Electrochemical synthesis of ba- and Sr-based titanate thin films using Ti electrode prepared by RF sputtering

Barium and strontium titanate films were electrochemically synthesized onto Ti thin film prepared by RF sputtering. Applied current waveform was modulated to investigate the film growth mechanism. Superimposed cathodic pulses accelerated the formation of titanate thin films, and both the electrode surface pH and (Ba²⁺, Sr²⁺) ion size had a strong influence on film formation. Titanate film formation mechanism was investigated with a scanning electron microscope, an X-ray diffractometer and an electrochemical quartz crystal microbalance (EQCM).Insitu mass change of Ti electrode during electrolysis indicated that electrochemical method sets a limit to film growth.     

Dielectric properties of Mn doped Bismuth Barium Titanate based ceramic thin films prepared by PLD technique

In this article, the effect of Mn doping on the permittivity and dielectric loss in 0.67BiFeO₃-0.33BaTiO₃ (BF-BT) based film bulk acoustic resonator test structures has been investigated. BF-BT thin films were deposited on the fused silica substrates with Pt/TiO₂/Ti as bottom electrode. During the study of the BF-BT based parallel-plate structures, it has been revealed that BF-BT is in the ferroelectric state at room temperature. Higher permittivity (ԑ) is observed at a growth temperature of 600 °C and lower dielectric loss is achieved at 0.3 wt% Mn doping contents. These results show that the proposed BF-BT based FBAR test structure has a great potential for applications in tunable thin Film Bulk Acoustic Resonator (FBAR) devices. Comparison of the measured and simulation results has been made by utilizing the Mason equivalent circuit.     

Barium strontium titanate nanocrystalline thin films prepared by soft chemical method

Barium strontium titanate (Ba_0.65Sr_0.35TiO₃) nanocrystalline thin films, which were produced by the soft chemical method, were crystallized at low temperature using a domestic microwave oven. A SiC susceptor were used to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are crack-free, well-adhered, and fully crystallized. The microstructure displayed a polycrystalline nature with nanograin size. The metal-BST-metal structure of the thin films treated at 700 °C show good electric properties. The ferroelectric nature of the BST35 thin film was indicated by butterfly-shaped C–V curves. The capacitance–frequency curves reveal that the dielectric constant may reach a value up to 800 at 100 kHz. The dissipation factor was 0.01 at 100 kHz. The charge storage density as function of applied voltage graph showed that the charge storage densities are suitable for use in trench type 64 Mb (1–5 μC/cm²) and 265 Mb (2–11 μC/cm²) DRAMs.     

Low-temperature preparation of hydrothermal lead zirconate titanate thin films

In preparing lead zirconate titanate thin films under hydrothermal conditions, we investigated the effects of concentrations of nutrient and mineralizer, reaction time and reaction temperature on crystallinity, grain size and shape. Experiments were performed in the ranges of 0.1-1.0M Pb(NO₃)₂, and 0-6.0M KOH with varying reaction time from 0 to 48 hours at 60-200 °C. In the experiment, lead zirconate titanate thin film of homogeneous crystalline grain was obtained through a 24 hour reaction with 0.4M Pb(NO₃)₂ and 5.0M KOH at 140 °C. The thickness of the film was 0.9-1.6 μm, and it exhibited a saturation polarization (Ps) of 18.3 μC/cm², remnant polarization (Pr) of 7.4 μC/ cm₂ and coercive field (Ec) of 0.41 kV/cm. The dielectric constant and loss (δ) measured at 1 kHz were approximately 1020 and 0.15, respectively.     

A study of deposition rate and characterization of bn thin films prepared by cvd

Triethylboron (TEB) and ammonia were employed as precursors in preparation of boron nitride thin films on Si(100) substrate by CVD. Operating parameters such as reactor pressure and feed rates of gases were varied to investigate their effects on deposition rate and film characteristics. Total gas pressure in the reactor was varied from near atmospheric to near 1 torr. Deposition temperature was in the range of 850-1,100‡C. Deposition rate increased with increase of partial pressure of TEB, but decreased with increase of total pressure in the reactor. Deposited films were examined with SEM, FTIR, XPS, AES and XRD. Films were BN of turbostratic structure and their texture and carbon content varied with deposition conditions.     

Crystallisation kinetics of hydroxyapatite thin films prepared by sol-gel process

Abstract

Abstract

In this study, the crystallisation of nano hydroxyapatite (HA) films on stainless steel 316L was studied. The film was prepared by sol-gel technique. The process was started with preparation of an HA sol. After aging of the sol at room temperature, a stainless steel 316L substrate was dip coated and then was heat treated from 350 to 450°C at different periods of time in air. The crystallisation behaviour and the transformation-temperature-time diagram of HA films were achieved and analysed using the avrami equation. The results showed that the crystallisation of HA began at 250°C and was increased up to 450°C. The obtained HA film showed a nanostructure character with a suitable crystalinity after heat treatment.     

Crystalline structure of YSZ thin films deposited on Si(111) substrate by chemical vapor deposition

Yttria-stabilized zirconia (YSZ) thin films were formed on Si(111) substrate by chemical vapor deposition (CVD) in a temperature range of 650–800 °C using β-diketone metal chelates. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) data evidenced that YSZ thin films have a smooth surface with fine grains and crystalline structure, respectively. The crystalline structure of YSZ films was affected by the deposition temperature. The X-ray photoelectron spectroscopy (XPS) data indicated that the YSZ film grows thick enough to prevent the diffusion of Si.     

Preparation and characterization of heteroepitaxial Zn2SnO4 single crystalline films prepared on MgO (100) substrates

Zinc stannate (Zn₂SnO₄) films were deposited on MgO (100) substrates by pulsed laser deposition, and Zn₂SnO₄ monocrystalline films were obtained by postannealing process. The structures, surface morphologies, and optical properties of the Zn₂SnO₄ films annealed at different temperatures were investigated in detail. Crystal structure analyses showed that the film annealed at 800°C was single crystal Zn₂SnO₄ with an inverse-spinel structure. The heteroepitaxial mechanism was further clarified by a schematic diagram, and the epitaxial relationships between the film and substrate were Zn₂SnO₄ (400) || MgO (200) with Zn₂SnO₄ [001] || MgO [001]. The obtained Zn₂SnO₄ films exhibited excellent transparency. The optical band gap of the 800°C-annealed Zn₂SnO₄ film was about 3.97 eV. The extinction coefficients and refractive indexes of the Zn₂SnO₄ films annealed at different temperatures as a function of wavelength were analyzed in detail.     

Controlled synthesis of Mg(OH)2 thin films by chemical solution deposition and their thermal transformation to MgO thin films

The chemical solution deposition of Mg(OH)₂ thin films on glass substrates and their transformation to MgO by annealing in air is presented. The chemical solution deposition consists of a chemical reaction employing an aqueous solution composed of magnesium sulfate, triethanolamine, ammonium hydroxide, and ammonium chloride. The as-deposited films were annealed at different temperatures ranging from 325 to 500?°C to identify the Mg(OH)₂-to-MgO transition temperature, which resulted to be around 375?°C. Annealing the as-deposited Mg(OH)₂ films at 500?°C results in homogeneous MgO thin films. The properties of the Mg(OH)₂ and MgO thin films were analyzed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and by circular transmission line model. Results by X-ray diffraction show that the as-deposited thin films have a brucite structure (Mg(OH)₂), that transforms into the periclase phase (MgO) after annealing at 500?°C. For the as-deposited Mg(OH)₂ thin film, a nanowall surface morphology is found; this morphology is maintained after the annealing to obtain MgO, which occurred with the evident formation of pores on the nanowall surface. The assessed chemical composition from X-ray photoelectron spectroscopy yields Mg_0.36O_0.64 (O/Mg ratio of 1.8) for the as-deposited Mg(OH)₂ film, where the expected stoichiometric composition is Mg_0.33O_0.67 (O/Mg ratio of 2.0); the same assessment yields Mg_0.60O_0.40 (O/Mg ratio of 0.7) for the annealed thin film, which indicates the obtainment of a MgO material with oxygen vacancies, given the deviation from the stoichiometric composition of Mg_0.50O_0.50 (O/Mg ratio of 1.0). These results confirm the deposition of Mg(OH)₂ films and the obtainment of MgO after the heat-treatment. The energy band gap of the films is found to be 4.64 and 5.10?eV for the as-deposited and the film annealed at 500?°C, respectively. The resistivity of both Mg(OH)₂ and MgO thin films lies around 10⁸?Ω·cm.     

Effects of Fabrication Conditions on the Crystallinity,Barium Deficiency,and Conductivity of BaZr0.8Y0.2O3–δ Films Grown by Pulsed Laser Deposition

Yttrium‐doped barium zirconate (BZY) thin films were deposited on MgO and sapphire substrates using a pulsed‐laser deposition (PLD) method with varying deposition rates. The films deposited with a low deposition rate exhibited highly oriented microstructures with little grain boundaries. The electrical conductivities of these films were higher than those of the films, deposited with high deposition rates, which showed little‐oriented polycrystalline microstructure. While the films deposited on the MgO substrates had a stoichiometric composition, those deposited on the sapphire substrates had a high barium deficiency, which was possibly due to the differences in the crystal structure and large lattice mismatch between the sapphire substrate and the BZY film. The electrical conductivity of the highly oriented BZY film, grown on MgO substrate with a low deposition rate, showed little barium deficiency and the highest conductivity value that is higher than the typical conductivity of sintered pellets.     

Metalorganic chemical vapor deposition of ferroelectric Pb(ZrxTi1- xO3thin films

Ferroelectric Pb(Zr_xTi_1-x)O₃ (PZT) thin films were successfully deposited on Pt/Ti/SiO₂Si substrates by metalorganic chemical vapor deposition (MOCVD). Pb(C₂H₅)₄, Zr(O-t-C₄H₉)₄, and Ti(O-i-C₃H₇)₄ were used as metalorganic precursors. Variations in crystalline structure, surface morphology, and grain size of deposited films were systematically investigated as a function of process parameters by using X-ray diffraction and scanning electron microscopy. The deposition temperature and gas composition in the reactor are the main parameters that control the microstructure and composition of films. An interrelationship between the grain orientation and surface roughness of the films was found. Films with (111) preferred orientation are significantly smoother than films with other preferred orientations. The ferroelectric properties of the films were also measured by RT66A ferroelectric tester for hysteresis loop and fatigue property. Electrical measurements revealed that the films had good ferroelectric characteristics with the high remanant polarization (32 μC/cm₂) and low coercive voltage (1.1 V).     

New formation process of plating thin films on several substrates by means of self-assembled monolayer (SAM) process

This review describes our recent works on the preparation of Ni-alloy films deposited by electroless deposition as a diffusion barrier layer for ultra large-scale integration (ULSI) interconnects by using an all-wet process.In this process, we create a novel wet fabrication process including a self-assembled monolayer (SAM) as an attachment technique between diffusion barrier layer and a substrate. Our proposal process was applied to the substrates of SiO₂/Si and both organic (methyl silsesquioxane) and inorganic (hydrogen silsesquioxane) low-k dielectrics. The key technique of this proposed process is using SAM as a catalyst trapping layer. The Ni-alloy films such as NiB were deposited on catalyzed SiO₂ or low-k substrates. The electrolessly deposited NiB films were found to exhibit sufficient thermal stability and an acceptable barrier property for preventing Cu diffusion into the SiO₂ and low-k dielectrics.     

High-performance flexible dielectric tunable BTS thin films prepared on copper foils

High-performance flexible dielectric tunable BaSn_0.15Ti_0.85O₃ thin films are prepared by barrier layer of Sb doped SnO₂ on the copper foils. Dielectric measurements indicate that the flexible thin films exhibit a low dielectric loss of below 0.007, a medium dielectric constant of ∼378, and the superior tunable dielectric properties at room temperature. Calculations of tunability and figure of merit (FOM) display a maximum value of 66.5% at 500 kV/cm and ∼77.3, respectively. In particular, the flexible BaSn_0.15Ti_0.85O₃ thin films show excellent fatigue properties during the bending cycle tests. The results demonstrate that the BaSn_0.15Ti_0.85O₃ thin films prepared on copper foils are an excellent candidate for electrically tunable applications in flexible and wearable electronics.     

Effect of rare earth doping on sol-gel derived PZT thin films

We have studied the effect of rare earth dopants (Nd, Gd and Ce) on the phase formation behavior and electrical properties of sol-gel derived Pb_1.05(Zr_0.53Ti_0.47)O₃ thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor behavior and a diffuse phase transition, characteristic of the relaxor material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO₃ lattice which causes the observed relaxor behavior     

Comparative analysis of barium titanate thin films dry etching using inductively coupled plasmas by different fluorine-based mixture gas

In this work, the inductively coupled plasma etching technique was applied to etch the barium titanate thin film. A comparative study of etch characteristics of the barium titanate thin film has been investigated in fluorine-based (CF₄/O₂, C₄F₈/O₂ and SF₆/O₂) plasmas. The etch rates were measured using focused ion beam in order to ensure the accuracy of measurement. The surface morphology of etched barium titanate thin film was characterized by atomic force microscope. The chemical state of the etched surfaces was investigated by X-ray photoelectron spectroscopy. According to the experimental result, we monitored that a higher barium titanate thin film etch rate was achieved with SF₆/O₂ due to minimum amount of necessary ion energy and its higher volatility of etching byproducts as compared with CF₄/O₂ and C₄F₈/O₂. Low-volatile C-F compound etching byproducts from C₄F₈/O₂ were observed on the etched surface and resulted in the reduction of etch rate. As a result, the barium titanate films can be effectively etched by the plasma with the composition of SF₆/O₂, which has an etch rate of over than 46.7 nm/min at RF power/inductively coupled plasma (ICP) power of 150/1,000 W under gas pressure of 7.5 mTorr with a better surface morphology.     

Nonlinear growth of zinc tin oxide thin films prepared by atomic layer deposition

Zinc tin oxide (ZTO) thin films can be deposited by atomic layer deposition (ALD) with adjustable electrical, optical and structural properties. However, the ternary ALD processes usually suffer from low growth rate and difficulty in controlling film thickness and elemental composition, due to the interaction of ZnO and SnO₂ processes. In this work, ZTO thin films with different Sn levels are prepared by ALD super cycles using diethylzinc, tetrakis(dimethylamido)tin, and water. It is observed that both the film growth rate and atom composition show nonlinear variation versus [Sn]/([Sn]+[Zn]) cycle ratio. The experimental thickness measured by spectroscopic ellipsometry and X-ray reflectivity are much lower than the expected thickness linearly interpolated from pure ZnO and SnO_x films. The [Sn]/([Sn]+[Zn]) atom ratios estimated by X-ray photoelectron spectroscopy have higher values than that expected from the cycle ratios. Hence, to characterize the film growth behavior versus cycle ratio, a numerical method is proposed by simulating the effect of reduced density and reactivity of surface hydroxyls and surface etching reactions. The structure, electrical and optical properties of ZTO with different Sn levels are also examined by X-ray diffraction, atomic force microscope, Hall measurements and ultraviolet–visible–infrared transmittance spectroscopy. The ZTO turns out to be transparent nanocrystalline or amorphous films with smooth surface. With more Sn contents, the film resistivity gets higher (>1 Ω cm) and the optical bandgap rises from 3.47 to 3.83 eV.     

Predicting dielectric tunability of compositionally-graded barium strontium titanate thin films on metal substrates by thermodynamic modeling

Dielectric properties of compositionally-graded barium strontium titanate (BST) thin films respectively on Ti and stainless steel (SS) plates were computed using a modified thermodynamic model. Calculated results predict that higher dielectric constant and tunability can be obtained when the films are onto Ti substrates, which have smaller thermal expansion coefficient (TEC). For Ti substrates, “up-graded” films (Ba/Sr ratio increases from substrate to surface) exhibit higher tunability than “down-graded” films; whereas “up-graded” films on SS plates have relatively lower tunability. The received larger dielectric constant and tunability are because of smaller total out-of-plane polarization, which is resulting from smaller total compressive strain. The calculated dielectric constant and tunability of such graded films are in accordance with those of the films fabricated via sol-gel approaches, indicating that the dielectric behavior of ferroelectric films can be adjusted by designing compositional gradient.     

Preparation of SnTe thin films on Au(1 1 1) by electrodeposition route

Tin telluride (SnTe) thin films were deposited onto Au(1 1 1) substrates from an aqueous solution containing SnCl₂, TeO₂, and C₆H₅Na₃ at room temperature (25 °C) for the first time via electrodeposition route. The electrodeposition of the thin films was studied using cyclic voltammetry, compositional, structural, optical measurements and surface morphology. It was found that the stoichiometric SnTe thin films could be obtained at −0.50 V. The as-deposited thin films were crystallized in the preferential orientation along the (2 2 0) plane. SEM investigations indicated that the shape of thin films could be altered from a spherical particle to a dendritic crystal by increasing the deposition potential. The growth of the dendritic films proceeds via formation of nanoparticles and growth of dendritic crystals on these nanoparticles. The optical absorption studies as a function of deposition time indicated that the band gap of the SnTe thin film increases as the deposition time decreases.     

Characterization of indium tin oxide (ITO) thin films prepared by a sol-gel spin coating process

Indium tin oxide (ITO) thin films were prepared by a sol-gel spin coating method, fired, and then annealed in the temperature range of 450-600°. The XRD patterns of the thin films indicated the main peak of the (2 2 2) plane and showed a higher degree of crystallinity with an increase in the annealing temperature. Upon annealing the films at 500 and 600°, two binding energy levels of Sn⁴⁺ ion of 486.9 eV and 486.6 eV, respectively, were measured in the XPS spectra. The ITO film that was annealed at 600° contained two oxidation states of Sn, Sn²⁺ and Sn⁴⁺, and it had a higher sheet resistance based on a rather low doping concentration of Sn⁴⁺. The film that was annealed at 500° and subsequently treated with 0.1 N HCl solution for 40 s showed a sheet resistance of 225 Ω/square. The surface treatment by the acidic solution diminished the RMS (root mean square) roughness value and the residual carbon content (XPS peak intensity of carbon) of the ITO films. It seems that the acid-cleaning of the ITO thin films led to a decrease of the surface roughness and sheet resistance.     

Study of photoconductivity in thin amorphous diamond-like carbon (a:DLC) films prepared by r.f. glow discharge technique

Thin a:DLC films were deposited by r.f. plasma system in which methane (CH₄) was admitted. Photoconductivity measurements were performed on an Al-a:DLC-Cu sandwich structure and an Al-a:DLC-Al planar structure. The photocurrent was measured in a wide interval of temperatures. The photocurrent signal of the sandwich device is about 100 times higher than the dark current measured under He-Ne laser incident light (2.5 mW) at 160 K. A photocurrent response time of τ_o ≈ 8 ms was measured at this temperature. In the planar device, under the same conditions, the photocurrent signal was twice the dark current. The maximum mobility-lifetime product of a:DLC (sandwich device) was about 2 × 10⁻¹⁰ cm²/V.