Samsung Display has developed a true RGB stripe AMOLED Display with 350ppi. Samsung Display use fine metal mask (FMM) technology to reach this milestone. The report says also that Samsung Display did not use laser induced thermal imaging (LITI) to reach higher resolution AMOLEDs.

FMM technology is used to deposit pixels on a substrate. A metal mask with small grooves is placed on the substrate and then sprayed with an organic substance.

The Retina Display from the iPHone has 326ppi, so if Samsung Display can produce that high resolution AMOLEDs this could be a really major step for the korean company.
Source

http://www.oled-display.net/samsung-display-reach-350ppi-rgb-stripe-amoleds-with-fmm-technology/