Thermal and optical performance of chemical vapor deposited zinc oxide thin film as thermal interface material for high power LED

Abstract

In a solid-state lighting, the thermal performance of light emitting diode (LED) is one of the crucial aspects in determining the quality of the LED. To improve the thermal performance of LED, thermal interface material (TIM) was employed and proven to help the transfer of heat in solid state lighting. In this study, zinc oxide thin films were deposited on aluminum (Al) substrates using chemical vapor deposition method and the effect of annealing temperature was discussed. The thermal and optical performances of OSRAM golden dragon white LED attached on bare and ZnO thin film coated Al substrate were measured by Thermal Transient T3ster (T3ster) and Spectrometer respectively. Noticeable improvement in the reduction of junction temperature (ΔTj = 13.79 ℃) was observed for ZnO thin film annealed at 400 ℃ compared with the bare Al (without ZnO) boundary condition and hence improvement in optical output was achieved with the same boundary condition. Overall, rise in junction temperature, Tj of ZnO thin film demonstrated positive result in reducing the temperature of the LED package. The total thermal resistance (Rth-tot) was low for the sample coated with ZnO thin film compared with the bare Al substrate at high driving currents with the lowest reported value of 7.37 K/W for ZnO thin film annealed at 400 ℃. Correlated color temperature (CCT) and illuminance (LUX) value showed that the ZnO thin film sample displayed better performance than bare Al sample. From the result, it can be suggested that ZnO thin film would be an effective and suitable thermal interface material (TIM) for the solid-state lighting application.