Kuibo Yin

Nonvolatile memory devices with Cu2S and Cu-Pc bilayered films

An organic bistable device with a structure Cu∕Cu2S/copperphthalocyanine (Cu-Pc)∕Pt was fabricated. Compared to the single layer organic device composed of Cu∕Cu-Pc∕Pt, the bilayer devices were observed to show distinct bistability with the resistance ratio of the off/on states up to 107 and low switch voltage (0.75–0.85V). At least 105 switching cycles were achieved in the “write-read-erase-read” cycle voltage. The filament mechanism for the device is supported by the “metallic” behavior in their temperature dependence of the resistance in the on state. Such a memory device provides a promising structure for the nonvolatile memory.

Resistive switching devices based on nanocrystalline solid electrolyte (AgI)0.5(AgPO3)0.5

Resistive switching devices with a sandwich structure Ag∕(AgI)0.5(AgPO3)0.5∕Pt were fabricated on silicon(001) wafer by using the pulsed laser deposition method and the focused ion beam nanofabrication technique. (AgI)0.5(AgPO3)0.5 films deposited at room temperature show a nanocrystal structure and the composition of the films was identified by using x-ray photoelectron spectroscopy. The current-voltage characteristics of the Ag∕(AgI)0.5(AgPO3)0.5∕Pt memory units show good switching behaviors. The ratio of the conductance between the “ON” state (high conductance) and the “off” state (low conductance) reaches 1×106. The ON and OFF states can be effectively written, read, and erased up to 4×105 scanning cycles by using a set of voltage pulses with an amplitude less than 3V. It also could be observed that the time for the writing and erasing operations could be less than 150ns. The switching mechanism of the Ag∕(AgI)0.5(AgPO3)0.5∕Pt memory devices was ascribed to the possible formation and dissolution of Ag...

Electrical field induced precipitation reaction and percolation in Ag30Ge17Se53 amorphous electrolyte films

The microstructural evolution and resistive switching of glassy Ag30Ge17Se53 electrolyte films clipped by Ag active electrode, at which a positive bias was applied, and Pt inert electrode, were investigated by transmission electron microscopy observations and I-V measurements as functions of the period of electrical field treatment. It is revealed that an electrical field induced precipitation reaction forming conductive particles with orthorhombic Ag2Se structure and followed growth and networking of these particles, leading to an electrical percolation, are responsible for the transition from high resistive to high conductive state of the system. The kinetics of the precipitation reaction was also analyzed.

The thermal stability and electrical properties of LaErO3 films as high-k gate dielectrics

Lanthanum erbium oxide thin films have been deposited on an Si (1 0 0) wafer by using the pulsed laser deposition technique. The thermal and electrical properties of LaErO3 films were investigated by x-ray diffraction, x-ray photoelectron spectroscopy and high resolution transmission electron microscopy. Capacitance measurements reveal good C–V curves with an equivalent oxide thickness of 1.4 nm and little hysteresis. Transmission electron microscopic images reveal that the 6.5 nm LaErO3 film shows a thin interfacial layer even after being annealed in N2 at 700 °C for 30 s. X-ray photoelectron spectroscopic spectra indicate that little SiO2 was formed at the interface during the deposition of LaErO3 films. The measured thermal and electrical properties of the thin film suggest that the LaErO3 film should be a promising candidate for future high-k gate dielectrics.

Studies of two distinct types of (Ba,Sr)TiO3∕Pt interfaces

High resolution transmission electron microscopy is used to investigate the interfacial layer at interfaces between (001) (Ba,Sr)TiO3 (BST) films and (111) Pt electrodes. Two distinct types of interfaces are observed. One case is the presence of interfacial layer with distorted structure, whereas another case is the good interfacial match without any interfacial layer. Based on the analyses of crystallographic relationships between BST and Pt, it is proposed that the in-plane lattice structure plays an important role in determining the feature of the interface. The impact of A-O and B-O terminations of BST films on the interfacial layer is also discussed.

Effect of NH3 and N2 annealing on the interfacial and electrical characteristics of La2O3 films grown on fully depleted SiGe-on-insulator substrates

The interfacial structure and the electrical properties of pulsed laser deposition derived La2O3 ultra-thin films on fully depleted SiGe-on-insulator (FD SGOI) substrates before and after post-annealing in NH3 and N2, respectively, have been investigated comparatively. The results from high-resolution transmission electron microscopy and x-ray photoelectron spectroscopic revealed that interface reactions take place after the NH3 and N2 annealing process, but, as compared with the N2 annealing process, the NH3 annealing process can effectively decrease the thickness of the interfacial layer and incorporate more nitrogen at the dielectric/SiGe interface, resulting in smaller equivalent oxide thickness. The La2O3 capacitors annealed in NH3 show good capacitance–voltage characteristics with negligible hysteresis, smaller interface trap density and lower gate-leakage current density in comparison with those of capacitors annealed in N2. It is demonstrated that the NH3 annealing process can be a promising technology in improving the quality of high-k dielectric on FD SGOI substrates.

Characterization of RbAg4I5 films prepared by pulsed laser deposition

RbAg4I5 solid electrolyte films have been prepared using the pulsed laser deposition technique. Their structures have been characterized by x-ray diffraction, and the surface and cross-section morphologies have been investigated by using scanning electron microscopy. It was found that larger energy density of the laser beam favoured the crystallization of RbAg4I5 particles and increased the resistance of the off state, and lower energy density of the laser beam induces the appearance of the AgI phase in the films and reduces the resistance of the off state. A narrow window of the substrate temperature (around 80 °C) for the deposition of pure RbAg4I5 films has also been observed. The RbAg4I5 film deposited on Pt/TiO2/SiO2/Si(1 1 1) substrates at 80 °C shows a uniform and flat surface. All the RbAg4I5 memory devices show obvious resistive switching behaviour.

Electrical hysteresis of the Ti0.25Al0.75Ox dielectric films after high-temperature treatment

The primary goal of this work is to investigate the electrical hysteresis of dielectric pseudobinary Ti0.25Al0.75Ox films after high-temperature treatment. The Ti0.25Al0.75Ox films show electrical hysteresis in the C-V measurements after high-temperature treatment. The C-V curves shifting to positive flatband voltage indicate the existence of negative fixed charges in the films. By virtue of high-resolution transmission electron microscopy, it is deduced that the films include several nanosized crystals regions, which are attributed to the hexagonal unreacted Al2O3 and orthorhombic solid state reaction product TiAl2O5 after high-temperature treatment. While the annealing treatment is up to 900°C, the preferable crystal direction is the direction perpendicular to the c axis in the orthorhombic TiAl2O5 lattice.

Conductance switching effect in the Cu/CuI0.76S0.14/Pt structure

We have proposed a novel memory device with the Cu/CuI0.76S0.14/Pt structure. The intermediate non-stoichiometric film is prepared by pulsed laser deposition. This compound is found with the zincblende structure at room temperature by using x-ray diffraction. Conductance?voltage characteristics reveal that a switching effect exists when the polarity of the voltage biased is changed. By applying a voltage of +0.5?V on the copper electrode, our device is switched on while ?0.8?V induces the OFF-state. The switching operation could be repeated at least 103 times, and the GON/GOFF ratio is more than 3 ? 103. It is expected to be a promising model of nonvolatile memories. With the TEM study, we have analysed the migration of Cu+, S2? and I? under an electric field and attribute the switching effect to the formation and annihilation of ionic conducting paths.