Effects of Residual Stress on the Electrical Properties of PZT Films

The effects of the residual stress (either compressive or tensile) induced during the heat-treatment process on the electrical properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT) films were investigated. The PZT films were deposited on platinized silicon substrates by the rf-magnetron sputtering method using a single oxide target. After their deposition, the films were bent elastically by means of a specially designed fixture during the annealing process. Residual stress was induced in the film by removing the substrate from the fixture after annealing. The ferroelectric and piezoelectric properties of the films were markedly changed by the residual stresses; the remnant polarization ( P _r) and saturation polarization ( P _sat) increased when a compressive stress was induced. On the other hand, the piezoelectric properties increased when a tensile stress was induced in the film.     

Si field emitter arrays coated with thin ferroelectric films

This paper demonstrates novel approach on Si field emitter arrays (FEAs) coated with thin ferroelectric films for vacuum microelectronic applications, which exhibit enhanced electron emission behaviors. The films were deposited using sol–gel and sputtering process, respectively. In sol–gel approach, the emission behavior is highly correlated to the crystallinity of (Ba,Sr)TiO₃ (BST) layer. The interfacial reaction between Si and BST film would deteriorate the crystallinity of the films, and in turn impede the electron emission from silicon tips. The film thickness and the dopants also affect the emission behaviors significantly. In sputtering process, the nitrogen-incorporated SrTiO₃ (STO) films are deposited with eliminated interfacial due to relatively lower processing temperature. The enhanced emission characteristics are highly correlated with nitrogen-incorporation and film thickness. These encouraging results have offered great promise for the application of ferroelectric films in field emission devices.     

Use of Stress To Produce Highly Oriented Tetragonal Lead Zirconate Titanate (PZT 40/60) Thin Films and Resulting Electrical Properties

Thin films of Pb(Zr_0.4Ti_O.6)O₃ produced by chemical solution deposition were used to study the effects of stress from different platinized single-crystal substrates on film orientation and resulting electrical properties. Films deposited on MgO preferred a (001) orientation due to compressive stress on the film during cooling through the Curie temperature ( T _C). Films on Al₂O₃ were under minimal stress at T _C, resulting in a mixture of orientations. Those on Si preferred a (111) orientation due to templating from the bottom electrode. Films oriented in the 〈001〉 direction demonstrated lower dielectric constants and higher P _r and − d ₃₁ values than (111) films.     

BaTiO3铁电薄膜在硅基片上的取向生长

采用脉冲激光沉积方法,在硅基片上先沉积MgO或CeO2缓冲层后再制备BaTiO3(BTO)铁电薄膜.通过原位反射高能电子衍射来监测MgO,CeO2缓冲层在硅基片上的生长行为.用X射线衍射测定BTO薄膜的结晶取向.并利用压电响应力显微镜观察了铁电薄膜的自发极化形成的铁电畴.结果表明:BTO薄膜在不同的缓冲层硅基片上以不同的取向生长,在织构的MgO/Si(001)基片上为(001)择优,择优程度与MgO织构品质有关,其中在双轴织构MgO缓冲层上为(001)单一取向;在CeO2(111)缓冲层上为(011)单一取向.(001)取向的BTO薄膜具有更大的面外极化,而(011)取向的BTO薄膜具有更大的面内极化.     

Synthesis and Microstructure of Highly Oriented Lead Titanate Thin Films Prepared by a Sol-Gel Method

Thin films of PbTiO₃ were deposited on fused silica, resistor-grade alumina, and single-crystal (100) MgO by a sol–gel processing method. Whereas the films deposited on silica and alumina substrates were randomly oriented and polycrystalline, highly {100} oriented PbTiO₃ films were grown on the MgO single crystals. The perovskite-type structure was observed with films deposited on the single-crystal MgO and annealed at temperatures as low as 470°C, whereas a pyrochlore-type strcuture was observed with films on fused silica and alumina processed in a similar manner. All films heat-treated at temperatures in excess of 570°C showed significant formation of a second PbTi₃O₇ phase. The films were characterized by electron microscopy and glancing-incidence-angle X-ray diffraction.     

Microstructure and Dielectric Properties of Textured SrTiO3 Thin Films

We investigate the relationship between microstructure and dielectric properties of textured SrTiO₃ thin films deposited by radio-frequency magnetron sputtering on epitaxial Pt electrodes on sapphire substrates. The microstructures of Pt electrodes and SrTiO₃ films are studied by transmission electron microscopy, atomic force microscopy, and X-ray diffraction. SrTiO₃ films grown on as-deposited and annealed Pt electrodes, respectively, consist of a mixture of (111)- and (110)-oriented grains. Temperature-dependent dielectric measurements show that differences in texture and microstructure are reflected in the Curie–Weiss behavior of the SrTiO₃ films. Phenomenological models that account for the effects of thermal mismatch strain on the dielectric behavior are developed for different film textures. The models predict that at a given temperature, paraelectric (111)-oriented films of SrTiO₃ on tensile substrates will have a higher Curie–Weiss temperature and a greater dielectric constant than (110)-oriented films or bulk SrTiO₃. The experimental dielectric behavior is compared with the predictions from theory, and different contributions, such as interfacial layers, film stress, and microstructure, to the Curie–Weiss behavior are discussed.     

The Effect of Deposition Temperature and Postanneal on the Bi3.63Pr0.3Ti3O12 thin Films Prepared by RF-Magnetron Sputtering Method

Praseodymium doped Bi₄Ti₃O₁₂ (BTO) thin films with composition Bi_3.63Pr_0.3Ti₃O₁₂ (BPT) were successfully prepared on Pt/Ti/SiO₂/Si substrates by RF-magnetron sputtering method at substrate temperatures ranging between 500° and 750°C. The structural phase and orientation of the deposited films were investigated in order to understand the effect of the deposition temperature on the properties of the BPT films. As the substrate temperature was increased to 700°C, the films started showing a tendency of assuming a c -axis preferred orientation. At lower temperatures, however, polycrystalline films were formed. The Pt/BPT/Pt capacitor showed an interesting dependence of the remnant polarization (2 P _r) as well as dc leakage current values on the growth temperature. The film deposited at 650°C showed the largest 2 P _r of 29.6 μC/cm². With the increase of deposited temperature, the leakage current densities of films decreased at the same applied field and the film deposited at 750°C exhibited the best leakage current characteristics. In addition, the ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BPT films. It was revealed that the BPT film postannealed in air exhibited the weakest fatigue-resistance characteristics and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in this film.     

Preparation of Highly Dense PZN–PZT Thick Films by the Aerosol Deposition Method Using Excess-PbO Powder

Lead zinc niobate–lead zirconate titanate thick films with a thickness of 50–100 μm were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as-deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 μm thick films annealed at 900°C were 43.1 μC/cm² and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process.     

Nanobelt Structure in Perovskite–Spinel Composite Thin Films

We report a nanobelt structure along the 〈110〉 direction in perovskite–spinel (BiFeO₃–CoFe₂O₄ or BFO–CFO) composite epitaxial thin films deposited on SrTiO₃ (STO) substrates by pulsed laser deposition. The results reveal the nucleation and growth mechanism of a nanostructure: first nucleation of perovskite phase regions on STO, followed by segregation of spinel out of the perovskite phase, and finally by evolution of spinel nanobelts that are elongated along the 〈110〉. The reason for control of the nanostructure evolution is a ledge growth mechanism of spinel along the 〈110〉 direction.     

Crystallization of Pseudo-orthorhombic Anorthite on Basal Sapphire

Anorthite-glass films were grown on basal Al₂O₃ substrates using pulsed-laser deposition. The substrates were cleaned and annealed in air at 1400°C to produce crystallographically flat (0001) terraces. The films were deposited in an oxidizing environment. X-ray microanalysis confirmed the composition of the glass films to be close to that of anorthite (CaO·Al₂O₃·2SiO₂). Although anorthite usually has triclinic symmetry, subsequent crystallization of these films in air at 1200°C resulted in the formation of pseudo-orthorhombic CaAl₂Si₂O₈ ( o -anorthite), a known metastable form of the mineral. Microstructural characterization was performed using visible-light microscopy, scanning electron microscopy, and transmission electron microscopy. The films dewetted the substrate either before or after crystallization to form o -anorthite islands which had strong orientation relationships to the Al₂O₃ substrate. The epitaxy of the o -anorthite islands was accompanied by a small lattice mismatch parallel to the substrate plane. The formation of three orientational variants is consistent with the symmetry of the basal Al₂O₃ surface. The dislocation network observed at the o -anorthite/Al₂O₃ interface indicates that nucleation and growth of the anorthite occurs directly on the substrate surface without an intervening interfacial amorphous layer. The study of anorthite-glass films is important because they are present in liquid-phase-sintered Al₂O₃, and may be devitrified by postsintering heat treatments.     

Influence of Crystal Structure on the Fatigue Properties of Pb1−xLax(Zry', Tiz)O3 Thin Films Prepared by Pulsed-Laser Deposition Technique

Lead lanthanum zirconate titanate (Pb_{1− x} La _x (Zr _y ,Ti _z )O₃, PLZT) films containing [00 l ] preferentially oriented grains were produced successfully on YBa₂Cu₃O_{7− x} -coated (YBCOcoated) SrTiO₃ (STO) or YBCO/CeO₂-coated silicon substrates; films containing randomly oriented grains were created on platinum-coated silicon substrates. The latter possessed significantly inferior ferroelectric properties, a fact ascribed to the presence of a paraelectric phase (TiO₂) at the PLZT/platinum interface. On the other hand, the PLZT/YBCO/STO films exhibited better electrical properties than did the PLZT/YBCO/CeO₂/Si films, and this phenomenon was attributed to better alignment of the grains in normal and in-plane orientations. In terms of fatigue properties, the [00l] textured films that were deposited on YBCO/CeO₂/Si substrates possessed substantially superior polarization-switching-cycle endurance versus the randomly oriented films grown on Pt(Ti)/Si substrates. Moreover, the tetragonal films behaved much more satisfactorily than did the rhombohedral PLZT films. The ferroelectric parameters of tetragonal PLZT films showed no significant degradation up to 10⁹ polarization switching cycles, whereas the remnant polarization and coercive force of the rhombohedral PLZT films had already degraded to 80% of their initial values after 10⁸ cycles.     

Fast-response photoconductive ultraviolet light detectors fabricated using high-quality ZnO films obtained by plasma-assisted molecular beam epitaxy

ZnO films form the core of numerous ultraviolet (UV) optoelectronic devices. Herein, a ZnO buffer layer produced by thermal plasma oxidation of metallic Zn was used to grow an active ZnO layer, with Zn film and active layer growth achieved by plasma-assisted molecular beam epitaxy. Although low-temperature ZnO buffer layer and Zn film growth was mainly three-dimensional (3D) due to a large lattice mismatch between ZnO/Zn and Si, the use of thermal plasma oxidation changed the growth mode from 3D to 2D, producing a smooth ZnO active layer. The thus fabricated ZnO active layer (sample 2) exhibited a lower tensile stress than that fabricated on a ZnO buffer layer using a conventional method (sample 1). Both samples were used to fabricate UV sensors, with that based on sample 2 exhibiting a faster photoresponse.     

Stresses and adhesion of thin metallic coatings on oxide substrates

The growth of thin metallic coatings on oxide substrates prepared by vapour deposition of gold or copper on alumina or magnesia was investigated by transmission electron microscopy. The stresses developed during the growth were followed by the bending method. The evolution of stresses is related to the growth mechanisms. The stresses are compressive for discontinuous deposits and change to tensile as the deposit becomes continuous. The compressive stresses are interpreted as due to the increase of the free energy of the metal–oxide system during the growth of metal particles. The tensile stresses result from the deposit lattice mismatch with the substrate. During the growth partial recrystallization and annealing of defects occur which modify the tensile behaviour of continuous coatings. The adhesion of deposits (Au and Cu) on oxide substrates (Al₂O₃ and MgO) was evaluated by the pull-off method as a function of deposition temperature. Au/Al₂O₃, Cu/Al₂O₃ and Au/MgO systems exhibit identical behaviour, while Cu/MgO shows a large dependence on deposition temperature compared to the others. This behaviour is interpreted as due to the formation of chemical bonds between the metal (Cu) and the oxide (MgO), leading to an interfacial oxide.     

Microstructure development of the single-step, low-temperature sintered SrTiO3, GBBL capacitor materials

The microstructure development of the single-step, low-temperature sintered SrTiO₃, GBBL capacitor materials is studied according to the microstructure analysis, mass transfer and defect chemical reactions during sintering process. The sintering mechanism is the reactive liquid phase sintering with the participation of solid state diffusion caused by the volatilization of oxygen. Insulating grain boundaries are formed by the grain boundary segregation of Li₂O, which is caused by the donor enhanced volatilization of oxygen. Grains are semiconductorized during grain growth process which incorporates the donor dopant into SrTiO₃ lattice.     

Microstructure, Orientation, and Properties of Sol-Gel-Derived KTiOPO4 Thin Films

Dense and crack-free thin films of potassium titanyl phosphate (KTP) were synthesized using a sol-gel process. The decomposition of the organic precursors and the formation of the KTP were studied using thermal analysis, DRIFT, and XRD. Several processing parameters such as the nature of the precursors, the aging of the alkoxide solution, the firing atmosphere, time, and temperature were found to affect the final film microstructure. Thin films were deposited on single-crystal KTP, LaGaO₃, MgO, and sapphire substrates to promote crystallographic orientation. SEM and XRD studies reveal that films deposited on KTP and LaGaO₃ single crystals are highly oriented. The films deposited on MgO or sapphire were found to detach or chemically degrade. The orientation as well as the degradation mechanisms were examined in detail.     

Effects of Plasma Bombardment on the Initial Growth of (Ba,Sr)TiO3 Films and Their Properties

Magnetron-sputtered (Ba,Sr)TiO₃ films were grown on Pt/SiO₂/Si and MgO substrates that were located inside and outside the plasma region. The effects of plasma bombardment on the properties of the grown films were observed. The films that were grown outside the plasma region exhibited better crystallinity, higher dielectric constants, higher electrical conductivity, and rougher surfaces than those that were grown inside the plasma region. However, plasma bombardment did not affect the initial growth of the films on Pt/SiO₂/Si or MgO substrates, as explored by atomic force microscopy. The films that were grown on Pt/SiO₂/Si showed island growth characteristics, whereas those that were grown on MgO substrates revealed layer-by-layer growth characteristics. Possible explanations for the different growth mechanisms are provided.     

Density functional theory and kinetic Monte Carlo simulation study the strong metal–support interaction of dry reforming of methane reaction over Ni based catalysts

Oxide supports modify electronic structures of supported metal nanoparticles,and then affect the catalytic activity associated with the so-called strong metal-support interaction(SMSI).We herein report the strong influence of SMSI employing Ni_4/α-MoC(111) and defective Ni_4/MgO(100) catalysts used for dry reforming of methane(DRM,CO_2+CH_4→2 CO+2 H_2) by using density functional theory(DFT) and kinetic Monte Carlo simulation(KMC).The results show that α-MoC(111) and MgO(100) surface have converse electron and structural effect for Ni_4 cluster.The electrons transfer from a-MoC(111) surface to Ni atoms,but electrons transfer from Ni atoms to MgO(100) surface;an extensive tensile strain is greatly released in the Ni lattice by MgO,but the extensive tensile strain is introduced in the Ni lattice by α-MoC.As a result,although both catalysts show good stability,H_2/CO ratio on Ni_4/α-MoC(111) is obviously larger than that on Ni_4/MgO(100).The result shows that Ni/α-MoC is a good catalyst for DRM reaction comparing with Ni/MgO catalyst.     

Raman spectroscopy of KTN thin films

The renewed interest in the KTa_1-x-Nb_xO (KTN) mixed perovskite materials, especially in single crystalline thin film forms, is connected with their remarkable dielectric properties in the dilute compositions. Off-center Nb ions in the highly polarizable KTaO₃ lattice provide a drastic increase in the dielectric peak up to 20 times in comparison with pure KTaO₃ and KNbO_3. KTN thin films with several Nb concentrations were prepared in the range 0 ≤ × ≤ 1 by pulsed laser deposition. The films were deposited onto MgO substrate. The effect of a substrate and symmetry-breaking defects was studied by micro-Raman spectroscopy. An anomalous residual intensity of the forbidden first-order scattering modes in the cubic paraelectric phase of the KTN films was connected with formation of polar microregions even far above the bulk T_c. On the whole, the KTN film behavior shows the existence of specific defects enhancing the unit perovskite cell in the film so that the activity of off-center Nb ions increases in producing larger electric dipoles and extending the precursor phase above T_c.     

Growth of Single-Crystal and Polycrystalline Thin Films of MgAl2O4 and MgFe2O4

Single-crystal and polycrystalline films of Mg-Al₂O₄ and MgFe₂O₄ were formed by two methods on cleavage surfaces of MgO single crystals. In one procedure, aluminum was deposited on MgO by vacuum evaporation. Subsequent heating in air at about 510°C formed a polycrystalline γ-Al₂O₈ film. Above 540°C, the γ-Al₂O, and MgO reacted to form a single-crystal MgAl₂O₄ film with {001} MgAl₂O₄‖{001} MgO. Above 590°C, an additional layer of MgAl₂O₄, which is polycrystalline, formed between the γ-Al₂O₃ and the single-crystal spinel. Polycrystalline Mg-Al₂O₄ formed only when diffusion of Mg²⁺ ions proceeded into the polycrystalline γ-Al₂O₃ region. Corresponding results were obtained for Mg-Fe₂O₄. MgAl₂O₄ films were also formed on cleaved MgO single-crystal substrates by direct evaporation, using an Al₂O₃ crucible as a source. Very slow deposition rates were used with source temperatures of ∼1350°C and substrate temperatures of ∼800°C. Departures from single-crystal character in the films may arise through temperature gradients in the substrate.     

Characteristics of La2O3 thin films deposited using metal organic chemical vapor deposition with different oxidant gas

La₂O₃ films were deposited using O₃ and the structural and electrical properties were investigated and compared with those of La₂O₃ films deposited using O₂. The deposition temperature of the La₂O₃ films using O₃ was slightly reduced compared to that of the La₂O₃ films generated using O₂. After a post-annealing process at 600 and 900 °C, the crystallinity of the La₂O₃ films using O₃ were smaller than that using O₂. The leakage current density increased after annealing at 600 °C due to densification and then decreased after annealing at 900 °C due to interfacial layer growth. The effective dielectric constant of the La₂O₃ films deposited using O₃ decreased at 900 °C due to interfacial layer growth. The La₂O₃ films deposited using O₃ showed better structural and electrical properties in this study.