Fabrication of sub-20 nm width ferromagnetic nanocontact structures by shadow evaporation.

The movement of the magnetic domain wall could result in the changing of the contact resistance. Such a resistance change is named as the domain wall Magnetoresistance (DWMR), which can be used as a basic signal of nanodevices. For application, a large DWMR is necessary to improve the device performance. An approach to improve the DWMR value is to fabricate magnetic structures with narrow contact width. However, due to the proximity effect during the process of electron beam lithography (EBL), it is not easy to fabricate sub-20 nm width structures by EBL technique directly. In this paper, we investigated the fabrication of sub-20 nm width nanocontact structures by combined techniques of EBL and shadow evaporation. Upon optimizing the resist thickness, opening width, and the evaporation angle, the contact width was tuned and the corresponding variation trends with these parameters were explored. Using the optimized fabrication conditions, 14 nm wide ferromagnetic contact structures were successfully fabricated.

The fabrication of ferromagnetic nanocontact structure.

In this paper, we report the fabrication of permalloy nanocontact structures with greatly improved surface and edge smoothness. Magnetic sputtering and thermal evaporation were used for metal film deposition, and lift-off and dry etching techniques were employed for nanocontact structure patterning. The compositional properties of the resulting nanocontacts were investigated using energy dispersive analysis of X-ray (EDAX). Atom force microscope and scanning electron microscope were used for morphological characterisation. We found that high quality permalloy nanocontact structures can be obtained by using the combination of thermal evaporation and lift-off with optimised processing parameters; meanwhile, in the case of depositing metal films using magnetic sputtering, dry etching technique rather than lift-off was used for improved surface morphology of the nanostructures.

Fabrication of nanopores for biomacromolecule detection.

Nanopores embedded in a thin membrane with diameter below 10 nm are suitable for the biomacromolecule detection. For such purpose, in this study, we developed a technique of how to obtain small nanopores in silicon nitride films using a focused-ion-beam (FIB) system. By changing the process parameters, such as the beam current, the film thickness of the membrane and the ion beam exposure time, the diameter of the nanopore can be tuned. Under an optimized condition, high quality nanopores with diameter as low as 6 nm was fabricated on a 7 nm thick membrane. Our result suggests that FIB direct writing technique might be a suitable approach for biomacromolecule detector fabrication.