Analysis And Research On Failure Mechanism Of Nitride-based White LED

As a new generation of lighting source, light emitting diode (LED) has thecharacteristics of energy saving, environmental protection, long life, high colorrendering and fast response, etc. It is one of the most promising high-tech fields of theworld in recent years. Thus LED will become the fourth generation lighting sourcereplacing incandescent, fluorescent and high intensity discharge lamp. Based on theneeds of energy saving and the lighting level enhancement, the photoelectric propertyand high reliability of LEDs becomes more and more important. Junction temperatureand current are the main factors influencing the reliability of LEDs, in the agingprocess which leading to degradation failure of light-emitting chip and packagematerial performance. Failure analysis aims to determine the failure mode andmechanism, put forward corrective measures, and prevents the occurrence of thesimilar failure event, that is why it is very important to the reliability research ofLEDs. This paper with low power and high power GaN base white LED as theresearch object, via the two different failure phenomenon tests and analysis,determined the cause of the failure occurred and internal mechanism. Meantime,optical parameters degradation of high-power GaN-base white LED was studiedunder different current and temperature stresses. The main research was shown asfollows:1. Black zone appeared on the surface of White LED with phosphor layer duringthe course of practical use and experiment was studied, the changes of photoelectricproperty during the aging test were measured. Optical Microscope, Scanning ElectronMicroscope (SEM) and Energy Dispersive Spectrometer (EDS) were carried out formorphological and elements analysis, also accelerated thermoelectricity stress testindicated the failure criterion.2. Invalidation of Low-power GaN base LED module (eight LEDs in series as aset of group) suffered voltage surge sometimes presented current leakage failure wereinvestigated. Pspice was applied for simulate the distribution of power and voltage offailure device in LED module. Light emission microscope (PEM) is used for thelocation and component analysis of the chip surface leakage, and current crowdingeffect which influenced the reliability of LEDs was simulated by Ansys. Finally theabnormal I-V characteristics of some failure devices has preliminary carried out. 3. Using the optical parameters of high power GaN base white LEDs measuredunder different temperatures and currents, mainly including luminous flux, radiationpower, color coordinates, correlated color temperature and color rendering index, etc,the phosphor conversion efficiency and degradation mechanism of LED chip wasdiscussed, this provided the beneficial reference for the high-power white LED indisplay application.