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.