MgO和STO基片上制备YBCO高温超导薄膜生长研究

用AFM和XRD研究在MgO和STO基片上外延生长2-200nm的YBCO高温超导薄膜的生长机制。采用倒筒式直流溅射装置,首次实现单轴驱动双轴旋转技术,本质上实现同时在MaO基片和STO基片上沉积同一均匀厚度的YBCO薄膜。     

斜切基片上同质,异质外延薄膜的TEM研究

钙钛矿结构薄膜如铁电和高温超导薄膜有极大的应用前景和探索新型多元素氧化物薄膜的前途,因此它的外延生长机制引起人们的极大关注。不少人认为螺旋位错岛状生长是YBa2Cu3O7-δ(YBCO)薄膜的本征生长模式[1],因此薄膜表面的平整度极差,使器件应用尚不能达到实现。近些年来,人们对于SrTiO3(STO)基片表面的重构处理作了大量的研究[1,2],得到平台形貌有利于改变钙钛矿结构薄膜的生长机制为台阶流动生长机制,可以得到表面平整的单晶薄膜。本文就是使用斜切1°和10°的STO(001)基片在激光镀膜仪中分别生长STO、YBCO薄膜,将所得薄膜用平…     

SRO薄膜的倒筒式直流溅射生长

采用倒筒式直流溅射方法在(001)LaAlO 3[LAO]基片上原位生长SrRuO3(SRO)薄膜,系统研究了基片温度、溅射气氛等工艺参数对SR O薄膜织构、表面形貌的影响。实验结果表明,在基片温度为720℃,氧氩比为1∶4的工艺条件下制备出了110取向、表面平整的SRO薄膜。     

铁电态-顺电态双层薄膜的高介电调谐

基于Landau-Devonshire自由能理论建立了热力学模型,对生长在(001)SrTiO3衬底上的PbZr0.4Ti0.6O3(PZT)/SrTiO3(STO)双层异质外延结构铁电薄膜以及不受约束的双层薄膜的介电响应与调谐率进行了研究。结果表明,在两层薄膜为无约束的自由薄膜情况下,STO厚度占双层薄膜总厚度的百分比为30%时,相对介电响应达到最大值约3.3×105,当两薄膜为异质外延结构时,其百分比为51%时,相对介电响应达到最大值约4×105。同时,调谐率还随外加电场的增大而增大,在临界百分比时,调谐率可达到约99%。     

氧分压对脉冲激光沉积SrTiO_3薄膜性质的影响

采用脉冲激光沉积(PLD)法在不同氧分压下于LaAlO3(100)基片上成功制备了SrTiO3(STO)薄膜。通过测试,表征了薄膜的微观结构、表面形貌和光学特性。研究表明,对于利用PLD法制备STO薄膜,氧分压是重要的工艺参数。随着氧分压的降低,薄膜的结晶性变好,并发生由立方晶系到四方晶系的形变;氧分压升高,薄膜晶粒尺寸变大、数目变少,薄膜的厚度减小。薄膜在400~2500 nm的可见光和红外波段呈现较低的光学吸收。在5,10和15 Pa氧压下制备的STO薄膜的能隙宽度分别约为3.84,4.13和4.05 eV。这为STO薄膜进一步的制备与分析提供了良好的实验数据支持。     

BST/LSCO异质结构的研究

利用脉冲激光沉积法在STO(001)基片上外延生长了La0.5Sr0.5CoO3(LSCO)导电氧化物薄膜,研究了基片温度对LSCO薄膜结构和电性能的影响,并制备了Ni-Cr/BST/LSCO多层膜结构。XRD谱发现,沉积温度在450~700℃均能得到高度(00 l)取向的LSCO薄膜,LSCO(002)峰的半高峰宽FWHM=0.1°~0.2°;在LSCO薄膜上制备的BST介质膜具有良好的c轴取向和较高的表面平整度,其εr约为470,tgδ为0.036~0.060。     

CeO_2缓冲层对蓝宝石基Ba_(0.6)Sr_(0.4)TiO_3薄膜结构和介电性能的影响

利用磁控溅射法制备Ce O_2缓冲层,通过脉冲激光沉积法制备Ba_(0.6)Sr_(0.4)TiO_3(BST)薄膜,在Al_2O_3(11—02)蓝宝石基片上构架了Pt/BST/Ce O_2/Al_2O_3和Pt/BST/Al_2O_3叉指电容器,对比研究了Ce O_2缓冲层对BST薄膜结构和叉指电容器介电性能的影响。通过X射线衍射仪、原子力显微镜和LCR表分别对叉指电容器的结构、表面形貌和介电性能进行了表征。实验发现,直接沉积在蓝宝石上的BST薄膜为多晶结构,生长在Ce O_2缓冲层上的BST为(001)取向的高质量外延薄膜。生长在Ce O_2缓冲层上的BST薄膜相对于没有缓冲层的BST薄膜具有更小的晶粒和均方根粗糙度。在40 V偏置电压下,Pt/BST/Al_2O_3和Pt/BST/Ce O_2/Al_2O_3叉指电容器的调谐率分别是13.2%和25.8%;最小介电损耗为0.021和0.014。结果表明Ce O_2缓冲层对生长在蓝宝石基片上的BST薄膜结构和介电性能具有重要影响。     

PZT/NFO/LSMO多层磁电外延薄膜微观结构研究

用脉冲激光沉积法在(110)取向的SrTiO3(STO)单晶衬底上制备了Pb(Zr0.52Ti0.48)O3/NiFe2O4/La0.7Sr0.3MnO3(PZT/NFO/LSMO)磁电复合外延薄膜,并用X射线衍射和透射电镜技术研究了外延薄膜的物相和显微结构。原子力显微镜结果表明PZT、NFO和LSMO薄膜表面均平整,晶粒尺寸分布均匀,表面粗糙度分别为1.8,1.7和0.2 nm。X射线衍射、选区电子衍射和高分辨透射电子显微镜(HRTEM)测试结果均证明各层薄膜沿(110)STO衬底外延生长,其外延关系为(110)PZT//(110)NFO//(110)LSMO//(110)STO和[001]PZT//[001]NFO//[001]LSMO//[001]STO。HRTEM结果显示,NFO/LSMO界面和LSMO/STO界面平整外延性好,无缺陷,而PZT/NFO界面较粗糙;NFO薄膜表面呈锯齿状,锯齿状面为立方NFO的能量最低{111}面,而PZT薄膜表面呈岛状,进一步的显微结构分析认为PZT薄膜为层状-岛状生长模式。     

C-轴取向PbTiO_3薄膜的制作及其结晶、介电和热电性能

采用RF磁控溅射方法在MgO单晶及外延Pt膜基片上成功地生长了高度c~-轴取向的外延PbTiO_3薄膜.在低淀积速率(<2nm/min)、低气压(<1Pa)及采用过量PbO靶的条件下,薄膜的c~-轴取向率为98%.用高温X-射线衍射研究了PbTio_3薄膜的相变.发现了当温度正好在Tc以下时四方相的c~-轴平行于基片,随着温度的下降c~-轴变成垂直于基片.薄膜具有高的电阻率(～10~(10)Ω·cm).在全部未经极化处理的样品中都检测到了较大的热电电流.薄膜的极化方向在全部样品中完全一样.未经极化处理样品之一的相对介电常数为97,热电系数高达25×10~(-8)C/cm~2K.这种薄膜适用于热电红外探测器和压电换能器.     

改善(Pb,Ca)TiO_3薄膜的铁电性能研究

用溶胶-凝胶法和快速退火工艺在LaNiO3/Si(111)基片制备出高度(100)取向生长的钙钛矿相(Pb0.76Ca0.24)TiO3(PCT)薄膜。用原子力显微镜分析了薄膜的表面形貌;测试了薄膜的铁电和介电特性。PCT薄膜的剩余极化强度和矫顽场分别为9.3μC/cm2和64kV/cm,在100kHz薄膜的介电系数和损耗分别为231和0.045。比较了在不同电极制备PCT薄膜的结果,用LaNiO3作底电极,改善了铁电性,降低了矫顽场。     

Comparison of Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films Grown on (100) LaAlO3 and (100) MgO Single-Crystal Substrates

The microwave properties of barium strontium titanate (Ba_0.6Sr_0.4TiO₃) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single-crystal substrates through the sol–gel technique were investigated. The interdigital capacitor (IDC) technique was used to measure the nonlinear dielectric properties in the frequency range from 1 GHz to 10 GHz. The results show that the Curie temperature, capacitance, and tunability of the films are strongly dependent upon the substrate. The film fabricated on the LaAlO₃ substrate has a higher tunability of 16.77% than that grown on the MgO substrate (～8.38%), measured at 10 GHz with an applied voltage of 35 V. The loss tangent is a linear function of the frequency in the microwave range, and the film grown on the MgO substrate has a lower loss tangent than that grown on the LAO substrate. This work reveals the great potential of Ba_0.6Sr_0.4TiO₃ (BST) films for application in tunable microwave devices.     

Effect of substrates on epitaxial PZT films by a coating photolysis process

Preparation of Pb(Zr,Ti)O₃ (PZT) films on single crystalline STO(0 0 1), LAO(0 0 1) and MgO(0 0 1) substrates was investigated by a coating photolysis process using excimer laser. The effects of the substrate on the product films were examined by FT-IR, UV, XRD (theta–2theta, pole-figure analysis). In the case of using STO and LAO substrates, c-axis oriented films were successfully obtained by an ArF laser irradiation without heat treatment. Crystallinity of the PZT films prepared by a coating photolysis was found to strongly depend on the substrate used compared to conventional thermal process. Using XRD pole-figure analysis for the PZT films on STO substrates, it was found that the films were highly in-plane aligned. The formation mechanisms by a coating photolysis process are also discussed by a photothermal reaction due to both substrate materials and MO starting materials.     

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.     

Oxygen Stoichiometry Effect on Polar Properties of LaAlO3/SrTiO3

Discovery of a ferroelectric‐like behavior of the LaAlO₃/SrTiO₃ (LAO/STO) interfaces provides an attractive platform for the development of nanoelectronic devices with functionality that can be tuned by electrical or mechanical means. However, further progress in this direction critically depends on deeper understanding of the physicochemical mechanism of this phenomenon. In this report, this problem by testing the electronic properties of the LAO/STO heterostructures with oxygen stoichiometry used as a variable is addressed. Local probe measurements in conjunction with interface electrical characterization allow to establish the field‐driven reversible migration of oxygen vacancies as the origin of the ferroelectric‐like behavior in LAO/STO. In addition, it is shown that oxygen deficiency gives rise to the formation of micrometer‐long atomically sharp boundaries with robust piezoelectricity stemming from a significant strain gradient across the boundary region. These boundaries are not ferroelectric but they can modulate the local electronic characteristics at the interface. The obtained results open a possibility to design and engineer electromechanical functionality in a wide variety of nominally nonpolar and non‐piezoelectric complex oxide heterostructures and thin films.     

Low-Dielectric-Loss Barium Strontium Titanate Thin Films with MgO Buffer Layer for Tunable Microwave Devices

The dielectric and microwave properties of Ba_0.6Sr_0.4TiO₃ (BST60) thin films with a MgO buffer layer deposited on Al₂O₃ substrates were investigated. Insertion of the MgO buffer layer is demonstrated to be an effective approach to fabricate low-dielectric-loss BST thin films. x-Ray pattern analysis indicates that the thin films exhibit good crystalline quality with a pure perovskite phase and that insertion of the MgO buffer layer does not change the crystal structure of BST. The nonlinear dielectric properties of the BST films were measured by using an interdigital capacitor (IDC). At room temperature, the tunability of the BST films with a MgO buffer layer was 24.1% at a frequency of 1 MHz with an applied electric field of 80 kV/cm. The dielectric loss of the BST thin films is only 0.005 to 0.007 in the frequency range from 20 Hz to 2 MHz, the same as for BST films prepared on single-crystal MgO substrates. The microwave dielectric properties of the BST thin films were also measured by a vector network analyzer from 50 MHz to 10 GHz.     

MgO缓冲层对Si衬底上制备Fe3Si薄膜性能的影响

采用磁控溅射方法和热加工工艺在n型Si衬底上溅射不同厚度的MgO层并制备Fe-Si薄膜层,退火后形成Fe3Si/MgO/Si多层膜结构.利用MgO缓冲层对退火时Si衬底扩散原子进行屏蔽,并分析MgO层对Fe3Si薄膜结构和电学性质的影响.通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)和四探针测试仪对Fe3Si薄膜的晶体结构、表面形貌、断面形貌和电阻率进行表征与分析.研究结果表明:当MgO层厚度为20 nm时生成Fe0.9Si0.1薄膜,当厚度为50,100,150和200 nm时都生成了Fe3Si薄膜,生成的Fe3Si和Fe0.9Si0.1薄膜以(110)和(211)取向为主.随MgO缓冲层厚度增加,Si衬底扩散原子对Fe3Si薄膜的影响减小,Fe3 Si薄膜的晶格常数逐渐减小,晶粒大小趋向均匀,平均电阻率呈现先增大后减小趋势.研究结果为后续基于Fe3 Si薄膜的器件设计与制备提供了参考.     

溶胶-凝胶法制备外延Ba1-xSrxTiO3薄膜及其结构与性能研究

应用溶胶-凝胶技术在Pt/MgO(100)衬底上成功地制备了Ba0.65Sr0.35TiO3外延薄膜.XRD和SEM分析结果表明该薄膜在O2气氛中650℃热处理1h后,其(001)面是沿着Pt(100)和MgO(100)面外延取向生长的;薄膜表面均匀致密,厚度为260nm,平均晶粒大小为48.5nm.当测试频率为10kHz时,BST薄膜的介电常数和损耗因子分别为480和0.02.介电常数-温度关系测试结果表明sol-gel工艺制备的Ba0.65Sr0.35TiO3薄膜其居里温度在35℃左右,且在该温度下Ba0.65Sr0.35TiO3薄膜存在扩散铁电相变特征.当外加偏置电压为3V时,BST薄膜的漏电流密度为1.5×10-7A/cm2.该薄膜可作为制备新型非制冷红外焦平面阵列和先进非制冷红外热像仪的优选材料.     

Sol-gel法制备SrTiO_3薄膜的电阻开关性能研究

采用sol-gel法制作了28nm厚的SrTiO3薄膜和Au/SrTiO3/LaNiO3/Si(100)三明治结构的器件,并研究其物理性能。结果显示:室温下,用直流电压可以使薄膜的电阻在高低阻态间进行转换。最大的电阻变化率约为10309。对I-V特性的分析,发现在高阻态时,有空间电荷限制电流机制(SCLC)和肖特基势垒导电机制存在。应用在高场区有非对称电子陷阱中心的空间电荷限制电流理论,解释了这种电阻开关现象。     

ZnO缓冲层和退火处理对MgO薄膜结构的影响

采用直流反应磁控溅射法在Si衬底上引入ZnO缓冲层制备了沿(200)晶面择优取向生长的MgO薄膜,然后分别采用快速退火和常规退火两种不同的方式对MgO薄膜进行晶化处理。利用X射线衍射仪(XRD)以及原子力显微镜(AFM)研究了ZnO缓冲层以及两种不同的退火方式对MgO薄膜的结构和形貌的影响。结果表明:具有合适厚度的ZnO缓冲层可以显著地提高MgO薄膜的结晶质量。另外,与快速退火相比,常规退火处理后得到的MgO晶粒均匀圆润,有着较大的(200)衍射峰强度以及较小的表面粗糙度。