Enhancement of Light Extraction Efficiency and High Reliable DPC Ceramic Base against Photochemical Damage by PVD Al Film for UV-LED Application

Due to the EU rules on mercury, the UV lamp will be disallowed to include mercury in 2020. Therefore, the UV LED becomes the alternative solution instead of UV lamp. However, based on the limitation of photoelectric efficiency in UV LED, most electricity will be dissipated and generate heat. Thus, the great thermal dissipation path will be the most concerned on LED package. Besides, the active reflector surrounding UV LED is necessary as well to increase radiant flux.In this paper, a high performance and reliable package is developed by using AlN ceramic substrate. The excellent thermal conductivity, 170W and lower heat capacity can help the heat spreading and transferring to cooling system. Based on the simulation results, the static thermal resistance, Θ
_jb
is 1.2 and 2.2°C/W for AlN and Al
₂
O
₃
substrate respectively. As for the cavity structure, it is formed by ceramic dam attached onto AlN substrate. Generally, the adhesive for dam attachment will be exposed under UV irradiation and get crack while the radiant exposure higher than bonding energy. Therefore, the additional process of depositing thin-film Al is applied after ceramic dam attachment. And it has been proved that the ceramic base can sustain more than 100,000 mJ of radiant energy which irradiance is higher than 100 mW/cm
²
. In addition to radiant resistance, the lifetime test during high heat and moisture (60°C, 90%) is performed and evaluated on the effect of applying Al thin-film. Based on Weibull distribution analysis, the characteristic lifetime shows 1.5 times of enhancement when Al thin-film applied. And the shape parameter becomes from 1.4 to 2.5 which indicates that deposited Al thin-film plays the role of protection against UV radiance and penetration of moisture.