BaTiO_3/LaAlO_3铁电超晶格中耗散因子与性能的关系

用横场伊辛模型模拟计算了BaTiO3/LaAlO3铁电超晶格的铁电、介电性能,研究了BaTiO3/LaAlO3铁电超晶格中的耗散因子对极化、居里温度和介电常数的影响,发现随着耗散因子的增加,BTO/LAO超晶格的极化强度和居里温度下降。当耗散因子为2.66时,模拟计算值与实验结果相近。     

不同介电层对HfxZr1-xO2薄膜铁电性能影响的研究进展

近年来,铁电Hf_xZr_1-xO₂(HZO)薄膜受到越来越多的关注,但是铁电层与电极材料层以及铁电层与半导体衬底层之间的界面问题并没有得到解决,阻碍了HZO薄膜的进一步应用。总结了通过引入不同介电层材料,如Al₂O₃、ZrO₂、HfO₂、Ta₂O₅等,调节HZO薄膜铁电性能的方法及其机理;详细介绍了各种介电层材料作为封盖层对HZO薄膜铁电性能的影响,如对HZO薄膜提供平面内应力、控制铁电层的晶粒尺寸及作为铁电层形核核心的作用;最后,总结并展望了利用介电层调控HZO薄膜铁电性能的一般规律,为后续相关研究的开展提供了指导。     

CuO-BaO掺杂对Ba(Ti_(0.91)Zr_(0.09))O_3介电性能的影响

采用固相反应法制备了添加1%(质量分数)CuO-BaO混合物的Ba(Ti0.91Zr0.09)O3铁电陶瓷,研究了r(Cu∶Ba)对Ba(Ti0.91Zr0.09)O3铁电陶瓷烧结特性及介电性能的影响。结果表明:随着r(Cu∶Ba)的增加,Cu开始进入晶格,Ba(Ti0.91Zr0.09)O3陶瓷的密度先增加后减小,r(Cu∶Ba)为1.5时,ρ达最大值5.85g/cm3,斜方-四方相变峰出现介电弛豫现象,居里温度向低温方向移动,电滞回线呈现典型弛豫型铁电体的特征。     

Sol-Gel法制备Bi4Ti3O12薄膜及其性能研究

采用溶胶-凝胶(Sol-Gel)法在Pt/Ti/SiO2/Si衬底上制备了Bi4Ti3O12(BTO)铁电薄膜,利用X-射线衍射仪(XRD)和原子力显微镜(AFM)对其晶格结构和表面形貌进行了表征,制备的BTO薄膜具有单一的钙钛矿晶格结构和表面平整致密。对700℃退火的BTO薄膜进行了铁电性能和疲劳特性测试,在测试电压为6 V时,剩余极化值2Pr约为12.5μC/cm2,矫顽电场2Ec约为116.7 kV/cm;经1×109次极化反转后,剩余极化值下降了24%,对其疲劳机理进行了探讨。     

制备工艺对PMN铁电陶瓷性能的影响

从材料组成、结构和性能的关系出发,系统地研究了探讨了制备工艺对弛豫型铁电陶瓷性能的影响,以及烧结后退火工艺对样性能的影响。研究PbTiO3组分2种不同的加入方式((1-x)(PbO 1/3MgNb2O6) x(PbO TiO2)和(1-x)(PbO 1/3MgNb2O6) x(PbTiO3))对Pb(Mg1/3Nb2/3)O3-PbTiO3固溶体陶瓷介电性能的影响规律。与用前一种方法制得的试样相比,用后一种方法得到的陶瓷试样的介电常数峰得到进一步展宽,并且呈现双峰。介电性能的这种变化表明微区化学组成的均匀程度对材料的宏观介电性能会产生显著影响。     

铁电（Ba,Sr）TiO3及介电Bi2O3-ZnO-Nb2O5薄膜材料应用于电调谐微波器件研究进展

铁电钛酸锶钡BaxSr1-xTiO3(BST)是一种拥有十分优越铁电/介电性能的材料,在可调谐微波器件方面具有很好的应用前景。本文概括介绍了BST薄膜的研究意义、基本结构、薄膜的制备方法,并针对可调谐微波器件应用需求,详细探讨了通过掺杂、组分梯度变化、纳米铁电多层薄膜以及将铁电BST与新型介电Bi2O3-ZnO-Nb2O5(BZN)薄膜相结合等对铁电薄膜性能进行优化的手段,最后对该领域的前沿问题从材料研究层面作了小结与展望。     

退火处理对0.5PZN-0.5PZT陶瓷弛豫性的影响

采用常规陶瓷工艺制备了Pb(Zn_(1/3)Nb_(2/3))_(0.5)(Zr_(0.5)Ti_(0.5))_(0.5)O_3 (0.5PZN-0.5PZT)铁电陶瓷,并在氧气氛下进行退火.运用XRD、直流电导率和介电温度谱测试氧气氛退火前后陶瓷相结构与电性能的变化,并对弛豫性与微结构的关系进行探讨.结果表明,氧气氛退火可有效补偿体系中的氧空位,降低四方相含量,材料的弛豫性显著增强.     

晶格失配应变对铁电薄膜铁电性能的影响

采用与时间有关的Ginzburg-Landau方程,在考虑表面效应的条件下研究了晶格失配应变对外延铁电薄膜铁电性能的影响,通过外推长度考虑表面效应。获得了不同应变情况下的铁电薄膜电滞回线及蝶形应变迟滞回线。结果表明,剩余极化强度和矫顽场与压应变和张应变密切相关,其值强烈依赖于晶格失配应变。     

不同厚度PZT薄膜的制备及电性能特性研究

采用sol-gel（溶胶-凝胶）法在Pt/Ti/SiO2/Si基底上分别制备了厚度为400nm,600nm,800nm的PZT（锆钛酸铅,Zr/Ti=52/48）薄膜,研究了厚度对薄膜介电性能与铁电性能的影响。通过对薄膜的铁电性能与介电性能进行测试,分析了不同厚度薄膜的剩余极化强度、介电常数与介电损耗;通过对介电调谐率与最大正切损耗的计算,进一步分析了薄膜的介电调谐性能。实验结果表明,薄膜的介电常数与介电损耗随薄膜厚度的增大而增加;厚度为600nm的薄膜具有最好的介电调谐性能与铁电性能。     

复合靶溅射Bi4Ti3O12铁电薄膜的结构和相变

采用金属与金属氧化物复合靶的射频溅射法，在Si基片上沉积制备了Bi4Ti3O12(BTO)铁电薄膜，用变温X－射线及热分析等方法研究BTO铁电薄膜的结构和相变，结果表明，在温度为350－445℃之间，薄膜经历由烧绿石相向钙钛矿相的结构相变，在670℃附近，薄膜由铁电相向顺电相转变，该相变是由于晶格畸变量b/a随温度上升连续减小，使得薄膜晶体对称性发生改变引起，在相变附近未观察到潜热的产生。     

Structural and Electrical Characters of Ba0.6Sr0.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). X-ray diffraction ~2 and Ф scan showed that the epitaxial relationship of BST/LSCO/LAO was [001] BST//[001] LSCO//[001] LAO. The atomic force microscope (AFM) revealed a smooth and crack-free surface of BST films on LSCO-coated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films. Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.6310-7 A/cm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate well-behaved ferroelectric properties with the remnate polarization of 6.085 C/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40) materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

Structural and Electrical Characters of Ba0.6Sro.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). Xray relationship of BST/LSCO/LAO was [001] BST//[001]LSCO//[001] LAO. The atomic force microscope (AFM)revealed a smooth and crackfree surface of BST films on LSCOcoated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films.Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.63×107 A/crm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate wellbehaved ferroelectric properties with the remnate polarization of 6.085 μC/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40)materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

Novel polymer-ceramic nanocomposite based on new concepts for embedded capacitor application (I)

A rapid growth of mixed-signal integrated circuits is driving the needs of multifunction and miniaturization of the component in electronics applications. Polymer-ceramic composites have been of great interest as embedded capacitor materials because they enabled companies to combine the processability of polymers with the high dielectric constant of ceramics. This paper presents the preparations and performance characterizations of novel polymer-ceramic nanocomposites based on new concepts for embedded capacitor application. First, metal particle nickel-filled nanocomposite with high dielectric constant was evaluated as a candidate for embedded capacitors. Two types of nickel particles were selected with the size of 400 and 150nm, respectively. With proper filler loading and highly dispersed, a high dielectric constant of over 90 was observed with a filler loading ratio of 60-vol%. Second, the surface modification of a barium titanate (BTO) particle was also attempted in nanocomposite. Phthalocyanine-coated BTO (Pc-coated BTO) was selected as filler to prepare the composite. Its dielectric constant was observed as over 80 at 1MHz, which was much higher than that of composite derived from commercial BTO. Last, in order to improve the processability of the nanocomposite, 4, 4'-diphenylmethane bismaleimide (BMI) was selected as a matrix polymer by the combination with polyamide (PA). Higher dielectric constant nanocomposite derived from PA/BMI and Pc-coat BTO was obtained, and its potential application towards embedded capacitors was also evaluated.     

基片对SrTiO3薄膜结构与介电性能的影响

对比研究了MgO和LaAlO3(LAO)单晶基片上采用脉冲激光法生长的SrTiO3(STO)薄膜的微观结构和介电性能。通过XRD,AFM和制备叉指电容测量的方法研究发现,在MgO基片上生长高质量(00L)织构STO薄膜需要较高的生长温度;LAO基片上的STO薄膜更加平整;而MgO上的STO薄膜具有更高的零偏压介电常数和更强的非线性介电性质。     

Planar microwave integrated phase-shifter design with high purityferroelectric material

Ferroelectric materials (FEM's) are very attractive because their dielectric constant can be modulated under the effect of an externally applied electric field perpendicular to the direction of propagation of a microwave signal. FEM may be particularly useful for the development of a new family of planar phase shifters which operate up to X-band. The use of FEM in the microwave frequency range has been limited in the past due to the high losses of these materials; tan δ=0.3 at 3 GHz is typical for commercial BaTiO₃ (BTO) and due to the high electric field necessary to bias the structure in order to obtain substantial dielectric constant change. In this paper, a significant reduction in material losses is demonstrated. This is achieved by using a new sol-gel technique to produce barium modified strontium titanium oxide [Ba_1-xSr_xTiO₃ (BST)], which has ferroelectric properties at room temperature. Also demonstrated is how the use of thin ceramics reduces the required bias voltage below 250 V, with almost no power consumption required to induce a change in the dielectric constant. A phase shift of 165° was obtained at 2.4 GHz, with an insertion loss below 3 dB by using a bias voltage of 250 V. Due to the planar geometry and light weight of the device, it can be fully integrated in planar microwave structures     

To optimize electrical properties of the ultrathin (1.6 nm)nitride/oxide gate stacks with bottom oxide materials andpost-deposition treatment

The electrical properties affected by the bottom oxide materials and the post-deposition treatment on the ultrathin (down to 1.6 nm) nitride/oxide (N/O) stacks, prepared by rapid thermal chemical vapor deposition (RTCVD) with two-step NH₃/N₂O post-deposition annealing, for deep submicrometer dual-gate MOSFETs have been studied extensively. N/O stack with NO-grown bottom oxide exhibits fewer flat-band voltage shifts and higher hole and electron mobility, but suffers from worse leakage current than that with conventional O₂-grown bottom oxide. In post-deposition treatment, increasing NH₃ nitridation temperature can effectively reduce the equivalent oxide thickness (EOT) and improve leakage current reduction rate, but can result in worse mobility. Furthermore, the subsequent N₂O annealing eliminates the defects and offers a contrary effect on the N/O stack in comparison with the NH₃ nitridation step     

钛酸钡改性及其聚酰亚胺复合材料的性能研究

采用化学还原法在直径100 nm的钛酸钡表面沉积直径约5~20 nm的铜纳米颗粒,分析了BaTiO3-聚酰亚胺复合材料的介电性能和作用机理。研究结果表明:铜纳米颗粒通过化学键与钛酸钡表面的晶体结构结合在一起,与聚酰亚胺组合成两相复合材料,这有别于BaTiO3/导电粒子/聚酰亚胺三相复合材料。另外,虽然铜纳米颗粒有部分被氧化,导电性能降低,但改性后的BaTiO3-聚酰亚胺的复合材料还是具有低损耗、高介电的性能,充分说明了这种新型的两相复合材料能够实现高介电、低损耗的目标。     

Effect of barrier layers on BaTiO3 thin film capacitors on Si substrates

The choice of the bottom electrode or barrier layer plays an important role in determining the electrical and structural properties of metal/ferroelectric/metal thin film capacitors. A substantial improvement of the electrical and structural properties of the capacitors was found by using RuO₂ as a bottom electrode. Electrical measurement on a capacitor with a structure of BaTiO₃(246 nm)/RuO₂ (200 nm)/SiO₂/Si, where the BaTiO₃ thin film was deposited at room temperature, showed a dielectric constant of around 15, leakage current density of 1.6 × 10⁻⁷A/cm² at 4 V, a dc conductivity of 9.8 × 10¹⁴S/cm, and a capacitance per unit area of 5.6 × 10⁴pF/cm². A similar structure but with polycrystalline BaTiO³ (273 nm) as the dielectric deposited at 680°C showed a dielectric constant of 290, leakage current density of 1.7 × 10⁻³A/cm² at 4 V, a dc conductivity of 1.2 × 10⁻⁸ S/cm, and a capacitance per unit area of 9.4 × 10⁵ pF/cm². Scanning electron microscopy analysis on the films showed differences in the microstructure due to the use of different bottom electrode materials, such as RuO₂ or Pd.