January 9, 2025 – Toyota Gosei Co., Ltd. has announced the successful development of an 8-inch gallium nitride (GaN) single-crystal wafer for vertical transistors, marking a significant milestone in GaN technology. This achievement follows Toyota Gosei's earlier success in manufacturing 6-inch GaN single-crystal wafers, further advancing GaN wafer size and potential applications.

Advantages of Vertical GaN Transistors

Compared to lateral transistors based on silicon GaN processes, vertical transistors built on GaN single-crystal wafers enable higher power density devices. This capability makes them suitable for use in larger wafer sizes such as 8-inch and 12-inch wafers, thereby increasing production efficiency and reducing per-device costs.

Overcoming the Challenges of Large-Diameter GaN Wafers

The development of GaN single-crystal wafers larger than 4 inches has long been a challenge in the semiconductor industry. To address this, researchers from Osaka University and Toyota Gosei employed a multi-point seed crystal (MPS) substrate and a sodium (Na)-assisted flux growth technique.

Multi-Point Seed Crystal Method:

This technique involves distributing numerous small GaN seed crystals across a large sapphire substrate. During crystal growth, these individual crystals merge into a single large-diameter GaN crystal. This method enables the production of high-quality, large-diameter single crystals.

Na-Assisted Flux Growth:

Invented in 1996 by Professor Hisanori Yamane from Tohoku University, this method dissolves gallium (Ga) and nitrogen (N) into liquid sodium (Na) to grow high-quality GaN single crystals. As a liquid-phase growth technique, it is particularly effective for producing large, defect-free crystals.

Combining these two techniques has resulted in a hexagonal GaN crystal slightly smaller than 8 inches, paving the way for further advancements in single-crystal growth technology.

The Impact of Larger Wafer Sizes

In the semiconductor industry, larger wafer sizes translate to significant cost advantages and efficiency improvements. For example:

8-inch wafers have an area 1.78 times larger than 6-inch wafers.

12-inch wafers offer an area 2.25 times larger than 8-inch wafers.

Larger wafers allow for the production of more devices per wafer, reducing per-unit costs and improving overall production throughput.

Future Implications

The successful development of 8-inch GaN single-crystal wafers by Toyota Gosei represents a major step toward high-performance power devices and supports the growing demand for energy-efficient technologies in fields such as electric vehicles (EVs), renewable energy, and industrial applications. Furthermore, this breakthrough sets the stage for the eventual commercialization of 12-inch GaN wafers, further enhancing the competitiveness of GaN in the semiconductor industry.