Emerging technologies enjoyed the spotlight at EuroDisplay 2005, where innovations in 3-D technology, OLEDs, plasma displays, and projection systems were just a few of the notable presentations.
by Ken Werner
DESPITE Samuel Johnson's 250-year-old comment that "The climate of Edinburgh is such that the weak succumb young … and the strong envy them," the old stone city was kind to EuroDisplay 2005, which took place September 19–22, 2005, at the Edinburgh International Conference Center in Edinburgh, Scotland, U.K. More than 600 display professionals descended upon Edinburgh for the event, which was the 25th edition of the International Display Research Conference (IDRC) and marked the first time that IDRC had been held in the U.K. in 9 years.
At a time when red ink was easy to find in the LCD industry, many EuroDisplay speakers accentuated the positive by focusing on emerging technologies.
Professor Sir Richard Friend opened the formal technical conference with a plenary talk, "Organic Materials in Future Displays." Much of the talk was a tutorial on organic polymers for displays and semiconductors, which was more exciting than it sounds because Friend has a rare talent for making device physics seem simple. He noted that although organic materials have the reputation of being unstable unless carefully encapsulated against oxygen and moisture, Plastic Logic, Inc., has made organic transistors that have performed 107 switch cycles in air and ambient light with no measurable degradation, despite being unencapsulated. "The trick," Friend said, "is to marry [such transistors] with an E-Ink-like front plane." He added that polymers are amazingly good semiconductor materials, which have no defects at the junctions. "This is a new world," he concluded. "As it develops, it will take over semiconductor electronics as electronics becomes truly ubiquitous. There are no intrinsic limitations."
Displaying the Third Dimension
Y. W. Yang, Director of the Image and Display Laboratory at Quanta Computer's Research Institute, had a very clear idea of why he was at EuroDisplay: European innovations in 3-D displays. Although Yang was not discussing details, one of the innovations that likely interested him was Ocuity's approach to switchable 2-D/3-D autostereoscopic (glasses-free) LCDs and the company's demonstration of real-time 2-D to 3-D conversion.
EuroDisplay 2005 was held September 19–22 at The Edinburgh International Convention Center.
The principles of Ocuity's Polarization Activated Microlens technology were described by company co-founders Graham Woodgate and Jonathan Harrold in an invited paper, "Key Design Issues for Autostereoscopic 2-D/3-D Displays." (At the conference, Woodgate was also presented with the SID UK/Ireland Chapter's Ben Sturgeon prize for significant contributions made to the display field through his work at Ocuity.)
As described in the paper, Ocuity's Polarization Activated Microlenses have different optical properties depending on which polarization of light passes through them. For one polarization of light, the index of refraction of the microlens is matched to that of its surroundings, and therefore no lensing takes place. For orthogonal polarization, there is an index step at the lens surface, and lensing does take place.
In 2-D/3-D displays, when the indices of the lens and surroundings are matched, the microlenses are transparent and a 2-D image of undiminished brightness is seen. When lensing does take place, the microlenses focus light to the left and right eyes from alternate columns of pixels, and the display is auto-stereoscopic. A major Asian manufacturer has already licensed Ocuity's technology on a non-exclusive basis.
Woodgate said that Ocuity's technology is the only reconfigurable autostereoscopic technology that maintains the brightness of the underlying display in both 2-D and 3-D modes and that the company's component can be fitted to existing LCD and OLED panels. Moreover, the component uses standard materials and manufacturing processes in its fabrication and is therefore available at a small premium to the base display-panel cost.
Ocuity's Paul May provided a private demonstration of the two 1.5-in. cellular-phone displays and also showed them publicly at the EuroDisplay author interviews. Despite using a very simple algorithm for converting 2-D to 3-D on the fly – apparently, the depth increased with the vertical distance from the bottom edge of the screen – the 3-D images on the 1.5-in. display were very effective and remarkable for their high resolution and lack of left–right cross-talk.
"The widespread adoption of 3-D displays has always been constrained by the availability of appropriate 3-D content," May said, "and this demo shows that high-quality 3-D video can be experienced using existing standard [DVD] media content."
One of Ocuity's cellular-phone displays shared these qualities and also used a more sophisticated 2-D to 3-D algorithm, so the 3-D space was substantially more convincing. The second cellular-phone display exhibited right–left cross-talk, which May acknowledged and attributed to poor alignment. This last display aside, the Ocuity demonstrators provided excellent autostereoscopic images.
Ocuity later announced that the company had been awarded a significant grant for research and development from the South East Development Agency. The project's goal is to develop next-generation manufacturing techniques for switchable microlenses that will enable the technology to be scaled to very large screen sizes.
In his keynote address, "Microdisplays: From Revolution to Evolution," Ian Underwood of MicroEmissive Displays (MED), Edinburgh, U.K., described the various technological options for camera and camcorder electronic viewfinders (EVFs), which led to his company's conclusion that polymer-OLED (POLED) microdisplays were the best choice. The company's initial product is a QVGA full-color display that was scheduled to go into commercial production at the end of 2005.
The 7.2-mm-diagonal display has an 18-μm pixel pitch, which is too fine a pitch for ink-jet printing – at least for now. That means there is no practical way to fabricate the display using RGB phosphors. As a result, MED uses "color-by-white" – white subpixels under a color-matrix filter. The display is the first commercial active-matrix OLED to be built on a silicon substrate that uses polymer rather than small-molecule organic electroluminescent materials.
The structure of this display is simple, light, and thin, Underwood said, and it has a large fill factor, i.e., there is very little inactive area between the pixels so there is virtually no "screen-door" effect. QVGA, Underwood added, is the minimum resolution for EVFs for "viewer satisfaction, as opposed to viewer tolerance."
In a subsequent conversation, Underwood said that MED believes QVGA is the right pixel format for consumer headsets as well as for EVFs and will be the standard format for Gen 3 multimedia phones because of the limited available bandwidth in that application.
Sharp Microelectronics Europe and Sharp Laboratories Europe hosted the conference banquet in Edinburgh Castle, former home of Mary, Queen of Scots, and Edinburgh's most popular tourist attraction.
The day before the technical sessions at EuroDisplay 2005 kicked off, the conference held a series of workshops designed to discuss the future commercial and technical developments in three vital sectors of display technology: displays for mobile phones, large-screen TVs, and OLEDs and organic electronics. Here are some of the highlights.
Jyrki Kimmel from the Nokia Research Center dropped clues as to what display technologies Nokia will be pursuing for mobile phones, while delivering a coherent survey of mobile-phone display technology. Among his comments include
• Megapixel camera phones require higher resolutions, which will soon be at 200 dpi and beyond.
• Mobile digital TV requires larger and wider displays.
• Advanced applications require solutions that will deliver enhanced user experiences. These solutions include autostereoscopic displays, near-to-eye virtual displays, and mini-projectors. OLEDs can satisfy many cellular-phone requirements, but no single solution satisfies all requirements.
Kimmel noted that the use of an OLED as the main display requires a radical redesign of what Nokia calls the "user-interface style." Specifically, to take advantage of the power savings that derive from the fact that an OLED pixel only consumes power when it is on, the user-interface style must be changed from icons and menu choices on a white background (similar to Microsoft Windows™) to icons on a black background. Kimmel's comments concerning OLEDs seemed to have a less skeptical tone than they have had in the past.
Kimmel was cautious about flexible displays. Although their lower weight and reduced thickness are attractive, Kimmel stated that flexible displays face significant challenges, among them is the difficulty in making 200-dpi displays on a substrate that has limited dimensional stability.
Ross Young from industry-research-firm DisplaySearch projected that the share of the TV market captured by 1080p sets will exceed 10 million units (5% share) by 2009. These projections include only liquid-crystal display (LCD) and microdisplay rear-projection TV sets because the number of 1080p plasma-display-panel (PDP) TVs has been minuscule until now.
Michiyuki Sugino of Sharp explored what must be done to pave the road to broad acceptance of large-area TVs. Among these factors is increased bit depth in the internal image processing to remove false contours, which can be realized by converting an incoming 8-bit signal to 10 bits for processing, and then converting the results to 8 bits to drive a conventional 8-bit LCD.
There is a serious effort among the leading manufacturers to reduce the black level in their LCDs. Soon after EuroDisplay, Sharp demonstrated a 37-in. full-HD LCD having a contrast ratio of 1,000,000:1. In displays with very dark black levels, the picture levels close to black must be extremely close to each other in order to provide dark details and avoid false contours. So, although Sharp has revealed only a few of the most basic specifications for its "Mega Contrast LCD," it is a good guess that enhanced-bit-depth processing is part of the package.
Also essential is the reduction of motion blur in LCDs, either by implementing an impulse-type drive, which shortens the hold portion of an LCD's sample-and-hold addressing – making the display behave more like an impulse-addressed cathode-ray-tube (CRT) display – or by increasing the frame rate. He compared different approaches to reduce motion blur, including black-data insertion (BDI), backlight flashing, frame-rate doubling, and motion-compensated inverse filtering, and finally proposed frame-rate conversion based on motion compensation.
But a tour of the trade-show circuit in the weeks following EuroDisplay suggests that BDI, gray data insertion (AU Optronics's clever variant on BDI), and blinking or scanning backlights will be the first solutions to reaching some level of volume production.
Larry Weber, former CEO of Plasmaco, noted that the power consumption of PDP TVs has been unfairly characterized as high because the 20% average picture level (APL) of typical video content has often not been taken into account. Nonetheless, power consumption has been sharply reduced by increasing the percentage of xenon in the ionizing gas and moving to single-sided addressing. Many more improvements are possible, said Weber. "PDPs are at a lower stage of maturity [than LCDs] and have greater potential to improve."
Robert Meyer of CEA-LETI, who was a leading contributor to the development of Spindt-tip field-emission displays (FEDs) in the 1980s and 1990s, asserted that the application of nanotechnology to cold emitters is now providing FEDs the chance to realize their potential as less-expensive large-screen displays. As early examples of an FED renaissance, Meyer cited Futaba's 3-in. FED, which uses the classic Spindt tip, and the Canon/Toshiba surface-conduction electron-emitter display (SED) that, at least initially, will be marketed as a high-end display.
CEA-LETI is working on a carbon-nanotube (CNT) display in which the nanotubes are grown by thermal chemical vapor deposition directly on the cathode, and the company has created a 6-in. QVGA video-capable monochrome display as a technology demonstrator. This so-called "direct" CNT approach is also being developed by Motorola.
Direct CNT, Meyer said, consumes less power than an SED, has lower drive voltage than indirect CNTs (in which the carbon nano-tubes are not grown in situ) and are combined with a carrier for spreading as an ink, and have higher current density and brightness.
Kimberly Allen from market-research-firm iSuppli Corp. noted that mobile phones are the dominant application for organic light-emitting-diode (OLED) displays and will remain so through at least 2011. However, that does not mean slow growth. Estimated OLED sales for 2005 are about 60 million units and $640 million; in 2011, estimated sales will be close to $3 billion, for a cumulative annual growth rate of 29%.
The OLED community has been abuzz about the development of small-molecule OLED (SMOLED) phosphorescent materials where all of the excited states are available for producing light, resulting in four times the maximum quantum efficiency. But small-molecule materials must be deposited by vacuum thermal evaporation and patterned through a shadow mask. This method is expensive and does not appear well-suited to large-area fabrication, creating an opportunity for polymer-OLED (POLED) materials, which can be applied by ink-jet printing, a potentially low-cost technique that is suitable for large areas. But Julie Brown from Universal Display Corp. described several lower-cost manufacturing techniques for SMOLEDs, including organic phase deposition, ink-jet printing, laser-induced thermal imaging (LITI), and organic vapor jet printing.
Does this development, combined with the high efficiency of phosphorescent OLEDs, have the POLED supporters quaking in their boots? Not noticeably. Nalin Patel of Cambridge Display Technology described how POLED materials and its supply chain have matured, making POLEDs ready to support more sophisticated and higher-volume products
Finally, Merck was letting it be known that in acquiring Covion Organic Semiconductor GmbH and the Avecia organic-semiconductor portfolio, it was making a major commitment to plastic electronics, having 25 members of the Avencia group in Manchester, U.K.; 75 in the Covion group in Frankfurt, Germany; and 10 at the Merck Organic Semiconductor Group in Chilworth, U.K.
Bill Campbell, MED's CEO, said there is increasing interest in personal viewers, i.e., headsets. The nascent video–on–cellular-phone could provide an attractive application for headsets. Campbell noted that in October 2005, Orange released a Gen 3 cellular phone and LCD headset in France. MED is receiving customer inquiries about headset applications; "We get them every week," Underwood stated. "They say LCDs are too heavy, too power-hungry."
In more detail, the message Nalin Patel (Cambridge Display Technology) had delivered previously was that POLED is well on the way to building the infrastructure for commercialization on all levels: materials suppliers, equipment suppliers, driver suppliers, display-panel makers, and consumer-product manufacturers.
One question that arises in discussions of POLED materials is why so little is discussed about developing phosphorescent polymer materials, as UDC is doing so successfully with small-molecule materials. Patel said it is not necessary. For reasons that are not yet clear, the usual 25%/75% singlet/triplet division found in small-molecule materials does not apply to polymers, where the singlet/ triplet fraction seems to be between 50% and 60%, according to studies Patel cited from Philips, Cambridge University, and elsewhere.
On the equipment side, Litrex, which CDT owns jointly with ULVAC, has sold 50 Gen 2 ink-jet printers and has now completed a Gen 7+ printer that can accommodate a 2.4 x 2.4-m glass substrate (the printer has been sold to a maker of color-matrix filters for LCDs).
Plasma's Next Act
The recent impressive advances in PDP technology and reductions in cost have focused on one basic PDP architecture. But now, new ideas for novel plasma designs could open new opportunities for the technology. If perfected, these could lead to bright large-scale wall displays for video signage or advertising.
These displays could be much brighter than conventional PDPs and could even be curved in one or two directions to conform to walls and building exteriors.
If successful, this next generation of plasma displays could compete with the large – and very expensive – LED displays currently used for many applications.
Two papers described the development of radically different PDP architectures. When the plasma display was first invented at the University of Illinois in 1964, three types of structures were discussed. The ionizing gas could be contained in small glass spheres, in glass tubes, or between glass plates. Plates quickly won the overwhelming share of research resources. But now, there is interest in exploring tubes and spheres more seriously than has been the case in the past, as the two papers indicated.
Manabu Ishimoto, speaking on behalf of a team of Fujitsu Laboratory co-authors that includes the legendary PDP designer Tsutae Shinoda, described the group's latest results in developing plasma-tube-array (PTA) display technology. Ishimoto reported a luminous efficiency of 5.4 lm/W and, in answering a question from moderator Shigeo Mikoshiba, said he expects to reach 7 lm/W when the system is fully optimized.
In the PTA display, the ionizing gas and phosphors are enclosed in thin, parallel glass tubes – in this respect, they are similar to the thin fluorescent lamps used in backlights to illuminate LCDs. The pixels are defined and energized by conductors located outside the tubes.
The individual pixels in the PTA Ishimoto described are larger than those in a conventional PDP, with an RGB pixel measuring approximately 3 x 3 mm, making them suitable for large video signs or wall displays viewed at greater distances than are living-room TVs. The target size for such displays is 3 x 2 m, and the tube size would be 2 m long by 1 mm in diameter. The display would have 1000 x 700 pixels. If the tubes in such a display are vertical, the display can be curved horizontally.
The authors discovered that the efficiency of such a display can be increased if the tubes have a cross section that is a rectangle with rounded corners, rather than a circular cross section, because this brings the plasma discharge closer to the phosphor layer, allowing more of the plasma's ultraviolet radiation to be captured by the phosphor. It was for a display with tubes of this kind that the team measured the luminous efficiency of 5.4 lm/W.
Enclosing the phosphor and ionizing gas in tubes allows the plasma display to be flexible in one direction. By enclosing them in small spheres that are mounted to a flexible substrate, the display can be made flexible in two dimensions. Potentially, the display can be manufactured by an inexpensive roll-to-roll process.
This was the subject of the very last paper presented, a late-news paper presented by Donald Wedding, who was standing in for his daughter Carol Ann Wedding, the President of Imaging Systems Technology (IST) of Toledo, Ohio. (Note that Carol Ann Wedding achieved some fame in the pictorial history of plasma displays when she appeared in a 1986 photograph next to the world's first 1.5-m plasma display. The display was made by Photonics Imaging, which was owned by Don Wedding. Reportedly, it was this photograph that convinced some Japanese companies that plasma should be pursued seriously as a television display.)
IST has made a monochrome technology demonstrator with 30 x 40 pixels using 2-mm spheres and a smaller color demonstrator. A 20-in. technology demonstrator is being developed. Advantages of the "plasma-sphere" display, Wedding said, are ruggedness, a much simpler manufacturing process, and the ability to fabricate custom and semi-custom displays inexpensively. Initial intended applications are for the military and for outdoor displays.
The Q&A session was lively. The first question related to the plasma-sphere sizes and pixel pitches IST has been able to fabricate. Wedding answered that they had achieved a 4-mm pixel pitch, but greater than 10 mm is more feasible and would deliver better efficiency.
Larry Weber, former CEO of Plasmaco, asked how are the spheres placed on the substrate? Wedding said we are working on that and making progress, but it is a challenge. He said that he originally thought that making and filling the spheres would be the most difficult part of the process, but the IST team has made remarkable progress with those issues.
In response to a question about the luminous efficiency, Wedding said that the luminous efficiency is now greater that 5 lm/W. At higher pressures, it could be better.
The Fujitsu work appears to be farther along than the work of IST, and it is a good guess that it has more funding. But IST has received support from NIST, NSF, and the State of Ohio.
Clearly, there are applications for these plasma technologies, and it will be interesting to look for two things: How closely the next prototypes Fujitsu and IST come up with approximate a commercial technology and whether any other companies decide that plasma tubes and spheres are worth exploring.
LED and Laser Projection
In a late-news paper, Yoshitaka Kurosaka and a team from Sanyo Electric Co. presented the results of a projection development effort aimed at using LED illumination and a single LCD panel. The solution has been embodied in a prototype projector that is part of the "Sanyo Evolution Project" to "fill a category that does not yet have suitable systems."
Most of the palmtop or pocket-projector prototypes demonstrated to date have used reflective DLP microdisplays from Texas Instruments. Frame-sequential color has been implemented by alternately illuminating the DLP with red, green, and blue LEDs. But the Sanyo team felt that this solution was too bulky for a palmtop, so they decided to use a single transmissive 1.5-in. full-color LCD. They still use LEDs as the light source, but now the light output from the LEDs has to be combined into a white light to serve as the illumination source for the LCD. This is done with an X-cube and a rod integrator.
The design team's target luminous output was a very modest 10 lm, but they quickly realized how demanding that target is for a projector of this configuration. Their solution involved using two LEDs for each primary color instead of one. But even with two LEDs per primary, too much light was being lost to meet the target.
To compensate for this, the team designed a complex collimator, an ingenious lens with four non-spherical surfaces that could not have been made before the advent of molded optics. One of these collimators is fitted over each LED and directs much more of the LED's light into the optical system.
As a result, the team exceeded their design goal and attained nearly 12 lm of output, along with a color gamut that exceeds the NTSC standard. The final prototype has a volume of 980 cc (with a 2880-mAh lithium-ion battery) and a weight of 970 g (with the battery). It uses an SD card as a storage medium and runs for 45 minutes on one battery charge.
Despite some clever ideas and very good optical engineering, there are some clear problems with the demonstration projector. At more than 2 lbs., it weighs more than some plug-in ultra-portables that produce 100 times its optical output. Compared to some of the DLP-based palmtop prototypes that have been shown, it has twice the weight and one-half to one-quarter of the luminous output.
There are many challenges in making an LED-based projector, especially with LCD or LCOS technology. Since these require polarized light, one-half of the light is instantly lost unless polarization recovery schemes are used, which add complexity, size, and cost. In addition, Sanyo is using an LCD with color filters, resulting in an overall transmission of under 10%. Also, just collecting the light from an LED, or multiple LEDs, into the useful étendue needed in a projection system is challenging for any microdisplay technology, even with the well-designed collimators.
IST has made a small color "Plasma-Sphere" display, and a larger 20-in. technology demonstrator is being developed. Initial intended applications are for the military and for outdoor displays.
Such concerns were reflected in the questions following the presentation. For instance, Grant Bourhill (Sharp Laboratories of Europe) asked about the team's ultimate luminous-output goal. The answer was 50–100 lm, which is reasonable for the intended applications but seems hard to attain.
Sanyo's prototype is certainly interesting, but it faces significant challenges compared to non-polarization-based systems.
In an interview with CRLO Displays (Dalgety Bay, Scotland), COO Greg Truman made an interesting comment. But first some background. After several changes of ownership, CRLO Displays' product development is now focused on consumer rear-projection television (RPTV). CRLO's technology is ferroelectric LCOS microdisplays, and the company currently has a niche market of near-to-eye headsets for military and aerospace customers. Truman and CEO Les Polgar, who previously led Eastman Kodak's AMOLED effort, know that a rear projector must offer excellent image quality and be less expensive than direct-view competitors.
Their target price for a 42-in.-plus 1080p field-sequential-color RPTV set is $999 in 2006. In 2007, they anticipate using RGB LED light sources. And in 2009, they plan to use laser light sources, which significantly simplifies the optical design and cost and will permit retailers to offer a complete 42-in.-plus RPTV set for about $650, said Truman and Applications Manager Keith Murray. That is an ambitious roadmap, and it depends on laser and screen developments that are beyond CRLO's control, but Truman and Murray are enthusiastic.
Not all large displays are plasma arrays or projectors, of course. The EuroDisplay regis-tration area showcased a tiled display by Screen Technology, Ltd., Cambridge, U.K., which used 15-in. LCDs with light guides that expanded the images from each LCD so that each image butted with that of its neighbors, resulting in only a fine seam between the tiles. The display is being marketed for digital-signage applications.
Overall, there was considerable enthusiasm in Edinburgh – for display technology and for the anticipated business opportunities greeting Scottish companies in particular, and U.K. and European companies more generally. As much as anything else, there was enthusiasm simply for this gathering of the European display community (along with its Asian and North and South American supporters).
The next gathering of the European display clans will be in Moscow, September 25–27, 2007. The next installment of IDRC will take place September 18–21, 2006, at Kent State University in Kent, Ohio. •