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Flexible light‐emitting devices have attracted attention as a novel bio‐interface connecting living tissues with electronics due to their high brightness, low power consumption, and durability in humid environments. Introduction of vertically current‐injected micro‐light‐emitting diodes (MicroLEDs) into this film can enhance the MicroLED effective area and improve device characteristics. In this study, the MicroLED transfer technology onto conductive materials is investigated. The feasibility of batch transferring MicroLEDs onto a conductive polymer is demonstrated by PEDOT:PSS layer. For non‐Ohmic characteristics between n‐GaN and PEDOT:PSS, a backside‐open MicroLED hollow structure is proposed, enabling the formation of Ti/Au electrodes on the backside of MicroLED. By transferring the fabricated vertically current‐injected MicroLEDs onto the PEDOT:PSS layer, a flexible vertically current‐injected LED film is achieved, observing uniform blue light emission. The developed MicroLED film holds promise as a new neuroscience tool for targeting specific areas of the brain with light. [ABSTRACT FROM AUTHOR]

Flexible MicroLEDs hold great promise as a novel tool for advancing optogenetics, enabling applications in biology. Such applications require the technology to assemble MicroLEDs onto ultra‐thin biocompatible films that conform to the delicate and uneven brain and biological tissues. In this study, a batch transfer technique using thermal release sheets is propsed. By optimizing the gate structures that support the hollow structure, a method to transfer MicroLEDs to the film without causing damage is established. It is successfully demonstrated that the flexible MicroLED films, fabricated using this technique, can be placed on the brain surface of transgenic mice and induce neural activity through optogenetic stimulation. [ABSTRACT FROM AUTHOR]

A neural probe with six micro-light-emitting diodes (MicroLEDs) and 15 neural electrodes was fabricated for optogenetic application. Local field potentials, which provide information about the neural activity, were successfully recorded using the neural probe, indicating the effectiveness of the neural electrodes. The MicroLEDs on the probe exhibited highly consistent current–voltage characteristics and sufficient light output of 20 mW mm−2 at 1 mA to manipulate neural activity. The light distribution in brain tissue was simulated to estimate the optical stimulation area and a number of optically stimulated neurons. The increase in LED temperature, i.e. ΔT, was investigated because high temperatures can damage brain tissue. A curve illustrating the relationship between ΔT and the wall-plug efficiency was derived. The wall-plug efficiency was increased 1.8 times by installing an Ag mirror on the back of a MicroLED. These results suggest that the MicroLED neural probe would significantly contribute to the development of neuroscience research-purposed optogenetic technology. [ABSTRACT FROM AUTHOR]