| 摘要: | 本篇論文中，我們成功的將thin-GaN 發光二極體(Lignt emitting diode，LED)鍵合在氮化鋁基板上，量測並分析thin-GaN LED鍵合在氮化鋁基板的光、電及導熱特性，並同時與鍵合在矽基板的thin-GaN LED做比較。 本研究使用單面拋光的氮化鋁基板，由原子力顯微鏡量測可知氮化鋁表面粗糙度約為40 nm；利用3-ω量測法測得氮化鋁基板及矽基板的熱導率分別為179 W/m-K及130 W/m-K。 利用金-銀晶圓鍵合及雷射剝離技術將高功率thin-GaN LED分別鍵合在380 μm厚、630 μm厚的氮化鋁基板及525 μm厚的矽基板上。LED的尺寸為1 × 1 mm2。當操作電流為350 mA，此三種元件測得的順向偏壓皆約為4 ± 0.2 V，發光強度分別為32 ± 4 mW、34 ± 5 mW及33 ± 7 mW，thin-GaN LED鍵合在氮化鋁基板與鍵合在矽基板的光電特性相同，因此氮化鋁適合用來作為thin-GaN LED的鍵合基板。利用順向偏壓法量測元件封裝後的接面溫度及熱阻，當操作電流為350 mA，此三種元件的接面溫度分別為112 ± 5 oC、113 ± 7 oC、117 ± 5oC，熱阻分別為18 ± 4 oC/W、18 ± 1.4 oC/W、17.6 ± 4.3 oC/W，顯示此三種元件具有相同的接面溫度及熱阻。由於氮化鋁的熱傳導率比矽高，因此LED鍵合在氮化鋁基板的熱傳導特性應比鍵合在矽基板上佳。但氮化鋁表面較粗糙，導致氮化鋁與元件的鍵合面有較大的孔隙，使得元件的熱傳導特性變差，造成元件鍵合在兩種基板上的熱傳導差異變得不明顯。 In this thesis, we demonstrate thin-GaN LEDs bonded on AlN substrate. The electric, optical and thermal properties of thin-GaN LEDs bonding on AlN and Si substrates were analyzed and compared. One side published AlN substrate was used in this study. Root-mean-square (RMS) roughness of published surface was about 40 nm. 3-ω method was used to determine the thermal conductivity of AlN and Si substrates. The thermal conductivities of AlN and Si substrates were 179 W/m-k and 130 W/m-k respectively. LED wafers were bonded on 380-μm-thick AlN, 630-μm-thick AlN, and 525-μm-thick Si substrates by Au-Ag bonding method. After wafer bonding, laser lift-off method was employed to take sapphire substrate off. Then thin-GaN LEDs with a chip size of 1 × 1 mm2 were fabricated. Forward voltages of these three kinds of LEDs with an input current of 350 mA were all about 4 V. The output power of LEDs bonding on 380-μm-thick AlN, 630-μm-thick AlN, and 525-μm-thick Si substrates which was measured in an input current of 350 mA is about 32 ± 4 mW, 34 ± 5 mW, and 33 ± 7 mW, respectively. This indicated that the electric and optical performance of thin-GaN LED bonded on AlN is as good as LEDs bonded on Si substrate. The thermal resistances and junction temperatures of LEDs were measured by diode forward voltage method. The junction temperatures of LEDs bonded on 380-μm-thick AlN, 630-μm-thick AlN, and 525-μm-thick Si substrates were about 112 ± 5 oC、113 ± 7 oC and 117 ± 5oC , respectively. The thermal resists of LEDs bonding on 380-μm-thick AlN, 630-μm-thick AlN, and 525-μm-thick Si substrates were about 18 ± 4 oC/W、18 ± 1.4 oC/W and 、17.6 ± 4.3 oC/W, respectively. Since thermal conductivity of AlN is higher than that of Si, thin-GaN LEDs bonded on AlN substrate should have better heat dissipation than LEDs bonded on Si substrate. However, the difference of thermal resistances between LEDs bonded on 380-μm-thick AlN, 630-μm-thick AlN, and 525-μm-thick Si substrates is not obvious. This should be due to that surface roughness of AlN was larger than that of Si therefore more voids were formed between Au-Ag interface when bonded on AlN. The voids between Au-Ag interface would result in the increase of thermal resistance. Hence the difference of thermal resistances between LEDs bonded on AlN and Si substrates is not obvious. |
