Since the early sixties, Silicon has been used as a semiconductor “switch” and the quest for higher switching frequencies, greater power densities, higher blocking voltages, lower losses, increased operating temperatures etc. has led to the introduction of Silicon Carbide (SiC) and other wide band gap materials in power devices.
Wide Band Gap Semiconducting Materials
Silicon Carbide is a Wide Band Gap (WBG) material that is becoming more widely used in power semiconductors as Silicon based devices have nearly reached their maximum theoretical performance. The term “band gap” defines the difference in energy levels between the material’s conduction and valence bands. In the image below, the “filled” bands refer to electrons occupying those regions and “holes” in the “unfilled regions. By applying external energy in the form of light or heat, electrons are excited to jump the band gap into the conduction band and current allowed to flow.
The wider band gap leads to a higher critical electrical field (approx 10 x greater than Silicon) giving rise to breakdown voltages of 10’s of kilovolts and therefore higher blocking voltages for power devices. Due to the high dielectric strength of SiC, it is possible to produce thinner die that can be doped to a much higher level. This leads to much lower losses and therefore greater efficiency and also higher current density (2-3 times higher than Silicon), a feature that also increases cost effectiveness. SiC devices are able to switch much faster than Si with lower losses. This allows passive and magnetic components to be downsized in the power electronic design, leading to greater power density for the converter as a whole.
The other main advantages of SiC are it’s high thermal conductivity (3 times that of Silicon) and high melting temperature. Temperature has little influence on switching performance and on resistance allowing SiC devices to operate at a junction temperatures of 200⁰C+ compared to 150⁰C for Silicon. Current packaging and soldering technologies however, limit the practical operating temperatures to a much lower level, albeit with greatly increased reliability. The high thermal conductivity combined with other chip differences allow more even heat distribution, which in turn allows downsizing of thermal management systems (heatsinks, fans etc.).
So Who Is Taking Advantage Of SiC Power Devices Today?
The increased reliability, higher operating temperature, increased efficiency, reduced size, higher voltage capabilities of SiC make it highly desirable in the electric vehicle and renewable energy industries. Traction inverters in electric vehicles are subjected to high thermal and load cycling and of course a high power to weight and physical size is very important. Renewable energy converters are also subjected to extreme environmental conditions (for example, solar inverters in desert locations, offshore wind farms etc.). In these instances the need for high reliability is paramount as maintenance and downtime can be extremely expensive for the operators. It goes without saying that maximising power conversion efficiency is of utmost importance in the energy conversion process. The applications that require magnetics for output voltage filtering, such as UPS (Uninterruptable Power Supplies) and Solar inverters are able to reduce the size of filtering components by using SiC power devices at much higher switching frequencies. This leads to cost savings as well as greater efficiencies and reliability.
What Type Of SiC Devices Are Available?
WBG materials (SiC, GaN etc.) have been used in light emitting devices and low power devices for many years but the first practical SiC power device was the Schottky Barrier Diode (SBD), introduced in the early nineties. Since then, many other SiC power devices have been introduced including rectifier diodes, MOSFETs, JFETs, BJTs and thyristors. Power Products International are Semikron’s UK franchised distributor and are able to supply both SiC hybrid (Si IGBT and SiC SBD) or full SiC (SiC MOS and SiC SBD’s) power modules. The modules are available in Semikron’s popular packages including SEMITRANS3(Industry standard 63mm modules), MiniSKiiP, SEMITOP, SEMIPACK2, SKiM93 and SEMiX 3p
Contact us today to discuss your SiC power module and thermal management requirements. Power Products have been manufacturing power electronic assemblies for over 30 years. This experience and knowledge of how to select the most appropriate module for the application and in-house precision machining of heatsinks, combine to ensure the most reliable and efficient power assembly.