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

Abstract

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 fieldeffect 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 co-design 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-equivalentpower (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. Index Terms-CMOS integrated circuit, on-chip antenna, TeraFET, terahertz power detector, wideband terahertz sensor. I. INTRODUCTIONE MERGING applications in the field of optoelectronic terahertz (THz) equipment are pushing the demand for compact, high-performing, cost-effective technology solutions for room-temperature operation in the THz range [1]-[3].

State-of-the-Art Room Temperature Operable Zero-Bias Schottky Diode-Based Terahertz Detector Up to 5.56 THz

“…The current responsivity of 100 mA/W is demonstrated with the table-top system. The calculated responsivity for the table-top system measurements assumes a lock in the peak-to-peak correction factor of ∼3 [ 37 ]. This correction factor was experimentally obtained from time-domain acquisitions as the ratio of the full-waveform peak-to-peak response and its fundamental component.…”

Sensitivity of Field-Effect Transistor-Based Terahertz Detectors

“…As the detection was studied under zero drain bias, thermal noise was the only source of noise for the transistor, which can be calculated by , where is the Boltzmann constant, T is the temperature, and is the DC drain-source resistance of the transistor. This statement has been tested on many different devices of the same kind and has been addressed in a series of reports [ 24 , 25 , 103 ].…”

“…Much progress has been reported in terms of improving the optical performance of devices implemented using CMOS technologies. For example, employing biquad antennas allows for reaching ∼25 pW/ at 1 THz with more than 400 GHz bandwidth [ 25 ], or larger than 1 THz bandwidth with ∼50 pW/ for the bow-tie antenna-coupled detectors [ 26 ], which are competitive to commercial quasioptical Schottky diode detectors [ 27 ]. In parallel to the progress in silicon technology-based devices, sensitive detectors have been produced using field-effect transistors fabricated using III–V technologies, mono- and bilayer graphene, as well as by invoking other detection principles, such as ballistic transport [ 28 ] or thermoelectric currents [ 29 , 30 , 31 ].…”

Coherent Terahertz Detection via Ultrafast Dynamics of Hot Dirac Fermions in Graphene

“…The frequency-dependent antenna impedance Z ant (ν) is obtained from EM simulations (Keysight Advanced Design System (ADS)), see Supporting Information. P D is the fraction of the total free-space beam power P THz op which is collected by the antenna and can be determined from P D = (1/2)·η op ·η gauss ·η ant (ν)· P THz op , , such that the total power delivered to the multilayer graphene is obtained from P THz = η tot (ν)· P THz op , where the total coupling efficiency, given by η tot (ν) = (1/2)·η op ·η gauss ·η ant (ν)·η m (ν), accounts for all losses toward the antenna gap. The free-space THz power P THz op from the Toptica emitter, incident at the air-to-silicon-lens interface of the detector, was measured with a calibrated Golay cell across the range 60–700 GHz, with the following values: 29.7 μW (60 GHz); 5.5 μW (70 GHz, local dip); 29.2 μW (80 GHz); 45.9 μW (90 GHz, spectral maximum); 5.9 μW (300 GHz); 0.35 μW (700 GHz).…”