Development of robust flexible OLED encapsulations using simulated estimations and experimental validations

Lee, Chang‐Chun; Shih, Yan-Shin; Wu, Cheng‐Li; Tsai, Chia‐Hao; Yeh, Shu‐Tang; Peng, Yi-Hao; Chen, Kuang‐Jung

doi:10.1088/0022-3727/45/27/275102

Cited by 38 publications

(15 citation statements)

References 11 publications

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“…Reducing the bending stress through display film stack design optimization is one of the critical design goals to enable the foldability of displays. Analysis of multi-layer structures for touch panel and OLED displays under bending can be found in works including the analysis of the roles of cover plate and barrier layer in managing bending neutral plane to reduce bending stress [Lee, et. al, 2012;2013;Cheng, et al, 2015;Chiang, et al, 2009], the analytical formulation to relate the bending stress and radius of curvature of the bend in a multilayer structure [Yeh, et al 2014], and the study of delamination, buckling, and cracking on the detailed multilayer TFT structures [van der Slius, et al 2009;.…”

Section: Introductionmentioning

confidence: 99%

64‐1: Modeling the Mechanical Performance of a Foldable Display Panel Bonded by 3M Optically Clear Adhesives

Salmon

Everaerts

Campbell

et al. 2017

Symp Digest of Tech Papers

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Among the multiple design goals for foldable displays to perform under repeated folding and unfolding is to reduce bending stress and various failure modes induced by bending of the film stack. In this work, we demonstrate, through modeling the folding of simplified display film stacks, that the optically clear adhesives (OCA) in a display can be leveraged not only to provide a secure bond between the functional layers, but also to improve the overall folding performance and mechanical durability of the display.Specifically, we discuss these OCA advantages through three topics commonly encountered in designing a flexible display:x reducing the bending stresses by neutral plane management, x facilitating large shear strains between layers to reduce shear coupling between the layers,x improving buckling resistance.

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Section: Introductionmentioning

confidence: 99%

64‐1: Modeling the Mechanical Performance of a Foldable Display Panel Bonded by 3M Optically Clear Adhesives

Salmon

Everaerts

Campbell

et al. 2017

Symp Digest of Tech Papers

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“…Poisson ratio adopted from the literature was 0.37. 29 These basic mechanical properties and the plastic stress–strain relationship were used in the FEA of the PET films with grooves.…”

Section: Methodsmentioning

confidence: 99%

Stress/strain and curvature analysis of laser-scribed polyethylene terephthalate films with multiple grooves using finite element method

Heo

Kang

Lee

et al. 2018

Advances in Mechanical Engineering

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Laser scribing can be used to enhance the flexibility of polymer films for flexible device applications. To optimize the bending curvature by controlling the scribing parameters—the depth, number, and interval of the scribed grooves, finite element analysis was conducted on the bending tests of scribed polyethylene terephthalate films. Moreover, the influences of the parameters on the stress/strain near the grooves were investigated. The maximum stress/strain and curvature generally increased with an increase in depth, whereas these values decreased with an increase in number and intervals. However, to maintain the mechanical stability of the films, the parameters were limited. The optimization results revealed that the maximum value of the curvature was 2.6 mm−1 at depth = 40 and intervals = 25 μm, for number = 7. An empirical equation relating the curvature to depth and intervals was also provided. The results of the analysis are useful for the design of laser-scribed grooves on various polymer films, for the enhancement of their bending curvature, while minimizing the mechanical instability.

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“…(b) are the good ohmic contact indicating that the resistances are accurate. The resistance of the layer on the specimen surface is used to monitor crack evolution . At 20% increment of resistance it determines the critical strain.…”

Section: Experiments and Process Flowmentioning

confidence: 99%

Improving the flexibility of AMOLED display through modulating thickness of layer stack structure

et al. 2016

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-A robust methodology is established to predict the critical bending radius of a flexible AMOLED. According to the methodology, the critical bending radius of display manufactured by the same process could be reduced from 7 mm to 4 mm by modulating the layer stack thickness.Keywords -flexible, neutral plane, stress, strain, simulation, AMOLED. DOI # 10.1002/jsid.443 Objective and backgroundRecently, there are many significant investments in the development of flexible display technology. Several flexible AMOLED products are already available in the display market. But, these products are only slightly curved and remain rigid, which are not as much different from the present glass-based portable device as one could anticipate from a flexible display. In order to realize flexible display applied to the rollable or foldable device of next generation, it is necessary to reduce the critical bending radius.The structure of a flexible AMOLED display can be divided into several parts: the flexible substrate, TFT backplane, OLED, and encapsulation layers. The AMOLED display contains functional brittle inorganic layers that have different purposes and could easily fail during bending. A number of literatures have pointed out that we can place the mechanically vulnerable components (TFT backplane and OLED) close to the zero-strain plane (the neutral plane) to improve the reliability and flexibility of flexible displays.1-4 But, the inorganic layers used for encapsulation layers would be far away from neutral plane and easily fail during bending.OLED materials are extremely sensitive to ambient water vapor and oxygen, which causes oxidation of cathode and results in the formation of black spots in electroluminescence. [5][6][7][8] Therefore, keeping the performance of encapsulation layers during bending is important. The most common technique of encapsulation for flexible AMOLED is the thin-film encapsulation (TFE) 9-12 that is fabricated by alternative stacks of inorganic and organic layers. In order to protect the TFE layer, we modulate the thickness of organic layers. In our structure configuration, we maintain the neutral plane located on TFT and OLED layers but change the thicknesses of organic layers. The inorganic layers in TFE component could get closer to the neutral plane and take lesser strain. Experiment and process flowA robust methodology consisting of a mechanical model of multi-films under bending loads and experiment of bending test is proposed to predict the critical bending radius of a flexible AMOLED display. Figure 1 shows the process flow. We apply this methodology in different layer stack structure configuration and try to reduce the critical bending radius.The flexible AMOLED interpreted below is fabricated by PI substrate with SiNx bottom barrier to perform the IGZO TFT process, then, deposit the OLED material and encapsulated by thin-film encapsulation (TFE) process. The TFE layer is made by stacks of SiNx layers and "organic coating for planarization (OCP)" layers, alternately. SiNx is dep...

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Development of robust flexible OLED encapsulations using simulated estimations and experimental validations

Cited by 38 publications

References 11 publications

64‐1: Modeling the Mechanical Performance of a Foldable Display Panel Bonded by 3M Optically Clear Adhesives

64‐1: Modeling the Mechanical Performance of a Foldable Display Panel Bonded by 3M Optically Clear Adhesives

Stress/strain and curvature analysis of laser-scribed polyethylene terephthalate films with multiple grooves using finite element method

Improving the flexibility of AMOLED display through modulating thickness of layer stack structure

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