Kinematics and kinetics of alternating electric field induced liquid mass transport on chromium thin films

Abstract

Long range mass transport driven by an electric field has many applications in the fields of nanoscience and technology. Liquid-phase mass transport ranging from the micrometer to the millimeter scale and its application to nanopatterning have been demonstrated on chromium (Cr) thin films using a DC electric field. Under the influence of an electric field, the metal seems to undergo a chemical reaction, and the resulting liquid material flows out radially in all directions. In this study, we have explored the effect of an alternating (AC) electric field on this kind of liquid-phase material transport. Within the scope of this work, mass transport has been studied on Cr films 30 nm thick using an alternating square waveform with frequencies ranging from 100 Hz to 1000 Hz in steps of 50 Hz. The dependence of the material’s formation, flow distance, and flow velocity on frequency, for a constant applied root mean square (RMS) voltage, was studied in detail. An analytical model is presented to explain the experimental results. This study, in particular the frequency parameter and the intermittent nature of the applied bias, will help us get a better control over the mass flow process, will lead to better resolutions for the electrolithography process.

Humidity- tunable liquefaction of Cr thin-film and its application to patterning

“…In an earlier study [24], regarding the effect of the frequency of the applied electrical signal on the extent of the said material formation, the following radius-time expression was introduced:…”

“…The electrochemical reaction-based liquefaction process of electrically stressed Cr thin-films has been studied and is known to be affected by different electrical parameters, namely the level of applied electric stress, or the magnitude of the voltage bias applied between the two probes [18]. If an AC signal is applied in between the two probes, the frequency of the applied signal also affects the rate and extent of liquid material formation [24,25]. Focusing on the effect of ambient conditions on the said phenomenon, temperature and pressure has been studied to affect the process significantly [20].…”

Decrypting the thermal effects on the electric field-induced material formation process on Cr thin films

“…The said liquid material formation process has been demonstrated under the effect of both unidirectional and alternating electric fields [14][15][16][17][18]. When using an alternating electric field, the spread of the liquid domain is much more expansive and steadier [16][17][18]. The frequency and other parameters of the applied electric field also play a major role in the process and the most aggressive liquid material formation was observed when a 250 Hz alternating electric field was applied [16][17][18].…”

“…The above-mentioned liquid material formation takes place only in the presence of the applied electric field and stops once the electric field is removed, with the formed material turning into a solid and losing all its liquid components, within a few minutes. The said liquid material formation process has been demonstrated under the effect of both unidirectional and alternating electric fields [14][15][16][17][18]. When using an alternating electric field, the spread of the liquid domain is much more expansive and steadier [16][17][18].…”

“…This liquid material then appears to flow towards the anode in a radially symmetric manner [13][14][15]. Simulation studies in COMSOL have revealed that the radial nature of the apparent material flow arises due to concentric electric potential contours around the cathode probe [16]. The above-mentioned liquid material formation takes place only in the presence of the applied electric field and stops once the electric field is removed, with the formed material turning into a solid and losing all its liquid components, within a few minutes.…”