Tuning of tunnel resistance of nanogaps by field-emission-induced electromigration using current source mode.

A newly investigated technique for the tuning of the tunnel resistance of nanogaps using electromigration method induced by a field emission current is presented to reduce the power consumption during the process. The method is called "activation" and is demonstrated with a current source. Planar-type initial nanogaps of Ni separated by 20-80 nm were defined on SiO2/Si substrates via electron-beam lithography and the lift-off process. Then, a bias current was applied to the initial nanogaps at room temperature, using a current source. The applied current was slowly ramped up until it reached the preset value. As a result, the process time of the current-source-based activation was 16 times shorter than activation using a voltage source. Furthermore, the tunnel resistance of the nanogaps was reduced from 100 T ohms to 70 M ohms by increasing preset current I(s) from 1 nA to 3.5 microA. Regarding the average power required for current-source-based activation, it can be successfully suppressed compared with that of voltage-source-based activation. These results imply that the current source directly and precisely tunes the field emission current passing through the nanogaps, and effectively causes the migration of atoms across the nanogaps, resulting in the successful control of the tunnel resistance of the nanogaps.