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The in situ characterization of the deformation and fracture behavior of brittle metal films is of great technological interest for many modern applications. A prominent example is the field of flexible electronics, which rely on the electrical and mechanical integrity of metal thin films on compliant substrates when exposed to straining or bending. Within this work, failure mechanisms, such as cracking and buckling, were studied as a function of film thickness and correlated with the elastic-plastic material response during straining. Mo thin films were synthesized with thicknesses between 40 and 500 nm on polyimide substrates using an industrial scale in-line direct current magnetron sputtering system. In situ synchrotron X-ray diffraction was employed to determine the evolution of lattice strain and film stress during uniaxial tensile straining while simultaneously measuring the change in electrical resistance. The results highlight that the electro-mechanical properties of Mo thin films scale with the film thickness. In general, a significant increase in fracture strength was observed with decreasing film thickness. Thus thinner Mo films were able to withstand higher tensile strains before cracking. In contrast, the 40 nm thick Mo film was the earliest to show delamination in the form of buckles, but the applied tensile strain of 12% was not high enough to induce buckling in the 500 nm thick Mo film. A model based on film buckling under uniaxial tensile tests was used to assess the interfacial adhesion energy between the Mo films and the polyimide substrates yielding values between 11±1 and 14±5 J/m 2 . [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • 500 nm Mo films on polyimide were strained under uniaxial tension. • The crack onset strain increased for a zig–zag microstructure. • After 1000 cyclic tensile cycles, the zig–zag structure is superior to columnar. Abstract Polymer supported metal thin films for flexible and stretchable applications need to have exceptional electro-mechanical behavior. Typically, brittle metal films thicker than 300 nm will fail at low strains. It will be demonstrated that with residual stress and microstructural tuning, a 500 nm thick Mo film on polyimide has a high crack onset strain and does not fail electrically after 1000 tensile straining cycles of 1% due to a novel zig–zag microstructure. The zig–zag microstructure imparts a crack deflecting behavior which ensures longer lifetimes. As a consequence, a high crack onset strain does not indicate better behavior under cyclic loading conditions. [ABSTRACT FROM AUTHOR]

The electro-mechanical performance of Mo thin films grown by dc magnetron sputter deposition on polyimide substrates was investigated. A series of 500 nm thick Mo films was synthesized at different discharge powers to evaluate the effect of deposition conditions on the structure–stress relationship and to correlate the intrinsic properties of the Mo films with their electro-mechanical response. Different in-situ fragmentation tests were performed to assess the crack morphology, the change in electrical resistance and the film stress during straining. A direct relation between the residual stress state of the Mo thin films and the discharge power was noticed as the stress changed from tensile to compressive with increasing discharge power. All Mo films showed brittle fracture when strained in tension and the critical crack onset strain correlated with the residual stress state. In-situ synchrotron diffraction experiments enabled the characterization of the fracture strength, which was unaltered by the discharge power and found to be approximately 1700 MPa for all Mo thin films studied. [ABSTRACT FROM AUTHOR]

In order to advance flexible electronic technologies it is important to study the electrical properties of thin metal films on polymer substrates under mechanical load. At the same time, the observation of film deformation and fracture as well as the stresses that are present in the films during straining are also crucial to investigate. To address both the electromechanical and deformation behavior of metal films supported by polymer substrates, in-situ 4 point probe resistance measurements were performed with in-situ atomic force microscopy imaging of the film surface during straining. The 4 point probe resistance measurements allow for the examination of the changes in resistance with strain, while the surface imaging permits the visualization of localized thinning and crack formation. Furthermore, in-situ synchrotron tensile tests provide information about the stresses in the film and show the yield stress where the deformation initiates and the relaxation of the film during imaging. A thin 200 nm Cu film on 23 μm thick PET substrate will be used to illustrate the combined techniques. The combination of electrical measurements, surface imaging, and stress measurements allow for a better understanding of electromechanical behavior needed for the improvement and future success of flexible electronic devices. [ABSTRACT FROM AUTHOR]

More and more flexible, bendable, and stretchable sensors and displays are becoming a reality. While complex engineering and fabrication methods exist to manufacture flexible thin film systems, materials engineering through advanced metallic thin film deposition methods can also be utilized to create robust and long-lasting flexible devices. In this review, materials engineering concepts as well as electro-mechanical testing aspects will be discussed for metallic films. Through the use of residual stress, film thickness, or microstructure tailoring, all controlled by the film deposition parameters, long-lasting flexible film systems in terms of increased fracture or deformation strains, electrical or mechanical reliability, can be generated. These topics, as well as concrete examples, will be discussed. One objective of this work is to provide a toolbox with sustainable and scalable methods to create robust metal thin films for flexible, bendable, and stretchable applications. [ABSTRACT FROM AUTHOR]

Fragmentation testing of thin films on substrates has in the past been mostly performedin situusing optical and scanning electron microscopy. While these techniques work well for brittle materials, they cannot always discern the difference between through-thickness cracks (TTCs) and localized plastic deformation of ductile films. Here, we describe fragmentation testing with atomic force microscopy and present criterion to distinguish TTCs and localized deformation for ductile films. [ABSTRACT FROM PUBLISHER]

• Ag films sputtered on polyethylene naphthalate (PEN) and polyimide (PI). • Electro-mechanical behavior of Ag with and without Ti adhesion layer. • Use Mo stressed overlayer and tensile-induced delamination to measure adhesion. • Films on PEN fracture early and have less recovery than same films on PI. • Ti adhesion layers increases the interface strength of Ag on PI, but not to PEN. With the wider use of flexible electronics and sensors it is necessary to better understand how the substrate chemistry as well as the use of relatively brittle interlayers influences the electro-mechanical and interfacial behavior of electrically conductive thin films. Here, silver (Ag) films sputter deposited on polyimide (PI) and polyethylene naphthalate (PEN) with and without a titanium (Ti) adhesion layer were studied with in-situ electrical resistance measurements during uniaxial straining to study the electro-mechanical response with the cracking factor. Additionally, a molybdenum (Mo) stressed overlayer was utilized with the tensile induced delamination method to quantitatively measure the adhesion energies of the different material systems. It is demonstrated that the substrate chemistry, in terms of the mechanical behavior and number of C = O groups, plays a significant role in how through thickness cracks elongate and how the Ag and Ti may chemically bond to the polymer substrates. In general, a Ti interlayer degrades the electrical behavior, but can improve the interface adhesion of Ag to PI substrates. For PEN substrates, Ti is found to lower the adhesion compared to Ag alone. This new knowledge on the material interactions can be used to improve future flexible electronic thin film systems. [ABSTRACT FROM AUTHOR]

The fracture toughness of Mo in Cu/Mo bilayers on polyimide was assessed with in situ X-ray diffraction during uniaxial tensile straining. The fracture resistance of Mo acting as an adhesion layer greatly depends on the thickness of the Cu layer exhibiting a toughening effect with increasing Cu layer thickness. In contrast, the presence of the Mo interlayer greatly decreases the apparent K Ic of the Cu layers. The quantification of K Ic for Mo with a Cu top layer provides further evidence that when brittle layers are used, a thicker ductile layer is advantageous to create fracture resistant stretchable systems. [Display omitted] [ABSTRACT FROM AUTHOR]

Cellulose fibers are a major industrial input, but due to their irregular shape and anisotropic material response, accurate material characterization is difficult. Single fiber tensile testing is the most popular way to estimate the material properties of individual fibers. However, such tests can only be performed along the axis of the fiber and are associated with problems of enforcing restraints. Alternative indirect approaches, such as micro-mechanical modeling, can help but yield results that are not fully decoupled from the model assumptions. Here, we compare these methods with nanoindentation as a method to extract elastic material constants of the individual fibers. We show that both the longitudinal and the transverse elastic modulus can be determined, additionally enabling the measurement of fiber properties in-situ inside a sheet of paper such that the entire industrial process history is captured. The obtained longitudinal modulus is comparable to traditional methods for larger indents but with a strongly increased scatter as the size of the indentation is decreased further. [ABSTRACT FROM AUTHOR]

The suitability of refractory high entropy metal sublattice nitride (HEAN) thin films to act as diffusion barrier between Cu and Si was evaluated. For this purpose, bi-layers comprising a 150 nm thick Cu layer and a 20 nm thick layer based on (MoNbTaW)N and alloyed with either Ti, V, Cr, Mn, Zr or Hf have been deposited onto Si substrates using high power impulse magnetron sputtering. Subsequently, the bi-layers were annealed up to 950 °C in vacuum and analyzed by X-ray diffraction, confocal laser scanning microscopy and resistance measurements to check for barrier failure. Depending on the elements present in the HEAN layer, two failure modes were identified: (1) interdiffusion of Cu and Si leading to the formation of Cu 3 Si starting at 850 °C and (2) dewetting of the Cu layer starting at 900 °C. A better barrier performance could be correlated to a lower formation enthalpy of the binary nitride of metals present in the HEAN layer leading to the conclusion that more stable metal‑nitrogen bonds in the HEAN phase are beneficial for its diffusion barrier performance. • Diffusion barrier performance of refractory high entropy alloy nitride films assessed • Synthesis by high power impulse magnetron sputtering at room temperature • No barrier failure observed up to 800 °C for all films • Cu 3 Si formation at 850 °C and dewetting of Cu at 950 °C identified as failure modes [ABSTRACT FROM AUTHOR]

Utilizing two-photon-lithography as a highly versatile additive manufacturing technique with micrometer precision, push-to-pull specimens incorporating a double edge notched tension geometry with different ligament dimensions were manufactured and compression tested via the grid function of a common nanoindentation device. Thus, the essential work of fracture characterization is determined in a high-throughput manner. 2100 specimens were tested, from which ∼ 2000 were used to assess the influence of printing parameters on resultant fracture properties. [Display omitted] • Two-photon-lithography for automated fracture specimen fabrication on the micrometer scale. • High throughput in situ SEM and ex situ testing of automatically manufactured specimens. • Essential work of fracture determination on additively manufactured micron specimens. • Influence of processing parameters on resulting fracture properties. Two-photon lithography (TPL) enables the design of novel micromechanical specimens, down to sub-micron resolution, thus extending the possibilities for device and material characterisation and pushing the boundaries of a broad range of miniaturized technologies such as optics, analytics, and medicine. Employing a push-to-pull geometry, incorporating double edge notched tension specimens loaded in mode I, the specimen manufacturing and testing can be automated to a large extent. This allows for the use of large parameter space characterisation methods as the essential work of fracture, with an experimentally simpler to realize compression testing setup. Within this work, a methodology is outlined for automated specimen direct laser writing with a TPL-device and subsequent testing via a nanoindenter. In total, 2100 specimens were manufactured, of which 1997 could be used for evaluation. Estimations for the essential work of fracture of the used photoresist is presented, with regards to influencing parameters such as testing displacement rate and laser writing power. A discussion of its statistical robustness and validity considerations is included. This will act as a basis framework for further statistical fracture evaluation schemes for other resin materials, as well as for probing thin film systems. [ABSTRACT FROM AUTHOR]

Cellulose foil is a biodegradable and carbon neutral material that is a poor substrate for most conductive silver inks. Herein, it is reported that a simple solution of silver acetate in 1-methylimidazole can be used to produce conductive patterns on a commercial packaging foil that is composed almost exclusively from cellulose. The reduction can be carried out thermally or by irradiation with UV light. In the latter case, the printed pattern may become conductive on both sides of the substrate and also exhibits conductivity across the cellulose foil, giving rise to fully printed vertical interconnect access. Control experiments confirm that the cellulose plays a crucial role in completing the reduction of the silver salt, obtaining conductive patterns. [ABSTRACT FROM AUTHOR]

Rapid progress in the reduction of substrate thickness for silicon-based microelectronics leads to a significant reduction of the device bending stiffness and the need to address its implication for the thermo-mechanical fatigue behavior of metallization layers. Results on 5 μm thick Cu films reveal a strong substrate thickness-dependent microstructural evolution. Substrates with hs = 323 and 220 µm showed that the Cu microstructure exhibits accelerated grain growth and surface roughening. Moreover, curvature-strain data indicates that Stoney's simplified curvature-stress relation is not valid for thin substrates with regard to the expected strains, but can be addressed using more sophisticated plate bending theories. [ABSTRACT FROM AUTHOR]

The effect of Cu alloying on the deformation behavior of Mo thin films is investigated as a feasible concept to overcome their poor ductility, which severely limits performance in flexible electronics. 50 nm thick Mo1-xCux films (with 0 ≤ x ≤ 0.51) were sputter-deposited on polyimide substrates and subjected to uniaxial tensile loading while measuring their electrical resistance in situ. A significant ductility enhancement is experimentally observed with increasing Cu content. This can be rationalized by considering the associated changes in bond character as the Cu additions weaken the covalent and hence shear resistant contribution to the overall bond character. [ABSTRACT FROM AUTHOR]

Fatigue is an important reliability issue for microelectronics. In this work, a technique for fast thermal cycling of thin films on substrates is introduced using an infrared laser beam. The advantages of this method are the significantly increased heating and cooling rates compared to conventional slow furnace processes, and the use of readily available small pieces of metallized wafers, which avoid complicated sample preparation. To demonstrate the applicability of the new experimental setup two copper metallization films, differing in their content of additives used for film deposition, on silicon substrates were investigated with respect to microstructural, topographical and electrical changes due to pulsed thermo-mechanical loading. The results, such as grain growth and roughness evolution, are compared to results from specimens which experienced slow infrared furnace cycling. Furthermore, changes in electrical sheet resistance are shown. When analyzing the outcomes from processes of different heating/cooling rates, it can be stated that accelerated laser heating leads to faster changes in these properties which enables fast screening of metallization materials under development. [ABSTRACT FROM AUTHOR]

In this study, two different electrodeposited 5 μm thick copper films were subjected to thermal cycling. The microstructural evolution of both films was studied with a site specific tracking technique. It was observed that the initially similar microstructures develop differently upon cycling with respect to grain size and texture. In detail, a Cu film which contains residual inorganic species from the organic additives used during Cu plating, in the ppm regime, showed a constrained surface roughness evolution and marginal grain growth coupled with a stable twin boundary network. Furthermore, voiding in the film interior was observed. In comparison, a high-purity Cu film exhibited strong surface roughening in conjunction with pronounced grain growth promoted by twin boundary migration. Moreover, the film showed a (100) texture intensity increase as a result of strain energy minimization upon cycling and no void formation. These observations underline the influence of film processing related impurities on the thermo-mechanical behaviour of Cu thin films. [ABSTRACT FROM AUTHOR]

We demonstrate a sustainable post-processing of carbon fiber reinforced epoxy polymer (CFRP) composites by air plasma etching that permits regular electroconductive surface patterning through direct Cu galvanic metallization, in contrast to the untreated composite. Our study reveals a significant property dependence of the composite with respect to the position to the fiber/matrix composite surface and treatment. The enhancement in electrical conductivity was not compromised by the lower structural integrity of the composite, as the embedded carbon fibers remained unaffected by the air plasma etching process. The metallized Cu domains on the composite exhibit good hardness and excellent solderability potential. Thus, the electroconductive surface patterning of the composite, preceding galvanic metallization, facilitates the selective deposition of Cu layer domains. This step by step process, relying on the creation of selective electroconductive areas on the composite by plasma etching, enables galvanic metallization. Consequently, it enhances the potential for multifunctional composite applications. The feasibility of galvanic metallization brings new perspectives in selective metallization of composites by allowing the tailoring of the metal layer thickness, microstructure and selection of the metal. [Display omitted] • Air plasma etching encompasses surface pattering of the carbon fiber reinforced polymers. • The electrical conductivity was promoted by surface exposed carbon fiber network enabling multifunctionality of the composite. • Metallized Cu layer domains on the composite exhibit good hardness and excellent solderability potential. [ABSTRACT FROM AUTHOR]

Abstract: Nanoparticles in the range of 20 to 100 nm in size can be deposited, isolated, and individually probed for their mechanical properties. With a hypersonic plasma particle deposition technique, this has been successfully accomplished for silicon and titanium. We have already shown that silicon nanoparticles are superhard in the 30 to 50 GPa range after work hardening (Gerberich, W.W., Mook, W.M., Perrey, C.R., Carter, C.B., Baskes, M.I., Mukherjee, R., Gidwani, A., Heberlein, J., McMurry, P.H., Girshick, S.L., 2003a. Superhard silicon nanospheres. J. Mech. Phys. Solids 51, 979). At the same time when small nanospheres are compressed, a fraction of the plastic strain is reversed after unloading. Initially, the amount of reverse dislocation motion was small but appeared to accelerate once a threshold strain was reached. The cumulative reverse plastic strain from repeated loading of the same nanosphere appeared to increase from less than 0.04 to approximately 0.4 as cumulative strain increased from 0.2 to 0.6. For large strains then, it appears that a greater amount of plastic strain is recovered after unloading. This can at least partially be understood in terms of the enormous back stress developed at the small scale when dislocations are only a few nm apart. As the ramifications to nanoscopic features on MEMS, micromachines and magnetic recording devices is considerable, it is desirable to understand if a length scale can be developed for such phenomena. In terms of classic dislocation theory an attempt is made. Problems and prospects are discussed with regards to predictive models for hardness and reverse plasticity. [Copyright &y& Elsevier]

• Detailed parameter variation during sputter deposition of MoNbTaWZr films. • Influence of duty cycle, Ar pressure and pulse frequency analyzed and discussed. • Parameters enabling high energetic growth conditions lead to amorphous microstructure. • Films deposited with low energetic growth conditions have a crystalline bcc structure. • Impact of microstructure and morphology on electrical resistivity discussed. Within this study a series of MoNbTaWZr thin films were synthesized using high power impulse magnetron sputtering (HiPIMS) with varying the deposition parameters: duty cycle from 0.5 to 100 % (i.e. DC magnetron sputtering (DCMS)), Ar pressure from 0.5 to 3 Pa and pulse frequency from 25 to 200 Hz. The structure of the deposited films was analyzed by X-ray diffraction and scanning and transmission electron microscopy. In addition, the electrical resistivity and the residual stress of the films was determined. The influence of the deposition parameter variation on structure and properties of the MoNbTaWZr films is discussed on the established framework of film growth conditions achievable with HiPIMS and DCMS and how they can be influenced by adapting the deposition parameters. The performed work is intended to contribute to a comprehensive understanding about synthesis-structure-property relations for refractory high entropy alloy thin films while using MoNbTaWZr films as a model system. [ABSTRACT FROM AUTHOR]

Although metallic thin films are widely used in microelectronics, their high-cycle fatigue properties are not well-understood. Cyclic testing was conducted on 150-nm thick freestanding gold thin films using nominal stress amplitudes between 50 and 150 MPa at 23–100 °C. As expected, lifetime decreases with increasing stress amplitude and temperature. The strain at failure hardly exceeds 1.5%, which is in agreement with previous studies on metallic thin films. The hysteresis stress-strain curves suggest that strain accumulates mostly due to cyclic creep. Based on this observation, we calculated the stress exponent n and activation energy Q – which are typical creep parameters – from the apparent steady-state strain rate observed during cyclic testing. Comparison to preexisting creep bulge tests show that the higher the temperature, the more pronounced the influence of creep on the fatigue behavior. Especially at 100 °C, creep mechanisms clearly dominate. At lower temperatures (23 °C) the data indicate that creep still plays a role, but intrinsic cycling effects become more pronounced. That leads us to postulate that the fatigue lifetime of gold thin films is closely connected to their creep properties. • Stress-controlled bulge fatigue tests on 150-nm thick, freestanding gold films at 23-100 °C. • Non-ambient S-N plots in typical microchip temperature operation range. • At elevated temperature (100 °C), creep clearly dominates the fatigue behavior. • Evaluation of stress exponent n and activation energy Q from cyclic creep. [ABSTRACT FROM AUTHOR]

This study presents detailed microstructural investigations on single and bilayer thin films of two medium entropy alloys (MEAs) synthesized using magnetron sputter deposition. Single layer thin films of CoCrFeNi and AlCoCrFe show single-phase face-centered cubic (fcc) and body-centered (bcc) structure, respectively. The bilayer thin film consisting of CoCrFeNi (fcc) and AlCoCrFe (bcc) has a sharp interface between them with an equiatomic composition. Nanodiffraction was used to characterize planar defects in the fcc films. This first study on bilayer film of two MEAs is transformative to other systems and will help fundamental studies on high entropy alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

High entropy alloy (HEA) thin films are potential candidates to act as diffusion barrier between Cu and Si in microelectronics. To evaluate the suitability of refractory HEAs, six different HEA thin films based on the MoNbTaW system and alloyed with Ti, V, Cr, Mn, Zr or Hf have been deposited by high power impulse magnetron sputtering with a thickness of 20 nm on Si substrates. The bi-layer architecture was completed by a 150 nm thick top-layer of Cu. The microstructure of the bi-layers before and after annealing in vacuum up to 800 °C was investigated by X-ray diffraction to observe possible phase changes or formations. In addition, resistance measurements and confocal laser scanning microscopy were employed to check for potential barrier failure. The lowest onset temperature for barrier failure of 600 °C was found for MoNbTaWZr, whereas the highest of 700 °C was observed for CrMoNbTaW. The obtained results for the failure temperature are discussed in terms of microstructure, strain and cohesive energy of the HEA films as well as the enthalpy of mixing between the elements in the HEA and Cu. A direct correlation between the mixing enthalpy of the fifth alloying element with Cu and the barrier failure temperature was observed. [Display omitted] • Suitability of refractory high entropy alloys as diffusion barriers. • Synthesis by high power impulse magnetron sputtering. • Best barrier performance for CrMoNbTaW with failure temperature at 750 °C • No correlation between film microstructure and diffusion barrier performance. • Mixing enthalpy of elements in HEA with Cu plays decisive role. [ABSTRACT FROM AUTHOR]

[Display omitted] • New family of Ag x Au 85-x Si 15 amorphous alloys for 20 < x < 60 is synthesized by co-sputtering. • Temperature dependence of electrical resistance indicated small amounts of nanocrystalline phase confirmed by HRTEM. • All alloys exhibit high hardness, 2% of elastic strain and 1–2% of tensile plasticity when tested on polymer substrates. • Complex chemistry-properties and structure-properties relationships of the alloy family are elucidated. To expand the basis for property-oriented material design, complex relationships between chemistry, atomistic structure, and properties of sputter-deposited Ag x Au 85-x Si 15 alloys are investigated using versatile experimental methods. According to differential scanning calorimetry and X-ray diffraction data, the alloys are amorphous within a wide compositional range of 20 ≤ x ≤ 60 at%. However, high-resolution transmission electron microscopy revealed noticeable amounts of crystallites in limiting compositions with x = 20 at% and x = 60 at%. Glass transition and crystallization temperatures grow with increasing Ag content, while room-temperature resistivity and temperature coefficient of resistance are shown to be highly sensitive to the amount of crystalline phase. Neither the existence of nanocrystallites nor the substitution of Ag by Au affected significantly the mechanical properties. All compositions exhibit similar nanoindentation hardness of about 4.3 GPa, Young's modulus of about 55 GPa, and macroscopic elastic limit of about 2%. The unique combination of high hardness, high elastic strain but low Young's modulus together with the expected chemical inertness inherited from noble metals makes this alloy family suitable for biomedical applications in form of coatings or in jewelry if an economic bulk production route will be developed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unique Al/Al 2 O 3 multilayers produced by combining atomic layer and physical vapor deposition without breaking vacuum. • Deformation behavior investigated in situ in biaxial tension with Synchrotron X-ray diffraction on polymer substrates. • Observed weakening of Al layers with increasing oxide thickness (0.14–9.4 nm) in contrast to uniaxial tensile results. • FE model of TEM cross-sections shows strain heterogeneities induced by wavy interfaces and a high young's modulus contrast. • Model describing the full biaxial yield surface of the multilayers appears to be valid up to 2.4 nm oxide thickness. A unique deposition approach combining atomic layer deposition (ALD) and magnetron sputtering was used to fabricate a series of thin film multilayer structures of Al (50 nm) and Al 2 O 3 (ALD, 2.4–9.4 nm) on flexible polymer substrates without breaking vacuum. The multilayers together with 50 nm and 150 nm Al reference films were analyzed by cross-sectional TEM analysis and experimentally strained in biaxial tension to investigate their deformation behavior. Al film stresses and peak widths, measured in situ with Synchrotron X-ray diffraction, are in good agreement with post-mortem surface SEM and through-thickness FIB analysis of the multilayers. It was revealed that brittle cracking of the multilayer can be avoided, and that the lateral and through-thickness crack resistance improve as a function of decreasing oxide layer thickness. An attempt to model the full biaxial yield surface of the multilayers, which remains experimentally challenging, appears to be valid up to 2.4 nm oxide thickness. Model predictions are further compared to compression data, obtained from the unloading segments of the tensile tests. Describing the mechanical behaviour under multiaxial stress conditions is of utmost importance for a diverse understanding of these multilayers across a variety of potential carrier systems and loading cases. [ABSTRACT FROM AUTHOR]

Abstract Cyclic bending tests of magnetron sputter-deposited Al/Mo bilayer thin films on flexible substrates were performed with a custom-built bending apparatus to evaluate the reliability of possible applications for metal wiring electrodes such as signal and data bus lines in flexible electronics. Intermittent measurements of mechanical damage and electrical resistance were performed to elucidate the damage evolution of Al/Mo bilayers with increasing cycle numbers. It was found that a 3:1 thickness ratio would have an extremely long lifetime when only compressive bending is applied for strains <1.3% (2 mm radius, 50 μm substrate thickness). Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Magnetron sputter deposited Mo thin films are frequently used as part of the metallization of thin film transistors. To ensure technological applications these Mo thin films are often combined with Al thin films, but are inherently brittle compared to the electrical charge carrying ductile Al thin films. To improve the fracture behavior of bilayered stacks containing Mo layers for future flexible devices like rollable or foldable displays, an optimum ductile/brittle layer thickness ratio is necessary. Within this work the electro-mechanical behavior of bilayered Al/Mo thin films grown by dc magnetron sputter deposition on polyimide substrates under tensile strain was investigated. Various Al/Mo layer thickness ratios (1:1, 3:1, 5:1 and 10:1), all with a base Mo film of 30 nm were tested. In situ tensile tests combining electrical 4-point probe resistance and optical measurements revealed an optimum thickness ratio between 5:1 and 10:1 for the crack onset strain. Post mortem analysis on the crack morphology revealed that higher thickness ratios better compensate cracks by leaving wider subsurface pathways for electron conduction of the layer stack than lower thickness ratios. Highlights • Different bilayer Al/Mo thickness ratios were strained with in situ methods. • Adding thicker aluminum layers suppresses the influence of the brittle layer. • Pathways for electronic conduction remain in aluminum layers after straining. • Electronic failure can be avoided by tuning the aluminum layer thickness. [ABSTRACT FROM AUTHOR]

Sputter deposited Mo-based thin films play a key role in the manufacturing of modern flat panel displays and microelectronic components. They are widely used as source/drain electrodes, as gate material or as metallization layer for signal and data bus lines. Within this work, the sputter performance of a Mo 0.70 Al 0.20 Ti 0.10 rotatable target was investigated to correlate processing conditions to thin film growth and chemistry. An industrial-scale in-line magnetron sputter system was used to deposit a series of thin films on silicon wafers at Ar pressures from 0.25 to 0.70 Pa. The center of the substrate carrier was kept at a constant offset from the target middle axis. Film thickness and chemical composition were evaluated for substrates located at different lateral positions. The morphologies and cross-sections of the films were examined by scanning electron microscopy and focused ion beam milling, revealing dense fibrous structures opposite the target and fine isolated columnar grain structures at extended positions from the center of the target. Energy dispersive X-ray spectroscopy showed a depletion of Al in favor of Mo enrichment opposite the target and a reverse trend at extended distances. The plasma used for sputtering was modelled after realistic target geometries using the S 3 M computer code and served as input for subsequent SRIM scatter simulations. It is demonstrated that the combination of experiments and simulations allows to distinguish a high- and low-flux regime, leading to different film structures and chemical compositions. [ABSTRACT FROM AUTHOR]

New advanced applications for flexible electronics and sensors require novel materials with multifunctional properties. Such engineered thin films find applications in structurally integrated batteries and sensors that can carry mechanical loads in addition to performing energy conversion functions. One example is poly(3,4-ethylenedioxythiophene) (PEDOT) thin films which are electrically conducting with good mechanical stability. Normally, organic thin film materials are loosely anchored to surfaces by weak physical interactions like Van der Waals forces or physisorption. In order to improve the generally poor adhesion of such polymer films, a novel molecular scale grafting technique using chemical vapor deposition (CVD) polymerization was utilized. Using a stressed overlayer, the adhesion energy of PEDOT films on Si with and without a graft was evaluated. It was found that the addition of a graft qualitatively and quantitatively improves adhesion of PEDOT to the substrate surface. Films without the graft delaminated spontaneously and areas of the film spalled off the Si substrate after the application of Molybdenum stressed overlayer. Similar PEDOT films with the graft only spontaneously delaminated after the same stressed overlayer was added. From the spontaneous buckling, the adhesion energy of the PEDOT-Si interface can be determined using the well-known Hutchinson and Suo model. Adhesion energies were compared to calculated bonding strengths to potentially identify the failing bonds. [ABSTRACT FROM AUTHOR]

In many applications metal foils are part of multifunctional composites exhibiting a wide range of (thermo-) mechanical fatigue loading. Data about low cycle fatigue of metallic foils subjected to tension-compression fatigue is sparse due to geometric limits. In this contribution, detailed information about design, tension-compression fatigue testing and data extraction of a layered sample are given. Fatigue failure of both copper and Pre-Preg are analysed using scanning electron microscopy and computed tomography. Numerical models are used to calculate the elastic and plastic strains for the copper foils within the composite sample, allowing a correlation to the observed fatigue life. • Fatigue behaviour is crucial to microelectronics, aviation and spacecraft. • A sample enabling R-1 fatigue testing of metallic foils was designed. • Using synchrotron radiation, neglectable residual deviatoric stresses were found. • SEM and CT analysis of fatigued samples were performed. • Finite elements method allowed fatigue life prediction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-simulation allowed calibration of a cyclic material model for copper within complex laminated structures without the need for costly measurement equipment. • Nanoindentation on cross-sections enabled the precise determination of the elastic modulus and hardness for the components of complex composites. • Results were interpreted using X-Ray Diffraction and Electron Backscatter Diffraction. • Tabor relation for estimating yield stress was shown not to be applicable for low displacements. Metallic foils are crucial to many applications ranging from printed circuit boards, aviation, aerospace, packaging, photovoltaics to batteries. In these applications they are often part of multifunctional composites, for which mechanical integrity is a prerequisite for the functionality. To ensure precise simulations and lifetime prediction, exact numerical material models are needed. In this work, material parameters of the Lemaitre-Chaboche model were fitted for electrodeposited copper foils. By using nanoindentation and microstructural characterisation, good agreement with literature was achieved. Additionally, it was found that the Tabor rule to estimate yield stress from indentation may not be applicable for metallic foils. [ABSTRACT FROM AUTHOR]

With the envisioned use as high-temperature materials, the thermal stability of three high entropy alloy thin films, based on the system MoNbTaW with additional Cr, Ti or V, was studied. All films were deposited by high power impulse magnetron sputtering and subsequently annealed in vacuum up to a temperature of 1200 °C and analyzed by X-ray diffraction. The obtained body-centered cubic structure in the as-deposited state remained stable up to the maximum annealing temperature. Measurements of the residual stress by wafer curvature and sin2Ψ method revealed a general reduction of the stress with annealing temperature due to defect annihilation. • Body centered cubic structure of high entropy alloy films stable up to 1200 °C • Stress evolution during annealing proceeds in two stages • Fifth alloying element (Ti, V and Cr) influences stress relaxation [ABSTRACT FROM AUTHOR]

The phase evolution of alloys is closely related to atomic diffusion. The influence of reactive diffusion on phase formation in high-entropy alloys (HEAs) is however still unclear. The present work systematically investigates the phase evolution of a multicomponent CoCrFeNi/Al diffusion couple through isochronous-reactive interdiffusion experiments. This provides a direct way to study the influence of enthalpy and entropy on the phase formation and element diffusion behavior. At temperatures below 1173 K, the enthalpy contribution dominates the total energy, leading to the formation of intermetallic compounds. When the temperature is in the range of 1173–1573 K, the entropy of mixing starts to play a more important role. This causes diffusion of Al towards the HEA without phase transformation, forming a more disordered state on the microscale. Even after the system reaches a disordered state, the enthalpy contribution cannot be totally ignored, which is reflected by the uphill diffusion of Ni towards Al. This demonstrates the combined effects of entropy and enthalpy on the phase formation in HEAs at elevated temperatures. Considering the homologous temperature for different equimolar alloys reveals that a multicomponent configuration does not stabilize the disordered state, while the mixing enthalpies between atomic pairs have a large impact on the transition temperature from ordered to disordered state. Finally, it is shown that surface modification of the HEA can be realized through a combination of film deposition and annealing processes. Compared to the HEA matrix, the formation of intermetallic compounds results in a hard surface layer. After the system becomes disordered, the higher hardness of the film side compared to the matrix can be attributed to the lattice distortion induced by Al. • Reactive interdiffusion of a CoCrFeNi high-entropy alloy and a sputter deposited Al layer are studied. • By changing annealing temperature, the transformation of the system from ordered to disordered state is captured. • Coupled influence of enthalpy and entropy has to be considered even in the disordered state. • Multicomponent configuration alone does not stabilize the disordered state. • Surface modification can be realized through a combination of film deposition and appropriate annealing. [ABSTRACT FROM AUTHOR]

Thin metal films on polymer substrates are key components for a variety of terrestrial and space applications such as flexible microelectronics or multilayer insulation systems. Although these applications seem to be quite different, there is a similarity in terms of thermal stress. In both cases the material undergoes a considerable amount of thermal cycling of ± hundreds of degree Celsius during its lifetime. Due to the composite nature of the material it is important to investigate interfacial properties as a function of this thermal cycling. This work investigates interface strength and electro-mechanical behaviour as a function of thermal cycling for vapour deposited Aluminum (Al) films (150 nm) on 25 μm Polyimide (PI). The material is subjected to various numbers of thermal cycles of ± 150 °C in a gaseous N 2 atmosphere. Tensile induced delamination with in-situ resistance measurements is used to measure adhesion values as well as the electro-mechanical failure behaviour. It was found that although the adhesion of Al-PI is unaffected by the applied thermal load, a strong decrease in the electro-mechanical properties of the system was observed. Since good electro-mechanical properties are crucial for flexible electronic applications the resistance against thermal cycling needs to be taken into account when assessing the suitability of a material for flexible applications. [ABSTRACT FROM AUTHOR]

The effect of residual inorganic elements on the local plastic deformation behaviour of two different copper films was investigated. It was found that a film containing inorganic elements in the ppm range, has a distinctively higher hardness at twin boundaries and high angle grain boundaries compared to the grain interior. An almost pure copper film shows no distinct difference regarding the plastic deformation compared to the same microstructural features. The results suggest that such residual elements form hard boundaries, leading to higher hardness on a local microstructural level. Moreover, the influence of the local topography was demonstrated. The use of atomic force microscopy before and after indentation illustrated that significant errors in the determination of hardness occurs when the local surface topography matches the dimensions of the indenter tip. This was further confirmed by the quantitative comparison of the elastic properties of the loading and unloading segments of the corresponding load-depth curves using Hertzian contact mechanics and the Oliver-Pharr method. It is demonstrated that the measured hardness values can be directly correlated to local microstructural and topographical features. [ABSTRACT FROM AUTHOR]

During service in power electronic applications, microelectronic chips encounter rapid changes in temperature, which are manifested by sub-millisecond-short heat pulses with amplitudes of a few hundred kelvin. When being subjected to such conditions repeatedly, in the long term, material fatigue of integrated metallization layers is caused, representing an important reliability issue. Within this work, dedicated test chips with integrated heating (poly-heaters) have been utilized to emulate aforementioned application-related loading conditions. Hence, the thermo-mechanical fatigue behavior of a 20-μm-thick copper metallization on silicon and its dependency on the two variation parameters starting base temperature and heating rate is studied. Monitoring of the electrical resistance and scanning electron microscopy image acquisitions have been performed in situ during the course of the stress tests comprising 12,000 heat pulses. For obtaining a more comprehensive picture of the investigated degradation behavior, focused ion beam inspections and roughness characterizations have been carried out at the end of the tests. For 0.2-ms-short heat pulses, distinct intergranular cracking is observed at base temperatures ≥95 °C. For longer heat pulses, a change in the dominant degradation mechanism from cracking to more and more pronounced dislocation-driven plastic deformation manifested in roughening is found. [Display omitted] • Thermo-mechanical fatigue of copper line structures on silicon is investigated. • Application-relevant heating conditions are replicated by special test chips. • Comprehensive characterization comprises in-situ and ex-situ measurements. • The test parameters base temperature and heating time affect the degradation mode. • Low base temperatures have less cracking; long heating times have more roughening. [ABSTRACT FROM AUTHOR]

Cyclic delamination is the root cause for many different failure modes in semiconductor devices that are related to a loss of mechanical, electrical, or thermal contact. Some of them, such as failure due to local melting, can be considered as catastrophic. An accurate root cause analysis or precise localization of the failure is very challenging or even not possible at all. For this reason, the development of experimental methods capable of assessing early-stage delamination is desired. This work introduces a novel delamination-sensing structure integrated onto an actively heated microelectronic test chip. Actuation of the chip causes thermo-mechanical stress that initiates and drives cyclic delamination of a metallization from a functional base layer. The delamination-sensing structure allows continuous monitoring of the delamination progress by in-situ electrical resistance measurements. Its distinct geometric layout features have the effect that, when passed by a gradually advancing delamination crack front, result in characteristic responses in the monitored signal. This allows a straightforward interpretation of the measurement data without having to rely on modeling or separate calibration. The proper function of the delamination sensor is validated by a comparison of independently determined delamination distances from electrical measurements and cross-sectional inspections, respectively. Its distinguishing property of allowing a simple and time-efficient quantification of delamination is demonstrated by a study comprising 80 delamination experiments. This study investigates the effect of different heating amplitudes Δ T on the delamination rate. [Display omitted] • A structure capable of electrically assessing delamination growth is introduced. • Integration onto a microelectronic test chip for fatigue testing is demonstrated. • The sensor layout makes monitored data easily and quantitatively interpretable. • The proper function of the delamination sensor is validated. • Studies comprising a large number (>80) of delamination experiments are possible. [ABSTRACT FROM AUTHOR]

In flexible and/or wearable electronics the thin films deposited on compliant substrates are not only subjected to straining and bending but also to tribological loading conditions. A frequently used method to assess tribological properties of materials systems is the ball-on-disc test. In the current work, Mo films were deposited by high power impulse magnetron sputtering on polyimide substrates to serve as a model system. To establish different tribological contact conditions, a series of different counterpart materials was chosen for the performed ball-on-disc tests. A detailed analysis by 3D confocal laser scanning microscopy and scanning electron microscopy revealed details about the wear mechanisms active during sliding where mainly abrasion of the softer one of the material pair was noticed. The obtained results for friction and wear together with the performed simulations of the induced stresses due to the loading conditions show that ball-on-disc tests can contribute to the understanding of the tribological response of metallic films on compliant substrates which in turn may help to improve the lifetime of components in flexible and/or wearable electronic applications. [ABSTRACT FROM AUTHOR]

To explore structure and properties of refractory high entropy alloy (HEA) thin films, targets with five different equimolar compositions based on the MoNbTaW system and alloyed with Ti, V, Cr, Mn or Hf were used for the synthesis of films by high power impulse magnetron sputtering. All HEA films showed a body-centered cubic structure and a dense, columnar morphology as revealed by X-ray diffraction and transmission electron microscopy, respectively. Alloying of the additional element affects the film stress and the mechanical properties. The overall compressive stress state present in the films was distributed inhomogeneously with an expected gradient along the film growth direction. Hardness and Young's modulus values ranging from 14 to 17 GPa and 230 to 295 GPa, respectively, were measured by nanoindentation. • Synthesis of MoNbTaW-based films using high power impulse magnetron sputtering • All films show a bcc microstructure and a dense columnar morphology. • Mechanical properties influenced by fifth alloying element (Ti, V, Cr, Mn or Hf) • Novel method applied to determine Young's modulus of thin films [ABSTRACT FROM AUTHOR]

Thin metal films on polymer substrates are of interest for flexible electronic applications and often utilize a thin interlayer to improve adhesion of metal films on flexible substrates. This work investigates the effect of a 10 nm Cr interlayer on the electro-mechanical properties of 50 nm Au films on polyimide substrates. Ex situ and in situ fragmentation experiments reveal the Cr interlayer causes brittle electro-mechanical behaviour, and thin Au films without an interlayer can support strains up to 15% without significantly degrading electrical conductivity. [ABSTRACT FROM AUTHOR]

A fundamental knowledge and understanding of the adhesion behaviour of metal–polymer systems is important as interface failure leads to a complete breakdown of flexible devices. A combination ofin situatomic force microscopy for studying topological changes andin situsynchrotron based stress measurements both during film tensile testing were used to estimate the adhesion energy of a thin bilayer film. The film systems consisted of 50–200 nm Cu with a 10 nm Cr adhesion layer on 50 μm thick polyimide. If the Cu film thickness is decreased to 50 nm the Cr interlayer starts dominating the system behaviour. An apparent transition from plastic to predominantly brittle deformation behaviour of the Cu can be observed. Then, compressive stresses in the transverse direction are high enough to cause delamination and buckling of the Cr interlayer from the substrate. This opens a new route to induce buckling of a brittle interlayer between a ductile film and a compliant substrate which is used to determine the interfacial adhesion energy. [ABSTRACT FROM PUBLISHER]

Thin metal films deposited on polymer substrates are used in flexible electronic devices such as flexible displays or printed memories. They are often fabricated as complicated multilayer structures. Understanding the mechanical behavior of the interface between the metal film and the substrate as well as the process of crack formation under global tension is important for producing reliable devices. In the present work, the deformation behavior of copper films (50–200 nm thick), bonded to polyimide directly or via a 10 nm chromium interlayer, is investigated by experimental analysis and computational simulations. The influence of the various copper film thicknesses and the usage of a brittle interlayer on the crack density as well as on the stress magnitude in the copper after saturation of the cracking process are studied with in situ tensile tests in a synchrotron and under an atomic force microscope. From the computational point of view, the evolution of the crack pattern is modeled as a stochastic process via finite element based cohesive zone simulations. Both, experiments and simulations show that the chromium interlayer dominates the deformation behavior. The interlayer forms cracks that induce a stress concentration in the overlying copper film. This behavior is more pronounced in the 50 nm than in the 200 nm copper films. [ABSTRACT FROM AUTHOR]

[Display omitted] Measurements of electrical resistance have been used extensively as a failure criterion in cyclically loaded conductive films. However, not much research has been performed on extracting additional information contained within such resistance data sets. This study shows that an increase in peak width evidences a transition from cracks bridging to through-thickness crack formation. A Au/Cr bilayer system on a polyimide substrate is used for data generation but the method is applicable to any material system where both necking and through-thickness cracks are formed and no immediate formation of electrically insulating oxide layers occurs upon damage initiation. The method is easy to implement, and has the ability to replace time-intensive and destructive inspection methods. [ABSTRACT FROM AUTHOR]

• Comparison of Al/Mo and Al/Mo-Ta bilayers. • Monotonic uniaxial tensile and cyclic bending tests of Al/Mo-Ta bilayers. • Al/Mo-Ta bilayers have higher fracture strain under uniaxial tensile loads. • Al/Mo-Ta bilayers experience no damage at 50 000 cycles under 1.3% bending strain. Sputter deposited Mo/Al/Mo multilayers are widely used material systems for electrodes in display technologies. In this study, the electro-mechanical behavior of simplified bilayer versions was improved for flexible applications through substitution of the Mo by Mo-Ta alloy layers. Sputter deposited Al/Mo-Ta bilayers were tested under uniaxial tensile and cyclic bending loads. Compared to similar Al/Mo bilayers from previous studies, the Mo-Ta interlayer with 50 at.% Ta improved the crack onset strain under tensile load by more than 1% strain. Furthermore, after 50 000 cycles under 1.3% bending strain, the Al/Mo-Ta bilayers were nearly undamaged and experienced a relatively small electrical resistance increase of 25%, compared to Al/Mo bilayers, which were 40 to 100 times higher. This work shows that the substitution of the brittle Mo interlayer with a more ductile Mo-Ta interlayer can improve the performance and lifetime of the electrodes and is more suitable for flexible displays than the currently used materials. [ABSTRACT FROM AUTHOR]

The influence of nitrogen incorporation on the chemical composition, structure, mechanical, and electrical properties of refractory (MoNbTaVW) 1−x N x high entropy alloy thin films is investigated. The films were synthesized by two different physical vapor deposition methods, cathodic arc deposition and direct current magnetron sputtering, onto silicon and polyimide substrates. Regardless of the deposition method, a change from body centered cubic to face centered cubic structure was observed with increasing nitrogen content in the film. This structural change was accompanied by an increase in hardness as measured by nanoindentation but also by a material embrittlement as determined from tensile straining tests. • Synthesis of (MoNbTaVW) 1-x N x films by cathodic arc and sputtering. • Phase transition from body to face centered cubic with increasing N content. • Phase formation is entirely controlled by the metal to N ratio in the film. • Structural change accompanied by increase in hardness and embrittlement. [ABSTRACT FROM AUTHOR]

• Sputter deposition characteristics of an industrial-size rotatable Ni80W20 target. • Lateral differences of film properties over substrate carrier. • Microstructure and morphology of films change with lateral position on carrier. • Rough target surface affects emission angles of sputtered Ni and W. • Emission angles of Ni and W dominate the lateral differences of film properties. A series of NiW thin films was magnetron sputter deposited from a rotatable Ni80W20 target at Ar pressures ranging from 0.25 to 1.00 Pa on a matrix of (1 0 0) Si substrates. All films were synthesized in static deposition mode. The chosen setup allowed to study the influence of lateral substrate position and Ar pressure on film microstructure and elemental composition. All films deposited opposite the target were dense and Ni-rich, whereas films grown at extended positions from the target center had an open voided morphology and were W-rich. The differences in elemental composition with respect to the lateral position on the substrate carrier are attributed to the respective emission profiles of Ni and W and to scatter events of sputtered particles with Ar gas. To assess the influence of the target surface on final film properties, a planar Ni81W19 target was sputter eroded and investigated. The observed roughening of the target surface stems from the interplay between the high and low sputter yield of Ni and W, influencing the emission angles of both elements. Additional SRIM simulations of a thin Ni top-layer atop a W under-layer provided evidence for the existence of sputter yield amplification active within the studied system. [ABSTRACT FROM AUTHOR]

Magnetron sputter deposited Mo-based thin films are widely used as diffusion barriers and metallization layers for signal and data bus lines of flat panel displays or back electrodes of thin film solar cells. These films are deposited at large-scale from rectangular planar sputter targets, with the necessity of constant film thickness and properties over target usage. Within this work, a new 600 × 125 mm2 planar Mo-target was sputtered at a constant power of 3.5 kW until the erosion track reached 80% of the maximum useable target thickness. Every other 50 kWh, films were deposited onto a 9 × 5 matrix of (100) Si in different deposition modes (i.e. static and oscillation of the substrate carrier). By investigating the individual sample sets, the sputter behavior at different stages of target usage could be assessed. The sputter behavior changes with the progressing evolution of an erosion groove and affects thickness, stress and electrical resistivity of the films. In the beginning and end of target usage, films with low electrical resistivity and high tensile stresses are grown, whereas a medium target erosion leads to films with increased resistivity and lower tensile stresses. This time variance is attributed to two competing effects changing with proceeding target erosion, which affect the growth conditions of the films: (i) the increase of the reflection angle of Ar neutrals due to the evolution of an erosion groove, lowering the energy input into the growing film, and (ii) a rising number of Ar+ ions due to an increase of target current, directly affecting the overall number of reflected Ar neutrals, increasing the energy input into the growing film. • A rectangular planar molybdenum target was eroded until the end of its lifetime. • Films were deposited at different stages of target erosion. • Target erosion affects film microstructure and properties. • Film microstructure is influenced by substrate position and carrier movement. • Observed differences are explained by target cross-corner effect. [ABSTRACT FROM AUTHOR]

The mechanical and electrical limits of magnetron sputter deposited Al/Mo bilayer thin film systems were tested for their potential use in flexible displays and sensors. Al/Mo bilayers with different Al layer thicknesses (30, 75 and 150 nm) and a constant Mo layer thickness of 30 nm were subjected to 20,000 cycles of combined tensile and compressive bending at different bending strains (0.6, 1.3 and 3.1%). Intermittent optical and electrical measurements allowed the quantification of their reliability as electrode materials. The reliability strongly depends on the used bending strains and the Al layer thickness. Crack nucleation and growth lead to an increase in electrical resistance beyond 50% within the first 100 bending cycles at bending strains larger than 1.3%. Here, most of the studied bilayers fail electrically due to fracture. Increasing the bilayers' Al layer thickness does not improve fracture behavior, which is dominated by the Mo layer, but lowers the measured electrical resistance values for all experiments. Al/Mo bilayers with layer thicknesses of 75/30 nm revealed the least amount of surface damage for all tested bending strains, however do not have the best electrical conductivity. • Cyclic bending of Al/Mo multilayers at different bending strains and Al thicknesses • Evolution of surface damage and electrical resistance can help predict lifetimes • Further insights on the relation between bilayer damage and electrical conductivity [ABSTRACT FROM AUTHOR]

Metallic glasses typically fail in a brittle manner through shear band propagation but can exhibit significant ductility when the sample size is reduced below a few hundreds of nanometers. To date the size effect was mainly demonstrated for free-standing samples and the role of extrinsic setup parameters on the observed behavior is still under debate. Therefore, in the present work we investigated the mechanical properties of polymer-supported sputtered amorphous Pd82Si18 thin films with various thicknesses. We show that the films exhibit brittle fracture for thicknesses far below 100 nm. A pronounced size effect resulting in extended crack-free deformation up to 6% strain was observed only in films as thin as 7 nm – a thickness which is lower than the typical shear band thickness. This size effect results in exceptional cyclic reliability of ultrathin metallic glass films which can sustain cyclic strains of 3% up to at least 30,000 cycles without any indication of fatigue damage or electrical conductivity degradation. Since the enhancement of mechanical properties is observed at ambient conditions using inexpensive substrates and an industrially scalable sputter deposition technique, a new research avenue for utilization of ultrathin metallic glasses in microelectronics, flexible electronics or nanoelectromechanical devices is opened up. [ABSTRACT FROM AUTHOR]