Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

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.     

Structural and ferroelectric properties of chemical solution deposited (Nd,Cu) co-doped BiFeO3 thin film

Effects of (Nd, Cu) co-doping on the structural, electrical and ferroelectric properties of BiFeO₃ polycrystalline thin film have been studied. Pure and co-doped thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Significant improvements in the electrical and the ferroelectric properties were observed for the co-doped thin film. The remnant polarization (2P_r) and the coercive field (2E_c) of the co-doped thin film were 106 μC/cm² and 1032 kV/cm at an applied electric field of 1000 kV/cm, respectively. The improved properties of the co-doped thin film could be attributed to stabilized perovskite structures, reduced oxygen vacancies and modified microstructures.     

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.     

Structural and electrical properties of sol–gel-derived Al-doped bismuth ferrite thin films

Al-doped BiFeO₃ (BiFe_(1?x)Al_xO₃) thin films with small doping content (x=0, 0.05, and 0.1) were grown on Pt(111)/TiO₂/SiO₂/Si substrates at the annealing temperature of 550 °C for 5 min in air by the sol–gel method. The crystalline structure, as well as surface and cross section morphology were studied by X-ray diffraction and scanning electron microscope, respectively. The dielectric constant of BiFeO₃ film was approximately 71 at 100 kHz, and it increased to 91 and 96 in the 5% and 10% Al-doped BiFeO₃ films, respectively. The substitution of Al atoms in BiFeO₃ thin films reduced the leakage current obviously. At an applied electric field of 260 kV/cm, the leakage current density of the undoped BiFeO₃ films was 3.97×10^?4 A/cm², while in the 10% Al-substitution BiFeO₃ thin films it was reduced to 8.4×10^?7 A/cm². The obtained values of 2P_r were 63 μC/cm² and 54 μC/cm² in the 5% and 10% Al-doped BiFeO₃ films at 2 kHz, respectively.     

Impact of Sr-doping on structural and electrical properties of Pb(Zr0.52Ti0.48)O3 thin films on RuO2 electrodes

In this paper, we investigated the impact of Sr-doping on the structural properties and electrical characteristics of lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films deposited on RuO₂ electrodes by a sol-gel process and spin-coating technique. We used X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy to explore the structural, morphological, chemical, and microstructural features, respectively, of these films as a function of the growth condition (strontium doping concentrations varied from 1, 3, and 5 mol%). The PZT thin film processed at the 3 mol% Sr exhibited the best electrical characteristics, including a low leakage current of 2.27×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a large capacitance value of 2.74 μF/cm² at a frequency of 10 kHz, and a high remanent polarization of 37.95 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of strontium in the PZT film forming a perovskite structure and a thicker interfacial layer at the PSZT film-RuO₂ electrode interface.     

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.     

Enhanced ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3–0.05PbTiO3 thin films with Pb(Zr0.52,Ti0.48)O3 seed layer

0.95Pb(Sc_0.5Ta_0.5)O₃–0.05%PbTiO₃ (PSTT5) thin films with and without a Pb(Zr_0.52,Ti_0.48)O₃ (PZT52/48) seed layer were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering. X-ray diffraction patterns indicate that the PSTT5 film with a PZT52/48 seed layer exhibited nearly pure perovskite crystalline phase with highly (4 0 0)-preferred orientation. Piezoresponse force microscopy observations reveal that a large out-of-plane spontaneous polarization exists in the highly (4 0 0)-oriented PSTT5 thin film. The PSTT5/PZT(52/48) possesses good ferroelectric properties with large remnant polarization P_r (12 μC/cm²) and low coercive field E_c (110 kV/cm). Moreover, The perfect butterfly-shaped capacitance–voltage characteristic curve and the relative dielectric constant as high as 733 is obtained in this PSTT5 thin film at 100 kHz.     

Characteristics of highly (001) oriented (K,Na)NbO3 films grown on LaNiO3 bottom electrodes by RF magnetron sputtering

(K,Na)NbO₃ ferroelectric films were grown on LaNiO₃ coated silicon substrates by RF magnetron sputtering. The conductive LaNiO₃ films acted as seed layers and induced the highly (001) oriented perovskite (K,Na)NbO₃ films. Such films exhibit saturated hysteresis loops and have a remnant polarization (2P_r) of 23 μC/cm², and coercive field (2E_c) of 139 kV/cm. The films showed a fatigue-free behavior up to 10⁹ switching cycles. A high tunability of 65.7% (@300 kV/cm) was obtained in the films. The leakage current density of the films is about 6.0×10^?8 A/cm² at an electric field of 50 kV/cm.     

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.     

Effect of excess lead on the structural and electrical characteristics of sol-gel synthesized RuO2/Pb(ZrxTi1−x)O3/RuO2

In this study, we investigated the effect of excess lead on the structural and electrical characteristics of lead zirconate titanate [Pb(Zr_xTi_1−x)O₃, PZT] thin films using the sol-gel spin coating method. X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy were used to study the structural, morphological, chemical, and microstructural features, respectively, of these films as functions of the growth conditions (excess lead concentrations of 10, 20, and 25 mol%). The PZT thin film prepared at the 20 mol% condition exhibited the best electrical characteristics including a lower leakage current of 6×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a larger capacitance value of 1.92 μF/cm² at a frequency of 1 kHz, and a higher remanent polarization of 20.1 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of excess lead in this PZT film forming a perovskite structure and suppressing the reaction of PZT film with RuO₂ electrode.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

Dielectric and ferroelectric hysteresis properties of 1–3 lead magnesium niobate–lead titanate ceramic/Portland cement composites

In this work, lead magnesium niobate–lead titanate (PMN–PT) ceramic was cut and filled with Portland cement (PC) to produce 1–3 connectivity PMN–PT/PC composites. Dielectric and ferroelectric hysteresis properties of these composites with PMN–PT ceramic volume content of 60% were investigated. Room temperature dielectric constant (?_r) at 1 kHz of the PMN–PT/PC composite was found to be ≈1500. At higher frequency (20 kHz), the dielectric constant was reduced to the value of ≈1300. Ferroelectric (polarization–electric field) hysteresis loops at 10–90 Hz and varying electric field were measured. The “instantaneous” remnant polarization (P_ir) at 50 Hz and at the electric field of 7 kV/cm of the PMN–PT/PC composite was found to be ≈10 μC/cm². These values of 1–3 composites therefore are promising when compared to previous results of composites at similar conditions.     

Dielectric properties and bright red emission of Y3+/Eu3+-codoped ZrO2 thin films prepared by chemical solution deposition

We report on an effective combination of good dielectric properties with bright red emission in Y³⁺/Eu³⁺-codoped ZrO₂ thin films. The thin films were deposited on fused silica and Pt/TiO₂/SiO₂/Si substrates using a chemical solution deposition method. The crystal structure, surface morphology, electrical and optical properties of the thin films were investigated in terms of annealing temperature, and Y³⁺/Eu³⁺ doping content. The 5%Eu₂O₃–3%Y₂O₃–92%ZrO₂ thin film with 400 nm thickness annealed at 700 °C exhibits optimal photoluminescent properties and excellent electrical properties. Under excitation by 396 nm light, the thin film on fused silica substrate shows bright red emission bands centered at 593 nm and 609 nm, which can be attributed to the transitions of Eu³⁺ ions. Dielectric constant and dissipation factor of the thin films at 1 kHz are 30 and 0.01, respectively, and the capacitance density is about 65.5 nf/cm² when the bias electric field is less than 500 kV/cm. The thin films also exhibit a low leakage current density and a high optical transmittance with a large band gap.     

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.     

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.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Enhanced ferroelectric properties of Ce-substituted BiFeO3 thin films on LaNiO3/Si substrates prepared by sol–gel process

The effects of Ce substitution on the structural and electrical properties of multiferroic BiFeO₃ thin films grown on LaNiO₃/Si(1 0 0) substrates by a sol–gel process have been reported. X-ray diffraction data confirmed the substitutions of Ce into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15%. The dielectric constants of the films increased from 90 to ～260 below 100 kHz with 5% molar Ce substitution and the films showed enhanced dielectric behavior. We observed a substantial increase in the remnant polarization (P_r) with Ce substitution and obtained a maximum value of ～71 μC/cm² by 5% molar Ce incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?6 to 10^?8 A/cm² for 5% molar Ce-substituted films under a field 150 kV/cm. The reduction of dc leakage current of Ce-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.     

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.     

Enhanced photovoltaic properties of PbTiO3-based ferroelectric thin films prepared by a sol-gel process

PbTiO₃ (PTO), Pb(Mn_0.1Ti_0.9)O₃ (PMTO), Pb(Sr_0.1Ti_0.9)O₃ (PSTO), and Pb(Zr_0.1Ti_0.9)O₃ (PZTO) were prepared on an indium tin oxide (ITO)/glass substrate by a sol-gel method. PTO, PMTO, PSTO, and PZTO films exhibited energy band gaps of 3.55 eV, 3.63 eV, 3.59 eV, and 3.66 eV, respectively. All these films generated high photocurrents due to high shift currents, because carrier migration channels were successfully introduced by a lattice mismatch between the films and ITO substrates. The PMTO thin film exhibited the best ferroelectric and photovoltaic properties, with a photovoltage of 0.74 V, a photocurrent density of 70 μA/cm², and a fill factor of 43.34%, which confirms that shift current and ferroelectric polarization are two main factors that affect the ferroelectric photovoltaic properties. The PSTO, PZTO, and PTO thin films displayed space-charge-limited current (SCLC) when the electric field strength was below 10 kV/cm, and these three films broke down when the electric field strength was above 10 kV/cm. Analysis of the shift current mechanism confirmed that the breakdown of the PZTO and PSTO thin films resulted from Pool Frenkel emission current. The PMTO thin film displayed SCLC in the test range, which indicates that doping with Mn could inhibit defect formation in ferroelectric thin films.