The resistance switching properties in Pt∕Ni–O∕Pt and Pt∕Co–O∕Pt synthesized by the magnetron sputtering have been investigated. The oxygen partial pressure during sputtering and the post-thermal process are crucial to forming of the trilayer. By investigating x-ray photoemission spectroscopy spectra, the increase of initial resistance in Ni–O was caused by the variation of the stoichiometry, while that in the Co–O was accompanied by the phase transformation between CoO and Co3O4. The resistance switching in Pt∕Co–O∕Pt and Pt∕Ni–O∕Pt exhibits the analogous electrode area and temperature dependences. As a result of the I-V measurements at the elevated temperature, the assistance of Joule heating in the reset process is implied.

Structural and resistance switching properties were investigated in the CoO resistance random access memory (RRAM) with the Ta electrode. The intermediate layer consisting of Co and Ta oxides was confirmed at the interface by the transmission electron microscopy and electron energy loss spectroscopy. The great affinity with oxygen in Ta together with a high resistivity of the Ta oxide improves the operational performance of RRAM. The controllability of the resistance after forming and the low-current operation property were substantially improved by using the load resistor connected in series with CoO RRAM with the Ta electrode. The reset current less than 0.2 mA and the switching speed faster than 20 ns were demonstrated.

We have recently developed a method to fabricate monodispersed Ni/NiO core-shell nanoparticles by pulsed laser ablation. In this report, the size-dependent magnetic properties of monodispersed Ni/NiO core-shell nanoparticles were investigated. These nanoparticles were formed in two steps. The first was to fabricate a series of monodispersed Ni nanoparticles of 5 to 20 nm in diameter using a combination of laser ablation and size classification by a low-pressure differential mobility analyzer (DMA). The second step was to oxidize the surfaces of the Ni particles in situ to form core-shell structures. A superconducting quantum interference device (SQUID) magnetometer was used to measure the magnetic properties of nanostructured films prepared by depositing the nanoparticles at room temperature. Ferromagnetism was observed in the magnetic hysteresis loop of the nanostructured films composed of core-shell nanoparticles with core diameters smaller than the superparamagnetic limit, which suggests the spin of Ni core was weakly exchange coupled with antiferromagnetic NiO shell. In contrast, smaller nanoparticles with core diameters of 3.0 nm exhibited superparamagnetism. The drastic change in the hysteresis loops between field-deposited and zero-field-deposited samples was attributable to the strong anisotropy that developed during the magnetic-field-assisted nanostructuring process.

The resistance switching in Pt/Co-O/Pt trilayers has been successfully demonstrated. The trilayers were prepared by radiofrequency magnetron sputtering. The partial pressure of oxygen during sputtering and the post thermal process for the trilayer are crucial to realize the reproducible resistance switching. By adjusting oxygen partial pressure as well as post-annealing temperature and time, large resistance switching was steadily obtainable in both the as deposited and post-annealed Pt/Co-O/ Pt trilayers. The resistance switching ratio exceeds 10 3 , being sufficiently large for the resistance random access memory (RRAM). Co-O is regarded as a very promising oxide for RRAM having compatibilities with the conventional complementary metal-oxide semiconductor process.

The Pt∕TiOx∕Pt trilayer with electrically asymmetrical interface have been synthesized by means of the reactive sputtering technique followed by the oxygen annealing. The initial current-voltage characteristics in the Pt∕TiOx∕Pt trilayer cell have rectifying behavior originated from the Schottky junction formed between TiOx and Pt top electrode layer. The series connection of Pt∕TiOx∕Pt trilayer cells brings about the control of the reset and set voltages depending on the resistance of the connected Schottky diode, which is the demonstration of the resistance switching in the resistance random access memory with the one diode and one resistance structure using Schottky barrier diode.