Electrons can’t travel fast enough in amorphous silicon to drive very high refresh rates in large TVs, he says, and that same limitation is a problem for the smaller TFTs needed to build very pixel-dense high-resolution displays. Although the new iPad does use amorphous silicon, some reports suggest that the device gets significantly hotter than previous models because it pushes a low-efficiency backplane to its limit. Hayden says the best way to make similarly dense displays at this size is to switch to a different backplane material and that making displays with a pixel density matching that of the new iPad, but in larger sizes, requires using IGZO. “Amorphous silicon is a limitation,” he says.
One alternative to amorphous silicon, called partially crystallized silicon, or LTPS, is already used in the iPhone 4S and other smart phones, but LTPS is about twice as expensive to use in a backplane as amorphous silicon. IGZO is only a third more expensive, says Hayden–low enough to enable a flood of TVs and tablets with significantly improved displays. IGZO could even become almost as cheap to use as amorphous silicon, as Applied Materials and its customers ramp up production, Hayden says.
Charles Annis, an analyst with DisplaySearch who tracks display manufacturing technology, says that before the year is out, Apple may be making iPads using IGZO displays. “We believe IGZO-based LCDs from Sharp are currently being evaluated by Apple, and they have a good chance of being adopted this year,” he says.
That would make the iPad one of the first gadgets to use the new design. “Although several companies are close to commercializing IGZO-based displays, they are not quite there yet,” says Annis. He says that Applied Materials’s new equipment should help change that, and that IGZO will also likely help establish the next upgrade to TV picture quality, known as “ultra definition,” which has four times the resolution of 1,080-pixel HD images.
However, Annis notes, the new equipment introduced by Applied Materials can’t perform every step in the process of making a display backplane using IGZO. The machines make building up the layers of the material needed easier, but they cannot be used to pattern the actual transistors of a backplane. Methods exist for making those transistors, says Annis, but they could stand to improve.
Looking further ahead, Applied Materials’s Hayden says that making it easier to use IGZO should also make flexible displays more practical to manufacture. The process takes place at room temperature, which is compatible with the plastic needed to make a bendy display. Amorphous silicon and other technologies in use today involve temperatures of several hundred degrees.