Ultraviolet LED has many advantages, such as small volume, long life and high efficiency. It has a wide application prospect. At present, the luminous power of ultraviolet LED is not high. In addition to the improvement of chip fabrication level, packaging technology also has an important impact on the characteristics of LED.


At present, ultraviolet LED mainly includes epoxy resin packaging and metal and glass lens packaging. The former is mainly used in near-ultraviolet LED at about 400 nm, but ultraviolet light has a great influence on the aging of the material. The latter is mainly used in ultraviolet LED whose wavelength is less than 380 nm. Because the refractive index of GaN and sapphire is 2.4 and 1.76 respectively, and the refractive index of gas is 1, the greater refractive index difference results in the severe limitation of total reflection on light, and the light output efficiency after packaging is low.


Packaging material is another important aspect of LED packaging technology. LED packaging materials mainly include glass lens, epoxy resin and silicone resin. The softening point temperature of quartz glass is 1 600 C, and the hot-working temperature is 1 700-2000 C. From the point of view of technology, quartz glass is not suitable for sealing LED chips; epoxy resin has general high-temperature heat resistance and poor ultraviolet resistance; silicone resin has been used for LED packaging in recent years. At present, there are few studies on the transmittance, heat resistance and ultraviolet light resistance of silicone resin in China. Especially for the ultraviolet LED encapsulated in silicone resin, there is still a lack of research.


Based on the packaging technology of ultraviolet LED with wavelength less than 380 nm, this paper compares the transmittance, ultraviolet light resistance and heat resistance of different packaging materials, and then proposes a high light efficiency and high reliability ultraviolet LED packaging structure.

Ultraviolet LED chips with peak wavelengths of 395 and 375 nm were fabricated by epitaxial growth of GaN on silicon carbide and sapphire substrates, respectively. At 20 mA injection current, the operating voltages of SiC and sapphire substrates are 3.8 V and 3.4 V, respectively.


Five kinds of typical packaging materials of quartz glass, epoxy resin and silicone resin were studied. Quartz glass is JGS1 material with thickness of 2 mm; epoxy resin A and B are bisphenol A and alicyclic epoxy resin respectively; silicone resin A and B are elastic silica gel and resin silica gel respectively.


Optical power and peak wavelength were measured on PMS-50 enhanced ultraviolet-visible-near infrared spectroscopy system of Hangzhou Distant Company. The measurement system of optical transmittance is shown in Figure 1. The monochrometer is CM200 of Jiangsu Weixin Science and Technology Company. The source of the lamp is GY-10 high-pressure spherical xenon lamp of Tianjin Top Company. The signal acquisition and processing system adopts the ultraviolet-visible light analysis system of the remote company.