Bi1.5Zn1.0Nb1.5O7 thin films deposited at low temperature and post-annealed for crystallization

Near-stoichiometric Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si (100) substrates at 400 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The as-deposited BZN thin films were post-annealed at 700 °C for 30 min in situ vacuum chamber (in situ) and in oxygen ambient oven (ex situ). The crystallinity, microstructure and electrical properties of BZN thin films were investigated. The X-ray diffractometer results indicate that BZN thin films deposited at 400 °C are amorphous in nature and the post-annealed thin films exhibit a cubic pyrochlore structure. The as-deposited BZN thin films show permittivity of 68 and loss tangent of 0.0011 at 10 kHz, respectively. After a post-annealing at 700 °C for 30 min, the dielectric properties of thin films are significantly improved. Permittivity and loss tangent of the in situ annealed films are 127 and 0.005 at 10 kHz, respectively. And the films post-annealed in O₂ oven show the largest permittivity of 170 and tangent of 0.006. The improved dielectric properties can attribute to the crystallization of thin films. BZN thin films deposited at low temperature and crystallized at high temperature show the dielectric tunability without an electric breakdown to the maximum measurement bias voltage. And BZN thin films also show the excellent leakage current properties.     

Bi2MoO6 dielectric thin films fabricated by thermal oxidation of Bi/Mo thin films at ultra-low temperature

Bi/Mo multilayer thin films are deposited on Si/SiO₂/Pt substrates by direct current magnetron sputtering. The effect of annealing temperature on the microstructure, dielectric and electrical properties of the as-sputtered films is characterized systematically. X-ray diffraction data indicate that the films annealed at 450–600 °C are a mixture of diphase with the main phase Bi₂MoO₆ and secondary phase Bi₂Mo₂O₉. Results of scanning electron microscope observation show that the films annealed at 500–550 °C are dense and uniform, in particular the films annealed at 500 °C exhibit optimal dielectric and electrical properties with dielectric constant as high as 37.5, dielectric loss 1.06 %, temperature coefficient of dielectric constant ?10.86 ppm °C^?1 at 1 kHz, and leakage current density of 1.46 × 10^?7 A mm^?2 at an electric field of 18.2 kV mm^?1. With the advantages of ultralow densification temperature (500 °C) and very high sputtering deposition rate (76 nm min^?1), it is anticipated that thermal oxidation method of the sputtered Bi/Mo thin films could be a promising technique for fabrication of Bi₂MoO₆ ceramic thin film embedded-capacitors.     

Stability and transport properties of microcrystalline Si1−xGex films

The crystallization evolution of boron and phosphorus doped amorphous Si_1−xGe_x films (5×10¹⁷–5×10²⁰ cm⁻³), deposited on SiO₂/Si(001) substrates by molecular beam in high vacuum at room temperature, were studied by XRD, TEM and SEM. The amorphous Si_1−xGe_x films were fully crystallized at ∼600°C. Up to 800°C no morphology changes were observed. Between 800 and 950°C, voids and hillocks were gradually developed in the films, which consequently collapsed. The Hall concentration and mobility were characterized in the Si_1−xGe_x films, annealed between 600 and 800°C. The mobility and conductivity of p-Si_0.5Ge_0.5 films at room temperature were found to be relative high: 60 cm²/V s and 2000 (Ω cm)⁻¹, respectively.     

The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films prepared by RF magnetron sputtering

(Ba_{1 − x} Sr _x )TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering. The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy and dielectric frequency spectra. It was found that the preferred orientation of BST thin films could be tailored by insertion of YSZ interlayer and adjusting the thickness of YSZ interlayer. The BST thin films deposited on YSZ interlayer exhibited a more compact and uniform grain structure than that deposited directly on Pt electrode. Dielectric measurement revealed that the BST thin films deposited on 10 nm YSZ interlayer have the largest dielectric constant and a low dielectric loss tangent. The enhanced dielectric behavior is mainly attributed to the YSZ interlayer which serves as an excellent seeding layer to enhance the crystallization of subsequent BST films layer, and a smaller thermal stress field built up at the interface between YSZ interlayer and BST film layer.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

Dielectric properties of lead zirconate titanate thin films seeded with barium strontium titanate nanoparticles

A low temperature synthetic method recently proposed by the authors was applied to the fabrication of lead zirconate titanate (PZT) thin films containing crystalline seeds of barium strontium titanate (BST) nanoparticles. PZT precursor and the BST particles were prepared with complex alkoxide methods. Precursor solution suspending the BST particles was spin-coated on Pt/Ti/SiO₂/Si substrate to film thickness of 500–800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and induced crystallization of PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10⁻⁶ A/cm² at applied electric field from 0 to 64 kV/cm.     

Growth of Bi1.5MgNb1.5O7 thin films on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering

In this letter, bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films were deposited on Pt/Ti/SiO₂/Si substrates by using radio-frequency magnetron sputtering at various substrate temperatures. Based on the phase compositions and microstructures of these samples, we discussed the nucleation and growth of the BMN thin films and how the substrate temperature influenced these processes. The thin film begins to crystallize at 450 °C, and the annealed films were all composed of the cubic pyrochlore phase with a strong (222)-preferred orientation. The film deposited at 450 °C exhibited a large dielectric constant of 173, and a tunability of 26.6 % was obtained at a max dc bias field of 0.8 MV/cm.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Structural and electrical properties of chromium and nickel films evaporated in the presence of oxygen

Electron-optical investigations of Cr films evaporated in the presence of oxygen (1 × 10^-7 to 5 × 10^-7 torr) have shown that the negative temperature coefficient of resistivity (TCR) is caused by small amounts of an amorphous oxide. On annealing these films in a vacuum of better than 5 × 10^-9 torr (e.g. for 140 h at 395°C) the amorphous phase crystallized and could be identified as Cr₂O₃. When Ni is evaporated in the presence of oxygen the TCR changes from positive to negative values at about 5 × 10^-5 torr. Since the negative TCR of oxygen-doped Cr-Ni (60/40) films did not change after annealing these films in a hydrogen atmosphere at 300°C (reduction of Ni oxide) it becomes plausible that the negative TCR of the Cr-Ni films, too, is caused by an amorphous Cr oxide surrounding the metal crystals.     

Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds

HfO₂ films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 Å) nearly stoichiometric monoclinic HfO₂. The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO₂ films varied between 2 × 10⁶ and 4.5 × 10⁶ V cm^?1. C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10¹¹ and 6 × 10¹¹ cm^t?2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V_FB values were between ?0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V² over a wide range.     

Ferroelectric properties of neodymium-doped Bi4Ti3O12 thin films crystallized in different environments

Neodymium (Nd)-doped Bi₄Ti₃O₁₂ (Bi_3.15Nd_0.85Ti₃O₁₂, BNT) ferroelectric films have been deposited on Pt/Ti/SiO₂/Si substrates by a sol–gel process and crystallized in nitrogen, air and oxygen environments, respectively. The crystallization environment was found to be important in determining the crystallization and ferroelectric properties of the BNT films. The film crystallized in nitrogen at a relatively low temperature of 650 °C, and exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2P_r=63.6 μC/cm², a coercive field of 130 kV/cm and a fatigue-free characteristic. While the films annealed in air and oxygen, they did not show good crystallinity and ferroelectricity until they were annealed at 710 and 730 °C, respectively. A correlation between the remanent polarization and dielectric constants of the BNT films has been observed.     

Mixed Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>:MoO<Subscript>3</Subscript> (95:5 and 85:15) thin films and their properties for electrochromic device applications

Nb₂O₅:MoO₃ (95:5 and 85:15) thin films were deposited onto glass and fluorine doped tin oxide coated glass substrates at 100 and 300 °C by RF magnetron sputtering technique. The physical and electrochromic properties of the films were studied. XRD result reveals that deposited films were amorphous. The XPS study confirms the compositional purity and the presence of Nb⁵⁺ and Mo⁶⁺ in the deposited film. Surface morphological study shows platelet like features of deposited film. The average transmittance of the film is varied between 91 and 85 %. Photoluminescence study exhibits three characteristic emission peaks and confirms the better optical quality of deposited film. Raman spectra show the LO–TO splitting of Nb–O stretching of the deposited film. Electrochromic behavior of the deposited films characterized by cyclic voltammetry using 0.5 M LiClO₄·PC and 0.5 M H₂SO₄ electrolyte solutions show all the films are having better reversibility and reproducibility in their electrochemical analysis.     

Rietveld analysis of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films obtained by RF-sputtering

Calcium copper titanate, CaCu₃Ti₄O₁₂, CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO₂/Si (100) substrates at a room temperature followed by annealing at 600 °C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N₂ atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O₂ treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency -independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600 °C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10^?7 A/cm² at a 1.0 V. The current–voltage measurements on MFS capacitors established good switching characteristics.     

Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Dynamic formation of zircon during high temperature deformation of zirconia–silica composites with alumina additions

A three phase ceramic composite of 8 mol% Y₂O₃ stabilized ZrO₂ (YSZ), SiO₂, and Al₂O₃ was evaluated for potential high temperature superplasticity. The amorphous SiO₂ content was 5 wt.%, and increasing additions of Al₂O₃ were made. The effect of varying the Y₂O₃ stabilizer concentration in ZrO₂ was also studied. Samples sintered at 1200 °C contained only YSZ, Al₂O₃, and amorphous SiO₂, but ZrSiO₄ formed in the samples above 1300 °C. Mullite (3Al₂O₃ · 2SiO₂) was not detected in any samples. Specimens of 1 wt.% Al₂O₃–YSZ/SiO₂ had an anomalously high deformation rate of ∼2 × 10⁻⁴ s⁻¹ at 1200 °C when compared to YSZ/SiO₂ without Al₂O₃ (∼4 × 10^-5 s⁻¹). Higher amounts of Al₂O₃ additions decreased the strain rate. Extensive deformation of Al₂O₃ doped YSZ/SiO₂ at 1200 °C induced the formation of ZrSiO₄ due to enhanced reaction rates. This distributed, yet locally interconnected, zircon phase rapidly eroded the strain rate after ∼60% deformation.     

Effect of firing temperature on microstructure and dielectric properties of chromium oxide based glass composite thick films on stainless steel substrate

We report the influence of firing temperature on Al₂O₃–chromium oxide based (Cr₂O₃–Bi₂O₃–B₂O₃–SiO₂–Al₂O₃) glass composite (named as GC-1 composite) thick films of thickness (27?±?3) µm deposited onto 0.6 mm thick austenitic grade stainless steel (DIN 1.4301/AISI 304) substrate by screen printing technique, which can be used as a substitute to alumina substrate. Prior to formulation of glass composite, the chromium oxide based glass (named as GC-1) phase was prepared separately by melt-quench technique. X-ray diffraction analysis confirmed amorphous nature of the GC-1 glass. The thermo gravimetric analysis and differential scanning calorimetry of the GC-1 glass shows thermal stability over the temperature range of 20–1000 °C. We observed that the firing temperature significantly influences microstructural and dielectric properties of the GC-1 composite film. The deposited GC-1 composite films onto stainless steel base were fired at temperatures between the range of 550–750 °C, showed the surface resistivity in the range of (1.0–6.9?±?0.2) × 10¹² ohms per square. The microstructure of these composite films recorded using scanning electron microscopy and electrical properties recorded using LCR meter were correlated with each other. The study revealed that the film fired at 600 °C were found to be superior among the samples under investigation in terms of microstructure, stable relative permittivity [36 (±?1)] and low loss tangent [0.02 (±?0.002)] in frequency range of 1–200 kHz, and surface resistivity (~?5.1?×?10¹² ohms per square).     

Influence of deposition temperature on the structure and optical properties of HfO2 thin films

Hafnium oxide (HfO₂) thin films were deposited on Si (001) substrates by electron beam evaporation at various growth temperatures. It was found that the film was amorphous when deposited at temperatures lower than 200°C. It was polycrystalline when deposited at 250°C and 300°C. At temperatures above 400°C, it was grown preferably along the [111] direction. The influence of growth temperature on the surface morphology and optical property was also investigated.     

Transparent and heat-reflecting indium tin oxide films prepared by reactive electron beam evaporation

Transparent and heat-reflecting indium tin oxide films were prepared by electron beam evaporation of In₂O₃9mol.%SnO₂ in an oxygen atmosphere of about 5×10^?4 Torr. A visible absorption of less than 2%, a thermal IR reflectance exceeding 90% and a d.c. resistivity of approximately 3×10^?4 Ω cm were obtained from films 0.4 μm thick deposited at a substrate temperature of 300°C. Films with similar properties could be prepared with substrate temperatures as low as 150°C.     

Crystal orientation dependent microwave dielectric properties of sputtered SBTi thin films on fused silica substrates

Thin films of SBTi (SrBi₄Ti₄O₁₅) were deposited on fused silica substrates by rf-magnetron sputtering at substrate temperatures from 600 to 725 °C. The effect of substrate temperature on preferential orientation, microstructure, Raman scattering characteristics and microwave dielectric properties of SBTi thin films were investigated. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. As the substrate temperature increases, the preferential orientation changes from (119) to (0010). Films deposited at 700 °C exhibits less lattice distortion. It exhibits a dielectric constant about 110 and loss tangent about 0.06 at 10 GHz. It is seen from the Raman analysis that the films deposited at higher temperatures orients more towards c-axis which releases the torsional vibration mode involving TiO6 octahedra with a higher oscillator strength resulting in larger values of dielectric constant and dielectric loss for those films.