Introduce the difference between SiC-MOSFET and IGBT

It is widely recognized that the performance and advantages of silicon carbide (SiC) materials have been extensively validated, making them a promising candidate for high-voltage and high-frequency power devices. The reliability of SiC-based components has become a major focus for engineers during development, as there are currently no mature SiC-based alternatives to traditional silicon-based IGBTs and MOSFETs.

Although SiC-MOSFETs differ significantly from IGBTs, what exactly sets them apart? This article aims to explore the key differences between SiC-MOSFETs and IGBTs, focusing on their operational characteristics and performance in various applications.

Difference from IGBT: Vd-Id Characteristics

The Vd-Id (voltage vs. current) characteristic is one of the most fundamental properties of a transistor. Below are the Vd-Id curves at 25°C and 150°C.

At 25°C, the Id vs. Vd curve for both SiC and Si MOSFETs shows a linear increase. However, IGBTs exhibit a higher voltage drop at low current levels, which means their Vds is higher compared to MOSFETs. This directly relates to on-resistance, where lower on-resistance leads to a flatter slope in the Vd-Id curve, improving efficiency.

In the low Vd or low Id range (around 1V in this example), IGBTs show negligible performance, which isn't a problem in high-voltage and high-current applications. However, when dealing with a wide range of power demands—from low to high—IGBTs may not be optimal due to their limited efficiency in low-power scenarios.

In contrast, SiC-MOSFETs maintain a low on-resistance across a broader current range, offering better performance in both low and high power conditions.

At 150°C, the slope of the Vd-Id curve for both SiC and Si-MOSFETs increases, indicating a rise in on-resistance. However, the change in SiC-MOSFETs is much smaller, and the variation in on-resistance remains minimal even when temperature increases.

Difference from IGBT: Turn-off Loss Characteristics

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

One well-known issue with IGBTs is the presence of tail current during turn-off, which increases switching losses. This is a fundamental limitation of IGBT technology.

From the waveform comparison, it’s clear that SiC-MOSFETs do not experience tail current, resulting in significantly reduced switching losses. In this example, using a SiC-MOSFET with an SBD (Schottky Barrier Diode) reduces the turn-off loss (Eoff) by 88% compared to an IGBT paired with an FRD (Fast Recovery Diode).

Additionally, the tail current in IGBTs tends to increase with rising temperature. For SiC-MOSFETs, proper gate resistance (Rg) adjustment is essential for high-speed operation.

Difference from IGBT: Conduction Loss Characteristics

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

During turn-on, the IGBT experiences a significant recovery current (blue curve), leading to higher losses. This is mainly due to the diode’s recovery characteristics. On the other hand, when using SiC-SBC in parallel with fast-recovery diodes, the conduction loss is significantly reduced.

Meanwhile, the conduction loss in IGBTs increases with temperature, especially due to the tail current effect. This makes SiC-MOSFETs more efficient under varying thermal conditions.

In summary, SiC-MOSFETs outperform IGBTs in terms of switching and conduction losses, making them suitable for a wide range of industrial applications. The data presented here comes from ROHM’s test environment, and results may vary depending on driving circuit configurations and other factors. Always perform specific analysis based on your application requirements.