KAIST stamps vertical microLEDs onto flexible substrates
In a first step, an array of individual vertical LEDs is picked up by a carrier stamp, then the carrier stamp is pressed into contact with a precisely aligned bottom flexible electrode substrate through the anisotropic conductive film by compression bonding. Because the ACF film contains conductive micro-particles, the compression bonding step simultaneously transfers the VLEDs and selectively connects them to the underlying flexible substrate. Such flexible micro LEDs could be designed into high resolution wearable displays and for wearable lighting.
For their research, the scientists led by Professor Keon Jae Lee from the Department of Materials Science and Engineering have designed the necessary transfer equipment. They fabricated a 50×50 f-VLED array just about 5µm thin, reporting an optical power density of 30mW/mm2 or three times higher than that of lateral micro LEDs, while improving the LEDs’ thermal reliability and lifetime by reducing heat generation within the thin film.
With the help of Professor Daesoo Kim from the Department of Biological Sciences, the new f-VLEDs were then applied to optogenetics, whereby light pulses are used to stimulate neurons within localized cortical areas of the brain. In a paper titled “Optogenetic Control of Body Movements via Flexible Vertical Light-Emitting Diodes on Brain Surface ” published in the February 2018 issue of Nano Energy, the researchers describe how they inserted the flexible VLEDs between the skull and the brain surface of a mouse to control her behaviour, illuminating motor neurons on two-dimensional cortical areas located deep below the brain surface.
Brain science aside, other biomedical applications envisaged by the researchers include phototherapeutic treatment and contact lens biosensors.
Back in 2016, Professor Lee has spun-off a startup called FRONICS (abbreviated from Flexible electRONICS) to commercialize its transfer technologies to companies willing to design their own IoT products, based on flexible micro LED technology. According to the company’s website, the anisotropic conductive film-based transfer and interconnection technology is applicable to both GaN and GaAs LEDs and can support resolutions from 400 to 1300ppi.
KAIST – www.kaist.edu
FRONICS – www.fronics.com
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