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The development of emerging technologies in microelectronics such as magnetic tunnel junction (MTJ) devices, tunneling field-effect transistors (TFETs), and single-electron tunneling transistors (SETs) calls for precise fabrication of ultrathin films down to a few atomic layers. A deep understanding of the physical and chemical mechanisms involved in the formation of such layers is required for successful device fabrication. One popular technique for the formation of thin dielectric barriers critical to MTJs, TFETs, and SETs is atomic layer deposition (ALD), which enables the precise growth of a number of materials down to a single monolayer. We report the use of ALD for SET fabrication to produce ultra-thin (≈ 1 nm) SiO2, Si3N4 and Al2O3 dielectric barriers in metal-insulator-metal (MIM) tunnel junctions. The nanoscale-sized (≈ 20 x 20 nm2) tunnel junctions were fabricated on thermally grown SiO2 substrates by using a combination of high resolution electron beam lithography and metal evaporation to define metal electrodes (source, drain, gate and SET island), and ALD to form tunnel barriers separating them. Several metals (Ni, Pt, Pd) were used to produce SET devices which were electrically tested at temperatures from 300K down to 0.3K. The experimental results reveal the formation of thin layers of non-metal compounds that on the one hand promote ALD growth but on the other hand modify and impede the operation of the devices (e.g. by exponentially increasing device resistance). Several treatment techniques were investigated in order to recover the desired properties of MIM junctions, including hydrogen-based treatments that enable decomposition and/or reduction of parasitic native oxides formed during the ALD process. We report two major research findings. First, our results show that by optimization of device definition techniques and post fabrication treatments it is possible to achieve nearly ideal MIM junction behavior. Second, we demonstrate that MIM SET devices offer a uniquely sensitive characterization platform, enabling the detection of interstitial layers and non-uniformities in nanoscale tunnel junctions.
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