掺镧钛酸铅铁电薄膜的电畴与热释电性能研究

采用射频磁控溅射技术在Pt/Ti/SiO2/Si(100)基底上生长了掺镧钛酸铅[(Pb0.9La0.1)TiO3, PLT10]铁电薄膜.用X射线衍射研究了PLT10薄膜的结晶相结构.分别使用原子力显微镜和压电响应力显微镜观察了PLT10铁电薄膜的表面形貌和对应区域的电畴结构.测试了PLT10铁电薄膜的电学参数,研究了PLT10铁电薄膜的制备条件与其性能之间的关系.发现在优化条件下制备的PLT10铁电薄膜的介电常数εr为365,介电损耗tgδ为0.02,热释电系数γ为2.20×10-8C·(cm2·K)-1,可以满足制备非制冷红外探测器的需要.     

Pb1-xLaxTiO3薄膜的制备及介电特性研究

用溶胶-凝胶法在Pt/Ti/SiO2/Si(100)基底上制备Pb1-xLaxTiO3(PLT,x＜0.2)薄膜,研究薄膜的结构及其介电、铁电性能.在600℃下退火1小时的PLT薄膜表现出单一的钙钛矿结构,(100)择优取向明显.在室温下PLT薄膜有典型的电滞回线.在x＜0.2(摩尔比)的范围内,PLT薄膜相对介电常数则随着La的增加而增加.     

Pb1-xLaxTiO3薄膜的制备及特性研究

用溶胶-凝胶法在Pt/Ti/SiO2/Si(100)基底上制备Pb1-xLaxTiO3(PLT,x≤0.2)薄膜,研究薄膜的结构及其介电、铁电性能.在600℃下退火1h的PLT薄膜表现出单一的钙钛矿结构,(100)择优取向明显.在室温下PLT薄膜有典型的电滞回线.在x≤0.2(摩尔比)的范围内,PLT薄膜的矫顽场、剩余极化强度都随着La的增加而降低,相对介电常数则随着La的增加而增加.     

Pb1-xLaxTiO3薄膜的制备及特性研究

用溶胶－凝胶法在Pt/Ti/SiO2/Si(100)基底上制备Pb1-xLaxTiO3(PLT,x≤0．2）薄膜,研究薄膜的结构及其介电、铁电性能。在600℃下退火1h的PLT薄膜表现出单一的钙钛矿结构,（100）择优取向明显。在室温下PLT薄膜有典型的电滞回线。在x≤0.2（摩尔比）的范围内,PLT薄膜的矫顽场、剩余极化强度都随着La的增加而降低,相对介电常数则随着La的增加而增加。     

不同基底对掺镧钛酸铅铁电薄膜结晶性能的影响

采用射频磁控溅射技术,使用相同的工艺条件在Si(100)基底和Pt/Ti/SiO2/Si(100)基底上生长了掺镧钛酸铅[(Pb0.9,La0.1)TiO3,PLT10]铁电薄膜。采用常规热处理工艺对两种基底上生长的PLT铁电薄膜在相同条件下进行了退火。用原子力显微镜(AFM)观察PLT薄膜的表面形貌。用X射线衍射技术(XRD)研究PLT薄膜结晶性能。XRD图谱表明硅基底上的PLT在晶化后,各主要晶面的衍射峰均出现,取向呈现多样化;而在铂上的PLT在晶化后,只出现了(111)晶面衍射峰和(222)晶面衍射峰,取向是单一的〈111〉方向。通过对XRD的数据计算可知,在相同条件下退火的PLT薄膜,在铂上的PLT的晶粒尺寸大于在硅基底上的PLT的晶粒尺寸。晶粒尺寸的差异反应出了由于基底的影响而造成薄膜晶化过程中成核方式的差异。     

(Pb0.90La0.10)Ti0.975O3/LaNiO3薄膜的射频磁控溅射制备和性能研究

采用射频磁控溅射技术,以LaNiO3(LNO)作为过渡层,在SiO2/Si(100)、Pt(111)/Ti/SiO2/Si(100)衬底上分别获得了(100)、(110)取向的(Pb0.90La0.10)Ti0.975O3(PLT)铁电薄膜.研究了LNO/Pt(111)/Ti/SiO2/Si(100)和LNO/SiO2/Si(100)基底对PLT薄膜微结构和铁电性能的影响.实验结果表明,与在LNO/Pt(111)/Ti/SiO2/Si(100)基底上沉积的(110)取向的PLT薄膜相比较,在LNO/SiO2/Si(100)基底上沉积的高度(100)取向的PLT薄膜具有更好的微结构和更高的剩余极化强度,其2Pr为40.4μC/cm2.     

CaRuO3电极对(Ba,Sr)TiO3薄膜的介电特性的影响

在Pt(111)/Ti/SiO2/Si(100)衬底上,用脉冲激光沉积工艺分别制备出了(110)外延取向生长的(Ba0.65Sr0.35)TiO3/CaRuO3(BST/CRO)异质结构薄膜;BST/CRO异质结构薄膜由纳米晶团簇组成,最大的团簇晶粒达500 nm,平均晶粒尺寸在60～80 nm,薄膜厚度为650 nm.BST/CRO异质结薄膜均为表面平滑和致密结构.BST/CRO异质结薄膜的介电常数和介电调谐率分别高达851和78.1%.与纯BST薄膜比较,用CRO作电极,增益介电常数与介电调谐率.     

基于非线性介电薄膜的电调滤波器优化设计

采用脉冲激光沉积(PLD)法在(001)MgO基片上制备出高质量的SrTiO3(STO)薄膜,构建了Au/STO/MgO结构的叉指电容.在77K、10KHz条件下,对叉指电容的特性进行了测试,结果表明:在40kV/cm的直流电场作用下,电容值从1.75 pF减小为1.25 pF,电容值的相对变化率为28.5%.在此基础上,根据多层介质叉指电容保角变换模型.定量计算和仿真了STO薄膜的介电常数和微波频率下叉指电容的性能参数,并由此设计了一个三阶带通滤波器,该滤波器可实现13.50%的中心频率移动.     

二氧化钛过渡层对脉冲激光沉积钛酸锶钡薄膜微结构和介电性质的影响

选取极薄Ti02作为过渡层,采用脉冲激光沉积法分别在Si(100)和Pt(111)/Ti/SiO2/Si(100)基底上制备了Bao.6Sro.4TiO3(BST)薄膜,研究过渡层对BST薄膜微结构及电学性质的影响.发现厚度20纳米以内的锐钛矿相结晶TiO2过渡层可使BST薄膜由无规则取向转变为(111)择优取向,而非晶和较厚TiO2过渡层对BST薄膜的取向无影响.结晶的TiO2过渡层也使薄膜的表面颗粒变细.还研究了不同厚度TiO2对BST薄膜电学性质的影响,结果表明BST薄膜在Pt(111)底电极上加入极薄的结晶TiO2过渡层后电学性质有明显改善,薄膜的介电常数和可调谐度提高,而介电损耗降低.加入膜厚约5nm的TiO2过渡层后,测试频率为10 kHz时薄膜相应介电常数、介电损耗及可调谐度分别为513、0.053和36.7%.     

射频磁控溅射制备(Pb,La)TiO3薄膜的结晶性能与铁电畴初步研究

采用射频磁控溅射技术在Pt/Ti/SiO2/Si衬底制备了(Pb,La)TiO3(简记为PLT)铁电薄膜.利用XRD对PLT薄膜的结晶性能进行了研究.实验结果表明,在一定的制备工艺条件下,可以制备出完全钙钛相的PLT铁电薄膜.PLT铁电薄膜的结晶性能与溅射的工作气压、氧氩比、退火温度等关系密切;PFM表明PLT薄膜的电畴具有180°结构.     

The effect of different electrode structures on the dielectric properties of lanthanum-doped lead titanate ferroelectric thin films

Lanthanum-doped lead titanate [(Pb_0.9,La_0.1)TiO₃, PLT10] ferroelectric thin films were grown on Si(100) and Pt/Ti/SiO₂/Si(100) substrates by radio frequency (RF) magnetron sputtering. The crystalline properties of PLT10 films were studied by X-ray diffractometry (XRD). Photolithographic technique was applied to fabricate the interdigital electrodes on PLT10 thin films on Si(100) substrates. The dielectric properties of PLT10 thin films with different electrodes were measured. At room temperature and 1 kHz testing frequency, the dielectric constant of the PLT10 thin film with interdigital electrodes is 386. The dielectric constant of the PLT10 thin film fabricated under the same technological conditions with parallel plate electrodes structure is 365, while the dielectric constant and loss of the PLT10 thin film with interdigital electrodes are decreased faster than those of the film with parallel plate electrodes with increasing frequency. This is because more influences of interface state are introduced due to the interdigital electrode configuration. Translated from Journal of Functional Materials, 2006, 10(37): 1,554–1,556, 1560 (in Chinese)     

Effects of bottom electrodes on dielectric properties of epitaxial 2% Mn doped Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> thin films

2 mol% Mn doped Ba(Zr_0.2Ti_0.8)O₃ (Mn-BZT) thin films were prepared by pulsed laser deposition (PLD) on single crystal oxide substrates LaAlO₃(001) and MgO(001), with conductive oxide bottom electrodes LaNiO₃ and SrRuO₃, respectively. Both the Mn-BZT films and the bottom electrode films could be c-axial oriented with a cube-on-cube arrangement on the corresponding substrates. The dielectric properties measured with parallel plate capacitor configurations of Au/Mn-BZT/LNO and Au/Mn-BZT/SRO revealed that the Mn-BZT film on LNO bottom electrode exhibited comparatively higher dielectric constant, larger dielectric tunability and lower dielectric loss than that on SRO. It could be mainly attributed to the better epitaxial growth characteristics and mismatch stress of Mn-BZT thin film on LNO, as well as less misfit dislocation and the better morphology of LNO bottom electrode.     

Microstructure and electrical properties of Pb(Zr0.52Ti0.48)O3 ferroelectric films on different bottom electrodes

The crystalline quality, dielectric and ferroelectricity of the Pb(Zr_0.52Ti_0.48)O₃ (PZT) films deposited on the LaNiO₃ (LNO), LNO/Pt and Pt bottom electrodes were comparatively analyzed to investigate the possibility for their application. LNO thin films were successfully prepared on Si (100) and Pt(111)/Ti/SiO₂/Si substrates by modified metallorganic decomposition (MOD). The PZT thin films were spin-coated onto the LNO, LNO/Pt and Pt bottom electrodes by sol–gel method. The crystallographic orientation and the microstructure of the resulting LNO films and PZT thin films on the different bottom electrodes were characterized by X-ray diffraction analysis. The dielectric and ferroelectric properties of PZT films on the different bottom electrodes are discussed. The PZT films deposited onto Pt/Ti/SiO₂/Si and LNO/Si substrates show strong (110) and (100) preferred orientation, respectively, while the films deposited onto LNO/Pt/Ti/SiO₂/Si substrates show the peaks of mixed orientations. PZT films on LNO and LNO/Pt bottom electrodes have larger dielectric constant and remnant polarizations compared with those grown on the Pt electrode.     

Complex electrical (impedance/dielectric) properties of electroceramic thin films by impedance spectroscopy with interdigital electrodes

The complex electrical properties of isotropic, electroceramic thin films can be measured with interdigital electrodes, analyzed by impedance spectroscopy (IS). A periodic two-dimensional film/interdigital electrode (IDE) structure was simulated by finite-difference numerical method and a generalized model was developed to characterize the electrical properties of thin films. Variable frequency simulations showed that the film/IDE system can be modeled as a parallel resistor-capacitor equivalent circuit. Equations were developed to extract from the equivalent circuit's fitted resistance and capacitance, the materials properties of the thin film, both conductivity and permittivity. The electrical properties of a polydomain BaTiO₃ film grown on a MgO substrate were measured with an IDE structure by IS to demonstrate how the methodology can be readily used.     

Effect of bottom electrodes on dielectric properties of high frequency Ba0.5Sr0.5TiO3 parallel plate varactor

Three types of Ba_0.5Sr_0.5TiO₃ (BST) thin film parallel plate varactor with different bottom electrodes were fabricated. The bottom electrodes of three types of varactor were perovskite conducting oxide La_0.7Sr_0.3MnO₃ (LSMO), Pt and Au, respectively. Dielectric properties of the BST thin films were characterized in the frequency range from 10 MHz to 15 GHz. The microstructure of the BST thin films was investigated by X-ray diffraction and scanning electron microscope. The microstructural analysis shows that the BST thin films grown on LSMO and Pt bottom electrodes are polycrystalline textured with columnar grains. Dielectric measurement indicates that the BST thin film grown on LSMO bottom electrode has a maximum dielectric constant and a little higher loss tangent.     

Improved dielectric properties of CaCu3Ti4O12 thin films on oxide bottom electrode of La0.5Sr0.5CoO3

We report on the effect of La_0.5Sr_0.5CoO₃ (LSCO) bottom electrode to the dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) thin films grown on Ir/Ti/SiO₂/Si substrates. Compared with the films grown directly on Ir/Ti/SiO₂/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode.     

The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films prepared by RF magnetron sputtering

(Ba_{1 − x} Sr _x )TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si and YSZ/Pt/Ti/SiO₂/Si substrates by radio frequency (RF) magnetron sputtering. The influence of YSZ interlayer on microstructures and dielectric properties of BST thin films were investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy and dielectric frequency spectra. It was found that the preferred orientation of BST thin films could be tailored by insertion of YSZ interlayer and adjusting the thickness of YSZ interlayer. The BST thin films deposited on YSZ interlayer exhibited a more compact and uniform grain structure than that deposited directly on Pt electrode. Dielectric measurement revealed that the BST thin films deposited on 10 nm YSZ interlayer have the largest dielectric constant and a low dielectric loss tangent. The enhanced dielectric behavior is mainly attributed to the YSZ interlayer which serves as an excellent seeding layer to enhance the crystallization of subsequent BST films layer, and a smaller thermal stress field built up at the interface between YSZ interlayer and BST film layer.     

Preparation and characterization of (Ba1−xSrx)TiO3 films by sol–gel processing

Barium strontium titanate ((Ba, Sr)TiO3) thin films were prepared on Pt/Ti/Si substrates by the sol–gel method using metal alkoxides. The dependence of the dielectric constant for the films on the film compositions and on the film thickness were investigated. The dielectric constant of the film of thickness 180 nm had the highest value of 230 at composition ratios of [Ba+Sr]/[Ti]=1.04 and [Sr]/[Ba+Sr]=0.6. The dielectric constant of the films with this composition decreased from 390 to 160 with a decrease in the film thickness from 440 to 100 nm. The decrease in the dielectric constant with increasing film thickness is attributed to the existence of a low-dielectric-constant interface layer adjacent to the electrodes. © 1998 Kluwer Academic Publishers     

Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown on thin Bi layer-coated Pt(111)/Ti/SiO2/Si substrates

In this work, the growth and study of dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown on thin Bi layer coated Pt(111)/Ti/SiO₂/Si substrates, depending on thin Bi layer thickness is reported. The BST thin film (thickness 180 nm) grown on 10-nm-thick Bi layer exhibited more improved structural and dielectric properties than that grown on bare Pt(111)/Ti/SiO₂/Si substrate. The 10-nm-thick Bi layer in optimum configuration was effective for the grain growth of BST phase and suppressed the formation of the oxygen-deficient layer at the interface between the BST thin film and bottom electrode, which resulted in an increase in dielectric constant and a decrease in leakage current density of the Pt/BST thin film/Pt capacitor.     

High tunabilty Ba0.6Sr0.4TiO3 thin films fabricated on Pt–Si substrates with La0.5Sr0.5CoO3 buffer layer

Ba_0.6Sr_0.4TiO₃ (BST) thin films for the tunable microwave devices were grown using pulsed laser deposition (PLD) on Pt/Ti/SiO₂/Si (Pt–Si) substrates with La_0.5Sr_0.5CoO₃ (LSCO) buffer layers. For comparison, the films were also grown on Pi-Si substrates. X-ray diffraction results showed that the BST films on Pt–Si displayed a highly (110) preferred orientation, while the films with the LSCO buffer layers were (100)-oriented. Atomic force microscope (AFM) revealed that BST films with LSCO buffer layers had smoother surface and smaller grain size. Compared with (110) BST films, the (100) BST thin films had the higher tunability and the better figure of merit (FOM). The dielectric constant, the dielectric loss and the tunability of the BST thin films on LSCO/Pt–Si substrates measured at 10 kHz were 1010, 0.031 and 82.4%, respectively. Additionally, the current–voltage(I–V) measurement indicated that the leakage current density of (100) BST thin films on LSCO/Pt-Si substrates was reduced compared with that of (110) BST thin films directly on Pt electrodes, due to the possible reduction of interface oxygen vacancies at BST/LSCO interface and smaller grain size of the films. The enhancement in dielectric properties may be attributed to (100) preferred orientation in the films.