Pulsed-Laser Deposition of Barium Titanate Thin Films

Barium titanate (BaTiO₃) thin films have been deposited on single-crystal magnesia (MgO) substrates by pulsed-laser ablation. Temperature dependence of capacitance measurements show a peak of 110°C, indicative that a ferroelectric phase transition has occurred at this temperature. This value is lower than that determined for single-crystal BaTiO₃, but consistent with that found for BaTiO₃ thin films produced by other methods. It has been demonstrated that the microstructure of the films can be varied by changes in the deposition parameters. Optimizing these variations permits the formation of thin films with controlled microstructures and properties.     

Morphological study of thin films: Simulation and experimental insights using horizontal visibility graph

We studied the morphological nature of various thin films such as silicon carbide (SiC), diamond (C), germanium (Ge), and gallium nitride (GaN) on silicon substrate Si(100) using the pulsed laser deposition (PLD) method and Monte Carlo simulation. We, for the first time, systematically employed the visibility algorithm graph to meticulously study the morphological features of various PLD grown thin films. These thin-film morphologies are investigated using random distribution, Gaussian distribution, patterned heights, etc. The nature of the interfacial height of individual surfaces is examined by a horizontal visibility graph (HVG). It demonstrates that the continuous interfacial height of the silicon carbide, diamond, germanium, and gallium nitride films are attributed to random distribution and Gaussian distribution in thin films. However, discrete peaks are obtained in the brush and step-like morphology of germanium thin films. Further, we have experimentally verified the morphological nature of simulated silicon carbide, diamond, germanium, and gallium nitride thin films were grown on Si(100) substrate by pulsed laser deposition (PLD) at elevated temperature. Various characterization techniques have been used to study the morphological, and electrical properties which confirmed the different nature of the deposited films on the Silicon substrate. Decent hysteresis behavior has been confirmed by current-voltage (IV) measurement in all the four deposited films. The highest current has been measured for GaN at ～60 nA and the lowest current in SiC at ～30 nA level which is quite low comparing with the expected signal level (μA). The HVG technique is suitable to understand surface features of thin films which are substantially advantageous for the energy devices, detectors, optoelectronic devices operating at high temperatures.     

Use of Thin-Film Substrates to Study Enhanced Solid-State Phase Transformations

A thin-film substrate geometry is described for the study of enhanced solid-state phase transformations. A thin film of the seed material is grown on a suitable bulk substrate forming the thin-film substrate. A sol of the material for which seeding is to be studied is then deposited and the sample heated. Cross sections are prepared to study both the extent of the transformation and its crystallography, using electron microscopy. The special feature of this approach is that the position of the original seed/coating interface is known precisely and the thickness of the transformed layer can be measured directly at different stages of the transformation. As an example of this approach, thin films of hematite have been used as substrates for the study of the seeded phase transformation of a boehmite-derived transition-alumina to α-Al₂O₃     

Influence of substrate material and ion bombardment on plasma-deposited fluorocarbon thin films

The influence of substrate material and ion bombardment on fluorocarbon thin films deposited using a C₂F₆ glow discharge in an rf, parallel plate reactor was investigated. Monitoring of the plasma process by optical emission spectroscopy indicated that the dominant species in the glow discharge was CF₂. Studies of bulk polytetrafluoroethylene (PTFE) and plasma-polymerized fluorocarbon thin-film samples in an XPS system demonstrated that the formation of non-CF₂ species can be induced by ion bombardment of CF₂ molecules. Characterization of the deposited fluorocarbon films by XPS found that the F/C ratio and CF_x distribution (0 < x < 3) in the films were dependent on processing conditions. Fluorocarbon films deposited simultaneously onto Al, glass, steel, and PTFE substrates using a C₂F₆ plasma and a graphite sputter target had measurably different F/C ratios, with the F/C ratio of the films deposited onto the Al substrates consistently lower than the F/C ratios of the films deposited onto the other substrates. When a C₂F₆ plasma was used without a graphite target, the F/C ratio in the film was constant, but the CF_x distribution was different for each of the substrate materials. Analysis of the plasma-polymerized films by TEM revealed that localized growth of fluorocarbon particles occurred during the initial stages of deposition, consistent with an activated growth mechanism. Differences in the F/C ratio for films deposited onto the various substrate materials were attributed to the interaction of the fluorocarbon plasma with the exposed surface of the substrate prior to complete coverage by the polymeric film. © 1994 John Wiley & Sons, Inc.     

在ITO玻璃衬底上制备锆钛酸铅铁电薄膜

利用射频反应性溅射沉积技术在掺的Ｓｎ的Ｉｎ２Ｏ３导电透明膜衬底上制备了钙钛矿型Ｐｂ（Ｚｒ,Ｔｉ）Ｏ３（ＰＺＴ）铁电薄膜。研究了沉积参量与热处理工艺对铁电薄膜结构和性能的影响。运用Ｘ射线衍射、Ｘ射线光电子能谱和扫描电镜等技术,分析了薄膜的晶体结构、表面形貌和表面元素化学状态。测量了不同处理条件下薄膜的铁电性能。结果表明：在掺Ｓｎ的Ｉｎ２Ｏ３导电透明膜衬底上可以得到表面无裂纹,化学计量比符合要求的ＰＺ     

Microstructure of LaNiO3 thin films obtained by the spin-on technique from citrate precursors

The morphology of perovskite LaNiO₃ (LNO) thin films is a very important feature considering the fact that they could be used as an electrode material in ferroelectric devices. In this work, LNO films were prepared from citrate precursors. The films were deposited on Si (100) and Pt covered Si substrates [Pt (111)/Ti/SiO₂/Si] using the spin-on technique. The phase composition of the films was confirmed by X-ray powder diffraction analysis, while the microstructures were investigated by atomic force microscopy. The influence of the metal ion:citric acid:ethylene glycol ratio on the morphology of the films was investigated. After optimization of these parameters, very homogenous, uniform and crack-free LNO films were obtained.     

Ferroelectric and structural instability of (Pb,Ca)TiO3 thin films prepared in an oxygen atmosphere and deposited on LSCO thin films which act as a buffer layer

Structural, microstructural and ferroelectric properties of Pb_0.90Ca_0.10TiO₃ (PCT10) thin films deposited using La_0.50Sr_0.50CoO₃ (LSCO) thin films which serve only as a buffer layer were compared with properties of the thin films grown using a platinum-coated silicon substrate. LSCO and PCT10 thin films were grown using the chemical solution deposition method and heat-treated in an oxygen atmosphere at 700 °C and 650 °C in a tube oven, respectively. X-ray diffraction (XRD) and Raman spectroscopy results showed that PCT10 thin films deposited directly on a platinum-coated silicon substrate exhibit a strong tetragonal character while thin films with the LSCO buffer layer displayed a smaller tetragonal character. Surface morphology observations by atomic force microscopy (AFM) revealed that PCT10 thin films with a LSCO buffer layer had a smoother surface and smaller grain size compared with thin films grown on a platinum-coated silicon substrate. Additionally, the capacitance versus voltage curves and hysteresis loop measurement indicated that the degree of polarization decreased for PCT10 thin films on a LSCO buffer layer compared with PCT10 thin films deposited directly on a platinum-coated silicon substrate. This phenomenon can be described as the smaller shift off-center of Ti atoms along the c-direction 〈001〉 inside the TiO₆ octahedron unit due to the reduction of lattice parameters. Remnant polarization (P_r) values are about 30 μC/cm² and 12 μC/cm² for PCT10/Pt and PCT10/LSCO thin films, respectively. Results showed that the LSCO buffer layer strongly influenced the structural, microstructural and ferroelectric properties of PCT10 thin films.     

Ferroelectric and Dielectric Properties of Bilayered PMN–PT/BNdT Thin Films

Bilayered thin films consisting of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ and (Bi_3.15Nb_0.85)Ti₃O₁₂ (PMN–PT/BNdT) layers have been successfully deposited on Pt/Ti/SiO₂/Si substrate by RF sputtering. Their ferroelectric and dielectric behaviors can be tailored by varying the thicknesses of the two constituent ferroelectric layers. An enhancement in both remanent polarization and fatigue resistance is observed by increasing the layer thickness of BNdT, which also leads to an increase in coercive field. The bilayered ferroelectric thin films demonstrate electrical behaviors in association with space charge at low frequencies, which can account for the observed ferroelectric and fatigue properties, as confirmed by frequency and impedance studies.     

Microstructure and Electrical Properties of MgAl2O4 Thin Films for Humidity Sensing

Active elements for humidity sensors based upon MgAl₂O₄ thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO₂ substrates by radiofrequency (rf) sputtering. Sintered MgAl₂O₄ pellets were prepared by traditional ceramic processing. Scanning electron microscopy (SEM) analysis showed that the thin films were rather dense and homogeneous, made up of clustered particles of about 20–30 nm, while the pellets showed a wide pore-size distribution. X-ray photoelectron spectroscopy (XPS) demonstrated that the thin films have a stoichiometry close to that of MgAl₂O₄. Sintered MgAl₂O₄ is crystalline, while it is disordered in thin-film form. The presence of two different components of the Al 2 p peaks was correlated with the structural difference between pellets and thin films. The relationship between good film–substrate adhesive properties and the chemical composition at the interface was studied. The electrical properties of the sensing elements were studied at 40°C in environments at different relative humidity (RH) values between 2% and 95%, using ac impedance spectroscopy. MgAl₂O₄ thin films showed interesting characteristics in terms of their use in humidity-measurement devices. Resistance versus RH sensitivity values showed variations as high as 4 orders of magnitude in the RH range tested for thin films, and 5 orders of magnitude for pellets. The differences in the electrical behavior of MgAl₂O₄ pellets and thin films were correlated with their different microstructures.     

Aerosol deposition of dense lead zirconate titanate thin films at room temperature

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) films were grown on silicon 1 0 0 substrate by aerosol deposition, using solid-state reacted powder containing donor oxide Nb₂O₅, while the substrate was maintained at room temperature. The PZT films were simultaneously sintered upon deposition on a highly densified ceramic layer. Crystalline phases of the deposited films have been determined by X-ray diffractometry (XRD), and microstructures analysed by transmission electron microscopy (TEM). The cross-section microstructure consisted of several thin layers, including the PZT film and the platinum electrode and titanium-buffered layers on the substrate. High-resolution images revealed that the PZT layer contained a mixture of randomly oriented grains of nanometre size, which were embedded in an amorphous matrix. In contrast to the conventional liquid-phase sintering mechanism, sintering of the PZT films involved amorphised phases generated by pressure-induced amorphisation (PIA) from plastic deformation when the initial powder particles collided amongst one another upon reaching the silicon substrate during aerosol deposition. An analogy may be drawn to the impact of extraterrestrial meteorites in which diaplectic glass, i.e., amorphised phase, was formed and retained metastably at room temperature. The individual PZT grains were joined with the amorphised phase(s) and sintered to become a dense, thin film on the silicon substrate.     

Pulsed laser deposition of Sm modified PbTiO3 ferroelectric thin films

Sm modified PbTiO³ thin films have been prepared by pulsed laser deposition on Pt/TiO₂/SiO₂/(100)Si substrates. It has been found that the Sm concentration of the films remains close its concentration in the target, however, a Pb loss exists during the deposition process. To compensate for the Pb loss we used Pb rich targets and an oxygen pressure of 0.1 mbar. Films deposited at 530°C are crystalline and preferentially oriented with the [100] film direction perpendicular to the substrate surface. In comparison to bulk ceramics, the films have a tetragonal distortion lower than that expected from their Sm concentration. This is likely due to the influence of the substrate. The films prepared are ferroelectric with aP_r = 3.2 μC/cm².     

Nanocolumnar Preferentially Oriented PSZT Thin Films Deposited on Thermally Grown Silicon Dioxide

We report the first instance of deposition of preferentially oriented, nanocrystalline, and nanocolumnar strontium-doped lead zirconate titanate (PSZT) ferroelectric thin films directly on thermal silicon dioxide. No intermediate seed or activation layers were used between PSZT and silicon dioxide. The deposited thin films have been characterised using a combination of diffraction and microscopy techniques.     

Properties of Compositionally Graded BiScO3–PbTiO3 Thin Films Fabricated by a Sol–Gel Process

The compositionally graded BiScO₃–PbTiO₃ (BSPT) thin films were fabricated on Pt/Ti/SiO₂/Si by a sol–gel method. For the up-graded thin film, the PbTiO₃ content increased from the film–substrate interface to the surface of the film, while the down-grade thin film showed the opposite trend. The graded thin films exhibited single-phase structures and dense microstructures. The dielectric and ferroelectric properties of the thin films were investigated. The results showed that the compositionally graded BSPT thin films had similar remanent polarization value but a higher dielectric constant, dielectric tunability, and piezoelectric coefficient d ₃₃ compared with the homogeneous thin film with a composition of 0.36BiScO₃–0.64PbTiO₃ at the morphotropic phase boundary.     

Carbon black thin films with tunable resistance and optical transparency

Layer-by-layer assembly was used to produce highly conductive thin films of carbon black and polymer. Positively and negatively-charged polyelectrolytes, polyethylenimine (PEI) and poly(acrylic acid) (PAA), were used to stabilize carbon black in aqueous mixtures that were then deposited onto a PET substrate. The effects of sonication and pH adjustment of deposition mixtures on the conductivity and transparency of deposited films was studied, along with drying temperature. Sonication and oven drying at 70 °C produced films with the lowest sheet resistance (∼1500 Ω/sq), which is a bulk resistivity below 0.2 Ω cm for a 14-bilayer film that is 1.3 μm thick. These two variables improve packing and connectivity amongst carbon black particles that results in increased electrical conductivity. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in transparent films due to increased polymer charge density. These pH-adjusted films have much higher sheet resistance values than their non-adjusted counterparts due to their reduced thickness and patchy deposition. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Carbon black-filled thin films able to achieve these levels of resistivity and transparency may find application in a variety of optoelectronic applications.     

ITO薄膜射频磁控溅射法制备及性能研究

以10%SnO2和90%In2O3(以质量计)烧结成的ITO氧化物陶瓷为靶材,采用射频磁控溅射法在玻璃基片成功地制备出光电性能优异的ITO透明导电薄膜。研究了基片温度和氧分压溅射工艺参数对ITO薄膜的结构和光电性能的影响。实验结果表明,采用氧化铟锡陶瓷靶射频磁控溅射制备的ITO薄膜沿(222)晶面生长,薄膜紫外透射光谱的吸收截止边带随着衬底温度和氧分压的升高向短波长方向漂移。     

Measurements of the surface resistance and conductivity of thin conductive films at frequency about 1 GHz employing dielectric resonator technique

A dielectric resonator technique has been developed for measurements of conductivity and surface resistance of thin metal films deposited on a dielectric substrate. This technique allows for measurements of films having surface resistances that are smaller than 5 Ω without requiring the need to perform measurements of the substrate thickness. The uncertainty of the surface resistance measurements is about 2–3% for both thin films and bulk materials. The accuracy of the conductivity measurements of the thin films is similar to the accuracy of the measurements of their thickness. Several samples have been measured having thicknesses that range from 66 nm to 50 μm.     

Textured ferroelectric SbNbO4 thin films deposited by ion-beam sputtering

In this letter, we report on the first synthesis of oriented SbNbO₄ ferroelectric thin films on Pt coated silicon substrates. Textured SbNbO₄ thin films are formed by rapid thermal annealing of films deposited by Ar⁺ ion-beam sputtering at room temperature. The films are characterized by X-ray diffraction spectra. Ferroelectric P-E loops are measured and dielectric properties are studied at low frequency. The effect of Pt electrodes on the formation of ferroelectric SbNbO₄ thin films is discussed.     

A New Method to Evaluate Thin Film Adhesion

This paper discusses a new method of evaluating thin film adhesion both qualitatively and quantitatively via a combination of peeling and image processing techniques. The adhesion of thin film on the entire substrate can be quickly evaluated and quantified to a continuous response variable which is superior to a discrete response variable as described in the ASTM D3359-78 publication. Feasibility of this technique has been demonstrated through a gauge capability study which resulted in 2.7% P/T (precision to tolerance) ratio at six sigma standard deviation for a tolerance of 100. Experimental results using the proposed method to evaluate the process/property relationship of aluminum films as deposited onto various dielectric substrates such as polyimide, silicon dioxide, and silicon nitride have been obtained and have been shown to agree with conventional stud pull test results. The estimated cycle time to evaluate thin film adhesion is five minutes per 4-inch size wafer once the sample is prepared. This short process cycle time and proven reliability show that there is merit in implementing this technique both in the laboratory for process development and in the factory for statistical process control of products.     

Metalorganic chemical vapor deposition of ferroelectric PbTiO3 thin films on amorphous substrate

PbTiO₃, thin films have been grown on amorphous glass substrate by metalorganic chemical vapor deposition. The as-deposited films were investigated using x-ray diffraction and scanning electron microscopy techniques. PbTiO₃, thin films fabricated were polycrystalline with highly c-axis-oriented textures. The films were dense-packed and showed uniformly distributed fine grain size. Growth mechanism and domain structure of the ferroelectric thin films on amorphous substrate were also studied.     

Effects of Fabrication Conditions on the Crystallinity,Barium Deficiency,and Conductivity of BaZr0.8Y0.2O3–δ Films Grown by Pulsed Laser Deposition

Yttrium‐doped barium zirconate (BZY) thin films were deposited on MgO and sapphire substrates using a pulsed‐laser deposition (PLD) method with varying deposition rates. The films deposited with a low deposition rate exhibited highly oriented microstructures with little grain boundaries. The electrical conductivities of these films were higher than those of the films, deposited with high deposition rates, which showed little‐oriented polycrystalline microstructure. While the films deposited on the MgO substrates had a stoichiometric composition, those deposited on the sapphire substrates had a high barium deficiency, which was possibly due to the differences in the crystal structure and large lattice mismatch between the sapphire substrate and the BZY film. The electrical conductivity of the highly oriented BZY film, grown on MgO substrate with a low deposition rate, showed little barium deficiency and the highest conductivity value that is higher than the typical conductivity of sintered pellets.