Mechanical failure of brittle thin films on polymers during bending by two-point rotation

\u3cp\u3eThe mechanical failure and internal strain when bending a brittle thin film on a flexible substrate was analyzed using an electro-mechanical method and optical microscopy. Bending was realized by clamping the ends of the sample and rotating the clamps in a two-point rotation (2PR) device, as elaborated in the paper. This test allows to impose both tensile and compressive strains on the brittle layer, in a single test, without remounting the sample. With the electro-mechanical method the real-time electrical resistance is measured in a very thin, conductive coating deposited on the brittle layer in which cracks develop across the width of the film. Simultaneously, the propagation of individual cracks is observed by optical microscopy. Real-time combination of both analyses in principle enables linking the fracture behavior (size, number and pattern of cracks) with the electrical resistance at a well-defined imposed strain. With this 2PR method, the subcritical mechanical failure of a 150 nm thick SiN\u3csub\u3ex\u3c/sub\u3e barrier layer was analyzed, as deposited on a 125 μm thick polyethylene naphtalate sheet (system 1). Its characteristic static failure time, as obtained from a Weibull analysis, was 0.10 s at a strain of 0.84% and 2.2 s at 0.77%. From the crack opening on reloading tests, an average internal compressive strain of 0.38% was deduced. In order to validate the results of the 2PR device, system 1 was also tested using two-plate bending (2PB), as described earlier. Results on characteristic failure strains as obtained with both methods for bending match very well and have similar accuracy. However, the option to assess tensile internal strains, together with the aforementioned advantages, renders the 2PR test the method of choice for testing brittle layers on polymer substrates. Comparison of system 1 with another barrier system (2), which only differs in processing conditions, indicates a considerable difference in time dependence of the characteristic failure strain, indicating the sensitivity of the resulting material properties on processing conditions.\u3c/p\u3

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

Mechanical failure resulting from subcritical crack growth in the SiN x inorganic barrier layer applied on a flexible multilayer structure was studied by an electro-mechanical two-point bending method. A 10¿nm conducting tin-doped indium oxide layer was sputtered as an electrical probe to monitor the subcritical crack growth in the 150¿nm dielectric SiN x layer carried by a polyethylene naphthalate substrate. In the electro-mechanical two-point bending test, dynamic and static loads were applied to investigate the crack propagation in the barrier layer. As consequence of using two loading modes, the characteristic failure strain and failure time could be determined. The failure probability distribution of strain and lifetime under each loading condition was described by Weibull statistics. In this study, results from the tests in dynamic and static loading modes were linked by a power law description to determine the critical failure over a range of conditions. The fatigue parameter n from the power law reduces greatly from 70 to 31 upon correcting for internal strain. The testing method and analysis tool as described in the paper can be used to understand the limit of thin-film barriers in terms of their mechanical properties

High-temperature thin-film barriers for foldable AMOLED displays

\u3cp\u3eWe present a thin-film dual-layer bottom barrier on polyimide that is compatible with 350°C backplane processing for organic light-emitting diode displays and that can facilitate foldable active-matrix organic light-emitting diode devices with a bending radius of <2 mm. We demonstrate organic light-emitting diodes that survive bending over 0.5 mm radius for 10.000× based on the high-temperature bottom barrier. Furthermore, we show compatibility of the bottom barrier with the backplane process by fabricating active-matrix organic light-emitting diode displays on GEN1-sized substrates.\u3c/p\u3