Development of the printing method for electrically conductive material using AFM probe integrated with microelectrode

Abstract

This work demonstrates the electrochemical deposition of micrometer-scale dots using a simple instrument based on an AFM (atomic force micro scope). Nickel micrometer-scale dots of 10µm width and 250 nm height nickel structure were deposited with different concentrations of electrochemical deposition solution. A positive potential was applied to a gold electrode integrated in the AFM cantilever and a negative potential was applied to a conductive substrate. The Au electrode on the AFM cantilever becomes an anode and substrate becomes a cathode. By applying a bias between a copper substrate and the Au electrode on the AFM cantilever, a strong electric field was generated at the limited area. And the localized electric field resulted in significant migration effect. This migration effect is the major factor of the localized electrochemical deposition (LECD) at substrate under the electrode of AFM cantilever. To verify the effect of migration and diffusion on electrochemical reaction, computational simulation was performed before localized electrochemical deposition experiment. In the localized electrochemical deposition process, bulk concentration, applied potential and distance between the substrate and electrode are the major parameters affecting migration and the diffusion of ions in the electroplating solution. The electrochemical reaction was analyzed by computational calculation. In the LECD simulation processes, electric field between the electrodes and size of the electrode determined the localized printed geometry. As the electrode approaches the substrate, stronger and more localized electric field is generated from the anode electrode. This electric field is determined by the bias and the distance of between anode and cathode. To generate constant electric field between anode and cathode, the distance of electrode and substrate should be fixed. In this localized electrochemical deposition process, we used the AFM cantilever integrated with an ultramicroelectrode fabricated from a conventional AFM cantilever using subsequent metallization and insulation layer deposition processes, as well as final FIB milling process exposing the micrometer scale electrode at a fixed distance from the tip apex. By following the fabrication process, two types of AFM cantilever were fabricated. One of them is the single electrode integrated AFM cantilever and the other is the double electrode integrated AFM cantilever. The microelectrode has geometry of half circular ring of which radius ranges from 2μm to 5μm with submicrometer thickness. By changing the size of electrode and the concentration of electrochemical solution, various metal patterns were printed.