【World Express】FOX develops 3.5-inch gallium oxide crystal without iridium

KEY POINTS

      FOX, C&A, Tohoku University and Mie University produce 3.5-inch gallium oxide single crystal with precious-metal-free OCCC method

      Process removes iridium crucibles, supports high-oxygen growth conditions and aims to cut cost while improving crystal quality

      FOX targets 2029 mass production; IWGO2026 presentation set for August 4 in Maryland

A 3.5-inch gallium oxide single crystal grown using a precious-metal-free apparatus.(PHOTO:FOX)

      FOX, a Tohoku University startup, said on July 28 that it had succeeded with C&A, Tohoku University and Mie University in producing a 3.5-inch-class gallium oxide bulk single crystal using a crystal growth system that uses no precious metals.

      The group achieved the result with a new method called Oxide Crystal growth from Cold Crucible, or OCCC, for gallium oxide, a material being developed for next-generation power semiconductors. The crystal has a straight body section large enough for practical use and reaches about 3.5 inches in diameter, a size comparable to large-diameter crystals produced by conventional pulling methods.

      Conventional gallium oxide growth methods have used iridium, a precious metal, in crucibles and heater components that hold the melt. That has made cost reductions difficult and has also led to defects such as micro- and nano-voids associated with low oxygen partial pressure environments. Iridium was priced at about 40,000 yen per gram in June 2026, equivalent to about $244 per gram.

      The group improved the OCCC crystal manufacturing system and high-frequency oscillator, and developed proprietary software for automatic crystal shape control. That enabled smooth expansion of the crystal diameter from a small seed crystal and stable growth of the straight body section without using iridium crucibles or other precious-metal components.

      Under the OCCC method, the raw material is directly heated and melted by a high-frequency magnetic field, while a solidified layer formed by the raw material itself holds the melt. The method also enables crystal growth under high oxygen partial pressure and avoids metal contamination from crucibles.

      Mie University evaluated the crystallinity and dislocation distribution of the gallium oxide single crystals grown by the OCCC method using synchrotron X-ray topography.

FOX said it will focus on further improving crystal quality, increasing wafer diameter and establishing stable production technology for gallium oxide single crystals made with the OCCC method. The company is aiming for mass production in 2029 and plans to strengthen cooperation with research institutions and device manufacturers in Japan and overseas toward practical gallium oxide power devices.

      C&A will commercialize the crystal growth equipment and promote deployment to research institutions and companies.

      The group said details of the technology will be presented on August 4 at the International Workshop on Gallium Oxide and Related Materials, or IWGO2026, in Maryland in the United States. The presentation title is "Bulk Single Crystal Growth of β-Ga₂O₃ with Automatic Diameter Control System Specialized for the OCCC Method," and the corresponding author is Akira Yoshikawa, a professor at Tohoku University's Institute for Materials Research.

      The work was supported by multiple projects of Japan's New Energy and Industrial Technology Development Organization, known as NEDO, as well as education ministry and scientific research grant programs.

      Gallium oxide is one of several wide-bandgap semiconductor materials under development for power electronics, alongside silicon carbide and gallium nitride, because such materials can handle high voltages and temperatures more efficiently than conventional silicon in some applications.