Electrical characteristics, stability, electromigration, Joule heating, and reliability aspect of focused ion beam fabricated gold and copper nanobar interconnects on SiO2 and glass substrates

The electrical characteristics and stability of rectangular nanobar interconnects are investigated owing to their importance and reliability concern in electronic devices. One dimensional gold and copper nanobars (cross section 150–180 × 80–150 nm2 and length 3.0–5.0 μm), fabricated by milling of respective thin films with a 30 keV Ga+ ion probe (size 10–20 nm) at a current of ∼1 nA, are studied for their current bearing capacity and temperature profile caused by Joule heating. The temperature attained is shown to depend on the length with a maximum lying at the bar center. The electromigration of species (drift velocity for gold being ∼0.92 nm/s) forms void and induces breakage in the bar at a current density of ∼1011 A m−2. The phenomenon is governed by the bar length, prevailing temperature gradient, crystal defects, and grain boundaries. The thermo-migration process facilitates or impedes the electromigration effects depending upon the direction of the thermal gradient and electric field. The I–V characteristics of a gold bar with a gap of ∼44 nm under a vacuum of ∼10−6 mbar follow a classical Child–Langmuir V3/2 law in the voltage range of 10–45 V, but the copper electrodes with a large gap of ∼250 nm (created by ion milling) demonstrate V0.05-dependence up to 32 V, V1/2-law at 39–58 V, and Fowler–Nordheim emission [with an effective area of 1600 nm2 and a field enhancement factor of 8.1] above 66 V.