Versatile platform for electrically reconfigurable THz devices based on silicon Schottky-metasurfaces

Abstract

We propose a versatile platform to design tunable metasurface devices based on Au/n-Si Schottky diodes embedded in a split-ring resonator (SRR) devised on a Si-on-insulator (SOI) wafer. The horizontally formed diodes are connected in the SRR radial direction, reducing the overall junction capacitance of the metasurface array compared to its counterparts with vertically formed Schottky junctions. This reduction in the junction capacitance has an essential role in the switching speed of the metasurface between the On and Off states. By carefully varying the externally applied bias voltage to the Schottky diodes, one can manipulate the incident THz signal at the metasurface resonance frequencies by converting its resonance mode by switching states. We use the forenamed platform to design three fundamental THz devices: a modulator, a polarization switch, and a polarizing beam splitter. A reverse bias of V R =5V excites two LC resonances at 0.3 THz and 0.89 THz in the modulator, which fade away by switching the gate voltage to V F =0.49V, exciting a dipole resonance in the metasurface at 0.75 THz. The numerical results show that this THz modulator enjoys modulation depths of ≥92% at the LC resonances and a phase modulation of ∼1.16rad at 0.86 THz. An identical electric bias change of the Schottky diodes in the polarization switch alters the resonators from anisotropic to isotropic, changing the output wave polarization from circular with nearly 99% of the circular polarization percentage to linear or quasi-linear at four frequencies simultaneously. Additionally, the proposed THz polarization splitter can deflect the cross-polarized transmitted component from the normally outgoing co-polarized one with an angle of 70° at 0.56 THz. The splitting ratio is switched from 1:1 in reverse bias to 14:1 in forward bias by changing the bias to forward bias. We expect that the proposed designs in the THz frequency domain, benefiting from the several hundred GHz switching speed of the Schottky diodes array, will be beneficial in applications such as analysis of the complex organic structures or polarization modulation and polarization-dependent multiplexing/demultiplexing in wireless communication systems.