Stretchable and transparent silicone/zinc oxide nanocomposite for advanced LED packaging

For current light-emitting diode (LED) packaging technology, one of the key challenges is light extraction, due to the difference in index of refraction between LED chip and air. Silicone nanocomposites have been widely researched for applications in LED encapsulant to reduce the difference in refractive index. Silicone is desirable for LED encapsulant because of its optical transparency and photothermal resistance. However, less attention has been paid to the elastic properties of silicone which would enable a stretchable LED encapsulant. Hence the objective of this study is to examine the stretch ability of silicone/zinc oxide (ZnO) nanocomposites for LED packaging. Wurtzite ZnO nanoparticles were prepared in colloids and subjected to silane treatment. Effects of both ex situ and in situ silane treatment on the final mechanical and optical properties of the silicone/ZnO nanocomposites were examined. Silicone/ZnO nanocomposites exhibit significantly more compliant stress-strain behavior than silicone control; silicone/silane-treated ZnO nanocomposites, in particular, exhibit more serrated stress-strain curves. Silicone/silane-treated ZnO nanocomposites exhibit higher transmittance than silicone/unmodified ZnO nanocomposites, indicating improved dispersion of the nanoparticles. The silicone/5% silane-treated ZnO nanocomposite using in situ method is able to deform over a range of up to 160%; its film (~40 microns thick) exhibits transmittance >70% throughout the visible range.