Sung-Woon Moon

V-band CPW 3-dB Tandem coupler using air-bridge structure

We present a uniplanar coplanar waveguide 3-dB tandem coupler operating at V-band frequencies. The uniplanar structure is monolithically fabricated by using two-section parallel-coupled lines and air-bridge crossovers replacing the conventional multilayer or the bonded structures. Due to an optimized tandem structure and nonbonded crossovers minimizing the parasitic components, a maximum coupling of 2.5dB is measured at 62GHz with a 2-dB bandwidth of 83%, while a high directivity factor of 33dB is simultaneously obtained at 58-62GHz. Over the entire design frequency range of 30-90GHz, we achieve good phase unbalance of 90/spl plusmn/6.0/spl deg/, return loss, and isolation lower than -23 and -16dB, respectively.

A Novel 94-GHz MHMET-Based Diode Mixer Using a 3–dB Tandem Coupler

We report a high-performance 94-GHz monolithic millimeter-wave integrated-circuit diode mixer using metamorphic high-electron mobility transistor (MHEMT) diodes and a coplanar waveguide tandem coupler. A novel single-balanced structure of diode mixer is proposed in this paper, where a 3-dB tandem coupler with two sections of parallel-coupled line and air-bridge crossover structures are used for wide frequency operation. The fabricated mixer exhibits excellent local oscillator-radio-frequency (LO-RF) isolation, greater than 30 dB, in the 5-GHz bandwidth of 91-96 GHz. A good conversion loss of 7.4 dB is measured at 94 GHz. The proposed MHEMT-based diode mixer shows superior LO-RF isolation and conversion loss to those of the W-band mixers reported to date.

A Technique for Converting Perhydropolysilazane to SiO x at Low Temperature

Spin-coated perhydropolysilazane films on Si(100) substrates were prepared by a dibutyl ether solution and converted into SiO x using a variety of low temperature curing methods. From the Fourier transform IR spectroscopy and the refractive index (RI) measurements, the successful conversion to a high density silica network was observed from the curing methods by dipping the coatings into either diluted H 2 O 2 (for > 10 min) or deionized water under a 405 nm UV irradiation (for >60 min) at near room temperature. The measured RI values of the cured SiO x films were 1.45-1.47, and the X-ray photoelectron spectroscopy showed that the O/Si stoichiometries of the cured SiO x films were in the range of 1.5-1.7.

600 V-18 A GaN Power MOS-HEMTs on 150 mm Si Substrates With Au-Free Electrodes

We present the development of an Au-free ohmic contact metallization for high voltage GaN-based high electron mobility transistors (HEMTs). In this letter, low contact resistance (0.81 Ω·mm) is obtained for Au-free electrodes on AlGaN/GaN HEMT structures. Using Au-free ohmic processes, large scale high power GaN metal-oxide-semiconductor HEMTs were successfully fabricated in a procedure fully compatible with standard Si CMOS manufacturing with the maximum drain current of more than 18 A and low OFF-state leakage current of 3×10-7 A at VDS of 600 V. The practicality of the devices was further demonstrated by measurements of the current collapse effects under severe operating conditions and the temperature dependence of the electrical characteristics.

High-Performance 94-GHz Single-Balanced Diode Mixer Using Disk-Shaped GaAs Schottky Diodes

We present a high-performance 94-GHz single-balanced monolithic millimeter-wave integrated-circuit (MMIC) mixer using the disk-shaped GaAs Schottky diodes grown on an n/n+ epitaxial structure. Due to the superior characteristics of the GaAs diodes with high diode-to-diode uniformity, the mixer shows a conversion loss of 5.5 dB at 94 GHz, a 1-dB compression point (P 1 -dB) of 5 dBm, and high local-oscillator to radio-frequency isolation above 30 dB in an RF frequency range of 91-97 GHz. To our knowledge, the fabricated mixer shows the best performance in terms of conversion loss at 94 GHz and P 1 -dB among the W-band MMIC mixers without amplifier circuits.

Millimeter-wave small-signal modeling with optimizing sensitive-parameters for metamorphic high electron mobility transistors

In this paper, we present a simple and reliable technique for determining the small-signal equivalent circuit model parameters of the 0.1 µm metamorphic high electron mobility transistors (MHEMTs) in a millimeter-wave frequency range. The initial eight extrinsic parameters of the MHEMT are extracted using two S-parameter (scattering parameter) sets measured under the pinched-off and zero-biased cold field-effect transistor conditions by avoiding the forward gate biasing. Furthermore, highly calibration-sensitive values of the Rs, Ls and Cpd are optimized by using a gradient optimization method to improve the modeling accuracy. The accuracy enhancement of this procedure is successfully verified with an excellent correlation between the measured and calculated S-parameters up to 65 GHz.

Method of Low-Temperature Conversion of Pehydropolysilazane into Amorphous SiOx in Aqueous Solutions

We investigated low-temperature SiOx conversion methods for the spin-coated perhydropolysilazane (a diluted dibutyl-ether solution) films prepared on (100) Si substrates under different curing schemes. From the Fourier transform-infrared (FTIR) spectroscopy and refractive index (RI) measurements, conversion to high-density SiOx was observed for the curing methods of dipping the coatings into various aqueous solutions such as H2O2, NH4OH, and deionized water with or without 405-nm ultraviolet irradiation at near room temperature. The SiOx films cured in H2O2 solution at 80 °C for 10 min exhibited a high conversion efficiency for the SiOx network, as observed from FTIR spectra, RI measurement (~1.46), O/Si stoichiometry (~1.5), surface smoothness (roughness <1.1 nm), and mechanical property (nanoindenter elastic modulus 42 GPa), which are comparable to those of the conventional chemical-vapor-deposited SiOx films.

High-voltage GaN-on-Si hetero-junction FETs with reduced leakage and current collapse effects using SiNx surface passivation layer deposited by low pressure CVD

We have investigated the effects of surface passivation on off-state leakage current and current collapse effects of high-voltage GaN-on-Si hetero-junction field effect transistors (HFETs) by using low pressure chemical vapor deposition (LPCVD) of silicon nitride (SiNx). In this work, the metal–oxide–semiconductor (MOS) structure-based HFETs are realized on AlGaN/GaN epitaxy grown silicon substrates by metal–organic chemical vapor deposition (MOCVD). For a comparative study, we have fabricated two types of HFETs, standard and modified MOS-HFETs. In the modified MOS-HFETs process, the surface passivation layer of SiNx is deposited by LPCVD after the mesa isolation step, while the gate is deposited and self-aligned in the trench etched in LPCVD-SiNx layer using inductively coupled plasma reactive ion etching (ICP-RIE). The high temperature deposition of LPCVD-SiNx prevents the degradation caused by the ohmic annealing and other process-induced surface damage. Compared to the standard MOS structure, the modified MOS-HFET devices exhibit 10 times lower off-state leakage currents within high voltage range (0–800 V) and significantly alleviated current collapse effects simultaneously.

94 GHz CPW branch-line bandpass filter for planar integrated millimeter-wave circuits

We report the 94 GHz CPW branch-line bandpass filter for planar integrated millimeter- wave circuits. The basic idea is to use the branch-line coupler as a transversal filtering section by connecting the coupled ports to the open load stubs and taking the isolated port as the output node. The 94 GHz bandpass filter exhibits an insertion loss of 2.5 dB with an 11.7 % 3 dB relative bandwidth at a center frequency of 94 GHz and the return loss is better than -18 dB at a center frequency. The designed and fabricated 94 GHz bandpass filter shows the good performance for planar integrated millimeter-wave circuits.

Dual Gate-Recess Structure of Metamorphic High-Electron-Mobility Transistors for Enhancing f max

We present a gate-recess structure for 0.1 μm metamorphic high-electron-mobility transistors to enhance the maximum frequency of oscillation (f max ). Among the established gate-recess structures, the narrow gate-recess structure shows a degraded f max , despite superior dc characteristics due to a large gate-to-drain capacitance (C gd ) caused by a small effective gate-to-drain spacing, while the wide gate-recess structure exhibits lower dc characteristics due to the surface effects. To minimize C gd and maintain the dc characteristics of the narrow gate-recess structure, an additional gate-recess is performed for an electrical isolation between the drain side cap layer and drain electrode. We obtain almost the same extrinsic transconductance of ∼600 mS/mm from this, while we achieve -18% enhancement of f max (∼317 GHz) due to -16% reduction of C gd by the increase of effective gate-to-drain spacing compared to the narrow gate-recess structure.