Electronic Design

Electroluminescent Display Triples Brightness To 150 Candelas/m<sup>2</sup>

By applying an inorganic electroluminescent technology to the fabrication of full-color flat-panel emissive displays, researchers at iFire Technology Inc., Toronto, Canada, have been able to achieve a brightness of 150 candelas/m2. This almost triples the brightness level the company, previously known as Westaim Advanced Display Technologies, produced just a year ago.

Over ten years of sustained company effort have gone into developing this brightness, which is essential for graphic displays. "The brightness level is the best filtered brightness performance ever reported for a pattern phosphor material system in a solid-state display," explains Shosaku Tanaka of Tottori University, Japan. The display, measuring 8.5 in. diagonally, delivers QVGA (320- by-240) pixel resolution. It was demonstrated at the DisplayWorks Conference in San Jose, Calif., earlier this year.

David Mentley, chief technical analyst at Stanford Resources in San Jose, Calif., believes there are three crucial factors in creating a successful flat-panel TV—a simple structure, inexpensive materials, and low-cost processing. Based on his findings, the iFire electroluminescence technology meets these criteria. A basic combination of screen-printed thick films, metal-organic processing, and vacuum-deposited thin films forms the display's structure. The low-cost thick-film technology predominates in the design. And, thick film scales well, so designers can anticipate favorable yields at any screen size.

Screen printing is employed to deposit the first two layers, which include the metallic row electrodes and the thick-film dielectic layer (see the figure). A metal-organic solution is deposited as a planarization layer in the liquid phase and then fired to change it from an amorphous state to a polycrystalline ceramic. The metal-organic deposited material fills in voids between the comparatively large thick-film particles, presenting a smooth surface for thin-film deposition.

As for operation, a symmetric ac waveform drives the iFire display device. Once the voltage is high enough, electrons begin flowing in the phosphor layer, exciting the dopant atoms in the phosphor. When a dopant atom relaxes to its ground state, it emits a photon of light.

The iFire display's maximum viewing angle is conical, so it remains constant regardless of the eye's X-Y coordinates. At 170°, the viewing angle is significantly larger than the wide viewing angle in the active-matrix LCDs most commonly employed in desk-top monitors today. By contrast, an LCD panel's typical nonconical viewing capability provides an X-Y orientation with maximums of 140° in the horizontal plane and 100° in the vertical plane.

Generally, LCDs have a 20-ms response time, while the iFire display's response time is only 1 ms. The panel's operating temperature range of ­40°C to 85°C also is superior to a typical LCD's ­20°C to 60°C. Having achieved its brightness goals for small-area devices, iFire plans to apply the technology to larger displays (panels with diagonals of over 30 in.) and to small-area displays (diagonals under 12 in.).

Joe Virginia, vice president of business development at iFire, thinks LCDs and plasma display panels (PDPs) fall short on several counts. Yield issues make the LCD unsuitable for screen sizes above 30 in. Despite the impressive breakthroughs and performance of plasma displays, he says, the technology is still very expensive as well. Construction is difficult, materials are costly, and processing equipment is complex. Consequently, Virginia doesn't expect the price tag on large-screen PDP-based TVs to descend to $3000 and below. On the other hand, he believes higher yields and lower-cost materials will let a 30-in. TV based on iFire technology break the $3000 price floor in the not-too-distant future.

According to Virginia's estimates, the total market for non-PC and non-portable small-graphics devices at 12 in. and below will reach $5.2 billion in 2002 and climb to $5.7 billion in 2004. Here, he feels, the iFire technology is an excellent fit. Costs in this market are expected to be on par or slightly lower than LCDs. For now, though, the iFire display doesn't seem to be a good match for the handheld portable market because the electroluminescent panels require high-voltage drivers. Still, the iFire technology should penetrate high-reliability, rugged-environment, and small-graphic applications such as center-console displays that house automotive climate controls, navigation, and audio.

Now ready for production, iFire is looking to establish a joint venture—possibly with an overseas firm—to build low-cost production displays.

For more information, contact iFire Technology at (416) 246-1030, or check out www.iFire.com.

TAGS: Components
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