High Voltage
Silicon carbide (SiC) can withstand high voltages up to ten times higher than silicon, making it the perfect material for power electronics applications. Furthermore, SiC’s higher thermal conductivity and electron mobility compared to silicon helps minimize switching losses. As a result of these characteristics, SiC diodes and transistors operate more efficiently than their silicon counterparts at higher frequencies without losing performance.
Traditional bipolar devices experience significant n-layer resistance when applied voltage exceeds their breakdown voltage. To combat this, p-doping can be employed to introduce minority carriers into the thick n-layer and allow electrons and holes with higher densities than donor density to contribute current flow and reduce n-layer resistance when operating in positive bias mode.
Minority carrier injection has proven highly successful at significantly decreasing n-layer resistance in SiC power devices, leading to higher voltages, reduced turn-on resistance, and fast operation – essential features of efficient power converters such as those found in electric vehicle traction inverters or grid-forming solar + energy storage systems.
Due to these considerations, an increasing number of power electronics manufacturers are adopting silicon carbide Schottky diodes and MOSFETs with voltage ratings up to 1200 V in order to build automotive on-board chargers, grid-forming solar inverters, EV direct current fast charging applications and direct current fast charging applications with higher driving voltage support as well as extend the electric vehicle range. By adopting these devices they are providing smaller, lighter and more cost effective solutions while supporting higher driving voltages for improved range expansion of electric vehicles.
High Frequency
Silicon (Si, bandgap: 1.1eV) has long been considered the ideal material for power devices. Si-based electronics enable electronics to be made smaller, run faster, and operate at higher temperatures, voltages, and frequencies than those constructed using other semiconductor materials.
However, Si-based devices are reaching their performance threshold due to the limitations posed by their materials. To meet the high voltages demanded of power applications, Si power devices must support significant off-state current. While such current is usually kept negligibly small in reverse biased diodes and transistors, if electric field strength exceeds critical breakdown voltage it could quickly increase and become sizable.
Due to these restrictions, wide bandgap semiconductors such as gallium nitride (GaN) and silicon carbide (SiC), which can withstand much higher electric fields, have experienced rapid market expansion.
Silicon Carbide offers four times more thermal conductivity than silicon, providing faster cooling and reduced power loss. As such, silicon Carbide devices are well suited to enable high frequency operations.
Low Harmonics
Silicon carbide (SiC) semiconductor properties enable high-speed switching at lower voltages for increased energy efficiency in DC/DC converters and AC/DC inverters, leading to smaller form factors, higher temperature operation and reduced design complexity–resulting in substantial cost and weight reductions of both systems.
SiC devices also provide significantly less harmonic current distortion, an important consideration in industrial UPS systems. Harmonic current distortion causes annoying trips and errors which lead to increased maintenance costs and decrease system uptime – something that clean power UPSs using active filters with merged SiC Schottky diodes can effectively avoid.
SiC is increasingly being relied upon in electric vehicle battery interfaces and motor drives for its superior power density, efficiency, switching speed and temperature tolerance. Conventional technologies like insulated-gate bipolar transistor (IGBT) and silicon metal-oxide-semiconductor field-effect transistor (MOSFET) technologies are reaching their limits in these applications.
Wolfspeed’s 3300 V Silicon Carbide MOSFETs deliver up to 30% lower losses and 15% savings compared with silicon counterparts, giving designers greater freedom in improving system efficiencies, shrinking form factors and operating at higher temperatures in demanding industrial applications, including uninterruptible power supplies (UPSs). A backup UPS featuring SiC MOSFETs may offer even greater performance for critical uses like industrial machinery or data centers.
Schottky Diodes
Schottky diodes offer much lower forward voltage drops compared to their silicon or germanium counterparts, due to the different work functions between metal and semiconductor. When these materials come in contact, an energy barrier known as the Schottky barrier forms at their junction due to electron migration between material surfaces. Under forward bias, this energy barrier begins to breakdown under forward bias to allow electrons from metals into semiconductor’s conduction band more freely resulting in current flow and rectifification. Furthermore, their reverse recovery time is much quicker enabling it to switch between rectifying and non-rectifying states much quicker.
The left side of this diagram depicts metal contact while the right side shows doped n-type silicon semiconductor material, with different energy levels between the two materials; Fermi level in metal being relatively higher and close to conduction band of semiconductor causing it to act as an anode while semiconductor acts as cathode; the difference in energy levels creates the Schottky barrier allowing electrons from metal contact into semiconductor without stopping by insulator of depletion region preventing any movement into depletion region allowing electrons to flow between these materials without being stopped by insulators of depletion region insulators of depletion region insulator of depletion region insulator that might otherwise stop their path into semiconductor material causing depletion region insulator from entering depletion regions.
Nexperia SiC is known for providing automotive-grade Schottky diodes with the lowest forward voltage drop in the industry and best surge current performance for electric vehicle applications. Leakage current can be limited by carrier recombination at interfaces; therefore Nexperia SiC developed a hybrid device called Merged PiN Schottky (MPS) diode which combines Schottky and traditional p-n diodes connected in parallel, in order to minimize leakage current while retaining excellent surge current performance of Schotttky diodes.
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