Apple continues to get a lot of promotional mileage out of its "Retina" display, which was unusual when it first appeared in the iPhone 4 for its very high pixel density of 326 pixels per inch (ppi). Premium Android phones are now exceeding the iPhone 4 display’s resolution, and coming very close to its pixel density. The iPhone 4 and 4S have a display that is 3.5 inches on the diagonal. That is now small for this segment, but it has the effect of pushing up the pixel density for a resolution - 960×640 - that is no longer impressive. (Samsung’s recent Galaxy Nexus has a 4.65-inch AMOLED display with 720×1280 pixels for 316 ppi.)
As impressive as these pixel-density numbers are for direct-view displays, they pale in comparison to what makers of microdisplays - used in electronic viewfinders (EVFs) and other near-the-eye applications - have been doing for years. But in January, MicroOLED (Grenoble, France) announced a product that raised the bar even for microdisplays. The company’s new OLED-on-silicon display packs 5.4 million dots ("dot" = subpixel in the microdisplay world) into 0.6-inch-diagonal display.
The full-color version has 1400×1044 pixels, using an RGBB subpixel pattern. (See photo.) Horizontally, that’s about 1400 pixels in 0.48 inches for a pixel pitch of about 0.00034 inches, or a pixel density of about 2916 ppi. There is also a monochrome version with 2500×2000 dots.
Both versions are intended for professional applications, including medical and broadcast-camera viewfinders. A consumer version with only 1.7 million dots in a 0.38-inch-diagonal display was introduced previously.
So, how do you get 1400×1044 full-color pixels on a 0.6-inch display? First, you don’t worry about glass substrates and thin-film transistors. As is true for liquid-crystal-on-silicon (LCOS) microdisplays, the display is fabricated on a silicon IC backplane that contains pixel switches made of single-crystal silicon. The subpixels are too small to be fabricated by RGB patterning on the front plane, MicroOLED CEO & co-founder Eric Marcellin-Dibon told Display Daily in a telephone conversation. Instead, a continuous white OLED layer is deposited on the silicon backplane, with the color provided by a matrix color filter.
The pixel density, said Marcellin-Dibon, is two to three times that of the competition, which includes Sony and eMagin. That allows MicroOLED to deliver greater resolution than its competitors on the same size of chip, or equal resolution on a smaller - and therefore cheaper - chip.
Depending on the number of pixels to processed, MicroOLED delivers a power efficiency that is better than its competitors by a factor of two or more, said Marcellin-Dibon. That means the 5.4-megadot display consumes only 200 mW in typical use.
Sony and eMagin (and Apple): Please feel free to comment.