Toshiba Corporation has developed the world’s first prototype of a full-colour polymer organic light emitting display (OLED), a 2.85-inch display supporting 260,000 colours in Q-CIF format and a 64-level (6-bit) grey scale.
The display was achieved by developing a technology for forming a light-emitting polymer film on a low temperature polysilicon thin film transistor (TFT) array.
An OLED displays data through an organic light-emitting diode in the pixels formed on a TFT array. The display emits light and, unlike LCD’s, does not require a backlight.
This is said to have opened the way to thinner, lighter display panels that consume less power. OLEDs are also said to offer the faster response time required for motion pictures. They also support a wider viewing angle.
Toshiba developed its prototype display by combining a breakthrough in the OLED manufacturing process with technologies it developed in pioneering low-temperature polysilicon TFT LCD’s.
All OLEDs commercialised to date are mono-colour or area-colour, and use small molecules in the light-emitting organic film rather than polymers. They require vacuum-evaporation technology in the production process, which is unsuitable for the fabrication of large-sized, high-resolution displays on a large mother glass substrate, as required in the TFT production process.
Toshiba has overcome these limitations with the development of new ink-jet printing and solvent-material technologies for depositing a polymer film.
Both advances can be applied to achieve high-resolution displays and efficient mass production without any need for a vacuum environment.
Like LCD’s, OLEDs fall into two broad categories, passive-matrix and active-matrix displays. A large-sized, full colour OLED requires an active matrix driver in respect of panel lifetime, power consumption and picture quality.
The high level of carrier mobility required for driving OLED in the active matrix TFTs can be realised only by polysilicon and not by amorphous silicon. Toshiba established such a technology when developing low temperature polysilicon TFT LCD’s and has transferred it to the OLED.
Toshiba expects to start production of OLEDs in 2002. Production will initially target cellular phones and small- and medium-sized PDA’s.