Active Terahertz Metamaterials Integrated with Metal–Semiconductor–Metal Varactor Diodes for Amplitude Modulation

Metal–semiconductor–metal (MSM) varactor diodes are integrated with a THz fishnet metamaterial with its resonance frequency in the terahertz (THz) frequency range. The electrically tunable capacitance enabled by MSM varactor diodes can shift the resonance frequency of the THz fishnet metamaterial and modulate the amplitude of transmitted THz waves. Conventional MSM varactor diodes can be represented by an equivalent circuit consisting of the series‐connected resistance and capacitance. When the frequency increases, the kinetic inductance associated with the two‐dimensional electron gas (2DEG) becomes significant in the THz frequency range. A very large resonance frequency shift as large as 0.57 THz is obtained due to the effect of the kinetic inductance change as well as the capacitance change in the THz metamaterial based on the fishnet structures. The fabricated THz fishnet metamaterial integrated with the MSM‐2DEG varactor diodes exhibits a modulation depth of 54.7% and an insertion loss of 3.32 dB at 0.66 THz.