Samsung is said to have developed AMOLED displays with pixel densities at 350ppi. ETNews carries a report that the South Korean manufacturer has managed to achieve scalable manufacture of displays featuring pixel densities in excess of of Apple's Retina technology due to advancements in in the Fine Metal Mask production technique. There's no word as yet as to when these displays may be appearing in mass market phones and tablets, but Samsung seems likely to roll out the technology in its next line of flagship devices.
At 350ppi, the new AMOLED displays easily outstrip the resolutions of the iPad (264ppi), iPhone 4, iPod Touch, and iPhone 4S (each 326ppi). Previously, Samsung was said to be working on producing high pixel density displays using the Laser-Induced Thermal Imaging technique, but that method is said to be difficult to scale up without encountering issues.
The FMM production advancement would allow Samsung to produce very high-resolution displays on the production infrastructure the company already has installed. So far, the company is only said to have produced these displays in the lab, so it is not clear how close Samsung may be to commercializing the technology.