OLEDs: Impressive Innovations

It reads: “If you read books or newspapers, please be careful not to disturb other travelers!” But here in Taiwan’s capital city, if you look around you will mainly see faces lit by the glow from the displays of various compact reading devices. Actual books are the exception, and newspapers on paper seem to be extinct. No reader interferes with his neighbor’s view. 

Displays are everywhere. As soon as people arrive at the office they sit down in front of one, and later they watch TV on yet another display. Does this mean that the age of printing, which was initiated by the Chinese around 2,200 years ago, is absolutely over? Not at all, because state-of-the art displays made of organic light-emitting diodes (OLEDs) are bringing the printer’s art into the electronic age. 

However, at the moment people are mostly viewing LC displays (LCDs). With this technology, liquid crystals control the light emitted by a backlight in a way that makes text appear on the display. LCD technology utilizes a complex array of components including colored and polarizing filters as well as a backlight. It was this technology that made smartphones, laptops, and large, flat-screen televisions possible. Now OLEDs are sparking the next stage in display technology, thanks to their obvious benefits, including the fact that they can be manufactured using less expensive printing processes.

The electronics industry is highly collaborative. Many producers of cell phones, TVs, and laptop and notepad computers get their displays from specialized suppliers. The world’s fourth-largest (Source: http://www.amorphyx.com/market/overview) of these companies, with a market share of over 16 percent, is AUO. 

It was founded in 1996 and is based in Taiwan. AUO has more than 45,000 employees and posted sales of around €10.2 billion (US$13.96 billion) in 2013. AUO develops and manufactures displays ranging in size from 1.5 inches (diagonal) to 65 inches (diagonal). 

AUO’s displays are based on several technologies, including OLED displays that are developed using inkjet processes. This highly innovative company owns more than 12,100 patents and has submitted applications for another 19,100. 

AUO’s strategy is to provide the industry with complete state-of-the-art solutions at competitive prices. Around 3,200 employees in research and development — over 80 percent of whom have at least a master’s degree — are responsible for maintaining the rapid pace of innovation.

Among the latest developments are ultra-high resolution displays with wide color gamut, as well as transparent, flexible and touchscreen displays. The company is also a total solar solutions provider. AUO considers environmental protection an integral part of its business model. 

The company’s generation 8.5 fabrication plant was the first of its kind to receive LEED (Leadership in Energy and Environmental Design) platinum certification from the U.S. Green Building Council.

AUO was the first display manufacturer to be certified as compliant with the standards ISO 50001 (energy management) and ISO 14045 (eco-efficiency rating).

In OLED displays, each pixel is either a red, blue or green light-emitting diode. This type of construction means that many energy-hungry layers are omitted compared to traditional LCD panels. The absence of these layers makes OLEDs very efficient. In addition, OLED displays are extremely bright and the images they present have high color saturation, high contrast, and exceedingly fast switching time. 

Since 2006, consumers have been able to glimpse the future presented by this display technology. “That’s when we delivered the world’s first OLED cellphone display,” says Yusin Lin, a physicist who heads the OLED Technology Center of the Taiwanese manufacturer AUO. Since 2000, the company has been working intensely on the research and development of OLEDs. The milestones in the evolution of this technology include a transparent display and a flexible display introduced in 2010 and 2011, respectively, a 65-inch (diagonal) full-HD television, and a 5-inch display with an amazing resolution of 443 pixels per inch (ppi) in 2013. 

“This 14-inch display was also recently created,” he says, gesturing toward a fully functional prototype that shows videos in brilliant quality. It is one of the first panels in this size from AUO that is “printed” using the promising inkjet technology. The printer in question was developed by AUO and its key suppliers. At the end of 2013 it was one of only a handful of units worldwide that could be used for displays with this diagonal measurement or even larger dimensions. 

This new printer is protected by numerous patents. Next to the new printer in the cleanroom is a “glovebox” — an enclosed work station that is pressurized with nitrogen gas and has rubber gloves attached by means of flanges. Employees use the glovebox to access the compounds that are combined to form the electronic ink used in printing out displays. With the aid of spatulas and a precision scale, workers continually try out new recipes in order to find the perfect mixture.

The inks are contained in small brown bottles, most of which carry the Merck KGaA, Darmstadt, Germany logo. A similar facility is located at the Merck KGaA, Darmstadt, Germany lab near Taipei. Here, the physicist Ming-Chou Wu is responsible for application-oriented developments. “We work closely with AUO and other companies,” he says, “in order to develop electronic inks for OLEDs that combine outstanding optical and electrical properties with long life time and easy processing in terms of future mass-production.” Every color presents challenges. With blue, for example, the challenge is service life.

Traditionally, the making of OLED displays involves the process of evaporation, by applying compounds to a substrate in a vacuum and then fusing them under heat. Only 20 to 40 percent of the material can be used with this process. In addition, cleaning the equipment is time-consuming. “So this isn’t the most optimized process for the mass production of large OLED displays for TVs” says Yusin Lin from AUO.

In order to find better solutions, employees are researching all aspects of the inkjet printing process, including the viscosity of the ink and the geometry of the jets used to create the minute droplets. These tiny blobs of ink, which are only 20 trillionths of a liter (picoliter), become the components of a colored light-emitting diode. Eight million of these pixels are needed for one of today’s high-resolution UHD 4K-standard TV displays. Every one of these pixels has to function perfectly, because the human eye is very sensitive to deviations in color and brightness.    

“These developments are mainly pursued by display developers like us, together with companies such as Merck KGaA, Darmstadt, Germany that have a great deal of experience with the associated compounds,” says Yusin Lin. Due to the high investment costs associated with their development, companies in the display industry often work on new products for years before offering them to device manufacturers. 

“At AUO we are mainly concerned with complete solutions,” he adds. Success in this highly competitive business often means receiving an order for millions of units — and, in the case of AUO, one that requires compliance with holistic environmental protection regulations covering everything from wastewater treatment to efficient logistics. No one doubts that OLED displays will be a huge success in the high-end segment of the market very soon, and that in the years to come they will also be used in less expensive devices. And because products in this market are characterized by an ever shorter lifecycle, developments never cease.

At the beginning of 2014, most OLED displays were still manufactured using complex vacuum evaporation technology. But this is not the most optimized process for the efficient mass production of large displays, which currently have up to eight million pixels. 

The solution is to print displays using inkjet technology. This process is similar to that of an office printer, but places much higher demands on the “ink” as well as the design and control of the printing head. 

One of the many challenges of this process is the exact control of the jetting of the substrate — a task that must be uniformly repeated millions of times during the printing process.

Another challenge is the creation of “microcavities,” structures that can be produced economically by using print technology. Microcavities create two facing surfaces. The distance between these surfaces must have a specific relationship to the wavelength of the relevant light in order to create harmonic resonance. 

This resonance raises the efficiency of the light emission. In printing processes, the size of individual drops can be controlled with such precision that different-sized microcavities can be produced for each of the three colors in one operation.