Near-infrared (NIR) absorbing films based on diimmonium dye and cyanine dye for high-performance NIR cut-off filter

In the CMOS (complementary metal-oxide-semiconductor) image sensor, the NIR cut-off filter is an important component to adjust the image quality by transmitting visible light and blocking near-infrared (NIR) light selectively. In this work, we developed NIR absorbing films applicable to NIR cut-off filter using anti-reflective coatings. A variety of polymeric binders were applied to NIR absorbing films to optimize the thermal stability to the process of anti-reflective coatings. The thermal stability of NIR absorbing films was improved by applying polysulfone (PSU) with high thermal stability. Furthermore, the simultaneous use of a diimmonium dye and a cyanine dye was evaluated to maximize the NIR cut-off ability of the filter. The effect of anti-reflective coatings of TiO2/SiO2 on both sides of the NIR absorbing films was investigated by the optical simulation. As a result, the NIR cut-off filter based on PSU films incorporating a diimmonium dye and a cyanine dye showed a superior NIR cut-off ability without incident angle dependence and leakage of incident light.