Semiconductors enable our electronic devices to connect the entire world. Silicon (Si) has long been the primary material for semiconductors, but a new alternative is silicon carbide (SiC).
Semiconductor materials have unique properties, such as electrical conductivity between that of an insulator and a conductor, with properties of both; and low resistivity at high temperatures, making them suitable for use in computer chips.
The properties of semiconductors can be customized by adding impurities (doping) to their molecular structure. This alters the flow path of electrons through silicon and silicon carbide and allows customization for a variety of electronic applications.
SiC devices far surpass Si devices in many highly sought-after semiconductor characteristics, making them a key player in the quest for greater efficiency and performance.
What are Silicon Carbide Characteristics?
Due to its atomic structure, silicon carbide (SiC) has different properties than pure silicon. The silicon crystal structure allows it to form a basic lattice connected to four neighboring silicon atoms. However, silicon combines with carbon to form a tightly packed tetrahedron in which four carbon atoms are interspersed with a silicon atom, resulting in a crystalline structure that maximizes power density, efficiency, and reliability.
Thermal Conductivity
Thermal conductivity is a measure of how easily heat can be transferred through a material. This is a key characteristic of semiconductors as it indicates the extent to which a material is able to dissipate heat efficiently (heat buildup due to increased power as a result of increased current), thereby increasing its voltage and current capabilities.
Silicon's thermal conductivity of 130 W/(m⋅K) is significantly lower than silicon carbide's 490 W/(m⋅K), allowing silicon carbide semiconductors to dissipate heat more efficiently and withstand higher operating voltages.
Thermal Expansion
Thermal expansion is when a material changes shape or size - but not phase - due to a change in temperature, such as from a liquid to a gas. A common example is applying hot water to a stuck bottle cap to expand it for opening.
Silicon carbide has a very low coefficient of thermal expansion, which means it is more able to maintain its shape, strength and properties at high temperatures (and high voltages), which silicon may not be able to do.
Electric Field Strength
Two other critical and related semiconductor properties are the material's band gap and maximum electric field strength.
In molecules of semiconductor materials, electrons move between different energy bands: regions they must occupy because there are no energy states between the bands. The band gap (or energy gap) is the amount of energy required for electrons to jump from the valence band to the conduction band, thus allowing electrical conductivity. When semiconductors receive electrical energy and enter this conducting state, they exhibit unique insulator/conductor hybrid properties.
Silicon carbide semiconductors have an energy gap three times higher than that of silicon-based semiconductors, which allows them to withstand higher electric field strengths than silicon and thus operate at higher voltages and temperatures.
Silicon Carbide Semiconductor Advantages
As mentioned above, silicon carbide semiconductors have a larger energy gap, which allows them to better withstand and dissipate heat compared to silicon-based semiconductors. They also offer other advantages:
The high energy gap of silicon carbide is useful in high-power applications because the higher energy gap allows for smaller semiconductor devices and higher operating performance.
For a diode, a common semiconductor device, the breakdown voltage is the voltage at which a reverse applied current can flow through the diode. The high breakdown voltage of silicon carbide makes it ideal for MOSFETs.
This leads to another important semiconductor characteristic in MOSFETs: reverse recovery time. If a MOSFET goes into reverse bias, the time it takes to return to its normal state is called reverse recovery time. During this time, current can flow in the reverse direction and the system experiences energy loss. In these cases, SiC devices have extremely fast reverse recovery times and negligible energy loss, while Si devices do not.
Silicon carbide has more flexibility in doping (adding impurities) than silicon. It can be tailored to conduct electricity only under specific conditions, such as experiencing a specific intensity of light (infrared, visible, or ultraviolet), which gives SiC semiconductors more applications.
