OLED encapsulation method reduces water intrusion

April 24, 2008
Georgia Tech researchers have replaced the glass enclosure with a thin-film barrier formed by a less expensive conventional deposition method.
Georgia Tech Research Institute (GTRI) scientists have developed an improved organic LED (OLED) sealing process to reduce moisture intrusion and improve device lifetime. The intrusion of moisture into the displays can damage or destroy an OLED's organic material.

"OLEDs have good color and flexibility and the possibility of large displays, but companies still need an inexpensive encapsulation method that can be used to mass-produce organic electronics that don't allow moisture in," said Wusheng Tong, a senior research scientist at the GTRI.

Manufacturers now seal displays in an inert atmosphere or in a vacuum environment. They glue a glass lid on top of the display substrate with a powder inside the display to absorb moisture that diffuses through the glue. These seals are expensive and labor-intensive to assemble.

With funding from GTRI's independent R&D program, Tong and his GTRI collaborators, senior research scientist Hisham Menkara and principal research scientist Brent Wagner, have replaced the glass enclosure with a thin-film barrier formed by a less expensive conventional deposition method.

The researchers chose a passivation coating process that could be performed at room temperature so that the organic material remained intact. Advanced ion-assisted deposition, which utilizes reactive ions to deposit a high-density, pinhole-free thin silicon oxynitride (SiON) film on the OLED surface, was used.

"Ideally, the film should be as thin as possible, but if it's too thin, a pinhole or other defect could appear and cause a problem," explained Tong. "We found that a film of 50-200 nanometer thickness was perfect."

During testing, the SiON-encapsulated OLEDs showed no sign of degradation after seven months in an open-air environment, while the OLEDs without the coating degraded completely in less than two weeks under the same conditions.

When Tong conducted accelerating aging tests in an environmental chamber that maintained a temperature of 50°C and 50% relative humidity, the OLEDs encapsulated with SiON films showed little degradation for at least two weeks. The OLEDs without encapsulation, however, decomposed immediately.

"We've demonstrated that this deposition process improves the lifetime of the OLEDs by blocking the intrusion of moisture, so now we're hoping to work with industry partners to develop a mass production process for our encapsulation technique," added Tong.