Friday, August 07, 2020

Samsung et al. Explores Subwavelength-Sized Color Pixel Approaches

Samsung, UCB, and Hong Kong University researches publish a Nature paper "Subwavelength pixelated CMOS color sensors based on anti-Hermitian metasurface" by Joseph S. T. Smalley, Xuexin Ren, Jeong Yub Lee, Woong Ko, Won-Jae Joo, Hongkyu Park, Sui Yang, Yuan Wang, Chang Seung Lee, Hyuck Choo, Sungwoo Hwang, and Xiang Zhang.

"The demand for essential pixel components with ever-decreasing size and enhanced performance is central to current optoelectronic applications, including imaging, sensing, photovoltaics and communications. The size of the pixels, however, are severely limited by the fundamental constraints of lightwave diffraction. Current development using transmissive filters and planar absorbing layers can shrink the pixel size, yet there are two major issues, optical and electrical crosstalk, that need to be addressed when the pixel dimension approaches wavelength scale. All these fundamental constraints preclude the continual reduction of pixel dimensions and enhanced performance. Here we demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. As a result, this subwavelength anti-Hermitian metasurface sensor, over 28,000 pixels, is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to sub-wavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems."

"Future directions for this work include integration with CMOS readout circuit arrays (Supplementary Fig. 11), extension of the spectral response to the blue end of the visible spectrum and optimization of the geometry to provide color-sorting for obliquely angled excitation.

As the demand for smaller pixel size and higher resolution in imaging and display technologies increases, our work advances the state-of-the-art by showing for the first time, PIN readout, three-color sorting over a two-dimensional surface without sacrificing responsivity. Furthermore, the sub-wavelength sized pixels are demonstrated based on the principle of AH coupling and fabricated via CMOS-compatible processes into vertical shallow junction PIN nanocylinders that efficiently convert optical energy to a clear electrical readout without crosstalk. Our work promises future compact, small pixelated, high-performance optoelectronic systems.

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