Sam-Dong Kim

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.

Chemical mechanical polishing of shallow trench isolation using the ceria-based high selectivity slurry for sub-0.18 μm complementary metal–oxide–semiconductor fabrication

In this article we investigate the effects of chemical mechanical polishing using a CeO2-based high silicon-nitride/silicon-dioxide selectivity slurry on 0.18 μm complementary metal–oxide–semiconductor (CMOS) shallow trench isolation (STI). When high selectivity slurry (HSS) is employed for STI, within-die and lot-to-lot variations of the remaining pad nitride thickness and the field oxide erosion are significantly reduced to ∼150 and ∼400 A, respectively, which are much smaller than for cases of conventional silica-based slurry. Scratches occupy ∼80% of the total defect in the case of HSS STI polishing, and are minimized by using an optimized in situ filtering method for the slurry. When in situ filtered HSS is used, the gate oxide integrity of 256 million isolated MOS capacitors improves compared to samples prepared by conventional unfiltered HSS slurry. In addition, the level of leakage current for n+/p-well junctions is not affected when in situ filtered HSS is used for STI polishing.

Characteristics of sputtered Ti1−xAlxN films for storage node electrode barriers

We report on the characteristics of sputter-deposited Ti1−xAlxN (TiAlN) thin films for storage node electrode barriers of Pt/(BaSr)TiO3(BST)/Pt metal–insulator–metal (MIM) capacitors with a comparative study of TiN films. The substrate temperature (Ts) was found to be one of the key factors affecting the properties of TiAlN thin films, i.e., the resistivity of TiAlN is ∼350 μΩ cm for high Ts deposition (∼450u200a°C) and ∼1100 μΩu200acm for low Ts (∼100u200a°C). The lower resistivity of TiAlN films deposited at high Ts (450u200a°C) is attributed to the (200) texture with larger grain size and smaller oxygen concentration compared to those prepared at low Ts. The electrical characteristics of Pt/BST/Pt MIM capacitors on TiAlN were superior to those on the TiN barrier in terms of smaller equivalent oxide thickness (tox), lower tangent δ, and lower leakage current. Better oxidation resistance of TiAlN over TiN appears to be responsible for the better electrical results, especially with the (111) or (200) texture. We also dis...

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.

Nanoscale floating-gate characteristics of colloidal Au nanoparticles electrostatically assembled on Si nanowires

Nanoscale floating-gate characteristics of colloidal Au nanoparticles electrostatically assembled on Si nanowires have been investigated. Colloidal Au nanoparticles with ∼5nm diameters were selectively deposited onto the lithographically defined n-type Si nanowire surface by 2min electrophoresis between the channel and the side gates. The device transfer characteristics measured at room temperature showed hysteresis, with the depletion mode cutoff voltage applied by the side gates shifted by as much as 1.5V, with the source-drain bias at 1.4V. The results demonstrate that the electrostatic assembly of colloidal Au nanoparticles is a useful method for the fabrication of Si nanowire based nanoscale floating-gate nonvolatile memory structures.

Strain relaxation in compositionally graded epitaxial layers

A model for strain relaxation in linear compositionally graded epitaxial layers is derived. Equilibrium dynamics for misfit dislocation generation is used in each compositional segment of the graded layers through the film thickness. A local relaxation thicknesses in the compositionally graded layers is calculated as a function of film thickness. The calculated critical thicknesses show good correspondence with the depth of dislocation‐free regions which are observed at the top of graded layers with different grading rates. From analysis of the model, we explain the origin of dislocation structures and minimized threading dislocation density in the compositionally graded layers. The compositional grading produces a large equilibrium dislocation spacing compared to that of highly mismatched conventional stepwise growths, and thus enables misfit dislocations to glide freely without dislocation–dislocation interactions. At successive local relaxation thicknesses, lateral dislocations pile up horizontally by ...

The X‐valley transport in GaAs/AlAs triple barrier structures

Electron transport through the X valley of GaAs/AlAs triple‐barrier structures (TBS) grown by molecular‐beam epitaxy has been studied. Negative differential resistance is observed at 77 K in one type of TBS and is identified as the result of electron transport through both the Γ and X valleys of TBS. In another type of TBS, resonant tunneling through the X valley of GaAs/AlAs TBS is observed. The Γ and X energy‐band profiles under bias have been calculated in order to identify the observed features.

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.

A Novel 94-GHz MHEMT Resistive Mixer Using a Micromachined Ring Coupler

In this letter, we present a high performance 94-GHz millimeter-wave monolithic integrated circuit resistive mixer using a 70-nm metamorphic high electron mobility transistor (MHEMT) and micromachined ring coupler. A novel three-dimensional structure of a resistive mixer was proposed in this work, and the ring coupler with the surface micromachined dielectric-supported air-gap microstrip line structure was used for high local oscillator/radio frequency (LO-RF) isolation. Also, the LO-RF isolation was optimized through the simulation. The fabricated mixer has excellent LO-RF isolation, greater than 29 dB, in 2-GHz bandwidth of 93-95GHz. The good conversion loss of 8.9dB was measured at 94GHz. To our knowledge, compared to previously reported W-band mixers, the proposed MHEMT-based resistive mixer using a micromachined ring coupler has shown superior LO-RF isolation and conversion loss

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.