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29 Mar 2016
Unpolished optics developed under US Air Force contract said to measure 30 inches long.
US-headquartered sapphire crystal growth and component specialist Rubicon Technology says it has produced two huge windows of the material, under a military-sponsored development project.
Cut from a three-foot-long slab of high-quality monocrystalline sapphire, the inch-thick windows measure 18 x 30 inches and 17 x 25 inches.
Rubicon says that the breakthrough means that it has now met the next two milestones in its “Large-Area Net-Shape Crystal Extraction (LANCE)” development contract with the Air Force Research Laboratory (AFRL).
It means that the LANCE project is on track for completion this year, adds the Illinois firm, with only a few more milestones remaining to be reached. They include producing full-size 18 x 36 x 0.86 inch windows.
“Crystal growth for these final milestones is expected to be complete by end of June 2016, with polishing targeted to be finished by the end of 2016,” added Rubicon.
Sensational sapphire
The large-area sapphire windows are wanted for military sensing and targeting applications, but until now production methods have proved incapable of fabricating crystals with the thickness desired by the US Air Force.
Rubicon’s senior VP for optical, Hap Hewes, said in a company announcement: “These very large sapphire windows have created a sensation in defense and commercial applications.
“Sapphire’s outstanding transparency in the infrared through ultraviolet spectra, combined with its incredible hardness and abrasion resistance, make this a very attractive solution for many optical applications that need durability and excellent optical performance. We are now exploring the scope of opportunity for these massive windows and assessing customer needs to determine our future capacity requirements.”
The large sapphire windows produced by Rubicon are primarily intended for use by the US military as infrared windows, in extreme environments where both durability and optical clarity are important. However, the company also expects to find commercial applications for the giant components in semiconductor manufacturing equipment.
Semiconductor requirements
Sapphire is useful in semiconductor wafer processing equipment because of its chemical inertness and durability at high temperatures. While the semiconductor industry is looking to migrate to 450 mm (18 inch) wafer manufacturing, there are as yet no sapphire windows available at the larger dimensions. “We expect that Rubicon’s LANCE sapphire, when commercially available, will meet a need in this market,” says the firm.
However, the first user of the giant windows will likely be the US Air Force. Its spokesman Jamie Hoff said: “Through the successful development of a unique technology for the production of large-area sapphire, Rubicon has taken another step forward toward meeting the advanced demands of military sensor technology.”
Rubicon has been working on the LANCE project since mid-2012, when it won a three-year support grant of $4.7 million from the US Air Force to develop the new growth method.
Previously the “Kyropoulos” crystal growth approach, named after the German scientist Spyros Kyropoulos and employed as long ago as the 1930s, has typically been used to make large-scale sapphire.
The method differs from the better-known Czochralski melt-growth approach in that the cone-shaped crystal grows downwards inside the growth crucible, rather than being pulled upwards. As a result, the crystal diameter expands to a diameter almost as large as the crucible itself.
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