Mechanically anisotropic stretchable and transparent composite substrates for distortion-free display

Developing new-form factor devices has led to the creation of foldable and rollable displays. However, next-step stretchable devices with shape changes face a new issue different from conventional displays. When the screen is stretched, screen distortion occurs due to the nature of contraction perpendicular to the stretching direction to preserve the volume. To address this issue, we focused on the composite approach with mechanical anisotropy using continuously aligned fiber fillers. In this study, we fabricated transparent mechanically anisotropic stretchable substrates with near-zero Poisson's ratio by incorporating continuous and aligned transparent ribbon arrays within a transparent, stretchable matrix. The aligned ribbon-reinforced composite substrates have mechanical anisotropy by mainly reinforcing stiffness only in the ribbon-aligned direction. When unidirectional stretchable devices in the direction perpendicular to the alignment are developed, the stiffness of the substrate contracting in the ribbon alignment direction is relatively high compared to the vertical direction, and thus the vertical displacement is diminishing, so substrates with Poisson's ratio close to 0 can be realized. Based on this approach, we realized a light-emitting device (LED) array system with near-zero vertical distortion by attaching LED arrays and printed intrinsically stretchable interconnections on our mechanically anisotropic composite substrate.