Excimer laser deposition and characteristics of tin oxide thin films

ArF excimer laser assisted chemical vapor deposition of tin oxide thin films on Si was obtained using SnCl₄ and O₂ as precursors. Experimental measurements revealed that the deposition rate increases with incident laser energy density. The composition, structure and ultraviolet-to-visible spectra of the thin films were investigated by means of XPS, SEM, XRD and a UV–Vis techniques. It was shown that SnO₂ and SnOCl₂ coexisted in the thin films, and SnOCl₂ was almost completely converted into SnO₂ after annealing. The SnO₂ thin films deposited at room temperature were amorphous in structure and the grain size of the films became larger after annealing. The transmittance of the SnO₂ thin films is above 90%, the absorption edge is 355 nm and the energy gap is 3.49 eV.     

铁电极化诱导的PbTiO3薄膜的取向聚集生长和晶粒尺寸调控

用溶胶凝胶法制备了PbTiO₃薄膜。将含量为0.2%、0.5%和0.8%(摩尔比)的钙钛矿铁电PbTiO₃纳米片加入溶胶体系中,利用纳米片的自发极化调控薄膜的生长。结果表明,纳米片的加入显著影响了薄膜的生长过程和结晶学取向,可制备出(100)高度取向的PbTiO₃薄膜;改变纳米片的浓度,可将薄膜晶粒尺寸由100 nm调控到2 μm。扫描电子显微镜(SEM)、透射电子显微镜(TEM)观测和原位X射线衍射(in-situ XRD)的结果表明,固态薄膜中的晶粒表现出类液相的取向聚集生长特征。其原因可能是,铁电纳米片极化表面的静电力诱导小晶粒的吸附和取向排列,调控了薄膜的(100)取向和晶粒尺寸。     

Grain Refining and Decoupling in FePt/SiO2 Nanogranular Films for Magnetic Recording

FePt/SiO₂ nanogranular thin films have been prepared by molecular-beam epitaxy system on MgO (001) substrates with the method of insertion dual SiO₂ layers into Fe/Pt multilayer films. We report the relationships between the inserting thickness of SiO₂ layers and the microstructural and magnetic properties of FePt thin films. It indicated the nanogranular FePt thin films were successfully formed by inserting amorphous SiO₂ layers into the Fe/Pt films. The reduction of grain/domain size and isolation of FePt particles can be achieved by such insertion and maintain (001) texture. The average grain size of FePt films with 5-nm SiO₂ insert layers is estimated to be around 8 nm, while domain rotation is enhanced depicting a decoupling of intergrain interaction. The isolated grains are less magnetically coupled in the rotation mode and the reversal of magnetization is more independent     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Structure and electrical properties of boron-added (Ba,Sr)TiO3 thin films fabricated by the sol-gel method

Thin films of Ba_xSr_1−xTiO₃ (BST, with x=0.5) were fabricated on a RuO₂/Ru/SiO₂/Si substrate by the spin coating of the multicomponent sol prepared using metal alkoxides. Boron alkoxide was intentionally introduced to establish a better microstructure and to reduce the leakage current. AFM indicated that a crack-free uniform microstructure having a smooth surface was gradually developed with increasing boron content. The relative dielectric permittivity of the 250-nm thick BST thin films fired at 700°C decreased with increasing content of boron, from 420 for the undoped film to 190 for the 10 mol% boron-added film at 1 MHz. This observation was interpreted in terms of a serial capacitance composed of the perovskite BST grain and the interfacial B₂O₃ glassy phase having a low dielectric permittivity. The leakage current density (J) also decreased with the amount of boron added. The leakage current for the applied voltage greater than 1 V showed a linear variation of logJ with E^1/2 at room temperature, suggesting that the interface-controlled Schottky emission was the dominant conduction process for the BST thin films fabricated on the RuO₂ electrode.     

溶胶－凝胶工艺参数对（Pb，La）TiO_3薄膜结构的影响

系统地研究了溶胶－凝胶（Ｓｏｌ－Ｇｅｌ）方法制备（Ｐｂ_（１－Ｘ）Ｌａ_ｘ）Ｔｉ_（１－ｘ／４）Ｏ_３（简称ＰＬＴ）薄膜时催化剂（或ｐＨ值）、溶液浓度在室温下对形成溶胶和凝胶的影响规律，用Ｘ射线结构分析和ＳＥＭ研究了热处理工艺对薄膜结构及晶粒尺寸的影响。实验表明，浓度、醋酸含量都存在一个最佳的范围，且随铜（Ｌａ）含量的增加，该范围减小；实验还发现，随着Ｌａ含量的增加，薄膜的晶化温度降低。在单晶（１００）Ｓｉ衬底上成功地制备出了具有钙钛矿型结构、厚度约为２００ｎｍ、均匀、致密、无裂纹的ＰＬＴ晶态薄膜。     

Elasticity and resistivity study on the electromigration effects observed in aluminum–silicon–copper alloy thin films

The early electromigration (EM) processes in the Al–Si(Cu) thin films several tens of nanometers thick deposited on Si reed substrates were investigated by means of the simultaneous anelasticity and electrical resistivity measurements below 360 K. The grain growth, the shortening of a and the probable lengthening of a take place during the EM tests at the current density of 10⁸ A/m², where a and a denote the atomic plane spacing normal to and the one parallel to the film surface, respectively. The activation energy, E_GB, for the grain growth is found to be as low as 0.32 eV, possibly suggesting that E_GB in very thin nanometer-thick films is much lower than that found in thin micrometer-thick films. The increase in the Young’s modulus of the Al–Si(Cu) thin films takes place during the EM tests, suggesting that the grain growth is responsible for it. The decrease in Q⁻¹ observed at 330 and 360 K may be explained by a decrease in the grain boundary regions too. The increase in Q⁻¹ found during the EM tests at 300 K is possibly associated with an increase in a certain anelastic process in the grain boundary regions.     

Crystallization by excimer laser annealing for a-Si:H films with low hydrogen content prepared by Cat-CVD

Crystallization by excimer-laser annealing (ELA) for hydrogenated amorphous silicon (a-Si:H) films with low hydrogen content (C_H) prepared by catalytic chemical vapor deposition (Cat-CVD) was systematically studied. From optical microscopy images, no hydrogen bubbling was observed during ELA, even without a dehydrogenation process. As the laser energy density was increased to 300 mJ cm⁻², the full width at half-maximum of the Raman signal from the crystalline phase decreased to approximately 4 cm⁻¹. This value is almost equal to or even smaller than that reported for polycrystalline Si (poly-Si) films prepared from plasma-enhanced CVD (PECVD) a-Si:H films by ELA so far. The average grain size, estimated from scanning electron microscopy, was approximately 500 nm for C_H of 1.3 at.%. On the other hand, the grain size of poly-Si films prepared from PECVD a-Si:H films with a dehydrogenation process was only 200 nm. The technique using Cat-CVD films is expected to be used for fabrication of low-temperature high-mobility thin-film transistors.     

Structural and optical properties of pulsed laser deposited V2O5 thin films

Pulsed laser deposited nanocrystalline V₂O₅ thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and optical spectroscopy. The films were deposited on amorphous glass substrates, keeping the O₂ partial pressure at 13.33 Pa and the substrate temperature at 220 °C. The characteristics of the films were changed by varying the laser fluence and repetition rate. XRD revealed that films are nanocrystalline with an orthorhombic structure. XPS shows the sub-stoichiometry of the films, that generally relies on the fact that during the formation process of V₂O₅ films, lower valence oxides are also created. From the HRTEM images, we observed the size evolution and distribution characteristics of the clusters in the function of the laser fluence. From the spectral transmittance we determined the absorption edge using the Tauc plot. Calculation of the Bohr radius for V₂O₅ is also reported.     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

Tungsten–carbon films prepared by reactive sputtering from argon–benzene discharges

Tungsten–carbon thin films have been deposited by reactive (Ar+C₆H₆) DC magnetron sputtering onto various substrates. Deposition onto glass, monocrystalline silicon, tantalum and stainless steel at room temperature yielded W–C films, having XRD patterns corresponding to the structure of heavily disordered W₂C or WC_1−x carbides. The samples deposited upon the Au or Cu foils were nanocrystalline cubic WC_1−x with the grain size of 2.9 nm. Disordered tungsten–carbon films were stable up to 1200°C. Microhardness of the films with disordered W₂C phase was about 5–6 GPa while that of the films with disordered WC_1−x phase was about 17 GPa. The characteristics of films can be understood considering the effects of the incorporation of free carbon and/or carbon–hydrogen fragments into the tungsten carbide layer.     

Grain dependence of ferroelectric domain switching on SrBi2Ta2O9 thin films observed by Kelvin probe force microscope

We have studied grain-shape dependence of Kelvin probe force microscopy of SrBi₂Ta₂O₉ thin films on epitaxial La_0.5Sr_0.5CoO₃/LaAlO₃ substrates. By changing the growth condition in pulsed laser deposition, we have grown the SrBi₂Ta₂O₉ thin films with various grain shapes. The shape and the orientation of SrBi₂Ta₂O₉ the thin films with various growth conditions have been analyzed by X-ray diffraction and scanning electron microscope. The large number of the long rectangular grains was observed accompanied with relatively larger (220) peaks than other peaks. From the Kelvin probe force microscope study, it has been observed that the long rectangular grains showed characteristics of easy ferroelectric domain switching at a low writing bias and weaker influence of surface charges.     

Pulsed laser deposition of NiTi shape memory alloy thin films with optimum parameters

A series of experiments was carried out to optimize the pulsed laser deposition parameters for the fabrication of high quality NiTi shape memory alloy thin films. Smooth NiTi shape memory alloy thin films were deposited at high growth rate with optimum deposition parameters based on the analysis of the relationships among the morphology of the target surface and the deposited thin film, the laser energy, the target–substrate distance, the thin film composition and its growth rate. Crystal structures and phase transformation temperatures of the annealed Ni_49.7Ti_50.3 thin film were characterized by using X-ray diffraction and differential scanning calorimetry, respectively. The martensitic transformation temperature of the crystallized Ni_49.7Ti_50.3 thin film is found to be lower than room temperature and 27°C lower than that of the NiTi target material. These results are attributed to the refined grain size of the thin film and its composition, which deviates slightly from Ni₅₀Ti₅₀.     

Spray deposition of lanthanum selenide (La2Se3) thin films from non-aqueous medium and their characterizations

The spray pyrolysis technique was employed to prepare lanthanum selenide (La₂Se₃) thin films on ordinary glass and fluorine doped tin oxide (FTO) coated glass substrates under optimized conditions. The preparative parameters are optimized to get good quality of La₂Se₃ thin films. X-ray diffraction (XRD) study reveals that only cubic La₂Se₃ is formed with a grain size of about 42 nm. The direct optical band gap is estimated to be 2.6 eV. The dispersions of dielectric constant and dielectric loss are studied with the variation of frequency. The room temperature electrical resistivity of the films is found to be of the order of 10⁵ Ω cm. The film is found to be a p-type semiconductor.     

Synthesis and Characterization of(Na0.5K0.5)NbO3（NKN） Thin Films Formed by a Diol-based Sol-gel Process

Lead-free(Na_(0.5)K_(0.5))NbO_3(NKN) thin films were fabricated by spin coating on Pt/Ti/SiO2/Si substrates by a diol-based sol-gel process.Na-acetate,K-acetate,Nb-pentaethoxide and 1,3 propanediol were used to prepare the NKN precursor solution.Thermal analysis showed two characteristic temperatures of 360 and 600 ℃.Based on these temperatures,a heat treatment program with pyrolysis at 360 ℃ and calcination at 600 ℃ after every layer was used.To avoid inhomogeneities and secondary phases,an excess of sodium and potassium was necessary.To evaluate the proper excess amount of sodium and potassium secondary ion mass spectrometry(SIMS) lateral element maps and X-ray diffraction(XRD) patterns were recorded.An excess amount of 20% led to homogeneous distribution of the elements and to single phase perovskite NKN films with random crystal orientation.Scanning electron microscopy(SEM) images showed a pore free surface with 100 nm grains.The leakage current measurements showed a current of 1×10~(-3) A/cm~2 at 150 kV/cm.     

Structural and electrochemical properties of vanadium oxide thin films grown by d.c. and r.f. reactive sputtering at room temperature

Vanadium oxide thin films were grown at room temperature by direct current and radio-frequency reactive sputtering systems to compare the structural and electrochemical properties. Rutherford backscattering spectrometry and Fourier transform infrared measurements reveal that the composition of the as-deposited films consists of the V₂O₅ phase regardless of the deposition methods. Wide-angle X-ray diffraction measurements show that the crystallinity of the as-deposited V₂O₅ films is different depending on the deposition method. Films deposited by direct current reactive sputtering were amorphous, whereas films deposited by radio-frequency reactive sputtering were crystalline. Scanning electron microscopy measurements show that the V₂O₅ films grown by radio-frequency reactive sputtering had a large grain size but the films grown by direct current reactive sputtering were amorphous. Charge–discharge measurements taken at room temperature with a constant current clearly indicate that the films grown by direct current sputtering demonstrated typical amorphous behavior, whereas the V₂O₅ films grown by radio-frequency sputtering demonstrated the discharge behavior of crystalline V₂O₅. The origin of the structural and electrochemical properties of film grown by radio-frequency reactive sputtering is a self-bias effect. The self-bias effect induces ion bombardment during the growth of vanadium oxide thin film. These results suggest that direct current reactive sputtering is more desirable for growing amorphous V₂O₅ thin film than radio-frequency reactive sputtering.     

硅片上集成高介电调谐率的柱状纳米晶BaTiO3铁电薄膜

钛酸钡(BaTiO₃)具有优异的介电、铁电、压电和热释电等性能, 在微电子机械系统和集成电路领域具有广泛的应用。降低BaTiO₃薄膜的制备温度使其与现有的CMOS-Si工艺兼容, 已成为应用研究和技术开发中亟需解决的问题。本研究引入与BaTiO₃晶格常数相匹配的LaNiO₃作为缓冲层, 以调控其薄膜结晶取向, 在单晶Si(100)基底上450 ℃溅射制备了结构致密的柱状纳米晶BaTiO₃薄膜。研究表明：450 ℃溅射温度在保持连续柱状晶结构和(001)择优取向的前提下, 能获得相对较大的柱状晶粒(平均晶粒直径27 nm), 一定残余应变也有助于其获得了较好的铁电和介电性能。剩余极化强度和最大极化强度分别达到了7和43 μC·cm^-2。该薄膜具有良好的绝缘性, 在 0.8 MV·cm^-1电场下, 漏电流密度仅为10^-5 A·cm^-2。其相对介电常数ε_r展现了优异的频率稳定性：在1 kHz时ε_r为155, 当测试频率升至1 MHz, ε_r仅轻微降低至145。薄膜的介电损耗较小, 约为0.01~0.03 (1 kHz ~ 1 MHz)。通过电容-电压测试, 该薄膜材料展示出高达51%的介电调谐率, 品质因子亦达到17(@1 MHz)。本研究所获得的BaTiO₃薄膜在介电调谐器件中有着良好的应用前景。     

强磁场退火处理对La0.5Ca0.5MnO3薄膜晶粒尺寸演化和磁性能的影响

采用脉冲激光沉积法制备了La_0.5Ca_0.5MnO₃(LCMO)薄膜,然后在不同强磁场作用下进行原位后退火处理。利用XRD、FESEM和SQUID对薄膜进行微结构表征和磁特性测量。结果显示,强磁场退火使得薄膜的面外晶格参数拉长,晶粒尺寸明显增大,同时使低温磁化强度降低。通过建立强磁场下的晶粒生长速率方程对晶粒尺寸演化机理做了分析。分析认为,强磁场引入的额外驱动力降低了LCMO薄膜的临界晶粒尺寸,有利于晶粒生长。此外,本文通过建立一个基于相分离的反铁磁-铁磁核壳模型对薄膜的磁结构演化进行了探讨。认为晶粒尺寸增大导致铁磁相体积分数下降,从而导致低温磁化强度下降。     

Characterization of the surface of bio-ceramic thin films

The biocompatibility and corrosion resistance of orthopaedic and dental implants are determined by their material composition and surface microstructural properties such as surface roughness, grain size, etc. Thin films of bio-inert materials such as oxides of Ti, Al, Zr, and bio-active materials such as hydroxy-apatite (Ca₁₀(PO₄)₆(OH)₂), compounds of calcium and phosphorous oxides are more attractive as bio-ceramic films because of their biocompatibility being higher, and toxicity being lower than those of the other materials. In this study, we mainly focused on characterization of the surface of bio-ceramics using atomic force microscopy (AFM). These films having a thickness of about 500 nm, had been processed using ion-beam sputter deposition, and ion-beam-assisted sputter deposition methods. Investigation of the surface of the films by AFM shows that irradiation with oxygen ions in the energy range of 3 keV increases the surface roughness. A detailed study of the grain size and roughness of several experimental cases of TiO₂ thin films showed that the films contained columnar grains with mean size of about 100 × 100 nm² grown in the z direction with a height of a few nanometers.     

Microstructural evolution in lubricious ZnO films grown by pulsed laser deposition

Zinc oxide (ZnO) is well known to the electronic industry as a piezoelectric material. Recent research from this laboratory also indicates the potential of ZnO as a tribological material. The current work describes the evolution of microstructure with deposition parameters in pulsed laser deposited ZnO thin films, specifically targeted for friction and wear applications. Films were characterized by high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Friction and wear measurements were made using a ball-on-disk tribometer. Films were grown in vacuum (V) as well as in 5 mTorr of oxygen (O₂), while the substrates were kept at room temperature (RT). The RT/V ZnO films have (002) columnar texture with an average column width of 20 nm. The RT/O₂ films also are nanoclumnar with (002) texture, but each column is a mosaic of low-angle boundaries. Deformation mechanisms associated with nanocrystalline grain structure were analyzed with particular reference to sliding contact. Mechanisms to provide the observed low friction of RT/O₂ films (μ=0.15–0.20) have been activated by its mosaic structure.