Sumitomo Chemical Develops a Material Capable of Forming a Transparent Thin Film with an Ultra-Low Refractive Index

Sep. 24, 2026

Sumitomo Chemical has successfully developed a coating solution capable of forming a transparent thin film with an ultra-low refractive index. The Company will expand the material’s applications across a wide range of next-generation optical devices able to meet diverse optical design needs. In particular, it will focus on the light-collecting sections of complementary metal-oxide-semiconductor (CMOS) image sensors and the optical interconnect sections of photonics-electronics convergence ^(*1) devices.

In recent years, optical design has become increasingly advanced in optical device fields, such as optical sensing for CMOS image sensors, next-generation displays for augmented reality and virtual reality, and next-generation semiconductors, where the use of photonics-electronics convergence is growing. With these advances, there is a greater need for precisely controlling light by utilizing the refractive indices of materials. In particular, there is strong demand for ultra-low-refractive-index materials, in which the refractive index has been reduced to the lowest possible level. Such materials are used to control the refractive index difference between materials to improve light utilization efficiency, as well as to control the phase and reflection of light in next-generation optical elements, such as meta-lenses ^(*2).

Through its business in optical materials, including those for displays, Sumitomo Chemical has developed and expanded a lineup of resin coating solutions covering a wide range of refractive indices from high to low. Building on the advanced resin design technologies it has cultivated through this work, the Company has pursued the development of ultra-low-refractive-index materials. As a result of these efforts, it has now successfully developed a new coating solution that can form a thin film with a refractive index of 1.06, one of the world’s lowest levels for practical applications ^(*3).

The newly developed coating solution can be applied to a substrate by spin coating or similar methods, and then formed into a thin film through heating or UV irradiation. The resulting film has a structure in which nanoscale pores are uniformly dispersed, and by adjusting the composition of the coating solution and the conditions under which the film is formed, the refractive index at a wavelength of 550 nm can be controlled within the range of 1.06 to 1.36. In addition, the film offers high transmittance in the visible-light region, excellent heat resistance up to 300°C, and high solvent resistance ^(*4). Film thickness can also be adjusted to suit the intended application.

Provision of samples of the developed product is scheduled to begin this year. By adding this ultra-low-refractive-index material to its product lineup, Sumitomo Chemical will have a material portfolio with one of the broadest refractive-index ranges in the industry. Going forward, the Company will continue to provide new solutions by developing materials that address diverse optical design needs in the advanced device field.

(*1) A next-generation semiconductor and data center technology that integrates electrical and optical circuits. It replaces electrical signal transmission with light to reduce power consumption while enabling high-speed, large-capacity data communications.
(*2) A flat lens formed by arranging fine pillar structures made of high-refractive-index material and filling the spaces between them with low-refractive-index material. Meta-lenses can be made significantly thinner than conventional lenses and are a next-generation technology expected to be applied in areas such as photonics-electronics convergence.
(*3) According to the Company’s research as of August 2026. Based on a comparison of publicly available information on materials capable of forming colorless and transparent thin films under atmospheric pressure.
(*4) Under the Company’s evaluation conditions, no changes in film thickness or optical properties were observed, even after 10 minutes of immersion in acetone.

Reference

Characteristics of thin films made using the developed product

Film thickness	Up to 4 µm
Refractive index	1.06-1.36 (550 nm)
Transmittance*	99.9% (400-700 nm)
Haze*	<0.1%

*Per 1 μm of film thickness

Contact

Sumitomo Chemical Co., Ltd.
Corporate Communications Dept.
https://www.sumitomo-chem.co.jp/english/contact/public/