高功率發光二極體效能之提升: 1.雷射剝離成長在圖案化藍寶石基板上之氮化鎵磊晶層 2.以添加鑽石的Sn-3wt.%Ag-0.5wt.%Cu銲錫降低LED晶片接著材料的熱阻

High brightness GaN-based Light-emitting diodes (LEDs) have a great potential become the next generation solid state lighting source due to their advantages of high illumination, high efficiency, long life, small size, environmental protection. To achieve better light output performance, it is necessary to drive the LEDs at a higher current. More heat will be generated when the current is increase because the restriction of LED’s photoelectric conversion efficiency. Such heating caused degradation of LEDs. With increase in operation temperature, both luminous efficiency and reliability of LEDs decreased. As a result, thermal management is very important in High power LEDs. In order to achieve better thermal dissipation performance, thermal resistance of LEDs must reduce. Conventional GaN-LED are usually grown on sapphire substrate. The poor electrical and thermal conductivities of sapphire substrate have a negative effect on the LED performance, and increase the thermal resistance of LED chip. A conventional die-attach material is silver paste. But the very low thermal conductivity (4W/mK) of silver paste increase the thermal resistance of die-attach material. Therefore, improve the thermal dissipation performance of LED substrate and die-attach material were investigated in this dissertation. Pattern sapphire substrate (PSS) has been employed to improve both internal quantum efficiency (IQE) and light-extraction efficiency (LEE). Thin-Gan LED process can solve thermal dissipation problem, in which GaN LED epi-layer was stripped off and transferred to conductive substrates by wafer bonding and laser lift-off (LLO) technologies. It is obvious that a combination of the advantage of PSS-LED with the thin-GaN LED process will improve the LED performance. However, the critical laser energy of pattern substrate thin-GaN LED (PT-LED) was high, the yield rate was very low, and the leakage current was high. The requirement of high laser energy and the root cause of low yield and high leakage current were investigated by SEM, TEM and the calculation of laser energy on Gan/sapphire interface. When laser power was below critical laser power (920mJ/cm2), the laser energy density was not high enough to separate GaN from the sidewall of pattern. When laser power reached 920mJ/cm2, GaN was lifted from the sapphire substrate. The pattern shape and reflection of laser induce a extreme high energy area at the top of PSS. Thermal decomposition of GaN at this area yielding H 2 gas, theses gas penetrated/separate GaN/sapphire interface of the sidewalls of PSS. The high laser energy and “mechanical stress” by H 2 penetrated cause the deformation and an increase in leakage current. The melted sapphire adhesive to GaN and sapphire lead to low yield of PT-LED. Die-attached (DA) material bonds LED chips onto a packaging board. Conventional DA material is silver paste, but the very low thermal conductivity (4W/mK) make DA a heat dissipation barrier, posing problem to removal of heat generated by LED. To reduce thermal resistance of DA material, diamond add Sn-3wt.%Ag-0.5wt.%Cu solder (SAC305D) was used. In SAC305D DA material, gaps were found at diamond/solder interface in bare diamond particle (SAC305DB) and Ti-coated diamond particle (SAC305DT). No gaps were found in Ni-coated diamond particle (SAC305DN) and the thermal resistance was reduced. The reduction of area thermal resistance per unit thickness ( RA/h ) of SAC305DN to silver-paste (Ag-P), sinter-silver (Ag-S) and SAC305 were 92%, 73% and 52%. The thickness of DA material and interfacial thermal resistance of diamond/metal play an important role in thermal resistance of SAC305DN.