Papers by Keyword: Ti₃SiC₂

Abstract: P-type Ti/Al-based contact vias of different sizes but identical processing were electrically characterized using linear transfer length method (TLM) patterns and metal-oxide-semiconductor (MOS) transistors. While the TLM patterns and MOS transistors with large vias follow ohmic contact behavior, Schottky contact properties were observed for smaller contact via dimensions. Focused ion beam (FIB) analysis of the contact vias verified the presence of Ti₃SiC₂ on large 66 μm x 25 μm contact vias and its absence on smaller 16 μm x 3 μm ones, correlating its absence with the electrical Schottky properties.

Abstract: The Ti₃SiC₂-TiB₂-TiC three-phase ceramics are prepared by Spark Plasma Sintering (SPS) method with Self-propagating High-temperature Synthesis (SHS) using Ti, Si, C andB₄C powders. The characterization of sintering product’s image and structure is analyzed by XRD and SEM. Most of TiB₂’s images are angular cuboid or short bar-shaped and most of TiC phase’s images are irregular spherical particles which are evenly embedded in Ti₃SiC₂ substrate and have a good combination interface with Ti₃SiC₂. In the composite ceramic SPS sintering process, sinter sample’s displacement along Z-axis goes through three stages of falling, balance and rising along with the change of heating temperature, which reflects the sample’s change rule between heated expansion force and pressure. Finally its machining performance is analyzed by wire cutting method and machining method. The Ti₃SiC₂-TiC-TiB₂ block composite ceramic proves to have a good machining performance.

Abstract: TLM structures on Al-implanted regions with different implanted Al concentrations and different annealing temperatures were processed and characterized by electrical measurements in order to determine the influence of these parameters on the ohmic resistivity. Based on these results, a TCAD model was developed that considers the carrier concentration of the implanted region, the effective density of states for holes and the hole tunneling mass at the Ti₃SiC₂-SiC interface. It could be shown that Ti₃SiC₂ allows to form ohmic contacts on Al implanted samples with an effective doping concentration down to 3·10¹⁷ cm^-3. Furthermore the effective density of states for holes in Ti₃SiC₂ was determined to 8.5·10¹⁸ cm^-3 and the hole tunneling mass in SiC and Ti3SiC2 in the range of 2·10^-34 kg to 6·10^-33 kg depending on the sample.

Abstract: Titanium silicon carbide (Ti₃SiC₂) were obtained by molten salt synthesis method using the Ti-Si-Fe alloy extracted from high titania blast furnace slag and natural graphite as the raw materials. The phase composition, microscopic structure of the products were characterized by powder X-ray diffraction, scanning electron microscope and transmission electron microscope. The influence of firing temperature and chloride salts species on the phase and morphology of the products were investigated. The results indicated that the synthetic temperature of Ti₃SiC₂ by molten salt synthesis method was about 100 °C, which was lower than that without molten salts. The “dissolution-precipitation” mechanism governed the overall molten salt synthesis process. The lamellar Ti₃(Si,Al)C₂ crystal growth obeyed by a two-dimensional ledge growth mechanism.

Abstract: Free Ti/Si/C powder mixtures with or without molten salt were heated under vacuum with various schedules. The effect of molten salt during synthesis on the morphology and phase composition of Ti₃SiC₂ powders were investigated. The combustion powders were analyzed by DSC, XRD, SEM and EDS. The results indicated that the existence of molten salt could promote the reaction process and decrease the synthesis temperature. The Ti₃SiC₂ powders obtained by molten salt method were uniform and well dispersive. The content of Ti₃SiC₂ phase was influenced by salt/powders ratio and molding pressure. The appropriate salt/powders ratio and pre-press pressure were 1:1and 100 MPa, respectively.

Abstract: Ti₃SiC₂ and three different kinds of Ti₃SiC₂ matrix composites (Ti₃SiC₂/SiC, Ti₃SiC₂/Al₂O₃ and Ti₃SiC₂/MgAl₂O₄) were fabricated by reactive hot pressing method. The oxidation resistance of four kinds of materials at 1373 K-1773 K was investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the main oxidation products of Ti₃SiC₂ were rutile and cristobalite. The oxidation layers were composed of two layers, the outer was consisted of TiO₂, and the inner was a two-phase mixture of TiO₂ and SiO₂. A large number of pores existed in oxide layers which leading to a poor oxidation resistance. For Ti₃SiC₂ matrix composites, rutile grains in oxidation layers were refined due to the introduction of the second phase. The volume expansion caused by reactions between Al₂O₃ (or MgAl₂O₄) and TiO₂ could close pores and improve the densification of oxide layers, which further improve the oxidation resistance of Ti₃SiC₂/Al₂O₃ and Ti₃SiC₂/MgAl₂O₄. As for the oxidation of Ti₃SiC₂/SiC, the SiO₂ content in oxidation layers was increased from the oxidation of SiC. The dense SiO₂ layer acted as a protective film which could prevent the inward diffusion of oxygen. Moreover, liquid phase under high temperature could also fill the pores in oxidation layers. Thus, Ti₃SiC₂/SiC composite had the best oxidation resistance among three Ti₃SiC₂ matrix composites.

Abstract: In this study, the electrical properties of Ti₃SiC₂ based ohmic contacts formed on p-type 4H-SiC(0001) 4°-off substrates were studied. The Ti₃SiC₂ thin films were grown by thermal annealing (from 900°C to 1200°C) of Ti₅₀Al₅₀ layer deposited by magnetron sputtering. XRD analyzes were performed on the samples to further investigate the compounds formed after annealing. Using TLM structures, the Specific Contact Resistance (SCR) at room temperature of all contacts was measured. The temperature dependence (up to 600°C) of the SCR was studied to understand the current mechanisms at the interface and to determine the barrier height value by fitting the experimental results using the thermionic field emission theory. Aging tests showed that Ti₃SiC₂ based contacts were stable up to 200h at 600°C under Ar.

Abstract: Layered ternary compounds Ti₃SiC₂ combines attractive properties of both ceramics and metals, and has been suggested for potential engineering applications. Near-fully dense Ti₃SiC₂ bulks were sintered from commercial Ti₃SiC₂ powders by hot press at 1350°C-1600°C for 60-120min under Ar atmosphere in this paper. The phase compositions and morphology of the as-prepared samples were evaluated by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). And the mechanical properties were measured by Three-Point bending method. It was found that the Ti₃SiC₂ had only a little of decomposition at sintering temperature above 1350°C. And effects of sintering temperature and holding time on the morphology of the bulk Ti₃SiC₂ are not obvious. Relative density of 98% and flexural strength of 480MPa were obtained for the Ti₃SiC₂ samples sintered at 30MPa and 1400°C for 90min.

Abstract: In order to form Ti₃SiC₂ on 4H-SiC(0001) 8°-off, 200 nm of Ti₃₀Al₇₀ was deposited onto SiC substrates by magnetron sputtering from pure Ti₃₀Al₇₀ targets. The samples were then annealed at 1000°C for 10 min under Ar atmosphere in a Rapid Thermal Annealing (RTA) furnace. Structural analyses reveal the formation of epitaxial hexagonal Ti₃SiC₂ (0001) oriented. Elemental analyses show that high amount of Al and O elements are present inside the deposit. Obviously, the formation of Ti₃SiC₂ is accompanied by parasitic Al oxide, probably due to some unwanted oxygen residual in the RTA chamber. By using proper backing steps before the annealing, the deposit is not anymore composed of only Ti₃SiC₂ but accompanied with other compounds (Al₃Ti, and Al). On the oxide-free sample, the specific contact resistance ρ_c of the Ti₃SiC₂ based contact on p-type 4H-SiC (having N_a= 2×10¹⁹ cm^-3) was measured to be as low as 6×10^-5 Ω.cm².

Abstract: Ti/Si/C element powders were used to synthesize Ti₃SiC₂ by spark plasma sintering. The synthesized products consisted of Ti₃SiC₂, together with TiC and Ti₅Si₃ as impurities. The addition of Al, excess Si, and appropriate sintering temperature increased the purity of Ti₃SiC₂ in the products. From the 3Ti/1.2Si/2C/0.2Al mixture, Ti₃SiC₂ with the purity 99 mass % was synthesized at 1300 °C for 5 min at 30 MPa.