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姓名 李皓鈞(Hao-chun Lee) 查詢紙本館藏 畢業系所 機械工程學系 論文名稱 高電壓發光二極體晶片之熱電耦合模擬研究
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摘要(中) 高電壓發光二極體(HV LED)為一種以串聯的方式將多顆微晶粒連結而成的新式LED陣列結構，HV LED可透過全波整流器將交流電壓轉換成全波電壓或直接由直流電壓驅動點亮。且透過該技術可使LED在高的工作電壓下驅動並降低流過每顆微晶粒的電流。也因為HV LED小電流、多微晶粒的設計，因此提高電流分布的均勻性。
本研究以有限元素法建立一套可應用於直流及全波電壓輸入之數值模擬模型，該模型可用以計算及分析HV LED的電流密度與溫度分布型態。此外，亦透過接面溫度及光學特性之量測實驗與數值模擬之結果相驗證，且活化層之電流密度模擬結果也與實驗測得之光強度有一致性的分布。由數值模擬之結果可知，隨著HV LED的功率提升將使晶片的電流往電極周圍聚集，使得該區域產生較高的溫度。在固定直流電壓與全波電壓的平均輸入電功率條件下，全波電壓驅動時所產生的熱堆積較直流電壓驅動時少，擁有較低的接面溫度，故較能提升光輸出功率。透過積分球量測實驗，於280 mW的輸入條件下，直流及全波輸入之光功率分別為45.63 mW及54.48 mW，可證實全波電壓驅動之光功率較直流驅動為佳。
最後，利用我們提出之數值模擬模型可針對電極設計方式進行分析。在p電極設計方面，我們發現當p電極的側向長度越長時，越容易將電流聚集至n電極周圍，造成熱點現象進而使得晶片的接面溫度升高;當p電極的縱向長度上下兩端各增加40 μm時，能降低0.9 K的接面溫度。又當p電極上下端各縮短40 μm時，晶片的平均接面溫度則大約升高2 K。將原本的n電極形狀修改成與p電極相同的長條狀時，可增加每顆微晶粒的電流均勻性，且經修改後的n電極與p電極的上下兩端同時往縱向延伸40 μm時， 達準穩態後之接面溫度比原設計降了4.6 K。推測電極的縱向長度越長，能達到較佳的效益。
摘要(英) High voltage light-emitting diode (HV LED) is a novel chip array formed as a series connection structure by joining multi-microchips. HV LED can be operated not only by using the DC voltage directly but also by the full-wave voltage converted from the AC one via the full-wave rectification. HV LED technology can be used to drive the LED at high operated voltage so that the current in each micro-chip can be decreased. Since the HV LED is based on designs of multi-microchips and small working current, the current spreading of LED chip will be more uniform.
In this study, we propose and establish a numerical model using finite element method. This numerical model can be used to calculate and analyze the distributions of current density and temperature in HV LED under two operating situations, DC or full-wave. Moreover, the simulation results of our proposed model were verified by two measuring experiments, temperature and optical measurements. The simulation results of the current density distribution in the active layer are agreed with the measured ones obtained by the optical experiment. We found that the phenomenon of current crowding will appear more obviously around the electrode edge when the input power is increased.This phenomenon also causes that the temperature near the crowded area is raised. When the input power is at 280mW, the light output powers of the HV LED by operating at DC and full-wave voltages are 45.63mW and 54.48mW, respectively. Because the HV LED driven by full wave voltage can decrease the heat accumulation, they will have lower junction temperature. Thus, the full-wave driving condition is better than the DC one under the same input power.
Finally, our proposed model can be further used to analyze the design of the electrode pattern. For the p electrode design, the current crowding effect will appear at the n electrode edge when the lateral length of p electrode is increased. Then the hot spot phenomenon at the n electrode edge is generated, the junction temperature in LED chip will be also increased due to the more serious current crowding at the n electrode edge. When the p-electrode is enlarged to the length of 40μm, the junction temperature can be reduced about 0.9K. When the length of p-electrode is reduced as 40μm, the junction temperature will be arisen about 2K. When we change the n-electrode pattern like the long narrow strip one, the current density distribution is more uniform on each micro-chip. Moreover, the p-electrode and modified n-electrode are both extended as 80μm; the junction temperature in LED chip at quasi-steady state is 340.5K (4.6K lower than the conventional one). The more extended length, the better thermal and electrical behaviors.
關鍵字(中) ★ 接面溫度
★ 全波電壓
★ 有限元素法
★ 高電壓發光二極體關鍵字(英) ★ high voltage LED
★ finite-element method
★ junction temperature
★ full-wave voltage論文目次 目錄
中文摘要 ............................................. i
Abstract ............................................. ii
致謝 ................................................. iv
目錄 ................................................. v
圖目錄 ............................................... viii
表目錄 ............................................... xi
符號說明 ............................................. xii
第一章 緒論 ..........................................1
1-1 前言 .............................................1
1-1-1 研究背景........................................2
1-1-2 白光發光二極體..................................2
1-2 相關研究 .........................................4
1-2-1 電流壅塞之改善及晶片熱管理技術..................4
1-2-2 交流電驅動發光二極體之進展......................5
1-3 高電壓發光二極體 .................................7
1-4 研究動機及目的 .................................. 9
第二章 理論基礎與數值方法 ...........................15
2-1 發光二極體之發光原理 ............................15
2-2 求解方法與分析步驟 ..............................16
2-3 電場之相關理論 ..................................17
2-3-1 統御方程式及邊界條件 ..........................17
2-3-2 活化層之等效導電率假設 ........................20
2-4 溫場之統御方程式及邊界條件 ......................21
第三章 HV LED量測系統及實驗方法 .....................25
3-1 接面溫度量測理論 ................................25
3-2 HV LED 接面溫度量測系統 .........................26
3-2-1 HV LED 溫度敏感參數之量測方法 .................27
3-2-2 HV LED 接面溫度之量測方法 .....................28
3-3 HV LED之光學特性量測系統 ........................28
3-3-1 HV LED 二維光強度分布之量測 ...................28
3-3-2 HV LED 光輸出功率之量測 .......................29
第四章 結果與討論 ...................................34
4-1 HV LED接面溫度量測結果 ..........................34
4-1-1 全波電壓輸入之接面溫度量測 ....................34
4-1-2 直流電壓輸入之接面溫度量測 ....................35
4-2 HV LED熱電耦合之相關模擬設定 ....................35
4-3 HV LED電流密度分布及溫度模擬結果.................37
4-3-1 直流電壓輸入之熱電耦合模擬.....................37
4-3-2 全波電壓輸入之熱電耦合模擬.....................39
4-3-3 相同功率下全波與直流電壓輸入之討論.............40
4-4 HV LED之電極設計.................................41
第五章 結論與未來發展 ...............................66
參考文獻 .............................................68
圖目錄
圖1-1 A) RGB LEDs、B)UV LED +RGB phosphor 、C) Blue LED +Yellow phosphor示意圖及其放射波段圖..................10
圖1-2 LED接面溫度溫度與光輸出功率關係圖..............10
圖1-3 指叉型陣列晶片(IMPA)結構示意圖.................11
圖1-4 交流/直流轉換器示意圖..........................11
圖1-5 AC LED 直接使用交流電源點亮情形................12
圖1-6 AC操作下平行式設計正負週期點亮圖...............12
圖1-7 (a)惠斯同電橋之電路(b)AC LED正負週期點亮圖.....13
圖1-8 SBD-ACLED晶粒之剖面結構圖......................13
圖1-9 晶元光電之HV LED結構...........................14
圖2-1 p-n 接面示意圖 (a)未接合 (b)接合後.............23
圖2-2 (a)零偏壓下之p-n接面 (b)順向偏壓下的p-n接面....23
圖2-3 數值模擬之流程圖...............................24
圖3-1 HV LED 之電流電壓曲線(I-V curve)...............30
圖3-2 全波整流器外觀及電路圖.........................30
圖3-3 HV LED接面溫度量測系統.........................31
圖3-4 HV LED於小烤箱內之情形.........................31
圖3-5 HV LED 於樣品測試箱內之情形....................32
圖3-6 HV LED 輸入全波電壓時之電流電壓波型............32
圖3-7 發光強度分布量測系統統.........................33
圖4-1 HV LED 之結構圖................................44
圖4-2 HV LED 點亮之情形..............................44
圖4-3 HV LED 在Vrms為28.7V下之電流與溫度關係圖.......45
圖4-4 電壓波型初始及達準穩態之電流波型(Vrms=31.82V)..45
圖4-5 HV LED 在 VDC 為 40.6V 下之電流與溫度關係圖....46
圖4-6 SEM下之 HV LED 剖面結構........................47
圖4-7 HV LED 之物理模型(a)晶粒剖面示意圖(b)整體結構
(c)晶片配置....................................48
圖4-8 HV LED 之網格示意圖............................49
圖4-9 三種網格總數下之電流密度在單一微晶粒之X-軸剖面
分布..........................................49
圖4-10 在ITO、發光層及n-GaN之電流密度分布............50
圖4-11 第一橫排微晶粒活化層電流密度與光強分布圖......51
圖4-12 第二橫排微晶粒活化層電流密度與光強分布圖......51
圖4-13 第三橫排微晶粒活化層電流密度與光強分布圖......52
圖4-14 在DC 43.8V驅動下之溫度分布 (a) 活化層
(b) 整體晶片..................................52
圖4-15 量測與模擬上隨不同直流電壓驅動的電流值........53
圖4-16 量測與模擬上隨不同直流電壓驅動的接面溫度值....53
圖4-17 HV LED 經由小到大的直流輸入功率下得到之
光輸出功率....................................54
圖4-18 t=0.004167s下之電位分布圖(Vrms=35.36V) .......54
圖4-19 1/60s 內的電流密度及溫度隨時間的變化圖
(a)Vrms=31.82 V (b)Vrms=35.36 V ..............55
圖4-20 HV LED 接面溫度於Vrms=31.82V及Vrms=35.36V
操作下之振盪情形..............................56
圖4-21 在Vrms=31.82V與Vrms=35.36V操作下於電壓峰值時，
位於活化層的電流密度分布圖....................56
圖4-22 在Vrms=31.82V與Vrms=35.36V操作下於電壓峰值時，整體 晶片之溫度分布圖..............................57
圖4-23 在相同功率下直流輸入之電流電壓值與全波輸入之
電壓電流波型..................................57
圖4-24 於DC 43.8V與Vrms=35.36V 的電壓輸入下，光輸出功率隨 著點亮時間之變化圖............................58
圖4-25 將 p 電極側向長度延伸之示意圖 (a)L'=50μm
（b) L'=100μm.................................58
圖4-26 在Vrms=35.36V之電壓峰值時三種不同的p電極位於活化層 之電流密度及溫度分布 (a) L'=0μm (b) L'=50μm (c) L'=100μm......................................59
圖4-27 將 p 電極縱向長度延伸之示意圖 (a) L'= 40μm (b) L'= -40μm....................................60
圖4-28 在Vrms=35.36V之電壓峰值時兩種不同的p電極位於活化層 之電流密度及溫度分布(a)L'=40μm(b)L'=-40μｍ..60
圖4-29 於Vrms=35.36V之電壓峰值(t=1.4875s)時，不同p電極形式 之晶片溫度分布圖 (a)側向延伸100μm(b)側向延伸50μm
(c)原設計(d)縱向延伸40μm (e) 縱向縮短40μm.....61
圖4-30 於Vrms=35.36V輸入下活化層中心溫度隨時間變化圖..62
圖4-31 將 p、n電極修改之示意圖 (a) n電極與p電極同長
(b) p、n電極皆縱向延伸40μm，加上右下方微晶粒之p電極 側向延伸180μm.................................62
圖4-32 在Vrms=35.36V之電壓峰值時，兩種 n 電極設計位於
活化層之電流密度及溫度分布(a)n電極與p電極同長
(b)p、n電極皆縱向延伸40μm加上右下方微晶粒之p電極
側向延伸180μm.................................63
圖4-33 於Vrms=35.36V輸入下，原設計與兩種n電極改良設計之活 化層中心溫度隨時間變化圖......................63
表目錄
表4-1 不同平均功率下的接面及基板溫度.................64
表4-2 數值模擬中使用之導熱性.........................64
表4-3 數值模擬中使用之比熱及密度.....................65
表4-4 輸入功率為280 mW之接面溫度比較.................65
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指導教授 陳志臣(Jyh-chen Chen) 審核日期 2011-7-25 推文 plurk
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