In the interest of full disclosure, I should preface this article by saying that I am the proud owner of a Pioneer PDP-6010FD, a 60-inch 1080p KURO series plasma, which is one of the highest-rated displays of the last several years. It was a monumental purchase for me and it changed the way I watch films and television. Since the day I brought it home I was confident that I was watching one of, if not the best picture, a human eye could hope to see for years to come. But technology has a time-line of its own.
Several weeks ago I laid my eyes on the 11-inch, 3 mm thick Sony XEL-1 OLED (Organic Light Emitting Diode) TV. The colours were rich and vibrant and the contrast between light and dark was like nothing I had ever seen before. Blacks were actually dead black, and off-angle performance was better than any other flat panel I’ve ever run across. While plasma displays and projectors are currently the choice of most videophiles I know, after seeing this brief example of OLED technology in action, I’m fairly confident in saying that this will be the way of the future.
What we now call OLED technology was developed in the late 70s by a researcher at Kodak named Dr. Ching Tang. He found that by passing electrical current through a certain carbon compound he was able to make it glow green. Dr. Tang and his team worked on this new development for several years, and in 1987 patented the technology that became what we now know as an OLED display. An OLED panel consists of two layers of organic (carbon-based) materials sandwiched between two conducting layers called the anode and the cathode. The anode and cathode are in turn sandwiched between two plates, a glass seal and the substrate, which support the OLED panel.
Affixing the organic material to the substrate is the most challenging and expensive part of manufacturing an OLED display, and can be done in one of three ways. Vacuum thermal evaporation, or VTE, an expensive and inefficient process whereby the organic molecules are slowly heated in a vacuum chamber until they start to evaporate and then are allowed to cool until they form as condensation on the substrate. Organic vapor phase deposition (OVPD) is a somewhat more cost-effective and efficient process where a carrier gas is used in a heated, low-pressure environment to transport semi-evaporated organic material onto a cool substrate, whereby it again forms condensation and cools. The use of the carrier gas significantly reduces the time and cost involved in making an OLED panel. Neither of these methods, however, are either as cost-effective or consume as little time as inkjet printing (yes, I said inkjet printing). Much the same way your computer printer sprays ink onto paper, special printing machines are able to spray partially vaporized organic material directly onto cooled substrates. This drastically reduces the cost of equipment and the time necessary to manufacture OLED displays and allows the displays to be made far larger than either of the other methods.
Once the organic material is affixed to the substrate, anode and cathode, a few simple physics laws explain to us how the OLED display works. Electrical current starts in the power source, be it a battery or AC power. The electricity then runs to the cathode, after which it makes its way through the organic layers to the anode, which removes electrons from the conductive layer and excites electrons in the emissive layer. As the electrons jump from the conductive layer to the emissive layer they give off their excess energy as light. The colour of that light varies depending on what colour of organic film the light passes through, and the intensity of that light is affected by how much current is passed. It’s worth noting also that OLED displays are direct emission displays. This means that they generate their own light, without the need for a backlight like an LCD. This gives them several benefits over other flat panel technologies, all of which we’ll cover later.
There are two types of OLED displays, both with unique features and benefits that are better suited to certain applications. Passive matrix OLEDs have strips of anode and strips of cathode running perpendicular to one another with organic material in between. The intersections of anode and cathode stripes make up each pixel in the display. PMOLED displays are easier and fairly affordable to make, but they use more power than other types because they require an external controller to illuminate those pixels needed for a certain image. PMOLEDs are already seen in such applications as car stereo displays and advertising signs, things that usually display text and don’t require very high pixel counts or refresh rates.
Active matrix OLEDs differ from PMOLEDs in that they have a full layer of anode, cathode and organic material attached to a substrate that has the pixel count (or fixed resolution) of the display permanently configured. They also have a Thin Film Transistor (TFT) layer which acts as the controller driving the pixels. AMOLEDs generally have much higher pixel counts and faster refresh rates and are usually seen in applications meant for moving video like display screens and media players. They also consume much less power than a PMOLED (or any other type of LCD for that matter) due to the fact that the TFT layer controls the luminescence and thus are perfect for applications that are battery-powered. AMOLED screens are already available in several portable media players, such as the Creative Labs Zen V. If you believe the rumours on the internet, Apple is also going to be using an OLED screen in the new 3G iPhone, slated to appear sometime this summer.
Given that you’re reading the CANADA HiFi magazine, it’s a pretty safe assumption to make that you’re interested primarily in OLED’s application in the world of video displays. OLED technology offers numerous benefits over both plasma and LCD. First, and most importantly to videophiles, OLED panels have the ability to display true black. LCDs are lit by a backlight, which is always on. Plasma displays’ gas-filled pixels are also always charged, due to the time necessary to go from “off” to “on” being long enough that the human eye would notice the lag. As a result neither of these technologies can truly display black. Without true black, no colour in the entire visible spectrum can ever be properly displayed. There are certain display technologies available today which are able to come close to black, but thus far plasma nor LCD have been able to reach this “holy grail” of flat panel TV design. Due to OLED being a directly emitting display with a very fast response time (less than 0.01 milliseconds as opposed to 4ms on most LCD displays), when a particular pixel doesn’t need to display a colour, it just rests idly, resulting in true, absolute black. This facet of OLED technology also results in a whopping contrast ratio, thoroughly destroying anything available in either LCD or plasma from any manufacturer. Sony claims a contrast ratio of 1,000,000:1 for the XEL-1 TV. Even if this ratio is inflated, which is common practice in the TV display business, the result is still a noticeable difference between light and dark portions of the picture, multiple times that of any other display available today. The afore-mentioned fast response time also completely and utterly eliminates motion blur or smearing in fast moving pictures, such as action films or sports.
Having read this far you might be thinking to yourself that OLED is the perfect display technology. But there are still some kinks to be worked out the technology is ready for the primetime. First and foremost is the cost. The Sony XEL-1, which retails for $2499, is an 11-inch TV with a resolution of only 960 by 540 pixels, half of a true 1080p HD picture. The same amount of dough can also buy you a 50-inch plasma or LCD TV today. Longevity of an OLED display is also an issue. While the green and red organic films have reasonable lifespans, the blue material usually has a lifespan as short as 14,000 hours. This translates to about 6 years assuming 6 hours of TV watching per day. Compare that to your typical plasma display, which has a lifespan of about 60,000 hours, and it’s a not-insignificant reduction in an expensive product’s life expectancy.
While it’s currently nowhere near perfect, OLED technology is one of the most exciting things to happen to the AV world in sometime. It’s been years since a new technology has come along and offered performance increases over current products in such leaps and bounds. Several manufacturers have their fingers deep into the OLED pie: Sony, obviously, who has already brought the XEL-1 to market and is promising a 27″ OLED sometime in 2008, Panasonic, LG and Samsung have all also announced their intentions of manufacturing OLED displays in the near future. As with any new technology, there will likely be many glitches and imperfections along the way, but I, for one, am really looking forward to the day that I can have a 60″ OLED display with absolute blacks and 1,000,000:1 contrast level in my living room, all without having to re-mortgage my home to pay for it!
Latest OLED Developments (April 2009)
Most consumers may be satisfied with the latest generations of flat panel plasma and LCD TVs. After all, flat panel TVs changed the way we view entertainment today in many ways. But a true technology enthusiast’s burning desire for a flat TV won’t be fulfilled until we have displays so thin that you can either hang them up on the wall like a poster, or fold them up and put them in your pocket. OLED is the most promising TV technology to date that just might make our science fiction dreams come true and do so in a short period of time.
If you haven’t heard already, OLED technology offers much more than just super thin displays - it offers numerous improvements over current flat panel technologies. OLED displays can produce the deepest blacks possible since black pixels in an OLED display do not emit any light. This allows the displays to achieve an unthinkably high true-contrast ratio of 1,000,000 to 1 or better. OLED pixels turn on and off instantly and hence there is no motion blur. To top it all off, OLED displays are incredibly energy efficient. As we witnessed firsthand with Sony’s 11-inch XEL-1 OLED TV, the picture is simply spectacular.
This year, a few of the major TV manufacturers have promised to bring their first OLED TVs to market. Let us fill you in on the latest developments on where this technology is heading.
Earlier this year at the CES, Sony showed 21- and 27-inch OLED TV models, although no release dates or pricing was announced. The company also displayed a concept VAIO notebook with a flexible, seamless OLED display and keyboard. The laptop casing is said to be made from a flexible bioplastic. Also shown were a Walkman bracelet concept and a bendable e-reader, both based on flexible OLED displays. During a keynote speech at CES, Sony also showed off a flexible 3-inch screen playing a Beyoncé video.
Samsung had 14- and 30-inch OLED TVs on display at the CES. The company also demonstrated a mockup of a rather large cell phone with a foldable display. The concept is indeed very cool and should find its way into future cell phone designs soon enough. Two other small OLED displays based on the AMOLED technology variant were also shown at the Samsung booth: a 3.3-inch WQVGA display and a 7.01-inch display with a 1,024 by 600 pixel resolution and a 30,000:1 contrast ratio. Yes, there are currently two variants of OLED technology: PMOLED and AMOLED. To learn more about how each one works check out our “OLED - The Future of TV Technology?” article on www.canadahifi.com/, in the A/V Articles section.
LG Electronics showed off a near production model of a 15-inch AMOLED widescreen display. At just 1.4 millimeters thick, this screen is said to be suitable for small TVs and laptops. It has a 1,366 pixel by 768 pixel resolution and a lifetime of 30,000 hours. The screen is expected to debut in components in the second half of 2009 (production will start in June 2009). Pricing has not been announced.
In early March, Asus said that the company is considering an OLED display for the next generation of Eee laptop computers. At the end of March, rumors surfaced that Apple has reportedly been talking with Sony about using their OLED displays in an upcoming Netbook to be released by the end of 2009. The main issue here is of course the price of the OLED panels.
Without a doubt, throughout 2009 we will see a large number of mp3/multimedia players, cell phones and other small electronic devices with OLED screens. As to the future of OLED TVs - as soon as the manufacturing process can be perfected and the production cost can be reduced, we are bound to see most TV manufacturers eventually releasing their own OLED TVs in the next few years.