Wavelength-dependent near-infrared microbolometer for short-wavelength infrared light with gold nanowire grating optical absorber

Abstract

Near-infrared (NIR) imaging has been used for nondestructive and non-contact inspections in various areas, such as food and medicine inspections and medical diagnoses. The short-wavelength infrared light (SWIR) sensor currently used requires a Peltier cooler and a diffraction grating spectroscope owing to its detection principle. Thus, realizing a lowcost and miniaturized SWIR imaging device remains challenging and has limitations for practical applications. In this study, we propose a bolometer-type detector element fabricated using a silicon-on-insulator (SOI) wafer as a low cost and miniaturized SWIR image sensor element. We adopted gold (Au) nanowire grating structures coated with silicon as wavelength-dependent SWIR absorbers and aimed at wavelength-selectivity imaging without using a spectroscope. A device was designed and fabricated with Au nanowire grating structures on a doubly clamped Si beam using microelectromechanical system (MEMS)) technology. The electrical characteristics of the device were measured depending on device temperature and SWIR irradiation intensity. It was found that electrical resistance decreased linearly with increasing device temperature and SWIR irradiation intensity (wavelength at 1530 nm), as semiconductors have negative temperature coefficients of resistance. The results show similar trends from both finite element method (FEM) analysis and theoretical calculation. The resistances at wavelengths ranging from 1530 to 1565 nm at 5 nm increment were evaluated. It was confirmed that absorber-integrated bolometer device enabled wavelength-dependent response of the resistance according to the absorption spectrum.

Spectroscopic measurement of water using an electrostatic transducer with near‐infrared absorber

“…A pad part is provided in the middle of device, and a gold (Au) nanostructure optical absorber is placed there. The Au nanostructure optical absorber used in this study has a grating structure and an absorption peak in near-infrared regio 18,19,21 so as to make up for low near-infrared light absorbance of Si. In addition, the central pad is sufficiently wider than the beam, and can be treated as a rigid body.…”

“…The structure of optical absorber used in this study allows obtaining a narrowband absorption peak, and the peak wavelength can be controlled through the pitch of nanowire grating. 18,19,21 In the experiments, the device is illuminated not with the Au optical absorber but with a wavelength selected by the monochromator so as to verify a possibility of application to near-infrared spectroscopy. In order to eliminate the influence of difference in optical absorbance, light detection was performed using an optical absorber with low wavelength dependence (Figure 5).…”