Bok-Hyung Lee

Two-stage broadband high-gain W-band amplifier using 0.1-/spl mu/m metamorphic HEMT technology

We report broadband high-gain W-band monolithic microwave integrated circuit amplifiers based on 0.1-/spl mu/m InGaAs-InAlAs-GaAs metamorphic high electron mobility transistor (MHEMT) technology. The amplifiers show excellent S/sub 21/ gains greater than 10 dB in a very broad W-band frequency range of 75-100 GHz, thereby exhibiting a S/sub 21/ gain of 10.1 dB, a S/sub 11/ of -5.1 dB and a S/sub 22/ of -5.2 dB at 100 GHz, respectively. The high gain of the amplifier is mainly attributed to the performance of the MHEMTs exhibiting a maximum transconductance of 691 mS/mm, a current gain cutoff frequency of 189 GHz, and a maximum oscillation frequency of 334 GHz.

Small-Signal Analysis of High Maximum Frequency of Oscillation 0.1-µm Off-Set Gamma-Shaped Gate InGaAs/InAlAs/GaAs Metamorphic High-Electron-Mobility Transistors

We examined the effects of gate recess process conditions on the electrical characteristics of 0.1-µm-gate-length metamorphic high-electron-mobility transistors (MHEMTs) by the comparative analysis of small-signal parameters. When the wide-gate-recess method is adopted, significant reductions in gate-to-drain conductance and gate-to-drain capacitance were obtained compared with those obtained by the of narrow-gate-recess method. These differences in small-signal parameters are due to the removal of the entire n+ cap layer and corresponding dissimilarity in gate structure when the wide-gate-recess method is used. The wide-gate-recess method produced ~1/2 drain-source saturation current and extrinsic transconductance compared with the narrow-gate-recess method. In contract to the DC performances, a markedly enhanced S21 gain of 3.5 dB and an fmax of 447 GHz were obtained from the MHEMTs processed by the wide-gate-recess method. This high fmax is responsible for the proper selection of the gate recess method for what and is one of the best data thus far reported for 0.1-µm-gate-length MHEMTs.

A 94 GHz diode mixer for low LO power operation

For low LO power and broadband characteristics of the mixer, an antipodal fin-line to microstrip transition for operation in the 94 GHz frequency has been designed and characterized. Back to back transitions fabricated on soft substrates have been measured and simulated to verify their behavior. A single balanced fin-line mixer was designed and fabricated. In the mixer, a wideband fin-line to coplanar waveguide 180/spl deg/ balun and low pass filter were used. Conversion loss is less than 10 dB at LO power of 6 dBm.

Fabrication of GaN Transistor on SiC for Power Amplifier

This letter presents the MISHFET with si-doped AlGaN/GaN heterostructure for power amplifier. The device grown on 6H-SiC(0001) substrate with a gate length of 180 nm has been fabricated. The fabricated device exhibited maximum drain current density of 837 mA/mm and peak transconductance of 177 mS/mm. A unity current gain cutoff frequency was 45.6 GHz and maximum frequency of oscillation was 46.5 GHz. The reported output power density was 1.54 W/mm and A PAE(Power Added Efficiency) was 40.24 % at 9.3 GHz.

Design and Fabrication of K-band multi-channel receiver for short-range RADAR

In this paper, K-band multi-channel receiver was designed and fabricated for low noise amplification and down conversion to L-band. The fabricated multi-channel receiver incorporates GaAs-HEMT LNA(Low noise amplifier) which provides less than a 2 dB noise figure, IR(Image Rejection) Filter for rejection of image frequency, IR(Image rejection) mixer to reject a image frequency and improve an IMD(Intermodulation Distortion) characteristic. Test results of the fabricated multi-channel receiver show less than a 3.8 dB noise figure, conversion gain of more than 27dB, and IP1dB(Input 1dB Gain Compression Point) of -9.5 dB and over.

Dual coupled X-band VCO using microstrip square multiple spiral resonator for composite metamaterials

A novel voltage controlled oscillator (VCO) using the microstrip square multiple spiral resonator for reducing the phase noise of VCO. Compared with the conventional microstrip square spiral resonator, the microstrip square multiple spiral resonators has strong coupling between the microstrips of the line with the multiple spiral resonator, which makes for a high Q value of the resonator. The phase noise and the tuning range of the proposed VCO are −115.0 ∼ −117.34 dBc/Hz at 100 kHz and 8.935 ∼ 9.4 GHz. Transmission and reflection properties of metamaterials composed line and square spiral have been simulated and compared with conventional metamaterials. The center frequency and transmission bandwidth of metamaterials have been varied through tuning of spiral resonator.

High Conversion Gain Millimeter-Wave Monolithic IC Quadruple Subharmonic Mixer

We report a high conversion gain millimeter-wave monolithic IC (MMIC) quadruple subharmonic mixer adopting a novel cascode harmonic generator for an improved conversion gain. The proposed cascode harmonic generator produces 2.9 dB higher fourth harmonic output powers on the average compared with those of the conventional multiplier. The fabricated mixer shows a high conversion gain of 3.4 dB at a local oscillator (LO) power of 13 dBm. High isolations were obtained the LO-to-intermediate frequency (IF) of -53.6 dB and the LO-to-radio frequency (RF) of -46.2 dB, at a frequency of 14.5 GHz. The conversion gain achieved in this work is the best performance among the millimeter-wave MMIC subharmonic mixers reported to date.

Influences of Gate Recess Structure on the DC Characteristics of 0.1 Micron Metamorphic HEMTs

Effects of the gate recess structures on the DC performances were investigated in 0.1-μm metamorphic high-electron-mobility transistors. Narrow gate recess structure showed significantly enhanced DC characteristics compared to wide gate recess structure in terms of drain-source saturation current increasing from 440 to 710 mA/mm and extrinsic transconductance increasing from 420 to 910 mS/mm. We propose that the observed variations in DC characteristics are due to the deep-level acceptor-type interface defects formed between the silicon-nitride passivation layer and the Schottky barrier layer. We performed hydrodynamic model simulation to verify the proposed mechanism, and the calculated result showed a good agreement with the experimental observation.