Fabrication of sub-micro spherical probes by liquid membrane pulsed electrochemical etching

This paper describes a reproducible method to prepare sub-micro spherical probe based on liquid membrane pulsed electrochemical etching. The formation mechanism of the sub-micro spherical tip is analyzed in-depth. The maximum energy density of the necking region correlates with the type of probe produced. Under a larger energy density larger than a threshold value, the necking region melts. The melt on the lower tip is rounded into a sub-micron spherical end due to the liquid surface tension. A pulse voltage rather than DC voltage should be used to prepare sub-micro spherical probes, because the maximum current at pulse voltage is larger than that at DC voltage. Experiments were conducted to investigate the effects of pulse peak voltage, pulse width and electrolyte concentration on the size of the obtained spherical probes. Sub-micro spherical probes with the smallest diameter of 180 nm have been fabricated by appropriate parameters. Micro holes and micro channels with diameter of 3 μm and 5 μm were processed by electrochemical micromachining with spherical probe as tool electrode.