Siloxane Hybrid Material-Encapsulated Highly Robust Flexible μLEDs for Biocompatible Lighting Applications

Flexible micro-light-emitting diodes (f-μLEDs) have been regarded as an attractive light source for the next-generation human–machine interfaces, thanks to their noticeable optoelectronic performances. However, when it comes to their practical utilizations fulfilling industrial standards, there have been unsolved reliability and durability issues of the f-μLEDs, despite previous developments in the high-performance f-μLEDs for various applications. Herein, highly robust flexible μLEDs (f-HμLEDs) with 20 × 20 arrays, which are realized by a siloxane-based organic–inorganic hybrid material (SHM), are reported. The f-HμLEDs are created by combining the f-μLED fabrication process with SHM synthesis procedures (i.e., sol–gel reaction and successive photocuring). The outstanding mechanical, thermal, and environmental stabilities of our f-HμLEDs are confirmed by a host of experimental and theoretical examinations, including a bending fatigue test (105 bending/unbending cycles), a lifetime accelerated stress test (85 °C and 85% relative humidity), and finite element method simulations. Eventually, to demonstrate the potential of our f-HμLEDs for practical applications of flexible displays and/or biomedical devices, their white light emission due to quantum dot-based color conversion of blue light emitted by GaN-based f-HμLEDs is demonstrated, and the biocompatibility of our f-HμLEDs is confirmed via cytotoxicity and cell proliferation tests with muscle, bone, and neuron cell lines. As far as we can tell, this work is the first demonstration of the flexible μLED encapsulation platform based on the SHM, which proved its mechanical, thermal, and environmental stabilities and biocompatibility, enabling us to envisage biomedical and/or flexible display applications using our f-HμLEDs.