Surface-plasmon-coupled optical force sensors based on metal\u2013insulator\u2013metal metamaterials with movable air gap

Taiyu Okatani,Kazuhiro Hane,Shota Sekiguchi,Yoshiaki Kanamori

doi:10.1038/s41598-020-71825-x

Abstract

We proposed surface-plasmon-coupled optical force sensors based on metal–insulator–metal (MIM) metamaterials with a movable air gap as an insulator layer. The MIM metamaterial was composed of an air gap sandwiched by a metal nanodot array and a metal diaphragm, the resonant wavelength of which was red-shifted when the air gap was narrowed by applying a normal force. We designed and fabricated a prototype of the proposed sensor and confirmed that the MIM metamaterial could be used as a force sensor with larger sensitivity than a force sensor based on Fabry-Pérot interferometer (FPI).

Highlights

We proposed surface-plasmon-coupled optical force sensors based on metal–insulator–metal (MIM) metamaterials with a movable air gap as an insulator layer
We propose a MIM-metamaterial-based force sensor which is composed of an air gap as an insulator layer sandwiched by a metal nanodot array and a metal diaphragm
The MIM metamaterial is composed of the Al film as a top metal layer, the movable air gap and the S iO2 cap as an insulator layer, and the Al nanodot array as a bottom metal layer

Summary

Introduction

We proposed surface-plasmon-coupled optical force sensors based on metal–insulator–metal (MIM) metamaterials with a movable air gap as an insulator layer. The resonant wavelength depends on the thickness of insulator layer and drastically shifts when the insulator layer becomes narrower[29] This shift per unit thickness change can be larger than that of FPI; there is a possibility to break through the tradeoff of the existing optical force sensors. We propose a MIM-metamaterial-based force sensor which is composed of an air gap as an insulator layer sandwiched by a metal nanodot array and a metal diaphragm. Compared to an FPI-based force sensor, the MIM-metamaterial-based force sensor shows larger resonant wavelength shift per unit thickness change of the air gap. Note that Al is chosen as the material of MIM metamaterials because Al is found better than Au in adhesiveness to SiO2 and better than Ag in oxidative resistance due to the oxide film near the Al surface

Methods

Results

Conclusion