Carbon Nanotubes Incorporated into Backlight Design

Anne L. Fischer

Scientists at Tatung University in Taipei, Taiwan, have produced a light panel that uses carbon nanotubes in the electrodes. The low-power plasma source has potential applications as a backlight for flat panel displays such as LCDs.

LCDs are commonly backlit by cold cathode fluorescent lamps or LEDs. The former have several drawbacks, including high power consumption, a limiting architecture and risky high-voltage operation. The main drawback to the latter is their prohibitive cost.

The light source, based on the low-voltage plasma ignition of gas by carbon nanotubes, offers the advantages of low cost, low power consumption and a simple fabrication process.

The researchers’ prototype light source combines carbon nanotubes and phosphor powders that are employed in white-light LEDs into a semitransparent 10-µm-thick film. Using a standard screen-printing technique, the investigators deposit this mixture in a square pattern on conductive indium-tin-oxide glass for use as the electrodes. Some of the carbon nanotubes stick out of the surface of the electrodes and act as spark plugs, igniting argon gas in the device to create a plasma that generates the ultraviolet excitation for the phosphors.

They chose to use argon rather than the more expensive xenon, explained Jeff T.H. Tsai, an assist-ant professor at the university, and they found it to be sufficient to produ-ce a fairly bright visible light.

The 2 × 2-in. prototype flat panel is attractive for use in backlighting LCDs, Tsai said, because it operates at lower voltages than cold cathode fluorescent lamps.

In terms of power efficiency, the prototype achieved 60 mW/in.², compared with 100 to 300 mW/in.² for conventional cold cathode fluorescent lamp or LED backlights.

The group will continue to study the plasma ignition process by various nanomaterials and would like to investigate further the low-voltage ignition mechanism.