Electronic Design

Microdisplays Gain Ground In Projector, Viewfinder Applications, Look Strong For Near-Eye Use

Growth opportunities in the rear-projection markets—particularly for liquid-crystal-on-silicon (LCoS) microdisplays—will be su-perb, according to Chuck McLaughlin, president of the McLaughlin Consulting Group in Menlo Park, Calif. This is especially true for near-eye applications that have yet to gain a firm foothold in the marketplace. McLaughlin discussed the promising future of the display market at the Microdisplay 2000 Conference held recently in Boulder, Colo.

"The beginning is over," says McLaughlin, pointing out that microdisplay sales have already crossed the billion dollar mark. He also believes that microdisplays are the single most successful new display of the past decade. "Before 1990, they simply weren't here," he adds.

Usually defined as high-definition displays with a diagonal dimension of less than one inch, microdisplays are taking a firm hold in projection and viewfinder applications. They also have shown promise in near-eye applications.

According to McLaughlin, the present market with the greatest penetration is front-projector viewfinders for camcorders. "But what the industry needs is new markets, not just increased competition in the two established markets," he cautions.

In the presentation-projector market, microdisplays receive high marks with regard to improved brightness and user friendliness. Plug-and-play is just about here, but price is hindering growth. Resolution has moved up from VGA (640- by 480-pixel) to SVGA (800- by 600-pixel) levels. Brightness levels in lumens have climbed from 200 to 800. Weight has fallen dramatically from twenty to less than four pounds. Yet despite the street-price decline in the last 10 years—$5000 to $3000—microdisplays are still seen as expensive compared to the falling prices of monitors, televisions, and flat panels.

Though the overall cost of an imaging module has come down some 65%, from $2000 to $700, shipments have climbed by more than an order of magnitude from 40,000 to 1 million annually. An imaging module includes one to three displays, plus all the required interface and buffer electronics. Nonetheless, volume expansion has been hindered by the microdisplay shortage. But microdisplays in this application need to be better and cheaper to dramatically expand the market.

The front projector is far and away the largest established market for microdisplays, with current sales at approximately $1 billion. This market is dominated by digital micromirror devices (DMDs) and polysilicon microdisplays, with the latter ranging in size from 0.6 to 1.8 in. Field-sequential, scrolling, and holographic color systems technologies will help lower costs.

Employed in digital camcorders as viewfinders, color polysilicon microdisplays deliver the highest performance. They are used today in most digital camcorders. Still, monochromatic CRTs remain well entrenched in analog camcorders. Kopin Corp. now has a foot in the door at camcorder manufacturers JVC and Panasonic. Kopin and Displaytech are breaking into the digital photography space as well.

Microdisplays have been quite an improvement over CRTs in the viewfinder market, due to their far smaller size and lower weight. But to be more competitive in this field, they'll need higher pixel counts, full color, and good video. They also will need to drop in price.

"It is easy to beat the brightness/viewing angle of incumbent, rear-projection CRTs (RPCRTs), but it is tougher to match the imaging of direct-view CRTs and plasma panels," McLaughlin says. Designers here trade off lumens, screen gain, and viewing angle. Instead, these devices need an increase in projection-engine output to use a lower-gain screen. This means reaching 1000 lumens for 40- to 50-in. systems and 1500 to 2000 lumens for 60- to 70-in. systems.

In McLaughlin's view, the large-screen TV market is a competitive free-for-all. The incumbent technology, RPCRT, is vulnerable due to very low lumen output. Polysilicon, DMDs, LCoS displays, and triads of LCoS displays all have to struggle to achieve 1000 lumens with a single, long-life, 100-W lamp. But even though the microdisplay rear-projection TV pumps out more than five times the lumens of a CRT RPTV, it doesn't even come close to delivering the screen lumens output of a standard, direct-view CRT.

Single LCoS displays offer the greatest promise. JVC's holographic, Philips' color scrolling, and Dis-play/Samsung's field-sequential systems all show potential as well, McLaughlin believes.

The system throughput in lumens favors scroll and hologram types over color field-sequential (CFS) techniques in LCoS displays. CFS, however, has a lower bill-of-material cost (Fig. 1). Surveying the display arena, the highest performers in terms of delivered lumens have a way to go before bringing bill-of-material costs down in line with the heavily entrenched CRT (Fig. 2).

The present rear-projection display market totals around $100 million annually. McLaughlin says, though, that this market will grow to over $4.5 billion by 2005. Big-screen displays are a sure bet. Value-priced monitors and TVs, however, offer the largest upside potential.

The near-eye market is rather perplexing. As things stand, it presents little opportunity. For starters, power consumption far exceeds power budgets in cell phones and PDAs, hindering near-eye display acceptance. Tethered operation is presently a headache as well because near-eye headsets have to be connected by a bothersome cable to a power source.

Compared to low-definition LCDs, module depth is another problem. There hasn't been much progress in ergonomics or comfort, either. McLaughlin points out that headset prices, now in the $600 to $1000 range, will have to come down by factor of three to five to make them attractive to the marketplace.

"Compelling near-eye designs are nowhere to be seen. Breakthrough architecture, design, and components are needed. And continuous improvement is not getting us there," McLaughlin says.

Overall, he expects polysilicon and DMD technologies to continue to dominate the microdisplay market, with a strong emergence of LCoS displays and explosive growth thereafter. As for potentially new markets, McLaughlin identifies rear-projection big-screen TVs, including rear-projection 30- to 40-in. HDTVs, and rear-projection high-performance monitors.

"Currently, flat-panel displays are running away with this market," he says. In his opinion, wireless mobile Internet appliances and cell-phone applications could become huge. The same goes for handsets and wearable microdisplays.

There is a need for improved imaging in monitors and TVs with higher pixel counts. HDTVs are heading toward UXGA (1980- by 1200-pixel) formats and above, with 200-dot/in. resolution and brighter screens. In personal displays, such as handheld and wearable monitors, microdisplays must move on to an XGA (1024- by 768-pixel) format and a 30° or more field of view. Power requirements need to fall to 100 mW or less.

There are many unknowns in the future, though. Can rear-projection displays successfully challenge direct-view CRTs and active-matrix LCDs? Will personal displays offer compelling solutions, furthering still the opportunities for microdisplays? The answers to these questions are anyone's guess.

TAGS: Components
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