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|Title: ||陶瓷基板上的高壓薄膜氮化鎵發光二極體之設計、製作與分析;Design, fabrication and analysis of high-voltage thin-film GaN LEDs on ceramic substrates|
|Issue Date: ||2014-10-15 14:45:16 (UTC+8)|
|Abstract: ||為了進一步提高發光二極體亮度和減少成本，發光二極體業者傾向於製作高功率和大面積發光二極體以減少晶粒製作和封裝成本。然而元件隨著操作功率與發光面積的增加，伴隨而來的熱和電流聚集使得效能下降，而此一現象又以藍寶石為基板的發光二極體更為嚴重。本論文提出一種結合了晶圓黏合、雷射剝離和高壓串聯製程，成功將氮化物薄膜移轉到具有高導熱係數的陶瓷基板上(230 W/m•K)。|
在中尺寸發光二極體方面(508*1066 um2)，我們證實了在陶瓷基板上具有3個微晶粒串聯的發光二極體，由於良好電流擴散使得在電流密度200 A/cm2，相較於同樣在陶瓷基板上非串聯發光二極體的插電效率提升26.7%。
在大尺寸發光二極體方面(1143*1143 um2)，我們在陶瓷基板上設計不同微晶粒串聯個數並搭配不同比例負電極面積的高壓薄膜氮化物發光二極體，試圖找出最佳化設計。我們發現雖然微晶粒串聯數目愈多，電流傳遞更為均勻，因而單一微晶粒有較低電壓輸出，但同時也因為正電極面積下降導致光輸出減少，因此最佳串聯數目為4個和9個並分別搭配 4.6% 和2.7% 負電極面積/發光區面積，使得在電流密度27 A/cm2的插電效率相較於在陶瓷基板上非串聯發光二極體提升6.4%。
我們比較三種不同結構大尺寸發光二極體(1143*1143 um2) 光電特性隨著電流密度的變化。其中包含了在矽基板上垂直導通氮化物薄膜發光二極體、藍寶石基板上具有16個微晶粒串聯發光二極體以及在陶瓷基板上具有16個微晶粒串聯發光二極體。我們發現雖然在矽基板上垂直導通氮化物薄膜發光二極體電流擴散不如藍寶石基板上具有16個微晶粒串聯發光二極體，但由於矽基板導熱係數(150 W/m•K) 優於藍寶石(36 W/m•K)，因此具有較高的飽和電流。而在陶瓷基板(230 W/m•K) 上具有16 個微晶粒串聯發光二極體除了良好電流擴散能力再加上比矽基板(150 W/m•K) 更好導熱係數，使得飽和電流密度能夠高於450 A/cm2 (電功率密度1800 W/cm2)。
;In order to further push the performance/cost ratio of solid state lighting, LED manufacturing favors the products with high operation power and large chip sizes, which can greatly save material cost in device fabrication and packaging. However, the devices with increased input power and emitting area are constantly haunted by severe thermal degradation and current crowding, which are the contributing factors to the undesired efficiency droop. The problem is particularly difficult for sapphire-based devices considering the poor thermal conductivity of the substrate. In this dissertation, III–nitride blue LEDs were successfully fabricated on ceramic substrates (thermal conductivity: 230 W/m•K) using thin-film and high-voltage processes.
In middle size aspect (508*1066 um2), we demonstrated ceramic-based high-voltage thin-film GaN LEDs comprising serially connected 31 sub-cells has 26.7% improvement in wall-plug efficiency at the current density of 200 A/cm2 comparing to 1*1 sub-cell owing to its superior current spreading.
In large size aspect (1143*1143 um2), we designed ceramic-based high-voltage thin-film GaN LEDs comprising serially connected 2*2, 3*3 and 4*4 sub-cells, which are fabricated with different n-electrode areas to optimize the wall-plug efficiency. We found that although current spreading can be improved by increasing the cell numbers, leading to lower voltage/cell characteristic and enlarge emitting area. However, owing to the loss of emitting area caused by the increased area of isolation trenches, the output power and the wall-plug efficiency decrease when the cell number exceeds 9 (3*3). Furthermore, 2*2 and 3*3 sub-cells with 4.6% and 2.7% n-electrode/mesa respectively show the optimized design, the wall-plug efficiency are improved by 6.4% comparing to 1*1 sub-cell.
We compared electrical-optical characteristics with increasing current density for large size (1143*1143 um2) light emitting diodes with three different kinds of structures. It include Si-based vertical thin-film LED, sapphire-based LED comprising serially connected 4*4 sub-cells and ceramic-based thin-film LED comprising serially connected 4*4 sub-cells. We found that although the current spreading of Si-based vertical thin-film LED worse than that of sapphire-based LED comprising serially connected 4*4 sub-cells, however, owing to better thermal conductivity of Si (thermal conductivity: 150 W/m•K) than sapphire (thermal conductivity: 36 W/m•K), the saturation current of Si-based vertical thin-film LED is superior to sapphire-based LED comprising serially connected 4*4 sub-cells. For the ceramic-based thin-film LED comprising serially connected 4*4 sub-cells, it simultaneously holds advantages on heat sinking and current spreading, leading to the saturation current density larger than 450 A/cm2, which is better than those of the devices fabricated with identical epitaxial structure on Si or sapphire substrates.
|Appears in Collections:||[光電科學研究所] 博碩士論文|
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