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Research on photoresist is an example of extending the current state of the art–the new materials are needed simply to continue improving an existing technology. But other work in organic materials could usher in technologies that are unlike anything else seen before, such as computer displays that are as light and flexible as an overhead transparency.

Flat-panel displays like those on laptop computers consist of a thin layer of liquid-crystal material sandwiched between two supporting sheets of glass and controlled by a network of thin-film amorphous-silicon transistors to create images. Researchers working with organic materials believe they can create displays that are lighter, more durable and more energy efficient.

Organic light-emitting devices, or

OLEDs, have been under development for years at various places around the world, and the first products incorporating OLEDs are now appearing on the market. OLEDs are exceptionally bright, can be made to shine in any color, operate efficiently at low voltages, and can potentially be made inexpensively. Furthermore, it should be possible to put them on plastic substrates and create displays that are thin, light-weight and flexible–and perhaps even able to be rolled up or folded when not in use. A team composed of researchers at IBM Research Centers in Zurich and Almaden is trying to develop the organic materials that will make such OLEDs feasible.

Other researchers are working to develop organic-inorganic hybrids that he hopes will do the job even better than purely organic materials. They want to combine the robustness and thermal stability of inorganic materials with the advantages of organic molecules, such as simple processing and the ability to transform electricity into light efficiently. To do this, organic-inorganic perovskites are chosen, materials made up of alternating inorganic and organic layers. In a typical hybrid, the organic layer contains relatively simple molecules. The scheme is to replace them with organic luminescent dye molecules, which give off light when ticked by an electric current. The inorganic perovskite framework would supply the necessary structural and electronic properties.

To date, researchers have managed to grow single crystals of such hybrids using an organic dye molecule and, they have incorporated the material into an electroluminescent device. While the preliminary devices are not particularly efficient at emitting light, the hybrid materials are easy to process. If they can improve the luminescent efficiencies, the hybrids could be a good choice for a new generation of light-emitting devices.

But if those devices, whether organic or hybrid, are to lead to flexible displays, researchers must also develop organic transistors. Silicon transistors would be impractical because the silicon used in thin-film transistors is grown at 350 degrees C–good transparent plastic melts below that temperature. Organic transistors, on the other hand, can be formed at room temperature.

It has proved difficult, however, to find the right mix of materials to create a practical organic transistor–in particular, one in which a relatively small voltage can switch on or off a relatively large current. Until this year, the best organic thin-film transistor was one developed in 1996 by scientists at Pennsylvania State University. But it demanded about 100 volts, more than what batteries of a portable computer can generate efficiently.

A way around such high voltages was announced. The key was the realization that the organic semiconductors contain ‘traps’ that capture the charge carriers–electrons or holes, thereby reducing the current between the transistor’s source and drain. At higher voltages, enough carriers are generated to occupy all the traps and still provide an adequate current. The voltage needed to reach the required concentration of charge carriers decreases as the dielectric constant of the insulator increases. Therefore, by replacing the usual silicon dioxide in the transistor’s gate insulator with barium zirconate

titanate, which has a higher dielectric constant, the team was able to reach the desired performance with just 5 volts.

The one remaining hurdle is to learn how to make the organic transistors with a process that is more suited to commercial production. When researchers created an experimental organic transistor, it was with a vacuum process that is likely to be more expensive than fabrication processes that deposit the organic material from a solution.