Development and evaluation of bend-testing techniques for flexible-display applications

Grego, Sonia; Lewis, John S.; Vick, Erik; Temple, Dorota

doi:10.1889/1.2001215

Cited by 65 publications

(36 citation statements)

References 10 publications

(10 reference statements)

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“…In such a case, bending radius can be approximately given by half of the distance between two ends (Figure 6a). [62] This setup was first used to evaluate bending testing of flexible display through synchronous data acquisition of electrical resistance at different bending radii, and is currently being extended to bending testing of flexible energy storage devices. [63,64] However, the bending shape is not exactly a perfect cylinder, and the bending deformation and stress are non-uniform at different positions of curved surface.…”

Section: Collapsing Radius Geometrymentioning

confidence: 99%

Mechanical Analyses and Structural Design Requirements for Flexible Energy Storage Devices

Mao

Meng

Ahmad

et al. 2017

Advanced Energy Materials

192

146

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degree of the entire electronic systems. In the integrated flexible electronic system, energy storage devices [14,[16][17][18][19][20] play important roles in connecting the preceding energy harvesting devices and the following energy utilization devices (Figure 1). Rechargeable secondary batteries and supercapacitors (SCs) are two typical energy storage devices. [21] Several excellent review papers [21][22][23][24][25][26] reported significant progresses achieved in flexible lithium-ion batteries (LIBs) and SCs by taking advantage of novel electrode materials, current collectors, and solid-state electrolytes. The application areas and lifetime of flexible power sources strongly depend on their mechanical deformation tolerance and the electrical property retention under deformation. Qualified flexible power sources should be able to endure high strain induced by external mechanical deformation, such as bending, compressing, stretching, folding, and twisting, while maintaining their electrochemical performance stability and structural integrity. Therefore, the mechanical reliability assessment and electrical property analysis of flexible devices need to be given much attention for future application.Tolerance in bending into a certain curvature is the major mechanical deformation characteristic of flexible energy storage devices. Thus far, several bending characterization parameters and various mechanical methods have been proposed to evaluate the quality and failure modes of the said devices by investigating their bending deformation status and received strain. Some of these mechanical metrologies were derived from the early research on flexible semiconductor devices of micro-electromechanical system (MEMS) [27,28] and TFTs. [29] However, comparing those numerous measurement data with one another is difficult because of the various theories and methods adopted by different research groups and the lack of unified assessment criteria. [26] The flexibility of flexible devices is generally realized not only by use of intuitive soft electrode materials but also by optimizing their mechanical structural design. [25] Detailed analysis on bending mechanics combining experimental and theoretical results provide not only reliable test methods to describe the bending state but also guidance for configuration design of devices against mechanical failure.The current review emphasizes on three main points: (1) key parameters that characterize the bending level of flexible energy storage devices, such as bending radius, bending Flexible energy storage devices with excellent mechanical deformation performance are highly required to improve the integration degree of flexible electronics. Unlike those of traditional power sources, the mechanical reliability of flexible energy storage devices, including electrical performance retention and deformation endurance, has received much attention. To provide the guideline for the construction design of devices, the strain distribution and failure modes in the entire architecture should b...

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Section: Collapsing Radius Geometrymentioning

confidence: 99%

Mechanical Analyses and Structural Design Requirements for Flexible Energy Storage Devices

Mao

Meng

Ahmad

et al. 2017

Advanced Energy Materials

192

146

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“…Tensile strain in the thin film may be applied either by uniaxial tension, 9 4-point bending, 12 2-point bending, 2 or free bending. 13 As a function of tensile strain, a succession of different fracture regimes characterizes the properties of the thin films: crack initiation and subcritical crack propagation, critical non-interacting cracks, critical interacting cracks, saturation, and finally transverse buckling. The results of the optical method have been used for sophisticated interpretation of these regimes in terms of the mechanical and statistical properties of the assemblies.…”

Section: Introductionmentioning

confidence: 99%

Direct measurement of intrinsic critical strain and internal strain in barrier films

Vellinga

Hosson

Bouten

2011

Journal of Applied Physics

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Resistance measurements during uniaxial tensile deformation of very thin (10 nm) conducting oxide films deposited on 150 nm SiN films on polyethylene naphthalate are discussed. It is first shown that certain characteristics of resistance versus strain curves are representative for the fracture behavior of the SiN film and not for that of the thin conducting oxide film. Subsequently, it is shown that the hysteresis in curves of resistance as a function of strain offers a way to directly measure the intrinsic critical strain of the SiN film without the need to determine internal strains from independent (curvature) measurements that rely on knowledge of moduli and geometry. The method should be applicable, in general, to measure intrinsic critical strain and residual strains of thin brittle films on polymers. Advantages and limitations of the method are discussed.

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“…When a sheet is bent, the outer surface experiences tensile stress and the inner surface compressive stress, while a plane inside the sheet (called the neutral plane) experiences no stress at all. When films are very thin relative to the substrate the simple approximation below describes the relationship between film strain

ε

and radius of curvature r , where d is the thickness of the substrate [31],

r = \frac{d}{2 ε} .

…”

Section: Resultsmentioning

confidence: 99%

Fabrication of Circuits on Flexible Substrates Using Conductive SU-8 for Sensing Applications

Gerardo

Cretu

Rohling

2017

Sensors

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This article describes a new low-cost rapid microfabrication technology for high-density interconnects and passive devices on flexible substrates for sensing applications. Silver nanoparticles with an average size of 80 nm were used to create a conductive SU-8 mixture with a concentration of wt 25%. The patterned structures after hard baking have a sheet resistance of 11.17 Ω/☐. This conductive SU-8 was used to pattern planar inductors, capacitors and interconnection lines on flexible Kapton film. The conductive SU-8 structures were used as a seed layer for a subsequent electroplating process to increase the conductivity of the devices. Examples of inductors, resistor-capacitor (RC) and inductor-capacitor (LC) circuits, interconnection lines and a near-field communication (NFC) antenna are presented as a demonstration. As an example of high-resolution miniaturization, we fabricated microinductors having line widths of 5 μm. Mechanical bending tests were successful down to a 5 mm radius. To the best of the authors’ knowledge, this is the first report of conductive SU-8 used to fabricate such planar devices and the first on flexible substrates. This is a proof of concept that this fabrication approach can be used as an alternative for microfabrication of planar passive devices on flexible substrates.

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Development and evaluation of bend-testing techniques for flexible-display applications

Cited by 65 publications

References 10 publications

Mechanical Analyses and Structural Design Requirements for Flexible Energy Storage Devices

Mechanical Analyses and Structural Design Requirements for Flexible Energy Storage Devices

Direct measurement of intrinsic critical strain and internal strain in barrier films

Fabrication of Circuits on Flexible Substrates Using Conductive SU-8 for Sensing Applications

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