According to a supply chain source, Apple has delayed the launch of their iPad mini with Retina because of a burn-in problem found in the LCD panel which is causing a malfunction of the TFT. This burn-in is not visible to the eyes of ordinary users, but does not meet the particular technological standards of Apple. So there was a yield problem. Primary suppliers are LG Display and Sharp. Particularly, rumor has it that Sharps' IGZO panel has a supply problem.
The burn-in problem, according to the report, was caused by the drastic reduction of the pixel size. The resolution of the 7.9-inch iPad mini with Retina display is 2048×1536, about four times clearer than the existing 1024×768 products. LG Display used the amorphous silicon (a-Si) for the substrate, whereas Sharp used IGZO. The pixel of the smartphone display is smaller than that of the iPad mini Retina panel, but as the Low Temperature Polycrystalline Silicon (LTPS) technology is used, it can be produced stably. The pixel of the iPad mini Retina is the smallest among those products using a-Si. Sharp failed to solve the chronic problem of IGZO, i.e. uniformity, and its yield went down.
Apple is known to be trying hard to come up with a solution. First of all, it is thinking to change suppliers. Apple is negotiating with Samsung Display for the supply of displays starting next year. Apple discussed cooperation with Samsung Display when it was planning on the iPad mini Retina. AUO, which was the iPad mini display supplier, was excluded from the retina version because of its yield problem.
The report further states that Apple was planning to receive 15 million panels from LG Display, Sharp and Samsung Display at the end of this year. However, as the negotiation with Samsung Display fell through, only LG Display and Sharp made it to the final list of primary suppliers.
When replacing the iPad display with the Retina, Apple experienced the burn-in problem. At that time, Samsung Display was the first to solve the technological problem, and that seems to have influenced this iPad mini Retina re-negotiation.
It is known that, if the burn-in problem cannot be solved, they are talking about upgrading the display substrate to LTPS. As LTPS has more masks than a-Si, it costs more to produce, and the production capacity is smaller too. But stable supply will be possible, which is a definite plus.