Self-Assembled Microlens on Top of Light-Emitting Diodes Using Hydrophilic Effect for Improving Extraction Efficiency and Increasing Viewing Angle

In this paper, we propose a self-assembled microlens on top of light-emitting diodes (LEDs) based on hydrophilic effect under ultraviolet (UV)/ozone treatment to improve extraction efficiency and to increase viewing angle. The LED chip was encapsulated by polydimethylsiloxane (PDMS) (n=1.44) before the fabrication process of microlens. The microlens was made of transparent negative photoresist SU-8 (n=1.63). The SU-8 photoresist became more hydrophilic after UV/ozone treatment. After hydrophilic zones were produced by using shadow masks and UV/ozone, the substrate with hydrophilic zones was dipped in and out of diluted SU-8 photoresist solution with slow and constant velocity. Meanwhile, a 200- microlens was formed by self-surface tension and cohesion of diluted SU-8. Finally, microlens was hardened after UV curing. This approach is cost effective and low time-consuming. It did not require photo masks, heating, or etch-transfer processes. It´s a new fabrication method that can be easily applied to opto-electronic devices. Integrated with LED, microlens can improve extraction efficiency 28% in total power and increase viewing angle 17 degree.