Folding stabilities of encapsulation layers at positions off the mechanical neutral plane

Lee, Haksoo; Han, Jin-Taek; Ham, Soung Bo; Jang, Choelmin; Huh, Myung Soo; Cho, Sung Min

doi:10.7567/apex.11.086502

Cited by 6 publications

(9 citation statements)

References 28 publications

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“…We investigated the device degradation with the mechanical strain in the films. [50][51][52][53][54][55] Young's modulus can be used to express the strain applying to OLEDs as a function of film radius and thickness given by In our OLED device on PI, the gas barrier consisting of five layers of SiO 2 /SiN x SiO 2 /SiN x /SiO 2 was deposited on the PI substrate to prevent the oxygen and moisture penetration through the PI substrate. As the TFE, two stacks of parylene and SiN x (total four layers) was used.…”

Section: Resultsmentioning

confidence: 99%

“…We investigated the device degradation with the mechanical strain in the films. [ 50–55 ] Young's modulus can be used to express the strain applying to OLEDs as a function of film radius and thickness given by

σ = E \times ε_{top} with

ε_{top} = (\frac{d_{normalf} + d_{normals}}{2 R}) \frac{(1 + 2 η + x η^{2})}{(1 + η) (1 + x η)} ≅ (\frac{d_{normalf} + d_{normals}}{2 R})

where E indicates Young's modulus, σ and

ε_{top}

are stress and strain, d f and d s are the thicknesses of film and substrate, η = d f / d s and x = E f / E s, R is the radius of curvature, respectively. In our OLED device on PI, the gas barrier consisting of five layers of SiO 2 /SiN x SiO 2 /SiN x /SiO 2 was deposited on the PI substrate to prevent the oxygen and moisture penetration through the PI substrate.…”

Section: Resultsmentioning

confidence: 99%

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Highly Robust, Flexible Top‐Emission Organic Light‐Emitting Diode Exhibiting Stable Performance under Infolding of Curvature Radius of 0.32 mm

Jeong

Kim

et al. 2021

Adv Eng Mater

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Flexible top‐emission organic light‐emitting diodes (TOLEDs) with a thin‐film encapsulation (TFE) are of increasing attention to improve the flexibility of foldable smartphone organic light‐emitting diode (OLED) displays. There are inevitable issues to achieve foldable display with smaller folding radius for the future portable display. Herein, the device flexibility is investigated with infolding and outfolding tests with the curvature radius from 2.5 to 0.32 mm. Parylene (1 μm)/silicon nitride (SiNx) (X nm)/parylene (1 μm)/SiNx (X nm) (X = 100, 70, 50, and 30 nm) of TFEs are applied on the TOLEDs. It is found that stable device performances can be achieved at the curvature radius of 0.32 mm after 100 000 cycles infolding testing when the SiNx thickness is 30 nm. The device has significant degradation upon outfolding of 5000 cycles at the same radius of 0.32 mm. Note that, the water vapor transmission rate (WVTR) of the TFT with 30 nm SiNx is higher than the TFE with thicker SiNx (e.g., 50 nm). The flexibility and WVTR can be much improved using four‐stacked TFE with 30 nm SiNx for foldable active‐matrix OLED displays.

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Section: Resultsmentioning

confidence: 99%

σ = E \times ε_{top} with

ε_{top} = (\frac{d_{normalf} + d_{normals}}{2 R}) \frac{(1 + 2 η + x η^{2})}{(1 + η) (1 + x η)} ≅ (\frac{d_{normalf} + d_{normals}}{2 R})

where E indicates Young's modulus, σ and

ε_{top}

Section: Resultsmentioning

confidence: 99%

Highly Robust, Flexible Top‐Emission Organic Light‐Emitting Diode Exhibiting Stable Performance under Infolding of Curvature Radius of 0.32 mm

Jeong

Kim

et al. 2021

Adv Eng Mater

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“…Another important asset related to the copper's thinness is its impact on the mechanical reliability of the stack, as maximum strain under bending is directly correlated to the thickness of the stiffest material (in our case copper). [15,23,24] To assess the mechanical and electrical reliability of the stack, we performed bending tests of copper tracks embedded in parylene using a dedicated setup depicted in Figure 2A. [15] We furthermore limited the strain induced in copper by using the ideal configuration where mechanical neutral plane lies in the metallic layer, therefore encapsulation and substrate have the same thickness.…”

mentioning

confidence: 99%

“…[15] We furthermore limited the strain induced in copper by using the ideal configuration where mechanical neutral plane lies in the metallic layer, therefore encapsulation and substrate have the same thickness. [24] First, a single folding test was performed on a 110-µm-wide track ( Figure 2B). The track shows electrical stability under progressive bending, down to complete folding corresponding to 0.1 mm of radius (right inset picture).…”

mentioning

confidence: 99%

“…To assess the mechanical and electrical reliability of the stack, we performed bending tests of copper tracks embedded in parylene using a dedicated setup depicted in Figure A . We furthermore limited the strain induced in copper by using the ideal configuration where mechanical neutral plane lies in the metallic layer, therefore encapsulation and substrate have the same thickness . First, a single folding test was performed on a 110‐µm‐wide track (Figure B).…”

mentioning

confidence: 99%

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Copper‐Leaf‐Based Process for Imperceptible Computational Electronics

Mulatier

Coulon²,

Delattre

et al. 2019

Adv Elect Materials

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Imperceptible electronics have a key role in tomorrow's wearable technologies. Individual elements such as ultra‐thin sensors, batteries, solar cells, and actuators are well described in literature, but there is a lack of methods to build the computing circuit itself. A new process is presented for the fabrication of flexible and imperceptible circuits that reach standards of microelectronics associated with significant integration density of components and interconnections, as well as multilayering. The stack uses a commercialized decorative copper leaf with a thickness of 450 nm as the conductive layer and a parylene substrate of a few micrometers. The copper leaf shows both high compliance and conductivity of bulk copper (5.96 × 107 S m−1), with electrical resistance stable over 5000 cycles of complete folding. The process requires stencil‐free laser patterning that reaches fine‐pitch integration, conventional soldering methods, and a three‐step via fabrication and assembly process for multilayered circuits. The functionality of an ultra‐thin, multilayered, lightweight, electrocardiogram‐monitoring device is demonstrated. This allows for direct transfer of microelectronic designs for rapid prototyping from rigid board to imperceptible electronics.

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Experimental study on the constitutive model of optically clear adhesive films under rapid loading

Huo

et al. 2022

J of Applied Polymer Sci

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The mechanical properties of optically clear adhesive (OCA) films can be anisotropy and viscoelasticity, and they are distinguished from conventional linear elasticity and hyper-elasticity. These properties should be considered to analyze the interfacial stress, which plays an important role in evaluating the failure of a structure containing OCA. Based on well-designed systematical experiments in the material's principal axes, a phenomenological constitutive model of OCA has been proposed in a transversely isotropic and ratedependent form. For the application to large deformation cases, the constitutive model was developed by using true stress and true strain. Results show that the well-known assumption of volume-incompressibility is not appropriate for OCA, and Poisson's ratio can vary with the loading rate and the current strain. Considering that the mono-axial mechanical behaviors along the material's principal axes present strong non-linearity, an incremental threedimensional constitutive model has been developed for finite element method (FEM) implementation. By comparing with traditional isotropic elastic and hyperelastic models, numerical examination results show that the proposed constitutive model can give a more accurate description of experimental stress-strain curves.

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Folding stabilities of encapsulation layers at positions off the mechanical neutral plane

Cited by 6 publications

References 28 publications

Highly Robust, Flexible Top‐Emission Organic Light‐Emitting Diode Exhibiting Stable Performance under Infolding of Curvature Radius of 0.32 mm

Highly Robust, Flexible Top‐Emission Organic Light‐Emitting Diode Exhibiting Stable Performance under Infolding of Curvature Radius of 0.32 mm

Copper‐Leaf‐Based Process for Imperceptible Computational Electronics

Experimental study on the constitutive model of optically clear adhesive films under rapid loading

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