PVP添加剂改善溶胶-凝胶法制备BST薄膜表面结构及介电性能

以聚乙烯吡咯烷酮(polyvinyl pyrrolidone, PVP)为添加剂采用改善的溶胶凝胶法制备了Ba0.6Sr0.4TiO3(BST)薄膜,并采用扫描电镜(SEM)及原子力显微镜(AFM)研究了薄膜的表面结构与介电性能.结果表明:PVP显著改善了BST薄膜的表面形貌,当PVP∶ Ti的物质的量比为0.7%时,BST薄膜表面形貌最佳,光滑致密无裂纹无缩孔.X射线光电子能谱(XPS)表明,PVP有助于减少BST薄膜表面非钙钛矿结构.介电性能测试表明,在40 V外加电压下BST薄膜的介电调谐率达45%,零偏压下的介电损耗低于0.02.另外,对PVP的作用机理进行了讨论.     

热处理工艺对Sol-gel法制备BST薄膜性能的影响

以醋酸锶、醋酸钡和钛酸四丁酯为前驱体原料,采用溶胶-凝胶(Sol-gel)法,利用旋转涂覆工艺,采用不同的热处理工艺制备了组分为Ba/Sr=0.65/0.35的Ba0.65Sr0.35TiO3薄膜.采用XRD、SEM和阻抗分析仪分析薄膜的结晶、表面形貌和介电性能.研究了不同热处理工艺对BST薄膜晶化行为、结构和性能的影响.结果表明,最佳热分解温度和时间为400 ℃和30 min,最佳升温速率为0.5～1 ℃;经650 ℃热处理后,BST薄膜已基本形成ABO3型钙钛矿结构,随着热处理温度的提高,薄膜的结晶程度提高,且沿(110)晶面择优取向.经750 ℃热处理的BST薄膜表面光滑致密无裂纹,颗粒均匀分布,晶粒发育较好,且介电性能最佳.     

退火温度对铁电薄膜钛酸锶钡的影响

用醋酸盐和钛酸酯为原料,采用Sol-Gel工艺在Pt/TiO2/SiO2/Si基片上制备出Ba0.5Sr0.5TiO(3BST)铁电薄膜,然后在650-800℃下对BST薄膜进行退火,研究退火温度对钛酸锶钡铁电薄膜的影响。X射线衍射分析表明:退火温度在750℃以上时,BST薄膜转变成较为完整的ABO3型钙钛矿结构;SEM分析表明:750℃热处理的薄膜颗粒较大,且颗粒生长较好;阻抗分析仪测试表明:750℃退火处理的薄膜介电性能最佳;TEM分析表明:750℃晶粒发育完善、清晰,晶粒与晶粒之间比较紧密,且存在微畴区域。     

CaZrO_3薄膜的微观结构与介电性能研究

采用射频磁控溅射技术在Pt/Ti/SiO_2/Si衬底上制备了单一钙钛矿结构的CaZrO_3薄膜。研究了CaZrO_3薄膜的介电性能和微观形貌,利用X射线衍射技术和扫描电子显微镜技术对所制备薄膜的微观结构进行了表征,并对所制备薄膜的介电性能进行了系统测试,侧重讨论了制备工艺参数O_2:Ar比对所制备薄膜的物相及电学性能的影响。研究结果表明,O_2:Ar比对所制备薄膜的相纯度有显著影响,在O_2:Ar比为10:40和20:40时获得单一钙钛矿相的CaZrO_3薄膜,O_2:Ar比为30:40和40:40时,薄膜中可观察到第二相Ca_(0.2)Zr_(0.8)O_(1.8)(CSZ)杂相。O_2:Ar比为10:40条件下所制备的单一钙钛矿相CaZrO_3薄膜在1MHz介电常数约为30,介电损耗为0.006,并且该薄膜在40 V直流电压下,漏电流密度为5×10_~7 A/cm~2。单一钙钛矿相的CaZrO_3薄膜在薄膜型电容器和微波器件方面具有潜在应用。     

La1-xCaxMnO3团簇薄膜的介电和光学性质研究

利用溶胶-凝胶法制备La1-xCaxMnO3薄膜.利用X射线衍射(XRD)、反射偏光显微镜和电感-电容-电阻测定计(LCR)仪对其结构、形貌和性质进行表征.XRD结果表明薄膜为钙钛矿结构,经不同温度退火后发生微小偏离.偏光显微图像显示薄膜表面形貌为菊花状团簇;经不同温度退火后的薄膜反射色有很大差异,因此反射色不能作为鉴定La1-xCaxMnO3的依据.随着退火温度升高,薄膜的介电损耗降低,说明高的温度退火后,薄膜质量较高.     

Bi_4Ti_3O_(12)掺杂(Ba,Sr)TiO_3基电容器陶瓷介电性能研究

采用传统固相法制备了Bi_4Ti_3O_(12)掺杂(Ba_(0.71),Sr_(0.29))TiO_3(BST)陶瓷。研究了Bi_4Ti_3O_(12)掺杂量对BST电容器陶瓷介电性能、物相组成和微观结构的影响。结果表明:随着Bi_4Ti_3O_(12)掺杂的增加,BST陶瓷的相对介电常数逐渐减小,介电损耗先减小然后增大,Bi_4Ti_3O_(12)掺杂后的BST陶瓷仍为钙钛矿结构。当Bi_4Ti_3O_(12)掺杂量为1.6 wt%时,BST陶瓷的综合介电性能最好,εr为3744,tanδ为0.0068,ΔC/C为+1.70%,-44.61%,容温特性符合Y5V特性。     

CaSnO_3掺杂BST基介电陶瓷介电性能的研究

采用传统固相法制备了CaSnO_3掺杂(Ba_(0.71)Sr_(0.29))TiO_3(BST)介电陶瓷。研究了CaSnO_3掺杂量对BST电容器介电陶瓷介电性能、物相组成和微观结构的影响。结果表明:随着Ca SnO_3掺杂量的增加,BST陶瓷的相对介电常数(εr)先减小后增大再又减小,介质损耗(tanδ)先减小然后增大,CaSnO_3掺杂后的BST陶瓷仍为钙钛矿结构。当CaSnO_3掺杂量为质量分数6.0%时,BST陶瓷的综合介电性能最好:εr为4963,tanδ为0.0069,ΔC/C为19.69%～-26.18%,容温特性符合Y5V特性。     

钙钛矿太阳电池中的液相制备法探究

在有机无机混合钙钛矿(例如CH_3NH_3PbI_3)太阳能电池的制备方法中,为了提高其制备效率,文中将主要采用溶液法,来探究对钙钛矿性能的影响。基于此,研究了溶液法制备器件的最新进展,各种高品质钙钛矿薄膜溶液生长重要的影响因素,以及在钙钛矿太阳能电池中基于电荷载流子动力的钙钛矿薄膜结构;同时,也将考虑到钙钛矿太阳电池的成本和稳定性。溶液法主要会对钙钛矿薄膜的微观结构、薄膜结构、材料组成、杂质相、缺陷/掺杂和界面性质等产生影响。解决方案的条件会最终影响钙钛矿的性能。     

双钙钛矿La_2NiMnO_6薄膜的制备及性能表征

通过化学溶液沉积法(CSD)在单晶Si(100)基片上制备了双钙钛矿La2NiMnO6薄膜。利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)等手段研究薄膜的晶形结构、相组成以及结构形貌。运用超导量子干涉仪(SQUID)进行磁性测量,结果表明该样品的居里温度为267K,接近室温,是良好的磁性材料。     

Cl离子掺杂对钙钛矿薄膜结构及光学性能的影响

有机-无机杂化钙钛矿光吸收层薄膜的结构、形貌及结晶度对电池的光电性能起决定性作用.采用一步溶液法通过改变CH3 NH3 I和PbCl2的摩尔比调控钙钛矿前驱体溶液中Cl离子的掺杂量,从而制备钙钛矿光吸收层薄膜.利用荧光光谱(PL)、X射线衍射(XRD)、扫描电子显微镜(SEM)及EDS能谱分别对钙钛矿溶液的荧光性能、薄膜的结构、表面形貌及反应后Cl离子的含量进行表征.结果表明,随着CH3 NH3 I和PbCl2的摩尔比的增加,前驱体溶液的荧光强度逐渐减弱(激发波长为325 nm);晶体结构由立方相CH3 NH3 PbCl3转换成了纯的四方相CH3 NH3 PbI3钙钛矿薄膜,晶粒尺寸增大,晶格应变随之增加;表面覆盖率逐渐升高,薄膜表面无针状结构出现;薄膜中Cl离子的含量逐渐减少,改善了薄膜的质量.     

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.     

Recrystallization of Oxygen Ion Implanted Ba0.7Sr0.3TiO3 Thin Films

The crystallization behavior of chemical-solution-deposited and amorphous Ba_0.7Sr_0.3TiO₃ (BST) thin films was analyzed with respect to the evolution of the structural and dielectric properties of the films as a function of the annealing temperature. The amorphous films were produced by oxygen ion implantation into crystalline BST thin films. In the amorphous thin films, the crystallization to the perovskite phase occurred at T = 550°C, whereas the as-deposited CSD films showed the first crystalline XRD-reflex only after annealing at T = 650°C. Here a carbon-rich intermediate phase delayed the crystallization process to higher temperatures.     

Preparation and characterization of crystalline Ba0.5Sr0.5TiO3 thin films on FTO transparent electrodes

To achieve an economic advantage, nanocrystalline Ba_0.5Sr_0.5TiO₃ (BST) thin films were prepared on FTO-coated glass substrates using an aqueous sol–gel process. The crystal structures and chemical states of the obtained thin films were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD patterns confirmed the perovskite structure of the BST samples, while XPS analysis demonstrated that Ba element was in its single oxidation state in the film with annealing temperature of 600 °C. In contrast, Ba was present in a mixed oxidation state upon increasing the annealing temperature. It was found that the BST thin film prepared at a relatively low annealing temperature of 600 °C exhibited optimal crystallinity and superior dielectric properties, along with excellent optical transparency. More specifically, this film exhibited a dielectric tunability of 44.81% (1.33 MV/cm), a figure of merit of 56.01, and an average transmittance of 87.2% in the visible region.     

Microwave dielectric properties of the (BaxSr1−x)TiO3 thin films on alumina substrate

Barium strontium titanate, (Ba_xSr_1?x)TiO₃ (BST) thin films have been prepared on alumina substrate by sol–gel technique. The X-ray patterns analysis indicated that the thin films are perovskite and polycrystalline structure. The interdigital electrode with 140 nm thickness Au/Ti was fabricated on the film with the finger length of 80 μm, width of 10 μm and gaps of 5 μm. The temperature dependence of dielectric constant of the BST thin films in the range from ?50 °C to 50 °C was measured at 1 MHz. The dielectric properties of the BST thin films were measured by HP 8510C vector network analyzer from 50 MHz to 20 GHz.     

Dielectric properties of Fe-doped Ba0.65Sr0.35TiO3 thin films fabricated by the sol–gel method

Fe-doped Ba_0.65Sr_0.35TiO₃ (BST) thin films have been fabricated on Pt/Ti/SiO₂/Si substrate using the sol–gel method. The structural and surface morphology, dielectric, and leakage current properties of undoped and 1 mol% and 2 mol% Fe-doped BST thin films have been studied in detail. The results demonstrate that the Fe-doped BST films exhibit improved dielectric loss, tunability, and leakage current characteristics as compared to the undoped BST thin films. The improved figure of merit (FOM) of Fe-doped BST thin film suggests a strong potential for utilization in microwave tunable devices.     

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.     

Microstructure and Dielectric Properties of Barium Strontium Titanate Thick Films and Ceramics With a Concrete-Like Structure

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thick films and ceramics with a concrete-like structure were fabricated by a novel sol–gel-based route. In this process, well-crystallized nano-sized or micrometer-sized BST powders or their combinations are dispersed into a sol–gel matrix. Crack-free thick films and dense BST ceramics have been fabricated at a low sintering temperature with a very inhomogeneous concrete-like structure. The dielectric properties of such thick films and ceramics have been investigated. The results show that the dielectric constant and loss tangent of the thick films are 1209 and 0.016, respectively, at 0°C, 10 kHz, and those of the bulk BST ceramics are 5510 and 0.02, respectively, at 0°C, 10 kHz.     

Preparation of KTaO3 and KNbO3 Solid Solutions through Sol–Gel Processing

Potassium tantalate–niobate solid-solution (KTN) powders and thin films were prepared from metallo–organic compounds through sol–gel processing. The KTN precursors were chemically modified and then prehydrolyzed with various concentrations of water. The stability of the modified solutions and the effects of prehydrolysis on the crystallization are discussed. Powder gels were obtained by exposing the solution to the atmospheric water, hydrolyzing the solutions. Alternatively, thin films were deposited on fused silica, silicon, sapphire, MgO, and SrTiO₃, using the spinning technique. The pyrolysis and crystallization of KTN powders and films were investigated by differential thermal analysis, theromogravimetric analysis, and X-ray diffraction. The effects of substrate and other processing parameteres on the crystal structure of the KTN phases were also investigated. KTN powders crystallized into a perovskite phase regardless of the processing conditions. The crystal structure of the KTN thin films had a strong dependency on the crystal structure of the substrates, while other processing parameters played smaller roles. Pyrochlore KTN was the major phase that crystallized on fused silica and silicon, whereas oriented perovskite KTN was obtained on single-crystal MgO and SrTiO₃.     

Reduced leakage current,enhanced energy storage and dielectric properties in (Ce,Mn)-codoped Ba0.6Sr0.4TiO3 thin film

Ba_0.6Sr_0.4TiO₃, Ce-doped Ba_0.6Sr_0.4TiO₃, Mn-doped Ba_0.6Sr_0.4TiO₃, (Ce,Mn) co-doped Ba_0.6Sr_0.4TiO₃ (abbreviated as BST, BSTCe, BSTMn, BSTCeMn) thin films were deposited on LaNiO₃(LNO)/Si substrates. The effects of ion doping on the microstructure and electrical properties of BST-based thin film have been researched and discussed. The X-ray diffraction pattern shows that each sample has pure perovskite phase structure with high (l00) peaks. The microstructure of each film is quite dense with uniform size. Compared with pure BST, improved insulating properties can be found in ion-doped BST thin films. For all the films, Ohmic conduction, space charge limited conduction and interface-limited Fowler-Nordheim tunneling should be the main conduction mechanisms within different electric field regions. For the case of BSTCeMn thin film, it possesses enhanced energy storage performance with a recoverable energy storage density (18.01?J/cm³) and a energy storage efficiency (75.1%) under 2000?kV/cm. This can be closely related to the small remanent polarization value (P_r=?1.89 μC/cm²), large maximum polarization value (P_max=?28.08?μC/cm²) as well as big maximum electric field (2000?kV/cm). Also, it exhibits a large dielectric constant of 405 and a small dissipation factor of 0.075 at 500?kHz.     

Recent Materials Characterizations of [2D] and [3D] Thin Film Ferroelectric Structures

A review is given of ceramic and single-crystal thin film ferroelectric oxides, emphasizing perovskite phases, together with some new developments on hafnia films. It is shown that single-crystal barium titanate films behave as bulk down to at least 77 nm, with no finite size effects, no phase transition temperature shifts, and no dielectric peak broadening or change from first- to second-order transitions, suggesting that the gradient defect model of Bratkovsky and Levanyuk correctly describes such effects as extrinsic in experimental studies of equally thin ceramic thin films. In ceramic barium–strontium titanate (BST) thin films, it is shown that there is also no intrinsic broadening or shifts in phase transitions, with sharp, unshifted, bulk-like transitions observed only as re-entrant upon warming from cryogenic temperatures; this shows that phase transitions in ceramic thin films are dominated by kinetics and not thermodynamics and are definitely not equilibrium measurements. At high fields (>1 GV/m), the films exhibit space charge-limited conduction; no variable-range hopping is observed, contrary to recent studies on SrTiO₃. Some novel, unconventional switching processes are discussed, comparing the "perimeter effect" (non-equilibrium, ballistic) with Molotskii's equilibrium model. Theory and experiment are described for [3D] nanotubes, nanorods, and nano-ribbons (or micro-ribbons). The layered-structure-perovskite–pyrochlore conversion in bismuth titanate is described together with the PbO+TiO₂ phase separation in lead zirconate titanate during electrical breakdown, as are novel HfO₂ precursors that demonstrate enhanced temperature crystallization from the amorphous state and hence commercial advantages for front-end processing.