Reconfigurable Spoof Surface Plasmon Polariton Band-stop Filter with Monolithic Schottky Diodes

Surface plasmon polaritons (SPPs) provide high electric field confinement and non-diffraction limit at optical, terahertz, and microwave frequencies. Several approaches have been explored to actively manipulate SPPs with a typical modulation capability of only a few percent. Here, active control of SPPs using monolithically fabricated Schottky diodes has been demonstrated with a significant modulation of transmission and reflection. The proposed device is based on a novel spoof SPP band-stop filter with single-loop split ring resonators (SRRs) and Schottky diodes connecting the SRR split gaps. Differing from the reported works, the SRRs are designed directly on a SPP waveguide to provide both a low-pass response as the conventional rectangular corrugations and an additional band-stop response, the latter of which is induced by the SRR resonance. The IGZO Schottky diode bridges each SRR split gap with a tunable resistance of a few orders of magnitude at various bias, and thus actively modulates the SPP attenuation. As the forward bias increases, the free carriers with increasing density short out the capacitor gradually, which leads to weaker resonance magnitude of SRRs and smaller attenuation. The measured S parameters of the proposed active SPP device reveal a remarkable modulation range of 40% for the transmission of SPPs at 49 GHz.