Temperature-controlled metasurface terahertz wave modulator based on high-temperature magnetron-sputtered strontium titanate

Abstract In this study, a series of temperature-controlled terahertz (THz) wave modulators based on a combination of magnetron-sputtered strontium titanate (STO) thin films and metasurfaces have been proposed. As the sputtering temperature increased from 25 to 600°C, the STO thin films exhibited an evolution from amorphous to polycrystalline states and thus different dielectric responses were observed in the THz band. Differences in the performance of the THz wave modulators such as differences in the variation trends of the amplitude and frequency of the resonance peaks as a function of the heating temperature were observed in the THz transmission spectra. The variation in the permittivity as a function of heating also exhibited different trends for the as-deposited STO films and fabricated modulators when the sputtering temperature was increased. Although a maximum amplitude modulation depth of 29.8% was obtained for the modulator with STO sputtered at 25°C, the frequency-shift exhibited nearly no regular variation on heating. On the contrary, amplitude as well as frequency modulations were achieved for the THz wave when the sputtering temperature of STO for the modulator exceeded 200°C. This study presents a high-temperature sputtering method for fabricating STO temperature-controlled modulators that can provide simultaneous modulation of amplitude and frequency of THz waves.