For a flat-panel display technology that's relatively more mature than other competitive approaches, liquid-crystal displays show an unstoppable trend of improvements in all key performance aspects of flat-panel displays: contrast ratio, color display brilliance, response time, viewing angle, and resolution. All of this applies across a very broad spectrum of display panel sizes, from micro-displays of an inch or smaller in diameter to very large displays of 60 inches or more for consumer and outdoor applications.
Much of the progress in LCD technology can be traced to process improvements and innovative design approaches, many leading to decreasing unit prices and a greater presence in a host of applications. While competitive approaches like CRTs, plasma discharge panels, electroluminescent displays, and organic LED (OLED) displays are making their own impressive gains, they're increasingly facing stiff competition from LCDs for flat panels and eventually winding up in more specific and "niche" applications.
SIZE DOES MATTER
Because of its pursuit of the large-screen consumer TV market, size is of paramount importance to LCD screen manufacturers. Developments in digital high-definition TV (HDTV) technology continue to push color LCD large-screen technology, even though its market share is still small. That should change, though, with large-scale investments in LCD production facilities and frenetic efforts to improve liquid-crystal performance for consumer HDTV applications (see "The Business of LCDs," p. 62). Of course, size and other important parameters such as response time, resolution, brightness, and viewing angle are all interrelated. Each of these areas is seeing marked improvements.
At the Society for Information Display (SID) Conference, Samsung announced a super patterned vertical alignment (S-PVA) technology that sets new state-of-the-art color performance for LCD TV screens. The company also announced the development of a 57-in. UXGA (1920 by 1080 pixels) LCD TV, the world's largest for HDTVs, with sub-10-ms response times and a 1000:1 contrast ratio. The S-PVA technique employs new color filters with a contrast ratio that's superior to presently used filters, because the liquid-crystal optical path is perfectly parallel to the optical path.
LG Philips reported good results in color-image quality for television-bound large-diagonal (up to 50 in.) LCDs using its super in-plane switching (S-IPS) technology. IPS LCDs may also provide better viewable angles than twisted-nematic (TN) LCDs. The main limitation of IPS and S-IPS technologies is that they require more power and may have a slower response time than a TN LCD.
Taiwan-based AU Optronics reported on a 46-in. TFT HDTV LCD that uses multidomain vertical-alignment (MVA) liquid crystals for color management and image enhancement that produce high-quality color (75% of the NTSC color gamut), bright (600 nits), and high-contrast-ratio (800:1) images. In MVA, the molecules of liquid crystals are normally aligned at right angles to the substrates, swinging through 90° to lie parallel with the substrates in the presence of an electromagnetic field.
This new mode produces a display that has an ultra-wide viewing angle (140° in all directions) and a high contrast ratio. It also features higher brightness and a response time of about 25 ms, which is shorter than IPS, super twisted-nematic (STN), and TN LCDs. The display consumes less power than IPS, but it is still too power hungry for battery-sensitive applications.
When it comes to the Qualia series of 40- and 46-in. LCD TV sets, Sony goes the route of LED backlighting. According to Sony, a large gamut of reproducible color hues is possible using backlighting LEDs, offering vivid, realistic scenes not possible by other techniques.
Samsung also uses LED backlighting on its TV sets, which the company says solves the life-span and color-quality limitations of traditional fluorescent backlighting lamps. The same can be said for NEC-Mitsubishi Electronics Display of America. In addition, many companies at SID, including Sharp and Toshiba, as well as LG Philips and Samsung, either exhibited or talked about LCD products with diagonals of 45 in. and larger that offer a resolution of at least 1024 by 1280 pixels.
If it hasn't already done so, Sharp will soon be in production with a 45-in. LCD color screen. The company is a leader in automotive color LCDs primarily for rear-seat entertainment. Sharp, which pioneered continuous-grain (CG) silicon technology, has shown that CG silicon can produce exceptionally crisp high-readability color LCDs for cell phones (Fig. 1).
PUMPED UP PERFORMANCE
Next to size, faster LCD response time is key to raising these displays to the new levels of performance. "We're continuously trying to improve LCD response times, which used to be in the 40-ms range when the technology started, down to the 12- to 18-ms range, and we're not too far off from the single-digit range," claims Bob Dunhouse, engineering manager for NEC Electronics.
Dunhouse credits a feed-forward technique developed by NEC that momentarily electrically overdrives the LCD's TFT drivers for reaching this speed. As mentioned earlier, such parameters as contrast ratios, brightness levels, viewing angles, and image resolution all interrelate with response times, so improvements in any one or two areas sometimes involve trading off from other performance.
According to Samsung, fast LCD response times may already be here. At the SID Conference, the company reported on getting sub-10-ms response times and blur-free video motion pictures on a 57-in. LCD TV screen, using its S-PVA technology. And, AU Optronics reported on a 46-in. TFT LCD for HDTVs with an 8-ms response time.
As for LCD resolution, a number of strides are being made. One particular example comes from Sharp. The company used its CG silicon know-how to produce exceptionally "sharp looking" and clear LCD panels. Sharp did it for cell phones (300 ppi in a 2.6-in. diagonal unit) and PDAs and notebooks (217 ppi for 3.7-in.-diagonal units). It also has produced a system-on-glass (SOG) LCD technology that uses a two-shot sequential lateral solidification process. It provides the highest resolution (200 ppi) for a 2-in. display with an integrated 6-bit source driver.
On another parameter front, viewing angles are becoming much wider. At the SID Conference, Optrex showed off a TN LCD with a 170° viewing angle horizontally and 150° vertically. Key to the development is a novel background film material. Sharp also demonstrated a 160° viewing angle using its Super Mobile CG silicon. Furthermore, Samsung reported on a 160° horizontal and 140° vertical viewing angle with a 300:1 contrast ratio using a unique transreflective low-temperature polysilicon LCD process with a cap-divided vertical-alignment mode.
Design methodologies are also key to improving viewing angle widths. "We've made many improvements in LCD in-plane switching (IPS) techniques and contrast ratios over wide viewing angles," says NEC's Dunhouse. At this time, the company cannot provide further detail on this proprietary material.
LCOS TAKES ON PROJECTION APPS
Manufacturers of large-screen consumer HDTVs featuring 60- to 70-in. diagonal sizes are taking a look at liquid-crystal-on-silicon (LCOS) technology. Also known as "micro-displays," LCOS-based TVs are projection TVs lacking the main attributes of all other flat-panel consumer TV technologies, namely thin panels and small and lightweight features that allow the TV receiver to be hung on a wall. They employ digital light engines but are still considerably thicker from front to back and bulkier than LCD, plasma-panel, and electroluminescent flat-panel displays.
LCOS technology was pioneered by Brillian Corp., which this year launched a 65-in. Gen II LCOS HDTV with resolution of 1280 by 720 pixels and a contrast ratio of 2000:1. Until now, the contrast ratio of LCOS-based projectors has been limited to a range of 500:1 to 800:1. "This is an extraordinary time in the evolution of HDTV products," says Vincent Sollitto, Brillian's CEO, as he touted the LCOS monitor's "near 3D picture quality and artifact-free performance."
LCOS is somewhat of a hybrid technology between digital light processing (DLP) technology pioneered by Texas Instruments and LCD technology. LCOS combines the reflective aspects of DLP technology with the transmissive qualities of LCD technology. It uses liquid crystals instead of the individual mirrors of DLP, where the liquid crystals are applied to the reflective DLP surface mirrors. As the liquid crystals open and close, light is either reflected from the mirror below or blocked. LCOS-based projectors typically employ three LCOS chips, one each to modulate light in the red, green, and blue channels of the spectrum.
LCOS technology has the inherent advantages of LCDs in terms of large form factors and higher resolution. Yet as the light is projected over a distance over large-size panels, the displayed image loses some brightness, contrast ratio, and resolution.
Because LCOS is more difficult to manufacture in chip form, it also is not as cost-competitive as other large-screen HDTV technologies. Even Intel Corp., which has expressed an interest in mass-producing LCOS TV chips, has delayed its plans. Philips has gone ahead with the technology, exhibiting 55- and 62-in. LCOS rear-projection HDTVs at the SID Conference.
SpatiaLight Inc. developed a different version of LCOS light engine chips that supply contrast ratios in excess of 2000:1. Its 1920 SCDTV microdisplay rear-projection system boasts a 90% reflectivity, resolution of 1920 by 1080 pixels, and overall display throughput of 65%, all on a die of just 18.7 mm in diagonal. The die utilizes a silicon backplane with a highly reflective pixellated aluminum top layer to control the orientation of the liquid-crystal molecules. The backplane contains all of the drive electronics as well as the liquid-crystal control circuitry, which simplifies the required input to the display and reduces the size of the control electronics as well as the overall size and weight of the rear-projection TV.
The mobile-phone market continues to be the largest application market for LCD flat panels in unit volumes shipped, and it's the third largest in dollar value according to market researcher iSuppli Corp. On top of that, LCD flat panels continue to dominate information-display applications in almost every other market segment.
One obviously huge market consists of PDAs, laptops, notebooks, and desktop computers. Then there's the growing market in consumer multimedia devices, like portable media players, digital video disks, and toys. You can't overlook the burgeoning automotive LCD-display industry either.
"We're getting closer to meeting requirements in terms of environmental capabilities," says Optrex America's Dale Maunu, director of Business Development and Procurement. "One area where this is so is the automotive field, where operating temperature ranges from 30°C to 85°C are possible. For non-automotive applications, we're moving forward toward the 20°C to 70°C range."
Wireless monitors using color LCDs are now in vogue for public information displays. This year, Three-Five Systems Inc. introduced a family of commercially available XGA-resolution (1024 by 768 pixels at 30 frames/s) wireless LCD monitors in diagonal sizes ranging from 15 to 40 in. (Fig. 2).
Outdoor signage is one of the newest and fastest-growing market segments. Recently, Sharp previewed 45-in. LCD monitors with 1920- by 1080-pixel resolution for digital signage applications. Plus, Global Display Solutions Ltd. showed off its 32- and 37-in. e-Signage LCDs at the SID Conference, as well as 32-in. moving-floor units with touch-screen panels for factory floor, airport, railway, bus station, supermarket, and shopping center uses (Fig. 3).
Use of proprietary anti-reflective coatings is helping to give LCD panels higher contrast ratios and better readability in outdoor and direct sunlight environments.
"We serve a multi-environment market for industrial applications with varying degrees of outdoor lighting," says Omid Malanie, director of NEC's Display Business Unit. "As a result, we developed a transreflective technology that does not require backlighting. We're investigating both internal and external transreflective methods, where the former has a TFT layer that's coated with a reflective material, and the latter uses a reflective back polarizer."
Optrex America developed an anti-reflective surface treatment for its 6.5- and 8.4-in. VGA and 12.1-in. SVGA TFT LCDs for high ambient-light readability (Fig. 4). The displays are finding homes in industrial applications. To help in high-ambient-light conditions, 3M Touch Systems came up with the MicroTouch M150 high-brightness, 15-in. TFT LCD monitors (Fig. 5). They deliver 400 nits of brightness and a 430:1 contrast ratio.
A BRIGHT FUTURE INDEED
Improved process and production methodologies are building a strong foundation for liquid crystals as a lower-cost technology for flat-panel displays. The ability to integrate more functions on the same panel will even further their cause. "With CG silicon, we can put all of the electronics into one corner of the display," claims Joel Pollack, vice president of Sharp's Display Unit.
One of the "coming attractions" is the 3D LCDs, which have now become a reality. SOG technology is the driving force behind the production of these 3D LCD panels. It has been used by NEC Electronics to develop 3D images of 470 by 235 pixels in a 2.5-in. diagonal. The company credits its horizontally double-density pixel (HDDP) architecture combined with a lenticular lens for this achievement.
Sharp Corp. and its European laboratories created a 15-in. XGA (1024 by 768 pixels) LCD monitor for desktop computers that can be switched from 2D to 3D views with the push of a button (pictured on page 57). Its LL-151-3D display uses a parallax barrier of light from the LCD. The light is divided so different patterns reach the viewer's left and right eyes. The left and right eyes will see different images because the direction in which the light leaves the display is controlled.
In the future, LCOS LCD micro-displays will likely revolutionize HDTV projection technology, with ferro-electric liquid crystals playing a large role. Also, look for improved substrate materials that will make possible advanced flexible LCDs on stainless steel, plastic, and many other materials—not just glass. The manufacturing process for liquid-crystal deposition together with electronic circuit elements has been so perfected that flexible substrate materials are the next natural step, broadening LCD display appeal to many new applications.
As for faster response times, there's a lot more left in liquid-crystal technology. For example, researchers at the School of Optics at the University of Central Florida have achieved 50-µs LCD response times at room temperature using UV-curable, high-birefringence, low-viscosity, isothiocyaniane liquid crystals. So stay tuned for better things to come.
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|AU Optronics Corp.||www.accelchip.com|
|Global Display Solutions Ltd.||www.gds.com|
|LG Philips LCD Co. Ltd.||www.lgphilips-lcd.com|
|Matsushita Electric Industrial Co. Inc.||www.panasonic.co.jp/global|
|NEC Electronics America Inc.||www.necelam.com|
|NEC-Mitsubishi Electronics Display of America||www.necmitsubishi.com|
|Optrex America Inc.||www.optrex.com|
|Royal Philips Electronics||www.philips.com|
|Samsung Electronics Americaw||ww.samsung.com|
|Sharp Electronics Corp.||www.sharp.com|
|Texas Instruments Inc.||www.ti.com|
|Three-Five Systems Inc.||www.tfsc.com|
|Toshiba America Electronic Components Inc. (TEAC)||www.toshiba.com|
|University of Central Florida||www.ucf.edu|