The impressive array of OLED displays and prototypes at Display Week 2008 speak to the increasing acceptance of the technology as a legitimate display format. Developers are getting more creative with their offerings, and discussions are shifting from issues such as lifetime to overall performance.

by Craig Cruickshank

HISTORY MAY WELL JUDGE 2008 to have been a pivotal year for the evolution of organic-light-emitting-diode (OLED) technology commercialization, and Display Week 2008 certainly played a key role in bringing this to the attention of the display community. Technical progress in OLED displays was quite rapid in the 12 months leading up to Display Week 2008, with key advances in materials, device architecture, optical performance, and manufacturing processes, all coming to the fore this year, along with a serious attempt to prove that broad commercialization is finally close at hand. Certainly, the amount of money being invested in product development and manufacturing infrastructure for OLEDs is increasing faster than ever before, and the impact can be seen in the growing maturity of demonstrators and increasing focus on applications rather than the technology itself.

Fig. 1: Among the most talked-about OLED displays at the Samsung SDI booth was its 31-in.-diagonal full-high-definition (FHD) AMOLED, a 1920 x 1080-pixel display that utilized the company's super microcavity bottom-emission technology.

The consistent message from the likes of Sony, Samsung, and Seiko Epson was clear – the active-matrix OLED (AMOLED) is being positioned as a high-end display for applications that demand superior image quality. Display Week 2008 featured numerous demonstrations of large-sized full-HD OLED-television formats as well as many innovative smaller-sized OLED prototypes in applications such as notebook computers, PDAs, electronic passports, and even wearable displays. The breadth of OLED products at Display Week 2008 was particularly impressive, ranging from large-area (31-in. on the diagonal) displays and smaller displays suitable for portable and mobile products, to microdisplays for head-up displays and viewfinders, to digital signage/lighting for information and illumination.

Another sign of growing industry confidence in OLED technology at Display Week 2008 was the notable shift away from debate over OLED lifetimes toward discussions of the look and feel of the actual OLED displays. With that in mind, here is a look at the most significant OLED developments at Display Week 2008.

Samsung SDI showed a wide range of OLED displays this year, from very small to very large displays. Its largest display was a 31-in.-diagonal full-high-definition (FHD) AMOLED, a 1920 x 1080-pixel display that utilized the company's Super Microcavity Bottom Emission technology (Fig. 1). This display attracted a great deal of attention and buzz on the show floor because the overall quality of the display was simply stunning. The marriage of OLED displays and high-definition (HD) content creates an incredible viewing experience. OLED displays offer unique crispness and warmth not found in technologies such as LCD or plasma, while HD provides image detail beyond what most viewers have experienced. An attendee who was looking at the Samsung SDI display said it best: "It's like looking through a window that does not have any glass."

In addition to the large FHD display, Samsung SDI also showed several "concept applications" that used OLED displays in a novel way, including

• A rather stylish notebook computer (Fig. 2) featuring a 5-in. WVGA 800 x 480-pixel OLED display having a thickness of just 1.21 mm and power consumption of 828 mW (250 cd/m² at 30% on).

• A laptop with a 12.1-in. 1280 x 768-pixel AMOLED display (Fig. 3).

• A high-tech golf glove featuring a 3.1-in. WVGA (800 x 480) OLED display that consumes 434 mW of power (Fig. 4).

• An electronic passport concept developed in partnership with the Bundesdruckerei in Germany, featuring a 2-in. QVGA AMOLED display (Fig. 5).

LG Display showed a 15-in. XGA (1024 x 768) AMOLED display that utilized a novel manufacturing process known as Dual-Plate technology, whereby the OLED display is made on the surface of the encapsulation glass and the a-Si active-matrix backplane is fabricated on the other glass substrate (Fig. 6). The two dependent parts are then joined together via contact spacers.

LG Display anticipates that the Dual-Plate technology will lead to an overall reduction in manufacturing costs for two reasons: it uses lower cost backplane technology and it increases yields. LG Display said that this technique is specifically for large-area displays and is not expected to be adopted for manufacturing small- and medium-sized displays. LG Display officials offered no confirmation on if or when this technique would be deployed in practice.

At Display Week 2008, the Cambridge Display Technology (CDT) booth had fewer displays than in previous years; however, two exhibits that caught my attention were the Add Vision fully screen-printed displays (see below) and the OSRAM OLED lighting tiles (Fig. 7). The fact that the OSRAM product was showcased at the CDT booth means that it is made of a polymer-based OLED (P-OLED).

Fig. 2: Samsung SDI showed several concept applications featuring OLED displays, including this stylish notebook computer featuring a 5-in. WVGA 800 x 480-pixel OLED display with a thickness of just 1.21 mm.

Fig. 3: Samsung SDI showed several concept applications featuring OLED displays, including this laptop with a 12.1-in. 1280 x 768-pixel AMOLED display.

CDT CEO David Fyfe stated during the investor conference that the recent OSRAM "future wave" OLED lighting demonstrator was based on polymer materials – an interesting development. Does that now mean that polymer-OLED (P-OLED) technology will soon be hitting the market in OLED lighting? Perhaps not just yet, as the recently announced OSRAM OLED lighting product "early wave" is, according to OSRAM literature, based on small-molecule materials and not polymer. Given the rapid performance improvement of P-OLED technology over the past few years, it may not be long before P-OLED lighting products are commercially available. CDT was actively promoting its total matrix addressing (TMA) and top-emission P-OLED technology.

While most OLED displays at the show were of high quality, made on glass and expected to last several years, it is not the only option available. CDT's Add-Vision (Fig. 8) offers flexible screen-printed P-OLED displays for low-resolution and specialty-lighting applications. These fully printed segmented displays have an impressive high-quality look and feel about them, especially considering that they are not expected to last long.

DuPont Display finally announced and presented its novel deposition technique known as the "Nozzle" printing process (a combination of coating and printing), which it developed in partnership with Dai Nippon Screen. This certainly generated lively discussion among attendees on the pros and cons of this novel deposition technique. DuPont's philosophy is to achieve superior performance at low cost via the close matching of materials and process – in this case, phosphorescent solution-processed materials and nozzle printing. Displays produced by this novel deposition technique seem to be of high quality (Fig. 9). DuPont plans to make the materials, process, and equipment available as a complete package commencing in 2010. DuPont Display will be installing Dai Nippon Screen Gen 4 equipment at the company's pilot-line facility in Santa Barbara, California.

Fig. 4: This golf-glove concept from Samsung SDI shows one potential use for AMOLED displays.

Fig. 5: Samsung SDI's electronic-passport concept featured a 2-in. QVGA AMOLED display.

Fig. 6: A schematic of how LG Display's Dual-Plate manufacturing process works.

The OLED displays shown by Seiko Epson featured what can only be described as superb contrast. Seiko Epson believes that achieving such high-contrast images is vital for positioning OLEDs in consumers' minds as the must-have display technology. The company describes this contrast as the "Ultimate Black." The OLED displays shown at its booth were 8 in. on the diagonal with a resolution of 800 x 400 pixels, a luminance of 200 cd/m², and a contrast ratio of >100,000:1. The company plans to accelerate efforts to develop uses for OLEDdisplays that benefit from superior image quality.

Seiko Epson started research and development of OLED technology way back in the mid-1990s. The company has been a long-term advocate of polymer solution-processing, but the displays on show were fabricated by vacuum deposition. Furthermore, Seiko Epson reports that it has successfully achieved OLED lifetimes (T50) in excess of 50,000 hours. The device architecture consisted of a white emissive layer coupled with a RGB color filter.

The company has already installed and commenced operation of a development and manufacturing facility in Nagano, Japan, capable of small-scale production. A Seiko Epson spokesperson said that the company might enter the market in a year's time, most likely using solution-processing as its production technology.

Kodak showed a portable AMOLED TV known as the EliTe Vision KTEL-30W. Currently available only in Japan and Brazil, this product, having a 3.0-in. QVGA AMOLED display, is a great example of the potential of OLED displays in consumer products (Fig. 10).

Flexible OLED displays, OLED lighting, and transparent OLED displays could all be found at the Universal Display Corp. (UDC)booth this year. The top-emitting flexible display, made in collaboration with LG Display, was fabricated on a metal-foil substrate and was shown on a rotating fixture, convincingly showcasing many of OLED's strongest attributes: thinness, viewing angle, and no color shift. UDC also reported progress with printable phosphorescent materials in Paper 22.2, presented in conjunction with Seiko Epson Corp. In terms of material performance, UDC continues to improve lifetime, efficiency, and color of its printable phosphorescent materials. Lifetimes of red (100,000 hours at 500 cd/m²) and blue (6000 hours at 500 cd/m²) have doubled since last year, and green is now 63,000 hours at 1000 cd/m². However, the long-life blue material has not yet reached a suitable "deep blue" as required for commercial adoption.

OLED lighting also featured prominently at the UDC booth. The company presented performance data on two white OLED devices achieved by optimizing materials and device structures and including outcoupling. The first device achieved 30 lm/W, at a luminance of 1000 cd/m² with more than 200,000 hours of lifetime and appeared as a "warm" white (0.45, 0.46). According to UDC, this performance is suitable for market entry of simple lighting products. The second device achieved higher efficiency – 72 lm/W at the same luminance (1000 cd/m²), although at a different and unspecified lifetime. LG Chem supplied both transport and injection materials.

Fig. 7: OSRAM's P-OLED lighting tiles at the CDT booth.

OLED microdisplays also appear in both flavors: small-molecule and polymer versions. MicroEmissive Displays (MED) showed a range of headsets having Eyescreen^™ P-OLED microdisplays. These QVGA 6-mm-diagonal microdisplays use silicon active-matrix backplanes with a white P-OLED emitter and color filters and require less than 25 mW of power. MED reported it has now shipped 60,000 units for use in the Estar headsets. At the time of the show, these headsets were only available in Asia.

In contrast to MED, eMagin Corp. offers higher-resolution small-molecule active-matrix OLED microdisplay technology. eMagin announced its SXGA OLED-XL micro-display, requiring less than 200 mW under typical operation. This 0.77-in.-diagonal display has a resolution of 1280 x 1024 pixels.

Ignis Innovation has positioned itself as an independent open-source provider of active-matrix-backplane technology for the emerging AMOLED market. The company has developed in-pixel compensation circuit technology coupled with pixel drivers that reduce the "image sticking," improves lifetimes, and eliminates brightness variations – "mura" was experienced by both LTPS or a-Si backplane technologies. The company envisages that such an open-source approach effectively eliminates the need for a vertical structure manufacturing approach, opening up the market for AMOLED displays. No longer are manufacturers reliant on the need to build their own active-matrix capacity; instead, they can purchase active-matrix backplanes via Ignis Innovation partners.

Fig. 8: CDT's Add-Vision offers flexible screen-printed P-OLED displays for low-resolution and specialty-lighting applications.

Fig. 9: This AMOLED display from DuPont Displays utilizes a Chi Mei Optoelectronics LTPS backlplane.

Fig. 10: Kodak's EliTe Vision KTEL-30W portable TV, currently available in Japan and Brazil, features a 3.0-in. QVGA AMOLED display.

Conclusion

Display Week 2008 once again provided attendees with the latest developments in OLED displays. The products on the exhibition floor and the papers presented at the symposium continue to demonstrate that there is growing confidence that developers of OLED displays understand the basic technology, understand it nuances, and are beginning to master the process of creative design. The opening speaker at the Business Conference was Gildas Sorin, CEO of Novaled, who said that "OLEDs are the new LCDs." Looking at the products at the show, I would tend to agree. Sorin also made the statement that the OLED industry would benefit from greater cooperation among the major OLED developers. The launch of the OLED Association is clearly a move toward creating the necessary framework for collaboration. I am already looking forward to next year's show to see what progress the next 12 months brings in terms of OLED display development. •