The unipolar resisitive switching properties of MOCVD deposited NiO in Ni/NiO/TiN stacks is reported. The switching quality is defined as function of RESET current and Roff/Ron ratio, and the importance of the Forming current and voltage on these parameters is discussed. The effect of structural stack variations as NiO thickness, Ti doping, and TiN thickness on the switching behavior of NiO is explained by the effect on the forming current and voltage conditions, and on Joule heating dissipation. Thinner NiO films, Ti doping, as well as thicker top electrode improve the switching quality by decreasing the RESET current and increasing the Roff/Ron ratio.

We present the memory performance of devices with bistable electrical behavior based on MEH-PPV (Poly (1-methoxy-4-(2-ethylhexyloxy)-p-phenylenevinylene)) containing metal (Zn or Fe-Ni) particles. Another memory device based on aluminum phthalocyanine chloride (PcAlCl) added to the composite material reveals the photoinduced switching, in addition to the electrical one. Possible mechanisms for resistive switching are discussed.

We investigated the resistive switching behavior of WOx films. WOx was obtained from the thermal oxidation of W thin layers. The parameters under investigation were the influence of the temperature (450-500 °C) and time (30-220 s) used to obtain the WOx on the resistive switching characteristics of Si\W\WOx\Metal_electrode ReRAM cells. The metal top electrodes (TE) tested were Pt, Ni, Cu and Au. The elemental composition and microstructure of the samples were characterized by means of elastic recoil detection analysis (ERD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray reflectivity (XRR).

Electrical measurement of the WOx-based memory elements revealed bipolar and unipolar switching and this depended upon the oxidation conditions and TE selected. Indeed, switching events were observed in WOx samples obtained either at 450 °C or 500 °C in time windows of 180-200 s and 30-60 s, respectively. Pt and Au TE promoted bipolar switching while unipolar behavior was observed with Ni TE only; no switching events were observed with Cu TE. Good switching characteristics seems not related to the overall thickness, crystallinity and composition of the oxide, but on the W6+/W5+ ratio present on the WOx surface, surface in contact with the TE material. Interestingly, W6+/W5+ ratio can be tuned through the oxidation conditions, showing a path for optimizing the properties of the WOx-based ReRAM cells.

Three synthesis techniques have been explored as routes to produce copper oxide for use in resistive memory devices (RMDs). The major results and their impact on device current-voltage characteristics are summarized. The majority of the devices fabricated from thermally oxidized copper exhibited a diode-like behavior independent of the top electrode. When these devices were etched to form mesa structures, bipolar switching was observed with set voltages <2.5 V, reset voltages <(-1) V and ROFF/RON ∼103-104. Bipolar switching behavior was also observed for devices fabricated from copper oxide synthesized by RT plasma oxidation (ROFF/RON up to 108). Voiding at the copper-copper oxide interface occurred in films produced by thermal and plasma oxidation performed at ≥200°C. The copper oxide synthesized by reactive sputtering had large areas of open volume in the microstructure; this resulted in short circuited devices because of electrical contact between the bottom and top electrodes. The results for fabricating copper oxide into ≤100 nm features are also discussed.