Fiber orientation tensors (FOT) are used as a compact form of representing the mechanically important quantity of fiber orientation in fiber reinforced composites. While they can be obtained via image processing methods from micro computed tomography scans (μCT), the specimen size needs to be sufficiently small for adequate resolution – especially in the case of carbon fibers. In order to avoid massive workload by scans and image evaluation when determining full-field FOT distributions for a plaque or a part, e.g., for comparison with process simulations, the possibilities of a direct interpolation of a few measured FOT at specific support points were opened in this paper. Hence, three different tensor interpolation methods were implemented and compared qualitatively with the help of visualization through tensor glyphs and quantitatively by calculating originally measured tensors at support points and evaluating the deviations. The methods compared in this work include two algebraic approaches, firstly, a Euclidean component averaging and secondly, a decomposition approach based on separate invariant and quaternion weighting, as well as an artificial intelligence (AI)-based method using an artificial neural network (ANN). While the decomposition method showed the best results visually, quantitatively the component averaging method and the neural network behaved better (that is for the type of quantitative error assessment used in this paper) with mean absolute errors of 0.105 and 0.114 when calculating previously measured tensors and comparing the components. With each method providing different advantages, the use for further application as well as necessary improvement is discussed. The authors would like to highlight the novelty of the methods being used with small and CT-based tensor datasets.

During hot rolling process, an oxide scale grows at the surface of steel slabs. To avoid surface defects such as embedded scale at the end of the finishing mill, descaling stands are added in the production line to remove it using high-pressure water jets. Different steel grades show different descaling capacities and final surface qualities, which may depend on composition through oxide and interface toughness. The idea of this study is to measure the latter using micro-indentation to feed thermomechanical models of the descaling process. After indentation, Focused Ion Beam (FIB) is employed to observe cracking and delamination of oxidized specimen and to calculate adhesion of oxide thanks to an analytical formula. The experimental study confirms that alloying elements have a strong influence on the adhesion of oxide film and suggests that difficult-to-descale grades are those showing a large scatter of interfacial toughness. In parallel, numerical finite element (FEM) simulations of indentation are carried out using Abaqus® to have a better understanding of cracking mechanism and delamination of oxide.

A new concept of a thermo-mechanical lateral switch activation is proposed. Embedded in standard aluminium BEOL (Back End Of Line), it is fully integrated in CMOS technology. The simplicity of this low cost one-mask fabrication allows the straightforward scalability of design. Most functional problems have been solved through process, simulation and design: stiction, bending, displacement, and robustness.The present study of a thermo-mechanical MEMS switch focuses on three points. Firstly, the design is modified to increase the apparent area contact and the force applied. Secondly, in order to ensure the reversibility of the movement, a running-in step before operation is implemented. Finally, a new design is proposed, simulated and manufactured to avoid the undesirable activations by spurious homogeneous heating. (C) 2015 Elsevier Ltd. All rights reserved.

Accelerated life tests on microelectronic devices are needed to estimate their degradation under severe environment. THB (Temperature Humidity Bias) [1] at 85°C and 85%RH (relative humidity) is commonly used for reliability studies. Empirical acceleration laws, used for THB test take into account the temperature change (from 22°C to 85°C), but they do not quantify its impact of the corresponding thermo-elastic stress which it adds to the residual stress in the die and of possible microstructure changes. The aim of this work is to determine the thermo-mechanical stresses induced in the active layer of a Gallium Arsenide (GaAs) chip by the THB test. They are due to the mismatch in Coefficients of Thermal Expansion (CTE) between the stack of thin film materials used as metallurgic interconnection and the intermediate dielectric layers above the active area of the chip. To estimate this stress, fist layers thicknesses measurement have been made with various techniques; second few configurations have been used to simulate heating and finally “complete” 2D Finite Element Analysis (FEA) has been performed. Elastic and thermo-physical materials data come from the literature. The results indicate compression of metal gate (Ti/Al/Au) and tensile stress concentration in the SiNx passivation layer. The outcomes is compared with THB test results from [2] and suggests that stress induced by heating must be considered to explain failure during THB test.

Stress control is a main factor in the operation, performance and reliability of GaAs devices. A precise understanding of the impact of the mechanical stress on the performance and reliability of GaAs devices can lead to the improvement of the device design and packaging. Most of the time, process flow parameter modifications help to change internal stress in multilayer properties and this has a direct impact on the electric parameters. Mechanical wafer bending is the method usually used to investigate the effects of external stress on Gallium Arsenide (GaAs) devices.The aim of this work is to quantify the sensibility of GaAs microwave devices used for Space applications under mechanical external stress in order to estimate the impact of packaging. In this innovative work, a bending-by-buckling system has been used to apply external mechanical stress on a single GaAs microwave die. To evaluate the value of this stress in device structure and precisely near the channel of the pseudomorphic High Electron Mobility Transistor (pHEMT), simulation based on the Finite Element Method has been carried out.The stress was increased gradually from 0 to similar to 210 MPa (in tension and compression) and then reduced from similar to 210 MPa to 0. The experimental results demonstrate that the threshold current changes linearly and reversibly in the range of the applied stress. The shift in the threshold current and voltage of the pHEMT was analysed by considering piezoelectric effects. (C) 2015 Elsevier Ltd. All rights reserved.

In the context of Back-End of Line (BEoL) roadmap, dimension reduces, density integration increases and new materials are introduced. These points associated to manufacturing thermal budget could induce mechanical failures. Thus, a metallic in situ sensor was developed to study residual stress on a single metal level: using standard CMOS BEoL processing on 8 '' silicon wafer, aluminum thin film is patterned on dielectric layer. The sensor is composed by arms and a flexible beam that are fixed to anchors. As the structure is released from its surrounding layer, the relaxation of residual stress induces a displacement of flexible beam. Therefore, the measurement of this displacement allows determining the initial residual stress. Using this structure, the purpose of this paper is not only to determine the residual stress state, but also the thermo-mechanical properties: coefficient of thermal expansion and thermal conductivity. For that reason, new designs are released to address electrical polarization and thus to locally heat this sensor by Joule effect. Due to thermal expansion, the flexible beam will move. The thermo-mechanical properties were determined by coupling SEM electrical nano-probing (displacement of flexible beam and electrical resistance as a function of applied current) with analytical modeling and Multi-physics Finite Element Method (FEM). As a result, a tensile stress state of 190 MPa in arm direction is identified in the aluminum thin film. The coefficient of thermal expansion of 22.5 x 10(-6) K-1 and thermal conductivity of 190 W/(K m) were identified, in agreement with literature. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.

We investigate the material depletion rate from a fatal void due to electromigration in a Cu interconnect structure ended by a TSV. Experiments show the formation of a fatal void above the TSV. Its volumetric growth rate is practically constant for an extended period, but at longer times a significant increase is observed. We have carried out numerical simulations to reproduce the aforementioned void growth behavior. The model incorporates the void size dependence on the incoming flux of vacancies due to electromigration. The simulation results have provided a good description for the void volume and for the growth rate increase for the entire time window of the experiments.

A freestanding cross-shaped structure designed as a planar rotation stress sensor [1], [2], [3] is manufactured using standard CMOS technology (Complementary Metal-Oxide-Semiconductor). The fabrication process induces thermal residual stresses which result in out-of-plane bending, which degrades the device reliability and precision. To control such movements, the design was studied under stress compensation using a bilayered aluminum (Al) / titanium nitride (TiN) structure. Likewise, a single layer of aluminum was studied, to determine a technological solution, with better compatibility. Fabrication stresses have been measured using Stoney's formula based on bending of full-wafer coatings. The Finite Element Method (FEM) is used to model the effect of these stresses on the geometry after release, and the results are compared with measurements. For this purpose, a comb-shaped structure has been designed to relate residual stress in a freestanding Al-TiN bi-layered structure with its bending. Based on this, conservation or elimination of TiN layer is judged, so that the design remains planar after release. The model is then applied to the movement of the cross-shaped sensor after release, and a second optimization variable is studied for maximum sensitivity: the shape of the hinge between the two arms of the cross.

A metallic in-situ stress sensor is modified to address electrical polarization and thus to locally heat this sensor by Joule effect. By coupling SEM electrical nano-probing with analytical modeling and multiphysics Finite Element Method (FEM), the thermo-mechanical properties are identified. As a result, a tensile stress state of 190 MPa, coefficient of thermal expansion of 22.5×10-6 K-1 and thermal conductivity of 190 W/(K·m) are identified in the aluminum thin film in agreement with literature. Moreover, high current induces irreversible deformation and breaking. Using multiphysics FE model with identified thermo-mechanical properties, the failure of the sensor under electrical solicitation is investigated. The evolution of local temperature and mechanical deformation on different sensor designs allows the determination of the breaking location and condition.

In order to develop 'More-than-Moore' technologies, interconnection by Through-Silicon Via (TSV) is a promising candidate, but TSV leads to fabrication and mechanical issues. In this paper, mechanical stress analysis in silicon surrounding 50@mm thick TSVs is performed. A calibrated micro-Raman spectroscopy (@mRS) is used as a non destructive method to determine local silicon stress. Results indicate that when a curvature radius is applied on 50@mm thick rectangular silicon lamella containing TSVs, a local mechanical stress is generated around TSVs. For non-metalized TSVs, the maximal stress is three times higher in the longitudinal direction compared to the transversal direction. Furthermore this local maximal stress depends linearly on the geometrical parameter R which is the ratio of via diameter by via-to-via spacing, and its intensity increases with R value. Micro-Raman Spectroscopy measurements were confirmed by Finite Element Analysis (FEA). Further FEA investigations of maximal stress when TSVs are lined with copper revealed that this stress level is reduced even though its linear dependence to the geometrical ratio R is conserved. The aim of the present work is thus to define design rules for optimal mechanical flexibility in a system that contains TSVs.

Contact material and more precisely surface properties are a major issue for RF MEMS ohmic switch reliability. Shallow ion implantation of boron and nitrogen on gold thin film is investigated to increase surface hardness with a limited impact on Electrical Contact Resistance (ECR). The implantation energies were chosen to place the concentration peak of the implanted species at a depth of 100 nm. A microstructural analysis shows that the hardness increases with boron concentration due to a solid solution hardening mechanism, whereas in case of nitrogen, for concentration above 1%, the nitrogen precipitates into a nitride phase correlated to a hardness decrease. The ECR is measured using a Nanoindenter XP which experimental setup reproduces MEMS ohmic switch contact (from 100 μN to 1 mN applied loads under 1 mA). A notable result is obtained with a boron dose of 7.37 × 10 16 ions/cm 2 at 90 keV into gold thin film: 50% hardness increase and 2.6 times higher ECR than pure gold.

Foldable, stretchable and flexible electronics is of constant increasing interest since the early 2000's. Its applications spread from OLED-based displays, bio-inspired detectors and “epidermal electronics”. Cylindrical curvature is largely studied through many 3 points and 4 points bending variations in electronic devices. However spherical curvature is poorly addressed, especially for monolithic approach. In this paper, a simulation and experiments of the elastic deformation of a thin silicon chip on a spherical holder are presented. The holder can have a concave or a convex shape. The chip is a square of 10 by 10 mm 2 . Its thickness is 50, 25 or 15 μm. The simulation is performed in 3 steps. First, the use of a shell model is validated by a convergence study and by a comparison with a 3D model and the literature. Then, the influence of the anisotropic elastic behavior (single crystal) is considered. In a given bulge test condition, isotropic and anisotropic silicon simulation gave similar deformations. At the end, the spherical forming is accomplished with a shell model and an anisotropic law. Experimental data is obtained by curving thin silicon plates of various thicknesses on different radii holders in a press. The comparison between experimental and computed results is realized. We found similar macroscopic deformations for both concave and convex shapes. The influence of chip thickness and applied pressure is studied on characteristic folds and flat part amplitudes. A heterogeneous stress distribution with hundreds of MPa variations can explain the difference observed between curved chips and perfect spherical holders. The stress level in electrical and optical active layers of thin curved silicon-based devices may affect their properties. A numerical example on a bolometer gives a stress-induced resistivity variation over 10%.

La durée de vie du contact des micro-commutateurs MEMS (micro electro mechanical systems) limite leur compétitivité. Le matériau de contact généralement utilisé, sous forme d’un film mince, est l’or. Les principales causes de défaillance sont liées à sa ductilité et à sa faible température de fusion. Une alternative consiste à utiliser un film ultra mince (20, 50 et 100 nm) de ruthénium déposé sur l’or afin d’améliorer les propriétés du contact car la dureté et la température de fusion du ruthénium sont plus élevées que celle de l’or. Dans ce cadre, il est nécessaire de caractériser l’augmentation de dureté apparente obtenue et d’être capable d’en extraire la dureté intrinsèque du ruthénium en film ultra mince. Pour cela, les propriétés mécaniques sont caractérisées par nano-indentation avec une mesure continue de la rigidité de contact. La dureté effective mesurée est ensuite analysée en combinant une loi de mélange volumique des duretés, la prise en compte du confinement de la déformation plastique de l’or et les effets de taille de type ISE (indentation size effect). Les valeurs de dureté trouvées, 1 GPa pour l’or et 15 GPa pour le ruthénium, sont cohérentes avec celles de la littérature.

Stress concentration in through-silicon via (TSV) is studied by a calibrated micro-Raman spectroscopy (μRS) and correlated with numerical simulation. Results show that stress concentration is in transverse direction and it depends on the ratio of via diameter to via spacing. Further investigations on bended TSV lined with copper revealed that the stress level is lower than the one in TSV without copper. Chip-to-wafer 3D-stacking using microinserts thermocompression bonding shows that the 50 μm thick TSVs have negligible mechanical stress effect.

Electrical Wafer Sort (EWS) is known to induce stress in the pad structure that can lead to mechanical failures. During the current study, various interconnect designs and stacking (thicknesses and copper layer architectures) are investigated through actual tests, nanoindentation and finite element modeling tools. Firstly, a dedicated design of experiment is set up and samples are probed. The failure analyses following the parametric test allow the ranking of the interconnect structures according to their mechanical robustness. Cracks are also observed with dedicated imaging tools to improve the understanding of the failure mechanisms. Then, nanoindentation with both Berkovich and cube corner tips is performed to mimic fracture occurrences. The former tip reproduces the failures observed during the tests in the oxide layers, and the load-displacement curves made with the latter are post processed using in-house indicators to weight the structures. On the other hand, a 3D finite element model is developed to reproduce the transient dynamic phenomena during probing. A stress analysis is performed in the layers of interest to rank the structures. A good agreement between all the techniques is found for most of the parameters, showing the ability of both the nanoindentation and the numerical modeling to reproduce EWS and forecast related failures. Indeed, the fracture hazard is reduced while increasing either the aluminium or pad open thicknesses. The design of the copper layer is also evaluated and lower cracks occurrence is found in pad layouts with small slotted lines compared to pad layouts with bigger slotted lines or to long lines. Both techniques are helpful to reduce the reliability issues in pad structures, and to investigate solutions with improved tests cycle time and reduced qualification costs.

This paper investigates the mechanical deformation and the electrical contact resistance of an electroplated Ni micro-cylinder called micro-insert inserted in an Al thin film. A modified nanoindentation apparatus is used to perform the experiments with 6 mu m, 8.5 mu m and 12.5 mu m diameters micro-inserts having the same 5 mu m height. Mechanical deformation of Ni micro-insert and Al film is described at different maximum loads corresponding to an equivalent stress of 0.8 GPa, 1.6 GPa and 3.2 GPa. At equivalent stress less than 1.6 GPa, Ni micro-insert exhibits an elastic deformation while at 3.2 GPa it presents an elastic-plastic deformation with a large amount of compression and penetration into micro-insert foundation. Visco-plastic deformation of Al film is noticed during hold at all maximum loads. Beside, Al creep parameters are extracted using a combined Maxwell/Kelvin-Voigt phenomenological model. Mechanical results are coupled to electrical contact resistance measurement. (C) 2009 Elsevier B.V. All rights reserved.

Mechanical stress in damascene copper/low-k interconnects has been studied by means of micro-rotating sensors embedded in chips and directly integrated in CMOS process flow. A new hinge sensor design has been elaborated and a new analytical model of the mechanical equilibrium of sensors is validated. These sensors allow the study of the average residual stress as a function of the line width in a range from few hundred nanometers to several microns. It was found that the residual stress increases from 290 to 850MPa in, respectively, 2 and 0.25μm wide lines. This trend shows a yield stress increase with the line width reduction. Copper grains microstructure change between large and narrow lines is probably one of the reasons for yield stress and so residual stress increase. This microstructure change has been observed by means of Transmission Electron Microscopy (TEM) observations.

Ultrathin silicon chips are becoming more and more popular because of market demand for small, light, and high- performance products with noticeable request of reliability and flexibility. In this paper, the flexibility of the Integrated Circuit package is investigated using finite-element (FE) analysis. ANSYS software is used to analyze a single ultrathin die package in a smart card under four-point bending with the aim of developing flexible smart card modules using chips with thickness below 50 μm. Thicknesses of different layers and Young's modulus of the die adhesive and the encapsulation resin are investigated to find their relative influence on the bending stress field in silicon. The thicknesses of some layers have important influence on bending stress distribution in the module. Decreased copper thickness can reduce considerably the maximal bending stress in silicon die under the same bending condition. As a result, some criteria for the design optimization are given in order to improve the flexibility of the package.

Ultrathin silicon chips are becoming more and more popular because of market demand for small, light, and high- performance products with noticeable request of reliability and flexibility. In this paper, the flexibility of the Integrated Circuit package is investigated using finite-element (FE) analysis. ANSYS software is used to analyze a single ultrathin die package in a smart card under four-point bending with the aim of developing flexible smart card modules using chips with thickness below 50 mum. Thicknesses of different layers and Young's modulus of the die adhesive and the encapsulation resin are investigated to find their relative influence on the bending stress field in silicon. The thicknesses of some layers have important influence on bending stress distribution in the module. Decreased copper thickness can reduce considerably the maximal bending stress in silicon die under the same bending condition. As a result, some criteria for the design optimization are given in order to improve the flexibility of the package.

A new variety of duplex steels with high content of manganese and aluminum has been elaborated in Arcelor Research. These steels contain two phases: austenite and ferrite combining the best features of austenitic and ferritic steels. In this work four duplex steels with different chemical composition and phase volume fraction are studied. The evolution of internal stresses for the two phases has been determined by X-ray diffraction during an in situ tensile test. These measurements results were used to determine the mechanical behaviour of the duplex steel using a micromechanical approach by scale transition for tensile tests. Though a good agreement between experiments and simulations is found at the macroscopic level, the calculated internal stresses of the austenitic phase do not match experimental results. These discrepancies are attributed to (i) a bad estimation of the austenite yield stress or (ii) the presence of kinematic hardening in the austenitic phase. A new step is then proposed to test these two hypotheses.