Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

纳米碳纤维在化学电源中的应用

作为一种新型碳基纳米材料,纳米碳纤维由于具有优异物理化学性能和可控微结构受到越来越多研究者的重视.对纳米碳纤维发现、纳米碳纤维制备和结构性能进行了论述,重点对纳米碳纤维在化学电源领域,包括在锂离子电池、燃料电池和超级电容器上的应用进行了分析和综述.     

Fabrication and evaluation of LaCrO3 thin film heaters

Lanthanum chromium oxide (LaCrO₃) has excellent high‐temperature properties. LaCrO₃ doped with alkaline earth metals also has high electric conductivity. The purpose of this study is to fabricate thin film heaters using LaCrO₃ doped with Ca by RF magnetron sputtering method. The crystal structure of thin films was evaluated and the surface form was studied. The results show that the thin film deposited on Si(100) single crystal and quartz glass substrates in Ar gas had a strong orientation and that its surface form was comparatively smooth. The crystal structure of the thin films deposited on Si(100) and quartz glass substrate at temperatures of 700 and 800 °C by sputtering in a mixture of Ar and O₂ gases was the same as the crystal structure of LaCrO₃. The heating characteristics of a thin film heater on Si(100) substrate with Pt electrodes were evaluated by measurement of the equilibrium temperature‐current (T–I) and resistance‐equilibrium temperature (R–T) characteristics. The maximum equilibrium heating temperature was about 1100 °C. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 18–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1156     

Tailoring the structural and optical properties of RF magnetron sputtered ZnO/graphene thin films by annealing temperature

Abstract

ZnO and ZnO/Graphene thin films were deposited on Cu substrate using a low pressure chemical vapor deposition (LPCVD) and the magnetron sputtering method. The impacts of graphene layer growth and annealing temperature on the optical properties ZnO and ZnO/Graphene thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), X-ray photoelectron spectroscopic (XPS), and photoluminescence (PL) measurements respectively. XRD and SEM results reveal that all the thin films preferred the crystalline [001] orientation along the c-axis direction, which were vertical grown on substrate surface. By comparing the results and analysis of their structure, morphology, chemical bonding and optical property, it is proved that using Graphene as a buffer layer can improve the crystal quality of ZnO thin films. For the annealed ZnO/graphene nanostructures, the area ratio of UV and visible emission region of ZnO/graphene thin films increase with increasing the annealing temperature, reaches a maximum at 500?°C and then starts decreasing with further increase in annealing temperature, which indicating that the controllable ZnO/Graphene thin films have the higher crystallization quality at the annealing temperature of 500?°C. Our results demonstrate that for high quality ZnO/graphene thin films deposition, decreasing the defect concentration should be preferable to simply applying the proper annealing temperature, which might have promising applications for various UV photodetectors devices.     

Large area deposition of Pb(Zr,Ti)O<Subscript>3</Subscript> thin films for piezoelectric MEMS devices

Pb(Zr,Ti)O₃ (PZT) thin films deposited on insulating ZrO₂ buffered silicon wafer are intended to be employed for in-plane polarized piezoelectric MEMS devices. Multi-target reactive sputtering system for large area deposition of in-situ crystallized PZT thin films and the ZrO₂ buffer layer has been employed. The interface analysis of multilayer structures by high resolution transmission microscope, X-ray diffraction, optical refraction, and absorption spectra studies has been presented. At a substrate temperature of 520°C and excess lead deposition condition, the formation of a PZT superstructure has been revealed. The substrate temperature of 580°C leads to the crystallization of PZT directly into a single phase perovskite crystal structure. A pronounced Urbach behavior in our PZT thin films has been observed by optical absorption studies. The surface roughness of PZT films deposited on a ZrO₂ buffer layer is much higher than that on conducting platinized silicon wafer.     

Preparation of Bi4Ti3O12 thin films by electron cyclotron resonance sputtering

Abstract

Ferroelectric Bi₄Ti₃O₁₂ thin films were deposited on Pt-coated oxidized Si substrate by electron cyclotron resonance (ECR) sputtering using ceramic targets. Crystal structure and dielectric properties of the films were investigated as functions of sputtering conditions such as substrate temperature and sputtering gas. Using a target with excess Bi content compared to stoichiometric composition was required to compensate Bi re-evaporation from the substrate and to obtain a perovskite single phase at 600°C. (117)-oriented films exhibited ferroelectric hysteresis loops. The remanent polarization and coercive field of the films were 9.8 μC/cm² and 180 kV/cm, respectively.     

Thermal stability of metal electrodes (Pt,Ru, & Ir) on polycrystalline silicon in ferroelectric capacitors

Abstract

Electrode materials such as Pt, Ru, and Ir on polycrystalline silicon were annealed and the thermal stability was investigated to check the feasibility of the structure. Sputtered Pt reacted with silicon to form PtSi at a low temperature of 400 °C and the top layer of silicide was oxidized in oxygen ambient. Ru and Ir films by sputtering were also silicidized above 550 °C and it made voids beneath silicide layers. All of the films are found to allow oxygen to diffuse through them and to get the underlying layers oxidized. However, Ir deposited by e-beam evaporation did not form silicide up to 700 °C and did not get oxidized up to 550 °C. Ir also allowed oxygen diffusion when annealed at 550 °C or lower temperature, but it was prevented when annealed at 700 °C.     

Structure and Dielectric Properties of Heteroepitaxial PMNT Thin Films

Thin films of PbMg_1/3 Nb_2/3O₃(PMN) and (1 ? x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ (PMNT) with x = 0.1 to 0.3 were epitaxially grown on (100) MgO and (100) SrTiO₃ (ST) substrates by magnetron sputtering. Typical film thickness was 300 to 900 nm. Pyrochlore free (001) PMN and (001) PMNT thin films were grown on the ST and MgO substrates at narrow temperature window of 500 ± 20°C. The cross-sectional TEM image showed that the sputtered PMN and PMNT thin films comprised high density and continuous structure. These sputtered films showed 3-dimensional epitaxy. The dielectric response of the sputtered thin films showed frequency dispersion similar to bulk relaxor-like behavior with a broad temperature anomaly. PMN-23PT (x = 0.23) thin films showed the temperature of maximum, Tm, at 80°C. The Tm coincided with that of corresponding bulk materials. However, the obtained maximum dielectric permittivity, ?_m, ?_m = 900 to 1000, was considerably smaller than that in the bulk. The relatively low dielectric permittivity was probably due to the presence of strained hetero-epitaxial layer having temperature independent dielectric properties.     

Mocvd growth and characterization of PbTiO3 thin films on Pt/Ti/SiO2/Si substrates

Abstract

PbTiO₃ thin films were grown by Metalorganic Chemical Vapor Deposition (MOCVD) on 6′′ platinized Si wafers. In a first stage of investigation, the quality of the platinum surface was correlated with the substrate temperature and the composition of the atmosphere of the warming-up procedure in the reactor. The Pt reflectivity and the surface roughness were clearly modified by higher temperatures and by oxygen environments, though no clear diffusion mechanisms could be observed with Auger. In a second stage of investigation, the growth of PbTiO₃ was studied. Using a standard PbTiO₃ growth procedure, we studied the influence of substrate temperature and gas phase composition. Below 650°C, PbO appears as the main phase; at 650°C, PbTiO₃ and PbO coexist; and at 700°C, only PbTiO₃ is detected. The morphologies were examined by SEM / AFM and the roughness at the interface was studied by ellipsometry.     

Influence of deposition parameters on physico-chemical and optical properties of sputtered PbTiO3 thin films

Abstract

Stoichiometric thin films of lead titanate (PbTiO₃) have been grown “in situ” without postannealing on (0001) sapphire substrates by rf magnetron sputtering technique. X-ray diffraction scans have revealed that as-grown films consist of the perovskite phase and are polycrystalline with a high (111) orientation. The structure, the microstructure and the optical properties have been studied as a function of the process parameters i.e., substrate temperature, gas pressure and the target composition, in particular the lead content. We report the dependence of the deposition conditions on the optical constants. The optimum experimental conditions (100m Torr and 600°C) to produce thin films with high transparency and refractive indices (n = 2.61 at 633 nm), similar to values for bulk materials, are given in this paper.     

Characteristics of ferroelectric gate mos and mosfets

Abstract

Electrical characteristics of metal-insulator-semiconductor (MIS) capacitors of a variety of ferroelectric materials like lead zirconate titanate (PZT), lead titanate (PT) and barium magnesium fluoride (BMF) on p-silicon have been studied. PZT was deposited by r.f. magnetron sputtering from a composite target and PT from co-evaporation. The films were annealed in oxygen atmosphere in the temperature range 550–700°C for various times. PZT and PT films which are directly deposited on silicon showed low effective dielectric constant.¹⁰ For normal applied bias voltages (±5 V), the C-V curves did not show significant hysteresis. The effective dielectric constant was improved significantly by the incorporation of a buffer layer. BMF film was deposited in ultra high vacuum on a heated substrate and the film was encapsulated by a zirconium oxide layer. The C-V curves for these MIS capacitors shows hysteresis and the direction of hysteresis corresponds to ferroelectric polarization.     

The effect of growth atmosphere and Ir contamination on electric properties of La<Subscript>3</Subscript>Ta<Subscript>0.5</Subscript>Ga<Subscript>5.5</Subscript>O<Subscript>14</Subscript> single crystal grown by the floating zone and Czochralski method

The influence of growth atmosphere and Ir contamination on electrical resistivity of langatate (La₃Ta_0.5Ga_5.5O₁₄; LTG) was studied. LTG single crystals were grown via the Czochralski method under different oxygen partial pressures with Ir contamination from the Ir crucible. In addition, LTG crystals were grown by the floating zone method and they were not contaminated by Ir. The electrical resistivity and ionic transport number of these crystals were measured in the temperature range 300–1000°C. The conduction mechanism of LTG changed at about 720°C. At T < 720°C, electronic conduction was dominant, and the resistivity was affected by growth atmosphere as well as Ir contamination. In contrast, at T > 720°C, ionic conduction was dominant, and the resistivity was affected only by Ir contamination. In both temperature regions, Ir contamination decreased the resistivity by an order of magnitude.     

Characterization of MOCVD Pt electrode for ferroelectric thin films

Abstract

Platinum thin films were deposited by low pressure chemical vapor deposition (LPMOCVD) on SiO₂/Si and (Ba, Sr)TiO₃/Pt/SiO₂/Si substrates using Pt-hexafluoroacetylacetonate at various deposition temperatures. The shiny mirror-like Pt thin films of a high electrical conductivity were obtained, when the deposition temperature is between 325°C and 350°C, whereas above 375°C Pt thin films showed rough surface as well as poor adhesion property to oxide substrate. Pt thin films had a good step coverage of 90%. The results indicate that LPMOCVD Pt thin films can be applied for the top electrode of high dielectric thin film, which is thought to be one of the best candidate materials for a capacitor of ULSI DRAM.     

Nano vanadyl‐phthalocyanine crystals fabricated on KBr substrate

Vanadyl‐phthalocyanine (VOPc) thin films deposited on a KBr substrate by molecular beam epitaxy (MBE) consist of nano‐VOPc crystals epitaxially grown. The nano‐VOPc crystals acquire a square shape as a result of annealing at 150^°C. The size of the nano‐crystals is controllable by changing the conditions of MBE deposition and thermal treatment. The growth processes of nano‐crystals on the KBr substrate are elucidated experimentally and are shown to be closely related to strong interaction between the VOPc molecules and the KBr substrate. Their mechanisms can be explained in terms of surface diffusion of the VOPc molecules on the KBr substrate. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 41–48, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20645     

Low‐resistive and transparent AZO films prepared by PLD in magnetic field

Al₂O₃‐doped ZnO (AZO) thin films have been deposited onto glass substrates using a split target consisting of AZO (1 wt%) and AZO (2 wt%) by pulsed laser deposition with an ArF excimer laser (λ = 193 nm, 15 mJ, 10 Hz, 0.75 J/cm²). By applying a magnetic field perpendicular to the plume, the lowest resistivity of 8.54 × 10^?5Ω·cm and an average transmittance exceeding 91% over the visible range were obtained at a target‐to‐substrate distance of 25 mm for approximately 279‐nm‐thick AZO film (1.8 wt%) grown at a substrate temperature of 230 °C in vacuum. From cross‐sectional TEM observations and the XRD spectrum, a reason why the low resistivity (54 × 10^?5Ω·cm) was reproducibly obtained was considered to be due to the fact that a disorder of crystal growth originating in the vicinity of the interface between the substrate and the film was suppressed by application of the magnetic field and the c‐axis orientation took preference, giving rise to the increase of mobility. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 40–45, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20026     

Phase evolution and Sn-substitution in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films prepared on a Pt/Ti/SiO₂/Si(100) substrate by pulsed laser deposition were studied with focusing on the effects of different processing conditions and Sn substitution on phase evolvement and surface microstructure. Major experimental parameters include substrate temperature up to 770 °C and working oxygen pressure of 50–250 mTorr. LiMn₂O₄ thin films became highly crystallized with increased grain sizes as the substrate temperature increased. Second phases such as LiMnO₂ and Li₂Mn₂O₄ were found at the temperature of 300 and 770 °C, respectively. As an optimum condition, films grown at 450 °C showed a homogeneous spinel phase with well-defined crystallinity and smooth surface. A high pressure of oxygen tended to promote crystallization and grain growth. Working pressure did not affect significantly the phase formation of the thin films except that unexpected LiMn₃O₄ phase formed at the lowest oxygen pressure of 50 mTorr. Tin-substituted thin films showed lower Mn–O stretching vibrations, which suggests that more Li-ions can be inserted into vacant octahedral sites of the spinel structure.     

Application of TiO<Subscript>2</Subscript> thin film with nanorods to surface acoustic wave type ultraviolet photo detection

TiO₂ thin films with nanorods grown on 128° Y?cut LiNbO₃ and 90° rotated 42°45′ ST?cut quartz were used to fabricate surface acoustic wave ultraviolet photodetectors. TiO₂ thin film was deposited by radio?frequency magnetron sputtering and TiO₂ nanorods were then synthesized on the thin film via the hydrothermal method. 128° Y?cut LiNbO₃ is a Rayleigh wave substrate with a high electromechanical coupling coefficient, whereas 90° rotated 42°45′ ST?cut quartz is a surface skimming bulk wave substrate with a high wave velocity. The effects of substrate characteristics and TiO₂ nanorod morphology on the ultraviolet sensitivity of the surface acoustic wave photodetectors were investigated. The variations of insertion loss, phase, resistance, and capacitance under ultraviolet illumination were examined. The performance of the TiO₂ thin film with nanorods deposited on 128° Y?cut LiNbO₃ is much greater than that of the film deposited on 90° rotated 42°45′ ST?cut quartz, which can be attributed to the former’s high electromechanical coupling coefficient.     

Growth of magnetite epitaxial thin films by gas flow sputtering and characterization by FMR

The growth of magnetite (Fe₃O₄) epitaxial thin films on MgO substrates were studied by using gas flow sputtering (GFS). Reflection high‐energy electron diffraction (RHEED) and atomic force microscopy showed that the surfaces of the films obtained at a substrate temperature T_s of 300 °C and oxygen flow rates F_O2 of 0.12 − 0.18 sccm are fairly flat for the film thickness of about 200 nm. The saturation magnetization and resistivity were close to the reported values of Fe₃O₄ for T_s= 300°C and F_O2 = 0.12–0.20sccm. The films obtained at T_s= 300°C and F_O2=0.16 and 0.18 sccm showed Verwey transition, which is persuasive evidence of the formation of Fe₃O₄. The epitaxial relationship of Fe₃O₄(100)//MgO(100) and Fe₃O₄[100]//MgO[100] was confirmed by using ferromagnetic resonance (FMR), and the anisotropy constants and magnetization were obtained by the fitting of resonance‐field versus applied‐field angle curves. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Low temperature metal-organic chemical vapor deposition of Ru thin films as electrode for high dielectric capacitors

Abstract

Low temperature metal-organic chemical vapor deposition (MOCVD) process of Ru films for use as electrode material was studied using a noble dome type reactor, liquid delivery technique and a new precursor. The films were grown at temperatures ranging from 275°C to 480°C in which film growth was controlled by a surface chemical reaction with a small activation energy of 0.21 eV. The root-mean-squared surface roughness was as low as 23 Å for a film grown at 290°C on a SiO₂ surface.     

Effect of Liquid Phase and Vaporization on the Formation of Microstructure of Pr Doped ZnO Varistor

Our previous works and our recent data were summarized to discuss the effect of liquid phase formation and vaporization of the components on the densification, grain growth and change of the microstructure of Pr doped ZnO ceramics in air. In the ZnO-Pr₂O₃ binary system, eutectic liquid forms at 1382± 5°C° and significant vaporization of the components occurred above the eutectic temperature. Below eutectic temperature (1350°C), only 0.1 mol % of Pr doping into ZnO brought about the grain growth of ZnO, however further addition of Pr brought about the suppression of the grain growth. Comparing the grain size distribution at the surface and inside part of Pr doped ZnO ceramics, it was clarified that wider grain size distribution was observed at the surface than inside part. At the temperature just below the eutectic (1370°C), abnormal grain growth was also observed. Depth profile of Pr content indicated that no concentration gradient was observed below eutectic temperature (1350°C), however above eutectic temperature (1500°C), condensation of Pr was observed at the surface. Grain growth rate as well as weight loss rate were drastically increased between 1350 and 1370°C, which suggested that formation of liquid phase accelerate the grain growth rate and weight loss rate. Consequently the microstructure of Pr doped ZnO ceramics was formed by both effects on the formation of liquid phase and on the vaporization of the components.