Sony has managed to make an OLED (organic light emitting diode) screen that's just one-fifth of a millimeter thick. The prototype screen was on show at last week's Display 2008 exhibition in Tokyo and ranks as the thinnest yet developed.

The prototype 3.5-inch panel, which has QVGA resolution (320 pixels by 240 pixels), started out as a normal OLED screen, but Sony ground down the glass substrate on which it was made to reduce the thickness to just 0.2 millimeters.

Typically OLED screens are pretty thin -- about a millimeter or two thick. That's because OLED pixels emit their own light and so don't require additional illumination. It's this additional illumination, usually in the form of a backlight, that adds to the thickness of LCD (liquid crystal display) panels and means they can't compete with OLED on thickness, at least using current technology.

Due to their thinness, OLED panels consume less power than LCDs, handle fast-moving images better and offer good color reproduction. For these reasons many display makers are developing OLED technology with an eye to it replacing LCD in the future.

At the end of last year Sony began sales of the world's first OLED television. The XEL-1 is based on an 11-inch panel that's 1.4 millimeters thick. Sony has stashed most of the TV's electronics in its base, so the set thickens to only 3 millimeters with a plastic case around the screen.

Using the same glass-grinding trick it could be made even thinner. Sony also showed an 11-inch panel that was 0.3 millimeters thick -- more than a millimeter thinner than the commercial panel it's using in the XEL-1.

The panels aren't Sony's first thin OLED screens. Last year it developed a prototype OLED built onto a plastic substrate, which has the benefit of allowing the screen to be flexible. The screens shown in Tokyo last week, while thin, were brittle because they are glass-based.

There was no word on when or if the thin OLED screens on show might be commercially available.