Dual-band uncooled infrared sensors employing Fano resonance in plasmonic absorbers

Wavelength-selective uncooled infrared (IR) sensors have significant advantages with regard to applications such as fire detection, gas analysis, hazardous materials recognition, and biological analysis. We have previously demonstrated an uncooled IR sensor based on a two-dimensional plasmonic absorber (2D PLA) that exhibited wavelength-selective absorption over a wide range spanning the middle and long-wavelength IR regions. This device had a Au-based 2D periodic dimple-array structure, in which surface plasmon modes were induced, leading to wavelength-selective absorption, such that the absorption wavelength was determined by the period of the surface dimples. However, dual-band operation based on this concept has not yet been investigated, even though the ability to absorb in two different wavelength bands is extremely important for object recognition. In the present study, a dual-band uncooled IR sensor was developed using a 2D PLA with asymmetric dimple periods (2-D PLA-AP). To achieve multiband absorption, the Au-based dimples in this device were fabricated so as to have different periods in the orthogonal x and y directions. Theoretical calculations predicted asymmetric absorption spectra, attributed to Fano resonance in the 2-D PLA-AP. A sensor was subsequently fabricated using complementary metal oxide semiconductor and micromachining techniques. Measurement of the spectral responsivity demonstrated that selective absorption occurred in two different wavelength bands, determined by the dimple periods in the x and y directions. The results obtained in this study will be applicable to the development of advanced sensors capable of multiband detection in the IR region.