Tag Archives: SiC MOSFETs

SiC MOSFETs Enhance Performance and Efficiency

Power applications across industries demand smaller sizes, greater efficiency, and enhanced performance from the electronic equipment they use. These applications include energy storage systems, battery chargers, DC-DC and AC-DC inverters/converters, industrial motor drivers, and many more. In fact, the performance requirements have become so aggressive that they surpass the capabilities of silicon MOSFETs. Enter new transistor architectures based on silicon carbide or SiC.

Although silicon carbide devices do offer significantly enhanced benefits across most critical performance metrics, the first-generation SiC devices had various application uncertainties and limitations. The second-generation devices came with improved specifications. With pressures for time-to-market increasing, manufacturers improved the performance of SiC MOSFETs, and by the third generation of devices, there were vast improvements across key parameters.

While silicon-based MOSFETs significantly enhanced the design of power electronic equipment, the insulated-gate bipolar transistor or IGBT also helped. The IGBT is a functionally similar semiconductor, its construction is vastly different, and its switching attributes are more optimized. This led to power electronic equipment adopting switched topologies, thus becoming far more efficient and compact.

The main characteristics of switched mode topologies are based on some form of PWM or pulse-width modulation. They use a closed-loop feedback arrangement for maintaining the desired current, voltage, or power value. With the increasing use of silicon MOSFETs, the demand for better performance also increased. Regulatory mandates demanded new efficiency goals.

With a considerable effort in R&D, an alternative emerged. This was the SiC power-switching device, that used silicon carbide as the substrate rather than silicon. Deep-physics changes have allowed these SiC devices three major advantageous electrical characteristics over silicon-alone products. These characteristics offer operational advantages and subtle differences.

The first of these three main characteristics is a higher critical breakdown voltage. While silicon-based products offer 0.3 MV/cm, SiC-based products offer 2.8 MV/cm. This results in products with the same voltage rating now being available in a much thinner layer, effectively reducing the drain to source on-time resistance.

The second main characteristic is higher thermal conductivity. This allows SiC-based devices to handle much higher current densities in the same cross-sectional area, as compared to that silicon-based devices can.

The final characteristic is a wider bandgap. This is the difference in energy measured in electron volts between the bottom of the conduction band and the top of the valence band in many types of insulators and semiconductors. This results in a lower leakage current at higher temperatures. Because of the above reasons, the industry also refers to SiC devices as wide bandgap devices.

In general terms, SiC-based devices can handle voltages that are ten times higher than Si-only devices can. They can also switch about ten times faster, besides offering an on-time drain-to-source resistance of half or lower at 25 °C, even when using the same die area as a Si-only device. Moreover, the switching-related loss at turn-off periods for SiC devices is significantly lower than those for Si-based devices. Additionally, it is easier to handle thermal design and management issues with SiC-based devices, as they can operate at much higher temperatures, such as up to 200 °C, as compared to 125 °C for Si-based devices.