Japanese electronics giant Sharp announced recently that it has begun producing high-resolution liquid-crystal displays (LCDs) featuring metal-oxide transistor arrays.
Metal oxides are expected to help bring down the price of high-resolution LCDs, which are similar in sharpness to the retina displays found in the latest iPad and iPhone, and may also cut the cost of making organic light-emitting diode (OLED) displays, a newer type of screen that is richly colored and energy-efficient, but which remains expensive to produce at large sizes.
Sharp has said that it will use indium gallium zinc oxide arrays to make LCDs for tablets, notebooks, and monitors. Some industry watchers have speculated that the company would provide metal-oxide displays for the next iPad, but the production specifications that Sharp has announced so far don’t match any Apple products.
To make high-resolution LCDs like the retina display, manufacturers currently rely on expensive processing steps, transforming amorphous silicon into higher quality polysilicon by treating it with lasers. Electrons zip through the treated material, which means smaller transistors can be packed more closely together to enable greater pixel densities. Smaller transistors also block less light, so LCDs built on polysilicon can use smaller, less power-hungry backlights.
Polysilicon is also normally necessary for OLED displays, which offer richer colors and lower power consumption than LCDs. OLEDs cannot be driven by amorphous silicon backplanes because their pixels require high current, which burns out the transistors. Sharp would not comment on whether it will develop the backplanes for OLED displays. LG has demonstrated OLED screens based on metal oxides, but no company has yet announced any products based on the technology.
The OLED market is growing, but polysilicon backplanes are still “too expensive,” says Stephen Forrest, a materials scientist and vice president for research at the University of Michigan in Ann Arbor.
A number of other companies—including industry leaders Samsung and LG—have been developing displays based on metal oxides, but Sharp is the first company to announce that it’s using the technology in production. A Sharp spokesperson says the company’s indium gallium zinc oxide backplanes have 20 to 50 times higher electron mobility than those made from amorphous silicon. This quality enables smaller transistors and greater pixel densities, though not as great as those in the iPad’s retina display.
Metal-oxide backplanes should also mean less power consumption and better touch-screen responsiveness, according to the spokesperson. Unlike silicon, metal oxides are transparent, so these backplanes impede the backlight less. When displaying a still image, some of the transistors can “pause” to save power; this cuts down on the electronic noise that can interfere with touch-screen sensors. And metal-oxide backplanes can be manufactured with fewer steps than polysilicon backplanes, which should lead to cost advantages.
Sharp’s move comes as the display market undergoes a significant shift, says Paul Semenza, a senior vice president at market research firm Display Search, which is headquartered in Santa Clara, California. Large television screens have become cheap to produce, and Japanese manufacturers cannot compete with the low prices offered by manufacturers in China and Taiwan. Competitors have responded to the pressure by merging—for example, Sony, Hitachi, and Toshiba’s mobile-display subsidiaries joined together to form Japan Display Incorporated on April 1, and the company has announced it will spend $1.85 billion on research and development over the next five years.
In late March, Sharp, headquartered in Osaka, announced a strategic partnership with Taipei manufacturing giant Foxconn. It also plans to research new display technologies. “They absolutely have to find a way to drive revenues, so they are compelled to go for the cutting edge,” says Semenza. Sharp may be trying to get there by manufacturing high-end displays at lower costs, he says. Metal-oxide backplanes offer a potentially profitable middle ground between inexpensive but low-performance amorphous silicon, and high-performance, high-price polysilicon.
Sharp is making the metal-oxide LCDs at its full-scale production line in Kameyama, Japan, rather than starting them on a pilot line. Moving from one-off demo screens to full-scale production shows that metal-oxide technology has legs, says Semenza. “That’s a big commitment,” he says.
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