Sekwon Na

Effects of Substrate Heating on the Amorphous Structure of InGaZnO Films and the Electrical Properties of Their Thin Film Transistors

This study examines the effects of substrate heating on the amorphous structure of InGaZnO4 (IGZO) films and the device performance of transistors produced from these films. By combining high-resolution transmission electron microscopy (HRTEM) and energy-filtered selected area electron diffraction (EF-SAED), we found that the atomic order improved significantly for the IGZO films deposited on a heated substrate, compared to the samples deposited on an unheated substrate and postannealed. Measurement of the electrical characteristics of the transistors discloses that the amorphous structure changes induced by substrate heating profoundly influenced the overall device performance, leading to a substantial increase in electron mobility.

New pathway for the formation of metallic cubic phase Ge-Sb-Te compounds induced by an electric current.

The novel discovery of a current-induced transition from insulator to metal in the crystalline phase of Ge2Sb2Te5 and GeSb4Te7 have been studied by means of a model using line-patterned samples. The resistivity of cubic phase Ge-Sb-Te compound was reduced by an electrical current (~1 MA/cm2), and the final resistivity was determined based on the stress current density, regardless of the initial resistivity and temperature, which indicates that the conductivity of Ge-Sb-Te compound can be modulated by an electrical current. The minimum resistivity of Ge-Sb-Te materials can be achieved at high kinetic rates by applying an electrical current, and the material properties change from insulating to metallic behavior without a phase transition. The current-induced metal transition is more effective in GeSb4Te7 than Ge2Sb2Te5, which depends on the intrinsic vacancy of materials. Electromigration, which is the migration of atoms induced by a momentum transfer from charge carriers, can easily promote the rearrangement of vacancies in the cubic phase of Ge-Sb-Te compound. This behavior differs significantly from thermal annealing, which accompanies a phase transition to the hexagonal phase. This result suggests a new pathway for modulating the electrical conductivity and material properties of chalcogenide materials by applying an electrical current.

Effects of film thickness and deposition rate on the diffusion barrier performance of titanium nitride in Cu-through silicon vias

The influence of morphology on the performance of TiN diffusion barriers was studied by investigating the effects of film thickness and deposition rate. Increasing the TiN film thickness was ineffective in preventing Cu migration due to the columnar growth of TiN, which left rapid diffusion paths for Cu. When the thickness of the TiN film was less than 10 nm, slowly deposited TiN films showed better Cu barrier performance than rapidly deposited TiN films due to the formation of an amorphous structure, which is an effective phase for preventing Cu migration.

Defect-free erbium silicide formation using an ultrathin Ni interlayer.

An ultrathin Ni interlayer (∼1 nm) was introduced between a TaN-capped Er film and a Si substrate to prevent the formation of surface defects during thermal Er silicidation. A nickel silicide interfacial layer formed at low temperatures and incurred uniform nucleation and the growth of a subsequently formed erbium silicide film, effectively inhibiting the generation of recessed-type surface defects and improving the surface roughness. As a side effect, the complete transformation of Er to erbium silicide was somewhat delayed, and the electrical contact property at low annealing temperatures was dominated by the nickel silicide phase with a high Schottky barrier height. After high-temperature annealing, the early-formed interfacial layer interacted with the growing erbium silicide, presumably forming an erbium silicide-rich Er-Si-Ni mixture. As a result, the electrical contact property reverted to that of the low-resistive erbium silicide/Si contact case, which warrants a promising source/drain contact application for future high-performance metal-oxide-semiconductor field-effect transistors.

Silicide formation process of Er films with Ta and TaN capping layers.

The phase development and defect formation during the silicidation reaction of sputter-deposited Er films on Si with ∼20-nm-thick Ta and TaN capping layers were examined. TaN capping effectively prevented the oxygen incorporation from the annealing atmosphere, which resulted in complete conversion to the ErSi2-x phase. However, significant oxygen penetration through the Ta capping layer inhibited the ErSi2-x formation, and incurred the growth of several Er-Si-O phases, even consuming the ErSi2-x layer formed earlier. Both samples produced a number of small recessed defects at an early silicidation stage. However, large rectangular or square-shaped surface defects, which were either pitlike or pyramidal depending on the capping layer identity, were developed as the annealing temperature increased. The origin of different defect generation mechanisms was suggested based on the capping layer-dependent silicidation kinetics.

Enhancement of electrical conductivity of silver nanowires-networked films via the addition of Cs-added TiO2

This study proposes a novel method of improving the electrical conductivity of silver nanowires (NWs)-networked films for the application of transparent conductive electrodes. We applied Cs-added TiO2 (TiO2:Cs) nanoparticles onto Ag NWs, which caused the NWs to be neatly welded together through local melting at the junctions, according to our transmission and scanning electron microscopy analyses. Systematic comparison of the sheet resistance of the samples reveals that these welded NWs yielded a significant improvement in conductivity. OLED devices, fabricated by using the NW film planarized via embedding the wires into PMMA, demonstrated device performance was comparable with the reference sample with indium tin oxide electrode.

Controlled Molybdenum Disulfide Assembly inside Carbon Nanofiber by Boudouard Reaction Inspired Selective Carbon Oxidation

Vertical stacking and lateral growth of molybdenum disulfide (MoS2 ) are controlled with remarkable precision, and MoS2 nanotubes are directly converted from nanofibers. Predictive synthesis is enabled by identifying the specific thermodynamic region where the Boudouard reaction becomes favored. It reveals how the chemical potential of each species in the MoSCO system can predict phase behaviors.

Study on the contact resistance of various metals (Au, Ti, and Sb) on Bi–Te and Sb–Te thermoelectric films

In this study, we explore various electrode materials (Au, Ti, and Sb) for use as contact materials on Bi2Te3 and Sb2Te3 thermoelectric films. Using the transmission line method (TLM), we measured the specific resistivity of the contacts, which showed that Au has the lowest contact resistivity for both the thermoelectric films (after annealing): 2.7 × 10−10 Ω m2 for Bi2Te3 and 2.9 × 10−11 Ω m2 for Sb2Te3. The specific contact resistivity data suggest that the dominant factor for the contact properties is interface states. After annealing, the contact resistivity does not change much for the Bi2Te3 contacts while it drops greatly for the Sb2Te3 ones. Analysis of the carrier transport mechanism across the contacts discloses that changes in the carrier concentration in the thermoelectric films after annealing are responsible for the different behaviors.

Effect of interfacial reactions between atomic-layer-deposited HfO2 films and n-GaAs (100) substrate using postnitridation with NH3 vapor

Using a variety of various physical measurements, the effects of postnitridation annealing using NH3 vapor on the interface between atomic-layer-deposited HfO2 films and n-GaAs (100) substrates were investigated. After the nitridation treatment, from x-ray absorption spectroscopy and high resolution x-ray photoemission spectroscopy data indicate that the incorporation of Ga oxides into HfO2 films was significantly suppressed during the annealing treatment, primarily because of chemical reactions at the interface between Ga2O3 and NH3. Microstructural analyses further confirmed that the HfO2 film was fully crystallized and a thin GaOxNy layer had been formed at the HfO2/GaAs interface during the annealing process. Compared with the energy band alignments before and after the annealing process, the valence band offsets and energy band gaps were not changed substantially, because the interfacial nitride layer effectively blocked the diffusion of Ga oxide into the film.

Effects of the Mo composition of Mo-alloyed Yb/Si contacts on the microstructures and electrical properties

In this study, we investigate the effects of the Mo composition of Mo-alloyed Yb/Si contacts on the microstructures during silicidation and the electrical properties of the contacts. We co-sputter Mo and Yb to produce Mo-alloyed Yb films with different Mo compositions (5, 20, 40, and 50 at. %) and anneal them at elevated temperatures (500–700 °C). Our material characterization elucidates a series of material reactions, including solid-state amorphization and the nucleation and growth of epitaxial YbSi2− x . The increase of the Mo content hinders the growth of the epitaxial layer, producing a thinner epitaxial layer, and increases the stability of the epitaxial layer against oxidation at high temperatures. Electrical measurement of the contact properties indicates that the Mo 20% sample has the best contact properties.