Display Week 2013 Review: OLEDs
TVs were not the only OLED-based products of interest at Display Week.
by Sven Murano and Anke Lemke
AMID the beautiful scenery of Vancouver, British Columbia, Canada, Display Week 2013 offered a great deal to visitors looking for the latest in OLED technology. Even before the exhibit opened, discussions about OLEDs and, in particular, OLED TVs were featured during the Business Conference on Monday and also in the keynote speech given by Samsung Display President & CEO, Dr. Kinam Kim. In his talk, Kim described how Samsung sees the display market of the future being dominated by OLEDs. He considers it the key display technology for coming display generations.
Dr. Kim also painted an enticing future of add-on features that OLEDs could enable for displays to come, ranging from the close-at-hand, such as transparency and flexibility, to the more visionary, such as displays with embedded gas sensors or piezo-elements that enable haptic feedback through the display surface.
Some of those visionary developments were on display on the exhibit floor in the form of demonstrators or products. The Futaba Corp. booth probably had the most interesting and futuristic OLED demos. What Futaba was showing were a number of transparent and flexible models, including a flexible OLED wristwatch with integrated touch functionality (Fig. 1). In addition to these demos, Futaba also showed its first transparent OLED display product, which is used for the Lenovo S800 smartphone.
Fig. 1: Futaba showed a futuristic watch with a curved OLED display.
Even though the displays at the Futaba booth were based on a passive-matrix approach, they all showed the potential of OLEDs very nicely. Futaba appears to be focused mainly on automotive applications, which explains the company’s strong interest in flexibility. This aligned nicely with an observation by Samsung’s Dr. Kim, who stated in his keynote speech: “There are no flat surfaces inside a car.”
Samsung emphasized its product portfolio of mobile devices at Display Week, showing new versions of its OLED-based Galaxy S4 smartphones. Among the technical aspects that the company highlighted were the excellent color space and low energy consumption of OLEDs. With regard to the latter, Samsung showed OLEDs and LCDs in direct comparison, claiming that 47% less energy is consumed by OLEDs in the so-called ALPM (AMOLED low-power mode). Even though this power-consumption comparison could conceivably be questioned by the LCD camp, the dynamic power consumption of OLEDs in contrast to the virtually constant consumption of LCDs in all driving situations was very apparent.
Samsung also showed its new pixel-arrangement scheme, which it calls the OLED diamond (Fig. 2). This new type of PenTile display (with twice as many green pixels as red and blue ones) is supposed to deliver even better image quality than the earlier striped-pixel PenTile display layout used in its Galaxy S3 model smartphone.
Fig. 2: Samsung demonstrated the brightness of an LCD (left) vs. an OLED (right) display using its new “OLED Diamond” pixel scheme.
TV Progress
LG Display showed its 55-in. OLED TV set, which has been commercially available for quite some time on the Korean market. In addition, it also showcased a curved 55-in. AMOLED TV, which is now available for sale in the U.S. as well as Korea (Fig. 3).
Fig. 3: LG Display showed curved OLED TVs at Display Week.
With those two items, LG Display certainly highlighted its commitment to OLED-TV technology. Until recently, it was the only company with a commercially available large-screen OLED TV. (At press time, Samsung Display had just introduced a curved 55-in. OLED TV for sale in the U.S. as well as Korea.) LG Display also showed a 5-in. HD flexible OLED screen on a plastic foil substrate (Fig. 4). Besides the obvious freedom of being able to shape the display in ways beyond the usual planar restrictions of glass, LG Display also emphasized the ruggedness of such panels.
Fig. 4: LG Display showed a flexible OLED display on plastic foil substrate.
Early visitors to the booth of LG Display at Display Week could try their luck with a hammer and a non-working dummy panel so as to experience the shock resistance of the plastic device themselves. However, shortly after the opening of the show, the dummy panel mysteriously vanished from the booth.
A major topic at both the technical symposium and business conference was the question of how OLED TV can be best produced. A common understanding throughout the talks was that eventually printing processes could be a workable solution for structuring and fabricating OLED TVs. However, it was also understood that such processes still need at least a few more years of develop-ment in order to become mature enough for manufacturing.
Therefore, for the time being, vacuum evaporation of the OLED structures seems to be the only feasible method of production. With regard to this technology, the principle line of debate spins around two very different methods of producing the color subpixel array. On one side is the method favored by LG Display, which deposits a four-subpixel array made up of a combination of fluorescent-blue- and phosphorescent-yellow-emitting materials in a white-emitting OLED structure. (LG Display calls this “WOLED” technology.) Each subpixel is then filtered with red, green, blue, or white filters, making up a four-subpixel matrix referred to as the “RGBW” approach.
Samsung Display meanwhile currently favors an approach in which the red, green, and blue pixels are separate native color emitters without the need for any filter overlay. The displays made by this method have only RGB subpixels (no fourth white emitter); however, in the case of Samsung Display implementing the PenTile approach, there is a higher ppi number for green than for R and B. These subpixels are fabricated by an evaporation step through a shadow mask, in which the RGB emitters are deposited through separate shadow masks next to each other. This structure is commonly referred to in the OLED community as an RGB side-by-side arrangement.
One new player in this field entered the ring during the symposium – the Taiwanese company AU Optronics Corp. (AUO) – which reported results from a 65-in. AMOLED TV that was also produced with shadow masks in an RGB arrangement. AUO did not, however, commit to production of devices with that method during the conference.
The other big question that remains to be answered is which backplane technology will serve the future AMOLED TV market best. Some presenters recommended oxide TFTs as a possible solution. The products by LG Display are based on this approach. On the other hand, Samsung Display stated that it prefers polycrystalline silicon at this time for its OLED-TV development. An idea of the currently running dispute over which technology is most effective could be obtained at the keynote sessions, in which Dr. Kim of Samsung Display advocated the polysilicon approach and John F. Wager of Oregon State University made a clear commitment to oxide TFTs as the most promising approach. A discussion of the details of this debate would go beyond the scope of this article, but it will be very interesting to watch how this technological competition evolves.
In any case, AMOLED-TV development will be strongly influenced by steadily increasing competition with LCDs, which are setting new standards in terms of resolution and color gamut. Clearly, it can be seen that the next generation of OLED-TV products will have to answer the challenge of 4K × 2K resolution and higher brightness, which require improved backplanes, manufacturing, and OLED pixel technologies.
Microdisplays and Lighting
Returning to the exhibition floor, micro- displays based on the current wave of interest generated by Google glass were of note. Products and demonstrators of this technology could be seen in the eMagin booth and also in the I-Zone exhibit from SA Photonics, Inc. The news that Google glass will use an OLED microdisplay produced by Samsung Display was announced on the last day of the exhibition.
Finally, a few words about OLED lighting. There were limited demos during the exhibition at UDC’s and Novaled’s booth. Impressive improvements were, however, reported at the symposium during the last sessions on Friday morning. Panasonic reported a new record, with a device achieving 114 lm/W in the laboratory, using the company’s proprietary light-outcoupling technology. Hitachi described progress in flexible lighting devices made from solution processing, and LG Chem reported on its 80-lm/W product, which will be launched later this year. Also, in terms of light extractions, some updates were given by the glass-manufacturing companies AGC and Saint-Gobain, which both reported on light-scattering substrates for enhanced light outcoupling for OLED lighting. In practical terms for comparing the efficiencies of LED and CCFL lighting products to the aforementioned OLED example, LEDs are passing the 200-lm/W limit in the lab, and commercial products are at around 150 lm/W. CCFLs are at around 80–100 lm/W, with little room for improvement.
Finally, it should be mentioned that for OLED electrode materials, several interesting contributions have been made. Cambrios reported on its “Bottom-Emitting Large-Area Stacked White OLED with Silver Nanowire Network as Transparent Anode,” which detailed the benefits of the company’s ClearOhm silver nanowire material as an alternative to ITO for OLED solid-state lighting. ClearOhm transparent electrodes enable efficiencies of more than 40 lm/W, improve angle dependence of color, and can enable metal-grid-free large-area OLED lighting tiles, such as the 100-cm² (10 cm × 10 cm) OLED tile that Cambrios created recently in collaboration with Novaled.
IBM showed some progress on making OLEDs on graphene electrodes, reaching up to 60% quantum efficiency for a green OLEDs using a laboratory outcoupling regime. The American start-up company nVerPix presented some OLED pixels on carbon-nanotube electrodes.
If and when these new electrode materials will be seen in OLED applications, such as lighting and display tiles, remains uncertain, but certainly the promises toward low cost and flexibility are exciting.
In summary, Display Week 2013 showed an overall positive momentum for OLEDs. In particular, the commitment of the two major players from Korea to OLED TV is reassuring for the industry. Even though several engineering problems still remain to be solved in terms of OLED manufacturing and lifetime, there can be little doubt that, in the long run, OLEDs will develop into a major display technology, especially with its promise for devices with additional functionalities such as transparency and flexibility. •