Tunable terahertz metamaterial using fractal microheater for refractive index sensing application

We present an electrothermally controllable electric split-ring resonator (eSRR) consisting of a fractal microheater with SRR structure and metallic lines on silicon substrate. All eSRR units are connected to generate Joule heat by input electric current. In this work, two designs of eSRR configurations are proposed. They are the symmetric (eSRR-1) and asymmetric (eSRR-2) designs. By applying a direct current (DC) bias voltage from 0 to 2.53 V, the ambient refractive index (RI) can be changed from 1.0 to 2.6. The electromagnetic response of eSRR-1 exhibits dual-resonance with tuning ranges of 96-116 GHz, while that of eSRR-2 exhibits triple-resonance with tuning ranges of 96 GHz, 93 GHz, and 107 GHz, respectively. For RI sensing application, the maximum quality-factor (Q-factor) of eSRR-1 can be tuned from 25.4 to 41.4, and the figure of merit value can be also tuned from 25.2 to 40.0 by increasing the driving voltage. For eSRR-2, the maximum Q-factors can be changed from 45.8 to 174.3, and FOM values can be tuned from 36.9 to 133.5, respectively. The maximum sensitivity (S) values are 81.1 GHz/RIU and 76.6 GHz/RIU for eSRR-1and eSRR-2, respectively. In addition, an extra resonance could be stimulated by lifting the metallic bar of eSRR. In the process of lifting the metallic bar, the generated extra resonance is firstly red-shifted 10 GHz due to the decoupling effect with the substrate and then blue-shifted 68 GHz originating from the increment of lifting height. These characteristics of eSRR designs provide the great potential possibility for actively tunable devices and RI sensors in future.