Thin V2O5 films synthesized by plasma-enhanced atomic layer deposition for memristive applications

Abstract

In the present study, the V₂O₅ films synthesized by plasma-enhanced atomic layer deposition on p-Si and fluorinated graphene on Si (or FG/Si) substrates were analyzed for memristive applications. A number of samples were grown with V₂O₅ films with an average thickness of 1.0–10.0 nm, as determined by ellipsometric measurements. The study of surface morphology by atomic force microscopy showed that an island growth occurs in the initial stages of the film growth. The Raman spectra of the synthesized V₂O₅ films with an average thickness of more than 2.0 nm on the SiO₂/Si substrates exhibit six distinct modes typical of the orthorhombic V₂O₅ phase. A large hysteresis was found in the C–V characteristics of the V₂O₅ films with a thickness of 1.0–4.2 nm. In general, the built-in charge in the V₂O₅ layers with an average thickness of 1.0–4.0 nm is positive and has a value of about ∼(2–8) × 10¹¹ cm⁻² at the 1 MHz frequency. Increasing the V₂O₅ film thickness leads to the accumulation of negative built-in charge up to −(1.7 to 2.3) × 10¹¹ cm⁻² at the 1 MHz frequency. The temperature dependence of the conductivity exhibits different electrically active states in V₂O₅/Si and V₂O₅/FG/Si structures. Thus, the FG layer can modify these states. V₂O₅ layers with an average film thickness of 1.0–3.6 nm demonstrate the memristive switching with an ON/OFF ratio of ∼1–4 orders of magnitude. At film thicknesses above 5.0 nm, the memristive switching practically vanishes. V₂O₅ films with an average thickness of 3.6 nm were found to be particularly stable and promising for memristive switching applications.