OLEDs Show Potential
The first applications of OLEDs were passive-matrix displays for car audio equipment. More recently, Eastman Kodak Co. and Sanyo Electric Co. introduced a full-color, active-matrix model that hints toward the OLEDs' greater potential. This 2.5-in. display with quarter-VGA resolution is a mere 1.8-mm thick, compared to 6 or 7 mm for an equivalent LCD (Fig. 2). While a backlit AMLCD would devour 800 mW of power, the OLED's power consumption is approximately 300 mW.
The plans at Kodak call for the development of bigger displays with higher resolution, including a 5.5-in. version with VGA resolution. Like some of its LCD counterparts, the 2.5-in. OLED display was built using low-temperature polysilicon that permitted the integration of row and column drivers. Down the road, control and DSP functions may be incorporated.
Kodak's display should be in production somewhere around 2001. This will provide some interesting competition for the more traditional direct-view AMLCDs.
The structure of the OLED actually makes microdisplays a possibility, as well. Because the OLED is an emissive device, the display aperture factor isn't significant like it is in LCDs, which modulate light from an external source by passing it through an aperture. As a result, pixel count, resolution, and size can be scaled down to produce microdisplays. Treading down this path is FED Corp., which has a 0.78-in. diagonal display in development that offers 256-level gray-scale and SXGA resolution. The company's roadmap calls for even further development of XGA and SVGA versions.
According to Gary Jones of FED Corp., an OLED microdisplay will have advantages over LCOS for applications like cell phones that would employ a microviewer or headset. With an OLED display, the microviewer wouldn't need to be held as precisely to see the complete image. Plus, its greater viewing angle would allow for smaller and cheaper optics. OLED isn't strobed like LCOS, so its display wouldn't suffer any color separation when vibrations are present, such as when the viewer is riding in a car or train. Lower power is another advantage for OLED over LCOS.
For now, though, LCOS microdisplays appear to be ahead in the race to bring high information content to the portable world. It remains to be seen how LCOS and OLED technology will fare against each other in the microdisplay arena and versus the steadily improving direct-view AMLCDs. The final outcome will put a new face on cell phones, PDAs, and other handheld communications devices. It also will change the ways that we interact with one another via the wireless world.
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