Because it has longer life and uses much less power than filament lighting, LED is expected to be the next-generation lighting device. Moreover, taking advantage of its special properties, LED's are not limited to general lighting. There have been advances in the application of LED's to LCD's and car headlamps. To raise the luminosity efficiency of LED's, the metallic reflective film with the highest reflectivity is used. As a reflective film material, Ag has the highest reflectivity in the visual light range (400–800nm) and is used in many cases. However, Ag is a thermally active material and we have concerns about the decrease in reflectivity by aggregation and heat treatment sulfuration. In this study we investigate an ultra high heat proof protective film for a thin Ag reflective film. Conventionally, SiO2 thin film is used as a protective film for Ag reflective film, but it is difficult to obtain heat proofing > 473K. In this research we consider a SnO2 protective film which combines high heat proofing and high crystallinity. We formed a SnO2 protective film on an Ag thin film under various conditions, and investigated its heat proofing characteristics. We succeeded in obtaining ultra-high heat proofing exceeding 773K using several 10 nm protective film. Furthermore, in trying to understand the mechanism of this outstanding high heat proofing reflective film system, it became clear that the crystallinity in high temperature diffusion plays a major role. In addition, we have found the possible beginnings of a general theory for high temperature stability for nanotechnology.

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