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i Délivré par l’Université Toulouse 3–Paul Sabatier Présentée et soutenue par Sovannarith LENG le 20 Février 2017 Identifying and Evaluating Aging Signatures in Light Emitting Diode Lighting Systems École doctorale et discipline ou spécialité ED GEET : Génie Electrique Unité de recherche Laboratoire PLAsma et Conversion d’Energie (LAPLACE) Directeurs de Thèse Dr. Laurent CANALE, CNRS, LAPLACE Prof. Georges ZISSIS, Université Paul Sabatier, LAPLACE Jury Christian GLAIZE, Professeur, Lab. IES, Groupe GEM, Montpellier, Rapporteur Yannick DESHAYES, Dr/HDR, IMS, Groupe ONDE, EDMINA, Talence, Rapporteur Geneviève DUCHAMP, Professeur, IMS, Groupe FIABILITE, Bordeaux, Examinateur Laurent MASSOL, Ingénieur, Directeur Société LED, Montauban, Invité Laurent CANALE, Dr, Ingénieur de Recherche CNRS, LAPLACE, Directeur de Thèse Georges ZISSIS, Professeur, Univ. Paul Sabatier, LAPLACE, Directeur de Thèse ii S.LENG, Identif. & Eval. Aging Signatures in LED Lighting Systems Université Toulouse 3–Paul Sabatier Laboratoire LAPLACE THÈSE Pour obtenir le grade de DOCTEUR DE L’UNIVERSITÉ Spécialité Identifying and Evaluating Aging Signatures in Light Emitting Diode Lighting Systems Sovannarith LENG Présentée et soutenue publiquement Le 20 Février 2017 Directeurs Dr. Laurent CANALE, Ingénieur de Recherche CNRS, LAPLACE Prof. Georges ZISSIS, Université Paul Sabatier, LAPLACE JURY Christian GLAIZE, Professeur, Lab. IES, Groupe GEM, Montpellier, Rapporteur Yannick DESHAYES, Dr/HDR, IMS, Groupe ONDE, EDMINA, Talence, Rapporteur Geneviève DUCHAMP, Professeur, IMS, Groupe FIABILITE, Bordeaux, Examinateur Laurent MASSOL, Ingénieur, Directeur Société LED, Montauban, Invité Laurent CANALE, Dr, Ingénieur de Recherche CNRS, LAPLACE, Directeur de Thèse Georges ZISSIS, Professeur, Univ. Paul Sabatier, LAPLACE, Directeur de Thèse iv S.LENG, Identif. & Eval. Aging Signatures in LED Lighting Systems v ACKNOWLEDGEMENTS This thesis was carried out within the PLAsma and Conversion d'Energie (LAPLACE) laboratory in Toulouse. This exciting and rewarding research has led to the contribution of several staff from the laboratory. I would therefore like to express my gratitude to certain individuals who have devoted their efforts and their availabilities to me during this thesis. First of all, I would like to express my deep gratitude to my supervisor, Georges ZISSIS, Professor at University Paul Sabatier in Toulouse, Head of Light & Matter Research Group at LAPLACE and Director of SH2D Research Federation, for his very important direction in my work and for his encouragement, his advice and his very valuable technical and moral support for the success of my work. I would also like to express my sincere thanks to my co–supervisor, Dr. Laurent CANALE, CNRS Research Engineer in Light & Matter Research Group and AFE Midi–Pyrénées Region Chairman, for his encouragement, his guidance, including his very useful advice which enabled me to acquire knowledge and skills that are very useful for my research and my career. I especially wish to thank my thesis committee: Professor Christian GLAIZE, at "Institut d'Electronique et des Systèmes" in Montpellier, Professor Geneviève DUCHAMP, and Dr Yannick DESHAYES, Associate Professor/HDR, both from University of Bordeaux and "Laboratoire de l'Intégration du Matériau au Système", for their valuable advices, thesis supervision, and their positive comment and evaluation on my thesis. I do not forget to express my gratitude to all staffs, lecturers, professors, PhD students and colleagues of the Laplace with whom I shared very pleasant moments and which allowed me to acquire various technical, social and cultural vi S.LENG, Identif. & Eval. Aging Signatures in LED Lighting Systems knowledges on countless occasions. I would like to specially thank to my best friends, Alaa ALCHADDOUD and Feng TIAN. I also do not forget to convey my thanks to my Cambodian friends who are / were in Toulouse and France, with whom I shared a lot of pleasant moments and who remain anchored in my memories. Very special and from bottom of heart thanks and gratitude to my beloved family: my wife, my son and my parent for their love, constant moral encouragement, and their invaluable sacrifice of everything for me. They always support and hold me when I am down so I never lost my spirit. No word I can say about their goodness. I am very proud to be their part of family. I also thank to my brothers and sisters for caring and support. It is to all of them that I dedicate this thesis. The last but not least, I would like to express my deepest appreciation to Erasmus Mundus Techno II project with the support of the Erasmus Mundus Program of the European Union for my financial support, to officers and staffs of the Techno II program for their kindness and help during my study. vii Contents INTRODUCTION ...................................................................................................... 1 1. STATE OF THE ART OF THE GaN LEDS TECHNOLOGY .............................. 5 1.1. HISTORY OF LIGHTING SYSTEMS ............................................................................ 6 1.1.1. The Sun ......................................................................................... 6 1.1.2. Incandescent Filament Lamp ............................................................. 7 1.1.3. Mercury and Sodium Vapor Lamps ..................................................... 7 1.1.4. Fluorescent Lamp ............................................................................ 9 1.1.5. Light–Emitting Diodes (LEDs) .......................................................... 10 1.2. LED CHIP STRUCTURES ....................................................................................... 14 1.2.1. Conventional Lateral and Vertical Structure ....................................... 14 1.2.2. Flip Chip Structure ......................................................................... 15 1.2.3. Vertical Thin Film Structure ............................................................. 16 1.2.4. Thin Film Flip Chip Structure ........................................................... 17 1.3. PACKAGING OF LEDS .......................................................................................... 18 1.3.1. Low Power LED Package ................................................................. 19 1.3.2. High Power LED Package ................................................................ 19 1.3.3. Packaging Process ......................................................................... 21 1.3.3.1. Dual in–Line (DIP) Packaging ................................................................... 22 1.3.3.2. SMD LED Packaging .................................................................................. 22 1.3.3.2.1. SMD Leadform Packaging ....................................................................... 23 1.3.3.2.2. SMD Leadless Package ............................................................................ 24 1.3.3.3. LED Array Packaging ................................................................................. 26 1.4. MAIN DEGRADATION OF LEDS TECHNOLOGY....................................................... 29 1.4.1. Degradation and Failure Modes at Chip Level ..................................... 29 1.4.1.1. Generation and Movement of Defect and Dislocation ............................... 29 1.4.1.2. Die Cracking ................................................................................................ 32 1.4.1.3. Dopant Diffusion ......................................................................................... 34 1.4.1.4. Electromigration ......................................................................................... 34 1.4.2. Interconnection Failure Modes ......................................................... 35 1.4.2.1. Bond Wire /Wire Ball Bond Failure ........................................................... 35 1.4.2.2. Electrical Contact Metallurgical Interdiffusion......................................... 37 1.4.2.3. Electrostatic Discharge ............................................................................... 37 1.4.3. Degradation and Failure Modes at Package Level ................................ 40 1.4.3.1. Carbonization of the Encapsulant .............................................................. 40 1.4.3.2. Delamination ............................................................................................... 41 1.4.3.3. Lens /Encapsulant Failure ......................................................................... 43 1.4.3.4. Phosphor Thermal Quenching .................................................................... 44 viii S.LENG, Identif. & Eval. Aging Signatures in LED Lighting Systems 1.4.3.5. Solder Joint Fatigue ................................................................................... 46 1.5. CONCLUSION – CHAPTER 1 ................................................................................. 47 2. ELECTRICAL AND OPTICAL CHARACTERISTICS OF LEDS ..................... 51 2.1. METHODOLOGY FOR JUNCTION TEMPERATURE EVALUATION ............................... 52 2.1.1. Temperature Dependence of Forward Voltage (Vf) .............................. 53 2.2. OPTICAL PROPERTIES OF LED ................................................................... 60 2.2.1. Internal, Extraction, External, and Power Efficiencies .......................... 60 2.2.2. Emission Spectrum ........................................................................ 61 2.2.3. Light Escape Cone ......................................................................... 64 2.2.4. Radiation Pattern–Lambertian Emission Pattern .................................. 66 2.2.5. Epoxy Encapsulant ........................................................................ 67 2.2.6. Temperature Dependence of Emission Intensity ................................. 68 3. EXPERIMENTAL SETUP FOR LED AGING EVALUATION ......................... 69 3.1. A NEW PROTOTYPE OF LED AGING BENCH ............................................. 70 3.2. TEMPERATURE CONTROLLER (REX–D100) ........................................................ 76 3.2.1. Software Program for REX–D100 Temperature Controller ..................... 78 3.2.2. Communication Protocol ................................................................. 80 3.2.2.1. Polling Procedure ........................................................................................ 80 3.2.2.1. Selection Procedure .................................................................................... 81 3.3. SOURCE–METER UNIT (SMU–KEITHLEY 2602A) ............................................... 81 3.3.1. 2–Wires and 4–Wires Feature .......................................................... 82 3.3.2. Software Program Measurement for SMU–Keithley 2602A .................... 83 3.4. IMPEDANCE ANALYZER (SOLARTRON MODULAB) ................................................ 87 3.4.1. Instrument Group Modules ............................................................. 87 3.4.2. PC Communication Setup ............................................................... 88 3.4.3. Software Program Control of Solartron ModuLab ................................ 89 3.5. SPECTROMETER (SPECBOS 1201) ........................................................................ 91 3.5.1. Optical Measurement Hardware Setup .............................................. 92 3.5.2. Software Program Measurement of Specbos 1201 .............................. 93 3.6. LED’S DRIVER .................................................................................................... 94 4. EVALUATION OF FAILURE MECHANISMS FOR LEDS STUDIED ............ 97 4.1. EFFECT OF TEMPERATURE ON LED PERFORMANCE............................................ 98 4.2. SELF−HEATING TEST........................................................................................ 100 4.3. INITIAL STATE OF ELECTRICAL CHARACTERIZATIONS....................................... 101 4.4. ELECTRICAL FAILURE SIGNATURES ................................................................... 110 ix 4.4.1. Electrical Aging Characteristic of Cree’s Devices................................ 111 4.4.2. Electrical Aging Characteristic of Osram’s Devices ............................. 115 4.4.3. Electrical Aging Characteristic of Philips’s Devices ............................. 118 4.4.4. Electrical Aging Characteristic of Seoul’s Devices .............................. 122 4.5. OPTICAL FAILURE SIGNATURES ......................................................................... 126 4.5.1. Initial State of Photometric Characterization .................................... 127 4.5.2. Photometrical Characterizations of LEDs under accelerated aging conditions ................................................................................... 136 4.6. CONCLUSION– CHAPTER 4 ................................................................................ 146 GENERAL CONCLUSION AND PERSPECTIVES ............................................. 149 REFERENCES............................................................................................................ 155 ANNEXES ...................................................................................................................I APPENDIX A: COMMUNICATION IDENTIFIER LIST OF REX–D100 ................................. II APPENDIX B: CONTROLLER SCANNED PARAMETER ...................................................... IV APPENDIX C: PROGRAM CODE FOR REX–D100 ............................................................ V APPENDIX D: PROGRAM CODE FOR SMU KEITHLEY 2602A ........................................ XI APPENDIX F: DATASHEET OF LEDS ........................................................................ XXXI x S.LENG, Identif. & Eval. Aging Signatures in LED Lighting Systems ...................................................................................................................................... Liste des tableaux Table I.1: Discoveries and History of LEDs ......................................................... 13 Table I.2: Comparison of Key Characteristics and Parameter Values for Commercial ............................................................................................................. 14 Table I.3: Factors influent LED packaging .......................................................... 21 Table II.1: Varshni parameters of common semiconductors. ............................... 57 Table III.1: Main characteristics of studied LEDs. ............................................... 71 Table IV.1: dispersion of I−V characteristic of 16 Samples each LED group computed at V=2.9V. ............................................................................................ 104 Table IV.2: Error of variation of luminance and spectrum of 16 samples each unstressed LED group @350mA. ......................................................................... 131 Table des illustrations Figure I.1: Sun, the first light source. ..................................................................... 6 Figure I.2: Artificial Lighting. ................................................................................. 6 Figure I.3: Mercury Vapor Lamp. ............................................................................ 7 Figure I.4: Low–pressure sodium vapor lamp......................................................... 8 Figure I.5: High–pressure sodium vapor lamp. ...................................................... 9 Figure I.6: Fluorescent lamp. ................................................................................. 10 Figure I.7: Publication of JH Round in Electrical World. ..................................... 11 Figure I.8: A replication of H. J. Round's LED experiments. ............................... 11 Figure I.9: a) Lateral structure, b) vertical structure. .......................................... 15 Figure I.10: Flip chip structure. ............................................................................ 16 Figure I.11: LED ThinGaN structure by Osram. .................................................. 16 Figure I.12: TFFC by Philips Lumiled. ................................................................. 17 Figure I.13: SEM images of PSS and GaN grown on PSS . .................................. 17 Figure I.14: SEM of an N–face GaN surface roughening etched by a KOH–based PEC method . .......................................................................................................... 18 Figure I.15: Al–oxide honeycomb nanostructure on thin–GaN LED . ................. 18 Figure I.16: a) LED with hemispherical encapsulant, b) LEDs with cylindrical and rectangular encapsulant . ............................................................................... 19

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