Enhanced Heat Dissipation of Phosphor Film in WLEDs by AlN-Coated Sapphire Plate

In this article, we developed a color converter of phosphor-AlN-sapphire (PAS) plate to enhance the heat dissipation of phosphor film in high-power white light-emitting diodes (WLEDs). The improved heat dissipation performance is observed by introducing the AlN film with high thermal conductivity (TC), which was demonstrated by finite-element analysis (FEA) simulation. The proposed PAS plate was prepared by printing and sintering a yellow phosphor film on an AlN-coated sapphire plate. It is observed that the TC of the AlN-coated sapphire plate is increased with the reduction of the threading dislocation (TD) density of the AlN film. High TD density decreases TC by causing strong scattering of heat transfer phonons. The thermal and optical characteristics of the converters were further measured after this structure was used for packaging WLEDs as a remote phosphor configuration. Notably, the surface temperature of the PAS converter with the highest TC is reduced by nearly 23 degrees C and the luminous efficiency (LE) is increased by 17% at the current of 900 mA compared with the converter without AlN film coated. It is believed that the PAS plate is an effective converter to improve the heat dissipation of the phosphor layer and optical properties of high-power WLEDs.