28 Oct 2002
A US firm boosts the lifetime of flexible displays made from organic LEDs.
The idea of a flexible display made from organic LEDs deposited on a thin plastic substrate has long been a dream of scientists. However, to date, progress towards commercial versions has been hampered because moisture causes the LEDs in the display to degrade quickly.
Now, a US firm has demonstrated a flexible plastic display that operates for thousands of hours thanks to a barrier coating that protects the OLEDs from the environment.
Universal Display Corporation (UDC) of New Jersey, US, says that its protected OLEDs have a half life of 3800 h - well on the way to the 10 000 h which is required for commercial displays.
"Lifetime is the fundamental key to making flexible OLED displays a viable technology," UDC's Mike Weaver told Optics.org: "OLEDs are susceptible to damage over time when exposed to trace amounts of water. This work has shown a significant advancement in the lifetime of flexible OLEDs and shows that this technology can be realized."
In a paper in Applied Physics Letters (Vol. 81, No. 16, p2929), the researchers describe how they made a moisture resistant substrate from a 175 micron thick polyethylene terephthalate (PET) substrate coated with alternate layers of polyacrylate film and 100-300 Å thick Al2O3 film.
The observed permeation rate of water vapor through the plastic substrate was estimated to be 2 x 10-6 g/m2/day within the maximum leak rate of 5 x 10-6 g/m2/day to achieve a device lifetime of 10 000 h. Driven at 2.5 mA/cm2, UDC measured a lifetime of 3800 h from an initial luminance of 425 cd/m2.
In the proof-of-principle displays, the company chose monochrome green phosphorescent OLEDs (PHOLEDs). At present red and green PHOLEDs are ready for commercialization with lifetimes exceeding 10 000 h. The company is busy developing blue PHOLEDs which currently have lifetimes of about 1000 h.
UDC intends to incorporate the new FOLEDs into a Universal Communication Device (UCD) for the US Army for which the company has just received a USD 2 million development contract (see photo).