Product Technology Review
OLED, otherwise known as organic light emitting diode, is a type of light emitting diode (LED) that utilizes an emissive electroluminescent layer comprised of an organic compound film that activates light emission via an electric current. Acting as an organic semiconductor, the film is set in between two electrodes, of which one will normally be transparent. OLED is the latest technological application of digital display. It can be found amongst the latest television screens, smartphones, tablet-pcs, portable gaming consoles and digital cameras. It also has potential for creative uses in lighting displays and art concepts.
What products can be produced with OLED?
- Mobile applications (smartphones, Tablet Pcs cameras, camcorder)
- Flexible products
- Television screens
- Lighting applications
Generally, OLED technology falls into one of two categories: passive matrix (PMOLED) or active matrix (AMOLED). Passive matrix technology utilizes a basic control scheme in which each row (or line) is controlled in a sequential manner. Because PMOLED technology does not maintain a storage capacitor, not every pixel will be in use. In fact, most pixels will be off in most cases. In order to compensate for the lack of illumination, PMOLED devices require increased voltage. The amount of voltage required will depend on the data received as that details what information needs to be displayed. In each case, the general assumption is that if a picture requires 10 lines illuminated, one line will receive electroluminescent data that is 10 times as bright and therefore illuminates the pixels that are essentially “off”. In general, PMOLEDs are cheap and relatively simple to manufacture. However, due to the higher voltage required they are not considered to be very efficient and generally have a smaller shelf life. They are also restricted in size and resolution (another requirement of the high voltage). Thus, PMOLED technology is only used in devices like MP3 players and smartphone sub displays.
AMOLED (Active-matrix organic light emitting diode) technology utilizes a more complex technology behind the pixels (as opposed to PMOLED). It consists of an active matrix of OLED pixels through which light is generated as a response to an electrical current. This current activates illumination through a deposit onto a thin film transistor, also known as a TFT array. In order to distribute the correct amount of current that activates each pixel, the TFT array functions as a control switch. In order to facilitate a steady continuous flow of current, two TFTs serving different purposes are required. One TFT commences and completes the charging of a storage capacitor. The second TFT serves as the voltage provider and controls a steady flow in order to create a constant current to the pixel. This eliminates the high voltage requirements of the passive matrix OLED technology.
In addition to the two main Thin Film backplane technologies, Polycrystalline Silicon (poly-Si) and Amorphous Silicon (a-Si), in the near future we will also see IGZO (Indium Gallium Zinc Oxide) as a major player in the backplane technology. IGZO has many advantages. One most important is that each liquid crystal cell flips from opaque to transparent. IGZO transistors have a high electron mobility and much lower leakage current characteristics than the two dominant silicon TFT processes. IGZO TFTs are smaller, wherefore displays can have higher resolution with less loss in light transmission.
Samsung Display uses different Sub Pixel Matrix technologies for their smartphone Super-Amoled Displays. For the Galaxy S4 and S5 they use the Diamond Pixel Matrix.
OLED televisions are the latest technology on the market. They provide a level of clarity and dynamic colors that are far greater than current LED/LCD TVs available on the market today. OLED technology revolutionizes television sets because they can be produced tremendously smaller. Some of the thinnest OLED TV panels weigh only 3.5 kgs and are astoundingly only 4 mm thick. They have shown to be greener options as they require less power to operate and do not contain toxic metals. In addition, OLED technology has shown the potential to produce flexible and transparent panels.
Due to the efficient structure of Active matrix OLED technology, there is no requirement for a backlight. This creates the potential for extremely thin and flexible OLED display panels. It would allow OLED displays to be shown on new mediums such as plastic, metal foil and flexible glass. Several large-scale companies already have products in development and are very close to market entry. While 2014 is deemed as the beginning of the flexible OLED display market, the technology is expected to surpass several billion dollars in sales in the US market alone by 2016.
There are two major production technologies at the market: Samsung Display uses the true pixel RGB technology, and LG Display uses the WRGB technology. LG Display’s WRGB technology is likely easier to produce as the True Pixel technology.
Another future capability of OLED technology is transparent displays. Researchers have already been able to successfully produce and utilize this sort of display. Transparent OLED pixels can be produced by using transparent TFTs that are comprised of a microscopically thin zinc tin oxide. This allows a nearly perfect transmission of visible light. Research in Germany has shown that positioning the TFT’s and OLED pixels side by side can help to create a transparent display medium. Due to how thin the TFT layers are, it has become possible to place them on large areas at extremely low temperatures. This also requires all sub components of transparent OLED displays to be transparent as well (substrate, cathode and anode). A two way transmission of light that can be both active and passive matrix is possible. Through the use of these types of displays, the brightness of a typical computer monitor can be almost doubled (as measured by candelas per square meter).
Lastly, OLED technology has been found useful in creating new forms of lighting. Because of the potential inherent with OLED technology in terms of its flexibility, transparency and thickness, a myriad of new possibilities exist for OLED illumination, lighting and light display shows. The potential is almost infinite, because OLED technology has proven to show lifetimes over 50,000 hours and because it burns at rates that surpass the efficiency of halogen and can reach up to 150 lm/W. In addition, OLED lighting utilizes less CO2, requires less energy and contains no toxic substances. This opens up a revolutionary concept of lighting displays and light based art conceptions.
OLED technology is preparing to take over the market by storm. Its uses continue to grow with the higher demands in efficient technology and lighting sources. The beauty of OLED lays in its high function matching its potential for aesthetic use and the flexibility it allows. As large scale technology companies grow in the awareness of the potential of OLED, the market will expand at an exponential rate opening up near infinite possibilities for this wonderful new advancement. The future has arrived in the form of OLED.
Diagram of an OLED display:
Check out our graphic to see the detail of an organic panel.
- Hole Injection Layer (HIL)
- Hole Transport Layer (HTL)
- Emissive Layer (EML)
- Electron Transport Layer (ETL)
- Thin Film Encapsulation Barrier (plastic)
- Glass, Plastic, metal foil Substrate