What is the difference between a superjunction MOSFET and a MOSFET? Why can RDSon be reduced?

The power electronics industry is experiencing rapid innovation as high-power electronics such as data centers and electric vehicles become more popular. To meet the growing demand for high power and high efficiency, many new technologies such as wide band gap (WBG) semiconductors are becoming increasingly important.

The power electronics industry is experiencing rapid innovation as high-power electronics such as data centers and electric vehicles become more popular. To meet the growing demand for high power and high efficiency, many new technologies such as wide band gap (WBG) semiconductors are becoming increasingly important.

One technology that has shown promise in these high-power applications is the superjunction MOSFET, an improvement over conventional technology that offers higher efficiency and smaller size.

This week, Alpha & Omega (A&O) announced two new superjunction MOSFETs that are directly targeted at these high-power applications.

In this article, we’ll discuss superjunction technology – why it’s critical for data centers, and A&O’s solutions.

MOSFET on-resistance challenges at high voltage

For MOSFETs in power switching applications, one of the most critical device parameters is the on-resistance, RDS(on).

RDS(on) measures the effective resistance of the transistor, which directly determines the power efficiency of the MOSFET.

One of the biggest factors affecting the RDS(on) resistance of a FET is the epitaxial (epi) layer of the device, which is the main voltage withstand region of the device.


Layout of conventional planar MOSFETs.

As the voltage increases, the epitaxial layers also need to increase in thickness and become more lightly doped to help block high voltages.

However, this increases the resistance of the epitaxial layer and thus increases the overall RDS(on) of the MOSFET, which has a negative effect.

For a MOSFET rated at 600 V, over 95% of the device resistance comes directly from the epilayer. Specifically, it is estimated that each doubling of the rated voltage increases the area required to maintain the previous RDS(on) by a factor of five.

Data Center High Voltage Applications

When designing power FETs in high voltage applications, there is a tradeoff between transistor size, its voltage isolation capability, and RDS(on).

Specifically, in high-voltage applications in data centers, designers need power FETs that can achieve high efficiency and a slim profile to accommodate increasingly thin systems, such as 1 U or 0.5 U. For these applications, superjunction MOSFETs have become a viable option.


Structure of a planar power MOSFET (left) and a superjunction MOSFET (right).

Superjunction MOSFETs overcome the resistance of the epitaxial layer by using techniques such as deep trench fill.

The super junction field effect transistor adopts a trench structure, and multiple vertical PN junctions are arranged, which effectively reduces the resistivity of the epitaxial layer while maintaining a high blocking voltage.

As a result, superjunction MOSFETs can achieve extremely low RDS(on) while maintaining small size and high blocking voltage. This feature makes the device a popular choice for high-power applications such as data centers.

A&O targets data centers

As mentioned, this week, A&O announced the release of two new superjunction MOSFETs for data center applications.

The two new products, the AONV110A60 and AONV140A60, are 600 V superjunction FETs designed for very low RDS(on) in small packages.


AONV140A60 On-Resistance vs. Drain Current and Gate Voltage.Image courtesy of A&O

According to the datasheet, the RDS(on) of these two devices is 0.11 Ω and 0.14 Ω, respectively, and both are packaged in an 8 mm x 8 mm x 0.9 mm DFN package.

In addition to data centers, A&O claims these products are ideal for a variety of other applications, including fast charging, solar inverters, and industrial power supplies.

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