Design, Fabrication and Characterization of Wide-Band Metamaterial Absorber for THz Imaging

In this paper, designs and optimization of wideband THz metamaterial absorbers (MMA) is proposed. By simulation, we reached four structures with absorptions higher than 50%, 70%, 80%, and 90% with relative absorption bandwidths (RABW) of 1.43, 1.29, 0.93, and 0.72, respectively. Terahertz absorbers can be used in many potential applications such as in imaging, energy harvesting, scattering reduction, and thermal sensing. Our intended application is to use an optimal absorber on a thermal detector for the detectivity in a wide THz range. Since a broadband absorption in the range of 0.3 to 2 terahertz is considered for use in medical imaging, the MMA with more than 50% absorption in the range of 0.35-2.1 THz has been selected to be achieved. The designs are also intended to have the capability to be implemented on different devices such as bolometers. The cost of the fabrication of the proposed absorbers is also low, because of the implementation of single-layer MMA design, and utilization of affordable and more accessible materials and techniques. Our proposed structure has a minimum feature size of 3 μm making the fabrication process convenient using the standard photolithography method as well. We used thin layers of Nickel as a metal for both single-layer pattern and ground layer which are placed on the front and back sides of the structure respectively. The Nickel thin film layers are deposited using the sputtering technique and are separated by a dielectric layer. The material chosen for the dielectric layer is SU8 which has proper properties and also has good adhesion to Nickel. Characterization of the fabricated absorber has been performed using a terahertz spectroscopy system, and the experimental results verified the high absorption of the sample.