SiC materials

It is important to note that the compacityfactor is defined by the ratio of the surface area offered to heat transfer over the volume of the reactive medium. The thermal performances are estimated from the product between this compacity factor and the global heat-transfer coefficient. Consequently, owing to the large value of this factor combined with the conductivity performances of the SiC material, the heat-exchange performances are expected to be very high, which can be noticed from the last column of this table. 

High-purity semi-insulating (SI) SiC material has the highest reported thermal conductivity with a value of 4.9 W/(cm-K). Lower values are measured for the doped crystals but they are all above 4 W/(cm-K) at room temperature [10]. 

Work is ongoing to reduce defects in SiC material. One of the more interesting concepts is the reduction of defects through epitaxial growth on porous SiC substrates [64]. This approach has clearly demonstrated a reduction in intrinsic defects, as evidenced by photoluminescence measurements. It is too early to tell whether this technique can provide a path forward for the bipolar devices but it will clearly find its applicability in several areas where SiC will have a market. 

Another p-n junction-based hydrogen sensor has been produced by implanting palladium ions into 6H n-type SiC material [67]. Gold-plated copper contacted the p-n junction device. The gas response was measured as (small) changes in current as the gas ambient was varied between air and 4% in argon in the temperature range 23-240°C. For an absolute voltage above 1.2V, the p-n junction broke down. 

As mentioned above, there are now several polymer systems that provide access to phase pure, fully dense SiC with the properties expected based on SiC materials made by traditional methods. This does not mean that no further development need take place in this area. There are still cost issues that limit the utility of many of these precursors. 

Some comparisons of production costs by SHS and conventional processes have been reported. Analysis for SisNa, AIN, and SiC materials has shown that combustion synthesis is economically favorable to existing technologies, as shown in Tables XIII, XIV, and XV (Golubjamikov et al, 1993). For all materials, the total cost per kilogram of material produced is lower for SHS-based processing than for conventional methods, with a major contribution to savings from reduced fixed costs (i.e., capital equipment costs). The significant difference in the raw material cost for SiC tiles occurs due to the use of Si+C powder mixtures in the SHS case, compared with SiC powder for conventional methods. 

The most widely manufactured carbide is SiC which has been in use for a long time as an abrasive because of its extreme hardness, either in powdered form or in that of tools bound by inorganic or organic binders. Electrical heating elements are made of SiC with a small excess of silicon which facilitates sintering and reacts with the tar binder producing secondary SiC. Materials bound with oxide or nitride bonds (see below) are used as refractory structural materials in the construction of furnaces... 

The effect of whisker-matrix interfaces on mechanical properties becomes clear when the same Al203-SiC materials are hot-pressed at different temperatures. While maintaining similar density, similar sizes of alumina grains, and identical whisker volumes, these composites have different fracture toughnesses as shown in Fig. 19. The differences in Klc values between A1203 with ACMC SC-9 SiC and A1203 with Tateho SCW... 

Table 3.11 compares the property differences of SiC materials prepared by four types of processing methods. CVD processes can fabricate very dense and near-net-shaped SiC components with a very high purity of 99.9995%. However, it is... 

Table 3.11. Property comparison of SiC materials by different methods [75]...

In the present paper, the properties of gradiently-bonded SiC materials were investigated with the following viewpoints the residual stress of SiC-TiC-Ni system and the electrical conductivity of SiC-TiC system. 

Chemical composition silica-based and silica-alumina-based materials, chrome, magnesia, chrome-magnesia, spinel, SiC, materials containing carbon (more than 1% carbon or graphite), and special materials (containing other oxides or materials such as zircon, zirconia, Si3N4, etc.)... 

Porous SiC material, to be used for various device applications, requires additional processing steps which are common for the fabrication of electronic devices. These steps include cleaning, etching, doping, oxidation, metallization, film deposition, annealing, etc. Such treatments of the porous layer can modify the properties of the porous layer and, moreover, the kinetics of the processes in porous material might be different from similar processes in nonporous substrates of the same material. 

In order to produce SiC material of the level of quality required for device applications, chemical vapor deposition (CVD) is currently used as the primary growth technique for SiC epitaxy [2], Due to the continuous improvements in commercial substrate quality, the presence of micropipes in SiC epilayers is not the device yield limiting issue as it was a decade ago. However, the epitaxially grown SiC films still suffer from other extended defects such as basal plane and threading edge dislocations as well as point defects. The vision of growing SiC on porous SiC was to reduce the concentration of these defects and thus improve the epitaxial layer quality for device applications. 

The identification and control of the background contamination level of transition metal impurities is required for the satisfactory performance of devices based on the SiC material system. 

The successful fabrication of SiC based devices cannot be realized without reliable etching and cleaning processes for this material. The purpose of this Chapter is to review the developments and methods of etching silicon carbide for device applications. The term etching is used to describe the processes by which SiC material can be removed. It also includes chemical machining of a semiconductor as part of the fabrication process, as well as defect delineation. 

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