Introduce the difference between SiC-MOSFET and IGBT

It is well known that the properties and advantages of SiC materials have been proven on a large scale and are considered to be ideal semiconductor materials for high voltage, high frequency power devices. The reliability of SiC devices is one of the key focuses for development engineers, as there are currently no SiC-based devices that can fully replace Si-based IGBTs and MOSFETs in the market.

SiC-MOSFETs differ significantly from IGBTs, but what exactly makes them different? This article will explore the main differences between SiC-MOSFETs and IGBTs, focusing on their performance characteristics and application scenarios.

Difference from IGBT: Vd-Id Characteristics

The Vd-Id (voltage vs. current) characteristic is one of the most fundamental parameters of a transistor. Below are the Vd-Id curves at 25°C and 150°C, which illustrate how these devices behave under different operating conditions.

At 25°C, the Id vs. Vd curve for both SiC and Si MOSFETs shows a linear increase, while the IGBT exhibits a rising voltage at low current levels. This means that, in the low current range, the Vds of the MOSFET components is lower compared to the IGBT's collector-emitter voltage. This behavior directly affects the on-resistance, which is a critical factor in determining efficiency.

In the low Vd or low Id range (approximately up to 1V in this example), the IGBT's behavior is relatively negligible. However, in applications where power demand varies widely—from low to high power—this can lead to reduced efficiency in low-power scenarios.

On the other hand, SiC-MOSFETs maintain a low on-resistance across a much wider current range, making them more efficient in a broader range of operating conditions.

Additionally, when temperature increases to 150°C, the slope of the Vd-Id curve for both SiC and Si-MOSFETs becomes less steep, indicating higher on-resistance. However, the variation in SiC-MOSFETs at 25°C is minimal, and even with temperature changes, the on-resistance remains stable, showing better thermal performance than traditional silicon devices.

Difference from IGBT: Turn-off Loss Characteristics

As previously mentioned, SiC power components are known for their excellent switching performance, allowing for high-speed and high-power operations. Here, we will discuss the differences in turn-off loss characteristics between SiC-MOSFETs and IGBTs.

It is well-known that when an IGBT turns off, a tail current is generated due to its internal structure, leading to increased switching losses. This is a typical limitation of IGBT technology.

From the waveform shown during the turn-off process, it is clear that SiC-MOSFETs do not exhibit a tail current in principle, resulting in significantly lower switching losses. In this example, the combination of a SiC-MOSFET with an SBD (Schottky Barrier Diode) reduces the turn-off loss by 88% compared to an IGBT paired with an FRD (Fast Recovery Diode).

Moreover, the tail current in IGBTs tends to increase with rising temperature, which further degrades performance. For SiC-MOSFETs, high-speed operation requires careful adjustment of the external gate resistance (Rg) to optimize performance.

Difference from IGBT: Conduction Loss Characteristics

Next, let's look at the conduction loss when the switch is turned on.

During the turn-on phase, the IGBT experiences a significant loss due to the recovery current of the diode, as shown by the red dotted line in the Ic curve. This is a major source of energy loss in IGBTs.

However, when using SiC-SBC in parallel, the fast recovery characteristics help reduce the conduction loss of the MOSFET. On the other hand, the conduction loss in IGBTs paired with FRD increases with temperature due to the tail current effect.

In summary, the switching loss characteristics clearly show that SiC-MOSFETs outperform IGBTs in terms of efficiency and performance. Additionally, SiC-MOSFETs have achieved quality levels suitable for a wide range of industrial applications. It's important to note that the data presented here comes from ROHM's test environment, and results may vary depending on the driving circuit and other conditions. Always perform a detailed analysis based on your specific application needs.