Thin oxide films with perovskite or related structures and with transition metal doping show a reproducible switching in the leakage current with a memory effect. Positive or negative voltage pulses can switch the resistance of the oxide films between a low- and a high-impedance state in times shorter than 100 ns. The ratio between these two states is typically about 20 but can exceed six orders of magnitude. Once a low-impedance state has been achieved it persists without a power connection for months, demonstrating the feasibility of nonvolatile memory elements. Even multiple levels can be addressed to store two bits in such a simple capacitor-like structure.

Combining scanning electron microscopy (SEM) and electron-beam-induced current (EBIC) imaging with transport measurements, it is shown that the current flowing across a two-terminal oxide-based capacitor-like structure is preferentially confined in areas localized at defects. As the thin-film device switches between two different resistance states, the distribution and intensity of the current paths, appearing as bright spots, change. This implies that switching and memory effects are mainly determined by the conducting properties along such paths. A model based on the storage and release of charge carriers within the insulator seems adequate to explain the observed memory effect. 61.16.Bg, 72.20.Jv, 73.40.Rw

A hybrid growth process was developed in order to epitaxially integrate nano-layers of the multi-functional perovskite BaTiO₃ onto Si(001) substrates. In particular, we combined molecular beam epitaxy (MBE) with radio-frequency sputtering. Due to its strong influence on the functional properties, the crystalline structure of the layers was thoroughly investigated throughout our study. MBE-grown seed layers are tetragonal and c-axis oriented up to a thickness of 20 nm. A transition into a-axis films is visible for thicker layers. When the seed layer thickness exceeds 6 nm, subsequently sputtered BaTiO₃ films are epitaxial. However, their crystalline structure, their orientation with respect to the substrate, and their morphology are strongly dependent on the deposition and post-deposition thermal budget. Consistently with their crystalline symmetry, thin MBE BaTiO₃ films are piezo- and ferroelectric with a spontaneous polarization perpendicular to the surface. Also for thick films, the functional response, as determined via piezo-force microscopy, is in good agreement with the structural properties.

Neutron diffraction and magnetic susceptibility experiments were performed on single crystals of the doped Mott-Hubbard insulator LaTiO 3ϩ␦ . The magnetic properties of the three-dimensional correlated electron system were investigated upon hole doping. The size of the ordered moment of Ti 3ϩ in the canted antiferromagnetically ordered phase reaches a maximum of 0.46(2) B for LaTiO 3 . Upon increasing the band filling, i.e., upon increasing the amount of nonstoichiometric oxygen ␦ from 0 to ϳ0.08, the ordered moment on Ti 3ϩ is shown to decrease rapidly. The weak-ferromagnetic saturation moment of LaTiO 3.07(1) , on the verge of the insulator-to-metal transition, is reached via a series of steps in the magnetization curve.

Thin epitaxial films of the high-perovskite SrHfO 3 were grown by molecular beam epitaxy on Si(100) and investigated by ellipsometry and X-ray photoelectron spectroscopy to determine its band gap and valence band offset. Conducting AFM shows a good correlation between topography and current mapping, pointing to direct tunneling conduction. Long channels MOSFETs with low equivalent oxide thickness (EOT) were fabricated and their channel mobility measured. Mobility enhancement can be achieved by post processing annealing in various gases but at the cost of interfacial regrowth. An alternative approach to increase mobility without changing EOT is by electrically stressing the gate dielectric at ~150 o C.