PMOLED

OLEDs are made from carbon based (organic) materials that emit light when electricity is applied. OLED displays feature bright images, fast response time and wide viewing angles. They are also very efficient. If you want to learn more about OLEDs, read our introduction to OLEDs.

PMOLED: Passive Matrix OLED

PMOLED stands for Passive-Matrix OLED, which relates to the way you control (or drive) the display. A PMOLED display uses a simple control scheme in which you control each row (or line) in the display sequentially (one at a time). PMOLED electronics do not contain a storage capacitor and so the pixels in each line are actually off most of the time. To compensate for this you need to use more voltage to make them brighter. If you have 10 lines, for example, you have to make the one line that is on 10 times as bright (the real number is less then 10, but that's the general idea).



A PMOLED panel by Univision
So while PMOLEDs are easy (and cheap) to fabricate, they are not efficient and the OLED materials suffer from lower lifetime (due to the high voltage needed). PMOLED displays are also restricted in resolution and size (the more lines you have, the more voltage you have to use).

PMOLED displays are usually small (up to 3" typically) and are used to display character data or small icons: they are being used in MP3 players, mobile phone sub displays, etc.

SonyEricsson LiveView with a 1.3-inch PMOLED

PMOLED vs AMOLED

The other kind of OLED displays is called AMOLED (or Active-Matrix OLED). AMOLED use a TFT that contains a storage capacitor which maintains the line pixels lit all the time (even though just one line is changed each time). AMOLEDs consume less power than PMOLEDs, have faster refresh rates and allows to build larger display with higher resolutions. AMOLEDs are also more complicated and expensive to fabricate.

A Nokia N8 with a 3.5-inch AMOLED

AMOLEDs today are being used as displays for smartphones, digital cameras and other gadgets - and are also starting to appear in OLED TVs.

The PMOLED market

PMOLEDs are being made by several companies today. The largest are RiTdisplay, Pioneer, TDK and Visionox. The market size in 2009 was around $290 million - and was actually down from 2008 as phone makers have stopped using sub-displays (because they were popular mainly for clamshell phones).

The future of PMOLED displays

One of the great features of OLED displays is that they can be made transparent and flexible.  In May 2011 TDK started to mass produce transparent PMOLED displays for mobile phones and other applications. TDK's transparent panels offer 320x240 with 50% transmittance and are 2" in size. Lenovo's S-800 is the first phone to use these panels. 

TDK transparent PMOLED

TDK has also been showing 3.5" (256x64) flexible panels - which are only 3mm thick (shown below). These come in two variants, color and monochrome, and TDK plan to start mass producing those towards the end of 2011.

TDK flexible PMOLED

Further reading

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