Rapid Nanomanufacturing of Metallic Break Junctions Using Focused Ion Beam Scratching and Electromigration

[+] Author and Article Information
Waseem Asghar, Adegbenro Adewumi, Mohammud R. Noor

Department of Electrical Engineering, Nanotechnology Research and Teaching Facility, University of Texas at Arlington, Arlington, TX 76019

Priyanka P. Ramachandran1

Department of Bioengineering, Nanotechnology Research and Teaching Facility, University of Texas at Arlington, Arlington, TX 76019

Samir M. Iqbal2

Department of Electrical Engineering, Nanotechnology Research and Teaching Facility, Joint Graduate Committee of Biomedical Engineering Program, University of Texas at Arlington and University of Texas Southwestern Medical Center at Dallas, University of Texas at Arlington, Arlington, TX 76019smiqbal@uta.edu


Present address: Department of Molecular Pathology, University of Texas MD Anderson Cancer Center, Houston, TX.


Corresponding author.

J. Manuf. Sci. Eng 132(3), 030911 (Jun 03, 2010) (4 pages) doi:10.1115/1.4001664 History: Received January 18, 2010; Revised April 20, 2010; Published June 03, 2010; Online June 03, 2010

Break junctions provide a direct way to interrogate electrical transport properties of molecules, in pursuit of molecular electronics devices. A number of approaches are used for the fabrication of break junctions, including optical/e-beam lithography, electromigration, mechanical control of suspended conductive electrodes/strips, and electrochemical deposition of conductive material and nanowires. All approaches either require serial and slow e-beam writing of nanoscale gaps or suffer from low-yield of nanogap electrode devices. Here, we report the use of focused ion beam (FIB) to “scratch” and remove a thin layer of gold from 3μm wide lines. The scratch results in thinning of the metal line and subsequent current-driven electromigration results into nanogaps at precise locations with high yield of devices. Combining FIB scratching with electromigration provides an elegant approach of creating nanoscale break junctions at an exact location and with a very narrow distribution of the nanogap sizes. Current-voltage measurements are done using a probe station before and after FIB scratch, and after the breaks were formed. Most of the gaps fall within 200–300 nm range and show negligible conductivity. The approach provides a novel, rapid, and high-throughput manufacturing approach of break junction fabrication that can be used for molecular sensing.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 3

Representative I-V data of metal lines after the FIB scratch. Inset shows the drop in current through the metal line as the electromigration resulted in complete break of the metal line resulting into nanoscale break junctions.

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Figure 4

SEM micrograph showing the nanogap between the gold electrodes

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Figure 5

The comparison of I-V measurements before and after the break

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Figure 6

The measured conductance (after break) plotted against the gaps between two electrodes of break junctions. Distribution of the devices showed that most of the gaps were in the range of 100–300 nm.

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Figure 2

SEM micrographs showing FIB scratches at different accelerating voltages, milling currents and time of scratching exposure: (a) 30 kV, 100 pA, 120 s; (b) 30 kV, 20 pA, 120 s; and (c) 30 kV, 1 pA, 60 s. Inset to (c) shows an angled magnified view of the FIB scratch.

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Figure 1

SEM micrograph of gold metal line defined with optical lithography



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