Feature Article - March 2006
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Ready for their Close-up

Scoreboards that steal the spotlight

By Dawn Klingensmith



  
From Sapphires to Scoreboards

See those green and blue light-emitting diodes in your new scoreboard? Before they grew up to be LEDs, they started out as sapphires.

The full-color LED displays that football fans can make out on a sun-drenched day rely on the semiconductor gallium nitride for their brilliance. Sapphires are key to the semiconductor's development.

Surpassed in hardness only by diamonds, sapphires actually are aluminum oxide crystals, which can be created in labs, says David Reid, the manager who oversees the process at Honeywell Electronic Materials in Victoria, British Columbia. The lab-grown crystals are cored to get rods, which are then sliced into thin disks. Polished on one side and rough on the other, the disks are placed in a reactor, where a process called Metal Organic Chemical Vapor Deposition takes place. Simply put, this reaction is the act of conception that leads to the birth of blue and green LEDs.

Gases flow over the sapphires, depositing elements in layers onto the disks. The resulting bonds form gallium nitride, the semiconductor needed to produce the blue and green light. When the disks reach the desired thickness, most of the sapphire substrate is ground off, though some remains in place for the sake of stability. The disks are then diced into chips, Reid explains. It takes 8,000 to 10,000 semiconductor chips, along with other materials and a plastic cap, to make a single LED that glows blue or green when electricity passes through it. LEDs are then incorporated by the hundreds or thousands into high-end scoreboards.

If you're imagining that shiny blue sapphires impart color to the LEDs, think again. Pure, lab-created sapphires are clear, like glass. Naturally occurring blue gemstones form when impurities creep in during crystallization, Reid says. These blue beauties play no part in the creation of colored LEDs; ironically, their crystal-clear cousins do.