Development of ultrathin robust substrate for flexible electronics via initiated chemical vapor deposition process

Abstract

With vigorous interests in flexible electronics, the performance degradation under applied strain during operation is major concern to overcome. We could expect awful performance improvement because the strain sensitive materials are consequently located near the neutral plane by decreasing substrates under few microns. Here, we fabricated the robust ultrathin copolymer film simultaneous in-situ cross-linked by urethane group for flexible electronic substrates. Poly(2-isocyanatoethyl acrylate-co-hydroxyethyl acrylate) was one-step copolymerized via initiated chemical vapor deposition (iCVD) process that facilitates retention of functional groups and stoichiometric control due to its mild deposition condition. The complete crosslinking urethane group provides intermolecular and self-associated hydrogen bond acting as physical entanglement in the polymer film for its robust mechanical properties even for few micrometer thickness. Through comprehensive analysis of requirements for flexible electronic substrates, the characteristics of synthesized copolymer showed comparable properties with commercialized substrate. It possesses extremely smooth surface without any pinholes, outstanding optical properties of high clarity and low haze, acceptable solvent resistance and enough mechanical properties even for few $\mu m$ thickness. We demonstrated its potential as a substrate material for flexible electronics by fabricating a flexible OLED fabricated by fully-dry process on 3 $\mu m$ thick polymer substrate synthesized via iCVD process. We suggest newly synthesized robust cross-linked copolymer thin film containing urethane group and its application to the fabrication of integrated flexible electronics under the all-dry process.