This paper presents the implementation of a 20- THz Far-Infrared (FIR) imager using an antenna-coupled Schottky barrier diode (SBD) structure fabricated in a 130-nm foundry CMOS process without any process modifications. The detector's performance is characterized using a 15.1 µm quantum-cascade laser (QCL) source. At a modulation frequency of 13 Hz, the detector achieves a peak optical responsivity (Rv) of 35.2 V/W, which is ~6 times higher than that of CMOS detectors operating in a similar frequency range. The measured shot-noise limited noise equivalent power (NEP) is 1.8 nW/√Hz which is comparable to that of commercially available thermopile detectors that are 47,000 times larger in area.