The technology of printing organic transistors onto a flexible substrate to create plastic circuits has existed for some time now and has found applications in the few instances in which flexibility is mandatory but speed, density, and energy efficiency are not important. The limiting factor in all these dimensions has been the organic-semiconducting material itself; all of the previously explored materials, although flexible and compatible with simple offset, ink-jet, or laser printing, have low carrier mobility.

However, researchers at Stanford University and the University of California —Los Angeles have conducted a series of experiments that may constitute a breakthrough (Reference 1). Instead of printing an organic semiconductor directly onto the substrate in an amorphous state, the new technique uses a patterned polymer stamp to print a crystal growth agent, OTS (octadecyltriethoxysilane), onto the desired transistor sites. The technique then introduces a vapor containing the intended organic-semiconductor material, and single-crystal structures grow where the growth agent is present.

Researchers have demonstrated monocrystalline transistors of rubrene and Buckyballs. The devices exhibit the high-carrier-mobility characteristic of single-crystal transistors and, hence, acceptable performance for many applications. Researchers have built devices with dimensions of microns, and experiments have shown that repeated flexing does not impair the transistors' electrical characteristics. Now, the researchers are turning their attention to controlling the orientation of the crystal that forms on the growth agent and improving the electrical contact between the crystal and previously printed metal electrodes.