Sharp’s new IGZO crystal structure for high density LCD and OLED displays
Sharp and Semiconductor Energy Laboratory have discovered a new IGZO crystal structure, called CAAC, and announced a new semiconductor technology that utilizes it.
By contrast to current IGZO, this technology enables TFTs to be made even more compact and high-performance, helping to achieve displays with higher resolution and lower power consumption.
Using this technology, Sharp has fabricated a prototype 4.9-inch display for use in smartphones, and a 6.1-inch display for mobile devices. The 4.9-inch display features a resolution of 720 x 1,280 pixels and a pixel density of 302 ppi, while the 6.1-inch, 2,560 x 1,600 pixel resolution display has a 498 ppi pixel density.
Sharp aims to quickly produce commercial LCDs using this new IGZO technology.
"In a crystal, the A, B, and C axes are aligned, but in this material, only the C axes are aligned. So in terms of crystallography, it's very unusual. This is the first time this structure has been known. Until now, single crystals resembled things like dice, but this material enables crystallization in thin films."
"The On characteristic is 10-20 times better than that of amorphous silicon. So, the transistors in pixels can be made smaller. This enables higher resolution than before."
This technology can also be applied to OLED displays. Sharp has made prototypes of a 13.5-inch 4K version and a 3.4-inch flexible version. Sharp and SEL don't currently plan to commercialize these OLED displays. Instead, they'll keep working on R&D, in preparation for future market needs.
"Until now, OLED displays have been crystallized using lasers, so they've had visible stripes. But with these new displays, stripes will be inherently invisible. We think that's revolutionary. In the good sense of the word, this new technology is a monster."
Meanwhile, in April, Sharp started to mass-produce LCD panels using IGZO.
The panels come in three types. For monitors, there's a 32-inch, 3,840 x 2,160 pixel, 140 ppi version. For notebook PCs, there's a 10-inch, 2,560 x 1,600 pixel, 300 ppi version. And for tablets, there's a 7-inch, 800 x 1,200 pixel, 217 ppi version. Using IGZO has enabled Sharp to achieve high resolution, low power consumption displays, with high yield.
Power consumption has been reduced by a factor of 5-10. By contrast to the conventional system where TFTs are continuously driven for each frame, smaller TFTs and high Off performance enable a new system, where driving is halted if the display doesn't change.
Using this high Off performance in a touchpanel also gives the touchpanel high performance. By touch-detecting while the liquid crystal panel isn't being driven, and halting the touchpanel while the liquid crystal panel is being driven, touch signals can be detected without noise from driving the liquid crystal panel. This greatly improves the detection precision of touchpanels.
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