“Double Exposure Method”: a Novel Photolithographic Process to Fabricate Flexible Organic Field-Effect Transistors and Circuits

Organic electronic devices are the expectation of future electronics due to its great potential mainly flexible electronics. But there are some limitations in the development of practical applications. It’s urgent to develop effective high-resolution patterning techniques. Photolithography show overwhelming advantages in reducing the minimal feature dimensions over other conventional printing techniques, with which high resolution highly integrated organic transistors could be fabricated.

Before getting into fully organic electronic devices there is the promise of making hybrid systems that have both Si electronic components and organic components. One of the applications of organic polymers that has been studied is to use them as dielectric material, replacing SiO₂ in conventional transistors. How ever, the use of organic polymers has the problem that many of them cannot endure conventional photolithography.

To solve these problems the researchers developed a novel photolithographic method called “double exposure method”. They starter with a Polysterine thin film spin coated over ITO/PET and annealed at 80º C. Then a photoresist was spin coated over the PS film and UV irradiated, patterned for the electrodes and irradiated again. Then a thin gold film was deposited and washed with a solvent and exposed again to the method. And finally deposited organic semiconductors of 50 nm (pentacene). This process was also used for other logic circuits.

Characteristic curves showing the performance of the OFET

In summary, they developed and tested a method to fabricate flexible organic field effect transistors and circuits. The performance obtained  was comparable to the ones from traditional Si techniques.