Performance of Chemical Vapor Deposited Boron-Doped AlN Thin Film as Thermal Interface Materials for 3-W LED: Thermal and Optical Analysis

Boron-doped aluminum nitride （B-AlN） thin films were synthesized on Al substrates by using chemical vapor deposition method by changing the synthesis parameters and were used as thermal interface material for high power light emitting diode （LED）. The B-AlN thin film-coated Al substrate was used as heat sink and studied the performance of high power LED at various driving currents. The recorded transient cooling curve was evaluated to study the rise in junction temperature （Tj）, total thermal resistance （gth_tot） and the substrate thermal resistance （Rth_sub） of the given LED. From the results, the B-AlN thin film （prepared at process 4） interfaced LED showed low Rth-tot and Tj value for all driving currents and observed high difference in Rth_tot （△Rth_tot =2.2 K/W） at 700 mA when compared with the Rth-tot of LED attached on bare Al substrates （LED/Al）. The Tj of LED was reduced considerably and observed 4.7 ℃ as ATj for the film prepared using process 4 condition when compared with LED/Al boundary condition at 700 mA. The optical performance of LED was also tested for all boundary conditions and showed improved lux values for the given LED at 700 mA where B-AlN thin film was synthesized using optimized flow of Al, B and N sources with minimized B and N content. The other optical parameters such as color correlated temperature and color rendering index were also measured and observed low difference for all boundary conditions. The observed results are suggested to use B-AlN thin film as efficient solid thin film thermal interface materials in high power LED.

Thermal resistance of high power LED on surface modified heat sink

For 3 W green light emitting diode （LED）, the top surface of commercial heat sink was machined with two different shapes （hole and ＇V＇ shaped） and the thermal performance was tested. The contact surface area of the heat sink was increased by machining process. The observed junction temperature （Tj） from transient cooling curve was high for ＇V＇ shaped surface for all driving currents. Hole shaped surface of heat sink did not influence much on the Tj values. In addition, total thermal resistance （Rth_tot） was not affected by the hole shpaed surface compared to plain surface. Noticeable increases in Tj as well as Rth-tot were observed for ＇V＇ shaped surface for all driving currents （100, 350 and 700mA）. The observed correlated color temperature （CCT） values were high for hole and ＇V＇ shaped surfaces and the variation in CCT with respect to time was high for all surfaces measured at 700 mA. Increased lux for modified surface at high driving current （700 mA） was also observed. Very small variation in color rendering index （CRI） values could be observed.