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 50x50 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.