A sign in the Taipei subway requests, “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.

AUO is one of the leading manufacturers of LC and OLED displays (photo courtesy of AUO)

The world’s first OLED cellphone display from AUO

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.

A flexible and transparent 4.3-inch display (2010) (photo courtesy of AUO)

Testing in a vacuum

The inks are contained in small brown bottles, most of which carry the Merck logo. A similar facility is located at the Merck 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 AUO’s Yusin Lin.. 

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.

Among other things, the Merck lab in Taiwan develops electronic inks for OLEDs (photo courtesy of Merck)

Intensive competition

“These developments are mainly pursued by display developers like us, together with companies such as Merck 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.