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

In the present study, the VO 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 VO 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 VO films with an average thickness of more than 2.0 nm on the SiO/Si substrates exhibit six distinct modes typical of the orthorhombic VO phase. A large hysteresis was found in the - characteristics of the VO films with a thickness of 1.0-4.2 nm. In general, the built-in charge in the VO layers with an average thickness of 1.0-4.0 nm is positive and has a value of about ∼(2-8) × 10 cm at the 1 MHz frequency. Increasing the VO film thickness leads to the accumulation of negative built-in charge up to -(1.7 to 2.3) × 10 cm at the 1 MHz frequency. The temperature dependence of the conductivity exhibits different electrically active states in VO/Si and VO/FG/Si structures. Thus, the FG layer can modify these states. VO 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. VO films with an average thickness of 3.6 nm were found to be particularly stable and promising for memristive switching applications.