As the lattice constant and thermal expansion coefficient of GGG single crystal match with YIG, GGG single crystal has been used as the substrate for thin film epitaxial growth of YIG and big. Krystron can provide stable GGG wafers with a maximum diameter of 4 inches (100 mm). Recently, we have provided 4-inch diameter GGG single crystal substrate to Saint Gobain group, which is the world leader in the design and production of practical materials. In the future, we will conduct more exploration and Research on the application of GGG substrate