The power electronics industry is undergoing rapid innovation as high power electronics, like data centers and electric vehicles, are gaining popularity. To meet the rising demands of high efficiency at high power, many new technologies such as wide-bandgap (WBG) semiconductors have become increasingly important.

One technology that shows promise in these high-power applications is the super-junction MOSFET, a spin on the traditional technology which affords better efficiency and smaller sizes. 

This week, Alpha and Omega Semiconductor released two new super-junction MOSFETs which aim directly at these high-power applications.

In this article, we’ll talk about super-junction technology, why it’s crucial for the data center, and what Alpha and Omega are bringing to the table.

MOSFET ON-resistance Challenges at High Voltage

When it comes to MOSFETs in power switching applications, one of the most key device parameters is ON-resistance or RDS(on).

RDS(on) measures a transistor’s effective resistance, a spec that directly determines the MOSFET’s power efficiency. 

One of the biggest contributors to a FET’s RDS(on) resistance is the geometry of the device’s epitaxial (epi) layer, which is the device’s main voltage-sustaining region. 

The layout of a traditional planar MOSFET. Image used courtesy of Vishay

As voltages increase, the epi layer needs to also increase in thickness and become more lightly doped to help block the high voltages. 

However, this has the undesirable effect of increasing the resistance of the layers, thus the MOSFET’s total RDS(on).

For MOSFETs rated at 600 V, more than 95% of the device resistance comes directly from the epi layer. Specifically, it is estimated that the area required to maintain the previous RDS(on) increases five-fold for every doubling of the rated voltage. 

Super-junction for Data Centers

The undesirable relationship between transistor size, its voltage blocking ability, and its RDS(on) creates a tradeoff when designing power FETs in high voltage applications. 

Specifically, in high voltage datacenters, designers need power FETs that can achieve a high efficiency along with a slim form factor to accommodate increasingly thinner systems such as 1 U or 0.5 U. For these applications, the super-junction MOSFET has become a viable choice.

Structure of a planar power MOSFET (left) and a super-junction MOSFET (right). Image used courtesy of Fuji Electric

As AAC contributor Adrian Gibbons writes, super-junction MOSFETs are devices that overcome device resistance from the epitaxial layer by instead using techniques such as deep trench filling. 

A super-junction FET employs a trench structure where multiple vertical PN junctions are arranged, which effectively cuts the resistivity of the epi layer while maintaining a high blocking voltage.

The result is that super-junction MOSFETs can achieve extremely low RDS(on) while maintaining a small form factor and high blocking voltage. This trait has made the device a trendy option for high-power applications like data centers.

Alpha and Omega’s MOSFETs Target Data Centers

As mentioned, this week, Alpha and Omega Semiconductor announced the release of two new super-junction MOSFETs targeting data center applications. 

The two new products, the AONV110A60 and AONV140A60, are both 600 V super-junction FETs designed to have extremely low RDS(on) in a small package.

AONV140A60 ON-resistance vs drain current and gate voltage. Image used courtesy of Alpha and Omega

According to the datasheets, the devices offer a <0.11 Ω and < 0.14 Ω RDS(on), respectively, while both come in an 8 mm x 8 mm x 0.9 mm DFN package.

Beyond data centers, Alpha and Omega claims the products are well suited for various other applications, including quick chargers, solar inverters, and industrial power. Both the AONV110A60 and the AONV140A60 are currently available for purchase.

Interested in other MOSFET advancements? Learn more in the articles down below.

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