Formation of ceramic thin films using electrospray in cone-jet mode

An electrostatic atomization technique has been developed to generate ultrafine spray droplets of ZrO₂ and SiC ceramic suspensions in a range of a few micrometers with a narrow size distribution. The aim of this paper is to deposit uniform thin films (from a few micrometers to a few tens of micrometers) of these ceramic materials on alloy substrates. Compared to some other thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma spray (PS), etc., the thin-film deposition process using electrostatic atomization is not only cheap but also capable of depositing a very thin multilayer with abrupt interfaces. CVD and PVD are expensive techniques. They require either a high vacuum, even an ultrahigh vacuum environment or complex gas handling system. Their deposition rate is also low. PS is normally used to grow thermal barrier coatings which usually have a thickness of a few tens to a few hundreds micrometers. Its application is limited by the quality of the coatings (high porosity, coarse and nonuniform microstructure). Preliminary results in this work have shown that, for low through-put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution, which is crucial to produce uniform thin films. It was found that the size of ceramic particles in ZrO₂ and SiC thin films is less than 10 μm. Microstructures of these thin films show very homogenous morphologies. These results indicate that ceramic thin films with high homogeneity can be deposited using electrostatic atomization. It was also observed that the morphology of the underlayer has some influence on the morphology of the top layer     

Novel patterning of composite thick film PZT

There is a clear need for thick PZT films (10–100 μm) in micro-electromechanical systems (MEMS). Some applications, like high frequency transducers operating in the thickness mode, require frequencies in the MHz region and thus thicker films, which in addition will provide more power. Thicker films are also important in actuator systems and sensors as it will generate more force and voltage, respectively. Integration of complex structures of thick films in thick films in MEMS is challenging. The use of normal thin film patterning techniques is difficult for thick films due to the amount of material that has to be removed and the isotropic nature of wet etching. A new patterning technique suitable for composite thick films using an epoxy mould is presented. By filling a micro mould of SU-8 photoresist with PZT paste details down to 20 μm with vertical feature walls could be patterned in a 15 μm thick film.     

Monolayer-Mediated Patterning of Integrated Electroceramics

Integrated electroceramic thin-film devices on semiconducting or insulating substrate materials offer a wide variety of attractive attributes, including high capacitance density, nonvolatile memory, sensor/actuator ability, and other unique electrical, electromechanical, magnetic and optical functions. Thus the ability to pattern such electroceramic thin films is a critical technology for future device realization. Patterned oxide thin-film devices are typically formed by uniform film deposition followed by somewhat complicated post-deposition ion-beam or chemical etching in a controlled environment i.e., a subtractive method. We review here an upset technology, a different way of patterning, by an additive approach, which allows for the selective deposition of electroceramic thin layers without such post-deposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers to modify the adhesion of subsequently deposited solution-derived electroceramics. The selective functionalization is achieved through microcontact printing (-CP) of self-assembled monolayers of the chemical octadecyltrichlorosilane on substrates of current technical interest. Subsequent sol-gel deposition of ceramic oxides on these functionalized substrates, followed by lift-off from the monolayer, yields high quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micron-scale dielectric oxide devices have been fabricated by this method, with lateral resolution as fine as 0.5 m. In this paper, we review the monolayer patterning and electrical behavior of several patterned electroceramic thin films, including Pb(Zr,Ti)O₃ [PZT], LiNbO₃, and Ta₂O₅. A multilevel example is also given which combines selective MOCVD deposition of metal electrodes and sol-gel patterned PZT for Pt//PZT//Pt//Si(100) ferroelectric memory cells.     

Formation of ceramic thin films using electrospray in cone-jet mode

The electrospray technique has been developed to generate fine droplets of SiC and ZrO₂ ceramic suspensions and to deposit these ceramic thin films and their bilayer on alloy substrates. SEM examinations of the microstructures of these thin films show that the films are very homogenous with a uniform particle size less than 10 μm. The deposition of a very thin bilayer with an abrupt interface indicates that the electrospray process can be well controlled. The theoretical prediction of droplet size and electric current is in good agreement with experimental results, indicating that fine suspension droplets can be generated in the cone-jet mode. Therefore it can be concluded that electrospray is a promising technique for the preparation and controllable distribution of uniform ceramic thin films and coatings with the added advantage of low cost. It could find a wide range of industrial applications in the future     

Substrate Surface Engineering for Functional Ceramic Thin Film Growth

A concept is introduced, using oxide substrates for functional ceramic thin film deposition beyond their usual application as chemical inert, lattice-matched support for the films. The substrates are applied as a functional element in order to controllably modify the atom arrangement and the growth mode of cuprate superconductors and colossal magnetoresistance materials. These materials have been chosen as prototypes of the general class of perovskite functional ceramics. One example studied is the use of epitaxial strain to adjust the relative positions of cations and anions in the film and thus modify their physical properties. The other makes use of vicinal cut SrTiO₃ which enables the fabrication of regular nanoscale step and terrace structures. In YBa₂Cu₃O_{7 – x} thin films grown on vicinal cut SrTiO₃ single crystals a regular array of antiphase boundaries is generated causing an anisotropic enhancement of flux-line pinning. In the case of La-Ca-Mn-O thin films grown on vicinal cut substrates it could be demonstrated that magnetic in-plane anisotropy is achieved.     

Theory of size effects in ferroelectric ceramic thin films on metal substrates

The aim of this paper is to show how a Landau thermodynamic theory might be utilized to study size effects in ferroelectric thin films on metal substrates via reflectivity measurements that could be carried out with terahertz radiation, particularly in the far-infrared region. The approach taken is to minimize a Landau free energy functional that includes a gradient term to describe the size effects. Landau-Khalatnikov equations together with Maxwell’s equations for the electromagnetic field are then solved simultaneously to describe how the radiation interacts with the film. From this reflectivity curves can be calculated and related to experimental studies. Attention is paid to how the metal substrate can influence the reflectivity curves compared to free standing films without substrates. The significance of the work lies in the fact that ferroelectric ceramic thin films are becoming of increasing technological importance, and films on metal substrates such as electrodes are of obvious relevance to applications such as memory devices which rely on applied electric fields to change the polarization direction. The main conclusion is that terahertz wave measurements in the far-infrared provide an informative and sensitive probe of the size effects and substrate influence.     

Thin films of novel ferroelectric composites

Abstract

Composites of BSTO combined with other non electrically active oxides have demonstrated adjustable electronic properteis which can be tailored for use in various electronic devices.^[1,2] These novel composites of barium strontium titanate (BSTO) and oxide III compounds have already exhibited promising results in their ceramic form.^[3] The additive oxides modify the dielectric constant, tunability (change in the dielectric constant with applied voltage), and dielectric loss of the material. One application has been for use in phased array antennas and insertion has been accomplished into several working antenna systems.^[4] To further accommodate the frequencies required by these phased array antennas, thin films of the composites have been fabricated. Preliminary studies have indicated that thin films of such composites exhibit similar behavior as their bulk ceramic counterparts.^[5] The purpose of this study is to investigate the properties of the BSTO/oxide III based compounds in thin film form.     

Structural and electrochemical properties of Nichrome anode thin films for lithium battery

Low cost anode materials having a high electrochemical efficiency have been critical in the success of thin film batteries that are applicable in ubiquitous environments as a portable energy source. Nichrome thin films are ideally suited for use in hybrid assemblies but their applications include precision integrated circuits in fields of telecommunications, instrumentation, power supplies, military and medical equipment where low noise and good power dissipation are required. With such a wide spectrum of applications, it is important to understand the electric behavior of the Nichrome alloy thin films by their microstructure. In this work, nanocrystalline films of nickel chromium alloys were deposited on alumina substrate by radio frequency (RF) magnetron sputtering technology. High purity nickel and chromium sputtering target were used for the deposition. First, aluminum was deposited on ceramic substrate acts as a current collector and over that NiCr was deposited by RF sputtering method. Both the layers were analyzed for structural and electrical properties using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry. The XRD peak confirms that deposited NiCr and Aluminum have tetragonal and cubic structures, respectively. The crystallite size was determined by full width at half maximum of XRD peaks. Structure, composition and the properties of the film are the major focus of this paper. Composition ratio between nickel and chrome obtained by EDS is 1:1. Particle size and microstructure of the film have been studied by SEM and AFM. Electrochemical properties of the films were analyzed. Reaction mechanism for the insertion and excretion is reported. After Lithium insertion and extraction the effect on the surface and structure of the thin film has been studied. The composition of equilibrium phases of NiCr as useful as attracting anode for the thin film battery. Nichrome on aluminum thin films as an anode has been attracted because it provides practical advantages including low cost production and competitive electrical performance.     

Ferroelectric thin films for Smart Spatial Light Modulator applications

Abstract

System, device and material issues for the use of ferroelectric ceramic thin films in the realization of Smart Spatial Light Modulators are considered. Results show that ferroelectric thin films such as PLZT PBN, KTN, and SBN are particularly attractive.     

Fabrication and characterization of micropatterned barium titanate ceramics

A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO₃) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO₃ nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO₃ nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO₃ nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO₃ ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films.     

Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.     

Review: Deposition of Ceramic Thin Films at Low Temperatures from Aqueous Solutions

Many techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures (25–100°C) have been reported. This paper reviews non-electrochemical, non-hydrothermal, low-temperature aqueous deposition routes, with an emphasis on oxide materials for electronic applications. Originally used for sulfide and selenide thin films, such techniques have also been applied to oxides since the 1970's. Films of single oxides (e.g., transition metal oxides, In₂O₃, SiO₂, SnO₂) and multicomponent films (doped ZnO, Cd₂SnO₄, ZrTiO₄, ZrO₂-Y₂O₃, Li-Co-O spinel, ferrites, perovskites) have been produced. The maximum thicknesses of the films obtained have ranged from 100 to 1000 nm, and deposition rates have ranged from 2 to 20,000 nm/h. Compared to vapor-deposition techniques, liquid-deposition routes offer lower capital equipment costs, lower processing temperatures, and flexibility in the choice of substrates with respect to topography and thermal stability. Compared to sol-gel techniques, the routes reviewed here offer lower processing temperatures, lower shrinkage, and (being based on aqueous precursors) lower costs and the potential for reduced environmental impact. This review emphasizes the influence of solution chemistry and process design on the microstructures and growth rates of the films. The current understanding of the mechanisms of film formation is presented, and the advantages and limitations of these techniques are discussed.     

Investigation of the effects of milling ceramic targets on the optical and electrical properties of BST thin films deposited by RF sputtering

Abstract

The RF sputtering method was utilized to deposit thin films of Ba_1-xSr_xTiO₃ (BST). The targets utilized in these experiments were prepared from ceramic powders with different particle size. The goal of this work is to examine whether the particle size distribution of the target can affect the properties of the thin films fabricated by the sputtering method. The Atomic Force Microscope (AFM) was used to examine the grain size in the thin films. The composition of the thin films and the bulk materials were examined by Fourier Transform Infrared (FTIR) spectroscopy. The dielectric properties of the thin films were measured and compared to its bulk counterparts. It was found that on lattice matched electrodes of SrRuO₃ on LaAlO₃ substrates, the thin films deposited from ceramic targets manufactured from ball-milled powders had finer grain size than those deposited from targets made from unmilled powders. However, this phenomenon was not observed in the case of polycrystalline films deposited on platinized silicon wafers.     

Processing and Dielectric Properties of Sol-Gel Derived PMN-PT (68:32) Thin Films

PMN-PT thin films near MPB were prepared using sol-gel technique. A transparent solution of the ceramic was prepared by using lead acetate trihydrate, magnesium ethoxide, niobium ethoxide and titanium isopropoxide as precursors along with 2methoxyethanol as solvent and acetic acid as catalyst. Thin films of the ceramic were prepared on Pt/Si and on ITO coated glass substrates. X-ray diffraction (XRD) studies show the formation of perovskite phase of the films with less than (5%) pyrochlore phase. Scanning electron microscopy (SEM) study of the films on different substrates show well developed grains of sub-micron size. Dielectric constant measurement at different temperature was carried out. Room temperature value of dielectric constant and dielectric loss at 1 kHz of the ceramic thin films on ITO coated glass and Pt/Si substrates were found to be 500, 0.03 and 415, 0.01 respectively. Dielectric measurements for different thicknesses of the films have also been carried out. P-E loop and I-V studies of the films were also carried out.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

用于燃料电池的氧化锆薄膜制备方法进展

固体氧化物燃料电池(SOFC)具有高效率、低污染等优点,氧化钇稳定氧化锆(YSZ)是目前用于SOFC的最成功的电解质材料,为了减小高温运行带来的困难,应用中需将YSZ制成薄膜。综述了制备YSZ 薄膜的各种方法,其中包括化学气相沉积(CVD)、电化学气相沉积(EVD)、溶胶-凝胶法(Sol-gel)和喷雾热解法等化学方法;物理气相沉积技术(PVD)和喷涂技术等物理方法;以及电泳沉积法(EPD)、注浆成型法和离心浇铸法等陶瓷成型方法,介绍了近年来采用上述方法制备的YSZ膜的性能及其用于SOFC电池研究取得的实验结果,最后评述了这些方法各自的特点。     

Focused ion beam nanopatterning for optoelectronic device fabrication

Recent photonic device structures, including distributed Bragg reflectors (DBRs), one-dimensional (1-D) or two-dimensional (2-D) photonic crystals, and surface plasmon devices, often require nanoscale lithography techniques for their device fabrication. Focused ion beam (FIB) etching has been used as a nanolithographic tool for the creation of these nanostructures. We report the use of FIB etching as a lithographic tool that enables sub-100-nm resolution. The FIB patterning of nanoscale holes on an epitaxially grown GaAs layer is characterized. To eliminate redeposition of sputtered materials during FIB patterning, we have developed a process using a dielectric mask and subsequent dry etching. This approach creates patterns with vertical and smooth sidewalls. A thin titanium layer can be deposited on the dielectric layer to avoid surface charging effects during the FIB process. This FIB nanopatterning technique can be applied to fabricate optoelectronic devices, and we show examples of 1-D gratings in optical fibers for sensing applications, photonic crystal vertical cavity lasers, and photonic crystal defect lasers.     

Preparation and properties of sol-gel derived PZT thin films for decoupling capacitor applications

Abstract

The use of ceramic thin films as decoupling capacitors offers the possibility of capacitor integration within the integrated circuit (IC) package, and potentially, directly onto the IC itself. Since these configurations minimize series inductance, higher operational speeds are possible. In the present study we have investigated the dielectric and leakage characteristics of sol-gel PZT films. For compositions near the morphotropic phase boundary, dielectric constants of 1000, and loss tangents of about 0.02, were observed. The current-voltage behavior of the capacitors was characterized by a non-linear response, and significant asymmetry in both the leakage and breakdown characteristics as a function of bias sign was observed. Breakdown fields for PZT 53/47 thin films were typically ～800 kV/cm at 25°C. We have also studied the effects of La and Nb dopant additions and alternate firing strategies on film leakage characteristics. Donor doping at 2–5 mol% lowered leakage currents by a factor of 10³ For films prepared by a multilayering approach, firing each layer to crystallization resulted in leakage currents that were a factor of 10² lower than films prepared by the standard process.     

Advances in electronic ceramic materials in Japan

A survey is provided of Japanese research on ceramic materials for substrates, microwave dielectric ceramics, piezoelectric ceramics, semiconducting ceramics, and superconducting ceramics. Novel processing technologies are described, covering the use of amorphous materials, superfine powders, lamination, multilayer thin films, porous ceramics, and superlattices