Jan 20, 2010
Thin-film edges crossed to give nanoscale junction
Hideo Kaiju and colleagues at Hokkaido University, Japan, have proposed a lithography-free fabrication method for creating nanoscale junctions. The idea is very simple – two thin films are contacted with their edges crossing. The area of the crossed section is determined by the film thickness, in other words 10 nm thick films could produce 10 × 10 nm2 nanoscale junctions. This method offers a way to overcome the feature size limit of conventional optical lithography.
The process is shown in the figure above. First, nickel thin films are thermally evaporated on polyethylene naphthalate (PEN) substrates. Then the fabricated nickel/PEN films are sandwiched between two polymethyl methacrylate (PMMA) resins and the edge of the PMMA/nickel/PEN/PMMA structure is polished by chemical mechanical polishing (CMP) methods. Finally, the two sets of polished PMMA/nickel/PEN/PMMA structures are attached to each other with their edges crossing.
Cross-sectional TEM images of the nickel/PEN films show that there is no diffusion of nickel into the PEN layer and reveal a clear and smooth nickel/PEN interface. Here the nickel thickness is 17 nm, which gives a junction area of 17 × 17 nm2.
The ohmic I-V characteristics of the nickel-nickel nanojunction show good quantitative agreement with calculated results within the framework of a modified Anderson model. The analysis also predicts a high switching ratio in excess of 100,000:1 for nickel/molecule/nickel nanoscale junctions, which indicates that these junctions could have potential applications in novel switching devices.
Thus, the nanostructure fabrication method using thin-film edges, proposed in this study, is an important technology in terms of not only exceeding the limitations of conventional lithography but also in helping to create new switching devices with an ultrahigh on/off ratio.
The researchers presented their work in the journal Nanotechnology.
About the author
Hideo Kaiju, PhD, is an assistant professor in the Laboratory of Quantum Electronics at the Research Institute for Electronic Science, Hokkaido University, Japan, and is also a JST PRESTO (Precursory Research for Embryonic Science and Technology) researcher. He is exploring nanoscale organic spintronics devices, which can be expected as beyond CMOS switching devices and novel magnetoresistance devices.