RiTdisplay 3.5-inch 480×320 AMOLED with a-Si Backplane

Engadget: First thing’s first. Let’s clean up some misunderstandings.

Sure, you’d expect to find an amorphous silicon backplane behind your LCD…

Not really. If you’re looking at this from your iPhone then the LCD backplane is not amorphous silicon (a-Si) it is low temperature polysilicon (LTPS). A lot of high-resolution mobile LCDs make use of LTPS as the backplane. With that out of the way let’s get to the real news:

…but RiTdisplay has now begun producing a-Si AMOLED displays that, according to the company, are a world’s first.

So, what is the big deal with a-Si? The biggest thing is that it’s cheaper to manufacture. So why haven’t OLED displays use a-Si as the backplane?

Unlike LTPS, a-Si has lower electron mobility, or electrons can’t move as fast. You can’t control electrons all that well either. OLED brightness and color is managed by controlling electron current and LTPS lets you do that even though it is more difficult and more costly to manufacture.

RiTdisplay showcased its a-Si backplane 3.5-inch OLED display during SID. The pixel format was limited to 320×480.

The much lower production costs for a-Si-based OLED displays will usher in a new era of low-cost OLED displays. Of course low-cost OLED displays will still cost more than the LCD equivalents.

And therein lies the problem. So far OLED has been associated with top-notch performance: super-fast response times, ultra-thinness, extreme blacks, colors that pop (not that this is a great thing if you’re looking for color uniformity), etc. But when you start marketing a low-end phone with a so-so OLED display then the cache of OLEDs will start to deteriorate.

The OLED industry wants to get OLED prices down to make it more competitive with LCDs, but at the same time performance should be maintained or improved, not decreased.

Update: Barry Young, Founder and Managing Director of the OLED Association, wrote in explaining in detail as to why a-Si has not been previously used as an OLED backplane:

a-Si has not been used previously because a-Si exhibits temporal changes due to the high duty cycle of the driver TFT. The sub-pixel architecture has two TFTs vs. LCDs , which have 1 TFT. The high usage causes a charge build up on the TFT and causes Vth changes. What Ignis provides is a way to compensate for the Vth reliability.

The result is the use of a very low cost backplane that RiTdisplay will buy from Fabs with excess capacity and combine that with the use of their fully depreciated OLED fab. They get the same performance as LTPS in terms of contrast ratio, viewing angle, response time etc. at a very low cost (likely to be less than a-Si LCDs).

The issue is can they compete with a Gen 2 fab against the larger a-Si Fabs.

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