Transfer printing of vertical-type microscale light-emitting diode array onto flexible substrate using biomimetic stamp.

We report the transfer printing of GaN-based microscale vertical-type light-emitting diodes (mu-VLEDs) using a functional layer and a biomimetic stamp. An oxide-based functional layer is inserted onto the structure of a mu-VLED and used to separate the chip from the mu-VLED wafer by absorbing the pulse of a UV pulse laser during pick-up of the transfer printing process. Polydimethylsiloxane (PDMS)-based biomimetic stamps have been fabricated to mimic the gecko lizard cilia for improved adhesion and repeatability. The biomimetic stamp has an adhesion force of 25.6 N/cm(2), which is 12 times the adhesion of a flat stamp; an adhesion force of 10 N/cm(2) or more was maintained after 100,000 repeated adhesion tests. A flexible 10 x 10 prototype array on a polyimide substrate was fabricated, and its bending test results indicated that the strain effect on the forward voltage and the output power was less than 1%. The stable bending test results of the prototype indicate that mu-VLEDs using biomimetic stamps allow the necessary stability for practical transfer printing. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement