LED热学性能测试方法的研究综述

LED是21世纪最具发展前景的照明光源之一。散热是限制功率型LED器件广泛应用的主要瓶颈,精确的热学测量则是有效热管理的重要前提。目前对于LED热学性能的测量方法研究主要有红外热成像法、电学参数法、瞬态热测试法、光谱法、光功率法等方法。从LED热学特性及热学参数测试的基本原理出发,综述了国内外关于LED热学性能的测试方法研究,分析比较了各方法测量LED热阻的优缺点,讨论了各自的适用范围。瞬态热测试法由于其测试精度高、可测热结构函数等优点,具有重要的研究价值和良好的应用前景。     

利用结构函数分析功率型LED的热特性

运用电学法测量功率型LED冷却瞬态温度曲线,通过数学方法将其转化为积分和微分结构甬数来分析器件各区域的热阻和热容.结果发现,各层材料的测量值与理论值基本一致.1μs的瞬态数据采集精度和高的重复性保证了实验结果的准确性和可靠性,运用这种方法比较了3种不同金属芯印刷电路板(MCPCB)对功率型LED的散热效果,贝格斯Al基板散热性能最好,ANT Al基板次之,普通Al基板最差.研究表明,利用结构函数分析功率型LED的热特性是一种强有力的方法.     

大功率白光LED封装技术面临的挑战

发光二极管（LED）是一类可直接将电能转化为可见光和热等辐射能的发光器件,具有一系列优异特性,被认为是最有可能进入普通照明领域的一种“绿色照明光源”。目前市场上功率型LED还远达不到家庭日常照明的要求。封装技术是决定LED进入普通照明领域的关键技术之一。文章对LED芯片的最新研究成果以及封装的作用做了简单介绍,重点论述了封装的关键技术,包括共晶焊接、倒装焊接以及散热技术,最后指出了未来LED封装技术的发展趋势及面临的挑战。     

LED器件热阻测试仪的研制

本文介绍了LED热阻测试仪的工作原理、实现方法、技术指标以及使用效果.主要研究测试系统中的程控时序控制和多路数据采集、高精度器件壳温测量与控制等技术,设计开发了LED热阻测试仪和配套恒温夹具.LED热阻测试仪的研制解决了国内LED生产和使用中迫切需要解决的热阻测试问题.对于提高我国功率LED产品的可靠性,填补国内LED热阻测试的空白,具有重要意义.     

基于NI DAQ的功率LED热特性测量分析系统

分析了功率发光二极管(LED)基于电学测量的热阻的测量方法,介绍了采用高性能数据采集卡构建了新型的功率LED热特性自动测量分析系统,实现对功率LED结温和热阻的精确、简便的测量.对几种典型功率LED样管的测试结果,与校正样品的标称值完全相符,并可对LED的瞬态热过程进行更深入分析.     

高压倒装LED照明组件的热性能

高压(HX)倒装LED是一种新型的光源器件,在小尺寸、高功率密度发光光源领域有广泛的应用前景.设计了4种不同工作电压的高压倒装LED芯片,进行了流片验证,并对其进行了免封装芯片(PFC)结构的封装实验,在其基础上研制出一种基于高压倒装芯片的PFC-LED照明组件.建立了9V高压倒装LED芯片、PFC封装器件及照明组件的模型,利用流体力学分析软件进行了热学模拟和优化设计;利用T3Ster热阻测试分析仪进行了热阻测试,验证了设计的可行性.结果表明,基于9V高压倒装LED芯片的PFC封装器件的热阻约为0.342 K/W,远小于普通正装LED器件的热阻.实验结果为基于高压倒装LED芯片的封装及应用提供了热学设计依据.     

芯片键合材料对功率型LED热阻的影响

分析了功率型LED热阻系统的构成,对采用银浆和环氧胶作为芯片键合材料的功率型LED热阻进行了对比研究。研究结果表明:采用银浆作为芯片键合材料可以显著改善功率型LED的热阻系统,同采用环氧胶作为芯片键合材料的功率型LED相比,其热阻下降了约100℃/W。     

基于光电热理论的LED热阻测量方法

热阻是反映发光二极管(LED) 器件散热能力的综合参数。本文基于光-电-热(PET)理论,简化了热阻与光通量、电功率 之间的关系,提出了一种利用LED光电特性测量其 热阻的新方法。即利用 光效随结温的变化率 k e 、 热耗散系数 k h 、 散热器 的表面温度 T hs 和最大光通量对应的电功率 P d, 计算 得到 LED 热阻。对不同型号器件进行热阻测量,与标称热阻具有 很 好的一致性,证实了本文方法 的可行性和通用性。 该热阻测量方法简单,无需昂贵的热阻测量仪器,具有较强的工程应用价值。     

多芯片贴片式LED器件结温测量

结温是多芯片LED器件热性能的关键参数。以SMD5050 LED器件为例,研究了多芯片贴片式LED器件结温测量方法。SMD5050 LED是一种多芯片贴片式封装的LED器件,器件内封装有3颗芯片,3颗芯片之间并联。根据单芯片LED器件热阻测试原理,模拟SMD5050 LED器件正常工作时的状态,对SMD5050 LED器件的结温进行了测量,并根据LED芯片特性,验证了测量结果的准确性,这种方法适用于封装结构相似的其他多芯片LED器件结温的测量。     

基于脉冲式U-I 特性的高功率型LED 热学特性测试

热学特性是影响功率型LED光学和电学特性的主要因素之一,设计了一套基于脉冲式U-I特性的功率型LED热学特性测试系统,可以测试在不同结温下LED工作电流与正向电压的关系,从而获得LED的热学特性参数。该系统通过产生窄脉冲电流来驱动LED,对其峰值时的电压电流进行采样,同时控制和采集LED的热沉温度,从而获得不同温度下LED的U-I特性曲线。与其他U-I测试系统相比,文中采用了窄脉冲(1 s)工作电流,LED器件PN结区处于发热与散热的交替过程,不会造成大的热积累,大大提高了测量精度。实验中,对某功率型LED进行了测试,获得了该器件的电压、电流和结温特性曲线,并利用B样条建立该器件的U-I-T模型,进而实现了对其结温的实时在线检测。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.