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

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.