Abstract

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-$\mu{\hbox{m}}$ 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.

© 2012 IEEE

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