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研究生： 杜昇翰
Sheng-Han Tu
論文名稱： 整合特殊晶粒製程與二次光學元件之發光二極體照明模組
Integration of special chip process and secondary elements for light emitting diodes illumination module
指導教授： 張正陽
Jenq-yang Chang
口試委員:
學位類別： 博士
Doctor
系所名稱： 理學院 - 光電科學與工程學系
Department of Optics and Photonics
畢業學年度： 98
語文別： 英文
論文頁數： 147
中文關鍵詞： 二次光學元件 、發光二極體 、光萃取效率 、固態照明
外文關鍵詞： light extraction efficiency, solid state lighting, light emitting diodes, secondary optical elements
相關次數： 點閱：9  下載：0 
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    • 為因應日漸短缺的地球資源，因此各國均致力於新能源與節能科技。因此採用低能耗、體積小與高使用壽命之發光二極體為光源之照明技術，已經成為各國爭相發展的目標。本論文整合特殊晶粒製程與二次光學元件之照明模組，以為各式光源應用；先將微結構製程與材料特性改質技術整合至發光二極體晶粒製程中，對發光特性進行調制，再針對調制後的光學特性設計可匹配之二次光學元件，整合成照明模組，豐富發光二極體之發光特性，並使其在液晶背光模組、投影機與路燈應用上取得良好的表現。
    本論文採用的製程技術涵括：室溫壓印、表面粗化、電極特性改質、電極結構優化，與共振模態波濾波器(Guided mode resonance filter)元件來提升發光二極體的出光效率，並調制其發光特性。二次光學元件則用來進行發光二極體之遠場光型(Far-field pattern)調制，以達到準直或擴展的遠場光型，以滿足不同的照明需求。
    為提升發光二極體的出光效率，並調制其發光特性，本論文採用無熱應力之室溫壓印技術，配合化學及物理性質穩定之旋轉塗佈玻璃(Spin on glass)壓印材料，製作一維與二維之表面結構於發光二極體的晶粒表面。它可得到17%至35%的外部出光效率增益；在發光特性上，閃曜式光柵(Blazed grating) 結構可以得到主發光強度偏折20°的遠場光型，而二維柱狀結構，則可以得到光強均勻分布散角達110°之擴展的遠場光型；這樣的光源特性，可應用在滑鼠及路燈等照明應用。
    傳統鉻金電極之吸收係數大，導致發光二極體的出光效率不彰。因此本研究採用高反射的銀鍍層來增加鉻金電極的底面反射率，經由數值模擬的分析，此可以大幅提升發光二極體的側面出光率；並透過p-型氮化鎵重摻雜的方法來降低該銀鍍層與p-型氮化鎵的接面電阻；濕蝕刻則用來增加透明氧化導電薄膜的表面粗糙度，以進一步提升發光二極體的外部取光效率。總合上述晶粒製程後，其電特性並未受到不良影響，而發光二極體的正面與側面出光率可大幅改善，總體光萃取效率可以增加達30%。
    為了探究發光二極體在高電流注入下所產生的電流擁擠(Current crowding)效應，本論文配合機械所陳志臣老師實驗室所開發之三維發光二極體電流數值模型以模擬空間電流散佈，並用實驗結果以驗證不同n-電極結構(包括不同遮蔽面積與不同空間密度)對薄膜(Thin GaN)發光二極體電流密度的影響。實驗結果顯示不同n電極結構所造成的電流擴散趨勢與模擬結果相當吻合。模擬與實驗結果均指出，電流擴散效應較好的n-電極結構，其電壓-電流與電流-出光特性均較優秀，在注入電流達1安培的狀況下，電流擴散較好的n-電極之出光效率的增益可逹11%。
    為了純化發光二極體的發光色度，使其在三色背光模組的應用上取得較佳的色域表現，本論文針對發光頻寬較寬的綠光二極體的頻譜進行縮減設計。為了適應綠光發光二極體的多角度出射與非極化的出光特性，本論文採用雙填充因子(Filling factor)設計了一個波導模態共振元件，以提供帶通頻帶寬(30nm)、大的角度容忍度(15度入射容忍度)與低的極化相依性(適用於亂數極化光)，並將其與綠光發光二極體整合成背光模組，可將綠光發光二極體的頻譜寬度縮減為原來的二分之一。經由色域模擬顯示這樣的背光模組，可使色域表現由原本的122提升至137。
    本研究整合壓印技術所得到的擴展遠場二極體及反射式二次光學元件，以開發一適用於路燈之照明光源。本論文藉由貝茲曲線設計一高度為0.3厘米，直徑為1.05厘米之杯狀反射光二次光學元件，以減少光在穿透不同介面時的浮瑞涅損耗(Fresnel loss)。在整合壓印發光二極體與該二次光學元件後，相較於現行路燈光源，該光源之發光表現為在出光角度正負40度的區間中，可提升40%的照明亮度；在出光角度正負55度的區間中，維持了一恆定的照明強度；在出光角度正負70度上所產生的出光峰值，則可彌補光強餘弦衰減；最後則是削減了出光角度大於正負85度的光強以抑制刺眼的炫光效應。

    For the sake of energy shortage, the developments of new energy and energy saving have attracted the interests of advanced nations. The light emitting diodes possesses advantages such as low power consumption, compact volume and long life time so that it has took the place of conventional light source gradually. In this thesis we developed a series of methods that to crossed the chip process and lighting module enhance the light performance of light emitting diodes. We integrated special chip process and secondary optics element to form a lighting module that can be applied to different applications such as back light module of liquid crystal display, projector and street lamp.
    The adopted methods include imprinting technique, pad reflector, surface roughness, ThinGaN LED pattern design, the guided mode resonance (GMR) filter to enhance the output power efficiency of LED and modulate the lighting performances. The secondary optics elements were used to modulate the far-field pattern of LED to achieve an expanded or a collimator far-field pattern.
    In order to increase the light extraction efficiency and modulate the lighting performance of LED, we adopted the thermal stress free and room temperature imprinting technique. We imprinted the one and two dimension onto the chip surface by stable material SOG. After imprinting structure application, the output power enhancement reached 17% to 35%. Furthermore, the blazed grating can deflect the peak intensity of far-field pattern to 20° and the two dimensional structure can achieve an expansion far-field pattern.
    A GaN-based light-emitting diode (LED) with non-alloyed metal contacts and textured Ga-doped ZnO (GZO) contact layer were served as the n- and p-type electrode pads, respectively. Compared with the conventional LEDs with flat surface and Cr/Au metal contacts, the non-alloyed Ag/Cr/Au contacts used in the present experimental LEDs play the role of reflector to prevent the emitted light from absorption by the opaque electrode pads. Enhancement of light output power observed from the experimental LEDs is also due to the textured GZO layer that can disperse the angular distribution of photons at the GZO/air interface. With an injection current of 20mA, the enhancement of the LOP approximately has a 30% magnitude compared with conventional GaN-based LEDs. Finally, the numerical method was used to discussion the relation between output power and pad reflectivity.
    Several n-type electrode patterns were designed to evaluate the current spreading effects in high power ThinGaN light emitting diodes. A proposed three dimensional numerical simulation was used to investigate the current spreading distributions. The experimental current spreading tendencies in various n-type electrodes were consistent with the simulation results. The maximum lighting output power was enhanced to 11% in our electrode pattern designs. The current-voltage and luminance-current performance of LED chips can apparently be improved with a better current spreading distribution. Therefore, this three dimensional simulation method could be used for the advanced analysis and optimization of LED performance.
    A simple and hybrid combination of a green light-emitting diode (LED) chip with an asymmetric guided-mode resonance (GMR) filter is proposed to reduce the full-width-at-half-maximum (FWHM) of LED emission spectrum for the LED backlight system. The color gamut consisting of multiple LEDs is significantly expanded from 122 to 137. It also possesses stable transmittance within 5 degree incident angle for the unpolarized light. This GMR filter provides superior transmittance efficiency (84%), and FWHM performance (15nm). The fabrication tolerances of asymmetric GMR are also analyzed and discussed.
    A cost effective, high throughput, and high yield method for the increase of street lamp potency was proposed in this paper. We integrated the imprinting technology and the reflective optical element to obtain a street lamp with high illumination efficiency and without glare effect. The imprinting technique can increase the light extraction efficiency and modulate the intensity distribution in the chip level. The non-Lambertian light source was achieved by using imprinting technique. The compact reflective optical element was added to efficiently suppress the emitting light intensity with small emitting angle for the uniform of illumination intensity and excluded the light with high emitting angle for the prevention of glare. Compared to the convectional street lamp, the novel design has 40% enhancement in illumination intensity, the uniform illumination and the glare effect elimination.

    Abstracts (in Chinese)…………………...……………………………………...I Abstracts...………………….…………………………………………………IV Contents...…………………………………………………………………….VII List of Figures………………………………………………………………….X List of Tables…………………………………………………………….....XVII Chapter 1 Introduction…..…………………….………..………………..1 Chapter 2 Paper review……………………………………………..8 2.1 Light extraction efficiency enhancement………………………………..8 2.2 Far-field pattern modulation……………………………………………18 Chapter 3 The light enhancement and far-field pattern modulation by the imprinting structure.…..…..…..….…23 3.1 Introduction……………………………………………….….…..……23 3.2 Experiment of LED chip and imprinting process………….…….……24 3.3 Output power enhancement and electric performance.……..................30 3.4 Brief conclusion.…………………………………………………........39 Chapter 4 Improvement of electrode property and structure for LED light extraction……...…………...................……..40 4.1 Pad reflector and TCL roughness……………………………………...40 4.1.1 Introduction…………………………………….….…………….40 4.1.2 Experiment chip and pad reflector process…………….………..41 4.1.3 Simulation of output power enhancement………………………48 4.1.4 Brief conclusion………………………………….……………..51 4.2 The n-pad pattern designs on thin GaN LED…….…….…….……...…52 4.2.1 Introduction………………………………………..………………52 4.2.2 Thin GaN fabrication and current density distribution simulation……………………………….……………………....53 4.2.3 Current spreading and electric performance……………….……...58 4.2.4 Brief conclusion……………………………………………….…..68 Chapter 5 Emitting spectrum width reduction by high angular tolerance GMR filter……...…….…………………….……69 5.1 Introduction……………………...……..……………………………...69 5.2 The principle of GMR filter………………...………………………….69 5.3 Angular tolerance analysis………………………...….………………..75 5.4 Color gamut analysis versus fabrication tolerance………....………….77 5.5 Brief conclusion………………………………………………………..79 Chapter 6 Secondary optics elements design for light source module………………………………………………………....81 6.1 Collimator elements……………………………………………………81 6.1.1 Introduction……………………………………………………...81 6.1.2 Simulation methods……………………………………………..81 6.1.3 Description of the new collection systems…………..………….83 6.1.4 Tolerance analysis…………………………………….…….......91 6.1.5 Brief conclusion………………………………………………...93 6.2 Integration of non-Lambertian LED and reflective optical element as efficient street lamp…………..………………………………………...95 6.2.1 Introduction…………..………………………………………….95 6.2.2 Imprinting and chip process…….…………….…………………98 6.2.3 Measurements………………………..……….…………..……102 6.2.4 Optical design and simulation…………...…………………….105 6.2.4 Brief conclusion……………………………..…………………109 Chapter 7 Summary and future work…….…………….……………111 Reference………………..……………………………………………….…116 Publication List………………………………………………………..…..129 List of Figures Fig. 1-1 Three parts of LED industry……………………………...…………….3 Fig. 1-2 The research issues of LED chip……………………………………….3 Fig. 1-3 The native far-field pattern of planar LED chip…………..…..………..5 Fig. 2-1 Analysis of the emitting light trapped inside different structure……….8 Fig. 2-2 The transmittance of transparent conductive layer versus wavelength.10 Fig. 2-3 The applied voltage versus current for different transparent conductive layer…………………………………………………………………...10 Fig. 2-4 The roughness of GaN surface………………………………………...11 Fig. 2-5 The photonic crystal fabricated on the GaN LED surface…………….11 Fig. 2-6 The structure scheme of photonic crystal applied on to the p-GaN surface...………………………………………………………………12 Fig. 2-7 The output power and electrical performance versus different structure period of photonic crystal LED chip………………………………….13 Fig. 2-8 The defect density difference resulted from the (a) conventional sapphire substrate and (b) pattern sapphire substrate…………………15 Fig. 2-9 The scattering photons caused by the pattern sapphire substrate……..16 Fig. 2-10 The different pad patterns for the current simulation………………..17 Fig. 2-11 The simulation result of output power and light extraction efficiency in different pad structures………………………………………………..17 Fig. 2-12 The structure of LED projector………………………………………19 Fig. 2-13 The theory of taper light pipe for LED projector application………..19 Fig. 2-14 The LED street lamp composed of the LED lighting module, the secondary optics devices and the thermal module……………………20 Fig. 2-15 The intensity distribution on the illumination area by an LED street lamp..………………………………………………………………….21 Fig. 3-1 The Lambertian far-field pattern of a native LED bare chip……..…...24 Fig. 3-2 The ray deflection to an expected direction by the embossed microstructure…………………………………………………………25 Fig. 3-3The flow chart of imprinted LED process: (a) the LED mesa etching (b) The deposition of Ni/Au TCL and the spinning of SOG (c) The imprinting process with Si mold and 1000 N pressure and (d) The additional SOG removing and pad deposition...………..……………...27 Fig. 3-4 The optical microscope pictures of the imprinting structures: (a) The optical microscope picture of SOG after soft baking (b) The optical microscope picture of 1D blazed grating (c) The optical microscope picture of 2D cylinder array…………………………………………29 Figs. 3-5 AFM images and geometric schemes of imprinted SOG structures: (a) AFM picture of 1D blazed grating structure (b) 1D blazed grating geometric scheme (c) AFM picture of 2D cylinder array structure (d) 2D cylinder array geometric scheme………………………………...31 Figs. 3-6 The electrical and optical performance of LEDs with and without imprinted structures: (a) Output power of LEDs with and without embossed structure, and (b) I-V curves of LEDs with and without embossed structure…………………………………………….…….33 Fig. 3-7 The equipment setup for far-field pattern measurement………………35 Fig. 3-8 Far-field patterns of LEDs with embossed 1D blazed grating, 2D cylinder structure, and without the embossed structure…………......36 Fig. 3-9 The illustration of LED far-field pattern modulation resulted from 1D blazed grating………………………………………………………..37 Figs 4-1 (a) schematic device structure and (b) photograph of GaN-based LEDs with reflective electrode pads and textured GZO transparent contact layer. The inset is a typical SEM image taken from etched GZO surface……………………………………………………………….43 Fig. 4-2 Typical I-V characteristics of the LEDs with the non-alloyed Ag/Cr/Au (LED-I) and Cr/Au (LED-II) electrodes…………………………….44 Figs. 4-3 Light output power versus injection current for the LED-I, LED-II and LED-III. The insets show the schematic light ray traces in a specular (a) and textured (b) surface corresponding to LED-I and LED-II (c)schematic cross-section device structure and light ray tracing of LED-I………………............................................................................46 Fig. 4-4 The output power enhancement versus the pad reflectivity………...…49 Fig. 4-5 The discussion of output power enhancement that come from different surface……………………………………………………………..….51 Fig 4-6 Flow charts of the GaN-based laser lift-off LED process in the experiment: (a) GaN-based LED epi-structure (not to scale); (b) chip isolation by introduced coupled plasma etcher; (c) contact metal deposition by electron beam; (d) an LED chip pasted to the electroplated Cu substrate; (e) removing the sapphire substrate with a KrF excimer laser lift-off; (f) n-GaN contact deposition by E-gun; and (g) optical microscope picture of a thin GaN LED chip…..………….55 Fig. 4-7 N-pad geometric parameters for the A and B series…………………..57 Fig. 4-8 Performance of A series pattern designs in the experiment: (a) injection current versus forward voltage and (b) injection current versus output power…………………………………………………………………60 Fig. 4-9 Emission intensity distributions of A series LED chip surfaces in the experiment………………………………………………...…………..61 Fig. 4-10 Performance of B series pattern designs: (a) injection current versus forward voltage and (b) injection current versus output power………62 Fig. 4-11 Emission intensity distributions of B series LED chip surfaces in the experiment…………………………………………………………….63 Fig. 5-1 The combination of the GMR filter and LED chip……………………72 Fig. 5-2 The structural parameters of the GMR filter…………………………..72 Fig. 5-3 The transmittance spectrum of the GMR filter, the LED-emitting spectral profile, and the filtered LED-emitting spectral profile………75 Fig. 5-4 The transmittance spectrum of the GMR filter with different incident angles………………………………………………………………….77 Fig. 5-5 The color gamut analysis for different fabrication tolerance levels…..79 Fig. 6-1 Relative positions between LED chips………………………………..82 Fig. 6-2 Structure of the traditional CPC……………………………………….84 Fig. 6-3 The energy distribution and collection efficiency of the traditional CPC: (a) Energy distribution of the traditional CPC and (b) Collection efficiency of the traditional CPC……………………………………...85 Fig. 6-4 Structure and ray tracing of New Design I……………………………86 Fig. 6-5 The energy distribution and collection efficiency of the New Design I: (a) Energy distribution for New Design I and (b) Collection efficiency for New Design I………………………...……………………………87 Fig. 6-6 Structure and ray tracing of New Design II…………………………...88 Fig. 6-7 The energy distribution and collection efficiency of the New Design II: (a) Energy distribution for New Design II and (b) Collection efficiency for New Design II……………………………………………………..89 Fig. 6-8 Structure and ray tracing of New Design III…………………………..90 Fig. 6-9 The energy distribution and collection efficiency of the New Design III: (a) Energy distribution for New Design III and (b) Collection efficiency for New Design III…………………………………………………....91 Fig. 6-10 Photograph of New Design I………………………………………...94 Fig. 6-11 Photograph of New Design III……………………………………….94 Figs. 6-12 The flow chart of imprinting process (a) The SOG layer spun onto the surface of LED chip (b) The imprinting process in chamber (c) The LED chip just separated from Si mold (d) The LED chip after removing SOG recover the pad area. (not to scale)……………………..……100 Figs. 6-13 The pictures and dimension scheme of imprinting structure (a) the OM top view of imprinting structure (b) the AFM tilt view of imprinting structure (c) the imprinting structure geometric parameters (not to scale)..………………………………………………………101 Figs. 6-14 The electric performance of imprinting and planar LED (a) The applied voltage versus current curve (b) The injection current versus luminous curve (c) The intensity distributions of planar and imprinting LED.………………………………………………………………...104 Fig. 6-15 The practical application of the imprinting LED chip (a) the side view of designed reflector for street lamp (b) The tilt view of designed reflector for street lamp (c) The far-field pattern of designed street lamp and OSRAM commercial product…………………………………108 Fig. 7-1 The summary of issues of LED output power enhancement and the corresponding methods proposed in this thesis……………………...113 Fig. 7-2 The summary of LED far-field pattern and emission spectral width modulation………………………………………………………...…114 Table list: Table 4-1 Comparisons between the results in simulation and experiment for B series samples………………………………………………………..66 Table 6-1 Characteristics of adopted LEDs……………………………….……82 Table 6-2 Tolerance analysis……………………….…………………………..92 Table 6-3 The street lamp design specifications…………………………....…105 Table 6-4 Specification comparisons between with designed street lamp and Golden Dragon with ARGUS lens………………………..………..109

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