Effect of excess Bi2O3 on structures and dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films deposited at room temperature by RF magnetron sputtering

To compensate for bismuth loss that occurred during the film deposition process, Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were deposited at room temperature from the ceramic targets containing various excess amounts of bismuth (0–20 mol%) on Pt/TiO₂/SiO₂/Si substrates by using RF magnetron sputtering technique. The effect of bismuth excess content on the microstructure and electrical properties of BZN thin films was studied. The microstructure and chemical states of the thin films were studied by SEM and XPS. EPMA was employed to assess the film stoichiometry. The X-ray diffraction analysis reveals that the BZN thin films exhibit the amorphous structure in nature. An appropriate amount of excess bismuth improves the dielectric and electrical properties of BZN thin films, while too much excess bismuth leads to deterioration of the properties. BZN thin film with 5 mol% excess bismuth exhibits a dielectric constant of 61 with a loss of 0.4% at 10 kHz and leakage current of 7.26×10^?7 A/cm² at an electric field of 200 kV/cm.     

Microwave dielectric properties of bismuth zinc niobate thin films deposited on alumina by pulsed laser deposition

Bi₂Zn_2/3Nb_4/3O₇ thin films were prepared on Al₂O₃ substrates by pulsed laser deposition. The phase compositions and microstructures were characterized by X-ray diffraction and atomic force microscopy. The as-deposited films were all amorphous in nature. All films were crystallized after the post annealing at the temperature range of 700–900 °C for 30 min in air. The texture characteristics change with annealing temperature. A split post dielectric resonator method was used to measure the microwave dielectric performance at the resonant frequencies of 10, 15 and 19 GHz. For the films annealed at 900 °C, the preferential orientation is similar to the monoclinic BZN bulk. The microwave dielectric constants at 10, 15 and 19 GHz are 69.4, 58.9 and 47.9, respectively, which are closer to these of the monoclinic BZN bulk.     

Dielectric properties and electrical behaviors of tunable Bi1.5MgNb1.5O7 thin films

The Bi_1.5MgNb_1.5O₇ (BMN) thin films were prepared on Au-coated Si substrates by rf magnetron sputtering. We systematically investigated the structure, dielectric properties and voltage tunable property of the films with different annealing temperatures. The relationships of leakage current and breakdown bias field with annealing temperature were firstly studied and a possible explanation was proposed. The deposited BMN thin films had a cubic pyrochlore phase when annealed at 550 °C or higher. With the increasing of annealing temperature, the dielectric constant and tunability also went up. BMN thin films annealed at 750 °C exhibited moderate dielectric constant of 106 and low dielectric loss of 0.003–0.007 between 10 kHz and 10 MHz. The maximum tunability of 50% was achieved at a bias field of 2 MV/cm. However, thin films annealed at 750 °C had lower breakdown bias field and higher leakage current density than films annealed below 750 °C. The excellent physical and electrical properties make BMN thin films promising for potential tunable capacitor applications.     

Phase development and crystallization of CuAlO2 thin films prepared by pulsed laser deposition

A polycrystalline CuAlO₂ single-phase target was fabricated by the conventional solid-state reaction route using Cu₂O and Al₂O₃. Thin films of CuAlO₂ were deposited by a pulsed laser deposition process on sapphire substrates at different temperatures. Then, post-annealing was followed at different conditions, and the phase development process of the films was examined. As grown thin films in the temperature range of 450–650 °C were amorphous. The c-axis oriented single phase of CuAlO₂ thin films were obtained when the films were post-annealed at 1100 °C in air after growing at 650 °C. Phi-scan of the film clearly showed 12 peaks, each of which are positioned at intervals of 30°. This is thought to be caused by the rhombohedral structured CuAlO₂ thin film growing in the states of 30° tilt during the annealing process. Hall effect analysis of the film was carried out.     

Microwave dielectric properties of the (BaxSr1−x)TiO3 thin films on alumina substrate

Barium strontium titanate, (Ba_xSr_1?x)TiO₃ (BST) thin films have been prepared on alumina substrate by sol–gel technique. The X-ray patterns analysis indicated that the thin films are perovskite and polycrystalline structure. The interdigital electrode with 140 nm thickness Au/Ti was fabricated on the film with the finger length of 80 μm, width of 10 μm and gaps of 5 μm. The temperature dependence of dielectric constant of the BST thin films in the range from ?50 °C to 50 °C was measured at 1 MHz. The dielectric properties of the BST thin films were measured by HP 8510C vector network analyzer from 50 MHz to 20 GHz.     

A low-loss BST thin film on initial nucleation layer for micro and millimeter wave tunable phase shifter

Barium strontium titanate, (Ba,Sr)TiO₃ (BST), thin films have been deposited on (1 0 0)-oriented MgO substrate by combining preparation of initial layer by Pulsed Laser Deposition and main layer by Metal-Organic-Decomposition method. Films with an initial layer of 20, 30 and 40 nm thickness and final thickness of 400, 650 and 800 nm have been obtained. Physical and dielectric properties of the BST thin films have been characterized from the viewpoint of frequency-agile micro and millimeter circuit applications. The results reveal that Ba_0.6Sr_0.4TiO₃ thin films have a good crystallinity with characteristic orientation that is affected by the deposition conditions of the initial layer. Interdigital capacitor with a gap of 10 μm has been characterized and the dielectric loss and tunability are as low as 0.002–0.004 and 12%, respectively, at frequency of 1 MHz for the applied voltage from ∓40 to ±40 V. At microwave frequencies, classic-shaped coplanar waveguide lines formed on BST/(1 0 0) MgO were investigated. A differential phase shift of 18° was obtained at 20 GHz with insertion loss of about −2 dB at 60 V for Au/Cr interconnection. Finally, a three-stage LC-ladder-type phase shifter with variable capacitors of BST thin film has been fabricated considering the experimental results obtained for the classic-shaped coplanar waveguide lines and a maximum phase shift of 40° is obtained at 20 GHz and 60 V.     

Anode-supported SOFCs based on Sm0.2Ce0.8O2−δ electrolyte thin-films fabricated by co-pressing using microwave combustion synthesized powders

Decreasing the electrolyte thickness is an effective approach to improve solid oxide fuel cells (SOFCs) performance for intermediate-temperature applications. Sm_0.2Ce_0.8O_2−δ (SDC) powders with low apparent density of 32±0.3 mg cm⁻³ are synthesized by microwave combustion method, and SDC electrolyte films as thin as ~10 μm are fabricated by co-pressing the powders onto a porous NiO–SDC anode substrate. Dense SDC electrolyte thin films with grain size of 300–800 nm are achieved at a low co-firing temperature of 1200 °C. Single cells based on SDC thin films show peak power densities of 0.86 W cm⁻² at 650 °C using 3 vol% humidified H₂ as fuel and ambient air as oxidant. Both the thin thickness of electrolyte films and ultra-fine grained anode structure make contributions to the improved cell performance.     

Effect of Ba(Zn1/3Nb2/3)O3 modification on structure and ferroelectric properties of 0.6Pb(Mg1/3Nb2/3)O3–0.4Pb(Zr0.52Ti0.48)O3 ceramics

In this study, (1−x)[0.6Pb(Mg_1/3Nb_2/3)O₃–0.4Pb(Zr_0.52Ti_0.48)O₃]–xBa(Zn_1/3Nb_2/3)O₃; (1−x)PMNZT60/40–xBZN having x=0, 2.5, 5, 7.5, and 10 mol% ceramics were prepared by mixed oxide powder method and sintered using a two-step process. Phase transitions were investigated by XRD, microstructure by SEM, crystal morphology by TEM, the dielectric and ferroelectric properties by capacitance measurement setup and modified Sawyer-Tower circuit, respectively. The dielectric constant and dielectric loss tangent were measured as functions of both temperature and frequency. The XRD results show the phase transition from tetragonal phase to pseudo-cubic phase with addition of BZN in PMNZT system. Grain size of about 1.23–2.42 μm and crystallite size in a range of 421–2152 nm were obtained. The pure-phase 0.6PMN–0.4PZT ceramics show the normal ferroelectric behavior. The 0.95(PMNZT60/40)–0.05BZN and 0.925(PMNZT60/40)–0.075BZN showed a broad and diffused dielectric properties and the dispersive phase transition, indicating the relaxor ferroelectric behavior. The transition temperature in the BZN-modified PMNZT system is seen to decrease from 166 °C in pure PMNZT60/40 to 102 °C and 54 °C with increasing BZN content to 5 and 10 mol%, respectively. In addition, the maximum dielectric constant is decreased with increasing BZN content. The P–E hysteresis loop measurements show the change from the normal ferroelectric behavior in PMNZT60/40 ceramic to more relaxor behavior that was induced with BZN addition. These results clearly demonstrated the significance of BZN to the electrical responses of the PMNZT60/40 system.     

Pulsed laser deposition BTS thin films: The role of substrate temperature

BaSn_0.15Ti_0.85O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrate by pulsed laser deposition and the effects of substrate temperature on their structure, dielectric properties and leakage current density were investigated. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of the BTS thin films which exhibit a polycrystalline perovskite structure if the substrate temperature ranges within 550–750 °C. The dielectric constant and loss tangent of the BTS thin films deposited at 650 °C are 341 and 0.009 at 1 MHz, respectively, the tunability is 72.1% at a dc bias field of 400 kV/cm, while the largest figure of merit (FOM) is 81.1. The effect of the substrate temperature on the leakage current of the BTS thin films is discussed.     

The effects of deposition temperature on structure and dielectric properties of Ba0.6Sr0.4TiO3 thin films produced by pulsed laser deposition

The effects of deposition temperature on orientation, surface morphology and dielectric properties of the thin films for Ba_0.6Sr_0.4TiO₃ thin films deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition were investigated. X-ray diffraction patterns revealed a (2 1 0) preferred orientation for all the films. With rising substrate temperature from 650 °C to 700 °C, the crystallinity and crystal grain size of the films increase, the relative dielectric constant increases, but the dielectric losses have not obvious difference. The film deposited at 350 °C and annealed at 700 °C has strongly improved roughness and dielectric permittivity compared with the film only deposited directly at 700 °C. Three distinct relaxation processes within tan(δ) were found for the Ba_xSr_1?xTiO₃ film: a broadened process of the film relaxation, an intermediate peak which originates from Maxwell–Wagner–Sillars polarization, and an extremely slow process ascribed to leak current. The complex dielectric permittivity and loss can be fitted by an improved Cole–Cole model corresponding to a stretched relaxation function.     

Dielectric properties of sol–gel derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(1 0 0) substrates

The ultrahigh relative dielectric constant (K′) values reported for the CaCu₃Ti₄O₁₂ bulk ceramics (10⁴ at RT) joined to their low thermal dependence, no phase transitions are expected between −173 and 330 °C, make this material very promising for capacitor applications and certainly for microelectronics. The interest in the preparation of this material in thin film form is twofold, the understanding of its physical properties and the integration of this high K′ oxide with the Si technology. In this work, the preparation of CCTO thin films onto Pt/TiO₂/SiO₂/Si(1 0 0) substrates is attempted using sol–gel processing and rapid thermal processing (RTP) at 650 °C. Structural, microstructural and dielectric characterization of the films is performed. The results are commented and discussed on the light of the grain boundary effect on the dielectric constant and the possibility of application of these thin films in microelectronic devices.     

Preparation and electrical properties of Bi2Zn2/3Nb4/3O7 thin films deposited at room temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited at room temperature on Pt/Ti/SiO₂/Si(1 0 0) and polymer-based copper clad laminate (CCL) substrates by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited in situ with no intentional heating under an oxygen pressure of 4 Pa and then post-annealed at 150 °C for 20 min. It was found that the films are still amorphous in nature, which was confirmed by the XRD analysis. It has been shown that the surface roughness of the substrates has a significant influence on the electrical properties of the dielectric films, especially on the leakage current. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates exhibit superior dielectric characteristics. The dielectric constant and loss tangent are 59.8 and 0.008 at 10 kHz, respectively. Leakage current density is 2.5 × 10^?7 A/cm² at an applied electric field of 400 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on CCL substrates exhibit the dielectric constant of 60 and loss tangent of 0.018, respectively. Leakage current density is less than 1 × 10^?6 A/cm² at 200 kV/cm.     

Effect of substrate temperature on structural and electrical properties of BaZr0.2Ti0.8O3 lead-free thin films by pulsed laser deposition

Barium zirconate titanate (BaZr_0.2Ti_0.8O₃, BZT) 250 nm thick thin films were fabricated by pulsed laser deposition and the influence of the substrate temperature on their preferred orientation, microstructure, morphology and dielectric properties was investigated. Dielectric measurements indicated the (1 1 0)-oriented BZT thin films deposited at 750 °C to show good dielectric properties with high dielectric constant (~500 at 100 kHz), low loss tangent (<0.01 at 100 kHz), and superior tunability (>70% at 400 kV/cm), while the largest figure of merit was 78.8. The possible microstructural background responsible for the high dielectric constant and tenability is discussed. In addition, thin films deposited at 750 °C with device quality factor of 8738 and dielectric nonlinearity coefficient of 1.66×10⁻¹⁰ J/C⁴m⁵ were demonstrated.     

Preparation of antireflective SiO2 nanometric films

Antireflective nanometric SiO₂ films were formed on glass substrates by dip coating from a colloidal SiO₂ sol having an average particle size of 9 nm. Withdrawal speed of dip coating was varied between 100 and 200 mm/min with 25 mm increments, and baking temperature of the films was altered between 300 and 550 °C with 50 °C increments. Obtained SiO₂ films were in 80–200 nm thickness range. Film thickness was seen to increase with increasing withdrawal speed and to decrease with increasing baking temperature. A maximum light transmittance of 95% was obtained with 4.5% points increase, from the films which were withdrawn at 100 mm/min and baked at 450 or 500 °C. It was seen from SEM observations that the films exhibited full coverage on glass surface and contained no voids or cracks. Size of SiO₂ particles in the film was seen in the AFM analyses to increase with baking temperature. Sintering of SiO₂ particles appeared to accelerate at temperatures over 450 °C.     

Lead zirconium titanate thin films prepared by thermal annealing of multilayer structures composed of PbO,ZrO2 and TiO2

Lead zirconium titanate [Pb(Zr_xTi_1?x)O₃ or PZT] thin films were prepared by the thermal annealing of multilayer films composed of binary oxide layers of PbO, ZrO₂ and TiO₂. The binary oxides were deposited by metal organic chemical vapor deposition. An interdiffusion reaction for perovskite PZT thin films was initiated at approximately 550 °C and nearly completed at 750 °C for 1 h under O₂ annealing atmosphere. The composition of Pb/Zr/Ti in perovskite PZT could be controlled by the thickness ratio of PbO/ZrO₂/TiO₂ where the contribution of each binary oxide at the same thickness was 1:0.55:0.94. The electrical properties of PZT (Zr/Ti = 40/60, 300 nm) prepared on a Pt-coated substrate included a dielectric constant ?_r of 475, a coercive field E_c of 320 kV/cm, and remnant polarization P_r of 11 μC/cm² at an applied voltage of 18 V.     

Effects of thickness on structures and electrical properties of K0.5Na0.5NbO3 thick films derived from polyvinylpyrrolidone-modified chemical solution

Lead-free ferroelectric K_0.5Na_0.5NbO₃ (KNN) films with different thicknesses were prepared by polyvinylpyrrolidone (PVP)-modified chemical solution deposition (CSD) method. The KNN films with thickness up to 4.9 μm were obtained by repeating deposition-heating process. All KNN thick films exhibit single perovskite phase and stronger (1 1 0) peak when annealed at 650 °C. The variation of dielectric constant with thickness indicates that there exists a critical thickness for the dielectric constant in the KNN films which should lie in 1.3–2.5 μm. The similar trend is observed for the ferroelectric and piezoelectric properties of KNN films. Both the remnant polarization P_r and the piezoelectric coefficient d₃₃ of KNN thick films increase with the film thickness and become saturated after the critical thickness.     

Low-temperature fabrication of Ba1−xSrxTiO3 thin films with good dielectric properties on platinized silicon substrates

Ba_0.7Sr_0.3TiO₃ (BST) thin films 500 nm in thickness were prepared on technologically desirable Pt/TiO₂/SiO₂/Si(1 0 0) substrates by ion beam sputtering (IBS) and post-deposition annealing method. The effect of annealing temperature on the structural and dielectric properties of BST thin films was systematically investigated. A sharp transition in their tunable dielectric behaviours was observed in good agreement with the evolution of crystal structure from amorphous to crystalline phase. It was demonstrated that the perovskite phase could crystallize in BST films at a very low temperature, around 450 °C. The lowering of perovskite crystallization temperature in the BST films was explained in terms of the high energetic process nature of IBS technique. A high dielectric tunability of 42% at E (electric field intensity) = 500 kV/cm and a low loss tangent of 0.013 at zero bias were both obtained in the 450 °C-annealed film, thereby resulting in the highest figure-of-merit factor among all the different temperature annealed films. Moreover, the 450 °C-annealed film showed superior leakage current characteristics with a low leakage current density of about 10^?4 A/cm² at E = 800 kV/cm.     

Microwave dielectric properties of BaTi4O9 thin film

BaTi₄O₉ thin films have been prepared by RF magnetron sputtering on the Pt/Ti/SiO₂/Si substrates and the dielectric properties of the BaTi₄O₉ film have been investigated at microwave frequency range. The homogeneous BaTi₄O₉ thin film was obtained when the film was grown at 550 °C and rapid thermal annealed (RTA) at 900 °C for 3 min. The circular-patch capacitor (CPC) was used to measure the microwave dielectric properties of the film. The dielectric constant (ɛ_r) and the dielectric loss (tan δ) were successfully measured up to 6 GHz. The ɛ_r of the BaTi₄O₉ thin film slightly increased with the increase of the film thickness. However, the tan δ decreased with increasing the thickness of the film. The ɛ_r of BaTi₄O₉ thin film was similar to that of the BaTi₄O₉ ceramics, which is about 36–39. The tan δ of the film with 460 nm thickness was very low approximately, 0.0001 at 1–3 GHz. Since BaTi₄O₉ film has a high ɛ_r and a low tan δ, the BaTi₄O₉ film can be used as the microwave devices.     

Processing and dielectric characterization of Ba0.3Sr0.7TiO3 thin films on alumina substrates

Ba_0.3Sr_0.7TiO₃ (BST) thin films were prepared from the sols based on alkaline earth acetates and titanium propoxide in 2-methoxyethanol–acetic acid solvents and deposited on polished alumina substrates by spin coating. The perovskite phase crystallizes upon heating at/above 700 °C. By increasing the annealing temperature from 700 to 900 °C the grain size increases from 40 to 80 nm, due to the increased driving force for crystallization. The annealing time has got only a minor influence on grain size as a consequence of constrained conditions of the film. The dielectric permittivity and tunability (ɛ_0 V/ɛ_200 V) of BST films, measured at 1 MHz, strongly depend on the grain size, exhibiting the values of 345 and 1.47, and 722 and 1.93 for the films with 40 and 80 nm-sized grains, respectively.     

Structure and dielectric properties of barium titanate thin films for capacitor applications

BaTiO₃ is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO₃ have been required. In this work, BaTiO₃ thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550 °C–750 °C show a pure tetragonal perovskite structure. The films deposited at 550 °C–625  °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650 °C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625 °C and 4.5 Pa has the relative permittivity of 630 and the loss tangent of 2% at 10 kHz.