Share: Explore the causes of white LED degradation

In recent years, countries around the world have become more and more concerned about energy issues such as environmental protection and energy conservation. Therefore, they indirectly influence investment and technology development in these fields. Among them, solar cells, lithium-ion batteries, SiC power transistors, and white LEDs are the most affected. Attention is generally considered that the above plan is expected to become a highly growing field in the future with the support of the national scale.

White LED has officially entered the field of general application lighting such as medical, automotive and plant cultivation from mobile phones and LCD TV backlight modules. Foreign companies have even introduced white LED bulbs with a price of 60W. This type of new generation of white LEDs Lighting sources are rapidly replacing traditional fluorescent lamps with incandescent bulbs.

Regarding LCD TV backlight modules or large-scale lighting, the use of a large number of white LEDs must have both traditional costs and performance issues. The Japanese industry generally believes that the target of 0.5 yen/lm and 200 lm/W is expected to be achieved in 2011, among which The improvement of chip performance, the development of phosphors and packaging technologies have always played a key role. Reliability is another important issue for white LEDs. It includes the durability of single LEDs and the luminance distribution of multiple white LEDs when lighting at the same time. To overcome these problems, domestic and foreign manufacturers have actively developed technology.

Regarding the durability of white LEDs, that is, the deterioration of LEDs, it is generally considered that the light beam, the package, and the temporal deterioration of the chip are the main causes of the life reduction. However, in fact, these deterioration factors are complicated, so the analysis of the deterioration mode is very difficult, especially It is a white LED that has a long life and is not easily tested for deterioration. The conventional deterioration test is, for example, a current acceleration test, a temperature acceleration test, an accelerated weathering test, and the like. Next, the results of the "overvoltage degradation test" and the analysis results of white LED degradation are described.

Analysis method and evaluation project

Fig. 1 is a list of basic structures and deterioration factors of a typical white LED for illumination; Table 1 is a main evaluation item of GaN-based LEDs and related materials, and a list of analysis techniques. TEM (Transmission Electron Microscope) can directly observe the index and defects according to the cross-sectional structure of the LED. It is very important to determine the skew, stress, composition, carrier concentration and defect evaluation of the fine parts during the degradation analysis, especially the nanometer. Grade carrier concentration and defect evaluation are generally used: Scanning Probe Microscope (SPM), Scanning Spread Resistance Microscopy (SSRM), Scanning Volume Resistance Microscopy (SCM; Scanning) Capacitance Microscopy), Cathodoluminescence (CL; Cathodo Luminescence).


Evaluation of resin and phosphor structure is generally considered to be: Fourier Transform Infrared Spectrometer (FT-IR), Solid-State Nuclear Magnetic Resonance (Solid-State Nuclear Magnetic Resonance), Raman Spectroscopic methods can achieve the desired results.

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