Dye-Doped Siloxane Coating Film for Camera Module Infrared Cut-Off Filter

Abstract

A Charge-Coupled Device (CCD) and a Complementary Metal Oxide Semiconductor (CMOS) are now widely used for the image sensor in the camera module. However, they sense not only visible light range but also infrared range which leads to high degradation of image resolution. Therefore Infrared cut-off (IRCF) filter is neccessary for camera modules used in smartphone and automobile. There are two types of IRCF filters, e.g. a reflection and an absorption type. In general, hybrid IRCF filter, the absorption filter with coated reflection layers is required for a high pixel camera module. [1] Until now, IR absorbing glass, so called ‘blue filter’ is widely used for a high quality absorption type IRCF filter. However, the slimization of the camera module for smartphone and automobile makes it inevitable to replace glass to thin film with a high strength. In this work, we fabricated dye doped siloxane resin for an absorption type IRCF flexible hard coating on the PET film. First, we synthesized dye dispersed siloxane via in-situ sol-gel condensation reaction and coated the resin on the PET film. After cationic polymerization was induced by UV, the IRCF flexible hard coating layer was well fabricated and attached to the PET film. Figure 1 (a-b) show the dye doped siloxane resin and the IRCF flexible hard coated PET film each. Figure 1 (c) shows a transmittance graph of the IRCF flexible hard coated PET film. It shows 80% transmittance at visible range with zero at 700nm to 800nm. Additional SiO₂ and TiO₂ layers will be deposited by evaporation method on the IRCF flexible hard coated PET film to get over 90% of transmittance. We also measured pencil hardness of the IRCF flexible hard coated PET films depending on coating thickness. With 20um and 50um coating layer, it shows 5H and 8H value each which is very high compare to bare PET (6B).