Nitride-Based High-Power Flip-Chip LED With Double-Side Patterned Sapphire Substrate

A nitride-based high-power flip-chip (FC) light-emitting diode (LED) with a double-side patterned sapphire substrate (PSS) was proposed and realized. Under 350-mA current injection, it was found that forward voltages were 3.24, 3.26, and 3.25 V for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. It was found that the 350-mA LED output powers were 79.3, 98.1, and 121.5 mW for the conventional FC LED, FC LED prepared on PSS, and FC LED with double-side PSS, respectively. In other words, we can enhance the electroluminescence intensity by 53% without increasing operation voltage of the fabricated LED     

图形化蓝宝石衬底形貌对GaN基LED出光性能的影响

近年来,图形化蓝宝石衬底(PSS)作为GaN基LED外延衬底材料被广泛应用.通过干法刻蚀和湿法腐蚀制备了不同规格和形状的蓝宝石衬底图形,并进行外延生长、芯片制备和封装验证,采用扫描电子显微镜(SEM)和3D轮廓仪进行形貌表征,研究了不同规格和形状的衬底图形对LED芯片出光性能影响,并与外购锥形衬底(PSSZ2)进行对比.结果表明,在20 mA工作电流下,PSSZ2的LED光通量为8.33 lm.采用类三角锥和盾形衬底的LED光通量分别为7.83 lm和7.67 lm,分别比PSSZ2衬底低6.00％和7.92％.对锥形形貌进行优化,采用高1.69 μm、直径2.62 μm、间距0.42 μm的锥形衬底(PSSZ3)的LED光通量为8.67 lm,比PSSZ2衬底高4.08％,优化的PSSZ3能有效地提高LED出光性能.     

Effect of Residual Stress and Sidewall Emission of InGaN-Based LED by Varying Sapphire Substrate Thickness

The effect of residual stress and the sidewall emission in InGaN–GaN films with different thickness of sapphire substrate were investigated. The peak wavelength of electroluminescence was blue-shifted as thinning the sapphire substrate, because the wafer bowing-induced mechanical stress alters the piezoelectric field in the InGaN–GaN multiple quantum-well active region of the light-emitting diode (LED). A sideview LED with 170-$muhbox{m}$ -thick sapphire exhibited the highest output power of 14.04 mW at a forward current of 20 mA, improved by 7% compared to that with 80-$muhbox{m}$-thick sapphire. The maximum output power can be obtained by considering both the photon escaping probability from the edges of the sapphire and the photon absorption probability in the sapphire as well as the residual mechanical stress induced by the wafer bowing.      

蓝宝石衬底nm级CMP技术研究

介绍了蓝宝石衬底的化学机械抛光工艺,讨论分析了影响蓝宝石衬底化学机械抛光的因素,定量确定了最佳CMP工艺。提出先以重抛过程提高蓝宝石抛光速率,然后以轻抛过程降低最终表面粗糙度的工艺路线。在配制抛光液时加入FA/OⅠ型活性剂保护SiO2胶粒的双电子层结构。在轻抛过程之前抛光垫用原液浸泡20～30min,抛光磨料直径为20～40nm。实验最佳工艺条件下的抛光速率达231.6nm/min,粗糙度降至0.34nm。     

Enhancement of InGaN-Based Vertical LED With Concavely Patterned Surface Using Patterned Sapphire Substrate

To improve the external quantum efficiency, we have proposed a new method utilizing surface roughening of vertical-type light-emitting diodes (VT-LEDs) fabricated on hemispherical patterned sapphire substrate by using a laser lift-off technique. The advantages of this method are simple and reproducible in transferring the well-defined patterns on sapphire into GaN layer. The VT-LED with concavely patterned surface showed a nearly twofold increase in the output power compared to the normal planar surface. This improvement in the VT-LED performances is attributed to the increase in the escaping probability of photons from the LED surface.     

Coupled Slots on an Anisotropic Sapphire Substrate

Two analytical approaches are presented for coupled slots on an anisotropic sapphire substrate using the network analytical methods of electromagnetic fields. One is based on the quasi-static approximation and it derives the transformation from the case with the anisotropic substrate to the case with the isotropic substrate. The other is based on the hybrid mode formulation and it gives the dispersion characteristics.     

Comparison of InGaN-Based LEDs Grown on Conventional Sapphire and Cone-Shape-Patterned Sapphire Substrate

To improve the external quantum efficiency, a high-quality InGaN/GaN film was grown on a cone-shape-patterned sapphire substrate (CSPSS) by using metal-organic chemical vapor deposition. The surface pattern of the CSPSS seems to be more helpful for the accommodative relaxation of compressive strain related to the lattice mismatch between GaN and a sapphire substrate because the growth mode of GaN on the CSPSS was similar to that of the epitaxial lateral overgrowth. The output power of a light-emitting diode (LED) grown on the CSPSS was estimated to be 16.5 mW at a forward current of 20 mA, which is improved by 35% compared to that of a LED grown on a conventional sapphire substrate. The significant enhancement in output power is attributed to both the increase of the extraction efficiency, resulted from the increase in photon escaping probability due to enhanced light scattering at the CSPSS, and the improvement of the crystal quality due to the reduction of dislocation.     

Polymer Inverter Fabricated by Inkjet Printing and Realized by Transistors Arrays on Flexible Substrates

We have fabricated organic thin-film transistors (OTFTs) and implemented inverters on flexible substrates using polythiophene (PHT) as the semiconductor and polyvinylphenol (PVP) as the gate dielectric. The semiconductor was defined by inkjet printing. The poor consistency of the printing process has affected the uniformity of inkjet-printed OTFTs enormously. We also proposed a method to increase the yield by incorporating a pre-testing step during circuit fabrication. We designed and fabricated a basic unit of circuits called a thin-film transistor (TFT) array. These devices were then connected to each other to form a gate via printed nano-silver. To verify the implementation flow, we designed and measured bootstrap inverters and ring oscillator composed of them. The five-stage ring oscillator has been fabricated and oscillated at the frequency, 60 Hz, when the supply voltage is 40 V      

LED蓝宝石图形化衬底的研究进展及发展趋势

图形化蓝宝石衬底作为GaN基LED照明外延衬底材料,由于其能降低GaN外延薄膜的线位错密度和提高LED的光萃取效率的显著性能在近几年来引起国内外许多科研机构和厂商的广泛兴趣。从衬底的制备工艺、图形尺寸角度出发,综述了图形化蓝宝石衬底GaN基LED的研究进展,并对其未来在大功率照明市场的应用进行了展望。     

蓝宝石图形衬底上GaN低温缓冲层的研究

低温下,在蓝宝石图形衬底上使用金属有机化学气相沉积(MOCVD)生长低温GaN(LT-GaN)缓冲层,并对其表面形貌进行了细致的观察,发现了不同于已报道的GaN选择性成核生长现象。基于不同厚度的低温GaN缓冲层生长了n型GaN(n-GaN),发现过厚或者过薄的缓冲层都会对n-GaN晶体质量产生负面影响,并结合初始成核阶段进行了原因分析。制备了基于不同厚度的n-GaN的发光二极管(LED)样品,分析了GaN晶体质量对LED输出功率的影响。同时发现,晶体质量较差的时候,光提取效率可能主导着对LED器件性能的影响。     

脉冲激光制备ZnO压敏电阻薄膜

利用脉冲激光沉积技术，在光学玻璃基片上制备了性能良好的ＺｎＯ压敏多晶薄膜，其非线性系数ａ≥６，压敏转折电压约３．５Ｖ。     

磨料对蓝宝石衬底去除速率的影响

蓝宝石晶体已经成为现代工业,尤其是微电子及光电子产业极为重要的衬底材料,提高其化学机械抛光效率是业界无法回避的问题。在CMP系统中,磨料是决定去除速率及表面状态的重要因素。分析了化学机械抛光过程中抛光液中磨料的作用以及抛光机理,在确保表面状态的基础上,研究了抛光液中磨料体积分数、粒径和抛光液的黏度对速率的影响,指出纳米磨料是蓝宝石衬底抛光的最佳磨料。选用合适的磨料体积分数、粒径及抛光液黏度,不仅获得了良好的去除速率,而且有效地解决了表面状态方面的问题。     

基于图形化蓝宝石衬底的HB-LED研究进展

为了制作高亮度LED,需要在图形化蓝宝石衬底上生长GaN材料。通过光刻在平坦蓝宝石衬底上制作掩膜图形,通过刻蚀将图形转移到蓝宝石衬底,得到图形化蓝宝石衬底。在图形化蓝宝石衬底上进行GaN的侧向外延生长,并做后续处理,就制成了基于图形化蓝宝石衬底的高亮度LED。图形化蓝宝石衬底上GaN的侧向外延生长使得外延材料的位错密度从1010 cm-2降低到107 cm-2,这减少了发生非辐射复合的载流子,多量子阱发射更多的光子,LED的内量子效率提高。此外,图形化蓝宝石衬底能够有效散射从多量子阱射出的光线,使得出射光射到逃离区的几率更大,从而提高光萃取率。内量子效率和光萃取率的提高大大改善了LED的光电特性。     

Quasi-Static Characteristics of Microstrip on an Anisotropic Sapphire Substrate

The well-defined and repeatable electrical properties of single-crystal sapphire make it an attractive substrate material for microstrip, but its dielectric anisotropy constitutes an important design complication. This paper describes investigations into the quasi-static characteristics of single microstrip lines on sapphire substrates cut with a specified orientation. To account for anisotropy, a new permittivity parameter epsilon/sub req/ is introduced, which is a function of the Iinewidth to substrate-height ratio W/h. The variation of epsilon/sub req/ with W/h is derived by finite-difference methods. Universal curves for microstrip on correctly orientated sapphire are presented, showing 1) epsilon/sub req/, 2) the low-frequency limit of effective microstrip permittivity epsilon/sub e0/, and 3) the characteristic impedance of the line Z/sub 0/, all as functions of W/h.     

采用MEMS工艺制作封装载体的LED封装技术

针对SiC衬底的白光LED技术研究和智能化半导体照明技术发展的需求,基于Si材料的功能特性和物理特性,研究了将Si作为SiC基LED封装载体的相关技术.采用MEMS的加工工艺,设计了精确尺寸的芯片安装腔体和高效率的反射层,抑制了Si本体材料对光的吸收,提高了芯片侧向光的导出效率.通过分析光窗形貌及封装胶折射率对白光LED光效的影响,给出了一个全新的SiC衬底的白光LED封装的技术路线,为LED芯片与驱动一体化封装的实现奠定了技术基础.实现了完整的加工过程和样品制备,测试表明光效大于130 lm/W,热阻小于4.6℃/W.     

ZnO薄膜的射频磁控溅射制备及性能研究

采用射频磁控溅射法在玻璃衬底上制备出高质量的ZnO薄膜.对薄膜的结构和性能进行了研究.所制备的ZnO是具有六角纤锌矿结构的多晶薄膜,最佳择优取向为(002)方向.ZnO薄膜的霍尔迁移率和载流子浓度分别为8×104m2/(V·s)和11.3×1020 cm-3.     

LED用蓝宝石晶片湿法腐蚀清洗技术的研究

介绍了蓝宝石晶片的清洗原理：通过分析蓝宝石的表面净化原理和对湿法腐蚀清洗工艺试验的研究,提出了一种适用于工业化生产蓝宝石晶片的清洗剂和净化工艺,满足了LED领域的蓝宝石晶片表面洁净度要求。     

制作在不锈钢薄膜衬底上的柔性电子图书显示器

2005年10月,LG.PhilipsLCD和EInk公司联合推出了一款10.1in的SVGA反射式柔性有源矩阵光电显示器,该显示器成功地制作在一个薄薄的不锈钢薄膜衬底上。该产品原型在外观上和手感上与真实的纸张极为相似,非常薄且轻,并且具有宽视角和高对比度。     

Low-Microwave Loss Coplanar Waveguides Fabricated on High-Resistivity Silicon Substrate

分别在普通的低阻硅衬底、带有3μm厚氧化硅介质层的低阻硅衬底和高阻硅衬底上设计并制备了微波传输共面波导.结果表明,低阻硅衬底导致过高的微波损耗从而不能使用,通过加氧化硅介质层,微波损耗可以大大减少,但是需要较厚的氧化硅厚度.直接制备在高阻硅衬底上的共面波导在所测试的26GHz的频率范围内获得低于2dB/cm的微波损耗,而且工艺十分简单.     

蓝宝石衬底上AIGaN／GaN HEMT自热效应研究

建立了包含“自热效应”的AIGaN／GaN HEMT（高电子迁移率晶体管）直流I-V特性解析模型。从理论的角度分析了自热效应对AlGaN／GaN HEMT器件的影响，并同已有的实验结果进行了对比，符合较好。证明基于这种模型的理论分析适于AIGaN／GaN HEMT器件测试及应用的实际情况。