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OLEDs on the look-out for unique application

16 Jun 2006

Analysts expect the OLED panel market to grow by more than $200 m in 2006 as the technology gathers momentum. Kimberly Allen of iSuppli looks at the prospects for passive and active OLEDs in the face of stiff competition from LCDs.

Liquid-crystal displays (LCDs) are ubiquitous in everyday technology, from mobile phones and laptops to car stereos and coffee machines. But the organic light-emitting diode (OLED) display is emerging as a credible flat-panel alternative thanks to some important advantages over LCDs.

OLEDs possess the most fundamental feature needed in a display - they look great. As the name implies, OLEDs are diodes and function by injecting holes and electrons into a recombination region from which coloured light emerges. Different organic materials emit red, green, blue or other wavelengths of light, and come in small molecule and polymer form. Because they are emissive, OLEDs also have an excellent viewing angle, good contrast and high brightness.

Unlike an LCD, an OLED does not need a backlight, which means that the display panel can be thinner. This is an important advantage in mobile devices. OLEDs also offer the potential for lower power consumption compared with an LCD, which is always constrained by the power consumption of the backlight. OLEDs supply power only to the pixels illuminated in a given image. OLED materials and device structures are becoming so efficient that an active-matrix OLED (AMOLED) a few inches in diagonal, showing video (on average 30% of full brightness), consumes less power than an equivalent LCD. In addition, because OLEDs can operate at high speed - around 100 times faster than an LCD - devices can support video rates without blurring.

Challenges

OLEDs fall into two categories: passive matrix and active matrix. Active matrix means that every pixel is individually switched, as opposed to a passive matrix arrangement, where row and column electrodes are used to control the pixel at a given intersection.

Unfortunately for manufacturers, OLED driving schemes tend to be more complicated than LCD devices. The reason behind this is that OLEDs are current-driven and are sensitive to slight fluctuations in current. LCDs on the other hand are voltage-driven. Instead of needing one thin film transistor (TFT) per pixel in an active matrix scheme, OLEDs need between two to five, arranged in a compensation circuit.

However, the biggest hurdle facing OLED developers is short lifetime. Although OLED materials and device structures have improved greatly over the past few years, manufacturers can still only guarantee between 5000 and 15,000 h of operation before the brightness of the panel is reduced to half of its initial value. This performance is sufficient for mobile phones and other consumer electronics, but inadequate for television and more sophisticated products. The organic materials simply do not hold up well under the driving current or the exposure to other materials within the device. What's more, the cathode material is highly sensitive to air and even when sealed, the OLED performance degrades slowly over time.

Device lifetime is shortened not only by declining brightness, but also by colour drift. For example, if the red, green and blue emitters degrade at different rates, the display shifts in hue over time. Typically, colour OLEDs are made by patterning red, green and blue emitters into subpixels, although it is also possible to mix multiple emitters together to form a single "white" material and use a colour filter.

With a commercial history of just seven years, OLED manufacturing remains at an early stage, both in terms of technique and equipment. Small-molecule OLEDs are made using vapour deposition techniques, such as evaporation through a shadow mask. OLED materials are too delicate for photolithography. Polymer OLEDs are made by solution processing, either spin-on techniques (for monochrome) or inkjet printing (for colour), although the latter has not yet been commercialized. Yields are quite high for simple panels, but established processes have not been put in place for most types of colour panels. This means that OLEDs are still priced higher than equivalent LCDs.

Early success

Despite the challenges involved, OLEDs have already reached the market in several key applications. The first commercial OLED product was a small-molecule, passive matrix monochrome car stereo display from Pioneer in 1999. Sold as an aftermarket device, the display was blue-green to resemble vacuum-fluorescent versions commonly in use. Since then, OLEDs have moved into mobile phones, MP3 players, a Kodak digital camera, various industrial and medical devices, and a few other consumer electronics.

Market value

The worldwide market for OLED panels was valued at $520 m (€400 m) in 2005, and is expected to reach $743 m in 2006, rising to $3.5 bn in 2012. This represents a compound annual growth rate of 29% from 2006 to 2012. Looking at the detail, the growing importance of portable media applications and mobile phone main displays is clear.

The biggest market for passive matrix OLEDs is subdisplays, followed by MP3 players. 2005 was a difficult year for OLED subdisplays with the number of units and value both declining in comparison to 2004. Colour subdisplays fared better than monochrome or area colour versions, showing a modest increase in units. However, even this category declined in value from $252 m to $206 m. The difficult subdisplay market was the result of the falling price of TFT-LCD panels (for main displays), which in turn forced down the price of colour super-twisted nematic (CSTN) LCD panels for both main displays and subdisplays. OLED manufacturers, unaccustomed to swift market changes and unwilling to greatly reduce prices because costs remained high, failed to keep up with the changes until later in the year. At that point, orders had already been placed for CSTN LCDs.

Simple OLEDs have been favoured in MP3 players, which are often used as fashion or status items by younger people, because an area colour OLED display is much more eye-catching than a monochrome LCD. MP3 players have played an important role in the PMOLED market over the past two years, leaping more than eight-fold in units between 2004 and 2005, and filling the gap in factory utilization during fluctuations in the subdisplay market. They have also provided an opportunity for smaller PMOLED makers to enter the market. Difficulties in the MP3 market include component shortages and an unstable base of OEMs. The OEMs making the MP3 players are largely Chinese, and shift suppliers readily, seeking the lowest price.

The OLED market is still heavily dominated by passive matrix panels, which are expected to account for 99% of value and more than 99% of units in 2006. But active matrix panels are poised for commercialization. A few products have already appeared, although full mass production at adequate yield has not yet been achieved.

Looking at the worldwide OLED display shipment value in terms of passive and active markets highlights the enormous changes that could soon occur within the industry. The PMOLED market is predicted to continue growing in units throughout the forecast period, but is expected to stagnate at a value of around $1 bn from 2008. This is due to the steep price competition already being seen with CSTN. It is worth noting that the PMLCD market has already stagnated and is now declining in value each year.

An active market

The growth of the OLED market depends heavily on the success of AMOLED. iSuppli believes that near-term commercialization is possible, and makes this assumption in its market forecast.

The first commercial AMOLED reached the market in April 2003. It was made by SK Display Corp - a manufacturing joint venture between Kodak and Sanyo - and was used in a Kodak EasyShare LS633 digital camera back display. The 174 (×RGB) × 218 pixel, 65,000-colour display measuring 2.2 inches has also been used by Ovideon and NeoSol for personal media players in 2005. However, SK Display folded in late 2005, primarily for financial reasons. In Japan, Sony released one model of its Clie PDA series fitted with an AMOLED during the first half of 2005 and is planning another AMOLED product, although no definite announcements have been made.

The most aggressive AMOLED company currently is Samsung SDI. It has invested heavily in building a factory and capital expenditures will reach $450 m. The plan is to release a mobile phone main display in early 2007 and samples are already shipping.

In the meantime, AU Optronics (AUO) has started selling a 2 inch AMOLED for a mobile phone. The OEM is BenQ-Siemens (which owns 40% of AUO), and the phone is being sold initially in Taiwan and then Europe. Other Taiwanese players are making definite plans. Chi Mei Electroluminescence (CMEL) was spun-off as a subsidiary of the Chi Mei Group in 2004 and plans to release both PMOLED and AMOLED panels in small sizes during 2006. Toppoly has built an AMOLED line and intends to release panels for a camera and a mobile phone near the end of 2006. Other players involved with AMOLED include Toshiba Matsushita Display, Hitachi, Samsung Electronics, LG.Philips LCD, RiTdisplay, Epson and Sharp.

The key application for AMOLED is the mobile phone main display. It offers the largest total available market (TAM), and is well-suited to the OLED's attractive image, low power consumption and thin profile. In addition, the increasing use of video on mobile devices also favours the OLED's fast speed. One challenge is the assurance of supply. Mobile handset makers need assurance from OLED panel suppliers that they can deliver at least 10,000 panels per month and often much more. Unfortunately, this figure is currently beyond the capability of most panel suppliers because of low yield and process development is continuing to improve manufacturing competence.

An interesting new idea is the possibility of area colour main displays for emerging markets such as India and South America. It is suggested that these markets could be like the MP3 market, where an inexpensive but attractive display is needed, so that area colour OLED is a superior choice to STN-LCD. However, it remains to be seen whether CSTN might actually emerge as the display of choice in these cases.

Looking further ahead

The ultimate dream of many OLED panel makers is to serve the large-screen television market. OLED is well suited to TV - it has fast speed, good colour, excellent viewing angle and high contrast ratio. TV does not require high resolution, so inkjet printing should be able to serve. The main challenges are the large size, long lifetime requirement (30,000 h), and low price point. Another hurdle is the competition from many other technologies, which is rarely acknowledged.

The TV market is already flooded with options: CRT, LCD, plasma, projection and the potential for a variety of novel technologies like SED and carbon-nanotube-based technology. Consumers, for the most part, do not care about the particular technology - they tend to look only at the picture quality and the price, followed by the size or depth. Having so many technology options makes it difficult to grab the attention of end-product OEMs and channel vendors, and display companies themselves may have to make strategic choices if they can offer multiple technologies.

Currently, OLEDs cannot be manufactured in large sizes. Even the more aggressive participants such as Samsung Electronics have announced that they plan to enter the market around 2008. More time is needed to establish manufacturing processes for large panels and to build equipment that can make such panels efficiently. Inkjet printers for large substrates are still in the beta phase.

Thus, it is likely that the first OLED TVs will be small, designed for novel locations such as the kitchen or bathroom. The TAM for this sort of TV is small, but OLEDs offer novelty. Later, as technical and manufacturing capabilities grow, OLEDs may move into more standard-sized TVs (20-30 inches, or even larger). This could happen around 2010, but only with continued investment and commitment from major players.

Beyond television lies the potential for OLED lighting. Some say that this application could be simpler because there is no need to pattern subpixels or provide a complex backplane to drive it. But the requirement for long lifetime remains, and so OLEDs must still grapple with the difficulties of organic material degradation and colour shift. These are exacerbated at the high brightness levels required for lighting applications.

Finding a niche

What OLEDs need most is a unique application that LCDs cannot serve. At this time, everything an OLED can do can also be done by an LCD - and for a lower price. Furthermore, most of the key companies developing OLEDs are also LCD players, and hence they are ramping up OLED products as part of a larger strategy that will not cannibalize their own LCD businesses.

One option for a unique product would be a flexible OLED. Flexible LCDs exist, but are less appealing than flexible OLEDs. The main difficulty with flexible LCDs is that the image quality is so strongly affected by the cell gap between the two substrates of the display. OLEDs have no cell gap challenge, although this advantage is balanced by the disadvantage of requiring a powerful barrier to protect against water in the air. While glass substrates provide such a barrier naturally, plastic allows too much water to pass and must have a barrier layer. Adequate barrier technology has not yet been developed.

Flexible OLEDs could be used in applications such as shop signage, electronic shelf labels, novel forms of advertising displays and even electronic books or paper. Most developers agree that even entry-level products are still at least 2-3 years away due to technical challenges, but this represents an important long-term option for OLEDs.

LightPath TechnologiesOmicron-Laserage Laserprodukte GmbHDelta Optical Thin Film A/SOcean InsightSynopsys, Optical Solutions GroupVR/AR AssociationDIAMOND SA
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