Yong-Hyun Baek

94-GHz Log-Periodic Antenna on GaAs Substrate Using Air-Bridge Structure

We fabricated a compact, 94-GHz log-periodic planar antenna on GaAs substrate. We used millimeter-wave monolithic integrated circuit (MMIC) process technology to fabricate the on-chip antenna. An air-bridge crossover is used to replace the conventional bonded structure for crisscross connection, which is compatible with active devices and circuits. The fabricated antenna chip size is 1.2 times 2.6 mm2 . Measurement results show that this antenna can operate from 87 to 99.5 GHz with its return loss better than -10 dB. At 94 GHz, the log-periodic antenna has a return loss of -11 dB and 4.8 dBi of gain.

A Transceiver Module for FMCW Radar Sensors Using 94-GHz Dot-Type Schottky Diode Mixer

In this study, we fabricated a 94-GHz transceiver module for a millimeter-wave (MMW) frequency modulation continuous wave (FMCW) radar sensor. The transceiver modules consist of a waveguide voltage-controlled oscillator (VCO) and Rx module using a single balanced mixer. We designed a mixer with a conversion loss of 6.4 dB, without using an amplifier. Also, the waveguide VCO consisted of an InP Gunn diode, a varactor diode, two bias posts with LPF, and a Magic Tee for the MMW radar transceiver. The fabricated VCO has a tuning range of 1280 MHz by a varactor bias of 0~20 V, 1.69% linearity range of 680 MHz, and current consumption of 154 to 157 mA. The completed module has a good conversion loss of 10.6 dB with an LO power of 11.4 dBm at 94 GHz. With this RF and LO input power, the conversion loss was maintained between 10.2-11.5 dB in the RF frequency range of 93.67-94.95 GHz.

Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar

In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.

Effects of Gate-Recess Structure on High-Frequency Characteristics of 0.1 μm Metamorphic HEMTs

We investigate effects of the gate-recess structure on the high-frequency characteristics of the 0.1 μm depletion-mode metamorphic high electron mobility transistors (HEMTs). We characterize the dc and radio frequency performances of two different gate-recess structures and perform a comparative study using the hydrodynamic device model simulation and small-signal parameter analysis. The narrow gate-recess structure shows significantly higher dc performances than the wide gate-recess structure, and this phenomenon is due to the presence of the negatively charged surface states on the InAlAs Schottky barrier layer surface in the wide gate-recess structure. Despite the superior dc characteristics, the narrow gate-recess structure shows more degraded maximum frequency of oscillation (f max ) of ∼296 GHz than that (∼ 340 GHz) of the wide gate-recess structure and almost the same cutoff frequency (f T ) of -130 GHz. The degraded f max of the narrow gate-recess structure is attributed to a -66% higher gate-to-drain capacitance (C gd ). The significant increase of C gd is caused by the reduction of effective gate-to-drain spacing due to the nonlinear electric potential distribution in the gate-to-drain region.

3-D 94 GHz single balanced mixer for low conversion loss with ring coupler by DAML

A 94 GHz single balanced mixer in 3-dimension was successfully fabricated. The GaAs-based low loss transmission lines, dielectric-supported air-gapped microstrip lines (DAMLs), have been developed using surface micromachining technology, and the DAML-based hybrid ring coupler is successively fabricated. We have developed the high-performance 94 GHz single balanced active mixer using hybrid ring coupler with 70 nm gate length MHEMT. The mixer showed the conversion loss of 2.5 dB ~ 2.8 dB and isolation characteristics less than −30 dB, in the range of 93.65 GHz ~ 94.25 GHz. These results are the best performances demonstrated from a 94 GHz single balanced mixer utilizing GaAs-based HEMTs in terms of conversion loss as well as isolation characteristics.

Radio Frequency Characteristics of Multifinger 0.1 µm Metamorphic High-Electron-Mobility Transistors Depending on Number of Gate Fingers and Gate Width

We investigate the effects of the number of gate fingers (N) and gate width (W) on the high-frequency characteristics of 0.1 µm depletion-mode metamorphic high-electron-mobility transistors (MHEMTs). The extracted gate-to-source capacitance (Cgs), gate-to-drain capacitance (Cgd), intrinsic transconductance (gm,int), and drain conductance (Gds) are proportional to total gate width (wt), whereas intrinsic resistance (Ri) and source resistance (Rs) are inversely proportional to wt. Gate resistance (Rg) linearly increases at various slopes with non-zero gate resistances at zero gate width depending on N. The cutoff frequency ( fT) and maximum frequency of oscillation ( fmax) are calculated using a small-signal model and curve-fitting equations extracted from each small-signal parameter. fT is almost constant; however, fmax is a strong function of Rg1/2 and is affected by both N and wt. A large wt produces a low fmax; however, at a given wt, increasing the number of gate fingers is more efficient than increasing single gate width for maximizing the fmax.

Design and fabrication of MMW module for 94 GHz radar sensor applications

We present design and fabrication of a 94 GHz radar sensor module. The 94 GHz sensor module has four components including 94 GHz single balanced diode mixer part, waveguide VCO (voltage controlled oscillator) part, magic tee part and bias PCB part. The 94 GHz single balanced diode mixer is developed on Duroid RT 5880 substrate with DC 1346 Schottky diode. The mixer has advantage of good conversion loss at high LO power and isolation characteristic. 94 GHz single balanced diode mixer has advantage of comparatively easy fabrication. The waveguide VCO consist of GaAs Gunn diode, varactor diode, two-bias post and cavity. The waveguide VCO is operated at 94 GHz. The magic tee has four waveguide arm regions with standard WR-10 and divides output power from VCO. Transmission frequency of 94 GHz MMW sensor module is 93.607 ∼ 94.727 GHz. Bandwidth is 1.12 GHz. 2% linearity range is 680 MHz. Power is 11.03 ∼ 11.47 dBm. Conversion loss about −7 dB at IF 500 MHz

Fabrication of hyperabrupt GaAs varactor diode for W-band waveguide VCO

In this work, we fabricated a hyperabrupt varactor diode and W-band waveguide VCO using fabricated varactor diode. With the anode diameter of 90 µm, a maximum reverse breakdown voltage of 40 V at a leakage current of 30 µA, a maximum capacitance of 5.82 pF, and a minimum capacitance of 0.7 pF were obtained, resulting in a Cmax/Cmin ratio of 8.31. Fabricated VCO showed an excellent linearity of 1.6 % within 800 MHz. The bandwidth of the VCO was 1.165 GHz from 93.305 GHz to 94.47 GHz, and the output power was from 14.6 dBm to 15.42 dBm.

94 GHz waveguide VCO using InP Gunn diode for FMCW radar applications

The 94 GHz waveguide VCO using InP Gunn diode was designed and fabricated. The fabricated VCO has excellent linearity of 1.7 % at 680 MHz bandwidth and power flatness of 0.68 dBm, respectively. The LPF is designed under -40 dB at 47 GHz and the resonator is designed for frequency generation at 47 GHz. From the measured results the fabricated waveguide VCO has excellent performances: the bandwidth is 1365 MHz at 93.98 ~ 95.345 GHz and the output power range is from 14.78 dBm to 15.46 dBm. The phase noise is under -100 dBc / Hz at 1 MHz offset.

D-band amplifier using metamorphic HEMT technology

In this paper, we successfully demonstrated the D-band MMIC amplifiers based on 0.1 mum InGaAs/InAlAs/GaAs MHEMT which has two fingers of 30 mum gate width. The device exhibited a cut-off frequency (fT) of 189 GHz, and a maximum oscillation frequency (fmax) of 334 GHz. The D-band MMIC amplifier exhibited a good RF gains of 7.8 dB at a frequency of 110 GHz. Actually, the D-band MMIC amplifiers exhibited the S21 gains of at 140 GHz in Momentum simulation. We try to measure a frequency range of 110-140 GHz because our measurement equipment can measure in a frequency range of 0.1-110 GHz. Proceeding from these results, we expect satisfactory results in S21 gain performance at 140 GHz.