The Science Of Sony’s Attraction To Flexible OLED

The dramatic progress of electronic technology in the 20th century was made possible by high-performance transistors made from inorganic substances, such as silicon and compound semiconductors. Future efforts will focus on the creation of more efficient and natural ways for human beings to interact with the complex information processed in these high-performance devices. The key priority will be the creation of user-friendly electronic products while embracing what we’ve been sensationalizing in science fiction movies. Organic transistors are the future of gadgets and technology, and the payoff will be products that completely blow away anything we’re currently using now. Sony aims to establish this approach though its ongoing research and development activities in the field of organic transistors.

Even large plastic substrates, which are tough and yet light, are ideally suited for use in electronic devices. Unlike inorganic substances, organic materials can be used to create high-quality thin films on plastic substrates, which have poor heat resistance. In this context, an organic material is one with molecules consisting of a carbon (C) skeleton linking together other elements. These materials are similar to resins, such as plastics and vinyl. Conventional transistors are made from silicon (Si), an inorganic substance. While silicon crystals are extremely hard, organic substances are light and flexible, making them ideal for creating flexible products. Normally organic materials are poor electrical conductor. However, in recent years it has become possible to produce organic compounds that conduct electricity. Examples include conductive polymers.

Examples of Organic Semiconductors

Organic transistors are transistors with organic semiconductors in the semiconductor layer. Organic transistors with several tens of nanometers-thick organic semiconductors are called “organic thin-film transistors” (OTFT), like a TFT LCD that is found in millions of devices today. As with a normal inorganic transistor, it is possible to switch the current flowing between the source electrode and drain electrode in an organic transistor on or off by varying the voltage at the gate electrode (*). One of the differences between organic and inorganic transistors is the temperature at which they are fabricated. Conventional inorganic transistors require high temperatures (500-1,000°C), but organic transistors can be made between room temperature and 200°C. Organic transistors can even be formed even on a plastic substrate, which is vulnerable to heat. Therefore organic transistors are not only light and thin, but also flexible device elements, allowing them to be used in a variety of unique devices, such as flexible displays and sensors.

Structure of an Organic Transistor

Another important characteristic of organic transistors is the simplicity of the method used to produce them. Inorganic transistors require massive vacuum systems and complex manufacturing processes. However, most organic materials can be dissolved in organic solvents to create “inks” that can be used to create circuits simply by printing them under normal atmospheric conditions. Printing technology can also be readily adapted to the production of flexible substrates and large substrates. With the methods used to manufacture conventional inorganic transistors, only a few percent of the materials are actually used. Printing is far more efficient, and by optimizing the method it is possible to achieve usage rates as high as 90%. For this reason, this manufacturing method is also attractive from an environmental perspective. Sony is currently conducting research into the fabrication of organic transistors through printing.

Displays play an important role in the interaction between human beings and information – it is almost impossible, unless you live in a remote locale, to not see someone else looking at a screen if you’re out and about. Organic materials are used in the display mechanisms of today’s LCD and OLED displays, but their control systems consist of inorganic transistors on glass substrates (silicon TFT). This type of display is difficult to bend. However, a display with organic transistors on a plastic substrate would be completely flexible. Such a display could also be dropped without breaking, rolled up, or folded. Sony has demonstrated its ability to create flexible, drop-proof displays by using organic transistors on plastic substrates to create drivers for a flexible transmissive LCD display nearly four years ago in July 2005, and to the surprise of Sony Insider, a flexible OLED display back in May 2007. So basically, what Sony showed off at CES 2009 was a year and half old prototype. Here it is again:

The organic transistor (and OLED) is a new technology that is still in the early stages of its evolution. Comprehensive development efforts targeting printing processes, device fabrication and design methods are expected to result in improvements in both performance and reliability, paving the way for practical implementation of the technology. If you’ve forgotten, Sony showed off three unbelievable concept videos at CES 2009 that demonstrated what future flexible OLED products will be like: