Metasurface-based subtractive color filter fabricated on a 12-inch glass wafer using a CMOS platform
Large-area metasurface devices on a 12-inch glass wafer
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).
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.
CMOS平台上实现基于超表面的减色滤波器
在12英寸玻璃晶圆上的大面积超表面器件
随着纳米技术的不断发展革新，基于光和微纳物质结构相互作用的可见光滤波器随之产生，并被视为必不可少的光学组件，广泛应用于日常生活中。这类基于微纳结构的可见光滤波器能够克服基于染料的传统可见光滤波器的缺点，如化学染料对环境的危害、长时间使用后染料褪色导致的性能下降等。
基于微纳结构的可见光窄通带滤波器（一般由周期性的圆柱或圆柱形空槽结构组成）已得到广泛研究。其中，增色滤波器（ACF）的通带通过调整亚波长结构的周期、间距或尺寸就可以实现。但是，当ACF和与其对应的减色滤波器（SCF）相比较时，由于SCF是基于互补色去除的工作原理，即不存在光谱中大部分光被滤除的问题，从而具有比ACF更高的透射和反射效率。与此同时，使用先进光刻技术在互补金属氧化物半导体 (CMOS)兼容平台上大规模制造SCF还有待探索。
针对以上研究现状，新加坡科技研究局（A*STAR）微电子研究院（IME）的研究团队在Photonics Research 2021年第1期发表的文章中（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）首次展示了使用CMOS兼容工艺在12英寸(300 mm)玻璃晶圆上制造的SCF。
该研究团队将经过刻蚀之后的非晶硅层作为超表面层，同时为了在透明玻璃晶圆上制造透射型SCF，还将新开发的薄膜层转移工艺用于解决微纳制造设备中的玻璃晶圆的处理难题。接着使用CMOS兼容工艺制造了三批具有不同高度（110，170和230 nm）的非晶硅纳米柱晶圆，并通过仿真和实验研究了非晶硅纳米柱高度对器件透射光谱的影响。此外，还发现通过对纳米柱高度和间距的改变，可以获得具有不同显示颜色的SCF（所显示的颜色由匹配红、黄、蓝（RYB）色轮内已过滤颜色的互补色来验证）。
与此同时，该研究团队还对仿真和实验获得的透射光谱进行了比较和讨论。并通过CIE 1931（由国际照明委员会于1931年创立的最先采用数学方式来定义的色彩空间）颜色匹配函数，绘制了SCF透射光谱的色度坐标。
研究团队表示，该工作一方面为大规模生产结构性滤波器奠定了基础，另一方面在大面积超表面光学组件的量产和商业化方面展示了有利的前景。