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. In this study we investigate an ultra high heat proof protective layer for a thin Ag reflective film. Conventionally, SiO2 thin film is used as a protective layer for Ag reflective film. But it is difficult to obtain heat proofing > 723K. In this research we consider a SnO2 protective layer which combines high heat proofing and high crystallinity. We formed a SnO2 protective layer on an Ag thin film under various conditions, and investigated its heat proofing characteristics. We succeeded in obtaining ultra-high heat proofing exceeding 723K using 5 nm protective layer. 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.
