SID 98: New FPD technologies catching on
08/01/1998
SID 98: New FPD technologies catching on
While active- and passive-matrix LCDs for notebook computers still represent the vast majority of current flat panel sales, new display technologies should soon begin to enable many new end-uses. From LCOS "wrist-top" microdisplays, to PALC displays for wall-mounted commercial and home use, a proliferation of display options could change the way we view information. Most of the process/manufacturing technology required for the new FPD designs is identical to that required for notebook LCDs, so existing equipment and materials infrastructures can be easily leveraged.
The Society for Information Display (SID) conference (May, Anaheim) showcased the changing FPD landscape. A highlight of the show was the first-time Display Technology Showcase, a single room in which the same sequence of images was sent to over 30 different displays for the ultimate comparisons. Various test patterns, video signals, desktop publishing images, and 24-bit photos provided attendees with ample opportunities to gauge relative merit among palm-top, desk-top, wall-mounted, and projection displays.
Microdisplays. Much that was new at SID fell into the microdisplay category. Most microdisplays are LCOS designs that combine traditional liquid crystal technology with silicon wafer CMOS manufacturing. A die from a silicon foundry partner`s wafer functions as the silicon "back-plane," and contains the CMOS transistors to drive the active matrix (replacing TFTs). LCOS displays target wrist-top, HMD, viewfinder, and projection markets (see table). With extreme competition driving silicon foundry prices ever lower, LCOS microdisplays will cost between $25 and $100 in volume within a few years.
There is wide diversity within the LCOS category. Kopin Corp. has been in the market the longest, and has more design wins to show with its transmissive designs (see figure).
Reflective LCOS devices are enabled by the proliferation of silicon foundries and oxide CMP processing. CMP creates a surface that is sufficiently planar so that a blanket aluminum layer can be patterned into reflective micromirrors for each pixel. Each mirror also functions as an electrode, with a transparent conductor (such as indium tin oxide (ITO)) on the inside of a top glass plate as the second electrode to apply potential across the liquid crystal.
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0.24-in. diagonal 1/4-VGA color AMLCD produced with 15-?m pixels. When directly viewed through an integrated lens, this microdisplay creates a virtual image comparable to a 20-in. diagonal screen viewed at 5 ft. (Courtesy of Kopin Corp.)
Other new technologies. As the table shows, there is a great variety of fundamentally different FPD technologies with unique advantages for one or more display applications. Active and passive matrix LCDs (on glass substrates) continue to offer the best combination of price and function for notebook computers, but other technologies are strong competitors in all other markets.
PALC technology, jointly developed by Philips, Sharp, and Sony, creates large displays that compete with PDPs for bright, high-end, wall-mount applications. Designed for 25-60 in. diagonal displays, PALC is a clever solution to the inherent addressing delays of large STN-LCD panels. The horizontal electrode of a TFT-LCD is replaced by a hollow tube filled with a gas; high voltage ignites a plasma in the tube to switch on each pixel row. PALC displays show comparable performance to traditional TFT-LCDs, with manufacturing costs that are similar to STN-LCDs. The first PALC product will be a 42-in. wide-VGA (854 ? 480) resolution wall-mount display that should be in volume production within two years. An HDTV resolution prototype is expected before the end of the year.
FEDs have finally hit the mainstream, with Motorola unveiling 2.9- and 5.6-in. models intended for palm-top, instrument, and automotive applications. FEDs - using arrays of cold-electron emitters and phosphor coated anodes - are bright, rugged, and have exceptional viewing angles. Power consumption is the main limitation, with 15% of the pixels in a 5.6-in. FED draining 2 W.USDC activity. A recent DOD report states that commercially available FPDs don`t meet the environmental stability requirements of the US military. Consequently, DARPA contributed $10 million in FY98 for the development of FPD manufacturing technology; USDC distribution of DARPA funds starts with requests for proposals to develop equipment. Total USDC funding of equipment and materials projects has reached $52.5 million, with another $70 million matched by industry. These investments have led to 19 products that are either commercialized or in beta-testing.
With the chip manufacturing world currently suffering from an over-supply sickness, compelling new end products are needed to stimulate another wave of demand. Display advances may fill the bill.- E.K.