Polycrystalline silicon carbide has many essential applications; however, processing this brittle material presents challenges. Most often the process relies on diamond grinding which may damage both surface quality and subsurface quality of material.
Elkem Processing Services supplies this material from their state-of-the-art facility in Liege, Belgium to ensure quality results.
High thermal conductivity
Silicon carbide (SiC) is an advanced polycrystalline material with excellent thermal and chemical conductivity properties, producing it via various methods such as reacting silicon dioxide and carbon at high temperatures in an electric furnace or by machined and polishing for use in hard disks, read/write heads or ballistic armor applications. SiC can withstand extremely high temperatures making it suitable for use in extreme environments and applications.
CVD SiC boasts high polishability and thermal conductivity, making it a less costly alternative than sintered or reaction bonded SiC. As an economical face-centered cubic polycrystalline form, CVD SiC can also be utilized in applications that require high temperature capabilities such as MEMS or power electronics.
CVD use of 5% monomethylsilane diluted with hydrogen (MMS, 6 sccm) as its precursor, with H2 (9 sccm). Deposition involves rotating a filament at 1Hz with contact between it and heated substrate; once completed, film exhibits a crystal order ratio of 100 and features that differ significantly from their Bragg diffraction counterparts in several degrees of width.
High electrical conductivity
Silicon carbide’s low electrical resistivity and strength make it a desirable material for applications requiring superior electrical conductivity, such as those involving elevated temperatures or extreme environments. Furthermore, its superior thermal conductivity and thermal stability also make it suitable for use in extreme conditions. Unfortunately, however, chemical and structural characteristics of porous SiC can significantly diminish its electrical conductivity, forcing researchers to conduct extensive trials using different chemical compositions and annealing conditions in order to increase its electrical conductivity properties.
Polycrystalline SiC’s electrical properties can be affected by its oxygen content. Oxygen reduces band gap energy, thus altering electrical conductivity of polycrystalline material and altering its electrical conductivity properties. Furthermore, the composition of its ions has an impactful impact on its electrical properties.
Attaining high electrical conductivity of polycrystalline SiC requires tight control of temperature gradients during crystal growth. A metal film can serve as a template to guide amorphous silicon growth; when exposed to high-temperature gradients, this amorphous silicon will crystallize into crystalline silicon carbide crystals.
High strength
Polycrystalline silicon carbide’s superior strength makes it a suitable substrate material for hard disk drives. Spinnable disks requiring up to 10,000 rotations per minute with heads gliding within 0.025 microns of substrate surfaces need a high-grade substrate material that can support magnetic media. In order to be effective, this requires a substrate with few defects that cause pitting, leading to data loss and other problems. This invention pertains to a polycrystalline silicon carbide body with flexural strength of 500 N/mm2, providing data security at room temperature. This body can be created using powder mixtures containing up to 3% by weight of an additive containing free carbon, such as carbon black. A temporary binder may also be added; suitable examples include acetylene black, polyvinyl alcohol or stearic acid.
Current porous silicon carbide ceramic monoliths made by consolidating finely divided particles are too porous to support circuit lines smaller than 0.25 microns wide. While sintering of these powders may help densify them, significant amounts of non-stoichiometric silicon metal and carbon will remain within surface pores and grain boundaries, due to impurities from raw materials or process equipment affecting their size or number of pores.
High temperature resistance
Silicon Carbide (SiC) is an industrial material with unique qualities that make it suitable for high temperature applications, including furnaces. SiC has high mechanical strength, chemical inertness, excellent creep resistance and low thermal expansion and conductivity – qualities which make it suitable for furnace use. Furthermore, SiC is extremely hard and abrasion resistant while possessing low frictional properties.
SiC is a wide bandgap semiconductor material with the potential to be doped to form either an n-type (with nitrogen or phosphorus dopants) or p-type (boron, aluminium or gallium dopants) depending on how it’s manufactured and doped with these elements. SiC can be found in electronic devices such as diodes and transistors due to its relatively high electrical conductivity, excellent heat dissipation capabilities and low coefficient of thermal expansion coefficient.
The present invention provides freestanding chemical vapor deposited b phase polycrystalline silicon carbide with reduced stacking faults and other crystalline defects and an order ratio less than 0.10. Additionally, this invention features phonon mean free path exceeding 100 nanometers that allows energy dissipation across its lattice without colliding with stacking faults, grain boundary features or point defects.
High temperature stability
Polycrystalline silicon carbide’s high temperature stability makes it an invaluable material in power electronics and electric vehicle applications, where its thermal conductivity withstands high heat loads without overheating components. Furthermore, its resistance to abrasion and chemical corrosion makes it suitable for cooling components as well.
Polycrystalline silicon carbide can be produced using various methods, including hot pressing and direct sintering. Sintering aids such as carbon can also help improve densification and mechanical properties of this material; carbon reacts with surficial SiO2 to stop evaporation while simultaneously densifying grains; while boron acts to eliminate surface diffusion while simultaneously altering grain boundary energy.
Ohmic and low resistance electrical contacts were demonstrated on b phase polycrystalline silicon carbide via chemical vapor deposition with hydrogen (H2, 94 standard cubic centimeters per minute) and methyl trichlorosilane (MMS, 6 standard cubic centimeters per minute). Long term aging tests conducted in an oxygen atmosphere have confirmed that their performance remains intact up to 900 degC.
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