Browse > Article

Evaluation of Residual Strains under Pure Bending Loading for Colorless and Optically Transparent Polyimide Film for Flexible Display  

Choi, Min-Sung (Department of Mechanical System Engineering, Kumoh National Institute of Technology)
Park, Min-Seok (Department of Mechanical System Engineering, Kumoh National Institute of Technology)
Park, Han-Yeong (Department of Mechanical System Engineering, Kumoh National Institute of Technology)
Oh, Chung-Seog (Department of Mechanical System Engineering, Kumoh National Institute of Technology)
Publication Information
Journal of the Semiconductor & Display Technology / v.20, no.4, 2021 , pp. 49-54 More about this Journal
Abstract
The display industry is transitioning from traditional rigid products such as flat panel displays to flexible or wearable ones designed to be folded or rolled. Accordingly, colorless and optically transparent polyimide (CPI) films are one of the prime candidates to substitute traditional cover glass as a passivation layer to accommodate product flexibility. However, CPI films subjected to repetitive pure bending loads inevitably entail an accumulation of residual strain that can eventually cause wrinkles or delamination in the underlying component after a certain number of static and cyclic loading. The purpose of this study is to establish an experimental method to systematically evaluate the bending residual strain of CPI films. Films were monotonically and cyclically wrapped on mandrels of various diameters to ensure a constant strain in each. After unwrapping the wound CPI film, the residual radius of curvature remaining on the film was measured and converted into residual strain. The critical radius of curvature at which residual strain does not remain was about 5 mm, and the residual strain decreased in proportion to the log time. It is expected that flexible displays can be reliably designed using the data between the applied bending strain and the residual strain.
Keywords
Flexible display; Residual strain; Polyimide film; Pure bending loading;
Citations & Related Records
연도 인용수 순위
  • Reference
1 Jeong, E.G, Kwon, J.H., Kang, K.S., Jeong, S.Y., Choi, K.C., "A review of highly reliable flexible encapsulation technologies towards rollable and foldable OLEDs", J. Inf. Displ., 21(1), pp. 19-32, (2020).   DOI
2 Yu, X.-H., Liu, J.-N., Wu, D.-Y., "Colorless PI structure design and evaluation for achieving low CTE target", Mat. Today Comm., 21, 100562, (2019).   DOI
3 Wisinger, C.E., Maynarda, L.A., Barone, J.R., "Bending, curling, and twisting in polymeric bilayers", Soft Matter, 15, pp. 4541-4547, (2019).   DOI
4 Shi, S., Li, Z., Tsai, P., Dong, L., Wang, D., Shi, Y., Du, S., Cai, P., Gao, M., Zheng, M., Wang, H., "Research on Commercial Foldable AMOLED and Relevant Technologies", SID Symposium Digest of Technical Papers, vol. 51, pp. 826-829, (2020).
5 Kim, J.-H., Lee, T.-I., Kim, T.-S., Paik, K.-W., "The effect of anisotropic conductive films adhesion on the bending reliability of chip-in-flex packages for wearable electronics applications", IEEE Trans. Comp., Pack & Manuf. Techn, 7(10), pp. 1583-1591, (2017).   DOI
6 Khan, M.U.A., Raad, R., Tubbal, F., Theoharis, P.I., Liu, S., Foroughi, J., "Bending analysis of polymer-based flexible antennas for wearable, general IoT applications: A review", Polymers, 13, 357, (2021).   DOI
7 Saleh, R., Barth, M., Eberhardt, W., Zimmermann, A., "Bending setups for reliability investigation of flexible electronics", Micromachines, 12, 78, (2021).   DOI
8 Cuddalorepatta, G.K., Sim, G.-D., Li, H., Pantuso, D., Vlassak, J.J., "Residual stress-driven test technique for freestanding ultrathin films: Elastic behavior and residual strain", J. Mat. Res., 34(20), pp. 3474-3482, (2019).   DOI
9 Park, J.-S., Chae, H, Chung, H.K., Lee, S.I., "Thin film encapsulation for flexible AM-OLED: a review", Semicond. Sci. Technol. 26, 034001, (2011).   DOI
10 Koo, J.H., Kim, D.C., Shim, H.J., Kim, T.-H., Kim, D.-H., "Flexible and stretchable smart display: materials, fabrication, device design, and system integration", Adv. Funct. Mater., 28, 1801834, (2018).   DOI
11 Yang, S.-Y. and Yuan, L.-L., "Advanced Polyimide Films", In S.-Y. Yang, Eds., Advanced Polyimide Materials, Elsevier: Chemical Industry Press, pp. 1-66, (2018).
12 Tapaswi, P.K., Ha, C.-S., "Recent trends on transparent colorless polyimides with balanced thermal and optical properties: design and synthesis", Macromol. Chem. Phys., 220, 1800313, (2019).   DOI
13 ASTM D522 / D522M-17, Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings, ASTM International, West Conshohocken, PA, 2017, www.astm.org
14 Jeong, J.-H., Kim, J.-H., Oh, C.-S., "Quantitative evaluation of bending reliability for a flexible near-field communication tag", Microelectronics Rel., 75, pp. 121-126, (2017).   DOI
15 Kallmayer, C., Parekh, D.P., Jiang, T., Atluri, V., Erickson, K., Chan, B., New Materials and Processes for Flexible Electronics. Oct, 2021, https://eps.ieee.org/images/files/enews/Chan_Flexible_Electronics_May_2021.pdf (May, 2021).
16 Yang, Z., Guo, H. Kang, C., Gao, L., "Synthesis and characterization of amide-bridged colorless polyimide films with low CTE and high optical performance for flexible OLED displays", Polym. Chem., 12, pp. 5364-5376, (2021).   DOI
17 Chang, C.-L., Zhu, W.-G., Lin, S.-H., "Flexible cover window with colorless polyimide hard coating thin film for foldable displays", Int. Conf. on Disp. Techn., 52(S2), pp. 961-964, (2021).