Fabrication and ferroelectric properties of sol–gel derived 1–1 intergrowth-superlattice-structured Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript>-Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

1–1 intergrowth-superlattice-structured Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT) ferroelectric thin films have been prepared on p-Si substrates by sol-gel processing. The precursor films are crystallized in the desired intergrown BTN–BIT superlattice structures by optimizing the processing conditions. Synthesized BTN–BIT thin films annealed below 750 °C are polycrystalline, uniform and crack-free, no pyrochlore phase or other second phase, and exhibited good ferroelectric properties. As the annealing temperature increases from 600 to 700 °C, both remanent polarization P _r and coercive electric field E _c of BTN–BIT thin films increase, but the pyrochlore phase in BTN–BIT films annealed above 750 °C will impair the ferroelectric properties. The BTN–BIT thin films annealed at 700 °C have a P _r value ~19.1μC/cm² and an E _c value ~135 kV/cm.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Electrical characteristics of the MOD-derived SrBi2xTa2O9 and SrBi2.4(Ta,Nb)2O9 thin films

Ferroelectric and leakage current characteristics of the MOD-derived SrBi_2xTa₂O₉ (0.8 x 1.6) and SrBi_2.4(Ta_1-yNb_y)₂ O₉ (0 y 1) thin films were investigated. The SBT and SBTN films were fully crystallized to Bi-layered perovskite structure by annealing at 800°C for 1 hour in oxygen atmosphere. The ferroelectric characteristics of the SBT films were optimized at the Bi/Ta mole ratio x of 1.2. The leakage current density of the Bi-excess SBT films decreased remarkably by the post-metallization annealing at 800°C for 10 minutes in oxygen ambient. The ferroelectric characteristics of the SBTN films were optimized with the SBN content y of 0.25. The SrBi_2.4(Ta_0.75Nb_0.25)₂ O₉ film exhibited 2P_r and E_c of 19.04 C/cm² and 24.94 kV/cm at ±5 V, which were superior to 2P_r of 11.3 C/cm² and E_c of 39.6 kV/cm obtained for the SrBi_2.4Ta₂O₉ film after the post-metallization annealing. The MOD-derived SrBi_2.4(Ta_0.75Nb_0.25)₂O₉ film did not exhibit the polarization fatigue after 10¹¹ switching cycles at ±5 V.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba_0.5Sr_0.5TiO₃(BST)/Bi_1.5Zn_1.0Nb_1.5O₇(BZN) multilayer thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. The structures and morphologies of BST/BZN multilayer thin films were analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscope. The XRD results showed that the perovskite BST and the cubic pyrochlore BZN phases can be observed in the multilayer thin films annealed at 700 °C and 750 °C. The surface of the multilayer thin films annealed at 750 °C was smooth and crack-free. The BST/BZN multilayer thin films annealed at 750 °C exhibited a medium dielectric constant of around 147, a low loss tangent of 0.0034, and a relative tunability of 12% measured with dc bias field of 580 kV/cm at 10 kHz.     

Electrical properties of non c-axis oriented SrBi2(Ta0.95V0.05)2O9 thin films

Pulsed laser deposition technique was used to grow off c-axis oriented SrBi₂(Ta_0.95V_0.05)₂O₉ (SBTV) ferroelectric thin films. X-ray diffraction studies revealed the c-axis suppression in the films grown at lower substrate temperature (350°C) followed by annealing at higher temperatures (650°C). In-plane lattice parameters of the films were decreased with increase in annealing temperature. SBTV films annealed at 750°C exhibited enhanced ferroelectric properties with remanent polarization (2P _r) of 31.5 C/cm² and coercive field (E _c) of 157 kV/cm. The dielectric permmitivity of the films increased with increase in annealing temperature and it was attributed to the grain size dependence. The films annealed at 750°C showed maximum value of dielectric permittivity 172 with a tangential loss of 0.1, at 100 kHz. Higher value of dissipation factor at lower annealing temperature is explained in terms of space charge accumulation at grain boundaries. The leakage current densities of the films follow ohmic behavior at low field regime and space charge limited current dominates at higher fields.     

Preparation, dielectric and ferroelectric properties of Pb5Ge3O11 and Pb5Ge2.85Si0.15O11 thin films fabricated by sol-gel process

Lead germanate-silicate (Pb₅Ge_2.85Si_0.15O₁₁) ferroelectric thin films were successfully fabricated on Pt/Ti/SiO₂/(100)Si substrates by the sol-gel process. The thin films were fabricated by multi-coating at preheating temperatures of 350 and 450 °C. After annealing the thin films at 600 °C, the films exhibited c-axis preferred orientation. The degree of c-axis preferred orientation of the thin films preheated at 350 °C was higher than that of films preheated at 450 °C. Grain growth was influenced by the annealing time. The thin films exhibited a well-saturated ferroelectric P-E hysteresis loop when preheated at 350 °C and annealed at 600 °C for 1.5 h. The values of the remanent polarization (Pr) and the coercive field (Ec) were approximately 2.1 μC/cm² and 100 kV/cm, respectively.     

The influence of annealing temperatures on the properties of Bi2VO5.5/LaNiO3/Si thin films

Bi₂VO_5.5 ferroelectric thin films were fabricated on LaNiO₃/Si(100) substrate via chemical solution deposition. Ferroelectric and dielectric properties of the thin films annealed at 500-700 °C were studied. The thin film annealed at 700 °C exhibited more favorable ferroelectric and dielectric properties than those annealed at lower temperatures. The values of remnant polarization 2P_r and coercive field E_c for the film annealed at 700 °C are 10.62 µC/cm² and 106.3 kV/cm, respectively. The leakage current of the film is about 1.92 × 10^− 8 A/cm² at 6 V. The possible mechanism of the dependence of electrical properties of the films on the annealing temperature was discussed.     

Enhancement of fatigue endurance and retention characteristic in Bi3.25Eu0.75Ti3O12 thin films

The effects of moderate annealing temperature (600–800 °C) on the microstructure, fatigue endurance, retention characteristic, and remnant polarization (2P_r) of Bi_3.25Eu_0.75Ti₃O₁₂ (BET) thin films prepared by metal-organic decomposition (MOD) were studied in detail. 2P_r (66 µC/cm² under 300 kV/cm), fatigue endurance (3% loss of 2P_r after 1.2 × 10¹⁰ switching cycles), and retention characteristic (no significant polarization loss after 1.8 × 10⁵s) for BET thin film annealed at 700 °C are better than those for thin films annealed at other temperature. The mechanisms concerning the dependence of microstructure and ferroelectric properties on the annealing temperature were discussed.     

Preparation of fatigue-free SrBi2Ta2O9 thin films by r.f. magnetron sputtering and their ferroelectric properties

Fatigue-free bismuth-layered SrBi₂Ta₂O₉ (SBT) films were deposited on Pt/Ti/SiO₂/Si substrates by r.f. magnetron sputtering at room temperature. The variation of structure and electrical properties were studied as a function of annealing temperatures from 750–850 °C. The films annealed at 800 °C had a composition ratio of Sr:Br:Ta = 0.7:2.0:2.0. X-ray photoelectron spectroscopy signals of bismuth show an oxygen-deficient state within the SBT films. The films annealed at 800 °C have a thickness of 200 nm and a relatively dense microstructure. The remanent polarization (2P _r), and the coercive field (2E _c), obtained for the SIBT films, were 9.1 C cm^–2 and 85 kV cm^–1 at an applied voltage of 3 V, respectively. The films showed fatigue-free characteristics up to 10¹⁰ cycles under 5 V bipolar square pulses. The leakage current density was about 7 × 10^–7 A cm^–2 at 150 kV cm^–1. The SBT films prepared by r.f. magnetron sputtering were attractive for application to non-volatile memories.     

Comparative investigating the properties of Pb-based multilayer ferroelectric thin films for FeRAM

The PbZr_0.3Ti_0.7O₃(PZT) thin film and multilayer PbZr_0.3Ti_0.7O₃/PbTiO₃(PZT/PT), PbTiO₃/PbZr_0.3Ti_0.7O₃/ PbTiO₃(PT/PZT/PT) thin films were prepared by a Sol-Gel method on the Pt(111)/Ti/SiO₂/Si(100) substrate for FeRAM application. The microstructure, ferroelectric, fatigue, dielectric, and leakage current properties of these thin films were investigated. The results indicate that the multilayer PT/PZT/PT thin film have a better ferroelectric, fatigue, dielectric and leakage current density properties. Its remanent polarization P_r reaches a maximum value of 21.2 μC/cm² and the coercive field E_c gets to a minimum value of 64.2kV/cm. After 10¹⁰ cycles, it still has more than 80% remnant polarization. The PT/PZT/PT thin film exhibits lower dielectric constant and lower dielectric loss, which is beneficial for FeRAM application. It also has the lowest leakage current density. The leakage current mechanism of the PZT, PZT/PT and PT/PZT/PT thin films is correlated to the microstructure and can be modeled in terms of GBLC and SCLC theory. The microstructure and electric properties of these films are correlated. The double-sided PT seed layers enhance not only the microstructure but also the electric properties. It is evident that the PT/PZT/PT multilayer thin film is a promising candidate for FeRAM application.     

Effects of annealing atmosphere on microstructure and ferroelectric properties of praseodymium-doped Bi4Ti3O12 thin films prepared by sol-gel method

Praseodymium-substituted bismuth titanate (Bi_3.2Pr_0.8Ti₃O₁₂, BPTO) thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by spin coating with a sol-gel technology and rapid thermal annealing. The effects of annealing atmospheres (vacuum, ambient atmosphere and oxygen) on the growth and properties of thin films were investigated. The results show that the intensity of the (117) diffraction peak of Bi_3.2Pr_0.8Ti₃O₁₂ film annealed in oxygen is stronger than those annealed in ambient atmosphere and vacuum. The XRD spectra demonstrated that a highly (117) orientation could be obtained when the Bi_3.2Pr_0.8Ti₃O₁₂ thin film was annealed in an oxygen-sufficient environment. The BPTO thin films annealed in oxygen atmosphere exhibits the maximum remanent polarization (2P_r) of 49 μC/cm² and a low coercive field (2E_c) of 130 kV/cm, fatigue free characteristics up to ≧ 10¹¹ switching cycles. These results indicate that the BPTO thin film is useful in nonvolatile ferroelectric random access memory applications.     

Annealing temperature dependence of effective piezoelectric coefficients for Bi3.15Eu0.85Ti3O12 thin films

The effects of annealing temperatures 600, 650, 700, and 750 °C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films prepared by metal–organic decomposition were studied in detail. The largest spontaneous polarization 2P _s (98.7 μC/cm² under 300 kV/cm), remnant polarization 2P _r (81.7 μC/cm² under 300 kV/cm), dielectric constant ε_r (889.4 at 100 kHz), effective piezoelectric coefficient d ₃₃ (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 × 10⁻⁶ A/cm² under 125 kV/cm) of BET thin film were obtained with annealing at 700 °C. The mechanisms concerning the dependence of the enhancement d ₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.     

Structure of post-annealed ferroelectric PbZrxTi1-xO3 and SrBi2Ta2O9 thin films

In order to fabricate good quality ferroelectric thin films, PbZr_xTi_(1-x)O₃ (PZT) and SrBi₂Ta₂O₉ (SBT) films were fabricated on SiO₂/Si(100) substrates and on Pt/Ti/ SiO₂/Si(100) substrates by pulsed laser excimer deposition (PLD). X-ray diffraction, Rutherford backscattering analysis, and atomic force microscopy were used to characterize the structural properties of the samples, which were post-annealed at different temperatures. The results showed that the PZT and SBT films fabricated on Pt/Ti/SiO₂/Si(100) substrates and annealed at 700 °C exhibited optimum properties.     

Preparation and characterization of highly (1 1 1)-oriented (Pb,La)(Zr,Ti)O3 thin films by sol-gel processing

Lanthanum modified lead zirconate titanate (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO₂/Si(1 0 0) and fused quartz substrates using a sol-gel method with rapid thermal annealing processing. The results showed that the highly (1 1 1)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO₂/Si(1 0 0) substrates. The electrical measurements were conducted on PLZT films in metal-ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm² and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.     

Electrical characteristics of SrxBi2.4Ta2O9 thin film and Pt/Sr0.85Bi2.4Ta2O9/Al2O3/Si structure

Sr _x Bi_2.4Ta₂O₉ (0.7 x 1.3) thin films were processed by metalorganic decomposition and their ferroelectric characteristics were investigated. The Sr-deficient Sr _x Bi_2.4Ta₂O₉ films exhibited well-developed ferroelectric hysteresis curves compared to those of the Sr-excess films, and Sr_0.85Bi_2.4Ta₂O₉ film had the optimum electrical characteristics among Sr _x Bi_2.4Ta₂O₉ films. Electrical characteristics of the Pt/SBT/Al₂O₃/Si structure using Sr_0.85Bi_2.4Ta₂O₉(SBT) film were investigated for metalferroelectric-insulator-semiconductor field-effect-transistor (MFIS-FET) applications. Memory window of C-V hysteresis characteristics of the Pt/SBT/Al₂O₃/Si structure became large with decreasing the Al₂O₃ thickness, and the Pt/SBT(400 nm)/Al₂O₃ (10 nm)/Si structure gave memory window of 2.2 V at sweeping voltages of ±5 V. The Pt/SBT/Al₂O₃/Si structure can be proposed for MFIS-FET applications.     

Structural and ferroelectric properties of La modified Sr0.8Bi2.2Ta2O9 thin films

La modified SBT (Sr_0.8La_0.1Bi_2.1Ta₂O₉) thin films of different thickness were fabricated on Pt/Ti/SiO₂/Si substrates by the metalorganic decomposition technique. All the films were annealed layer-by-layer at 800 °C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that the relative intensity of the (2 0 0) diffraction peak [I(2 0 0)/I(1 1 5)] increased with the increase of the film thickness. Eventually, an a-axis preferentially oriented SLBT film was obtained. These results are discussed with respect to the anisotropy of the grain growth. The a-axis preferentially oriented SLBT film, whose relative intensity of the (2 0 0) peak [I(2 0 0)/I(1 1 5)] was 1.05, had a remanent polarization (2P_r) value of 21 μC/cm² and a coercive field (2E_c) value of 70 kV/cm under the electric field of 200 kV/cm.     

Structural and electrical characteristics of chemical solution derived (Bi3.2La0.4Nd0.4)Ti3O12 thin films

(Bi_3.2La_0.4Nd_0.4)Ti₃O₁₂ (BLNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using chemical solution deposition technique, and the effects of annealing temperatures in the range of 550-750 °C on structure and electrical properties of the thin films were investigated. X-ray diffraction analysis shows that the thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The surface morphology observation by field-emission scanning electron microscopy confirms that films are dense and smooth with uniformly distributed grains. The grain size of the thin films increases with increasing annealing temperature; meanwhile, the structural distortion of the thin films also increases. It was demonstrated that the thin films show good electrical properties. The dielectric constant and dielectric loss are 191 and 0.028, respectively, at 10 kHz for the thin film annealed at 600 °C, and the 2Pr value of the thin film annealed at 700 °C is 20.5 μC/cm² at an electric field of 500 kV/cm.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film annealed at different temperatures

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of annealing temperature on microstructure, ferroelectric and dielectric properties of PZT films was investigated. When the films were annealed at 550–850 °C, the single-phase PZT films were obtained. PZT films annealed at 650–750 °C had better dielectric and ferroelectric properties. The sandwich composites with epoxy resin/PZT film with substrate/epoxy resin were prepared. The annealing temperature of PZT films influenced their damping properties, and the epoxy-based composites embedded with PZT film annealed at 700 °C had the largest damping loss factor of 0.923.