Studies on Laser Ablated SrBi 2 Ta 2 O 9 and Sr 0.8 Ca 0.2 Bi 2 Ta 2 O 9 Ferroelectric Thin Films

Ferroelectric thin films of SrBi 2 Ta 2 O 9 (SBT) and (Sr 0.8 Ca 0.2 )Bi 2 Ta 2 O 9 (SCBT) were grown on platinized silicon substrates by using pulsed laser deposition technique. The effect of annealing temperature on the structural and electrical properties of the films was studied. Films were grown at 200 mTorr oxygen pressure with a constant substrate temperature at 500°C and annealed at different temperatures ranging from 700-800 °C in an oxygen ambient. X-ray diffraction data showed that as-grown films were crystalline nature. Atomic force micrographs showed that the grain size and surface roughness increased with increase in annealing temperature. The SBT films annealed at 800 °C showed ferroelectric properties with remanent polarization of 9.1 w C/cm 2 and coercive field of nearly 72 kV/cm. Whereas the SCBT films showed maximum remanent polarization of 7.3 w C/cm 2 with higher coercive field of 86 kV/cm. The higher coercive field in case of SCBT is attributed to the higher electronegativity of partially substituted Ca at Sr site. The dielectric constant increased with increase in annealing temperature and was attributed to the higher grain size.     

Chemical Processing and Properties of (Sr,Ca) 2 (Nb,Ta) 2 O 7 Thin Films

Ca-doped Sr 2 (Nb,Ta) 2 O 7 thin films have been synthesized by the chemical solution deposition. Homogeneous and stable (Sr,Ca) 2 (Nb,Ta) 2 O 7 precursor solutions were prepared by optimizing the reaction of starting metal alkoxides in ethanol with a key additive of 2-ethoxyethanol. The improvement of ferroelectric properties of the Sr 2 (Nb,Ta) 2 O 7 based films were achieved through the Ca substitution into Sr 2 (Nb 0.3 Ta 0.7 ) 2 O 7 as well as the optimization of heating conditions. The crystallization temperature of the layered perovskite (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films on Pt/Ir/Ti/SiO 2 /Si substrates was found to be above 750C. (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films crystallized at 750C exhibited P r of 0.51 w C/cm 2 and E c of 69 kV/cm.     

Preparation of SrBi 2 Ta 2 O 9 Ferroelectric Thin Films by RF Magnetron Sputtering

Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were deposited by RF magnetron sputtering on a Pt/Ti/SiO 2 /Si(100) structure. The deposition temperature of the film was varied from RT (room temperature) to 600C. It was found that the SBT films were crystallized at temperatures between 500C and 600C, which was much lower than the annealing temperature (700C to 800C) of the RT-deposited film. The maximum remnant polarization value (2Pr) of the SBT film was 15 w C/cm 2 , which was deposited at 575C.     

Y_2O_3插层对Ni_(81)Fe_(19)薄膜各向异性磁电阻的影响

以Y_2O_3作为Ni_(81)Fe_(19)薄膜的氧化插层,利用磁控溅射法制备了一系列不同插层厚度的Ni_(81)Fe_(19)薄膜样品Ta(4nm)/Y_2O_3(t)/Ni_(81)Fe_(19)(20nm)/Y2O3(t)/Ta(3nm),利用非共线四探针法测量薄膜样品的各向异性磁电阻(AMR),用振动样品磁强计测量样品的磁滞回线,利用X射线衍射仪(XRD)分析样品薄膜结构,研究了Y_2O_3插层厚度对Ni_(81)Fe_(19)薄膜各向异性磁电阻的影响。结果表明,在基片温度为450℃时,Ni_(81)Fe_(19)薄膜AMR值随插层厚度增加先增后减,在插层厚度为2.5nm时样品具有最大AMR,其值为4.61%,比无插层样品的2.69%提高了71.3%。     

Preparation of SrBi 2 Ta 2 O 9 Thin Films by Liquid-Delivery MOCVD Without Additional Solvents

SrBi 2 Ta 2 O 9 thin films were prepared by ECR plasma enhanced metalorganic chemical vapor deposition (ECR-MOCVD) with a liquid-delivery system using one cocktail source without an additional solvent. The strontium-tantalum double alkoxide, Sr{Ta[OC 2 H 4 H(CH 3 ) 2 ](OC 2 H 5 ) 5 } 2 , was dissolved in stabilized trimethyl bismuth, Bi(CH 3 ) 3 / dioxane. This source system has been used in a conventional bubbling system. Deposition rate and the composition of the films were strictly controlled by the concentration and the composition of the cocktail source. Therefore, high reproducibility was realized by using this system. The constituent phase of the stoichiometric SBT film as-deposited at 500 C on a (111)Pt/TiO 2 /SiO 2 /Si substrate was a fluorite phase and transformed to the single phase of SBT by the post annealing at 800 C. It showed almost the same ferroelectricity as the stoichiometric composition film.     

Improvement in the electrical properties of ferroelectric SrBi2Ta2O9 capacitors by electron beam irradiation on precursor films

Abstract

Ferroelectric SrBi₂Ta₂O₉ (SBT) capacitors were fabricated by the Electron-Beam-Induced Patterning process and their electrical properties were evaluated in detail. In this process, the dose of an electron beam irradiated on precursor films had a great influence on the electrical properties of the SBT capacitors. The appropriate electron dose significantly improved the electrical properties of the SBT capacitors although the excess electron dose made severe deterioration in the properties. The SBT capacitors fabricated with the optimum electron dose, 1.5 mC/cm² for Sr:Bi:Ta = 0.8:2.2:2.0 solutions, exhibited excellent ferroelectric properties: a remanent polarization of 11.5 μC/cm², a coercive field of 40 kV/cm, a leakage current of 8×10^?8 A/cm²@ 1V and fatigue-free up to 1010 cycles. It seems that such improvements were caused by the adjustment of Bi contents in the films and the modification or the decompositon of precursors before heat treatment by electron beam irradiation.     

制备条件对Fe-Ta-N薄膜的结构和软磁性能的影响

应用射频磁控溅射法制备了Fe-Ta-N薄膜,系统地研究了制备工艺地Fe-Ta-N薄膜结构和软磁性能的影响,首先,制备了不同钽含量的薄膜,发现（Fe89.5Ta10.5）-N薄膜具有很好的软磁性能,氮分压P（N2）=5%时,矫顽力获得最小值,Hc=14A/m。此时,样品呈现纳米晶结构,晶粒尺寸D≤10∧-8m,并且,钽掺杂能抑制铁氮化合物的生成,使薄膜在高氮分压范围内具有高的饱和磁化强度,Ms=1242kA/m。其次,考察了热处理对（F89.5Ta10.5）-N薄膜结构和磁性能的影响,P(N2）=5%时,沉积态薄膜为非晶结构,矫顽力很大;在热处理过程中,薄膜逐渐晶化,400℃热处理后,晶化度达到40%,形成纳米晶结构,矫顽力迅速减小,最后,比较了不同溅射功率和总气压对（Fe89.5Ta10.5）-N薄膜结构和磁性能的影响,发现薄膜可在较大的溅射功率和总气压范围内保持优异的软磁性能,是非常适于工业生产的薄膜磁头材料。     

Aqueous Chemical Solution Deposition of Ferroelectric Thin Films

Thin films of various ferroelectric multimetal oxides such as (Bi 1 m x La x ) 4 Ti 3 O 12 (BLT), SrBi 2 Ta 2 O 9 (SBT) and PbZr 1 m x Ti x O 3 (PZT) have been prepared by an entirely aqueous chemical solution deposition (CSD) route. Two critical issues related with aqueous CSD have hereby been worked out: in spite of the high degree of hydrolysis of tetra- and pentavalent metal ions (Ti 4+ , Zr 4+ , Ta 5+ , ) we managed to prepare stable aqueous precursor solutions by chemical modification of these individual metals, avoiding phase segregation. Another problem related with aqueous CSD is the wetting of the substrate (both metallic and metal oxide) by the aqueous solution. The hydrophilicity of the substrates is optimized by a chemical treatment of the substrate surface. In this manner, the addition of wetting agents, hence possibly disturbing the gelation reactions, is avoided. In order to study the gelation, decomposition, crystalization and the morphology of the thin films, various characterization techniques ((cryo-)TEM, SEM, EDX, TGA-MS/FTIR, HT-DRIFT, HT-XRD, ) are used.     

Low temperature growth of sol-gel SrBi2Ta2O9 thin films by low-pressure annealing

A new low-temperature processing method to prepare SrBi₂Ta₂O₉ thin films is proposed. These thin films were prepared on Pt/Ta/SiO₂/Si substrates by a sol-gel method, and their structural and electrical properties were investigated. Films were annealed before and after the top Pt electrode deposition. The first annealing was performed in a 760-Torr oxygen atmosphere at 600 °C for 30 min, and the second annealing was performed in a 5-Torr oxygen atmosphere at 600 °C for 30 min. The films were well crystallized and fine-grained after the second annealing. The electrical characteristics of the 200-nm-thick film obtained by this new process were as follows: remanent polarization, P_r = 8.5 μC/cm²; coercive field, E_c = 36 kV/cm; and leakage current density, I_L = 1 × 10⁻⁷ A/cm² (at 150 kV/cm). This process is very attractive for highly integrated ferroelectric nonvolatile memory applications. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(2): 27–33, 1997     

(V2O5,Ta2O5)双掺杂的WO3陶瓷的电学行为研究

用电子陶瓷工艺制备(V2O5,Ta2O5)双掺杂的WO3电子陶瓷,研究了(V2O5,Ta2O5)双掺杂对WO3陶瓷的微观结构与电学行为的影响。X射线衍射结果表明,(V2O5,Ta2O5)双掺杂能明显抑制WO3中三斜相的形成,使WO3陶瓷单相化。I-V特性测试表明,掺杂V2O5和Ta2O5后,陶瓷的压敏电压明显增大,非线性系数显著减小。     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

Polycrystalline SrBi2Ta0.8Nb1.2O9 thin films

Abstract

The growth, microstructure and micro-Raman properties of SrBi₂Tao_0.8Nb_1.2O₉ (SBTN) thin films deposited on Si(100) substrates using pulsed laser deposition (PLD) technique were studied at various substrate temperatures. Films were characterized using X-ray diffraction(XRD), atomic force microscopy(AFM), energy dispersive X-ray analysis (EDAX) and micro-Raman studies. AFM studies indicated that the average grain size of the films increased between 0.08 μm to 0.1 μm with the increasing growth temperatures. Micro-Raman studies of SBTN films revealed the fact that shifting of Raman modes corresponds to the BO₆ (where B' Ta/Nb) octahedral symmetry, to higher frequencies, is in accordance with the different masses of the B site atoms and the force constants involved due to Nb doping at Ta sites.     

NiFe层溅射气压对顶部钉扎NiFe/FeMn薄膜静态磁性能的影响

用直流磁控溅射制备了系列Ta/NiFe/FeMn/Ta薄膜样品。利用振动样品磁强计(VSM)、X射线衍射(XRD)等手段研究了溅射气压对NiFe层交换偏置场、矫顽力、截止温度的影响。结果表明,交换偏置场随NiFe层溅射气压和NiFe层厚度的增加均减小;在较低的NiFe层溅射气压下,可以获得具有较高交换偏置场He和较低矫顽力Hc的样品;截止温度Tb随着NiFe层溅射气压的减小而增高。通过对比研究0.8Pa、0.4Pa、0.2PaNiFe层溅射气压下NiFe/FeMn薄膜的静态磁性及微结构变化,发现以上现象是由于在较低的溅射气压能够获得较好织构的NiFe(111),进而诱导出较好取向的FeMn(111)。取向良好的NiFe/FeMn薄膜产生较大的交换偏置场和较小的矫顽力及更高的截止温度。     

Structural and Electrical Properties of Bi 3.25 La 0.75 Ti 3 O 12 and Bi 3.25 Pr 0.75 Ti 3 O 12 Thin Films for Memory Applications

In this work, Bi 3.25 La 0.75 Ti 3 O 12 (BLT) and Bi 3.25 Pr 0.75 Ti 3 O 12 (BPT) thin films were prepared by chemical solution deposition and characterized by X-ray diffraction, scanning electron microscope and electrical measurements. Layered perovskite BLT and BPT films can be achieved by 180 s annealing at a temperature as low as 650 C. Both BPT and BLT films are composed of closely packed spherical grains. BPT shows larger remnant polarization ( Pr ) and smaller coercive field. The Pr values of 700 C annealed BLT and BPT films are 18.3 w C/cm 2 and 20.5 w C/cm 2 , respectively, while BLT films show better-saturated hysteresis loops. The leakage current density of BPT films is significantly (about one order) lower than that of BLT. The dielectric properties of BLT and BPT films were measured and compared. Both films exhibit large dielectric constant and small loss tangent. Under bipolar switching cycles, BLT films showed little polarization reduction but a 30% polarization loss was observed for BPT films after 2 2 10 9 cycles.     

Preparation of SrBi2(Ta,Nb)2O9 thin films by rf sputtering for ferroelectric memory production

Abstract

Ferroelectric SrBi₂(Ta, Nb)₂O₉ (SBTN) thin films were prepared by rf magnetron sputtering utilizing a multi-chamber type production tool (ULVAC CERAUS ZX1000). Accurate and dynamic compositional control results in excellent ferroelectric performances such as large 2Pr up to 15μC/cm², fatigue free at least 10⁹ cycles as well as good uniformity and process repeatability. These results indicate that the SBTN sputtering process is promising for ferroelectric memory production.     

Low Temperature Process for Synthesis of (100) Textured Pb(Zr0.48Ti0.52)O3 Thin Films on Si Substrate by Laser Lift-Off Transferring Technique

(100) textured Pb(Zr_0.48Ti_0.52)O₃ (PZT) films were prepared on silicon substrates by MOD process and laser lift-off technique. Textured PZT films were first grown on (001) Sapphire substrate, using Ba(Mg_1/3Ta_2/3)O₃ (BMT) materials as buffer layer. The (100) textured PZT/BMT/Sapphire films were attached to Si substrate using a transient-liquid-phase Pd-In bonding process, and then were separated from Sapphire substrates by a laser lift-off process, in which, a 38 ns pulse from excimer laser (248 nm) at 600 mJ/cm² fluence melted BMT buffer layer, expelling the Sapphire. The crystallinity of the surface of films was further improved by laser annealing. X-ray diffraction analysis of the PZT films showed that the crystallographic structure of films is maintained during laser lift-off process. Electrical testing of the films after laser lift-off process followed by laser annealing demonstrated that the ferroelectric properties are retained for the transferred films (P_r = 9μ C/cm² and E_c = 74 kV/cm).     

Ferroelectric SrBi2Ta2O9 thin films deposited by liquid injection MOCVD using novel bimetallic alkoxide precursor

Abstract

The ferroelectric SBT films were deposited on Pt/Ti/SiO₂/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)₅(dmae)]₂ and Bi(C₆H₅)₃. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 400°C, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5～1.0. As-deposited film was amorphous. However, after annealing at 750°C for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 750°C were 4.7 μC/cm²and 115.7 kV/cm at an applied voltage of 5 V, respectively. The SBT films annealed at 750°C showed practically no polarization fatigue up to 10¹⁰ switching cycles.     

Raman scattering in the aurivillius-layered ferroelectric SrBi2Ta2O9 – Bi3TiNbO9 thin films

Abstract

We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi₂Ta₂O₉)_x(Bi₃TiNbO₉)_1?x layered structures and to compare them with the corresponding bulk materials. Various compositions, with x ' 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were prepared by metal organic solution deposition method on Pt/TiO₂/SiO₂/Si substrates. A topographic micro-Raman study revealed very homogeneous films at each composition. The Raman spectrum of x ' 0.0 film shows bands around 170, 232, 337, 522, 608, 677 and 832 cm^?1, which indicates Bi₃TiNbO₉ formation. The evolution of the Raman bands with the inclusion of SBT material shows frequency shifts and a broadening of the bands due to the differences in mass between Sr and Bi in the A-sites, and Ta, Ti, and Nb in the B-sites A lower degree of crystallization was found in the films compared to the bulk due to the presence of stress in the films. Strong contributions from defects were also observed in the temperature-dependent Raman spectra.     

Chemical solution processing of sr2(nb,ta)2o7 thin films

Abstract

Sr₂(Nb,Ta)₂O₇ thin films have been synthesized by chemical solution deposition. Homogeneous and stable Sr₂(Nb,Ta)₂O₇ precursor solutions with various Nb/Ta ratios were prepared by controlling the reaction of metal alkoxides in ethanol with a key additive of 2-ethoxyethanol. The crystallization temperature of the perovskite-type Sr₂(Nb,Ta)₂O₇ slabs structure decreased with increasing Nb substitution in amount. The crystallization temperature of Sr₂(Nb_0.2Ta_0.8)₂O₇ films on Pt/Ti/SiO₂/Si and Pt/Ir/Ti/SiO₂/Si substrates was above 800°C. On the other hand, by using Pt(100)/MgO(100) as a substrate, Sr₂(Nb,Ta)₂O₇ thin films crystallized into the Sr₂(Nb,Ta)₂O₇ phase at 700°C.     

MOCVD preparation of SBTN thin films from two organometallic sources bottles

Abstract

SrBi₂(Ta_0.7Nb_0.3)₂O₉ (SBTN) films were first prepared on (111)Pt/Ti/SiO₂/Si substrates by MOCVD from only two organometallic source bottles. Bi(CH₃)₃ and the mixture of Sr[Ta(O°C₂H₅)₆]₂ and Sr[Nb(O°C₂H₅)₆]₂ were used as source materials. High compositional reproducibility was obtained; the Nb/(Ta+Nb) ratio was the same as the mixing ratio of the source. Sr/(Ta+Nb) and Bi/(Ta+Nb) ratios can be controlled by the reactor pressure and the input gas flow rate ratio of the source gases. Almost single phase of SBTN was obtained for the film deposited at 500°C and the following heat-treated at 800°C in O₂ atmosphere. Pr and Ec values of 330 nm-thick SBTN film were 8.5 μC/cm² and 91 kV/cm, respectively and were larger than those of SrBi₂Ta₂O₉ film. There was no degradation after 5x10¹⁰ cycles polarization switching.