Samsung OLED Developments
Brian Berkley, vice president Mobile Display Technology Center discussed his organization and its work on Organic LEDs (OLED). The group started in November of 2003 as a consolidation of the R&D efforts that were previously spread across many Samsung divisions. The focus of the group is to work on active-matrix organic LEDs (AMOLED) based on low-temperature polysilicon and amorphous silicon. They are responsible for all OLED development work in the company. In their first year of production, the group shipped $3 billion worth of displays.
Berkley showed device adoption over a period of several decades using a logarithmic scale for both time and unit volume. The adoption of OLED for displays is growing faster than any other display technology. The use patterns for the devices have been growing in application areas like location services, social networks, and virtual reality. New use patterns are evolving in the latest generation of smart phones. Smart phones are growing as a percentage of all phones, and are expected to account for 20 percent of cellphone purchases this year, increasing to 42 percent of all cellphones by 2015.
Smart phones are driving larger displays with the latest phones migrating from 2 to 4 inches diagonal measurement and much greater definition and resolution. At the same time, consumers are asking for much lower power consumption, brighter colors, and even larger screens for their next generation phones and all of these characteristics have to be included in a much thinner phone.
The emerging standard user interface for a smart phone is via a multi-touch screen. Touch enabled screens are growing and should achieve 44 percent market penetration by 2013. The many applications for smart phones including cameras, GPS, MP3 player, Web browser, and the phone. The growth in smart phones has created challenges for the touchscreens and overall user interfaces. The technology is changing from resistance which can sense a single contact to capacitive for multi-touch. The next generation of touchscreens will include integrated capacitive touch sensors
Next-generation displays will continue the trend seen in other displays. Flat panel displays started with monochromatic text-focused imagery, changing to super twist in the ’02 timeframe and then complex super twist two years later. Current technology uses thin film transistor LCDs with LED backlighting. In the future many displays will be using AMOLED as their display technology.
OLED have the flexibility to drive convergence in existing applications and divergence into new areas. The technology has the capability to include bright colors, high speed, a wide viewing angle, and high contrast. The issues of emitter efficiency and lifetime are improving with each new generation and in the near future, will appear on a TV set near you. The greatest challenge is scaling up the technology from small screens up to 4 inches to large screens greater than 10 inches.
The industry and technologies have changed a lot between 2008 and 2010. At first, there was no mass-produced product available. Manufacturing yield and line efficiency were very uneven. The first generation products are now being displaced by new materials and backplanes. The process and materials technologies have been improved, leading to advances in color and emitter lifetimes. Improvements in color patterning are leading towards significant increases in size making large OLED displays viable in future.
Transition to OLED display technologies are helped by the much lower costs compared to LCDs.the loser costs are due to much simpler construction and lower cost materials and production processes. In addition, changing to a bottom emission topology eliminates the need for a back substrate, further reducing materials and manufacturing costs. As a result, OLED displays can have significant benefits versus plasma and LCD displays. An OLED display is projected to have power consumption much lower than the alternative technologies, about 10 W versus 35 for a 40 inch LED backlight LCD.
Samsung is working on new enabling technologies for fourth-generation displays. LCDs operate on voltage and are essentially binary devices. OLEDs are current-controlled devices enabling a more precise degree of intensity control. Research efforts are investigating many device improvements, including improved carrier mobility and a tighter threshold voltage. Existing technologies needing migration into production include polysilicon and high quality gate insulation. Because current designs use multiple transistors per pixel, they need P- type devices to simplify designs.
One factor in their favor is that OLED backplane production is a superset of their existing LCD backplane production. Existing manufacturing flows only need to add laser re- crystallization for the polysilicon. Super grain silicon shows promise with lower temperature anneal and relatively low leakage. Eventually, they would like to develop a non-laser-based high-mobility device.
The greatest challenge in producing larger displays is the requirement to perform all process and in an oxygen free environment. The major challenges in scaling to large sized displays are in areas like mask saggy and materials efficiencies. The basic chemistries and production technologies are applicable to many types of substrates and the eventual goal is to have a process compatible with non-glass substrates.
Alternatives for production include some unspecified development while other work is progressing on printing as a manufacturing process. Printing brings its own challenges including solutions and impurities as well as requirements for very high pixel or stripe color purity control and position accuracy.
Given a possible solution to all the challenges in device structures and manufacturing, a TV size display is reasonable and possible within a few years. For stereo 3-D, OLED is going to be better than LCDs because there will be no left/right crosstalk. It will still require active shutter glasses.
At the SID conference, they are presenting a talk on simultaneous emissive active displays as well as other applications including 3-D and flexible substrates. They have a low-temperature polysilicon process suitable for application on plastic substrates.
Some specialized applications for OLED displays include an ultrathin 50 µ substrate for passport pictures. The passport is placed into a reader and the person’s image lights up. This display technology would make passports much harder to counterfeit, so a number of countries are looking into the technology. They can also create ruggedized displays for consumer appliances.
They showed a short video with a transparent display being hit with a hammer and still operating. Other transparent display applications could be like the monitors similar to those shown in the movies “Avatar” and “Minority Report”. Large area displays for telepresence applications should be viable as soon as the large screen processes become manufacturable.
