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Sharpening Crystal Growth Technology in Salem

By Cindy Atoji Keene

Behind every high-intensity LED is a precious gem – a sapphire that comes not from the jeweler but from the laboratory, grown as a synthetic gem that has almost the exact chemical and physical properties as the natural specimen. As the applications for LEDs (light emitting diodes) have expanded, used in cell phones, liquid-crystal TV displays, laptops, remote controls, and of course, lighting, manufacturers are honing in on more efficient ways to create this durable, optical-friendly crystal. “The challenge comes in consistently creating sapphires that are pure and free of defects,” said Bob McGlone, who is charged with the task of overseeing crystal growth at GT Advanced Technologies, a supplier and servicer for the solar and LED industries.

At the GTAT plant in Salem, in a city more known for crystal witchcraft than state-of-the-art crystalline technology, giant sapphires weighing 100 kilogram (220 pounds) are pulled glowing hot from furnaces, sometimes up to 80 at a time. The sapphires start from a “seed” of aluminum oxide that has a certain lattice structure and orientation that will slowly grow, layer by layer, as it is heated and then cooled.

Q: How long does it take to create a sapphire?
A: You have to grow crystals slowly. We use extreme temperatures and pressure to take powered aluminum oxide, which is sapphire in its raw form, heat it to a molten state then cool it to solidify in a crystal form. The sapphire expands over three weeks in a huge 6x6 foot furnace until the temperature reaches 2,100 degrees Celsius, then the cooling process makes or breaks the crystal. The finished sapphire is perfect enough to Mother Nature jealous and lowers the price of crystal for industrial uses. One two-inch diameter wafer can provide about 20,000 LEDs or more.

Q: What is your role in sapphire production?
A: Sapphire production requires very controlled conditions because the boules, or single-crystal ingots, can crack. The “recipe” has to be correct, and the furnaces need to be tight, including the gas, computer and electrical systems. If you were to walk into our facility, you would see high vacuum chambers with monitors; high tech helium pumps, computers, and alarm systems that all work together to create the perfect growing conditions.

Q: What sort of safety hazards do you have to be aware of?
A: Sapphire is razor sharp and very dense and heavy. When removing it from the furnace, it has to be handled with care because of the heat. Overhead cranes extract the ingot out of the furnace but there is still a fair share of handling it.

Q: How do you check the sapphires for impurities?
A: A block of sapphire will go to quality control, where it is put under high-intensity, polarized lighting to check for defects in the crystal structure, which can affect the electrical and thermal qualities. A synthetic crystal isn’t blue but clear, because it has no impurities.

Q: How does it feel to pull a perfect crystal out?
A: I’m in awe. It’s a good feeling when I pull out a perfect crystal. It is round, 15 inches in diameter, 11 inches tall, so it looks like a big piece of glass.

Q: Do you have any crystals of your own?
A: Employees were given a gift of cut gemstones from manufacturing byproducts, so my wife has a four-carat piece that I was awarded. It’s still sitting in her jewelry box since she isn’t sure how she wants to mount it.

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