Nano-structural study of organic-inorganic hybrid composites for flexible electronic applications

Abstract

Owing to the development of information and communication technology, and public expectations for novel designs have led to the diversification of electronic device form factors from rigid to flexible types. For this reason, the protective layers of electronic devices have been required to have flexibility while maintaining sufficient protective characteristics. Conventional protective materials for rigid devices such as glass and metal lack flexibility, further polymers or elastomers, such as CPI, PET, TPU, ECOFLEX, and PDMS, which are used as protective layers for flexible devices, have an adequate elongation but poor mechanical properties. Therefore, a protective layer that satisfies both two characteristics is required. In this study, organic–inorganic hybrid materials with an adequate flexibility and mechanical properties were fabricated. Their mechanical properties were evaluated according to the Si–O–Si bond structure to address the aforementioned trade-off. First, three types of resins with different inorganic siloxane bonds (random, cage, and ladder structures) were synthesized. The chemical structures of the synthesized resins were analyzed through FT-IR, 29Si-NMR, XRD, and MALDI-TOF-MS. Thereafter, the resins were crosslinked using a cationic photoinitiator, yielding unique organic–inorganic composites with organic epoxy and inorganic Si–O–Si bonds. The surface mechanical properties of the manufactured hybrid coatings were evaluated through nano-indenter. A ladder structure with a double-stranded Si–O–Si bond structure longer than those of other structures exhibited the best mechanical properties with a high flexibility. Further, the superior wear resistance of the ladder structure was confirmed via the steel wool test. The folding stability, light transmittance, pencil hardness, and resistance of the flexible sensor with a protective layer were determined to verify the applicability of the prepared ladder-structured organic–inorganic hybrid composite as a protective layer for flexible devices. Overall, the ladder-structured coating exhibited excellent performance as a protective layer for flexible devices.