Electronic Design

OLEDs Set To Become Staples Of High-Res Displays

Samsung SDI and Clairvoyante have teamed up to make OLED performance and manufacture practical for handheld applications.

On Oct. 9, Samsung SDI Co. Ltd. revealed that it will create the market's first high-resolution active-matrix (AM) display panel using organic light-emitting diodes (OLEDs).

Samsung SDI will use Clairvoyante's PenTile RGB proprietary subpixel rendering technology to achieve this feat. Mating Samsung's expertise in display design and Clairvoyante's unique technology appears to be the ticket for meeting the top challenges-performance and manufacturing-that have kept highresolution OLED panels on the sidelines.

OLEDS vs. LCDS
Unlike LCDs, OLEDs can be implanted on a substrate using screen-printing technologies or a simple inkjet printer, two highly cost-effective methods. The ability to imprint OLEDs onto flexible substrates also hints at novel applications such as roll-up displays and light shows embedded in clothing. Overall, OLEDs surpass LCDs with extended options for brightness, colors, and viewing angles. With OLEDs, colors allegedly appear correct as the viewing angle approaches a 90° offset.

Also, OLEDs don't require backlighting. Due to backlighting constraints, LCDs do not show true black. When an off-state OLED produces no light, delivering a true-black aesthetic, it consumes zero power. LCDs need polarizers and color filters to cut significant levels of backlight illumination. Another plus, OLEDs have a response time in the realm of less than 0.01 ms. Standard LCD screens, on average, specify 8 to 12 ms.

However, OLEDs offer a limited lifespan compared to other technologies. For example, the typical working life for a blue OLED is about 5000 hours. In general, LCD and plasma technologies log in around 60,000 hours, depending on the model. One solution, switching a phosphorescent for the chemical compound, boosts blue OLED longevity to 20,000 hours, which may not be significant in terms of projected applications.

Challenge two is improving the resolution. The highest resolution for OLED display formats is qVGA (240 by 320). As denser media feeds into handheld consumer products, this may not be acceptable for emerging designs. A third concern is the fragility of the organic compound, which moisture and other contaminants can easily damage. More detail and cost may go into sealing and packaging OLED-based displays. Finally, there's the bottom line. Development of OLED applications requires a license from the technology's creator, in this case Eastman Kodak and possibly a few other companies. Naturally, this takes another chunk out of the budget.

The power of the pen
According to Clairvoyante, an OLED's lifespan is a function of current density. Pushing the resolution up from qVGA to VGA requires decreasing the dot pitch, resulting in an increase in current density, which, in turn, leads to significantly shorter OLED life.

The PenTile technology can achieve VGA resolutions with onethird fewer subpixels (see the figure). In an AM OLED display, this leads to lower current density, restoring OLED longevity levels to those exhibited in qVGA configurations. Essentially, PenTile technology enables both VGA and wVGA formats without the lifetime penalties encountered in legacy methods.

Defective transistors on the backplane are one of the most critical concerns regarding an AM OLED design. Reducing the required backplane transistors by one-third improves backplane yield by the same factor of one-third. Also, PenTile reduces power by 50% for equivalent brightness and offers higher resolutions, flexible settings for color control and power savings, easier to read displays, and the acceleration of next-generation devices.

Next-gen OLED products
Samsung SDI is using PenTile RGB to develop what it is calling the first handheld wVGA (480 by 800) OLED panel. The component will target handheld Web browser, GPS, and video applications where the demand for product durability plus precise detail and viewing characteristics is high. Specifications include a diagonal viewing area of 3 in., luminance of 200 cd/m2, contrast ratio of 10,000:1, color gamut (NTSC) of 100%, and a power consumption of 400 mW.

According to Samsung SDI, OLED technology will yield some of the industry's thinnest and most power-efficient packages. A demonstration of the module will take place at Flat Panel Display International in Japan, Oct. 24-26 at Samsung SDI's booth #571. We can expect samples in the first quarter of 2008 with mass production set for the third quarter.

TAGS: Components
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