White Led Aging Mechanism

GaN based white LED is a new kind of semiconductor light source which has attracted much attention for it's incomparable performance especially in Lumen efficiency,life time and less power. For the moment white LED is being improved ceaselessly and being pushed to light market. And the reliability is more important.In this thesis, in order to improve the Lumen efficiency,Lumen Flux and reliability, the aging characteristics of GaN based white LED were inspected and analyzed by experiment research. The main research is given as following:1 The published search on aging theory of white LED was summarized. The reasons included creation of deep levels and non-radioactive recombination centers, electro migration and degradation of contact metal, slow or disaster mode electrode failure caused by high temperature, degradation of the encapsulation material, and obsolescence of fluorescent powder. And the improving methods according to these results were introduced.2 We aged f5mm White-LED using invariableness current on settled temperature, and measured the conditions of Lumen Flux,the color coordinate and other parameters, which were connected to the quality level of LED.3 In order to research the degradation rule of fluorescent powder in White-LED, we performed aging study using White-LEDs and Blue-LEDs with same batch of chips under same invariableness current and same conditions. It's indicated that the transition rate from blue light to yellow light in White-LED reduced following the rule of exponential function. And it reduced faster when the electrical current was bigger.4 We counted the increased temperature taken by aging current with given thermal capacity, and concluded that high chip temperature caused by aging current is the main reason for the aging degradation. We compared the different increased temperature under different aging current, to explain the reason for faster aging under bigger aging current.5 The lifetimes of the LED aged were computed by two different mathematics methods. The advantage and disadvantage were both compared.6 Methods to improve the reliability were discussed according to research results. Some better ideas were brought forward.