Broadband Sensing Around 1 THz Via a Novel Biquad-Antenna-Coupled Low-NEP Detector in CMOS

We report on the design and characterization of a novel backside-radiating antenna-coupled direct terahertz detector fabricated in 65 nm CMOS technology. The novelty of the design lies in the low-metal coverage of the biquad antenna geometry, which adapts well to the particular challenging conditions of on-chip antenna integration in silicon and allows optimization for a versatility of operation conditions. The biquad antenna was modified here to achieve wideband radiation and matching to a gate-coupled single-finger field-effect transistor with ac open condition at the drain terminal. The successful detector performance was the result of a careful treatment of transistor, antenna, and optics from a codesign perspective, since the beginning of the design. This included the frequency-dependent complex impedance for optimum matching, the technology restrictions to ensure proper chip fabrication, and the overall detection efficiency after backing the device with a silicon lens. Calibrated detector measurements for 7777 Hz modulation frequency yielded minimum optical noise-equivalent power (NEP) of 25 pW/ √ Hz at 1 THz, with NEP values below 50 pW/√Hz in the 0.84-1.29 THz frequency range. These figures achieve state-of-the-art of wideband CMOS-based detectors and are only a factor of ~2 inferior to the best reported narrowband devices close to 1 THz.