15 November 2013

IGZO display tech finally makes it to mass market: iPad Air now, high-res desktop display soon

If you ever wondered how Apple made the iPad Air lighter, thinner, and significantly smaller than its predecessor, here’s the answer: IGZO. IGZO, or indium gallium zinc oxide, is the future of high-resolution displays, allowing for significantly higher pixel densities and reducing power consumption. The technology has been on the verge of commercial adoption for years, and now, as with other emerging technologies in the past, Apple will shepherd IGZO to market with the iPad Air.

Layers of an LCD screen, including polarizers, transparent electrodes, backlight, etc. If the display is touch-sensitive, there’s another bunch of layers that go on top of this as well.

In every kind of flat-panel display, whether they’re OLED or LCD, there are layers. In your laptop’s LCD display, there are probably at least five thin layers, ranging from polarizers to transparent electrodes to light diffusers to the actual liquid crystals themselves. Each of these layers, except for the LCD/OLED, are transparent otherwise light wouldn’t be able to escape, and you wouldn’t be able to see the display. It is fairly hard to believe, but there’s actually a transparent layer of glass containing millions of tiny electrodes in front of and behind the LCD/OLED layer. As you can imagine, it’s rather hard to make a transparent mesh of millions of metallic electrodes. Every pixel is also accompanied by a transistor (so it can be turned on and off) and not only is it hard to make these transistors transparent, but the performance and quality of the display is tightly coupled to the performance and size of these transistors. This is where IGZO comes in.

IGZO, or indium gallium zinc oxide, is a semiconductor that not only can be used to make transparent transistors, but also has 20 to 50 times the electron mobility of amorphous silicon (a-Si). Most flat-panel displays currently feature transistors fabricated from a-Si, which isn’t transparent, but can be etched thin enough that some light can pass through it. By virtue of having huge electron mobility, IGZO transistors can be much smaller, allowing for higher pixel densities and lower-power operation. Due to their transparency, image quality is improved and less illumination is required  again reducing power consumption. The gains from IGZO are significant: We’re talking about the technology that will bring high-resolution displays to the desktop (the Asus/Sharp 32-inch 4K monitor is IGZO), and large gains to mobile battery life, resolution, and image quality.

Low-temperature polycrystalline silicon (LTPS) is another alternative to a-Si that has higher electron mobility and thus excellent image quality, but LTPS is difficult and expensive to manufacture. One of the best examples of LTPS is the new Kindle Fire HDX, which is probably the only device on the market that has a better display than the iPad Air. According to Raymond Soneira at DisplayMate, the iPad Air’s use of IGZO reduces the display’s power consumption by 57% over last year’s iPad 4 — a huge reduction for a single generation. The Fire’s use of LTPS, however, allows its display to go one step further and use 30% less power than the iPad Air. While LTPS is better than IGZO, IGZO is expected to win out because it’s easier and cheaper to manufacture. LTPS will probably stick around in smaller, flagship smartphones and tablets, while IGZO eventually takes the rest of the smartphone/tablet/laptop/desktop/TV market.
 IGZO vs. a-Si

More IGZO vs. a-Si

Commercial IGZO panels were first brought to market by Sharp, but teardowns of the iPad Air have revealed an IGZO panel made by LG. There is very little (public) info about LG’s IGZO capabilities, but it may have acquired the necessary patents from JST, or somehow partnered with Sharp to ramp up production (LG is one of the world’s largest producers of LCD and OLED displays). Either way, it would seem that LG is now producing huge quantities of 9.7-inch IGZO-TFT panels for Apple — and hopefully, in the next year or two, we’ll see some IGZO laptop and desktop displays. I can’t tell you how much I want a 24-inch 4K monitor.

Now read: New OLED tech could make smartphone screens cheaper and more power-efficient


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