Next-generation power semiconductors using “SiC” and “GaN”

Minamikawa: Power semiconductors made from new materials such as silicon carbide (SiC) and gallium nitride (GaN) can increase power conversion efficiency to around 97% to 98%, for example. A 1% or 2% improvement is a great difference.

SiC was first adopted for mass production by Tesla. While the maximum heat resistance for ordinary silicon is approximately 125 degrees, SiC is designed to withstand even 250 degrees. This makes it possible to place SiC power semiconductors very close to the engine and motor, even in places that get hot such as the engine compartment of the car. As such, it is very advantageous because the form factor (factors that determine shape and size) is smaller.

GaN is characterized by its suitability for high frequency applications. The higher the frequency, the higher the efficiency in converting the power supply from AC into DC or DC into AC, or in converting the frequency.

It is advantageous for power supply efficiency and contributes to the miniaturization of PC power supplies.

Currently, SiC is said to be five to six times more expensive than regular silicon, and GaN seven to eight times more expensive. The market is still limited, but if the price range decreases with mass production, applications will expand.

Abe: Yes, that’s right. From a materials perspective, SiC and GaN have a history of development that has solved the difficulty in achieving stable crystal growth.

Minamikawa: What do you think is important in the development of materials for power semiconductors?

Abe: TANAKA Precious Metals has been long involved in packaging materials for semiconductors. Starting with bonding wire, we have now expanded to die bonding materials and active brazing filler metals.

Based on this knowledge, we consider both thermal cooling and reliability to be important for power semiconductors.

I have heard that the physical properties of the newly emerging SiC and GaN are different from those of silicon. For example, when processed to the thickness of an actual chip, silicon becomes flexible, while SiC becomes hard.

When a chip is finally bonded to a substrate, warping occurs due to the difference in the thermal expansion coefficient. If the substrate is hard, stress relief will not be adequate, resulting in gaps and voids between the chip and substrate. Voids affect the denseness of the bonding layer and thus the thermal cooling and reliability of the chip.

The key point in the development of next-generation materials is to ensure performance and reliability through optimizing relay materials and bonding materials for chips and substrates with different physical properties.

Minamikawa: Indeed, power semiconductors are often used for long periods of time. In the case of solar power, the lifespan of panels is said to be 15 years, so it is important they last long. Reliability is still very important.

Abe: In addition, SiCwith high withstand voltage allows for a smaller chip size for the same current and voltage. Compared to silicon, the chip size is said to be one-third to one-fourth for the same withstand voltage. However, heat tends to accumulate easier in miniaturized chips, increasing the need for thermal cooling. I believe that the development of materials for next-generation power semiconductors involves the pursuit of thermal cooling, low resistance, and reliability.

Minamikawa: Material development is something that requires perseverance. I think a large aspect of that is continuing development steadily over a long period of time. Japanese companies are good at this, so I think Japan holds an important position in the field of power semiconductors.

next page Expectations for the U.S., China, and India

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