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iPad 5 rumor rollup for the week of Jan. 21

More than usually stunning display, thinner and lighter, canceled

By , Network World
January 25, 2013 09:36 AM ET

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The Rollup is not a display technology specialist. From what we understand, the use of metal oxide is one emerging option that can be used in TFTs, which form a sheet or layer that actually drives all the pixels on a high-resolution display. This TFT backplane can be paired with either LCD or OLED technology. Metal oxide's real benefit is much higher "electron mobility," which is critical to let screens support high definition and high refresh rates. One oxide in particular, indium gallium zinc oxide, has been widely rumored for many months as about to be used in the Next iPad, or Next iPhone's display.

According to Wikipedia, "An OLED display works without a backlight. Thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD)." No backlight is needed because in OLED, the "emissive electroluminescent layer is a film of organic compound which emits light in response to an electric current."

But, according to this blog post at Applied Materials, a vendor that builds manufacturing equipment for semiconductor and flat-panel display vendors, OLED displays on smartphones and tablets are not good candidates for metal oxide.

"Because each pixel of an OLED emits light directly, without the need for a backlight, each pixel requires two transistors," writes Applied Materials' Kerry Cunningham. "One is used to switch the pixel on and off, and one to control the current fed to the pixel. The problem is that metal oxide transistors aren't stable enough for this application. This causes unpleasant pixel-to-pixel variations that can be visible to the viewer. ... That's why OLED screens for mobile applications use more stable LTPS [low temperature polysilicon] backplanes instead."

A year ago, this Forbes post by a self-describe electrical engineer, Nigam Arora, argued that "Steve Jobs' Failure To See Light In OLED Could Cost Apple," as the headline summed it up.

"In 2010 at the Apple World Wide Developers Conference, Jobs touted Retina Display, which relies on traditional silicon LED technology," he wrote. "Jobs said, 'You can't make an OLED display with this resolution, we think it is quite superior.'"

It still seems to be. The iPad 4, released in November 2012, had the same Retina Display as its predecessor: 9.7-inch screen, 2048 x 1536 pixels. But in his review of the latest iPad, Anand Lal Shimpi, writing at his AnandTech blog, noted, "The real advantage however is color accuracy thanks to Apple's factory calibration on all of its devices with an integrated display." With Apple's factory-calibrated displays, you get "appreciably better color accuracy than any other tablet on the market today," Shimpi concluded. And the newest iPad "offers over other iPads ... a much better text reading experience. Individual letters look so much smoother."

His conclusions were echoed by colleague Chris Heinonen in his review of the iPhone 5. "The iPhone 5 display is a quantum leap better than the display on the iPhone 4. Contrast levels and light output have both been increased, and color performance is astonishing," Heinonen wrote. "While many were hoping for a move to OLED or some other screen innovation, this really is a huge step up that is very easy to quantify. To put this in perspective, in the past few years I've reviewed probably 30-40 different displays, from PC monitors to TVs to projectors. Not a single one, out of the box, can put up the Gretag Macbeth dE numbers [a color checker measurement] that the iPhone can, and perhaps one projector (which listed for $20,000) can approach the grayscale and color accuracy out of the box."

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