The improvement of pyroelectric properties of PZT thick films on Si substrate by TiOx barrier layer

The effects of TiO_x diffusion barrier layer thickness on the microstructure and pyroelectric characteristics of PZT thick films were studied in this paper. The TiO_x layer was prepared by thermal oxidation of Ti thin film in air and the PZT thick films were fabricated by electrophoresis deposition method (EPD). To demonstrate the barrier effect of TiO_x layer, the electrode/substrate interface and Si content in PZT thick films were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The TiO_x barrier thickness shows significant influence on the bottom electrode and the pyroelectric performance of the PZT thick films. The average pyroelectric coefficient of PZT films deposited on 400 nm TiO_x layer was about 8.94 × 10⁻⁹ C/(cm² K), which was improved by 70% than those without diffusion barrier layer. The results showed in this study indicate that TiO_x barrier layer has great potential in fabrication of PZT pyroelectric device.     

XPS and SIMS characterisation of TiOxNy solar absorber films

Solar thermal collectors have been prepared with thin TiO_xN_y films deposited using ion beam assisted deposition, on Si and Cu substrates. The films are amorphous and x and y were controlled by altering the O₂/N₂ ratio in the gas source. After annealing at temperatures of 200 – 400 °C, films have been depth profiled using Secondary Ion Mass Spectrometry. Profiles reveal the degradation of the film, particularly for films on Cu substrates, by migration of the substrate atoms through the films, to the sample surface. In general, films with x<1 and y>1 show improved temperature stability, ultimately at the expense of a reduced transmission window. Contrary to previous suggestions in the literature, the degradation mechanism initially involves the formation of a nitrogen rich phase, rather than an oxide at the film surface. On copper substrates, the nature of the films and of this phase, formed by diffusion of the substrate atoms, have been investigated by X-ray photoelectron spectroscopy (XPS). These investigations reveal complex behaviour in the early stages of film failure, with the suggestion that the initial films, at least near the surface, are two phase, and the reaction layer mixes the TiO_xN_y with some Ti replacement by ions from the Cu substrate.     

TiSi2薄膜形成中扩散标记的研究

用Xe离子注入作扩散标记,确定了TiSi₂薄膜形成过程中主要扩散元素是Si。应用Kidson和Tu推导的方程根据试验结果计算了600℃退火TiSi₂形成中Si和Ti的扩散系数。 关键词：     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Polarization characteristics of graded thick Ba<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> films

The barium strontium titanate ceramics Ba_{1 − x} Sr _x TiO₃ with a spatially variable composition has been prepared according to the thick film technology (tape casting). The strontium content over the film thickness is varied from 0 to 30 mol %. The structure and polarization characteristics of the samples prepared have been investigated. It has been found that the polarization characteristics of multilayer structures are determined by the ratio between the thicknesses of layers with different compositions and by their properties. No shift of the hysteresis loops in the graded thick Ba_{1 − x} Sr _x TiO₃ ( _x = 0–0.3) films has been revealed. The results obtained have been analyzed in the framework of modern theoretical approaches.     

Reaction products and oxide thickness formed by Ti out-diffusion and oxidization in poly-Pt/Ti/SiO2/Si with oxide films deposited

In the paper, we present experimental results to enhance the understanding of Ti out-diffusion and oxidization in commercial poly-Pt/Ti/SiO₂/Si wafers with perovskite oxide films deposited when heat-treated in flowing oxygen ambient. It indicates that when heat-treated at 550 and 600 °C, PtTi₃+PtTi and PtTi are the reaction products from interfacial interaction, respectively; while heat-treated at 650 °C and above, the products become three layers of titanium oxides instead of the alloys. Confirmed to be rutile TiO₂, the first two layers spaced by 65 nm encapsulate the Pt surface by the first layer with 60 nm thick forming at its surface and by the next layer with 35 nm thick inserting its original layer. In addition, the next layer is formed as a barrier to block up continuous diffusion paths of Ti, and thus results in the last layer of TiO_2−x formed by the residual Ti oxidizing.     

An XPS study on ion beam induced oxidation of titanium silicide

Titanium silicides (TiSi₂) films grown on Si(1 0 0) substrate were investigated by ex situ XPS depth profiling after athermal ion beam induced oxidation (IBO) at 12 keV O₂⁺ incident energy and normal incidence. The composition and stoichiometry of these films were quantitatively determined as chemical state relative concentrations versus sputter time. “In depth” silicon and titanium oxidation states have been obtained after spectra deconvolution, showing a mixture of silicon dioxide, titanium dioxide, titanium suboxides, elemental titanium and residual traces of titanium nitride. Thermochemical data based on the corresponding enthalpies of formation of the oxides cannot explain our experimental results as in the case of low energy IBO, an oxygen defective altered layer is formed, presenting features of a reduced TiO_x phase.     

Preparation and characterisation of compositionally graded BaxSr1-xTiO3 thin films

Ba_xSr_1-xTiO₃ thin films with a compositional gradient of x=0.3 to 1 (in 0.1 mole fraction increments) were fabricated on Pt/Ti/SiO₂/Si substrates using a modified sol–gel technique. The graded film crystallised in a perovskite structure and consists of a uniform microstructure with comparatively larger grains. The room-temperature relative dielectric constant (ε_r) and dielectric loss (cosδ) at 100 kHz were found to be 305 and 0.03 respectively. Dielectric peaks were not observed in the temperature range from -20 °C to 120 °C. The dielectric constant and dielectric loss were almost independent of temperature. Polarisation–electric field measurements at room temperature revealed a saturated but slim hysteresis loop with a remanent polarisation (P_r) of 0.6 μC/cm² and a coercive field (E_c) of 2.4 kV/mm. The graded film behaves as a stack of Ba_xSr_1-xTiO₃ capacitors connected in series and hence the dielectric Curie peaks are removed. Received: 4 October 2001 / Accepted: 17 October 2001 / Published online: 23 January 2002     

Synthesis and characterization of nanostructured (Pb1− x Sr x )TiO3 thin films by a modified chemical route

The coating solutions of nanostructured (Pb_{1– x} Sr _x )TiO₃ (PST) thin films have been prepared by the sol–gel combined metallo-organic decomposition method. The coating solutions were deposited on Pt/Ti/SiO₂/Si substrates using a spin-coating technique with spinning speed of 4300 rpm and annealed at 650°C. The effect of Sr content in reducing the grain size and tetragonal distortion of PST films has been studied. The optimum conditions for crystalline phase formation in the films have been analyzed by thermogravimetric, differential thermal analysis and Fourier transform infrared spectroscopy. The phase and microstructure of the films were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD pattern shows that the PST thin films are crystallized into tetragonal structures without any impurity phase and the distortion ratio reduces with increasing Sr concentration. The AFM results indicate an increase in grain size with increasing annealing temperature of the film and reduction in grain size with increasing Sr concentration.     

Unusual vortex dynamics in the quantum-liquid phase of a-MoxSi1−x films

We find the unusual vortex dynamics in the low-temperature liquid phase of amorphous Mo_xSi_1−x films by measuring the fluctuating component of the flux-flow voltage δV(t) about the average voltage. For the thick film, in which the quantum vortex liquid (QVL) phase has been well-determined in the field-temperature plane, δV(t) originating from the vortex motion is clearly visible in the QVL phase, where the distribution of δV(t) is anomalously asymmetric, implying large velocity and/or number fluctuations of driven vortices. For the thin film, in which the QVL phase has not been determined from the static transport measurements, similar unusual vortex motion is observed in nearly the same reduced-temperature regime. We suggest that vortex dynamics in the low-temperature liquid phase of thick and thin films is dominated by common physical mechanisms related to quantum-fluctuation effects.     

Properties of reactively sputtered Mo1−x O x films

Molybdenum oxide (Mo_1–xO_x) films were prepared by reactive rf sputtering of a Mo target in O₂/Ar plasma. The dependence of film properties on various sputtering parameters is investigated. The atomic percentage of oxygen (x) in the Mo_1–xO_x films decreases with sputtering power and increases with the partial pressure of oxygen. Mo_1–xO_x films that exhibit metallic conductivities can be obtained over a wide range of sputtering conditions. The intrinsic film stress of conducting Mo_1–xO_x is compressive. Such M_1–xO_x films were shown by backscattering spectrometry to be excellent diffusion barriers between Al and Si up to 600 °C annealing for 30 min.     

Sr/Si界面沉积SrTiO3初始生长阶段的扫描遂道显微术研究

本文工作利用脉冲激光沉积术(PLD)和超高真空扫描隧道显微术(UHV-STM),研究了在Sr/Si(001)-(2×1)衬底表面上真空室温沉积几个单层SrTiO₃薄膜的初始生长过程.经660 ℃退火处理后,Sr/Si衬底表面上形成了纳米岛状结构.经分析,这些纳米小岛为C49-TiSi₂和 C54-TiSi₂.实验结果表明,在没有氧气的情况下退火,Sr/Si界面无法有效阻止SrTiO₃薄膜与Si衬底之间的相互作用. 关键词： 脉冲激光沉积术(PLD) 扫描隧道显微镜(STM) 3')" href="#">SrTiO₃ 2')" href="#">C54-TiSi₂     

Thermal stability and diffusion processes in Mo x Si y /Si multilayers studied with high-resolution RBS

Mo _x Si _y /Si multilayers with a period thickness of ∼7.5 nm and bilayers Mo _x Si _y /Si have been fabricated by e⁻-beam evaporation in UHV at a deposition temperature of 150°C [1]. The composition of the as-deposited layer systems and changes in the composition after baking the samples have been studied with high-resolution RBS. For a multilayer with a mixing ratioy/x≃2, no interdiffusion is observed up to a baking temperature of 830°C. For samples with a mixing ratioy/x≃1, diffusion is observed up to a baking temperature of 630°C, resulting in a mixing ratio close toy/x≃2. This mixing ratio remains almost stable up to ∼830°C, and considerable interdiffusion is only observed in those systems where regions with a mixing ratio smaller than 2 still exist. Possible reasons for the high thermal stability of the samples are the lack of a concentration gradient for Si in the system and/or the crystallization of MoSi₂.     

Structure and transport properties of ultrathin YBa2Cu3O7−x films

The crystal structure and transport properties of epitaxial c-oriented YBa₂Cu₃O_7−x films are investigated for high-T _c layer thicknesses from 5 to 300 nm. The films were prepared by laser deposition. Films less than 30 nm thick become predominantly single-domain in the direction of the c axis. As the thickness decreases, the orthorhombicity parameter of the YBaCuO lattice decreases, which correlates with the critical temperature degradation observed in films less than 9 nm thick. The obtained thickness dependence of the effective microwave surface resistance of a YBaCuO film agrees well with the computational result obtained in the framework of local electrodynamics for samples with a constant microwave conductance. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 608–613 (25 April 1996)     

Influence of electrical and optical losses on fundamental solar-cell parameters

Summary We present here an analysis of the dependence of the light-generated current on the current at maximum power in lossy solar cells. that is, cells with both series and shunt resistances present simultaneously — that is, a real cell. It is essentially seen that this dependence is highly sensitive to series resistance. However, for cells with series resistance of the order of 3 Ω, ϖI _g/ϖI _mp=1. We also look at the influence of TiO_x antireflection coatings on the open-circuit voltage and short-circuit current in silicon solar cells.

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Riassunto Si presenta un'analisi della dipendenza della fotocorrente dalla corrente di massima potenza nelle celle solari quando sono contemporaneamente presenti le resistenze serie e di shunt. Su tale dipendenza influisce molto la resistenza serie. Tuttavia, se questa è dell'ordine di 3 Ω, è ϖI _g/ϖI _mp=1. Si studia anche l'influenza di rivestimenti antiriflettenti di TiO_x sulla tensione di circuito aperto, sulla corrente di circuito aperto e sulla corrente di corto circuito nelle celle di silicio.

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Magnetic, electrical, and crystallographic properties of thin La1−x SrxMnO3 films

A study is reported of the magnetic, electrical, and crystallographic properties of La_1−x Sr_xMnO₃ (0.15⩽x⩽0.23) epitaxial films grown on single-crystal substrates of (001)ZrO₂(Y₂O₃) having the fluorite structure and (001)LaAlO₃ having the perovskite structure. It was found that films with close compositions for x=0.15 and 0.16, grown on different substrates, have different properties, namely, the film on a fluorite substrate is semiconducting and has a coercive strength 30 times that of the film on a perovskite substrate; the temperature dependence of electrical resistance of the latter film has a maximum around the Curie point T _C and follows metallic behavior for T<T _C. These differences are explained as due to different structures of the films. The x=0.23 film on the perovskite substrate has been found to exhibit a combination of giant magnetoresistance at room temperature with a resistance of ≈300 Ω which is useful for applications. The maxima in resistance and absolute value of negative magnetoresistance are accounted for by the existence of two-phase magnetic states in these films. Fiz. Tverd. Tela (St. Petersburg) 40, 290–294 (February 1998)     

Si–Si optical phonon behavior in localized Si clusters of Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy nanocrystals

Raman spectra acquired from Si _x Ge_1−x -nanocrystal-embedded SiO₂ films show dependence of the Si–Si optical phonon frequency on Si content. The frequency upshifts, and peak intensity increases as the silicon concentration increases. For a given Si content, the frequency remains unchanged with annealing temperature. Spectral analysis and density functional theory calculation reveal that the optical Si–Si phonon is related to the formation of localized Si clusters surrounded by Si/Ge atomic layers in the Si _x Ge_1−x nanocrystals and the intensity enhancement arises from the larger cluster size. The synergetic effect of surface tensile stress and phonon confinement determines the Si–Si optical phonon behavior.     

Gradient-stress on polarization in Ba1−x Sr x TiO3 films

A group of position-thickness-dependent stresses are used to modified Landau-Devonshire theory to investigate the second-order phase transition in Ba_1?x Sr _x TiO₃ films. The result shows that the short-range interaction between the unit cells of the film and the substrate induces the phase transition dispersion and the rise of the transition temperature in the films. The dependence of the effective dielectric constant on the temperature and the average spontaneous polarization on the film thickness are computed, which qualitatively agree with the experiments.     

Study of graded Ni-Ti shape memory alloy film growth on Si(100) substrate

In-situ X-ray diffraction (XRD) was employed to study the effect of the deliberate change of the Ti/Ni ratio during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (XTEM), and electrical resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film (thickness of ≈ 420 nm) with a Ti-rich composition in the central part (ranging from 50 to ≈60 at. %) and near-equiatomic composition in the extremities, following four distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2–3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti₂Ni. When stopping the Ti co-sputtering, Ti₂Ni dissolves and, thus, plays the role of a Ti reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the morphology of the interface has shown the presence of NiSi₂ silicides (A-NiSi₂ and B-NiSi₂), Ti₄Ni₄Si₇, Ti₂Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, ER measurements revealed phase transitions associated with the B2, R-phase and B19^′ phases. These type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation. PACS 81.15.Cd; 61.10.Nz; 68.55.Jk     

Magnetoelectric properties of Mn-substituted BiFeO3 thin films with a TiO2 barrier

Multiferroic thin films with the general formula TiO₂/BiFe_1−xMn_xO₃ (x=0.00, 0.05, 0.10 and 0.15) (TiO₂/BFMO) were synthesized on Au/Ti/SiO₂/Si substrates using a chemical solution deposition (CSD) method assisted with magnetron sputtering. X-ray diffraction analysis shows the thin films contained perovskite structures with random orientations. Compared with BFMO films, the leakage current density of the TiO₂/BFMO thin films was found to be lower by nearly two orders of magnitude, and the remnant polarizations were increased by nearly ten times. The enhanced ferroelectric properties may be attributed to the lower leakage current caused by the introduction of the TiO₂ layer. The J-E characteristics indicated that the main conduction mechanism for the TiO₂/BFMO thin film was trap-free Ohmic conduction over a wide range of electric fields (0-500 kV/cm). In addition, ferromagnetism was observed in the Mn doped BFO thin films at room temperature. The origin of ferromagnetism is related to the competition between distortion of structure and decrease of grain size and decreasing net magnetic moment in films due to Mn doping.