Fabrication of flat micro-gap electrodes for molecular electronics

Recently, organic molecular electronic devices such as molecular thin-film transistors have received considerable attention as possible candidates for next-generation electronic and optical devices. This paper reports on fabrication technologies of flat metallic electrodes on insulating substrates with a micrometer separation for high-performance molecular device evaluation. The key technologies of fabricating planar-type electrodes are the liftoff method by the combination of bilayer photoresist with overhang profile, electron beam evaporation of thin metal (Ti and Au) films, and SiO₂-CMP (Chemical Mechanical Polishing) method of CVD (Chemical Vapor Deposition-deposited TEOS (tetraethoxysilane)-SiO₂ layer. The raggedness of the electrode/insulator interface and the electrode surface of the micro-gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were on the order of 10¹³ ohms at room temperature, which is sufficient for evaluating electronic properties of organic thin-film devices. Finally, pentacene FET (Field Effect Transistor) characteristics are discussed fabricated on the micro-gap flat electrodes. The mobility of this FET was 0.015 cm²/Vs, which was almost on the order of the previous results. These results suggest that high-performance organic thin-film transistors can be realized on these advanced electrode structures.