Influence of interface structure on microstructure and dielectric properties of bismuth magnesium niobate thin films

Bismuth magnesium niobate (Bi_3/2MgNb_3/2O₇, BMN) thin films were prepared on bare SiO₂/HR-Si and Pt/TiO₂/SiO₂/HR-Si substrates by using sol-gel spin coating technique followed by rapid thermal annealing process. The influence of the interface on crystalline structure and tunable dielectric properties of the two types of BMN films were investigated. It was found that the BMN films prepared on SiO₂/Si substrate with a BMN/SiO₂ interface structure had higher orientation and better crystallinity. The deposited BMN thin films with a BMN/SiO₂ interface structure exhibited superior tunability of 52.5%, while it showed a relative small tunability value of the film with BMN/Pt interface structure. It suggests that the interface state between the films and substrates, electric field distribution, and orientation degree are responsible for the impacts on the microstructure and tunable dielectric properties of the BMN thin films.     

Fabrication of CaLa4(Zr0.05Ti0.95)4O15 thin films by RF magnetron sputtering

Crystalline CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films deposited on n-type Si substrates byRF magnetron sputtering at a fixed RF power of 100 W, an Ar/O₂ ratio of 100/0, an operating pressure of 3 mTorr, and different substrate temperatures were investigated. The surface structural and morphological characteristics analyzed by X-ray diffraction and atomic force microscopy were sensitive to the deposition conditions, such as the substrate temperature. The diffraction pattern showed that the deposited films had a polycrystalline microstructure. As the substrate temperature increased, the quality of the CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films improved, and the kinetic energies of the sputtered atoms increased, resulting in a structural improvement of the deposited CaLa₄(Zr_0.05Ti_0.95)₄O₁₅ thin films. A high dielectric constant of 16.7 (f=1 MHz), a dissipation factor of 0.19 (f=1 MHz), and a low leakage current density of 3.18×10⁻⁷ A/cm² at an electrical field of 50 kV/cm were obtained for the prepared films.     

Improved physical properties of Al-doped ZnO thin films deposited by unbalanced RF magnetron sputtering

Room temperature Al-doped ZnO (AZO) thin films with improved crystalline and optical properties were grown on normal glass substrates using unbalanced RF magnetron sputtering technique. To modify the plasma density towards the substrate and enhance the crystalline nature, an additional magnetic field ranging from 0 to 6.0 mT has been applied to the AZO target by proper tuning of solenoid coil current from 0 to 0.2 A respectively, which plays a significant role for controlling the physical properties of AZO films. The results from XRD studies indicate that all AZO films were composed of hexagonal wurtzite structure with better crystal quality through the applied magnetic field, ZnO (002) plane as a preferred growth. Furthermore, XPS studies suggested that symmetric chemical shifts in the binding energies for the Zn 2p and O1s levels with applied magnetic field. SEM analysis revealed the formation of a smooth, homogeneous and dense morphological surface with applied magnetic field. From AFM analysis, it was observed that the applied magnetic field strongly influenced the grain size and the films showed decreasing tendency in electrical resistivity. Films exhibited superior optical transmittance more than 94% in the visible region essentially due to the formation of better crystalline nature. The results indicate that improved band gap from 3.10 to 3.15 eV with additional magnetic field varied from 0 to 6.0 mT respectively.     

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.     

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.     

Submicron periodical poling by local switching in ion sliced lithium niobate thin films with a dielectric layer

Lithium niobate LiNbO₃ (LN) on insulator wafers (LNOI) representing a submicron-thick LN film bonded to a SiO₂ layer deposited on a thick LN substrate have been manufactured recently by ion slicing. Today, LNOI is one of the most promising materials for fabrication of various integrated optical devices, including waveguides, electro-optical modulators, and wavelength convertors, due to their high drop in refractive index at the interface between the film and the SiO₂ layer. Creation of the stable domain structures with submicron periods in LNOI will improve the properties of nonlinear optical devices. Periodically poled LN with periods below 300 nm can be used to implement an optical parametric oscillator in the backward configuration. We have studied experimentally the ways to create the stripe domains and periodical domain structures in LNOI with a dielectric layer under the film by local switching. The identified scenarios of the domain evolution were attributed to the ineffective screening of depolarization field. We have shown that stripe domains and periodic domain structures can be produced by scanning with a biased tip only at temperatures above 80 °C. Periodical stable domain structures with periods down to 300 nm have been created.     

Effect of magnesium content on structure and dielectric properties of cubic bismuth magnesium niobate pyrochlores

Structure and dielectric properties of cubic pyrochlore Bi_1.5Mg_NNb_2.5−NO_8.5−1.5N (BMN) compositions with N=0.6–1.3 have been studied. X-ray diffraction (XRD), infrared reflectivity spectra and Raman spectra were employed to analyze the crystal structures and phonon vibration modes of BMN compositions. The vibration spectra were sensitive to the content of Mg²⁺ ions, which is caused by the randomness of Mg²⁺ ions partially filling both the cubic pyrochlore A and B sites. The intensity of A3O stretching vibrations became stronger with increasing Mg²⁺ content, but B3O stretching vibrations were quite opposite. With the increase of Mg²⁺ content, the dielectric constant and loss tangent both increased. Temperature dependent dielectric constant was observed in the samples with N>0.8. The tendency of the dielectric constant with the increasing temperature showed a quick drop in the samples with higher Mg²⁺ content, which seems to be associated with the disorder in the A₂O′ network.     

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.     

Mixed grains and orientation-dependent piezoelectricity of polycrystalline Nd-substituted Bi4Ti3O12 thin films

Polycrystalline Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were prepared on Pt/Ta/glass substrates by a pulsed laser deposition method. X-ray diffraction measurements revealed that the BNT thin films were preferentially oriented along the (117) direction although they possessed a polycrystalline structure. Good ferroelectric properties of the BNT thin film were observed with a remnant polarization of 13 μC/cm² (2 P_r ~26 μC/cm²). The fatigue resistance test exhibited that the ferroelectric polarization of the BNT thin film degraded significantly after around 10⁹ switching cycles, which can be attributed to its crystal structure. We investigated the surface morphology and ferroelectric domain structure by atomic force microscopy (AFM) and piezoresponse force microscopy (PFM), respectively. Interestingly, mixed grains consisting of long and circular shapes were observed on the BNT film surface, which corresponded to a- and c-axes orientations of crystal growth, respectively. The PFM study revealed that the piezoelectric coefficient (d₃₃) of the long grains was much larger than that of the circular grains.     

Influence of frequency and temperature on dielectric and electrical properties of Ca-substituted barium iron niobate

This paper presents the dielectric and electrical behavior of (Ba_1-xCa_x)(Fe_1/2Nb_1/2)O₃ (x?=?0.0, 0.2, 0.6, 1.0) solid solutions. The dielectric and electrical properties were investigated with respect to variation in temperature (25–250?°C) and frequency (10–970?kHz) using impedance analyzer. This study suggests that the relative permittivity increased with increase in Ca content up to x?=?0.2 and then decreased for higher Ca concentration. Dielectric anomaly observed in ?_r-T plots is frequency dependent which indicates that the relaxation in the system is due to electrons trapped in oxygen vacancies The occurrence of maxima of Z" and M" at different frequencies indicate the presence of Non Debye type relaxation in the studied materials. The purposed materials are potential candidate for multilayer capacitor applications.     

Effect of annealing on structure and properties of Ta–O–N films prepared by high power impulse magnetron sputtering

High power impulse magnetron sputtering of a Ta target in various $\mathrm{Ar}+{\mathrm{O}}_2+{\mathrm{N}}_2$ gas mixtures was utilized to prepare amorphous tantalum oxynitride (Ta–O–N) films with a finely controlled elemental composition in a wide range. We investigate the effect of film annealing at $900°\mathrm{C}$ in vacuum on structure and properties of the films. We show that the finely tuned elemental composition in combination with the annealing enables the preparation of crystalline Ta–O–N films exhibiting a single TaON phase with a monoclinic lattice structure, refractive index of $2.65$ and extinction coefficient of $2.0\times {10}^2$ (both at the wavelength of $550\mathrm{nm}$), optical band gap width of $2.45\mathrm{eV}$ (suitable for visible light absorption up to $505\mathrm{nm}$), low electrical resistivity of $0.4\text{Ω}\mathrm{cm}$ (indicating enhanced charge transport in the material as compared to the as-deposited counterpart), and appropriate alignment of the band gap with respect to the redox potentials for water splitting. These films are therefore promising candidates for application as visible-light-driven photocatalysts for water splitting.     

Effect of Fe-doping on the structural,optical and magnetic properties of ZnO thin films prepared by RF magnetron sputtering

In this paper, we report the fabrication and systematic characterization of Fe Doped ZnO thin Films. Fe_xZn_1−x O (x=0<0.05) films were prepared by RF magnetron sputtering on Si (400) substrate. Influence of Fe doping on structural, optical and magnetic properties has been studied. The X-ray diffraction (XRD) analysis shows that Fe doping has affected the crystalline structure, grain size and strain in the thin films. The best crystalline structure is obtained for 3% Fe Doping as observed from Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). The magnetic properties studied using Vibrating Sample Magnetometer reveals the room temperature ferromagnetic nature of the thin films. However, changing the Fe concentration degrades the magnetic property in turn. The mechanism behind the above results has been discussed minutely in this paper.     

Annealing-induced changes in the nanoscale electrical homogeneity of bismuth ferrite dielectric thin films

In this study, we investigated the effects of forming gas (7% H₂ + 93% Ar) annealing (FGA) and recovery annealing (RA) in ambient oxygen on the structure and electrical properties of BiFeO₃ (BFO) thin films. X-ray diffraction results indicate that BFO remains in the perovskite phase following FGA. However, the spatial distribution of current maps obtained by conductive atomic force microscopy shows that FGA-treated BFO thin films are less electrically insulating than those without prepared thermal annealing. Recovery annealing improves the structural and chemical homogeneity of the FGA-treated films, thereby increasing the electrical resistance of the films.     

Effect of MgO addition on the microstructure and dielectric properties of BaTiO3 ceramics

MgO-doped BaTiO₃ (BaTiO₃/MgO) ceramics were prepared by a solid-state sintering method. The effects of MgO doping on the dielectric properties of BaTiO₃/MgO were investigated in terms of its microstructural development. The BaTiO₃/MgO was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and x-ray powder diffraction. Results show that grain growth of the BaTiO₃/MgO during sintering was inhibited by adding MgO at least 0.5 mol%. It resulted in a high resistance of the BaTiO₃/MgO sintered at high temperature. The BaTiO₃/MgO possessed a broad temperature stability and met Electronic Industries Association (EIA) ×7R specification. The improved dielectric properties of the BaTiO₃/MgO are attributed to the decreased tetragonality of BaTiO₃ lattice due to Mg²⁺ substitute for Ti⁴⁺.     

High temperature dielectric properties of cubic bismuth zinc tantalate

Electrical properties of the parent phase in the Bi₂O₃–ZnO–Ta₂O₅ ternary system, cubic Bi_1.5ZnTa_1.5O₇ (α-BZT), P, are investigated using impedance spectroscopy. P has permittivity (?′) of 58, dielectric loss (tan δ) of 0.0023 at 30 °C and 1 MHz; temperature coefficient of capacitance (TCC) of −156 ppm/°C in the range of 30–300 °C at 1 MHz. A high degree of dispersion in the permittivity at low frequencies (<1 kHz) and temperatures above 500 °C is apparent. Dielectric losses exhibit non-frequency dependence at low temperatures presenting an increase at temperatures above 500 °C. A decrease of the loss occurs with increasing frequency.     

Preparation and dielectric tunability of bismuth-based pyrochlore dielectric thick films on alumina substrates

Metal–insulator–metal capacitors structures, employing the cubic pyrochlore Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thick films, were fabricated by screen-printing techniques on alumina substrates. Chemical compatibility and microstructure between layers was studied by EDS/SEM analysis. The dielectric properties of BZN thick films have been investigated as a function of temperature and frequency. The films exhibited the dielectric constant up to 130, and the dielectric loss less than 0.005 at 1 MHz. The dielectric tunabilities of the films have been compared at different temperature. The BZN thick film showed low tunability of about 1.8% at 10 kHz under 100 kV/cm dc bias voltage in temperature from −150 to 180 °C. The temperature stability of dielectric properties for BZN thick film should be useful for designing temperature stable frequency agile.     

Low-temperature growth of lead magnesium niobate thick films by a hydrothermal process

Pyrochlore free PbMg_1/3Nb_2/3O₃ (PMN) thick films were prepared by using a hydrothermal process from oxide-based suspension precursors. PMN thick films have been grown on titanium substrates at 150 °C for 8 h. The effect of processing parameters such as reaction durations and mineralization conditions on perovskite phase formation on the microstructures is very critical. By controlling the operating parameters, high quality PMN thick films on titanium substrates were fabricated. The films with a single perovskite structure were smooth and the surfaces were free of micrometer scale cracks. The thickness of the film was about 20 μm. Dielectric responses of the PMN films were characterized in detail. The samples showed excellent reproducibility in the measurement of dielectric responses.     

Enhancing the thermal stability of switched domains in lithium niobate single-crystal thin films

Lithium niobate on insulator (LNOI) is widely used in optical, acoustic, domain wall current (DWC)-based integrated circuits and other domain engineering devices, enabling higher material performance, higher domain integration density and more advanced applications. However, there are hidden dangers of thermal failure in these highly integrated domain engineering devices. Therefore, maintaining thermal stability of domain structures in ferroelectric single-crystal thin films is an important and challenging task. Here, thermally induced structure reconstruction of tailored metastable switched domains was research in a 500 nm thick congruent lithium niobate (CLN) thin film, and a method for enhancing the thermal stability of switched domains was proposed. Piezoresponse force microscopy (PFM) and a polyheater are used to accurately monitor the thermal evolution of switched domains in CLN thin film sample. The results indicate the switched domain structures determine the thermal stability, and the enhanced thermal stability of the switched domains increases from 55 to 85 °C–150 °C. In this contribution, the thermal failure in domain engineering devices can be avoided effectively. The investigation paves the way for the development of domain engineering devices based on lithium niobate (LN) thin films.     

Cofiring characteristics and dielectric properties for dielectric composites with macroscopic inhomogeneity and X7R characteristics

A multilayer dielectric composite with a compositional gradient and temperature-stable characteristic was successfully prepared through the conventional tape casting technique. The cofiring behaviors and dielectric properties of the composite were investigated. It was shown that processing parameters not only affected the physical integrity of the composites, but also altered their final dielectric properties. The processing sensitivity was attributed to the interfacial interdiffusion and mismatched sintering shrinkage. Microstructural observation and compositional analysis indicated that the sintered dielectric composite had macroscopic inhomogeneity and layer-like structure. By suitable structural and processing designs, the X7R EIA specification of the composite was obtained, together with low-sintering temperature and high dielectric constant.     

Dielectric and ferroelectric properties of lead indium niobate ceramic prepared by wolframite method

The dielectric and ferroelectric properties of lead indium niobate (Pb(In_1/2Nb_1/2)O₃, PIN) ceramic prepared by an oxide-mixing method via wolframite route were investigated. The 98.5% perovskite fine-grained PIN ceramics with average grain sizes of 1–2 μm were obtained by sintering at 1050 °C for 2 h. The dielectric properties of the PIN were of relaxor ferroelectric behavior with temperature of dielectric maximum (T_m) 53 °C and dielectric constant (_r) 4300 (at 1 kHz). The P–E hysteresis loop measurements at various temperatures showed that the ferroelectric properties of the PIN ceramic changed gradually from the paraelectric behavior at temperature above T_m to slim-loop type relaxor behavior at temperature below T_m. Moreover, the P–E loop became more open at temperatures much lower than T_m. At −25 °C, the maximum polarization is found to be 8 μm/cm² at a field of 30 kV/cm, with P_r value of 2.5 μm/cm² and E_c of +7.5 kV/cm.