Several techniques have been demonstrated to be able to fabricate nanogaps with sub-10 nm spacing. One of these techniques includes an electromigration method. However, the typical electromigration procedure entails an abrupt break that yields a nanogap with a random tunnel resistance [1]. Here, a simple method, based on electromigration and field emission, is developed to control a tunnel resistance on metallic nanogaps. We study a controllability of the resistance on nanogaps by only passing the current through it.
Initial planar nanogaps of Ni, separated by less than 50 nm, were defined on SiO2/Si substrate by electron-beam lithography and lift-off process. The thickness of Ni thin films is 10 nm. Initial nanogaps exhibit high resistance around 1014 Ω. Experimental procedure is as follows. First, the voltage was applied to the nanogaps while monitoring the current at room temperature. Then, the voltage was stopped when the current reached a preset value. Consequently, the resistance of the nanogaps was controlled by adjusting the preset current from 1 nA to 100 µA, ranging from about 1014 to 106 Ω. AFM observation shows that the separations of the nanogaps become narrower from around 50 nm to below 10 nm after applying the current. It is considered that the decrease of the resistance is due to the motion of atoms in nanogaps caused by the effect of very high current density. These results suggest that this simple method possesses a potential in fabricating tunnel devices.
References:
[1] H. Park, A. K. L. Lim, J. Park, A. P. Alivisatos, and P. L. McEuen, Appl. Phys. Lett. 75 (1999) 301
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