Flexible vertical InGaN micro-light emitting diode (micro-LED) arrays have been fabricated and characterized for potential applications in flexible micro-displays and visible light communication. The LED epitaxial layers were transferred from initial sapphire substrates to flexible AuSn substrates by metal bonding and laser lift off techniques. The current versus voltage characteristics of flexible micro-LEDs degraded after bending the devices, but the electroluminescence spectra show little shift even under a very small bending radius 3 mm. The high thermal conductivity of flexible metal substrates enables high thermal saturation current density and high light output power of the flexible micro-LEDs, benefiting the potential applications in flexible high-brightness micro-displays and high-speed visible light communication. We have achieved ~40 MHz modulation bandwidth and 120 Mbit/s data transmission speed for a typical flexible micro-LED.

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Biodegradable long-chain branched (LCB) poly­(butylene succinate-co-butylene terephthalate) (PBST) copolyesters were prepared via a two-step direct esterification and melt polycondensation process, using a small amount (0–2 mol %) of diglycidyl 1,2,3,6-tetrahydrophthalate (DGT) as an in situ branching agent (BA). The chemical structures of LCB PBSTs were characterized and the thermal, mechanical, and rheological properties were investigated. With increasing DGT loading, PBSTs with higher branching degree, broader molecular weight distribution, and lower melt flow index were synthesized in shorter polycondensation time. The branching of PBSTs results in a slight decrease in crystallizability, melting, and Vicat softening temperatures, but leads to an obvious decrease in elongation at break. On the other hand, the existence of LCB greatly improved the rheological properties of PBSTs. PBST with higher branching degree possesses higher storage and loss modulus, higher zero-shear viscosity, longer relaxation time, more obvious shear-thinning, and lower loss angle tangent. The Han plot of the rheological data also indicates higher elasticity of LCB PBSTs.