Wook-Ki Park

Design and Characterization of Plasmonic Terahertz Wave Detectors Based on Silicon Field-Effect Transistors

We report the first implementation of a modeling and simulation environment for the plasmonic terahertz (THz) detector based on the silicon (Si) field-effect transistor (FET) with a technology computer-aided-design (TCAD) platform. The nonresonant plasmonic behavior has been modeled by introducing a quasi-plasma electron box as a two-dimensional electron gas (2DEG) in the channel region. The alternate-current (AC) signal as an incoming THz wave radiation successfully induced a direct-current (DC) drain-to-source voltage as a detection signal in the broadband sub-THz frequency regime. The simulated dependences of photoinduced DC detection signals on structural parameters such as gate length and dielectric thickness confirmed the operation principle of the nonresonant plasmonic THz detector in the Si FET structure. We evaluated the design specifications of THz detectors considering both responsivity and noise equivalent power (NEP) as the typical performance metrics. The proposed methodologies provide the physical design platform for developing novel plasmonic THz detectors operating in the nonresonant detection mode.

Frequency-Tunable Waveguide Antenna With Miniaturized Aperture Using a Varactor-Loaded Split-Ring Resonator

We propose a frequency-tunable waveguide antenna with a size-reduced aperture. Up to now, waveguide antennas with split-ring resonators have exhibited narrow-frequency bandwidths. To expand the operating frequency band, the resonant frequency of a split-ring resonator is tuned by adjusting the capacitance of the gap. A capacitor-loaded split-ring resonator is simulated and experimentally tested to validate its performance, and a varactor-loaded split-ring resonator is then investigated. The effective capacitance of the varactor-loaded split-ring resonator is changed by varying the external dc voltage. The tunable frequency range extends from 1.96 to 2.36 GHz (a fractional frequency range of 18.5%). The simulations and experiments yield good results for the reflection coefficient, radiation pattern, and gain. The proposed antenna retains the 70% aperture reduction of previously developed split-ring-resonator-loaded waveguide antennas.

Photoresponse enhancement of plasmonic terahertz wave detector based on asymmetric silicon MOSFETs with antenna integration

We report the experiments of a plasmonic terahertz (THz) wave detector based on silicon (Si) field-effect transistors (FETs) in the nonresonant sub-THz (0.2 THz) regime. To investigate the effects of the overdamped charge asymmetry on responsivity (RV), a FET structure with the asymmetric source and drain area under the gate has been proposed. RV as a function of gate voltage in Si FET-based detectors integrated with an antenna has been successfully enhanced by the asymmetry ratio (ηa = WD/WS) of gate-overlapped drain width (WD) to source width (WS) in agreement with the nonresonant quasi-plasma wave detection theory. The experimentally measured photoresponse has been enhanced by about 36.2 times on average from various samples according to the 10-fold increase in ηa. The effect of the integrated bow-tie antenna on the performance enhancement has also been estimated as 60-fold at the maximum incident angle for the polarized THz wave source.

Plasmonic terahertz wave detector based on silicon field-effect transistors with asymmetric source and drain structures

In this letter, we report the experimental demonstrations of the enhanced responsivity in Si metal-oxide-semiconductor (MOS) FET-based plasmonic THz detector [2, 3] with asymmetric source and drain region considering the device width variations.

TCAD modeling and simulation of non-resonant plasmonic THz detector based on asymmetric silicon MOSFETs

We report the experiments of plasmonic terahertz (THz) wave detector based on silicon field-effect transistors (FETs) in the nonresonant sub-THz (0.2 THz) regime. The detector responsivity (RV) as a function of gate voltage has been successfully controlled by the radiation power in agreement with the plasma wave detection theory. To investigate the effects of the overdamped charge asymmetry on RV, FET structure with the asymmetric source and drain area under the gate has been proposed. The enhanced RV according to the increase of asymmetry ratio between source and drain region has been confirmed experimentally.

Design of a Bidirectional Antenna inside a Vehicle and Measurement of Power Link for Vehicle-to-Vehicle Communication at 5.8 GHz

Communication between moving vehicles is very important for safety. In this paper, a bidirectional antenna that can be installed inside a vehicle is proposed and tested in a real vehicular environment at 5.8 GHz. The forward link and backward link seated by two persons and three persons were compared in terms of received RF power and the peak-to-average power ratio (PAR). It was found that, even with three persons, the power link fulfilled the communication requirements using the proposed antenna.

Highly-Sensitive Thin Film THz Detector Based on Edge Metal-Semiconductor-Metal Junction

Terahertz (THz) detectors have been extensively studied for various applications such as security, wireless communication, and medical imaging. In case of metal-insulator-metal (MIM) tunnel junction THz detector, a small junction area is desirable because the detector response time can be shortened by reducing it. An edge metal-semiconductor-metal (EMSM) junction has been developed with a small junction area controlled precisely by the thicknesses of metal and semiconductor films. The voltage response of the EMSM THz detector shows the clear dependence on the polarization angle of incident THz wave and the responsivity is found to be very high (~2,169 V/W) at 0.4 THz without any antenna and signal amplifier. The EMSM junction structure can be a new and efficient way of fabricating the nonlinear device THz detector with high cut-off frequency relying on extremely small junction area.

A Frequency-Tunable SRR-Adopted Two-Pole Waveguide Filter Operating below the Cutoff Frequency

A frequency-tunable filter operating below the cutoff frequency of a metallic hollow waveguide is proposed, which has two-pole bandpass characteristics and incorporates a split-ring resonator (SRR). The tuning procedure is achieved by inserting two metal screws. The screws adjust the magnetic- field passing through the center of the SRR. The effect of SRR orientation was investigated and the optimum orientation proposed. Our results indicated an operating frequency range of 2.0 to 2.35 GHz, which is lower than the cutoff frequency of the waveguide of 4.9 GHz by more than 2.55 GHz. The proposed filter could be utilized for communication, such as software-defined radio (SDR) systems.

Terahertz antenna compatible with CMOS array detector for a real-time T-ray imaging system

This paper reports a miniaturized patch antenna capable of detecting multi-frequencies in conjunction with CMOS detector arrays for real-time imaging in THz-band. The proposed antenna is designed at three-bands of 218, 338 and 400 GHz corresponding to the atmospheric transmission windows. And the performance of the triple-band THz antenna is demonstrated using the finite-difference time-domain method.