脉冲激光沉积Ba0.5Sr0.5TiO3、Pb0.5Ba0.5TiO3和Pb0.5Sr0.5TiO3薄膜及其介电性质

采用脉冲激光沉积法,在Pt／Ti／SiO2／Si基底上分剐制备厚度为350nm的Ba0.5Sr0.5TiO3(BST)、Pb0.5Ba0.5TiO3(PBT)和Pb0.5Sr0.5TiO3(PST)薄膜并研究了它们的介电性质。XRD显示,在相同的制备条件下三者具有不同的择优取向,PST具有(110)择优取向,PBT具有(111)择优取向,而BST则是混合取向。SEM显示三者样品表面均匀致密,颗粒尺寸大约在50nm至150nm之间。PST与BST、PBT相比有更高的介电常数,在频率为10kHz时,分别为874、334和355,而损耗都较低,分别为0．0378、0．0316和0．0423,同时PST漏电流也是最小的。测量薄膜的C-V特性扣铁电性能表明室温下BST呈现的是顺电相,PST和PBT则呈铁电相。本文也测量了薄膜在不同频率下的介电温度特性,BST、PBT和PST均表现出频率弥散现象,即随着频率的降低．居里温度降低而介电常数会升高。并测得BST和PST的居里温度分剐为-75和150℃。而PBT的居里温度在250℃以上。本文研究表明：与BST相比较,PBT的介电常数与之相近,漏电流较大;而PST具有高介电常数,较小的漏电流和较大的电容-电压调谐度,在相关半导体器件中的应用将有很大的潜力。     

溅射工艺参数对Ba0.5Sr0.5TiO3薄膜沉积速率和介电性能的影响

铁电/介电BST(BaxSr1-xTiO3)薄膜在微电子学、集成光学和光电子学等新技术领域有广泛的应用前景.用射频磁控溅射方法制备了厚约700 nm的Ba0.5Sr0.5TiO3薄膜,采用Al/BST/ITO结构研究了溅射功率、溅射气压、O2/(Ar O2)比和基片温度对上述BST薄膜沉积速率和介电性能的影响,并根据这些结果分析了较优的工艺条件,同时用XRD、XPS和SEM研究了薄膜的晶相、组成和显微结构.     

Ba0.5Sr0.5 TiO3薄膜、Ba0.1Sr0.9 TiO3/YBa2 Cu3O7-δ异质薄膜的制备及介电性能研究

铁电钛酸锶钡(BSTO)薄膜具备十分优越的铁电/介电性能,在可调谐微波器件和动态随机存储器(DRAM)方面显示出十分诱人的应用前景.而YBa2Cu3O-δ(YBCO)高温超导薄膜作为其电极引入,明显降低了微波损耗,能够大大优化器件的性能.本文针对微波器件性能要求对比了各种常用基片的性能参数,描述了目前BSTO薄膜与BSTO/YBCO异质薄膜制备中存在的问题以及薄膜介电性能测试表征方法.利用脉冲激光沉积(PLD)技术成功制备出结构完整和质量较高的Ba0.5Sr0.5TiO3薄膜.同时,在1.2°斜切LaAlO3基片上研制有Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ异质双层膜,在1MHz频率、77K温度条件下,其介电常数为1200,介电损耗为0.0045,±30V直流偏压时可调性达到60%,在液氮温度下表现出良好的应用前景.     

Study of the electrical properties of pulsed laser ablated (Ba0.5Sr0.5)TiO3 thin films

The laser ablated barium strontium titanate (BST) thin films were characterized in terms of composition, structure, microstructure and electrical properties. Films deposited at 300°C under 50 mTorr oxygen pressure and 3 J cm⁻² laser fluence and further annealed at 600°C in flowing oxygen showed a dielectric constant of 467 and a dissipation factor of 0.02. The room-temperature current-voltage characteristics revealed a space charge limited conduction (SCLC) mechanism, though at low fields the effect of the electrodes was predominant. The conduction mechanism was thoroughly-investigated in terms of Schottky emission at low fields, and bulk-limited SCLC at high fields. The change over to the bulk-limited conduction process from the electrode-limited Schottky emission was, attributed to the process of tunneling through the electrode interface at high fields resulting into the lowering of the electrode contact resistance and consequently giving rise to a bulk limited conduction process. The predominance of SCLC mechanism in the films suggests that the bulk properties are only revealed if the depletion width at the electrode interface is thin enough to allow the tunneling process to take place. This condition is only favorable if the film thickness is high or if the doping concentration is high enough. In the present case the film thickness ranged from 0.3 to 0.7 μm which was suitable to show the transition mentioned above.     

Optical properties of Ag nanoparticles embedded Ba0.5Sr0.5TiO3 films prepared by alternating pulsed laser deposition

Nanocomposite thin films consisting of nanometer-sized Ag particles embedded in amorphous Ba0.5Sr0.5TiO3 matrix were prepared on fused silica substrates by an alternating pulsed laser deposition method. Their optical nonlinearities have been studied using the Z-scan method. The surface plasmon resonance (SPR) peak shifts to red and increases with the increasing the volume fraction of Ag in the nanocomposite films. The magnitude of the third-order nonlinear susceptibility of the nanocomposite with an Ag volume fraction of 3.3% was calculated to be approximately 2 x 10(-8) esu at the SPR wavelength.     

高度取向的(Pb_(0.5)Sr_(0.5))TiO_3/LaNiO_3异质结构铁电薄膜性能

用sol-gel方法在Pt(111)/Ti/SiO2/Si(100)衬底上制备了具有LaN iO3(LNO)缓冲层的(Pb0.5Sr0.5)TiO3(PSrT50)/LNO/Pt异质结构铁电薄膜。X射线分析发现PSrT50薄膜在(100)方向高度取向,同时扫描电镜图像显示薄膜结构致密、表面平整。通过和直接在Pt上制备的、相同厚度的PSrT50薄膜比较,PSrT50/LNO/Pt结构薄膜在室温下具有更大的剩余极化(Pr=4.5μC/cm2)和更高的介电常数(rε=850)。同时,漏电流机理分析表明,PSrT50/LNO/Pt结构薄膜在低电场作用下呈现Pool-Frenkel发射效应,在高电场作用下则表现为空间电荷限制电流。     

The effect of sintering on the properties of Ba0.7Sr0.3TiO3 ferroelectric films produced by electrophoretic deposition

Ba_0.7Sr_0.3TiO₃ (BST) films were produced on metal substrate using electrophoretic deposition (EPD) followed by high temperature sintering. The composition, crystal structure and microstructure of the deposited films were characterised using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The sintered BST films showed a sharp perovskite structure with uniform microstructure. The results indicated that a typical BST film of 20 μm thick after sintering for 2–10 h exhibited the relative dielectric constant ranging from 3100 to 5100 at 20 °C and dissipation factor of 0.061–0.118 at 1 kHz. The density, crystallinity, microstructural uniformity and dielectric properties of the BST films reached their best values after 8 h annealing at 1350 °C. These films also possess excellent adhesion to the substrate.     

沉积温度和退火处理对Ba0.5Sr0.5TiO3介电性能的影响

采用射频磁控溅射法在ITO/Corning1737玻璃基片上制备了用于无机EL绝缘层厚约700nm的Ba0.5Sr0.5TiO3介电薄膜,研究了沉积温度和退火处理对薄膜介电性能的影响.实验表明,随着沉积温度的升高,薄膜的介电常数、介电损耗、正反向漏电流密度增加,击穿场强下降.对于在500℃下沉积的薄膜在550～700℃、1.8×10-2Pa氧气氛中进行30min退火处理,结果发现在550℃和600℃下热处理介电损耗有所改善,其它参数都劣化;在650℃和700℃下热处理介电常数显著增加,其它性能都变差.     

Influence of bismuth on properties and microstructures of Sr0.5Ba0.5−xBixTiO3 thin films

The influence of bismuth (Bi) on the dielectric and ferroelectric properties of Sr_0.5Ba_0.5−xBi_xTiO₃ (BST, 0 ≤ x ≤ 0.030 mol) thin films was studied. The results showed that the dielectric constant (ε_r) and dielectric loss (tan δ) decreased, and temperature, T_m, for maximum and ε_r (Curie temperature), moved to lower temperature with increasing Bi content. The P_r, P_s and E_c were 0.22 μC/cm², 0.32 μC/cm² and 60 kV/cm, respectively for Sr_0.5Ba_0.485Bi_0.015TiO₃ thin films measured at 100 Hz, 20 V. The microstructure of BST thinfilms was studied by XRD and TEM. Tetragonal perovskite grains existed in BST thin films, but the grain size decreased with increasing doping ratio in BST. The characteristic absorption band for octahedron [TiO₂] (471.65 cm⁻¹) was shifted to lower wave number.     

Dielectric properties of La2O3-doped Ba0.8Sr0.2TiO3 ceramics

La₂O₃-doped Ba_0.8Sr_0.2TiO₃ dielectric ceramics were prepared by conventional solid state ceramic route. Scanning electron microscope was employed to observe the surface morphologies. The capacitance C and dielectric loss factor D of the samples were measured with automatic LCR Meter 4225 at 10 kHz respectively. The results show that: ε _r of the samples decreases and tgδ first decreases then increases with increasing amount of La₂O₃ doping. ε _r reaches better value, tgδ obtains the minimum value at 0.5 mol% La₂O₃. ε _r increases and tgδ decreases when sintering temperature increases. The samples doped with 0.5 mol% La₂O₃ sintered at 1,350 °C for 10 h exhibited attractive properties, including high relative dielectric constant (>4,000), low dielectric loss (16.8 × 10^?4), low temperature coefficient of relative dielectric constant(<±21 %) in the temperature range of +25 to +85 °C.     

Yb~(3+)/Tm~(3+)共掺杂BST铁电厚膜的制备及其上转换发光

利用丝网印刷工艺制备出稀土Yb3+/Tm3+共掺杂的Ba0.8Sr0.2TiO3铁电陶瓷厚膜,利用XRD、SEM、EDS、Raman和荧光光谱仪研究了稀土掺杂对厚膜微结构和发光性能的影响。实验发现,在低掺杂量时Yb3+、Tm3+离子在BST晶格中首先替代B位离子,高掺杂量时则同时占据A位和B位离子。掺杂后的厚膜仍表现为典型的铁电四方相结构。在800nm近红外激光激发下,共掺杂的BST厚膜中的Tm3+离子通过Yb3+离子的敏化作用在468与533nm处实现了间接上转换蓝色与绿色荧光输出,分别对应于Tm3+离子的1 G4→3 H6跃迁和1 D2→3F4跃迁。468nm蓝色荧光强度随着Yb3+、Tm3+离子比的增加先增强后减弱,在Yb3+、Tm3+离子共掺比为2∶1达到最大,并对上转换发光的机理进行了分析。     

Dielectric properties of Sb2O3-doped Ba0.672Sr0.32Y0.008TiO3

Sb₂O₃-doped Ba_0.672Sr_0.32Y_0.008TiO₃ (BSYT) dielectric ceramics were prepared by conventional solid state method, and their dielectric properties were investigated with variation of Sb₂O₃ doping content and sintering temperature. The X-ray diffraction patterns indicated that all the BSYT specimens possessed the perovskite polycrystalline structure. The experimental results reveal that the introduction of Sb₂O₃ into Ba_0.672Sr_0.32Y_0.008TiO₃ can control the grain growth, reduce the relative dielectric constant and dielectric loss, shift the Curie temperature to lower temperature and significantly improve the thermal stability of the BSYT ceramics. The samples doped with 1.6 wt.% Sb₂O₃ sintered at 1320 °C for 2 h exhibited attractive properties, including high relative dielectric constant (> 1500), low dielectric loss (< 40 × 10^− 4), low temperature coefficient of capacitor(< ± 35%) over a wide temperature range from − 25 °C to + 85 °C.     

Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–MgO–Mg2TiO4 composite ceramics

Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics were prepared by a solid-state reaction method, and the dielectric tunable properties were investigated. It is observed that the addition of MgO–Mg₂TiO₄ into the Ba_0.5Sr_0.5TiO₃ forms ferroelectric (Ba_0.5Sr_0.5TiO₃)–dielectric (Mg₂TiO₄–MgO) composites. Increasing Mg₂TiO₄ content causes an increase of Curie temperature T_c towards room temperature and a decrease of dielectric constant peak ε_max. The dielectric constant and loss tangent of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composites have been reduced and the overall tunability is maintained at a sufficiently high level. With the increase of Mg₂TiO₄ content and the decrease of MgO content, the dielectric constant and tunability of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics increase and the Q × f values decrease. Ba_0.5Sr_0.5TiO₃–Mg₂TiO₄–MgO composites have dielectric constant of 123.0–156.5 and tunability of 14.4–28.5 % at 10 kHz under 3.9 kV/mm, indicating that they are promising candidate materials for tunable microwave applications requiring a low dielectric constant.     

Nb元素对Ba0.5Sr0.5NbzTi1-zO3薄膜结构与性能的影响

采用溶胶-凝胶法制备了Ba0.5Sr0.5NbzTi1-zO3薄膜（Nb=0-4．12mol％）,采用HPAgilent 429A阻抗分析仪等测试方法研究了微量元素铌对Ba0.5Sr0.5NbzTi1-zO3（BSNT）薄膜介电性能的影响。当Nb分别为0-4．12m01％时,相对介电常数占,降低而介质损耗tanδ均得到了改善,当测试频率为1kHz,tanδ由0．09降低到0．067;居里温度Tm逐渐移向低温;在测试频率2．0-10MHz范围内,εr、tanδ均能表现出较好的频散特性。采用XRD、TEM等测试方法分析了薄膜的结构特征。薄膜为四方钙钛矿晶体结构,但Nb的溶入改变了晶胞参数的c／a比,减小了薄膜的晶粒尺寸,提高了薄膜的致密度。     

Dielectric dispersion and tunability of sol-gel derived Ba x Sr1−x TiO3 thin films

Ba_0.5Sr_0.5TiO₃, Ba_0.6Sr_0.4TiO₃, Ba_0.7Sr_0.3TiO₃ and Ba_0.8Sr_0.2TiO₃ thin films were fabricated by a modified sol-gel technique on Pt(111)/Ti/SiO₂/Si(100) substrates. All Ba _x Sr_1–x TiO₃ films crystallized in the perovskite structure with a crack free microstructure and clear grain boundaries. Highest relative permittivity and dielectric tunability was observed in the Ba_0.7Sr_0.3TiO₃ thin film. Ba_0.7Sr_0.3TiO₃ and Ba_0.8Sr_0.2TiO₃ compositions demonstrated ferroelectric hysteresis loops indicating the presence of ferroelectricity at room temperature. The paraelectric compositions of Ba_0.5Sr_0.5TiO₃ and Ba_0.6Sr_0.4TiO₃ showed significant tunability with negligible loss tangent. The tunability of Ba_0.5Sr_0.5TiO₃ thin film decreased with the increase of frequency from 100 kHz to 100 MHz. As the frequency increases, especially above 10 MHz, the relative permittivity decreases while the loss tangent increases. Since Ba_0.5Sr_0.5TiO₃ thin film is paraelectric at room temperature, relaxation due to ferroelectric domains cannot occur. Therefore this behaviour has originated from the contact resistance and finite sheet resistance of both the bottom and top electrodes. To analyse the thin film capacitor, the parallel plate capacitor structure can be modeled based on an equivalent circuit, which contain electrode and contact resistance.     

Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films

Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.     

Dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3)) thin films

The structural and dielectric properties of sol-gel derived barium-strontium-titanate (Ba(0.4)Sr(0.6)TiO(3 )) thin films have been investigated. The as-fired films are found to be amorphous, and films crystallize to a cubic phase after a post deposition annealing at 700 degrees C for one hour in air. The variation of dielectric constant with temperature and field was investigated as a function of film thickness. These films display a nonlinear dielectric response that can be described in terms of a power series expansion of the free energy in polarization as in Landau-Ginzburg-Devonshire approach. The measured room temperature dielectric constant (epsilon') of the film was about 320. The dielectric constant did not show any significant frequency dependence up to 100 kHz. The temperature dependence of dielectric constant exhibited a diffused ferroelectric to paraelectric phase transition at -60 degrees C. The room temperature dielectric constant and magnitude of the dielectric peak at the Curie point was dependent on the thickness of the film. The obtained dielectric data on sol-gel barium strontium titanate thin films on platinized substrates were analyzed in the light of a barrier layer model.