Epitaxial growth of SrTiO₃ on silicon by molecular beam epitaxy has opened up the route to the integration of functional complex oxides on a silicon platform. Chief among them is ferroelectric functionality using perovskite oxides such as BaTiO₃. However, it has remained a challenge to achieve ferroelectricity in epitaxial BaTiO₃ films with a polarization pointing perpendicular to the silicon substrate without a conducting bottom electrode. Here, we demonstrate ferroelectricity in such stacks. Synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy reveal the presence of crystalline domains with the long axis of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and are reversibly switched with a phase change of 180°. Open, saturated hysteresis loops are recorded. Thus, ferroelectric switching of 8- to 40-nm-thick BaTiO₃ films in metal-ferroelectric-semiconductor structures is realized, and field-effect devices using this epitaxial oxide stack can be envisaged.

Memristive devices, whose conductance depends on previous programming history, are of significant interest for building nonvolatile memory and brain-inspired computing systems. Here, we report half-integer quantized conductance transitions G = (n/2) (2e(2)/h) for n = 1, 2, 3, etc., in Cu/SiO2/W memristive devices observed below 300 mV at room temperature. This is attributed to the nanoscale filamentary nature of Cu conductance pathways formed inside SiO2. Retention measurements also show spontaneous filament decay with quantized conductance levels. Numerical simulations shed light into the dynamics underlying the data retention loss mechanisms and provide new insights into the nanoscale physics of memristive devices and trade-offs involved in engineering them for computational applications.

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Addition of yttrium in HfO 2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range ͑2.0-99.5 at. % ͒. The cubic structure of HfO 2 is stabilized for 6.5 at. %. The permittivity is maximum for yttrium content of 6.5-10 at. %; in this range, the effective permittivity, which results from the contribution of both the cubic phase and silicate phase, is of 22. These films exhibit low leakage current density ͑5 ϫ 10 −7 A/cm 2 at −1 V for a 6.4 nm film͒. The cubic phase is stable upon postdeposition high temperature annealing at 900°C under NH 3 .

SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide–semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.

In this paper, the authors focus on two well-identified switching mechanisms, namely, interfacial (or homogeneous) switching and filamentary switching. These switching mechanisms have been reported in various devices, but a broader analysis remains to be conducted. By comparing the performances of TiO2- and HfO2-based resistive switching devices in terms of variability, retention, controllability, and switching energy, the authors discuss how oxygen vacancies organization can determine a general set of properties that will define the range of applications that could be envision for each material/device technology.

An epitaxial layer of SrTiO3 grown directly on Si may be used as a pseudo-substrate for the integration of perovskite oxides onto silicon. When SrTiO3 is initially grown on Si (001), it is nominally compressively strained. However, by subsequent annealing in oxygen at elevated temperature, an SiOx interlayer can be formed which alters the strain state of SrTiO3. We report a study of strain relaxation in SrTiO3 films grown on Si by molecular beam epitaxy as a function of annealing time and oxygen partial pressure. Using a combination of x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy, we describe the process of interfacial oxidation and strain relaxation of SrTiO3 on Si (001). Understanding the process of strain relaxation of SrTiO3 on silicon will be useful for controlling the SrTiO3 lattice constant for lattice matching with functional oxide overlayers.

The magnetic anisotropy of (001) oriented La0.7Sr0.3MnO3 films of thickness t=7–156 nm, deposited on LaAlO3 substrates, was measured by torque magnetometry in the temperature range T=10–300 K. For t⩾50 nm and H rotating out of plane the anisotropy Ku agrees well with shape anisotropy. For thinner films, Ku is reduced and its sign is reversed for t=7 nm and T<70 K; this can be explained by a perpendicular anisotropy Kuε due to lattice strain. The crystal anisotropy constant K1 was determined from the biaxial in-plane anisotropy. At T=100 K K1 differed by no more than 50% from the mean value −8 kJ/m3 in the thickness region investigated. K1 was much less dependent on the thickness t and strain relaxation in the films than Kuε.