[논문]Mechanical Modeling of Rollable OLED Display Apparatus Considering Spring Component

Ma, Boo Soo; Jo, Woosung; Kim, Wansun; Kim, Taek-Soo

doi:10.6117/kmeps.2020.27.2.019

Mechanical Modeling of Rollable OLED Display Apparatus Considering Spring Component 원문보기

마이크로전자 및 패키징 학회지 = Journal of the Microelectronics and Packaging Society, v.27 no.2, 2020년, pp.19 - 26

Ma, Boo Soo (Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST)) , Jo, Woosung (Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST)) , Kim, Wansun (Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST)) , Kim, Taek-Soo (Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST))

Abstract ▼ AI-Helper

Flexible displays have been evolved into curved, foldable, and rollable as the degree of bending increases. Due to the presence of brittle electrodes (e.g. indium-tin oxide (ITO)) that easily cracked and delaminated under severe bending deformation, lowering mechanical stress of the electrodes has been critical issue. Because of this, mechanical stress of brittle electrode in flexible displays has been analyzed mostly in terms of bending radius. On the other hand, in order to make rollable display, various mechanical components such as roller and spring are needed to roll-up or extend the screen for the rollable display apparatus. By these mechanical components, brittle electrode in the rollable display is subjected to the excessive tensile stress due to the retracting force as well as the bending stress by the roller. In this study, mechanical deformation of rollable OLED display was modeled considering boundary conditions of the apparatus. An analytical modeling based on the classical beam theory was introduced in order to investigate the mechanical behavior of the rollable display. In addition, finite element analysis (FEA) was used to analyze the effect of mechanical components in the apparatus on the brittle electrode. Furthermore, a strategy for improving the mechanical reliability of the rollable display was suggested through controlling the stiffness of adhesives in the display panel.

주제어

표/그림 (8)

그림 Fig. 1. (a) Structure of rollable display panel, (b) overall view of rollable display in FE modeling.
표 Table 1. Mechanical properties of each layer in rollable display panel
그림 Fig. 2. Boundary conditions of rollable display for each steps in FE modeling.
그림 Fig. 3. Free body diagram of rollable display panel in rollable display apparatus.
그림 Fig. 4. FEA result of strain distribution for ITO electrode (a) before the screen extension and (b) after the screen extension (Extended length = 35 mm).
그림 Fig. 5. (a) Strain distribution of ITO electrode at the extended length = 35 mm. (b) Maximum strain of ITO electrode as a function of the extended length of screen. (c) Effect of number of revolutions of display panel on maximum strain of ITO electrode.
그림 Fig. 6. Effect of elastic modulus of two adhesives in display panel on maximum strain of ITO electrode.
그림 Fig. 7. FEA result of strain distribution and cross-sectional view of rolled portion in display panel (Extended length = 48 mm).

AI 본문요약
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가설 설정

(a) Strain distribution of ITO electrode at the extended length = 35 mm. (b) Maximum strain of ITO electrode as a function of the extended length of screen. (c) Effect of number of revolutions of display panel on maximum strain of ITO electrode.

제안 방법

In this study, mechanical deformation of the brittle electrode in rollable OLED display is analyzed by analytical modeling and numerical analysis with consideration of boundary conditions in the rollable display apparatus. Analytical model of the rollable display is validated by comparing with finite element analysis (FEA).
Mechanical behavior of rollable OLED display was investigated by using analytical modeling and numerical analysis with consideration of the boundary conditions of the apparatus. The brittle electrode in the display panel was subjected not only the bending strain by the roller but also additional tensile strain due to the retracting force of the spring component.
The analysis was performed in 3 steps to reflect the boundary conditions of the rollable display apparatus. The detailed boundary conditions at each step were explained in Fig.
Analytical model of the rollable display is validated by comparing with finite element analysis (FEA). Then, the effects of the various factors such as the spring and number of revolutions on the mechanical deformation of the display panel are analyzed. Moreover, controlling compliance of adhesive layers in the OLED panel using shear lag phenomenon has been proposed as a strategy to improve mechanical reliability of the rollable display.

이론/모형

In order to analyze the mechanical behavior of rollable display panel, the FE modeling was conducted using a nonlinear static solver in ABAQUS 6.14, which is commercial FEA software. As shown in Fig.

성능/효과

Moreover, the effects of spring and number of revolutions on the brittle electrode were investigated to reduce the tensile strain of the electrode in the rollable display. From the results, it was confirmed that the strain of the brittle electrode can be lowered by optimizing stiffness of the spring component and extension length of the screen. Furthermore, the strain of the brittle electrode could be lowered by controlling compliance of the adhesives, which are sandwiched between cover and back films in the display panel.
In conclusion, the brittle layer in the rollable display should be protected from mechanical fracture considering strain decoupling between the layers.

후속연구

Furthermore, the strain of the brittle electrode could be lowered by controlling compliance of the adhesives, which are sandwiched between cover and back films in the display panel. In conclusion, our works provide essential guidance to improve mechanical robustness of the display panel for commercialization of the rollable display apparatus.

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