Bulge Techniques Research Articles

In-situ irradiation creep behavior of dilute Al-Sc alloys: Using a thin film bulge test method

• In situ thin film bulge test on nc-AlSc is effective method for irradiation induced creep. • Preexisting Al 3 Sc precipitates suppress irradiation induced creep deformation. • Transition regime of AlSc binary system is located between room temperature and 75 °C. In-situ irradiation induced creep(IIC) measurements on a nanocrystalline AlSc 1.1 binary alloy were performed using a thin-film bulge test technique. A thin film bulge technique was employed since any substrate effect can be excluded, and hence is beneficial to analyze the intrinsic properties of specimen. Here, an as-deposited film and a pre-annealed film, both underwent heavy ion irradition with 1.8 MeV Kr ions. Al 3 Sc precipitates in the pre-annealed samples appear to reduce the irradiation creep compliance. Dissolution of these precipitates during irradiation led to increased irradiation creep rates. Microstructural evolution during irradiation was investigated by transmission electron microscopy and high resolution transmission electron microscopy.

Tuning Optical Signatures of Single- and Few-Layer MoS2 by Blown-Bubble Bulge Straining up to Fracture.

Emerging atomic layer semiconducting crystals such as molybdenum disulfide (MoS2) are promising candidates for flexible electronics and strain-tunable devices due to their ultrahigh strain limits (up to ∼20-30%) and strain-tunable bandgaps. However, high strain levels, controllable isotropic and anisotropic biaxial strains in single- and few-layer MoS2 on device-oriented flexible substrates permitting convenient and fast strain tuning, remain unexplored. Here, we demonstrate a "blown-bubble" bulge technique for efficiently applying large strains to atomic layer MoS2 devices on a flexible substrate. As the strain increases via bulging, we achieve continuous tuning of Raman and photoluminescence (PL) signatures in single- and few-layer MoS2, including splitting of Raman peaks. With proper clamping of the MoS2 crystals, we apply up to ∼9.4% strain in the flexible substrate, which causes a doubly clamped single-layer MoS2 to fracture at 2.2-2.6% strain measured by PL and 2.9-3.5% strain measured by Raman spectroscopy. This study opens new pathways for exploiting 2D semiconductors on stretchable substrates for flexible electronics, mechanical transducers, tunable optoelectronics, and biomedical transducers on curved and bulging surfaces.

Study of mechanical-magnetic and electromagnetic properties of PZT/Ni film systems by a novel bulge technique

A novel multiple functional bulge apparatus was designed to study the mechanical-electronic-magnetic characteristics of electromagnetic materials. The elastic modulus difference effect of Ni thin film was observed and it was about 22.16% in the demagnetized and magnetization saturated states. The mechanical-magnetic behaviors of Ni and lead-titanate zirconate (PZT)/Ni films were in-situ measured by using the new bulge systems, respectively. The evolutions of three key material properties in hysteresis loop including saturation magnetization, remanent magnetization and coercive field were discussed in detail, respectively. The mechanisms of mechanical-magnetic coupled behaviors of Ni and PZT/Ni films were analyzed with the aid of the competitive relationship of stress and magnetization. Similarly, the electronic-magnetic characteristics of PZT/Ni films were in-situ measured by using this experimental system. The evolution of saturated magnetization, remanent magnetization and coercive field Kerr signals were discussed with the magneto-elastic anisotropy energy point. In this paper, a suitable mechanical-electronic-magnetic bulge measurement system was established, which would provide a good choice for further understanding the multi field coupling characteristics of electromagnetic film materials.

Effect of deposition conditions on thermo-mechanical properties of free standing silicon-rich silicon nitride thin film

Even small differences in gas composition in low pressure CVD deposition make substantial changes in residual stress and significant but smaller changes in the elastic modulus and thermal expansion coefficient of silicon-rich silicon nitride thin films. ► An investigation on the mechanical properties of the SiN x thin film was performed. ► The elastic modulus linearly depends on SiCl 2 H 2 /NH 3 gaseous ratio. ► Thermal expansion coefficient of the SiN x thin film for each SiCl 2 H 2 /NH 3 gaseous ratio was obtained. ► The SiCl 2 H 2 /NH 3 gaseous ratio has also an effect on the residual stress of each sample. Using resonance and bulge techniques, the mechanical properties of free standing Si-rich SiN x membranes were precisely measured to evaluate the effect of deposition conditions on them over a narrow range of particular technological interest. Values of the elastic modulus, the residual stress and the thermal expansion coefficient were obtained. It was found that even small differences in gas composition in low pressure CVD deposition make substantial changes in residual stress and significant but much smaller changes in the elastic modulus.

Mechanical durability of proton exchange membranes with catalyst platinum dispersion

The durability of proton exchange membrane (PEM) fuel cells remains a challenging issue for their long term operational use. Degradation of the PEM related to dissolution of the adjacent catalyst and re-deposition into the PEM significantly reduces cell efficiency. We investigate the effects of platinum (Pt) dispersions intended to simulate the re-deposited catalyst on the mechanical durability of the PEM. The bulge technique was applied to characterize the mechanical properties of PEMs simulating pressure loading on fully hydrated membranes in fuel cells. The results showed that with increasing Pt dispersion concentration the stiffness of the PEMs increased, and the membranes became less ductile and inclined to fracture at lower stresses under pressure loading. We also used the out-of-plane tearing test to characterize membrane fracture behavior which revealed the harmful effects of Pt dispersion on the fracture resistance under different environmental conditions. Deterioration in fracture resistance was explained in terms of the Pt distribution and aggregation as defects inside the membranes as characterized by electron microscopy. Fracture was shown to initiate preferentially at the interface of Pt particles and the polymer matrix, and propagate through the defect regions in polymer with lower energy, thus reducing the overall fracture resistance of the PEM.

Anelastic Stress Relaxation in Gold Films and Its Impact on Restoring Forces in MEMS Devices

In order to evaluate the importance of stress relaxation on device performance of capacitive RF MEMS switches, stress relaxation has been measured in 1.2-mum-thick Au films using a membrane bulge technique. When the residual stress in the films is small, the stress relaxation is fully recoverable and is well described by linear anelasticity (viscoelasticity) theory. A 27% reduction in the effective elastic modulus occurs over a three-day period under constant strain conditions at room temperature. The time dependence of the relaxation can be represented by a series of time constants with values extending from seconds to days. Linear superposition of the anelastic response can be used to accurately predict the stress under any time dependence of the strain. The prediction is accurate even during cyclic loading and unloading, and even when the strain is cycled at rates that are fast compared with any of the relaxation times. The restoring force available to open a capacitive RF MEMS switch is modeled for two different switch designs. The restoring force is shown to drop by approximately 7% or 20% at room temperature for the two cases presented.

Reliability of MEMS Materials: Mechanical Characterization of Thin-Films using the Wafer Scale Bulge Test and Improved Microtensile Techniques

AbstractThis paper reports on recent improvements of the bulge and microtensile techniques for the reliable extraction of material parameters such as the Young's modulus E, Poisson's ratio ν, plane strain modulusEps=E/(1–ν2), prestress σ0, fracture strength μ, Weibull modulusmand strain hardening coefficientsn, and on the direct comparison between the two methods. The bulge technique is extended to full wafer measurements enabling throughputs of data with statistical relevance whereas key improvements of a previous fabrication process of microtensile specimens lead now to much higher yields, approaching 100%. Both techniques are applied to an extensive set of materials, brittle and ductile, typically used in MEMS applications. These include thin films of silicon nitride, silicon oxide, polycrystalline silicon and aluminum deposited by techniques such as thermal oxidation, LPCVD, PECVD and PVD.

High precision stress measurement of ion projection lithography mask membranes

In this article, we describe an instrument for measuring the mean stress of large-area membranes for ion projection lithography (IPL) stencil masks. The apparatus incorporates two improvements over the conventional bulge technique, where the deflection at the center of a membrane is measured as a function of differential pressure across it, that provide a hundred-fold improvement in the precision of the measurement. The first is to simply place the membrane, without an o-ring or mechanical clamp, on an optically flat silicon ring separating the two pressure chambers. This eliminates the in-plane mounting forces that previously resulted in 1–2 MPa errors. The close contact between the integral ring supporting the mask and the silicon ring provides an adequate vacuum seal between the chambers. The second improvement is to provide an isothermal environment to reduce stress errors due to temperature variations in the membrane. As a result, the measured stress is independent of temperature and the standard deviation (1σ̣) of measured stress is 0.02 MPa.

Hardness and Young's modulus of amorphous a-SiC thin films determined by nanoindentation and bulge tests

Due to its interesting mechanical properties, silicon carbide is an excellent material for many applications. In this paper, we report on the mechanical properties of amorphous hydrogenated or hydrogen-free silicon carbide thin films deposited by using different deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a-SixC1−x: H PECVD, a-SiC LAD, and a-SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoindentation and bulge techniques, respectively. Hardness (H), Young's modulus (E), and Poisson's ratio (v) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a-SixC1−x: H PECVD films, both hardness and Young's modulus are dependent on the film composition. The nearly stoichiometric a-SiC: H films present higher H and E values than the Si-rich a-SixC1−x: H films. For hydrogen-free a-SiC films, the hardness and Young's modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a-SiC films present both hardness and Young's modulus values higher by about 50% than those of hydrogenated a-SiC: H PECVD films. By using the FTIR absorption spectroscopy, we estimated the Si-C bond densities (NSiC) from the Si-C stretching absorption band (centered around 780 cm−1), and were thus able to correlate the observed mechanical behavior of a-SiC films to their microstructure. We indeed point out a constant-plus-linear variation of the hardness and Young's modulus upon the Si-C bond density, over the NSiC investigated range [(4–18) × 1022 bond · cm−3], regardless of the film composition or the deposition technique.

Mechanical properties of silicon carbide films for X-ray lithography application

Hydrogenated amorphous silicon carbide a-SixC1−x:H films of various compositions [Formula: see text] were deposited using a plasma-enhanced chemical vapour deposition technique. The as-deposited films are under high compressive stress (1 GPa). The control of the stress relaxation is an important stage in the X-ray mask technology. The stress of the a-SixC1−x:H films is measured by the wafer bow technique, whereas the resonance frequency and the bulge techniques are used to measure the stress of the a-SixC1−x:H free-standing membranes. These three methods give similar results and it is pointed out that the wafer bow technique can be used with confidence to determine the stress of a-SixC1−x:H films intended to X-ray membrane processing. From the bulge method, the biaxial Young's modulus E/(1–ν) of the a-SixC1−x:H membranes is also deduced. Values of 200 ± 25 GPa are obtained for a-SixC1−x:H films at x = 0.4 and 0.5 film compositions. At x = 0.67, E/(1–ν) is reduced by a factor of about two. The structure and composition of the a-SixC1–x:H films were investigated by means of elastic recoil detection, X-ray diffraction, and Fourier transform infrared absorption techniques. It is shown that the biaxial Young's modulus increases with the Si–C bond density in the film.

Mechanical Properties of Copper Films

The mechanical properties of polycrystalline copper films, 700–5000-Å thick, were measured using the bulge technique. The breaking strength increased with decreasing film thickness, the greatest increase occurring below 1000 Å. The equivalent bulk breaking strength was found to be 61 000 lb/in2. Young's modulus was independent of film thickness and had the normal value 18×106 lb/in2.