Study of Blue/Green Dual Wavelength LED Chip for Wide Color Gamut in Backlighting Application

Utilizing downconverters with a narrow emission lin- ewidth and a precisely tunable peak is a common approach to obtain wide color gamut (WCG) in today's backlighting for TV and monitor displays. Narrow band green and red phosphors such as b-SiAlON and KSF or quantum dots (QDs) are used to convert blue LEDs to white lights. How- ever, the narrow band green color needs improvement, es- pecially in on-chip configuration. The green b-SiAlON phosphor has FWHM around 50nm and its peak wave- length is in the range of 529nm to 540nm and can't be low- er, while the green quantum dots is less reliable than red ones due to its smaller size and high tendency to decay in high temperature and high humidity conditions. This paper explores a new structure by using a blue/green dual-color monolithic LED to excite narrow band red color converter for WCG backlighting. The LED chip comprises a regular blue wavelength region for the electroluminescence (EL) emission, and a native photoluminescence (PL) region for green color conversion. It can precisely tune the wave- length and green to blue spectral power ratio. We will dis- cuss the LED packaging structure, the backlighting metrics, and reliability test results in comparison to the conventional single wavelength blue LED and narrow band phosphor approaches. It shows that the blue/green dual-color chip combining with KSF red phosphor can achieve a wider color gamut than blue LED combining with b-SiAlON and KSF approaches. The optoelectrical characteristics depend- ence of junction temperature as well as the reliability test results will be discussed.