Organic light-emitting diodes (OLEDs) are a type of LED in which a film of organic compounds emits light in response to an electric current. They're used in lighting applications and in appliances that include mobile phones, MP3 players, lighting applications and high definition televisions.
MBRAUN and its partners offer clean environment solutions for all stages of OLED/PLED/OPV development and manufacturing—from laboratory systems to automated lines in leading-edge production environments. Supported by process tools including ovens\hotplates, coating equipment, and encapsulation equipment, MBRAUN covers every aspect of OLED/PLED/OPV research and production.
Contamination control is the key to OLED manufacturing because of the devices' complexity. OLEDs have four components:
- Organic layers
- Sub-layers made of a conductive layer, emissive layer and a cathode. Generally, at least one of the electrodes is transparent.
OLEDs fall into two families: those based on small carbon molecules and those made of polymers. Each type has unique characteristics, challenges and manufacturing processes, requiring different process tools.
Common to both, however, is sensitivity to moisture and oxygen. In-process OLEDs have to be protected from ambient conditions (air). So processing requires either high-vacuum or inert environments, encapsulated to prevent harm to the deposited multi-layer structure.
Particle contamination is a big threat to OLED quality and manufacturing yields. Particles deposited onto the devices can create Mura defects such as dark spots.
Special counter measures in processing equipment design are available to address this problem.
OLED displays can use either passive-matrix or active-matrix addressing schemes. Active-matrix OLEDs require a thin-film transistor backplane to switch individual pixels on or off, permitting high resolution and large display sizes. OLED lighting applications usually use the passive-matrix approach, for two reasons: less technical complexity and lower cost than active-matrix technology.
OLED manufacturing has three steps. First is preparing the substrate for subsequent coating processes. Second is deposition of the multi-layer structure onto the substrate. Third is encapsulation of the OLED device. Process and equipment solutions for each step have been developed and refined within industry, demonstrating their maturity.
Today's commercially available OLEDs are based on small molecule materials and usually involve thermal evaporation under high-vacuum conditions. This manufacturing process, however, tends to increase costs and has limited use for large-area devices. But in contrast to polymer-based devices, the vacuum deposition process enables the formation of well-controlled homogeneous films, as well as the construction of very complex multi-layer structures.
Vacuum deposition is unsuitable for forming thin films of polymers. But polymers can be processed in solution under ambient pressure conditions, potentially reducing initial investment and operating costs.
These materials are sensitive to moisture, oxygen and particles and have to be protected from them. Common techniques for depositing thin polymer films are spin coating, ink jetting, spray coating and even slit coating. All these methods are more suited to forming large-area films than is thermal evaporation.
However, as the application of subsequent layers tends to dissolve those already present, formation of multilayer structures becomes difficult and the metal cathode may still need to be deposited by thermal evaporation under high vacuum.
The encapsulation of OLEDs is the final processing step. Depending on device design, several approaches are available and have to be evaluated independently.
The most common method is the end-sealing process, in which desiccants and UV-Curing, epoxies laminate a glass cover to the substrate for a gas-tight device. This approach is usually sufficient for OLED lighting devices and passive-matrix OLEDs.
More advanced device structures and high-end displays may require alternative processes such as glass-frit-laser sealing, thin-film encapsulation or dam-and-fill processes. These are emerging technologies currently enjoying great acceptance throughout industry.
Please contact us for more information regarding our solutions in OLED/PLED/OPV research, development, and production.
An introduction to CPI's OLED prototype line facility
© Centre for Process Innovation Ltd (CPI) (www.uk-cpi.com) – All Rights Reserved