required. In this paper, an approximation methodology for the calculation of scattering parameters of transmission-line transducers is presented. The transducer cell is partitioned at each interface and the partial scattering equations are calculated, considering two interfaces at a time. Next, standard techniques are applied to solve the signal-flow diagrams to obtain the full scattering equations. Transmission-line transducers are used for the measurement of power absorption and reflection of different materials, such as: liquids, granular medium, and ground, in the RF/microwave range. Such measurements are used to extract materials properties. The proposed methodology has been applied to a coaxial transducer cell filled with different low-loss liquids. The results have been validated with computer simulations and experimental measurements. Measurements and simulations were carried out in the 300 kHz to 3 GHz frequency range.