Broadband polarization-selective uncooled infrared sensors using tapered plasmonic micrograting absorbers

Polarization-selective uncooled infrared (IR) sensors are promising for IR polarimetric imaging with respect to enhancement of the object recognition ability. Polarization-selective absorbers that operate in the broadband wavelength region and have simply fabricated small structures are strongly required for high-performance IR polarimetric imaging. In the present study, plasmonic micrograting absorbers (PMGAs) were designed as broadband polarization-selective absorbers. The PMGAs have an Au-based one-dimensional periodic grating structure. Numerical calculations demonstrated that tapered-sidewalls with deep groove depths produce broadband polarization-selective absorption with wavelengths larger than the grating period. Microelectromechanical systems-based uncooled IR sensors with tapered-PMGAs were fabricated using complementary metal oxide semiconductor and micromachining techniques. Tapered-sidewalls were formed by isotropic etching using reactive ion etching equipment. The responsivity could be selectively enhanced according to the polarization angle, and an absorption wavelength longer than the surface period and broadband absorption were realized due to the effect of the tapered-sidewalls. The PMGAs enable detection wavelengths longer than the grating period and broadband polarization-selectivity by control of the taper angle and the grating depth. The results obtained in this study will contribute to the advancement of polarimetric IR imaging.