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Thermal Technology recently announced the successful testing of the first commercially available edge-defined, film-fed growth (EFG) crystal grower with the capacity to grow sapphire crystals up to 12 in. wide, 20 in. long and 0.6 in. thick (300 x 500 x 15 mm). The first sapphire test plate grown was over 15 mm thick throughout, 8 in. wide and 16 in. long, with no visible bubbles in the useable area and no cracks, grain boundaries or twins.
Thermal Technology will ship its first EFG sapphire crystal grower to the customer in September. The EFG process was invented in the U.S. over 40 years ago for the production of sapphire filaments. Since then, it has been used to produce a wide variety of shaped sapphire parts, including plates, tubes, rods and ribbons. It uses a molybdenum die or shaping unit to define the cross-sectional shape of the part being grown.
“We are very excited about this system,” said Matt Mede, president and CEO of Thermal Technology. “The market is requiring larger crystals, and up until now large sapphire crystal producers had to build their own machines.”
In order to meet the customer’s acceptance criteria, Thermal Technology was required to develop a crystal growth process demonstrating the successful operation of the machine. Using a hot zone and die assembly, as well as control software provided by Frank J. Bruni, Ph.D., a crystal growth consultant, Thermal Technology was able to grow the first slab after just a few operational tests.
“This was a challenging project, given the very high temperatures (over 2000°C) and the large volume of sapphire that had to be melted,” said Bruni. “Of particular difficulty was achieving a uniform temperature across the surface of such a large die. The crystal is separated from the die by a thin layer of molten sapphire. One side of that layer, the crystal interface, must be at the freezing point of sapphire, while the other side must be slightly higher to maintain the flow of liquid by capillary action. Getting the temperature field that uniform over a large surface area is not easy.”
For more information, visit www.thermaltechnology.com.