Modified coffee rings for quasi‐1D interconnects

Abstract

Phone: þ1 301 405 0253, Fax: þ1 301 314 2029Silver nanowires (AgNW) in solution with isopropyl alcohol are deposited on photolithographed gratings of varying depth. The deposition results in a modified coffee ring where the flow is redirected along the grating direction. We investigate the anisotropic character of the flow by performing electrical measurements at different concentrations of the nanowires, and for each of the grating depths used. We measure the electrical current along the directions perpendicular and parallel to the gratings. The current anisotropy tends to disappear at higher concentrations. The flow arranges the NW's into a 2D anisotropic arrangement by analyzing how the electrical percolation behaves. By observing the properties this 2D anisotropic arrangement as a function of concentration and grating depth, we can predict where a quasi-1D interconnect can be obtained.

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“…There are two main contributors to this velocity, one that we will call v NCrecirculation and the speed due to the gratings’ depth v NC_X , where X = d / w . [ 1,15 ] The relation can be expressed as …”

“…We now consider the mixture of AgNW and NCNW. There are three competing flows when NCNW and AgNW are combined in a grating: 1) The recirculation flow due to the water [ 13 ] ; 2) The outward radial flow due to the alcohol [ 1,11 ] ; 3) The aspect ratio of the grating, X = d / w . [ 15 ] The depth d of the grating is the most important aspect, if we keep the width w constant.…”

“…Nanowires, specifically AgNW are used to obtain quasi‐1D transparent electrodes. [ 1 ] 1D refers to the fact that the length of the obtained electrode far exceeds its width, and not to the individual AgNWs. The metallic nanowires (NWs) form lyotropic liquid crystals, depending on the concentration.…”

“…[ 11,12 ] Substituting a grating for the flat substrate yields a quasi‐rectangular coffee ring that concentrates the material along the two of the edges due to a differential in the velocities parallel to the grating and perpendicular to the grating. [ 1 ] The differential in the velocities and the orientation of the AgNW, in this case, leads to a differential in the electrical percolation, with percolation occurring between 0.2 and 0.3%wt for gratings that are 0.35 and 0.5 μm deep. [ 1 ] In this article, we investigate if AgNW mixed with the NCNW will yield a similar result.…”

“…[ 1 ] The differential in the velocities and the orientation of the AgNW, in this case, leads to a differential in the electrical percolation, with percolation occurring between 0.2 and 0.3%wt for gratings that are 0.35 and 0.5 μm deep. [ 1 ] In this article, we investigate if AgNW mixed with the NCNW will yield a similar result. We find that the mixture yields ellipsoidal‐shaped coffee rings.…”