Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform
With advanced nanotechnology, the emerging structural color filter which works based on the light-matter interaction is able to overcome the drawbacks of the traditional dye-based color filters including environmental hazards and performance degradation. Therefore, it has been regarded as an essential optical component and widely applied in daily life.
The structural color filters with narrow passband contributed by the periodic pillar or hole structure have been widely studied. The passband of the additive color filter (ACF) can be designed by tuning the period, pitch, or dimension of the subwavelength structures. However, ACFs have relatively lower transmission/reflection efficiency compared with its counterpart, which is the subtractive color filter (SCF), since most of the light in the spectrum is filtered out. The SCFs can achieve higher transmission/reflection efficiency since they work based on the removal of the complementary color. In the meanwhile, the SCF fabricated on CMOS-compatible platform in large scale using photolithography patterning technology remains unexplored.
In this study conducted by the group from Institute of Microelectronics (IME), Agency for Science, Technology and Research (A*STAR) Singapore, SCFs on 12-inch (300-mm) glass wafer substrate fabricated using the CMOS-compatible process is demonstrated. It was published in Photonics Research, Vol. 9, No. 1, 2021 (Zhengji Xu, Nanxi Li, Yuan Dong, Yuan Hsing Fu, Ting Hu, Qize Zhong, Yanyan Zhou, Dongdong Li, Shiyang Zhu, Navab Singh. Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform. Photonics Research, 2021, 9(1): 01000013).
Large-area metasurface devices on a 12-inch glass wafer
An amorphous Si layer has been patterned and used as a metasurface layer. To make the transmissive-type SCF on a transparent glass wafer substrate, an in-house developed layer transfer process is used to solve the glass wafer handling issue in fabrication tools. Three batches of wafer with pillar height variation (110, 170, and 230 nm) are fabricated. The effect of a-Si nanopillar height on the device transmittance spectra is investigated through both simulation and experiment. With pillar height and pitch variation, SCFs with different displayed colors are achieved. The displayed colors are verified by matching the complementary color of filtered color within red-yellow-blue (RYB) color wheel. The transmittance spectra obtained from simulation and experiment have been compared and discussed. Also, by utilizing the CIE 1931 color matching function, the chromaticity coordinates of transmittance spectra for SCFs are plotted.
This work paves the way toward the large-scale mass production of the structural color filters and this is promising for the potential commercialization and large-scale deployment of the metasurface-based optical devices.