Large infrared absorptance of bimaterial microcantilevers based on silicon high contrast grating

Manufacturing sensors for the mid-IR spectral region (3-11 μm) are especially challenging given the large spectral bandwidth, lack of convenient material properties, and need for sensitivity due to weak sources. Here, we present bimaterial microcantilevers based on silicon high contrast grating (HCG) as alternatives. The grating integrated into the cantilevers leverages the high refractive index contrast between the silicon and its surrounding medium, air. The cantilevers with HCG exhibit larger active spectral range and absorptance in mid-IR as compared to cantilevers without HCG. We design and fabricate two types of HCG bimaterial cantilevers such that the HCG resonance modes occur in mid-IR spectral region. Based on the measurements using a Fourier transform infrared (FTIR) microspectrometer, we show that the HCG cantilevers have 3-4X wider total IR absorptance bandwidths and 30% larger absorptance peak amplitude than the cantilever without HCG, over the 3-11 μm wavelength region. Based on the enhanced IR absorptance, HCG cantilevers show 13-47X greater responsivity than the cantilever without HCG. Finally, we demonstrate that the enhanced IR sensitivity of the HCG cantilever enables transmission IR spectroscopy with a Michelson interferometer. The HCG cantilever shows comparable signal to noise ratio to a low-end commercial FTIR system and exhibits a linear response to incident IR power.