Silicon Carbide Insulator

Silicon carbide (SiC) is a crystalline compound of silicon and carbon used since the 19th century in applications as varied as sandpaper, grinding wheels, cutting tools and even industrial furnace linings. Additionally, SiC can also serve as wear-resistant parts in pumps and rocket engines.

SiC can act both as an insulator and semiconductor depending on how the crystal structure has been altered by adding impurities into its crystal structure; this process is known as doping.

Electrical Conductivity

Silicon carbide is a ceramic material with properties that make it both an electrical insulator and semiconductor depending on how its impurities or dopants are added. Silicon carbide’s versatile nature make it an invaluable industrial tool used in many different fields of application.

Energy-intensive applications that need to operate at high temperatures, like turbines and heating systems, benefit from its superior thermal conductivity. Furthermore, its physical robustness and hardness make it suitable for use in cutting tools like grinding wheels. Furthermore, its wide bandgap allows it to handle higher voltages and frequencies than traditional silicon-based devices.

This invention relates to sintered silicon carbide ceramic materials with extremely high electrical resistivity (up to about 108 ohm cm) that have been produced using sintering processes and used as substrates for integrated circuits.

To accomplish this goal, the inventors utilized a hot pressing process to produce a body of sintered silicon carbide with submicron beta phase silicon carbide particles distributed evenly throughout a non-porous matrix of nitrogen at temperatures close to 2,000deg C for sintered silicon carbide production. Resultant material displayed high electrical resistivity as well as low coefficient of linear expansion similar to silicon.

Sintered silicon carbide bodies produced through pressureless sintering have electrical resistivities below those needed for substrates for integrated circuits and significantly lower thermal conductivities than their counterparts, single crystal SiC materials.

The inventors have discovered that sintered silicon carbide containing significant quantities of boron has very high electrical resistivity. To assess this relationship between carrier concentration n and specific dielectric constant es, they conducted several experimental samples where BeO and other elemental dopants from Va and Vb families with an ion valence of +5 were added to powdery particle mixtures of silicon carbide powder before sintereding them.

Thermal Conductivity

Silicon Carbide (SiC) is one of the hardest materials available and features an extraordinarily high Young’s modulus of over 400 GPa, enabling it to withstand extreme pressures and temperatures. SiC is also among the lightest and most insulating ceramic materials; capable of withstanding corrosion, abrasion erosion wear as well as frictional wear while possessing excellent thermal conductivity and low thermal expansion properties when used as electrical insulating material.

Silicon carbide is a covalent bond crystal and its single crystal has a relatively large thermal conductivity, while in sintered state this number drops due to phonon scattering at crystal grain boundaries, creating depletion layers of carriers within each crystal grain on both sides of each boundary, thus inhibiting heat flow.

The present invention involves creating a silicon carbide insulator with enhanced properties by combining p-type semiconductor material with a sintered body of SiC. The insulator comprises silicon carbide as its primary constituent and an element providing electrical insulating properties (BN or Be), such as increasing carrier concentration by 5×1017 cm-3 or less on either side of grain boundary in its sintered state, providing high electrical insulation properties.

Doping silicon carbide with aluminum, boron, or gallium results in the creation of p-type semiconductor materials that possess semi-conductivity properties. Insulators containing this p-type silicon carbide feature low electrical resistivity and high thermal conductivity for maximum effect.

The present invention involves an insulator which can be used to support semiconductor elements, such as a resistor, sputtering target or thin film resistor. Not only does it possess excellent electrical and thermal properties but it also boasts an extremely low dielectric constant value. Furthermore, its narrow neck manufacturing allows high current density without exceeding thermal limitations of substrate material.

Thermal Expansion Coefficient

Silicon carbide (SiC) is an exceptional material with superb thermal properties. With a low coefficient of thermal expansion and resistance to cracking when exposed to high temperatures, SiC can dissipate heat effectively – an essential trait when applied in applications requiring high thermal efficiency. Furthermore, SiC boasts a large specific heat capacity so it can absorb vast amounts of energy before beginning its expansion process.

Silicon carbide’s thermal expansion depends on its temperature and crystal structure, which may affect its performance and durability. To ensure that silicon carbide components can work reliably even under adverse environmental conditions, it is vital that we understand its temperature dependence.

Composition can also have an effect on silicon carbide’s thermal expansion; beryllium oxide (BeO) helps suppress scattering of phonons at grain boundaries, leading to lower thermal expansion compared to pure silicon and leading to lower coefficients of thermal expansion (CTE) than when operating under high mechanical stress. This factor is especially significant for high power semiconductor devices which experience heavy mechanical strain during operation.

Corrosion- and abrasion-resistant material makes it an excellent building material, ideal for chemical plants and mills with temperatures reaching 1,400 degrees Celsius, as well as its high Young’s modulus of 400 GPa making it suitable for high pressures kilns.

Natural moissanite occurs only in trace amounts in certain types of meteorites and corundum deposits, but most moissanite sold as gemstones or used to reinforce metals is synthetically produced using methods such as the vapor deposition of silicon carbon, sintering silicon-containing polymer fibers or firing silicon-containing refractory linings.

To enhance its machinability and tensile strength, a new formulation of SiC was recently created that contains less beryllium oxide than traditional SiC products; less brittle; has lower thermal expansion coefficient; can be used in higher-power devices; less costly to produce than pure silicon carbide;

Dielectric Constant

Silicon carbide is one of the hardest and lightest ceramic materials, boasting excellent corrosion resistance to acids and alkalis, excellent thermal conductivity and low thermal expansion coefficient values – qualities which make it suitable for use in high-temperature environments such as molten metals furnaces or the chemical industry. Furthermore, its high Young’s modulus (>400 GPa) helps withstand bending stresses that would otherwise destroy other ceramics.

Silicon has a relatively narrow bandgap that limits temperature and electric field variations, providing the advantage needed for power electronics applications. Silicon, the most commonly used semiconductor, is reaching its limits due to lack of bandgap width and breakdown voltage; therefore niobium offers another possible option that could outshone silicon when applied at higher temperatures and electric fields.

To maximize 4H-SiC’s full potential, high-k dielectrics must be applied to its surface via silane sputtering targets in order to decrease interface state density at its interface with silicon carbide and dielectric materials and improve electrical properties of devices.

Multiple studies have focused on developing high-k dielectrics capable of working on the surface of 4H-SiC. HfO2 and Y2O3 have proven their value by improving electrical performance by increasing breakdown electric field, but their high interface state remains an obstacle to full deployment in devices.

Stanford researchers have devised a method to create high-quality wafer-scale silicon carbide insulator using photochemical etch and chemical mechanical polishing, then using less doped device layers on a heavily doped sacrificial layer before using photochemical etch and chemical mechanical polishing to remove it using photochemical etch and chemical mechanical polishing, thus exposing SiC and making possible high quality insulators suitable for quantum and nonlinear photonic applications.

Even with these exciting developments, it remains too soon for high-k dielectrics to be implemented into commercial devices based on 4H-SiC. Therefore, other methods for fabricating metal-insulator-semiconductor devices on SiC will need to be explored until this goal can be realized.

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