Thermal characteristic analysis of high-power LEDs by structure functions

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函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,AnTAl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。The cooling transient temperature curves of high-power LEDs are measured by electritical method.The cumulative and differential structure functions are extracted from these curves to analyse thermal resistances and thermal capacitances of all regimes of high-power LEDs with numeric computational method.It is found out that calculated and measured values of various materials are essentially conformable.The sampling resolution of 1 μs of transient data and high repetition assure the veracity and reliability of experimental result.Subsequently,thermal conduction capabilities of three different metal core printed circuit boards(MCPCBs) with high-power LEDs are compared by this method,and it is discovered that bergquist′s MCPCB has the best thermal conduction capability,ANT′s MCPCB takes second place,and the common MCPCB is the worst.So the structure functions are powerful tools for thermal characteristic analysis of high-power LEDs.国家“863”计划资助项目(2006AA03A175);福建省科技项目(2006H0092;2008J0030);厦门市重大专项资助项目(3502Z20061004

Infrared thermographic analysis of LED lights on a ceramic layer

LED svetila intenzivno nadomeščajo žarnice z volframovo žarilno nitko, pri čemer je poleg doseganja dobrih optičnih lastnosti pomembno zagotavljati njihovo učinkovito hlajenje. V tej nalogi obravnavamo infrardečo termografsko analizo dveh različnih LED svetil na keramični plasti z debelinami od 0,25 mm do 5 mm. Razvita je bila eksperimentalna proga, ki omogoča napajanje LED svetila z omejevanjem električnega toka in napetosti ter sočasno spremljanje porabe električne moči in merjenja temperature s pomočjo hitrotekoče infrardeče kamere. V okviru meritev smo analizirali segrevanje keramičnih plasti različnih debelin, vpliv orientacije LED svetila, dinamični odziv segrevanja in čas, potreben za doseganje ustaljenega temperaturnega stanja pri različnih električnih močeh. Prikazani so tudi temperaturni profili in dvodimenzionalna temperaturna polja. Rezultati meritev kažejo, da razviti merilni postopek omogoča vrednotenje segrevanja LED svetil in določanja maksimalne dovoljene električne moči, da zadostimo temperaturnim omejitvam.LED lamps intensively replace incandescent lamps, and in addition to achieving good optical properties, it is important to ensure their efficient cooling. In this paper, the infrared thermographic analysis of two different LED lamps on a ceramic layer with thicknesses from 0.25 mm to 5 mm is considered. An experimental track has been developed that enables the power supply of LED lights by limiting current and voltage, while simultaneously monitoring electrical power consumption and temperature measurement using a high-speed infrared camera. As part of the measurements, the heating of ceramic layers of different thicknesses, the influence of LED light orientation, the dynamic heating response and the time required to achieve a steady-state temperature at different electrical powers were analyzed. Temperature profiles and two-dimensional temperature fields are also shown. The measurement results show that the developed measurement procedure enables the evaluation of the heating of LED lights and the determination of the maximum allowable electrical power in order to meet the temperature limits

COMPREHENSIVE ELECTRICAL/OPTICAL/THERMAL CHARACTERIZATIONS OF HIGH POWER LIGHT EMITTING DIODES AND LASER DIODES

Thermal characterizations of high power light emitting diodes (LEDs) and laser diodes (LDs) are one of the most critical issues to achieve optimal performance such as center wavelength, spectrum, power efficiency, and reliability. Unique electrical/optical/thermal characterizations are proposed to analyze the complex thermal issues of high power LEDs and LDs. First, an advanced inverse approach, based on the transient junction temperature behavior, is proposed and implemented to quantify the resistance of the die-attach thermal interface (DTI) in high power LEDs. A hybrid analytical/numerical model is utilized to determine an approximate transient junction temperature behavior, which is governed predominantly by the resistance of the DTI. Then, an accurate value of the resistance of the DTI is determined inversely from the experimental data over the predetermined transient time domain using numerical modeling. Secondly, the effect of junction temperature on heat dissipation of high power LEDs is investigated. The theoretical aspect of junction temperature dependency of two major parameters – the forward voltage and the radiant flux – on heat dissipation is reviewed. Actual measurements of the heat dissipation over a wide range of junction temperatures are followed to quantify the effect of the parameters using commercially available LEDs. An empirical model of heat dissipation is proposed for applications in practice. Finally, a hybrid experimental/numerical method is proposed to predict the junction temperature distribution of a high power LD bar. A commercial water-cooled LD bar is used to present the proposed method. A unique experimental setup is developed and implemented to measure the average junction temperatures of the LD bar. After measuring the heat dissipation of the LD bar, the effective heat transfer coefficient of the cooling system is determined inversely. The characterized properties are used to predict the junction temperature distribution over the LD bar under high operating currents. The results are presented in conjunction with the wall-plug efficiency and the center wavelength shift

GaN-on-Si 기반의 고주파/고전력 소자의 제작 및 특성 분석

학위논문 (박사)-- 서울대학교 대학원 : 전기·정보공학부, 2016. 2. 서광석.Owing to the unique capabilities of achieving high current density, high breakdown voltage, high cut-off frequency and high operating temperature, AlGaN/GaN high electron mobility transistors (HEMTs) are emerging as promising candidates for RF power amplifier and power switching devices. Nevertheless, despite the great potential of these new technologies, they still suffer from physical and fabrication issues which may prevent devices fabricated on GaN from achieving the performance required. This thesis presents a comprehensive study on the development of GaN-based high frequency, high power transistors. This work can be divided into two parts, namely D-mode AlGaN/GaN schottky HEMTs on silicon substrate for high power X-band operation and E-mode Si3N4/AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) for power switching devices. One of the main obstacle is the trapping effects, may be exacerbated when devices are operated in Radar systems. In this work, we will use a novel fluoride-based plasma treatment technique to reduce trapping phenomenon which originated from the surface, and then apply this treatment technique in conjunction with a field plate structure to a device for GaN-based RF applications. To improve overall device performance, a backend process with individually grounded source via formation has been developed to integrate large periphery devices. Based upon it, GaN HEMT amplifier with single chip of 3.6 mm gate periphery has been successfully developed. It exhibits very high power density of 8.1 W/mm with 29.4 W output power under VDS = 38 V pulse operating condition. Compared to the conventional depletion-mode AlGaN/GaN (D-mode), Enhancement mode (E-mode) devices are attracting a great interest as they allow simplistic circuity and safe operation. It is difficult to obtain E-mode operation with a low on-resistance and a high breakdown voltage. A gate recess technique will be crucial to realize an enhancement-mode operation and improve the transfer characteristics. To reduce the on resistance and enhance the drain current density, partially recessed MIS-HFETs are investigated. The gate recess was carried out using a low-damage Cl2/BCl3-based RIE where the target etch depth was remains AlGaN barrier layer in order to improve the transfer characteristics. The occurring degradation of the mobility due to plasma etching-induced damage and scattering effect were effectively removed by partial gate recess technique. The technologies we developed have helped to give definitive direction in developing GaN-based high frequency, high power transistors.CHAPTER 1 Introduction 1 1.1 Background 1 1.2 Substrate for Epitaxial Growth of GaN 6 1.3 Research Aims and Objectives 8 1.4 Organization of Thesis 9 1.5 References 11 CHAPTER 2 Technology Development and Fabrication of AlGaN/GaN HEMTs on Si substrate 15 2.1 Introduction 15 2.2 Epitaxy Layer Structure 16 2.3 Device Fabrication Processes 17 2.3.1 Sample Preparation 18 2.3.2 Mesa Isolation 19 2.3.3 Ohmic Formation 20 2.3.4 Schottky Contacts 24 2.3.5 Contac Pads 26 2.3.6 Air-bridge Interconnection 26 2.4 References 33 CHAPTER 3 Au-Plated Through-Wafer Vias for AlGaN/GaN HEMTs on Si substrate 36 3.1 Introduction 36 3.2 Via-hole Fabrication 37 3.2.1 Experiments 38 3.2.2 Tapered Source Via Formation 40 3.2.3 GaN Etching Process 50 3.2.4 Au Electroplating 53 3.3 Back-side Process Flows 54 3.3.1 Individual Source Via 58 3.3.2 Au-Sn Eutectic Solder Die Attach 60 3.3.3 Thermal Resistance Measurement 61 3.4 References 66 CHAPTER 4 AlGaN/GaN HEMTs for RF applications 69 4.1 Introduction 69 4.2 Advantages of AlGaN/GaN HEMTs for RF Power Devices 70 4.3 RF Performance Limitations 73 4.3.1 Surface States 73 4.3.2 Current Collapse Phenomenon 75 4.4 Device Fabrication 79 4.4.1 Device Layout 85 4.4.2 Slant Gate Process 86 4.4.3 Fluorine Plasma Treatment process 89 4.5 Device Characterization 93 4.5.1 DC and Small Signal Performance 93 4.5.2 Pulse Characteristics 98 4.5.3 Large Signal Performance 99 4.6 Wide Periphery Devices 103 4.6.1 Large Signal Performance 104 4.7 Summary 109 4.8 Reference 110 CHAPTER 5 AlGaN/GaN HEMTs for Power applications 115 5.1 Introduction 115 5.2 Advantages of AlGaN/GaN HEMTs for Power Switching Devices 116 5.2.1 Enhancement-mode Operation 117 5.2.2 High Breakdown Voltage 119 5.3 Device Fabrication 121 5.3.1 Gate Recess Process 124 5.3.2 Plasma Enhance ALD SiNx Film 138 5.4 Characterization for Normally-off GaN Transistors 140 5.4.1 DC Characteristics 140 5.4.2 Breakdown Voltage Characteristics 144 5.4.3 Dynamic Ron Characteristics 146 5.5 Summary 148 5.6 Reference 149 CHAPTER 6 Conclusions and Future Works 155 6.1 Conclusions and Future Works 155 Appendix 159 Abstract in Korean 169 Research Achievements 174Docto

High power gallium nitride micro-electronics: thermal management using microfluidics

Last four decades have seen unprecedented development in communication, defence, electronics, and computing technologies. The increased power density plus the miniaturisation of the device present challenges in managing the high heat flux in the microchip level. Besides, the highly heterogeneous heat flux in electronic devices presents more challenges to thermal management (TM). This calls for the development of more efficient cooling technologies for these high-power microelectronic devices. This PhD study aims to address this challenge by developing the high performance of heat transfer fluids (HTFs) and compact cooling devices. Gallium Nitride (GaN) based transistors which acted as inhomogeneous high heat flux output were targeted in this work. The work involves formulating, characterisation and performance measurements of various heat transfer fluids (including base fluids and nanofluids), design, fabrication and assemble, and package and experiments of microfluidics including foam metal, micro-jet impingement. Both experimental work and modelling were performed and the following main conclusions were obtained. • Heat transfer fluids study Two types of nanofluids were formulated and investigated for the application in room temperature and the low temperature. The BN/DI water nanofluids used in the room temperature shows 5.2 % enhancement in the thermal conductivity compared to the base fluid for the 0.5 wt.%. The other material rGO/EG+DW nanofluids used for the temperature as low as -50 ℃ has 17 % thermal conductivity increase with the concentration of 2.0 wt.%. This suggests that the nanofluids can have a better thermal performance for the microfluidic channel than the base fluids. • Performance of the microfluidics With the experimental comparison of the copper-foam based microfluidic channel and the micro-jet channel, the micro-jet channel was chosen due to a higher heat transfer coefficient. Both base fluids and nanofluids were experimental tests and the numerical simulation was validated with the micro-jet channel. The test showed that the BN/DI water nanofluids with a concentration of 0.5 wt.% can increase the heat transfer coefficient 5 % compared to the DI water. Meanwhile, the 2.0 wt.% rGO/EG+DW nanofluids showed a similar trend with an 11% increase in the heat transfer coefficient compared to EG+DW base fluid. The direct measurement of the temperature with Raman thermography was used to measure the temperature in the finger of the die. The experiment test suggests that with the target power density of 5 W/mm in the finger (1×10⁷ W/mm² in the finger), the peak temperature in the devices was 120 °C far below 200 °C. The thermal resistance for the jetting channel was 19.76 °C/W. The device used in the experiment was GaN-on-SiC. For the GaN-on-Diamond, a higher power density can be obtained. Thus, for the thermal management of the GaN devices, the nanofluids, material selection for the devices thermal package and micro-jet channel play important roles once the specific GaN transistors are selected