C. Dubourdieu

Stabilization of the cubic phase of HfO2 by Y addition in films grown by metal organic chemical vapor deposition

Addition of yttrium in HfO2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range (2.0–99.5at.%). The cubic structure of HfO2 is stabilized for 6.5at.%. The permittivity is maximum for yttrium content of 6.5–10at.%; 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 (5×10−7A∕cm2 at −1V for a 6.4nm film). The cubic phase is stable upon postdeposition high temperature annealing at 900°C under NH3.

Microstructure and electrical characterizations of yttrium oxide and yttrium silicate thin films deposited by pulsed liquid-injection plasma-enhanced metal-organic chemical vapor deposition

Results on yttrium oxide and yttrium silicate films elaborated by an innovative metal-organic chemical vapor deposition process combining plasma assistance and a liquid precursor supply setup are presented. Plasma assistance enables deposition at a much lower substrate temperature and the pulsed-liquid precursor source allows an accurate control of the injected reactive species. According to x-ray photoelectron spectroscopy (XPS) analyses, we show that ultrathin yttrium oxide deposition can be performed at temperature less than 380°C. Yttrium oxide films contain carbon contamination that can be reduced by increasing the deposition temperature. The plasma plays a key role in the deposition mechanisms and thus in the chemical structure of the films and of the interface. It is shown that the injection frequency, i.e., the reactive species incoming frequency, plays a significant role in the silicate and interface formation. A detailed study is presented using angle-resolved XPS. A high injection frequency lim...

Structural and Electrical Characterizations of Yttrium Oxide Films after Postannealing Treatments

We investigated annealing effects on yttrium oxide films elaborated at 350°C by pulsed injection plasma-enhanced metallorganic chemical vapor deposition. A certain amount of carbon is present in the as-deposited layers due to incomplete metallorganic precursor decomposition. Because the carbon is known to be disadvantageous for the dielectric permittivity, several annealing post-treatments (under Ar or O 2 at 700°C and under H 2 at 450°C during 30 min at atmospheric pressure) were performed. Chemical modifications in the yttrium oxide layer and also at the interface were investigated combining several analyses [as infrared spectroscopy, (angle-resolved) X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy, and Rutherford backscattering spectrometry] carried out on thick and thin films (respectively, ∼40 and ∼5 nm). High-temperature post-treatments result in a significant reduction of carbon content. However, the presence of oxygen at high temperature (even for low residual oxygen partial pressure) involves SiO 2 formation at the interface and leads to the transformation of the yttrium oxide into Y-based silicates, which, for the thin films, results in the absence of Y 2 O 3 crystalline phase. The H 2 /450°C anneal does not modify the films chemical nature except for a significant reduction of hydrogen content. After annealing under H 2 /450°C, a strong improvement of the capacitance behavior is observed, especially on the thin films.

Effect of substitution of Ti by Zr in BaTiO3 thin films grown by MOCVD

Abstract Thin films of the solid solution BaTiO3–BaZrO3 were studied. Such lead-free, environmental friendly materials are known, from dielectric measurements, to exhibit relaxor behaviour in bulk materials with increasing the Zr content. Ba[Ti(1−x)Zrx]O3 thin films with various x values were prepared by liquid injection MOCVD by varying the corresponding x′ value in solution (from 0.00 to 0.80). The films were studied by X-ray diffraction, Raman spectroscopy and microprobe analysis. A single perovskite phase with a linear evolution of the out-of-plane lattice parameter was identified by X-ray diffraction up to x′=0.25. For higher Zr contents a secondary ZrO2 phase was detected. Raman spectroscopy was used to follow the subtle evolution of the crystal structure as a function of the chemical composition. The dielectric properties of single-phase layers were investigated in the range 20–600xa0K and 0.02–100xa0kHz. For some composition, the measured dielectric constant displayed a frequency-dependent behaviour.

Crystallization and related magnetotransport properties of amorphous manganite films grown by metalorganic chemical vapor deposition

La1−xSrxMnO3 films were grown at 450u200a°C by pulsed liquid-injection metalorganic chemical vapor deposition on silicon substrates. The films were amorphous and exhibited a high resistivity (> 10 kΩu200acm). Different kinds of annealing (650u200a°C for 1, 3, 6, and 10 h, 800u200a°C for 15 mn, 900u200a°C for 5 mn, and rapid thermal annealings) were performed in order to achieve crystallization through both variations of nucleation and growth rates. X-ray diffraction and transmission electron microscopy were used to characterize the different microstructures obtained. After annealing, the perovskite La1−xSrxMnO3 (x∼0.3) phase was obtained. The resistivity of the films ranged within two orders of magnitude depending on the annealing temperature and time. The magnetoresistive properties were also recovered and similar to those obtained on as-grown polycrystalline films. The rapid thermal annealing process proved to be efficient: the amorphous films exhibited, after a 90 s flash-annealing, an ordering temperature of 340 K, a res...

Structure and properties of artificial [(La0.7Sr0.3MnO3)m(SrTiO3)n]15 superlattices on (001)SrTiO3.

Complex [(La0.7Sr0.3MnO3)m(SrTiO3)n]u200a[(LSMO)m/(STO)8]15 superlattices with different layer thicknesses (m=5,u20098,u200912,u200916,u200932) have been prepared using pulsed liquid injection metalorganic chemical vapor deposition. Transmission electron microscopy and electron diffraction reveal a very clear and well-separated layer sequence. The remarkable microstructure, as well as the ferromagnetic transition temperature, depends on the LSMO layer thickness. Apart from a very clear layer sequence, electron microscopy shows evidence of a self-assembled nanostructure formation: SrMnO3 nanoinclusions and associated SrTiO3–SrMnO3 thin walls. A formation model and growth mechanism for the self-assembled structure is proposed, based on high resolution and energy filtered elemental imaging.

Evidence of the magnetoimpedance effect up to microwave frequencies in polycrystalline La0.7Sr0.3MnO3 films

We present broadband measurements of the magnetoimpedance of polycrystalline La0.7Sr0.3MnO3 films grown on silicon as a function of three parameters: (i) the frequency (0–1GHz), (ii) the temperature (4–275K), and (iii) the applied magnetic field (0–6T). In this paper it is evidenced that the magnetoresistive effect still exists up to 1GHz. The impedance variation with the frequency is well modeled considering that the polycrystalline film is equivalent to a random resistive-capacitive network. Similar behaviors of the impedance versus temperature variation are observed in dc and high frequency range.

Structure and properties of artificial [(La_{0.7}Sr_{0.3}MnO_{3})_{m}(SrTiO_{3})_{n}]_{15} superlattices on (001)SrTiO_{3}

Complex [(La0.7Sr0.3MnO3)m(SrTiO3)n]u200a[(LSMO)m/(STO)8]15 superlattices with different layer thicknesses (m=5,u20098,u200912,u200916,u200932) have been prepared using pulsed liquid injection metalorganic chemical vapor deposition. Transmission electron microscopy and electron diffraction reveal a very clear and well-separated layer sequence. The remarkable microstructure, as well as the ferromagnetic transition temperature, depends on the LSMO layer thickness. Apart from a very clear layer sequence, electron microscopy shows evidence of a self-assembled nanostructure formation: SrMnO3 nanoinclusions and associated SrTiO3–SrMnO3 thin walls. A formation model and growth mechanism for the self-assembled structure is proposed, based on high resolution and energy filtered elemental imaging.

Twinning orientation in YBa2Cu3O7−x films deposited on YAlO3 substrates

An x‐ray diffraction study of YBa2Cu3O7−x (YBCO) films deposited on YAlO3 (001) substrates by metal organic chemical vapor deposition is reported. The twinning orientation of YBCO on YAlO3 is compared to the one observed for films deposited on MgO (001), SrTiO3 (001), and LaAlO3 (012) substrates. The φ scans performed on hhl type reflections and the grazing incidence x‐ray diffraction on the 020/200 reflections of YBCO reveal a particular epitaxial relationship on YAlO3: there is only one twinning direction relatively to the substrate. The [110] and [110] directions of YBCO are aligned with the [010] direction of YAlO3. This twinning geometry may be explained by coherency strains.

Application of pulsed liquid-injection MOCVD to the growth of ultrathin epitaxial oxides for magnetic heterostructures

We illustrate the capabilities of pulsed-liquid injection metal–organic chemical vapor deposition in the nano-engineering of complex oxides with results obtained on (La0.7Sr0.3MnO3/SrTiO3)15 (LSMO/STO) superlattices. Superlattices with ultrathin films of a few monolayers have been successfully prepared, as shown by synchrotron radiation diffraction experiments. Laue oscillations were observed between the satellite peaks, indicating a smooth upper surface. Sets of superlattices with varying LSMO or STO thickness were synthesized on different substrates (LaAlO3, SrTiO3, MgO). By varying the relative thickness of each compound and changing the substrate, the strain in the stackings could be changed.