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We report the use of plasma-enhanced atomic layer deposition (PEALD) tofabricate single-electron transistors (SETs) featuring ultra-thin (~1 nm)tunnel-transparent SiO2 in Ni-SiO2-Ni tunnel junctions. We show that as aresult of the O2 plasma steps in PEALD of SiO2, the top surface of theunderlying Ni electrode is oxidized. Additionally, the bottom surface of theupper Ni layer is also oxidized where it is in contact with the deposited SiO2,most likely as a result of oxygen-containing species on the surface of theSiO2. Due to the presence of these surface parasitic layers of NiO, whichexhibit features typical of thermally activated transport, the resistance ofNi-SiO2-Ni tunnel junctions is drastically increased. Moreover, the transportmechanism is changed from quantum tunneling through the dielectric barrier toone consistent with thermally activated resistors in series with tunneljunctions. The reduction of NiO to Ni is therefore required to restore themetal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealingin a forming gas ambient at elevated temperatures is presented as a techniqueto reduce both parasitic oxide layers. This method is of great interest fordevices that rely on MIM tunnel junctions with ultra-thin barriers. Using thistechnique, we successfully fabricated MIM SETs with minimal trace of parasiticNiO component. We demonstrate that the properties of the tunnel barrier innanoscale tunnel junctions can be evaluated by electrical characterization ofSETs.

Experimental Demonstration of Single Electron Transistors Featuring SiO2 PEALD in Ni-SiO2-Ni Tunnel Junctions