Novel Display Technologies Seen at SID 2006

From a plethora of reflective displays to the latest innovations in 3-D, SID 2006 provided a glimpse at emerging technologies whose novelty speaks to their innovativeness.

by Alan Sobel

ONE of the most interesting aspects at the annual Society for Information Display (SID) Symposium, Seminar, and Exhibition year after year is the emergence of truly novel display technologies, the products that show the true creative and innovative spirit that has become the hallmark of the display industry. Here is a look at some of the unique display technologies demonstrated at SID 2006.

Reflective Displays

Reflective displays were one of the hot topics at SID 2006. Viewed by ambient light much like print on paper, these displays operate on low power because they do not require a backlight. Most are bistable, so that once written, the image remains until it is changed. (Some require a very small holding voltage to remain written, but the required power is still far less than that of a backlight.) Many of these displays are flexible, which adds to their versatility. Reflective displays can be as large as posters, which makes them attractive for use in signs or other applications where the image changes infrequently, but most of the displays on the show floor were small, aimed at handheld devices such as cell phones.

A variety of techniques is used to produce reflective displays. Bistable liquid-crystal displays (LCDs) include polymer-dispersed liquid crystals (PDLCs), invented at Kent State University and now being marketed by spin-off Kent Displays. A newer class is bistable nematic liquid crystals, which is being promoted by the French firm Nemoptic. Both can be mounted on flexible substrates and have wide viewing angles.

Electrophoretic displays (EPDs) use small particles suspended in tiny liquid-filled capsules arrayed in a sheet. The particles can be moved to the front or back of the micro-capsules by an applied electric field, thus changing the local reflectance of the sheet. The substrate for the sheet of microcapsules can be flexible, and there are various arrangements for producing gray scale and color.

 Liquavista

Fig. 1: Liquavista, a Philips spin-off, unveiled its line of electrowetting displays at SID 2006. This 2.5-in.-diagonal display is 160 ppi and is just one of a plethora of brightly colored displays shown by the company.

EPDs do not appear to require the same extreme impenetrability to moisture and oxygen as dosome other display technologies, such as organic-light-emitting diodes (OLEDs). Several companies showed competing versions of EPDs, including E Ink, SiPix Imaging,and Bridgestone. Some of these utilize passive addressing; however, active-matrix backplanes can be fabricated using various forms of thin-film transistors (TFTs) in a manner similar to the manufacture of LCDs. Plastic Logic makes active-matrix backplanes and incorporates EPDs.

A potential killer application for this technology is the electronic book (e-book), a device the size of a paperback book but capable of holding dozens of volumes of text and (limited) graphics. Philips and Sony have shown these in the past (utilizing E Ink's EPD technology), but the product has not yet caught on, due apparently both to the high cost of the devices and the limited available content. Signage and flexible credit cards that can carry electronic encoding are among the applications currently being deployed; at SID 2006, SiPix Imaging showcased such a "SmartCard," the winner of the 2005 SID/ Information Display Display Application of the Year Gold Award, announced and presented at SID 2006.

One of the more intriguing technologies shown at SID 2006 was the electrowetting display invented at Philips, which in April spun off a new company, Liquavista, to further develop and market it (Fig. 1). Here's how it works. A drop of colored oil is held in a capsule with a transparent liquid. The oil drop changes shape when a voltage is applied, thus changing the local reflectance. A voltage is required to maintain the changed shape, but no current is required, so this is another very-low-power technology, with the further advantage that it can be operated at video rates (which requires more power, of course). This technology can be applied to variable-focus lenses, among other things, but it is not clear that it has major advantages over its competitors. Marketing muscle will have a major effect on the outcome of this race.

Qualcomm MEMS Technologies, Inc., unveiled the iMoD^™ technology that it acquired in 2004 when it purchased iMoD's creator,Iridigm (Fig. 2). A flexible membrane is either electrostatically attracted to its substrate or allowed to spring away, producing either constructive or destructive interference to the incoming light. A zero-current holding voltage is required to retain the image, but there is sufficient non-linearity in the device to ensure that an active backplane is not required. The displays shown at SID 2006 were attractive. There is some change in color with angle, but in the proposed applications (cell phones and PDAs) precision of color is probably not very important. A cell-phone or PDA display that is always on with no power consumption can change the way these devices are used, making them far more convenient. The devices can be made in LCD fabs with minimum changes to the plant.

3-D Displays

Stereo vision or 3-D really has been a collection of solutions looking for real problems for lo these many years. There have been two general approaches to achieving 3-D displays. The first approach is to provide separate images for each eye using polarizing or switched glasses so that each eye sees only the appropriate image. The other method, the use of autostereoscopic displays, avoids the use of glasses by projecting two images through barriers so that each eye sees only the correct image. However, these systems, whether they use lenticular arrays or liquid-crystal shutters, have the problem that there is a limited "sweet spot," the volume in which the viewer's eyes must be in order to achieve a satisfactory illusion rather than seeing a blurred, non-stereoscopic image. If a single display is used, then either resolution is lost in the horizontal plane or the frame rate must be doubled.

 Qualcomm MEMS Technologies, Inc.

Fig. 2: Qualcomm unveiled its iMoD^™ displays for mobile applications. Qualcomm secured the technology for these reflective sunlight-readable displays when it acquired Iridigm in 2004.

 Planar Systems, Inc.

Fig. 3: Planar's 23-in. StereoMirror system creates stunning 3-D images by using two high-resolution LCDs, a half-silvered mirror, and polarized glasses.

One of the most impressive autostereoscopic displays shown at SID 2006 was from SeeReal Technologies, with notably improved quality from previous SID shows.

In a small black tent at the booth of Toshiba America Electronic Components, Inc., a small 3-D display (perhaps 1 ft. square), viewed from above, demonstrated an excellent illusion and the claim that it is simple to mix real-world and virtual objects. There was no way to tell how big the sweet spot was on this display or what the limitations were of this approach. No additional information was available.

Planar Systems showed a system using two high-resolution LCDs viewed via polarizing spectacles through a half-silvered mirror (Fig. 3). The system is expensive (two displays) and rather bulky, but the image quality is excellent.

Philips's elegant 3-D system, which won the 2005 SID/Information Display Display of the Year Gold Award, features an LCD panel that operates as either a 2-D or 3-D display. The required lenticles are overlaid with a liquid-crystal layer; when a voltage is applied, the index of refraction of this layer is made the same as that of the lenticles, so these no longer have any effect. Associated software determines whether the applied signal is 2-D or 3-D. As 3-D displays, these large panels were excellent, with a big sweet spot working with either stored programs or imagery from two cameras above the panel.

However, I was struck by the three-dimensional quality of some imagery on big, bright, 2-D high-definition Philips panels just around the corner from its 3-D system – no limited sweet spot, no extra gadgetry. This leads to another way of generating the illusion of three dimensionality; extend the image so that it stimulates the viewers' peripheral vision (IMAX is an outstanding example).

None of the 3-D direct-view demonstrations could rival a simple binocular approach with a high-quality pair of imagers such aseMagin's head-mounted near-to-eye display (Fig. 4). This binocular device uses color OLEDs on a silicon active backplane. The picture is bright and excellent, with a resolution of 800 ´ 600. The available head tracker and associated software immerses the wearer in a virtual world at every turn. Plugging this into a laptop can double the battery life because the laptop screen is no longer in use; an added bonus is that on an airplane, the user can be totally unconcerned with the angle of the seat in the row ahead. This product is still quite costly at $550, but if the price can be brought low enough, near-to-eye displays for laptops could be a killer app.

Projection Devices

Now that the first group of thin rear-projection televisions (RPTVs) has reached the market, the next innovations for this sector will be in the area of light sources. Light-emitting diodes (LEDs) and solid-state lasers [laser diodes (LDs)] are getting bright enough to compete with discharge lamps, offering the advantages of much-longer life, higher efficiency (less fan noise and lower operating cost), and much smaller space requirements. New LED designs use various tricks to extract more light from the die, such as index-match-ing encapsulants and the new photonic crystals. Several papers at SID 2006 described arrange-ments of LED- and LD-powered light engines, and several companies showed portable projectors the size of a paperback book.

eMagin Corp.

Fig. 4: eMagin's Z800 3DVisor^™ offered one of the most alluring 3-D options shown at SID 2006.

An interesting approach from Forth Dimension Displays used a ferroelectric liquid-crystal–on–silicon (LCOS) active backplane to generate a holographic projection using laser illumination. The company claims high speed, including new algorithms to create the holographic pattern from input video, and a very compact package. Paper 73.4, Banks, et. al., describes the technology in detail.

A problem with laser-powered projectors is speckle – a "boiling" effect caused by the coherence properties of the laser light. (This can also be seen in small projectors with short throw distances.) There is not yet a consensus as to how to remove this effect without an unacceptable loss of light. Some vendors of laser-illuminated projectors simply ignore the problem and hope that customers will as well.

Projection screens continue to improve. An interesting wrinkle from SuperImaging is a transparent phosphor coated onto a transparent substrate (Fig. 5). When excited with ultraviolet light of the appropriate wavelength, an image is produced. Three different colored phosphors could be excited by three different UV lines to produce a full-color display. This has the potential to overcome the speckle problem for laser-driven projectors. •

 SuperImaging

Fig. 5: A transparent projection screen from SuperImaging was one of the more unique items on display at SID 2006.