Preparation and Dielectric Properties of YMnO3 Ferroelectric Thin Films by the Sol-Gel Method

Thin films of YMnO3 are proposed as a new candidate for non-volatile ferroelectric memory devices. They were prepared via solutions through two different processes: thermal decomposition and reflux using yttrium acetate tetrahydrate and manganese acetate tetrahydrate as starting materials. For coatings prepared by thermal decomposition process, the starting materials were dissolved in ethanol containing diethanolamine, and single phase YMnO3 was obtained with heat-treatment at 900°C. When the starting materials were refluxed using 2-ethoxyethanol as a solvent, single phase YMnO3 was obtained with heat-treatment at 800°C. Scanning electron microscopy showed that the 300 nm thick films with a stoichiometric Y/Mn ratio had many pinholes, and a very large dielectric loss, 0.83 at 100 kHz. Inclusion of 5–10% excess of Y in the coating solution produced dense structures with improved dielectric properties. The dielectric constant and loss tangent of the thin films with Y/Mn ratio of 1.00/0.90 were about 20 and 0.05 at 100 kHz, respectively.     

Enhanced ferroelectric,dielectric and leakage properties in Ce and Ti co-doping BiFeO3 thin films

Pure BiFeO₃ (BFO), Ce and Ti individual doping and co-doping BiFeO₃ thin films were fabricated via sol–gel process on Pt/Ti/SiO₂/Si substrates. The microstructure, surface morphology, ferroelectric and dielectric properties of BFO and doped thin films were investigated in detail. X-ray diffraction reveal that all thin films are confirmed the formation of the distorted rhombohedral perovskite structure. No impure phase is identified in all the films. The Ce and Ti co-doping BiFeO₃ (BCFTO) thin films exhibited the enhanced ferroelectricity with a large remnant polarization (2P _r) of 130 μC/cm², and low leakage current density of 9.10 × 10^?6 A/cm² which is more than two orders of magnitude lower than that of pure BFO films at 100 kV/cm. The dielectric constant (364 at 1 kHz) of the BCFTO thin films is much larger than that of pure BFO thin films. These results suggest that the introductions of Ce and Ti provides an effective route for improving the ferroelectric, dielectric and leakage properties of BFO thin films.     

Preparation and Characterization of a Sol-Gel Prepared Ferroelectric Sandwich Structure

A novel silicon-based PbTiO₃/Pb(Zr,Ti)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure has been prepared using a sol-gel method. The annealing temperature is greatly reduced compared with those structures without PT layers. Capacitance-voltage (C-V), leakage current-voltage (I-V), polarization-field (P-E), dielectric-frequency response and polarization fatigue of the sandwich structure are examined. The relative dielectric constant, the coercive field and the remanent polarization of the PZT films are measured to be about 900, 18 kV/cm and 16 C/cm² respectively. The current density is less than 5 × 10^–9 A/cm² below 200 kV/cm. The dielectric constant of the structure remains constant at low frequency, and decreases to some degree at high frequency. The retained polarization does not change significantly after 8 × 10⁹ read/write cycles. The PZT films are proved to have very good dielectric and ferroelectric properties. The new PT/PZT/PT sandwich structure can be valuable for memory devices and other applications.     

Ferroelectric Thin Films of Bismuth Strontium Tantalate Prepared by Alkoxide Route

Study of the interactions in Bi(OR)3-Ta(OR)5-ROH (R = Me, Et, iPr) at 20°C show that metal ethoxides are the best of the investigated precursors for the production of bismuth tantalates via alkoxides. Polycrystalline SrBi2Ta2O9 (SBTO) and BiTaO4 films on Si-SiO2-Ti-Pt substrates with thicknesses of 0.4–0.5 m and 0.4 m, respectively, have been formed by sol-gel processing. The most stable solutions for film application were obtained by using mixed-metal Bi-Ta ethoxides and solutions of Sr carboxylate (2-ethylhexanoic acid derivative) in 2-ethylhexanoic acid. Films annealed at 700–750°C for 30 min were single-phased. SBTO films demonstrated good ferroelectric properties: remanent polarization ranged from 3.5 to 4.0 C/cm2 and coercive voltage 1.5–2.0 V, whereas BiTaO4 films showed dielectric behavior.     

Improving ferro- and piezo- electric properties of hydrogenized poly(vinylidene fluoride-trifluoroethylene) films by annealing at elevated temperatures

After annealing the solution cast P(VDF-TrFE) films at elevated temperatures, which were synthesized via a full hydrogenation process from P(VDF-CTFE) with a composition of VDF/TrFE = 80/20(mol%), a series of P(VDF-TrFE) films were fabricated in present work. The crystalline and ferroelectric phases of the films were carefully characterized and their dielectric, ferroelectric and piezoelectric properties were systematically investigated. The improved crystalline and ferroelectric phases in the films induced by annealing at elevated temperatures are responsible for the significant improved electric properties of the films. The optimized annealing temperature is found to be 130 °C and the best performance including the highest dielectric constant of 12.5 at 1 kHz, the largest maximum polarization of 11.21 μC/cm~2 and remnant polarization of 7.22 μC/cm~2, the lowest coercive electric field of 56 MV/m, and the highest piezoelectric coefficient of -25 pC/N is observed.     

Ferroelectric and dielectric behaviour of Bi0.92La0.08FeO3 multiferroic thin films prepared by soft chemistry route

Bi_0.92La_0.08FeO₃ (BLFO) thin films were grown on platine substrates by the soft chemical route. Ferroelectric and dielectric behaviors of BLFO films deposited by spin-coating technique and annealed at 773 K for 2 h in air atmosphere were explained. BLFO thin films obtained presents a rhombohedral structure. The BLFO films present dielectric and ferroelectric behaviors with dielectric permittivity and dielectric loss of approximately 81 and 0.0144 at 1 kHz. The Au/BLFO/Pt capacitor shows a hysteresis loop with remnant polarization of 20.6 μC/cm² and coercive field of 53.88 kV/cm. The polarization switching and the fatigue behavior of the BLFO films were significantly enhanced.     

Preparation of highly (111)-oriented (Pb,La)(Zr,Sn,Ti)O<Subscript>3</Subscript> (PLZST) antiferroelectric thin films by modified sol-gel process using a novel tin source,dibutyloxide of tin

Highly (111)-oriented Pb_0.97La_0.02Zr_0.85Sn_0.13 Ti_0.02O₃(PLZST) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates through a modified sol-gel process technique. The electric field-induced antiferroelectric-to-ferroelectric (AFE‐FE) phase transformation behaviour was examined by C-V measurement. The results indicated that antiferroelectric (AFE) to ferrroelectric (FE) switching field , FE to AFE switching field were 315 kV/cm and 240 kV/cm respectively. The temperature dependence of the dielectric constant showed that the Curie temperature (T _c) of the PLZST antiferroelectric thin films was 171°C. The voltage dependent current density of the highly (111)-oriented PLZST film was less than 1.3 × 10⁻⁶ A/cm² over electric field range from 0 to ± 427 kV/cm.     

Ion dopants tuning the interband electronic structure for huge saturated ferroelectric polarization in bismuth ferrite films

Bismuth ferrite (BiFeO₃, BFO) as a prototype multiferroic has been extensively studied in past years; however, there are several key issues not to be clearly expressed. Especially, the relationship of structure and physical properties still remains obscure. In this case, the interband electronic structure of BFO was elaborately manipulated by appropriation dopants of Ni and Gd to realize the huge saturated ferroelectric polarization in the polycrystalline films. For instance, a huge saturated polarization P_S of 96?μC/cm² and remnant polarization Pr of 91?μC/cm² were achieved in Bi_0.925Gd_0.075Fe_0.95Ni_0.05O₃ film. The results and analysis show that the alteration in the interband electronic structure and the improvement of morphology derived from the ion doping effect indeed play key roles on the improved ferroelectric property of the doped BFO films. The decreased leakage current density and thereby the enhanced ferroelectric polarization in the doped BFO films should be attributed to the decrease in both Fermi level and Urbach energy closely related with the defects, as well as the improved surface uniformity and compactness of the films. Finally, the mechanism and relationship of structure and physical properties in BFO were systemically analyzed and discussed.

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The ferroelectric polarization for pure and doped BiFeO₃ films

     

Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties

The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH₃COO)₂· 2H₂O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR)₃-Ta(OR)₅-ROH (R = Me, Et or ⁱ Pr) were studied as precursors for preparation of SrBi₂Ta₂O₉ films. Films prepared from these solutions and annealed at the temperature between 700 and 750°C demonstrated the remanent polarization P_r* – P^{^} _r = 7–9 C/cm². Ba_1-xSr_xTiO₃ films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO₃, SrZr_0.2Ti_0.8O₃, Zr_0.8Sn_0.2TiO₄ is briefly discussed.     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

Structural and electrical properties of chemical solution deposited (Bi0.9Tb0.1)(Fe0.975 TM 0.025)O3±δ (TM = Ni, Mn and Ti) thin films

Effects of Tb and transition metal (TM = Ni, Mn and Ti) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO₃ thin films prepared by using a chemical solution deposition method were reported. From X-ray diffraction and Raman scattering analyses, distorted rhombohedral perovskite structures were observed for all thin films. Improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 2.67 × 10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2P _r ) of 82.2 μC/cm² and low coercive field (2E_c) of 680 kV/cm (at 1,036 kV/cm) were measured for the (Tb, Mn) co-doped thin film.     

Microstructure and ferroelectric properties of r.f. magnetron sputtering derived PZT thin films deposited on interlayer (PbO/TiO2)

Lead zirconate titanate (PZT) thin films were deposited on Pt/Ti/SiO₂/Si and interlayer/Pt/Ti/SiO₂/Si substrate by radio frequency (r.f.) magnetron sputtering with a Pb_1.1Zr_0.53Ti_0.47O₃ target. The crystallization of the PZT thin films was formed only by substrate temperature. When interlayer (PbO/TiO₂) was inserted between the PZT thin film and the Pt electrode, the grain growth and processing temperature of the PZT thin films were considerably improved. Compared to PZT/Pt structure, the dielectric constant and polarization properties of the PZT/interlayer/Pt structure were fairly improved. In particular, PZT/interlayer/Pt at the substrate temperature of 400 °C showed prevalent ferroelectric properties (_r=475.97, tanδ=0.0591, P_r=23 μC/cm²). As a result of an X-ray photoelectron spectroscopy (XPS) depth-profile analysis, it was found that PZT/interlayer/Pt deposited only by substrate temperature without the post-annealing process via r.f. magnetron sputtering method remained independent of each other regardless of substrate temperatures.     

Sol-gel processing and properties of cerium doped Barium Strontium Titanate thin films

A stock solution sol-gel based method for making Barium Strontium Titanate (BST) thin films has been developed. A modified titanium alkoxide was combined with a barium and/or strontium inorganic salt in methoxyethanol and ethylene glycol to form the solution. The effect of chemistry on the stability of this BST solution is discussed. The crystallization temperature of 700–725°C for rapid thermally processed films dropped by 100°C using cerium doping. The permittivity for undoped films was 250 and doping by 3 at. % Ce increased the dielectric constant by 20%. A remanent polarization of approximately 0.5 C/cm² and coercive field of 28 kV/cm were measured for the undoped films. The leakage current densities were <10 nA/cm² at E=60 kV/cm and improved for cerium concentrations up to 3 at. %. The charge storage density was 50 fF/m² at 200 kV/cm and the DC breakdown voltage was 300 kV/cm for Ce doped films.     

Electric-field-induced antiferroelectric to ferroelectric and ferroelectric to paraelectric phase transition at various temperatures in (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> antiferroelectric thick films

(Pb, La)(Zr, Ti)O₃ antiferroelectric thick films with (100)-preferred orientation were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates via a sol–gel method. The electric-field-induced antiferroelectric (AFE) to ferroelectric (FE) phase transition characteristics were studied by C (capacitance)–E (electric field) measurements at different temperature. The films were in AFE state under 0 kV/cm below 122 °C, and the switching field values decreased, with increasing temperature. The films were in FE state between 122 and 135 °C, and when the temperature above 135 °C, the films were in PE state. The temperature-dependent dielectric parameters were deconvoluted using a Gaussian fit multi-peaks showed that two typical phase transitions were discovered. The first peak is the AFE-to-FE phase transition and the second peak is the FE-to-PE phase transition which has been verified by C–E tests.     

Dielectric and Pyroelectric Properties of Compositionally Graded Pb(Zr1-xTix)O3 Thin Films Prepared by Sol-gel Process

"Compositionally graded ferroelectric lead zirconate titanate Pb(Zr1-xTix)O3 (PZT) thin films were grown on Pt/Ti/SiO2/Si substrates by using a sol-gel process. The final structure consists of six layers, up-graded graded films starting from PbZrO3 on the Pt electrode to the top PZT(50) layer, it consists of no Ti, 10%Ti, 20%Ti, 30%Ti, 40%Ti, and 50%Ti respectively. Whereas films with opposite gradient are called down-graded graded films. Structure and dielectric properties of the graded films was investigated by X-ray diffraction, Auger electron spectroscopy and by impedance analysis. The up-graded and down-graded PZT films annealed at 600 o, exhibited the remanent polarization values of 18.0 and 24.2 1C/cm2, respectively. The typical small signal dielectric constants and loss tanffi at a frequency of 100 Hz were 523 and 0.018, 544, and 0.020, respectively, for up-graded and down-graded PZT thin films. The temperature dependence of pyroelectric coeoients of the graded PZT films was measured by a dynamic technique. From 20 o to 82 o, the pyroelectric coeoients of the up-graded and down-graded PZT films up to 374 and 407 1C/m2K, respectively."     

LaNiO3衬底上Pb(ZrxTi1－x)O3铁电薄膜及梯度薄膜的制备和研究

报道了在镍酸镧 (LaNiO₃, 简称LNO)衬底上锆钛酸铅 [Pb(Zr_xTi_1－x)O₃, 简称PZT]铁电薄膜及其成分梯度薄膜的结构、介电性能、铁电性能以及热释电性能. 首先通过金属有机化合物热分解(MOD)法在Si(100)基片上制备出LaNiO₃, 薄膜, 再通过溶胶-凝胶(sol-gel)法, 在LNO/Si(100)衬底上制备出Pb(Zr_0.80Ti_0.20)O₃, [PZT(80/20)]和Pb(Zr_0.20Ti_0.80)O₃, [PZT(20/80)]铁电薄膜及其成分梯度薄膜. 经俄歇微探针能谱仪(AES)对制备的梯度薄膜进行了成分深度分析, 结果证实成分梯度的存在. 经XRD分析表明, 制备的梯度薄膜为四方结构和三方结构的复合结构, 但其晶面存在一定的结构畸变. 经介电频谱测试表明, 梯度薄膜的介电常数比每个单元的介电常数要大, 但介电损耗相近. 在10 kHz下, 梯度薄膜的介电常数和介电损耗分别为317和0.057. 经电滞回线的测试表明, 梯度薄膜的剩余极化强度比每个单元都大, 而矫顽场却明显较小. 梯度薄膜的剩余极化强度和矫顽场分别为29.96 μC•cm^-2 和54.12 kV•cm^－1. 经热释电性能测试表明, 室温下梯度薄膜的热释电系数为5.54×10-8 C•cm^－2•K^－1, 高于每个单元的热释电系数.     

Structure and voltage tunable dielectric properties of sol–gel derived Bi1.5MgNb1.5O7 thin films

Bi_1.5MgNb_1.5O₇ (BMN) thin films were fabricated on Au/Ti/SiO₂/Si(100) substrates using a sol?Cgel spin coating process. Thermo decomposition of the BMN precursor gel was discussed. The structures, morphologies, dielectric properties and voltage tunable dielectric properties were investigated. The deposited films showed a cubic pyrochlore structure after annealing at 550?°C or higher temperatures. With the annealing temperature increased from 500 to 800?°C, the root-mean-square surface roughness of the films increased from 0.6 to 6.8?nm. Additional phase, MgNb₂O₆, emerged after annealing at 800?°C due to the volatilization of Bi element. The dielectric properties and tunability of the films were annealing temperature dependent. BMN thin films annealed at 750?°C had a high dielectric constant of 135 and low dielectric loss of 0.002 at 1?MHz. The high tunability of 31.3?% and figure of merit of 156.5 were obtained under an applied electric field of 1?MV/cm at room temperature.     

Stress Measurements and Processing Optimization for Solution Derived SrBi2Ta2O9 Thin Films

The development of stress in the SrBi₂Ta₂O₉ (SBT) films generated from a chemical solution deposition method was monitored during processing using wafer curvature measurements. Stress measurements of the entire Si/SiO₂/Pt/SBT stack revealed an overall tensile stress of 536 MPa. The greatest increase in tensile stress was recorded for the anneal of the Pt bottom electrode and was due to the thermal expansion mismatch. Deposition of an amorphous SBT layer on the Pt, followed by a low temperature anneal (300°C), had little overall effect on the stress of the stack; however, upon crystallization, significantly more tensile stress was introduced into the stack. To further investigate the effect that stress has on the various electrical properties SBT films, wafers with different stress states were produced and SBT films deposited on them. Initial investigations indicate that SBT films on wafers with a higher tensile stress displayed improved ferroelectric hysteresis and switchable polarization.     

Ferroelectric ceramics by sol–gel methods and applications: a review

New advances in the sol?Cgel processing of ferroelectric ceramic powders and thin films and recently, scientific and technological interests in ferroelectric ceramics have been focused particularly on thin films. This is mainly due to their great potential applications in integrated electronics as passive components and as non-volatile ferroelectric memories, optoelectronic devices, etc. Special attention has been paid to the effects of the microstructure and composition on the piezoelectric properties of ferroelectric ceramic powders and thin films, and various characterization techniques are reported. This paper introduces the basic principles governing ferroelectricity and lists the various materials which exhibit these properties. The processing of ferroelectric ceramics and thin films in general and sol?Cgel processing in particular, with some examples are described. Finally, important applications of ferroelectric films and microstructure examination as well as powerful techniques are briefly discussed.     

Ferroelectric Polymer Nanotubes with Large Dielectric Constants for Potential All‐Organic Electronic Devices

To fabricate ferroelectric ultrathin polymer films with large dielectric constants for potential all‐organic electronic devices, ferroelectric polymer nanotubes and a composite of the nanotubes with a dispersed organic semiconductor have been fabricated by template‐assisted methods. The ferroelectricity drops markedly in spin‐coated ultrathin films less than 100 nm thick, whereas P(VDF‐TrFE) nanotubes with a wall thickness of a few ten nm sustain ferroelectricity. The composite nanotubes exhibit a giant dielectric constant as a result of significantly enhanced interface polarization between the nanosized fillers and the polymer matrix. They could be of practical use in supercapacitors, optoelectronic devices, and sensors.