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. One key priority will be the creation of user-friendly electronic products (Figure 1), and the development of efficient manufacturing technologies for these products. With inorganic transistors, the focus has been on performance improvement through the development of ever smaller circuits. A totally different approach will be needed for organic transistors. Sony aims to establish this approach though its ongoing research and development activities in the field of organic transistors.

Flexible Electronics

Mechanically flexible organic materials

Plastic substrates, which are tough and yet light, even those with a large total area, are ideally suited for use in human-friendly 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, human-friendly devices. 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.

Organic Transistors Manufactuable at Room Temperature

Organic transistors are transistors with organic semiconductors (Figure 2) in their semiconductor layer (Figure 3). Organic transistors with several tens of nanometers-thick organic semiconductors are called "organic thin-film transistors" (OTFT). 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 enable to realize 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.

Using Organic Transistors-Flexible Displays

Displays play an important role in the interaction between human beings and information. 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 (announced in July 2005, [1]) and a flexible OLED display (announced in May 2007, [2]).