We report the successful implementation of antenna-coupled terahertz field-effect transistors (TeraFETs) as homodyne detectors in a scattering-type scanning near-field optical microscope (s-SNOM) operating with radiation at 246.5 GHz. The devices were fabricated in Si CMOS foundry technology with two different technologies, a 90 nm process, which provides a better device performance, and a less expensive 180 nm one. The high sensitivity enables s-SNOM demodulation at up to the 10th harmonic of the cantilever's oscillation frequency. While we demonstrate application of TeraFETs at a fixed radiation frequency, this type of detector device is able to cover the entire THz frequency range.
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