Bending Beam Technique Research Articles

Detecting the Impact of Micro and Nano Size Additives on Deformation of Asphalt Concrete

Permanent deformation is considered as one of the major distress type of asphalt concrete pavement in the hot climate region. It can be controlled by the use of additives either for asphalt binder or for the asphalt concrete mixture. In the present assessment, the impact of micro and Nano size additives (fly ash and silica fumes) on the deformation behaviour of asphalt concrete mixtures was assessed. Such additives were implemented as partial substitute of mineral filler. Asphalt concrete slab samples were prepared in the laboratory with the aid of roller compaction. The optimum percentages of the additives are (2 and 4) % of silica fumes and coal fly ash respectively by the weight of the binder. Beam specimens were obtained from the slab samples and tested for fatigue life under three constant strain levels using four point bending beam technique. It was observed that for mixture treated with Nano additive (silica fumes), the reduction in the permanent deformation starts at 0.0001 MJ/m3 loss in energy for 750 microstrain level. However, for mixture treated with Micro size additive (fly ash), as the dissipated energy vanishes, the permanent deformation was in the range of (3 - 4.5) microstrain. It was concluded that as the dissipated energy vanishes, the permanent deformation was lower by (29.4 and 11.7) % for mixtures treated with silica fumes and fly ash additives respectively as compared with the control mixture.

Stress, Hardness and Elastic Modulus of Bismuth Triiodide (BiI3)

ABSTRACTBismuth triiodide (BiI3) has been studied aiming the development of lead-free photovoltaic materials. It can also be used as X-ray detectors due to the high density of its elements (bismuth and iodine). We investigate the mechanical stress, hardness, and elastic properties of BiI3 thin films deposited by thermal evaporation. The stress was determined by the bending beam technique using the Stoney equation. The films are tensile with stress of approximately 27 MPa. The hardness and the elastic modulus were determined by nanoindentation technique using a Berkovich diamond tip. The hardness of the films is approximately 0.8 GPa and the reduced Young´s modulus is ∼28 GPa for maximum penetration depth of 10% of the film thickness.

Stress and stress relaxation behaviors of multi-layered polarizer structures under a reliability test condition characterized by use of a bending beam technique

The bending curvature, stresses, and stress relaxation of various multi-layered structures with different adhesive layers pertaining to the polarizer in a thin-film transistor liquid-crystal display (TFT-LCD) have been successfully characterized by using bending beam technique under reliability test. To be more specific, three different types of pressure-sensitive adhesive (hard-, middle-, and soft-type) and various poly(vinyl alcohol) (PVA) stretched directions are devised to examine to key stress contributors and correlations with light leakage. The shrinkage stress in stretched PVA film and stress relaxation ability of pressure-sensitive adhesives (PSA) layers are found to be the key factors determining the stress distribution and out-of-plane displacement of a polarizer stack. For hard-type PSA, its polarizer stack generates the highest bending curvature with maximum out-of-plane displacement but minimum in-plane displacement, leading to anisotropic stress distribution with high stress around the edges. On the other hand, polarizer stack with soft-type PSA yields the maximum in-plane displacement but the minimum out-of-plane displacement, resulting in isotropic stress distribution.

Modeling crack propagation for advanced 4-point bending testing of metal–dielectric thin film stacks

For monitoring and improving mechanical properties of BEoL (back-end of line) interconnect structures in microprocessor technology, it is crucial to analyze their adhesion and crack propagation properties. In the present investigation, a camera assisted 4-point bending beam technique has been used to obtain fast and reliable adhesion measurements including locally resolved crack length information. To interpret the obtained crack propagation data, a finite-element modeling approach has been utilized. The combination of local measurement of the crack energy release rate and modeling enables to evaluate measurement curves for both symmetric and asymmetric crack propagation modes and to describe the crack propagation properties of the involved film stacks not attainable in such detail by conventional 4-point bending technique.

Characterization of thermal stresses in through-silicon vias for three-dimensional interconnects by bending beam technique

Through-silicon via is a critical element for three-dimensional (3D) integration of devices in multilevel stack structures. Thermally induced stresses in through-silicon vias (TSVs) have raised serious concerns over mechanical and electrical reliability in 3D technology. An experimental technique is presented to characterize thermal stresses in TSVs during thermal cycling based on curvature measurements of bending beam specimens. Focused ion beam and electron backscattering diffraction analyses reveal significant grain growth in copper vias, which is correlated with stress relaxation during the first cycle. Finite element analysis is performed to determine the stress distribution and the effect of localized plasticity and to account for TSV extrusion observed during annealing.

Isothermal stress relaxation in electroplated Cu films. I. Mass transport measurements

Recent studies on Cu interconnects have shown that interface diffusion between Cu and the cap layer dominates mass transport for electromigration. The kinetics of mass transport by interface diffusion strongly depends on the material and processing of the cap layer. In this series of two papers, we report in Part I the interface and grain-boundary mass transport measured from isothermal stress relaxation in electroplated Cu thin films with and without a passivation layer and in Part II a kinetic model developed to analyze the stress relaxation based on the coupling of grain boundary and interface diffusion. We show that a set of isothermal stress relaxation experiments together with appropriate modeling analysis can be used to evaluate the kinetics of interface and grain-boundary diffusion that correlate to electromigration reliability of Cu interconnects. Thermal stresses in electroplated Cu films with and without passivation, subjected to thermal cycling and isothermal annealing at selected temperatures, were measured using a bending-beam technique. Thermal cycling experiments showed the effect of passivation and provided information to select the initial stresses and temperatures for isothermal stress measurements. Isothermal experiments at moderate temperatures showed a significant transient behavior of stress relaxation. Based on the kinetic model developed in Part II, grain boundary and interface diffusivities were deduced. While the deduced grain boundary diffusivity reasonably agrees with other studies, the diffusivity at the Cu∕SiN cap layer interface was found to be generally lower than the grain-boundary diffusivity at the temperature range of the present study.

Simultaneous oscillations of surface energy, superficial mass and electrode potential in the course of galvanostatic oxidation of formic acid

Simultaneous oscillations of electrode potential, surface mass and specific surface energy have been detected in the course of galvanostatic oxidation of formic acid on platinum by using a Koesters laser interferometer combined with an electrochemical quartz crystal microbalance. Changes of surface energy data measured with the electrochemical Koesters laser interferometer and with the electrochemical bending beam technique are shown to be equivalent. Problems related to the interpretation of the measured data are discussed.

Stresses induced by hydrogen absorption and desorption in Pd nanofilms

The stresses induced by hydrogen absorption in Pd nanofilms were studied by the electrochemical quartz crystal microbalance (EQCM) and bending beam methods. In the EQCM method, hydrogen was charged electrolytically into a Pd nanofilm that was coated on an AT- or BT-cut quartz crystal. For Pd films in a thickness of 120-nm on the AT-cut and 158-nm on the BT-cut quartz crystal, compressive stresses of 1.07×10 3 MPa and 1.70×10 3 MPa, respectively, were measured. With the bending beam technique, the bending curvature of the Si substrate during gas-phase hydrogenation was monitored. The maximum compressive stress induced in a 50-nm Pd film on the Si substrate during hydrogenation at 0.2 MPa of hydrogen gas was 944 MPa. When hydrogen was desorbed from the film, a tensile stress of 708 MPa in the film was observed. When the thickness of the Pd film was increased to 130 nm, peeling of the Pd film from the substrate occurred.

Magnetoelastic effects in ultrathin epitaxial Ni films: an ab initio study

The effect of the nonlinear magnetoelastic coupling on the magnetostrictive stress and the magnetic anisotropy of epitaxially grown ultrathin Ni films with large epitaxial strain is investigated by the ab initio density functional electron theory. The nonlinear coupling has a considerable influence on the magnetostrictive stress, in agreement with the experimental results from the optical bending beam technique, but a weaker influence on the stress-induced magnetic anisotropy. Estimates are given for the nonlinear magnetoelastic coupling coefficients m 1 γ,2 and m 2 γ,2 . The results are compared with those for Fe.

On-wafer characterization of thermomechanical properties of dielectric thin films by a bending beam technique

A bending beam technique has been developed for on-wafer characterization of thermomechanical properties of dielectric thin films including Young’s modulus (E), the coefficient of thermal expansion (CTE), and the Poisson ratio (ν). The biaxial modulus E/(1−ν) and CTE were determined by measuring the thermal stresses of the dielectric film as a function of temperature on two different substrates. The Poisson ratio and Young’s modulus were determined by measuring the temperature dependence of the thermal stress of periodic line structures of the dielectric film. Three dielectric thin films were selected for this study, consisting of silica made from tetraethylorthosilane (TEOS), hydrogen silsesquioxane (HSQ), and biphenyltetracarboxylic dianhydride-p-phenylene diamine (BPDA-PDA). The deduced biaxial modulus and CTE are 77 GPa and 1.0 ppm/°C for TEOS, 7.07 GPa and 20.5 ppm/°C for HSQ, and 11.1 GPa and 3.4 ppm/°C for BPDA-PDA. The Poisson ratio is determined to be 0.24 and Young’s modulus is 59 GPa for the TEOS film. The error limit and the valid range of E/(1−ν) and CTE for applying this technique are also discussed.

Magnetoelastic coupling in Ni and Fe monolayers on Cu(001)

The correlation between mechanical stress and magnetic anisotropy of Ni and Fe films on Cu(001) is investigated. The magnetoelastic coupling and the film stress during the growth are measured in situ with a highly sensitive optical bending beam technique. For Ni a dramatically reduced magnetoelastic coupling of B1=3.5 MJ/m3 is found for films thinner than 10 ML, roughly one third of the bulk value of 9.4 MJ/m3. This change is explained by a strain correction to the magnetoelastic coupling. The influence of the interfaces does not significantly contribute to the magnetoelastic coupling. A very small magnetoelastic coupling of 0.4 MJ/m3 for Fe films in the range from 12 ML to 25 nm is attributed mainly to the crystallographic orientation of the bcc–Fe.

Diamond-like carbon coatings prepared in an asymmetric bipolar pulsed d.c. plasma

Abstract High quality diamond-like carbon (DLC) coatings can be routinely produced in r.f. (13.56 MHz) based capacitively coupled plasma-assisted chemical vapour deposition processes. In practice, this process is limited to relatively small batch volumes ( 3 ). Bipolar pulsed d.c. processes may offer an alternative to way forward to large-scale processing. In this work, DLC coatings were deposited from CH 4 using an asymmetric bipolar pulsed d.c. power supply. The positive pulse was fixed at a low voltage of +75 V, while the negative pulse amplitude was varied between −300 V and −1100 V. The following coating properties were characterized: CH and CC bonding structure using Fourier transformed IR and Raman spectroscopy, hardness using depth sensing indentation and internal stress using the bending beam technique. Substrate heating during deposition was evaluated using the annealing characteristics of hardened 100Cr6 steel pins. These properties are correlated with the major variables of the power supply: pulse frequency (120–250 kHz) and pulse amplitude. Under optimised plasma conditions, coating hardnesses as high as 18 GPa could be obtained.

The correlation between mechanical stress and magnetic properties of ultrathin films

The cantilever bending beam technique was applied to measure film stress, film magnetization and magneto-elastic coupling in nanometre Fe films grown epitaxially on W substrates. A simple optical deflection technique yielded sub-monolayer sensitivity for stress measurements and was used to determine magnetization and magnetostrictive properties of nanometre Fe films in situ. The combination of an electromagnet inside an ultra-high-vacuum chamber with a rotatable external magnet was employed to perform magneto-optical Kerr-effect measurements in the transversal, longitudinal and polar geometry in fields of up to 0.4 T. Examples for stress-driven structural changes in monolayer Fe films are discussed with respect to the unusual high coercivity found for sesquilayer Fe films and the re-orientation of the easy axis of magnetization in Stranski-Krastanov Fe films. The direct correlation between strain and magnetism was exploited to measure the magnetostrictive bending of the film-substrate composite. The magnitude and sign of the magneto-elastic coupling coefficient were found to depend on the film thickness, in contrast to the respective bulk values.

Linewidth dependence of stress relaxation and microstructural change in passivated Al(Cu) lines

Relaxation of thermally induced stresses in passivated line structures can lead to void formation, and its rate is strongly correlated with microstructural change in the lines. A bending beam technique was used to measure the thermal stress relaxation behavior of passivated Al (1 wt % Cu) line structures with 3, 1, and 0.5 μm linewidths as a function of temperature up to 15 h. Our data indicate that stress relaxation in Al(Cu) lines depends on line geometry and temperature, and exhibits log (time) kinetics, which is consistent with a thermally activated dislocation glide mechanism. The observed behavior can be explained by a combined result of the driving force due to the effective shear stress and kinetics due to thermally activated mass transport. Scanning electron microscope and transmission electron microscope techniques were used to study stress-induced voiding as a function of aging time and temperature. A strong correlation between stress relaxation rate and void density was observed for 1 μm wide lines, but not for 0.5 μm wide lines. A lower void density of 0.5 μm wide lines suggests that the bamboo grain structure may influence the mass transport and retard void formation.

Isothermal Stress Relaxation in Passivated Alsicu- and Al- Lines with Different Aspect Ratios

ABSTRACTMechanical stress relaxation in passivateci metal lines generally has two components, shear relaxation at constant volume, changing the stress distribution, and volumetric relaxation changing the hydrostatic stress. In order to contribute to the understanding of the underlying mechanisms we have collected detailed data on relaxation of passivated Al- and AlSiCu-lines with different aspect ratios a (0.2 ≤ a ≤ 1) and different thicknesses. A bending beam technique was used to measure the stress of these lines during thermal cycling from RT to 450°C and isothermal relaxation at different temperatures between RT and 350°C. Main results are: i) During thermal cycling the stress at RT and the total stress amplitude increase with increasing aspect ratio a, while stress hysteresis formation increases with decreasing a. ii) During isothermal relaxation the relaxed stress is strongly dependent on temperature with maxima between 150 and 250°C. The maximum shifts to lower temperatures with decreasing aspect ratio. From the temperature dependence the effective activation energy of 0.6±0.3eV for AlSiCu can be determined, iii) Finite element calculation and the method of “eigenstrains” are used to estimate seperately volumetric (voiding) and shear plasticity in these lines. Clearly voiding dominates the isothermal stress relaxation in all measured samples.

Measurements of equi-biaxial stress in adhered polyimide films by tilted beam polarized light microscopy

The equi-biaxial tension, developed during the drying process of the adhered polyimide films on a rigid substrate, was determined by measuring the out-of-plane birefringence of the dried films. Using a polarized light microscope and a tilting sample stage, the out-of-plane birefringence of a linear polyimide film that was dried during a given thermal process was determined to be (7.0 ± 0.5) × 10 −3. The equibiaxial tension was calculated by using the stress-optical law to be around 60 MPa, in agreement with that by the commonly used bending beam method. Due to the additional spatial resolution of stress distribution and the higher accuracy for measuring soft polymer coatings, the birefringence method described here is considered to be a useful alternative to the bending beam technique, which measures only the macroscopically averaged stress and its accuracy is generally limited by the huge modulus ratio between the rigid substrate and the polymer.

Determination of the mechanical properties of r.f.-magnetron-sputtered zinc oxide thin films on substrates

The variation of stress with respect to temperature in ZnO films, prepared by r.f. magnetron sputtering on Si and GaAs substrates, has been studied by using a bending beam technique. The thermal expansion coefficients and biaxial moduli of the films have been determined from the stress-temperature curves upon cooling. For most of the films, the obtained biaxial modulus ranges from 250 to 360 GPa at temperatures from 25 to 400 °C, whilst the thermal expansion coefficient increases from 5 × 10−6 to 8 × 10−6 °C−1. X-ray diffraction results reveal that the films deposited at a higher total gas pressure, i.e. 5.3 Pa, or a lower substrate temperature, i.e. 250 °C, have further crystallized upon annealing. The crystallization has caused the films to exhibit an irreversible stress behaviour upon thermal cycling.

Effect of Annealing and Passivation on the Electromigration and Linewidth Dependence

AbstractContinued miniaturization of conductor geometry below 0.5μm has by a concomitant decrease in Al deposition temperature, typically below 300°C. The degree of reliability exhibited by these films is strongly dependent on the grain size distribution and metallurgical configuration. This investigation focuses on the impact of post-deposition processing on changes in conductor microstructure and electromigration for films deposited at low temperature. AlCu(l%)Si(l%) was deposited at 300°C on PECVD phosphosilicate glass. The impact of post-deposition thermal budget on the as deposited grain size and distribution, preferred orientation and stress/strain states were analyzed using scanning electron microscopy, X-Ray diffraction and bending beam technique, respectively. These characteristics were also measured on unpassivated films subjected to the same thermal budget as SiO2 passivated films so that the geometric confinement and Al-SiO2 surface interaction could be quantified. Electromigration characteristics were measured for linewidths in the range W=1.0μm to W=10μm, for passivated and unpassivated films. A direct correlation between passivation and grain size was observed for both failure modes. This paper will also discuss the relationship between film stress and preferred orientation, the observed failure modes and their linewidth dependence.

Internal stress of chemical vapour deposition diamond film on silicon

The internal stress and strain of chemical vapour deposition (CVD) diamond film deposited on silicon were observed and quantitatively determined by the bending beam technique and the X-ray diffraction peak broadening. The internal stress of the diamond film varies with the growth parameters during the deposition. The crystallinity and quality of the diamond film decline with increasing concentration of CH4H2, the result of which is the build-up of compressive stress.The compressive stress can be partly released by improving the diamond crystallinity of the film. For instance, the addition of argon to higher concentrations of CH4H2 can effectively enhance the concentration of hydrogen atoms and therefore increase the ratio of sp3sp2 which is required for a high quality of diamond film. It is interesting to note the variation in the morphology of the CVD diamond film synthesized at higher ratios of CH4H2 from a ball-like shape to a mixture of {111} and {100} facets and finally to {100} facets as the concentration of argon increases from 0% to 33.3%.

Measurements of equi-biaxial stress in adhered polyimide films by tilted beam polarized light microscopy

The equi-biaxial tension, developed during the drying process of the adhered polyimide films on a rigid substrate, was determined by measuring the out-of-plane birefringence of the dried films. Using a polarized light microscope and a tilting sample stage, the out-of-plane birefringence of a linear polyimide film that was dried during a given thermal process was determined to be (7.5 ± 0.5) × 10 -3. The equi-biaxial tension was calculated, using the stress-optical law, to be around 60 MPa, in agreement with that determined by the commonly used bending beam method. Owing to the additional spatial resolution spatial resolution of stress distribution and the higher accuracy for measuring soft polymer coatings, the birefringence method described here is considered to be a useful alternative to the bending beam technique which measures only the macroscopically averaged stress and its accuracy is generally limited by the huge modulus ratio between the rigid substrate and the polymer.