Fabrication of Micro-Gap Electrodes for Molecular Electronics

Recently, organic molecular electrical devices such as molecular thin film transistors have received considerable attentions as possible candidates for next generation electrical and optical devices. This paper reports fabricating technologies of flat metallic electrodes on insulating substrates with micro-gap separation. The key technologies of fabricating the planar type electrodes are liftoff method by the combination of bi-layer photoresist with overhang profile and 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 on the micro-gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were in the order of 10¹³ ohm at room temperature, which is enough for analyzing electronic properties of organic thin film devices. Finally, pentacene FET characteristics are discussed fabricated on the micro-gap flat electrodes. The mobility of this FET was 0.015cm²/Vs, which was almost on the order of the previous results. These results suggest that high performance organic thin film transistors would be realized on these advanced electrode structures.