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The conduction process as well as the unipolar resistive switching behavior of Au∕HfO2∕TiN metal-insulator-metal structures were investigated for future nonvolatile memory applications. With current-voltage measurements performed at different temperatures (200–400K), the Poole–Frenkel effect as conduction process was identified. In particular, we extracted a trap energy level at ϕt=0.35±0.05eV below the HfO2 conduction band to which a microscopic origin is tentatively assigned. From current-voltage measurements of Au∕HfO2∕TiN structures, low-power (as low as 120μW) resistive switching was observed. The required forming process is shown to be an energy-induced phenomenon. The characteristics include electric pulse-induced resistive switching by applying pulses up to 100μs and a retention time upon continuous nondestructive readout of more than 104s.

Titanium-added praseodymium silicate layers on Si(001) are promising high-k insulators for silicon-based nanoelectronic devices. Synchrotron radiation x-ray photoelectron spectroscopy was applied to study the effect of titanium additives on the praseodymium silicate/Si system. Nondestructive depth profiling by variation of the photon energy shows that thermal annealing activates the diffusion of deposited titanium into the praseodymium silicate. A homogeneous praseodymium titanium silicate layer is formed that shows high-quality electrical properties.

We report the experimental results on the band alignment of Pr2O3 films on Si(001) as prepared by molecular beam epitaxy. Using x-ray photoelectron spectroscopy, we obtain a valence band offset at the Pr2O3/Si(001) interface of (1.1±0.2) eV. High field tunneling was used to extract the conduction band offset of (0.5–1.5) eV. Thus, the Pr2O3/Si(001) interface band alignment is symmetric, desired for applying such materials in both n- and p-type devices. The band gap of bulk Pr2O3 should be between 2.5 and 3.9 eV. Using scanning tunneling spectroscopy, we find a surface-state band gap of about 3.2 eV for monolayer coverage. In agreement with recent pseudopotential calculations, the electron masses in the oxide appear to be very large. This effect, together with the suitable band offsets lead to the unusually low leakage currents recently measured.

Twin-free epitaxial cubic (111) praseodymium sesquioxide films were prepared on Si(111) by hexagonal-to-cubic phase transition. Synchrotron radiation grazing incidence x-ray diffraction and transmission electron microscopy were applied to characterize the phase transition and the film structure. As-deposited films grow single crystalline in the (0001)-oriented hexagonal high-temperature phase of praseodymium sesquioxide. In situ x-ray diffraction studies deduce an activation energy of 2.2eV for the hexagonal-to-cubic phase transition. Transmission electron microscopy shows that the phase transition is accompanied by an interface reaction at the oxide/Si(111) boundary. The resulting cubic (111) low-temperature praseodymium sesquioxide film is single crystalline and exclusively shows B-type stacking. The 180° rotation of the cubic oxide lattice with respect to the Si substrate results from a stacking fault at the substrate/oxide boundary.