Fig. 1. (a) Schematic illustration of our top-gate GFETs. (b) The photograph of the terahertz modulator based on top-gate GFET. The boundaries of the channel of GFET and the top electrode with graphene are marked with red dotted lines and black solid lines, respectively. (c) Typical Raman spectrum of monolayer graphene transferred onto SiO2/Si substrate. (d) Schematic of the experimental composition in our terahertz TDS system. The direction of the terahertz wave is incident from the graphene side and perpendicular to the surface of the terahertz modulator.

Fig. 2. Total resistance Rtotal as a function of the gate voltage in (a) PI- and (b) SiO2-based GFET.

Fig. 3. Normalized intensity of transmitted terahertz wave through the (a) SiO2- and (b) PI-based GFET under different gate voltages. (c) The modulation depth of PI-based GFET as a function of the applied gate voltage. (d) The comparison of the amplitudes of the terahertz wave transmission through the SiO2- and PI-based GFETs at 0.8 THz.

Fig. 4. (a) Transmittance and attenuation of PET and terahertz graphene modulator on PET substrate. (b) Transmittance and attenuation of p-Si and terahertz graphene modulator on the p-Si substrate.