300mm wafer for GaN devices
Shin-Etsu Chemical in Japan has created a 300mm (12in) substrate for GaN epitaxial growth and recently started supplying samples.
The QST 300mm wafer from Shin-Etsu have the same coefficient of thermal expansion (CTE) as that of GaN, avoiding warping and cracks on the GaN epitaxial layer and boosting yield. Shin-Etsu Chemical has sold 150mm (6in) and 200mm (8in) QST substrates and GaN on QST epitaxial substrates
The QST (Qromis Substrate Technology) substrate licensed from Qromis consists of a polycrystalline aluminium nitride ceramic core with a CTE that matches GaN and multiple layers of inorganic film that coat the core. A silicon dioxide SiO2 bonding layer on top of the encapsulation layers allows for a single crystalline silicon layer that forms a nucleation layer for the epitaxial GaN growth.
GaN device manufacturers cannot benefit from increasing the diameter of materials because of the lack in large-diameter substrate suitable for GaN growth, despite the fact that they can use the existing silicon production line for GaN. The 300mm QST substrate enables GaN epitaxial growth without warping or cracks, which was unattainable on silicon wafer substrates, significantly reducing device costs.
This substrate material allows for high-quality and thick GaN epitaxial growth with a large diameter. Customers are evaluating QST substrates and GaN on QST epitaxial substrates for power devices, high-frequency devices and LEDs and have moved to the development phase for power supplies for data centres says the company.
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