FAQ

Introduction to OLED Technology

Organic Light Emitting Diode (OLED) technology was invented in the 1980's, initially by Kodak researchers. Since then there have emerged two competing types of technologies. One was Eastman Kodak's molecular type, Small Molecule OLED (SMOLED). The other was the Large Molecule or polymer type OLED (PLED). This thick film technology was mostly developed at the University of Cambridge, which spawned Cambridge Display Technologies (CDT).

OLED

In the late 1970s, Eastman Kodak Company scientist Dr. Ching Tang discovered that sending an electrical current through a carbon compound caused these materials to glow. Dr. Tang and Steven Van Slyke continued research in this area. In 1987, they reported OLED materials that became the foundation for OLED displays produced today. Eastman Kodak is the key patent holder for small-molecule OLED (SMOLED) technology.

PLED

In 1989, researchers at the Cambridge University Cavendish Laboratory found that passing an electric current through certain polymers made them emit light. Cambridge Display Technology (CDT) was formed in 1992 to commercialize the technology that evolved from this discovery. CDT owns the fundamental intellectual property and expertise in light-emitting polymers (PLEDs). A team of over eighty scientists is now responsible for the development of this technology. Cambridge Display Technology (CDT) now owns the fundamental intellectual property and expertise in light-emitting polymers (PLEDs).

How an OLED Works

An OLED sandwiches organic semi-conducting materials between two metallic compounds. Positive and negative charges are injected from the conducting electrodes into the OLED material. When these electrons and holes find each other light is created. The color or wavelength of the emitted light can be controlled by the doping of the emissive layer in the display.

There are two types of OLED display drive schemes, Passive matrix and Active matrix. Current OLED, both SMOLED and PLED, displays rely on Passive matrix technology due to its lower cost and relatively simple implementation. However, to achieve larger resolution panels and longer display life times Active matrix OLED panels are being developed.

Passive matrix (PM) OLED displays stack layers in a linear pattern, much like a grid, with "columns" of organic and cathode materials superimposed on "rows" of anode material. Each intersection or pixel contains all three substances. External circuitry controls electrical current passing through the anode "rows" and cathode "columns," stimulating the organic layer within each pixel. As pixels turn on and off in sequence, pictures form on the screen.

PM OLED displays' function and configuration are well-suited for text and icon displays in dashboard and audio equipment. Comparable to semiconductors in design, PM OLED displays are easily and cost-effectively manufactured with today's production techniques.

Active matrix (AM) OLED displays stack cathode, organic, and anode layers on top of another layer - or substrate - that contains circuitry. The pixels are defined by the deposition of the organic material in a continuous, discrete "dot" pattern. Each pixel is activated directly: A corresponding circuit delivers voltage to the cathode and anode materials, stimulating the middle organic layer.

AM OLED pixels turn on and off more than three times faster than the speed of conventional motion picture film - making these displays ideal for fluid, full-motion video. The substrate, low-temperature polysilicon (LTPS) technology, transmits electrical current extremely efficiently, and its integrated circuitry reduces the AM OLED displays' weight and cost.

OLED Advantages

OLED panels are emissive so they do not require a separate backlight like LCD technology does. The elimination of the backlight helps reduce the OLED display's overall power consumption when compared to LCDs. The OLED also does not suffer from loss of contrast due to bleed through of the backlight in the "off" pixels. OLEDs, being emissive, have a consistent contrast ratio greater than 100:1 with no limitation in viewing angle.

Since OLEDs are solid state devices they do not suffer from temperature related response time delays and contrast changes. OLEDs offer a wide temperature range, -20C to +60C operation, -40C to +70C storage with no change in response times.