Subwavelength pixelated CMOS color sensors based on Anti-Hermitian metasurface
Journal
Nature Communications
Date
2020.08.06
Abstract
As the form factor of optoelectronic systems becomes ever smaller, the specifications for color and image sensors become increasingly challenging to meet. The size of conventional pixels, which ultimately limits the image resolution for a given sensor area, or the sensor area for a specified resolution, cannot be continually decreased due to the fundamental constraints of lightwave diffraction and charge carrier diffusion. For example, conventional pixel designs using transmissive filters and planar absorbing layers lead to optical and electrical crosstalk when the pixel dimension approaches wavelength scale, drastically reducing the utility of detectors with small pixels. Despite these seemingly fundamental constraints, herein we demonstrate subwavelength scale pixels based on anti-Hermitian coupling that circumvent the problems of conventional pixels. Spectral filtering is achieved through structural color rather than transmissive filters, namely through Mie resonances in shallow junction PIN silicon nanocylinders with carefully controlled doping profiles, diameters, and separation distances, leading to simultaneously high color purity and quantum efficiency. Our anti-Hermitian metasurface pixels are the first demonstration of anti-Hermitian coupling in a CMOS compatible platform, sorting three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. The two-dimensional, 60 μm by 60 μm array, contains over 28,000 pixels, each with an area less than half a squared wavelength of the absorbed light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration lays the foundation for the realization of CMOS color and image sensors with revolutionarily small pixel sizes.