Infrared broadband metasurface absorber for reducing the thermal mass of a microbolometer

Joo-Yun Jung,Kyungjun Song,Jihye Lee,Dean P Neikirk,Jun-Ho Jeong,Jun-Hyuk Choi,Dae-Geun Choi

doi:10.1038/s41598-017-00586-x

Joo-Yun Jung, Kyungjun Song + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-00586-x

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Abstract

We demonstrate an infrared broadband metasurface absorber that is suitable for increasing the response speed of a microbolometer by reducing its thermal mass. A large fraction of holes are made in a periodic pattern on a thin lossy metal layer characterised with a non-dispersive effective surface impedance. This can be used as a non-resonant metasurface that can be integrated with a Salisbury screen absorber to construct an absorbing membrane for a microbolometer that can significantly reduce the thermal mass while maintaining high infrared broadband absorption in the long wavelength infrared (LWIR) band. The non-dispersive effective surface impedance can be matched to the free space by optimising the surface resistance of the thin lossy metal layer depending on the size of the patterned holes by using a dc approximation method. In experiments a high broadband absorption was maintained even when the fill factor of the absorbing area was reduced to 28% (hole area: 72%), and it was theoretically maintained even when the fill factor of the absorbing area was reduced to 19% (hole area: 81%). Therefore, a metasurface with a non-dispersive effective surface impedance is a promising solution for reducing the thermal mass of infrared microbolometer pixels.

Highlights

There are two major classes of infrared detection: photon detection and thermal detection
We demonstrated that a large fraction of periodic patterned holes in a thin lossy metal layer with optimised surface resistance can produce an absorbing membrane for a microbolometer that significantly reduces the thermal mass while maintaining high infrared absorption over a wide range of wavelengths
NiCr for the fabricated metasurface absorbers was assumed to have dc resistivity in the long wavelength infrared (LWIR) band. This was confirmed by using calibration structures, which were simple unpatterned Salisbury screen absorbers with three different surface resistances of Rs = 85, 110, and 370 Ω corresponding to absorbing resistive layers of t = 35, 25, and 12 nm, respectively

Summary

Introduction

There are two major classes of infrared detection: photon detection and thermal detection. We demonstrated that a large fraction of periodic patterned holes in a thin lossy metal layer with optimised surface resistance can produce an absorbing membrane for a microbolometer that significantly reduces the thermal mass while maintaining high infrared absorption over a wide range of wavelengths. This can be accomplished by incorporating a non-resonant metasurface characterised with a non-dispersive effective surface impedance into a classical Salisbury screen absorber to form an asymmetric Fabry–Perot cavity. Our proposed metasurface absorber can provide an efficient solution for reducing the thermal mass of the absorbing membrane of a microbolometer

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