GaN Power Semiconductors: Benefits of Efficiency and Miniaturization

GaN Slashes Losses by Half – Why GaN is Reshaping Power Supply Design

If you've ever grappled with improving power conversion efficiency by just one percentage point in inverter design, the numbers alone will tell you how much GaN (Gallium Nitride) has changed the game. While silicon MOSFETs reach their limit at switching frequencies in the tens of kHz, GaN can handle frequencies in the MHz range. Higher frequencies allow for smaller passive components (inductors and capacitors), reducing board area and ultimately the overall enclosure size. Efficiency and miniaturization are not trade-offs; for GaN, they are simultaneously achievable goals.

So why is adoption finally gaining traction now? The material's advantages have been known for over a decade. What has changed is that mass production costs and device reliability have reached practical levels, coinciding with major demand surges from EVs, data centers, and industrial equipment. This article will provide a concrete breakdown of the technical advantages and offer perspectives needed for adoption decisions.

What Does "Three Times the Bandgap" Mean?

GaN's most significant characteristic is its wide bandgap, approximately three times that of silicon. The bandgap is the energy required for an electron to move into the conduction band within a semiconductor; a larger bandgap allows the semiconductor to maintain its properties even in high-voltage and high-temperature environments.

In the context of power conversion, the difference in critical electric field strength is more directly impactful. GaN's critical electric field strength for breakdown is about 10 times that of silicon. This means that to achieve the same breakdown voltage, GaN devices require a much thinner active layer than silicon devices. A thinner layer reduces resistance, leading to lower on-resistance (RDSon). Low on-resistance directly contributes to reduced conduction losses.

This graph illustrates that GaN and SiC significantly outperform silicon at the material level. The difference in electric field strength is noteworthy, as this value directly relates to the design freedom of being able to create devices that are "thinner and smaller for the same breakdown voltage."

What distinguishes GaN from SiC is the device structure employed. GaN is typically realized as a lateral HEMT (High Electron Mobility Transistor), utilizing a GaN layer epitaxially grown on a silicon or SiC substrate. The characteristic feature of HEMTs is the extremely high electron mobility due to the two-dimensional electron gas (2DEG) formed at the AlGaN/GaN interface. This structure, with electron mobility approximately twice that of silicon, is the basis for simultaneously achieving high-speed switching and low loss.

The Reality of Efficiency Improvement – Breakdown of Losses by Numbers

Power circuit losses are broadly divided into "conduction losses" and "switching losses." Conduction losses are heat generated by resistance when the device is in the on-state, while switching losses occur during the on-off transitions.

Silicon power MOSFETs have large gate capacitance, requiring significant gate current to increase switching speed. GaN HEMTs have extremely small gate capacitance, needing less drive power for high-speed switching. This difference leads to a substantial reduction in switching losses.

In actual circuits, cases have been reported where total losses in GaN-based systems are reduced by 40-50% compared to 100W-class power circuits using silicon MOSFETs. Conversion efficiencies, which had plateaued around 94%, have been improved to nearly 98% by replacing them with GaN. This small numerical difference enables fundamental re-evaluations of cooling costs and thermal design in high-power systems.

The Mechanism of Miniaturization – Why Passive Components Shrink

The explanation that "GaN enables miniaturization" is often heard, but a deeper understanding emerges when tracing the specific reasons. In power circuits, the bulk of the volume is occupied not by transistors, but by passive components like inductors and capacitors.

The size of an inductor is inversely proportional to the switching frequency. If the frequency doubles, the required inductance is halved, and the core size also decreases. The MHz-range switching enabled by GaN has the potential to reduce inductor volume to less than one-tenth compared to 100kHz-range silicon designs.

Capacitors follow a similar trend. As frequency increases, less capacitance is needed to absorb ripple current, allowing for smaller and fewer components. The overall mounting area of the power supply board shrinks, leading to cascading miniaturization and weight reduction of the enclosure. This "shrinking passive components" mechanism is behind the rapid adoption of GaN in smartphone fast chargers. The ability to fit a 65W charger into a credit card size would not have been possible without GaN.

Differentiation from SiC – Criteria for Selection

While GaN and SiC are often discussed together as wide bandgap semiconductors, their application-based differentiation is relatively clear.

SiC primarily uses a vertical structure and excels in power density and reliability in high-voltage (above 1200V) applications. SiC is expected to remain dominant in high-power, high-voltage applications such as electric vehicle traction inverters and large industrial UPS systems.

GaN, centered around lateral HEMT structures, has its main products concentrated in the 650V breakdown voltage range. Leveraging its fast switching speed and low gate capacitance, it is adept at high-frequency, high-efficiency designs, and its adoption is rapidly expanding in mid-voltage consumer and industrial power supplies, automotive OBCs (on-board chargers), and data center server power supplies.

Just as SiC MOSFETs face challenges with the trade-off between short-circuit withstand time and on-resistance, GaN has its own inherent issues. Many devices are normally-on, meaning they conduct current at room temperature, requiring careful safety design to prevent malfunction. While normally-off devices, such as those using a cascode structure (a configuration combining a GaN HEMT and a silicon MOSFET), are becoming common, the different gate drive design prerequisites should be confirmed during selection.

Technical and Procurement Considerations Before Adoption

For GaN device selection, the interplay with the gate driver is critical for practical implementation, beyond the device's standalone characteristics. GaN HEMTs exhibit extremely fast voltage rise and fall times (high dV/dt), making PCB parasitic inductance a potential cause of ringing and false triggering. Layout design that minimizes gate loop inductance and selection of a compatible gate driver are prerequisites.

Similar to SiC, GaN devices also tend to heat up quickly due to their high current density. The response time setting for protection circuits must be determined based on the device's thermal tolerance. Whether the gate driver IC can ensure this response time during the selection phase is a point to consider from both design and procurement perspectives.

On the supply side, products using silicon as the substrate for GaN wafers (GaN-on-Si) are driving cost reduction, and the ability to leverage existing 8-inch Si wafer manufacturing lines contributes to lower procurement costs. Compared to the transition from 6-inch to 8-inch SiC substrates, GaN-on-Si can more easily repurpose manufacturing infrastructure, potentially offering an advantage in terms of responsiveness to increased production.

From both technical and procurement standpoints, the barriers to GaN adoption have shifted from device characteristics themselves to "system-level optimization experience." Know-how in high-frequency design and the engineering resources that accumulate this expertise will likely be the decisive factor in the speed of adoption.