Preparation and ferroelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 thin films deposited on Pt electrodes using LaNiO3 as buffer layer

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1) and LaNiO₃/Pt/Ti/SiO₂/Si (1 1 1) substrates by a sol–gel process. The phase structure and ferroelectric properties were investigated. The X-ray diffraction pattern indicated that the (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin film deposited on Pt/Ti/SiO₂/Si (1 1 1) substrates is polycrystalline structure without any preferred orientation. But the thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates shows highly (1 0 0) orientation (f ≥ 81%). The leakage current density for the two thin films is about 6 × 10^?3 A/cm² at 250 kV/cm, and thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates possessed a much lower leakage current under high electric field. The hysteresis loops at an applied electric field of 300 kV/cm and 10 kHz were acquired for the thin films. The thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates showed improved ferroelectricity.     

Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Electrical properties of chemical solution deposited (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb) thin films

Pure BiFeO₃ (BFO) and (Bi_0.9RE_0.1)(Fe_0.975Cu_0.025)O_3?δ (RE=Ho and Tb, denoted by BHFCu and BTFCu) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The BHFCu and BTFCu thin films showed improved electrical and ferroelectric properties compared to pure BFO thin film. Among them, the BTFCu thin film exhibited large remnant polarization (2P_r), low coercive field (2E_c) and reduced leakage current density, which are 89.15 C/cm² and 345 kV/cm at 1000 kV/cm and 5.38×10^?5 A/cm² at 100 kV/cm, respectively.     

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.     

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.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Enhancement of electrical properties of (Gd,V) co-doped BiFeO3 thin films prepared by chemical solution deposition

Pure BiFeO₃ (BFO) and (Bi_0.9Gd_0.1)(Fe_0.975V_0.025)O_3+δ(BGFVO) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The improved electrical properties were observed in the BGFVO thin film. The leakage current density of the co-doped BGFVO thin film showed two orders lower than that of the pure BFO, 8.1×10^?5 A/cm² at 100 kV/cm. The remnant polarization (2P_r) and the coercive electric field (2E_c) of the BGFVO thin film were 54 μC/cm² and 1148 kV/cm with applied electric field of 1100 kV/cm at a frequency of 1 kHz, respectively. The 2P_r values of the BGFVO thin film show the dependence of measurement frequency, and it has been fairly saturated at about 30 kHz.     

The phase formation process of Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared using the sol-gel method

Lead-free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ (abbreviated as BNKT) thin films were grown on Pt(111)/Ti/SiO₂/Si substrates using a sol-gel/spin coating technique and were then annealed at different temperatures (350 °C, 550 °C, 750 °C and 850 °C). Analysis of the XRD patterns and FT-IR spectra were used to determine the main reactions and the phase formation process of BNKT thin films during the sol-gel process. The results show that the dielectric constant of the thin films attains a maximum at a set temperature and then decreases at higher annealing temperatures, which can be attributed to phase formation and transformation. Moreover, the morphologies of the BNKT thin films improve with the increase in grain size and the formation of distinct grain boundaries. Furthermore, through increasing the pH of the precursor solutions, the size of the sol-gel colloidal particles increases slightly and the grains formed from the corresponding solutions tend to be small and uniform.     

Micro-patterning of PZT thick film by lift-off using ZnO as a sacrificial layer

Micro-pattern of 8.2-μm-thick PZT films was prepared on Pt/Ti/SiO₂/Si (1 0 0) substrate wafer by combining composite sol–gel and a novel lift-off using ZnO as a sacrificial layer. The processes include ZnO sacrificial layer deposition and patterning, PZT film preparation, and final lift-off. The results reveal the micro-pattern was better than that formed by wet etching, the PZT thick films patterned by lift-off possessed similar dielectric characters, better ferroelectric properties, and higher breakdown voltage than those of films patterned by wet etching. The lift-off is suitable for micro-patterning of PZT thick films.     

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E_DLC/Si=5.6 V/μm, E_DLC/Au/Si=14.3 V/μm, and E_DLC/Ti/Si=5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J_DLC/Si=15.2 μA/cm², J_DLC/Au/Si=0.4 μA/cm², and J_DLC/Ti/Si=175 μA/cm² is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.     

Laser-transfer processing of functional ceramic films

Pulsed excimer laser irradiation through a UV-transparent fabrication substrate has been successfully employed to separate PZT thick films from their sapphire host substrates. Films of 20 μm in thickness were prepared by a hybrid particle sol–gel synthesis route. The microstructure, morphology and ferroelectric properties of the thick films after laser-transfer have been examined. Films were irradiated with a 248 nm, 15 ns pulse, and transferred to a platinised silicon substrate (Pt/Ti/SiO₂/Si). A laser fluence of 250 mJ/cm² was sufficient to delaminate the original PZT/sapphire interface. The pulsed energy density used here is lower than reported by other groups utilising a laser-transfer process for PZT. This is believed to be due to higher levels of porosity at the film/substrate interface in this study.     

The effects of solvents on the formation of sol–gel-derived Bi12SiO20 thin films

The sol–gel method was used to synthesize Bi₁₂SiO₂₀ thin films. Two synthesis routes with two different solvents, i.e., 2-ethoxyethanol and acetic acid, were used and compared. Thin films were deposited onto Pt/TiO₂/SiO₂/Si substrates by spin-coating at 3000 rpm and annealed at 700 °C for 1 h. A different coordination of the bismuth ion was observed in the sols prepared with acetic acid (AcOH), and as a result, stable sols were formed with a shorter gelation time t_G = 84 h (c = 0.76 M), when compared with the sols prepared from 2-ethoxyethanol (EtoEtOH) t_G = 580 h (c = 0.76 M). The microstructures of the Bi₁₂SiO₂₀ thin films prepared from sols using EtoEtOH were homogeneous and dense. On the other hand, a porous microstructure was observed for the Bi₁₂SiO₂₀ thin films deposited from the sol in which AcOH was used as the solvent.     

Enhanced ferroelectric properties of La-substituted BiFeO3 thin films on LaSrCoO3/Pt/TiO2/SiO2/Si (1 0 0) substrates prepared by the soft chemical method

Bi_0.85La_0.15FeO₃ (BLFO015) thin films were deposited by the polymeric precursor solution on La_0.5Sr_0.5CoO₃ substrates. For comparison, the films were also deposited on Pt bottom electrode. X-ray diffraction data confirmed the substitutions of La into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15% at a temperature of 500 °C for 2 h. A substantial increase in the remnant polarization (P_r) with La_0.5Sr_0.5CoO₃ bottom electrode (P_r ≈ 34 μC/cm²) after a drive voltage of 9 V was observed when compared with the same film deposited on Pt substrate. The leakage current behavior at room temperature decreased from 10^?8 (Pt) to 10^?10 A/cm² on (La_0.5Sr_0.5CoO₃) electrode under a voltage of 5 V. The fatigue resistance of the Au/BLFO015/LSCO/Pt/TiO₂/SiO₂/Si (1 0 0) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10⁸ switching cycles at a frequency of 1 MHz.     

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.     

Synthesis and microstructural characterization of Bi12SiO20 (BSO) thin films produced by the sol–gel process

We have produced Bi₁₂SiO₂₀ (BSO) thin films using the sol–gel process. The stable sol was synthesized using Bi(NO₃)₃·5H₂O and Si(OC₂H₅)₄ (TEOS) as the precursors, acetic acid and 2-ethoxyethanol as the solvents, and ethanolamine as the stabilizer. The stability of the solution, which depends on the concentration and the R_h value (R_h = [H₂O]/[M]), directly affects the microstructure of the BSO thin film. We determined that the optimal concentration for the preparation of BSO thin films is 0.76 M. The influences of the substrates, the annealing temperature, the concentration and the R_h = value of the solution on the microstructure of the Bi₁₂SiO₂₀ thin films were investigated. X-ray diffraction (XRD) showed that the Bi₁₂SiO₂₀ starts to form at 500 °C and that single-phase Bi₁₂SiO₂₀ polycrystalline thin films are formed at 700 °C. The coated films were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).     

Bottom electrode crystallization of PZT thin films for ferroelectric capacitors

The bottom electrode crystallization (BEC) method was applied to the crystallization of PZT thin films deposited by laser ablation over Si/SiO₂/Ti(Zr)/Pt structures, with the platinum films being deposited at two different temperatures. The results were compared with those obtained by rapid annealing with halogen lamps and furnace annealing. PZT films crystallized over Pt made at lower temperature with Ti adhesion layers tend to have a (1 1 1) preferential orientation, while those deposited on platinum made at higher temperature tend to have a (1 0 0)/(1 1 1) mixed orientation. When Zr adhesion layers are used, the PZT films crystallized over Pt have a preferential (1 0 0) orientation, except for films deposited over Pt made at 500 °C and crystallized with a high heating rate. The ferroelectric properties of the films crystallized with the BEC method are good, being similar to those obtained with the other crystallization methods using the same parameters.     

Influence of seed layer on crystal orientation and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films prepared by a sol–gel process

Sol–gel derived lead-free (Na_0.85K_0.15)_0.5Bi_0.5TiO₃ (NKBT) thin films, with and without a Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) seed layer, were fabricated on (111)Pt/Ti/SiO₂/Si substrates. The influences of the seed layer on crystal orientation and electrical properties were investigated in detail. XRD indicated that the NKBT thin films fabricated with a seed layer were fully crystallized into a single perovskite structure, while the films fabricated under the same conditions, but without a seed layer, possessed a certain amount of pyrochlore phase. The NKBT film with a 14 nm-thick seed layer showed high (100) orientation, and exhibited enhanced electrical properties, such as a higher remanent polarization (Pr～18 µC/cm²), a lower dielectric loss tangent (tan δ ～0.023) and smaller transient current density (J<10^?5 A/cm²).     

Crystallization kinetics of PbTiO3 ferroelectric films: Comparison of microwave irradiation with conventional heating

Lead titanate (PTO) films were deposited onto Pt/Ti/SiO₂/Si substrates by a sol-gel method and annealed by microwave irradiation and conventional heating. In contrast to conventional heating, microwave irradiation can crystallize the PTO films at a low temperature of 450 °C or at 550 °C for only 5 min. The XRD and TEM studies reveal that microwave radiation can reduce the nucleation time, and increase the growth rate of perovskite grains in the crystallization process. Moreover, the results using the Avrami’s model show that the effective activation energy for crystallization process by microwave irradiation is 131 kJ/mol, much lower than that for the PTO films by conventional heating (216 kJ/mol). Therefore, microwave irradiation can reduce the effective activation energy for the nucleation and grain growth of the perovskite phase during the crystallization process, contributing to a low-temperature or a short-time preparation process of ferroelectric films.     

Dielectric enhancement of BaSrTi1.1O3/BaSrTi1.05O3/BaSrTiO3 multilayer thin films prepared by RF magnetron sputtering

BaSrTi_1.1O₃/BaSrTi_1.05O₃/BaSrTiO₃ multilayer (BSTM) thin films and BaSrTiO₃ (BST) thin films were deposited on LaNiO₃ (LNO)/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering at substrate temperature of 400 °C, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigations revealed that all the films have uniform and crack-free surface morphology with a perovskite structure. The dielectric constant of the BSTM thin films was increased and dielectric loss was decreased compared with those of uniform BST thin films. The dielectric constant of 420, dielectric loss of 0.017, and dielectric tunability of 38% were achieved for the BSTM thin films.     

Dielectric properties of composition spread SiO2–Al2O3 mixed phase thin films deposited at room temperature by off-axis RF magnetron sputtering

The dielectric properties of composition spread SiO₂–Al₂O₃ thin films deposited by off-axis radio-frequency magnetron sputtering at room temperature were explored to obtain optimized compositions, which have low dielectric constants and losses. The specific points (compositions) showing superior dielectric properties of low dielectric constants (8.13 and 9.12) and losses (tanδ ～0.02) at 1 MHz were found in area of the distance of 25.0 mm (Al₂Si₃O₈) and 42 mm (Al_2.4Si₃O₈) apart from SiO₂ target side in 75 mm × 25 mm sized Pt/Ti/SiO₂/Si(1 0 0) substrates, respectively. The specific thin films were amorphous phase and the compositions were Al₂Si₃O₈ (k ～8.13) and Al_2.4Si₃O₈ (k ～9.12).