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Ceramic Thin Films: Fabrication and Applications
Abstract
Ceramics are a distinct class ofmaterials whose properties range from extreme hardness to unique electrical behavior. New
methods of creating thin films of complex oxides and electronic ceramics allow the integration of these properties with semiconductor
technology and raise the possibility of a new range of electronic devices.
... 2017. Esquema de funcionamento básico de uma evaporadora térmica.FONTE: Autores.A espessura do filme depositado é inversamente proporcional à distância entre o filamento e a amostra, por outro lado, quanto mais distante a amostra do filamento, menor será o gradiente de espessura observado na amostra, uma vez que a parábola da frente do vapor de metal tende a ficar plano com a distância(HEAVENS, O. S., 1952;SAYER, M.;SREENIVAS, K., 1990). ...
... 2017. Esquema de funcionamento básico de uma evaporadora térmica.FONTE: Autores.A espessura do filme depositado é inversamente proporcional à distância entre o filamento e a amostra, por outro lado, quanto mais distante a amostra do filamento, menor será o gradiente de espessura observado na amostra, uma vez que a parábola da frente do vapor de metal tende a ficar plano com a distância(HEAVENS, O. S., 1952;SAYER, M.;SREENIVAS, K., 1990). ...
Existe um mercado promissor de deposição de filmes finos metálicos para aplicações de alta tecnologia no Brasil. Esse mercado não tem sido explorado pelos microempreendedores por falta de um estudo de viabilidade básico da construção de equipamentos que possam evaporar metais com qualidade e controle. Neste trabalho, foi feito um estudo de viabilidade da construção de uma evaporadora de metais que foi construída para uma primeira avaliação prática. Os resultados sugerem que com investimentos da ordem de R 15.000,00, é possível fabricar evaporadoras de filmes finos com qualidade industrial. Uma atenção especial deve ser dada ao circuito de vácuo para controle da qualidade do filme depositado. O mercado pode ser facilmente explorado no desenvolvimento e fabricação de placas de energia solar, deposição de camadas metálicas em vidros instalados em automóveis, antenas de satélites e até na fabricação de joias e bijuterias.
... The high-output voltage can be tune able by varying its film thickness using thinning process. Influence of back switching which is stronger in thin film than in bulk ceramic and will increases the tan-delta (loss factor) [3][4][5]. ...
... In the present work, the PLZT powder is prepared by ball milling technique, which enhances homogeneous mixing of PbO, La 2 O 3 , TiO 2 and ZrO 2 powder followed by calcination at 900 C for 4 h, to get required phase pure ultrathin desired PLZT composition powder. The concentrated suspension of PLZT is prepared using DI water as solvent, poly (vinyl alcohol) (PVA) binder, poly (propylene glycol) plasticizer and dispersant to achieve a well dispersed slurry [3,4]. The slurry is casted on a movable carrier sheet by means of tape casting facility which allows to form thickness controlled single layered consisting of a polymeric matrix filled with the ceramic powder [3], using doctor blade technique. ...
We have made an attempt to fabricate free standing warpage free PZT thick films of 100 µm thickness by tape casting method. The poly crystalline nature and nanoscale polarization switching of free standing thick film were confirmed using X-ray diffraction technique and piezo force microscopy, respectively. The piezoelectric coefficient (d33) of 100 µm free-standing Pb(Zr0.56Ti0.44)O3 [PZT] thick film was calculated using double beam laser interferometer and found to be 400 pm/V. From the results, it indicates that free-standing PZT thick films are suitable candidate for miniaturization of harvesting device by directly bonding them on microsystem components for microelectromechanical systems (MEMS) applications.
... In recent decades, oxide ceramics, such as SrTiO 3 (STO) and BaTiO 3 (BTO), have undergone tremendous development and are increasingly crucial in applications, such as solid oxide fuel cells [1,2], sensors [3,4], capacitors [5,6], actuators [7,8], and memristors [9,10]. Oxide ceramics can be fabricated via sintering or deposition processes [11][12][13][14]. When manufactured through sintering, oxide ceramics exhibit a polycrystalline microstructure, with their macroscopic properties heavily influenced by the synthesis conditions [15]. ...
Dopants can significantly affect the properties of oxide ceramics through their impact on the property-determined microstructure characteristics such as grain boundary segregation, space charge layer formation in the grain boundary vicinity, the resultant microstructure features like bimodality due to abnormal grain growth. To support rational oxide ceramics design, we propose a multiphysics-based and defect-chemistry-informed phase-field grain growth model to simulate the microstructure evolution of oxide ceramics. It fully respects the thermodynamics of charged point defects (oxygen vacancies and dopants) in the grain interior and boundaries and considers the competing kinetics of defect diffusion and grain boundary movement. The proposed phase-field model is implemented through the finite element method and benchmarked against well-known simplified bicrystal models, including the Mott-Schottky and Gouy-Chapman models. Various simulation results are presented to reveal the impacts of defect formation energy differences between the grain interior and the grain boundary core on the key microstructural aspects, including space charge layer formation, grain boundary potential, solute drag effect, resultant bimodal abnormal grain growth and also dopant cloud within the grain interior imprinted by the vanished grain boundaries during sintering. In particular, simulation results confirm that the solute drag effect alone can lead to bimodal grain size distribution, without any contribution from grain misorientation and other anisotropy. Interestingly, abnormal grain growth simulations demonstrate that grain boundary potentials can vary substantially: grain boundaries of larger grains tend to have lower potentials than those of smaller grains. Such heterogeneous grain boundary potential distribution may inspire a new material optimization strategy through microstructure design.
... It also has applications in waveguide lasers, enabling the transmission and manipulation of light for various optical applications. Because of its ability to stand against high temperatures, it is being used as a protection system for elevated temperature environments [22][23][24]. ...
... It possesses excellent properties such as high refractive index, large optical band gap, low optical loss and high transparency in the visible and near-infrared region, high resistivity, low thermal conductivity, high chemical inertness and high hardness (Ohtsu et al., 2005). Correspondingly, the films are broadly utilized as heat-resistant materials (Ohtsu et al., 2005), sensors (Sayer and Sreenivas, 1990), optical filters (Lowdermilk et al., 1980), fuel cells (Gottmann et al., 1998;Minh, 1993), ion conductors (Gottmann et al., 1998), high-reflectivity mirrors (Zhao et al., 2008), broadband interference filters, (Zhao et al., 2008) active electro-optical devices (Zhao et al., 2008)and so on. ...
Thin films of zirconium oxide were synthesized by magnetron sputtering process using Zr target. The effect of oxygen partial pressure variation at 22%, 50%, 71% and 82% values on deposited zirconium oxide thin films was studied. The crystallinity of nano-structured zirconium oxide thin films was determined by X-ray Diffraction (XRD) technique. The increase in oxygen partial pressure leads to increase in crystallinity of (111) m-phase giving maximum intensity at 71% oxygen partial pressure. Contact angle measuring system was used to determine the wettability properties of zirconium oxide thin films namely: contact angle and surface energy. The zirconium oxide thin films changes its behavior from hydrophilic to hydrophobic with increase in oxygen partial pressure. The transmission and band gap were investigated to examine the optical properties of deposited nano-structured zirconium oxide thin films
... Moreover, line width miniaturization and high integration are being explored in depth to improve technical competitiveness in the semiconductor industry, where processes such as chemical vapor deposition (CVD) and etching are absolutely necessary. Since most of these processes are performed under various plasmas and active gases at high process temperatures [5][6][7][8][9][10], there is a risk that the parts in the equipment are exposed to the risk of corrosion. ...
... In 2007, [2] etched PLD-grown 500 nm ZnO films using NH 4 Cl concentrations ranging from 1-15 wt%. In 2011, [3] wet-etched 150 nm ZnO films that were deposited by RF magnetron sputtering. More recently, in 2020, [14] etched 100 nm ZnO samples grown using plasma-enhanced atomic layer deposition (PEALD). ...
Zinc oxide (ZnO) is an attractive material for microscale and nanoscale devices. Its desirable semiconductor, piezoelectric and optical properties make it useful in applications ranging from microphones to missile warning systems to biometric sensors. This work introduces a demonstration of blending statistics and chemical etching of thin films to identify the dominant factors and interaction between factors, and develop statistically enhanced models on etch rate and selectivity of c-axis-oriented nanocrystalline ZnO thin films. Over other mineral acids, ammonium chloride (NH 4 Cl) solutions have commonly been used to wet etch microscale ZnO devices because of their controllable etch rate and near-linear behaviour. Etchant concentration and temperature were found to have a significant effect on etch rate. Moreover, this is the first demonstration that has identified multi-factor interactions between temperature and concentration, and between temperature and agitation. A linear model was developed relating etch rate and its variance against these significant factors and multi-factor interactions. An average selectivity of 73 : 1 was measured with none of the experimental factors having a significant effect on the selectivity. This statistical study captures the significant variance observed by other researchers. Furthermore, it enables statistically enhanced microfabrication processes for other materials.
... Much attention has been paid to perovskite-based oxides due to their promising superconducting, ferroelectric, ferromagnetic and optical properties. Ferroelectric BaTiO3 is one of the most important perovskite oxide materials in electronics owing to its various device applications (Cohen 1992;Sayer and Sreenivas 1990). An interesting feature of BaTiO3 is that its electrical properties can be effectively tuned by incorporation of dopants. ...
... Much attention has been paid to perovskite-based oxides due to their promising superconducting, ferroelectric, ferromagnetic and optical properties. Ferroelectric BaTiO3 is one of the most important perovskite oxide materials in electronics owing to its various device applications (Cohen 1992;Sayer and Sreenivas 1990). An interesting feature of BaTiO3 is that its electrical properties can be effectively tuned by incorporation of dopants. ...
Starting with the history of the fundamental science of the relation of structure to composition delineated completely by Goldschmidt, we use the perovskite structure to illustrate the enormous power of crystal chemistry-based intelligent synthesis in creating new materials. The general formula of perovskite-type oxides is ABO3. The classical ceramic solid-solid reaction, hydrothermal and sol-gel methods, commonly used for the synthesis of perovskite-type oxide, involve high reaction temperature and hence yield perovskite-type oxides with a low surface area due to their sintering. A method based on hydrothermal treatments is described for increasing the surface area of sintered ABO3-type perovskite oxides. In a perovskite solid solution, the Curie temperature can be tuned by varying the compositions of the end members. For example, for the Pb(Zr,Ti)O3 (PZT) binary system, the Curie temperature of the MPB composition can be considered as an average (386°C) of the Curie temperature of two end members (PbZrO3: 230°C, PbTiO3: 490°C). This chapter is concerned with piezoelectric perovskite materials and their properties. Perovskite compositions are the best known and the largest family of ferroelectric and piezoelectric materials. In this review, an attempt is made to review recent developments on lead-free piezo materials emphasizing their preparation, piezoelectric property relations, and consequent physical properties. Piezoelectric properties of the most promising lead-free compositions/families including titanates, alkaline niobates and bismuth perovskites and their solid solutions, along with perovskites such as KNN and BaTiO3 ferroelectrics are reviewed in detail. Piezoelectric perovskite type ceramics seem to be suitable for actuator and high power applications that are required a large piezoelectric constant, d33 and a high Curie temperature. By appropriate changes in composition one can modify the most * Corresponding Author address. et al. 206 significant electroceramic piezoelectrics (BaTiO3 and KNN) phase in industry, into metallic conductors, superconductors or the highest pressure phases in the earth. A brief coverage of the recent developments in the area of piezoelectric energy harvesting is also encompassed.
... | (2021) 11:7109 | https://doi.org/10.1038/s41598-021-86572-w www.nature.com/scientificreports/ of diversification and reinforcement of the interfacial configuration [11][12][13] . The oxide film fabrication basically requires high calcination temperature above 500 °C. ...
The hydrogel of biomolecule-assisted metal/organic complex has the superior ability to form a uniform, continuous, and densely integrated structure, which is necessary for fine thin film fabrication. As a representative of nature-originated polymers with abundant reactive side chains, we select the gelatin molecule as an element for weaving the metal cations. Here, we demonstrate the interaction between the metal cation and gelatin molecules, and associate it with coating quality. We investigate the rheological property of gelatin solutions interacting with metal cation from the view of cross-linking and denaturing of gelatin molecules. Also, we quantitatively compare the corresponding interactions by monitoring the absorbance spectrum of the cation. The coated porous structure is systematically investigated from the infiltration of gelatin-mediated Gd0.2Ce0.8O2−δ (GDC) precursor into Sm0.5Sr0.5CoO3−δ (SSC) porous scaffold. By applying the actively interacting gelatin–GDC system, we achieve a thin film of GDC on SSC with excellent uniformity. Compare to the discrete coating from the typical infiltration process, the optimized thin film coated structure shows enhanced performance and stability.
... Understanding the role of charged defects in ferroelectric lead zirconate titanate (Pb(Zr x Ti 1−x )O 3 ) (PZT) is a fundamental interest in view of its widespread applications in nonvolatile ferroelectric random access memories (NVFRAM), microelectromechanical systems (MEMS), power harvesting, domain walls electronics, etc [1][2][3][4][5]. It has been shown that exposure to charge defects like Pb and oxygen vacancies, strongly affects the intrinsic properties such as polarization, leakage current, fatigue and imprint of PZT [6,7]. ...
We report the formation and the role of defect dipoles in Fe doped Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial thin film grown on SRO/LSAT substrate by pulsed laser deposition. The observed enhancement of spontaneous polarization in Nb-doped PZT thin film is found to be due to easy orientation and mobility of domain walls. The presence of defect complexes in Fe doped PZT film is responsible for the voltage offset or asymmetric polarization versus electric field hysteresis loop. Topography and nanoscale polarization switching of pure and doped PZT films are investigated by piezo force microscopy. X-ray photoelectron spectroscopy (XPS) study is used to confirm the presence of defect dipoles in Fe-doped PZT thin film. Detailed analysis of the XPS spectra also revealed that the defect dipoles are only formed in the Fe doped system and is absent in Nb- modified PZT thin film.
... Ferroelectric materials are of technological importance mainly due to their wide range of applications in electronics and micromanipulation industries. [1][2][3][4][5][6][7] Many ferroelectric devices are designed by exploiting their pyroelectric and dielectric effects, such as pyroelectric detectors and piezoelectric sensors. [8][9][10][11] By using the hysteretic characteristics of ferroelectric materials, ferroelectric random access memory can be designed and manufactured. ...
The phase field approach has been widely used to study the domain structure of ferroelectric crystals in both two and three dimensions (2D and 3D), but in the 3D case, little has been done to address the frequency dependence of ferroelectric characteristics. In this work, we adopt the 3D time-dependent Ginzburg-Landau kinetic equation to calculate the evolution of local polarization vectors and the overall hysteresis loops of ferroelectric crystals under the frequencies from 0.4 kHz to 120 kHz, and then use the fast Fourier transform to analyze the frequency characteristics of the polarizations. It shows the phenomenon of multiple frequencies at low field frequency but not at high one. The distribution and evolution of polarization vectors in x, y, and z directions are obtained, and various forms of electrical hysteresis loops are found from the average of local polarization vectors. The results indicate that, as the frequency increases, the hysteresis loops of P z versus E z change from the standard shape to the oval shape, but the loops for P x and P y change from the dumbbell shape to an oblique ellipse, and then to figure-eight curve and eventually to the superparaelectric one. The detailed distribution and evolution of the polarization vectors in the crystal are also vividly displayed. Finally, the effects of lattice size, amplitude of the applied field, depolarization energy, and the initial state of polarizations in the crystal are investigated. It shows that the nature of polarization evolution in a 3D crystal is highly complex and that each of these factors can have a significant effect.
... Ferroelectric materials are of great interest in a wide range of applications such as actuators, sensors, microelectronic mechanical systems (MEMS), microwave circuits and, recently non-volatile ferroelectric random access memories (Fe-RAMs), with functionalities that include large remnant polarization, high and switchable electric polarization, strong piezoelectricity, high non-linear optical activity and outstanding pyro-electricity [1][2][3][4]. Ferroelectric field effect transistors (Fe-FETs) with a ferroelectric material as a gate dielectric are potential candidates for next generation non-volatile memory technology because of their low operating voltage and non-destructive read-out, unlike capacitor type Fe-RAMs that are destructive reads [4][5][6]. However, the integration of ferroelectric materials with conventional silicon electronics (complementary metal-oxide-semiconductor (CMOS) technology) is difficult due to the lattice mismatch between Si and ferroelectrics and the inter-diffusion of ions and chemical reactions across the semiconductor and ferroelectric interface [6,7]. ...
We demonstrated polarization induced switching in lead zirconium titanate (PZT) back gated multilayer MoS2 ferroelectric field effect transistors (Fe-FETs) for low power non-volatile memory devices. In this work, we investigate the influence of the interface between ferroelectric and 2D (MoS2) materials on the transistor characteristics for non-volatile memory applications. We fabricated Fe-FET devices with multilayer MoS2 as a channel material and polycrystalline and single crystal PZT thin films as the ferroelectric gate materials. The Fe-FET with polycrystalline PZT as a gate shows good memory characteristics; however, the hysteresis in transfer characteristics of the Fe-FET is in the clockwise direction (anti-hysteresis), which indicates that the transistor characteristics are not purely controlled by the ferroelectric charge. On the other hand, the Fe-FET devices with a single crystal PZT as the gate shows stable memory characteristics with a clear anti-clockwise hysteresis, which shows that the transistor characteristics are purely controlled by the ferroelectric charge. To understand the source of the anti-hysteresis and the interface between the ferroelectric and 2D materials, we have performed polarization switching at nanoscale using piezo force microscopy (PFM). The local piezoelectric hysteresis loop measured by PFM reveal that the polarization reversal in polycrystalline MoS2/PZT heterostructures is due to inhomogeneous polarization distribution, oxygen vacancies and high surface roughness of the polycrystalline PZT thin films. Our MoS2 Fe-FET devices with epitaxial PZT as a gate exhibit low switching voltages ≤2 V (much lower than the reported 2D-FET devices (8–20 V)), high ON-OFF ratios ≥10⁴ (comparable to state of the art Fe-FET devices) and reproducible hysteresis behaviour with good sustainability over 200 cycles of switching operations. This study helps with the understanding of the fundamental phenomenon for anti-hysteresis, and the realization of low power and reliable non-volatile memory devices.
... Isso se deve ao fato de que o BT é um ferroelétrico, que se destaca por sua alta permissividade dielétrica, baixas perdas dielétricas e ótimas propriedades piroelétricas e piezoelétricas [1] apresentando potencialidade para diversas aplicações em dispositivos eletrônicos, tais como capacitores, atuadores, memórias, transdutores piezoelétricos, dispositivos eletroópticos, além de mostrar excelentes propriedades semicondutoras [2]. Dentre o grande número de trabalhos sobre o sistema BT reportados na literatura muitos são associados à vasta gama de aplicações para a indústria eletroeletrônica, dentre as quais se destacam o uso em dispositivos para capacitores, termistores, entre outros [3,4]. A dopagem do BaTiO3 com íons doadores implica na mudança de algumas propriedades físicas, que conduzem a comportamentos anômalos em determinados parâmetros físicos, cuja natureza ainda não tem sido muito esclarecida entre elas as propriedades semicondutoras. ...
... It possesses excellent properties such as high refractive index, large optical band gap, low optical loss and high transparency in the visible and near-infrared region, high resistivity, low thermal conductivity, high chemical inertness and high hardness (Ohtsu et al., 2005). Correspondingly, the films are broadly utilized as heat-resistant materials (Ohtsu et al., 2005), sensors (Sayer and Sreenivas, 1990), optical filters (Lowdermilk et al., 1980), fuel cells (Gottmann et al., 1998;Minh, 1993), ion conductors (Gottmann et al., 1998), high-reflectivity mirrors (Zhao et al., 2008), broadband interference filters, (Zhao et al., 2008) active electro-optical devices (Zhao et al., 2008)and so on. ...
Thin films of zirconium oxide were synthesized by magnetron sputtering process using Zr target. The effect of oxygen partial pressure variation at 22%, 50%, 71% and 82% values on deposited zirconium oxide thin films was studied. The crystallinity of nano-structured zirconium oxide thin films was determined by X-ray Diffraction (XRD) technique. The increase in oxygen partial pressure leads to increase in crystallinity of (111) m-ZrO2 phase giving maximum intensity at 71% oxygen partial pressure. Contact angle measuring system was used to determine the wettability properties of zirconium oxide thin films namely: contact angle and surface energy. The zirconium oxide thin films changes its behavior from hydrophilic to hydrophobic with increase in oxygen partial pressure. The transmission and band gap were investigated to examine the optical properties of deposited nano-structured zirconium oxide thin films.
... BaTiO 3 (BTO) is a classical perovskite oxide material with wide potential applications based on its ferroelectricity, piezo electricity and photorefractivity [1,2]. Stoichiometric BaTiO 3 is an insulator with a bandgap in the range of 3.2-3.4 ...
Nb-doped BaTiO3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal–semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.
... Recently, a number of studies have been focused on barium titanate (BaTiO 3 ) thin films due to their remarkable ferroelectric, electro-optical, high dielectric constant, and nonlinear optical properties. [1][2][3][4] To meet the need of advanced integrated electronic devices, BaTiO 3 films with small dimensions and perfect crystallinity and surface morphology are required. It has been found that the crystallinity and surface morphology of thin films can be improved by decreasing gas pressure during growth. ...
Raman scattering technique was used to study structure dynamics of strongly reduced epitaxial barium titanate (BaTiO 3−x) thin films grown on MgO (1 0 0) substrates by laser molecular beam epitaxy under different oxygen pressures from 10 −2 to 10 −5 Pa. X-ray diffraction and asymmetric rocking curves indicate that lattice parameters c and c/a ratio increase, and a slightly decreases with decreasing oxygen pressure, indicating increased lattice volume of BaTiO 3−x thin film. Raman spectra confirm that BaTiO 3−x thin films are in tetragonal phase with some deviated features, which maybe origin from tensile strain at film–substrate interface due to lattice parameter mismatch. Moreover, two weak peaks in Raman spectra of BaTiO 2.52 thin film grown under 3.0 × 10 −5 Pa may be induced by second-order two-phonon processes. Raman peaks shift towards lower frequencies with decreasing oxygen pressure during deposition, suggesting a decrease of the stress in BaTiO 3−x thin films. In the meantime, Raman peaks become broadened, which may be attributed to higher degree of structural disorder in strongly reduced BaTiO 3−x lattice structure.
Perovskite structure materials based on the Ba1-xGdxTiO3 system, where x = 0, 0.001, 0.002, 0.003 and 0.005, were prepared via the Pechini chemical synthesis route. The dielectric properties have been analyzed over a wide temperature and frequency range, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. In fact, by using the Davidson-Cole formalism, the observed electrical behavior was found to be associated with relaxation processes related to intrinsic defects mobility promoted by a thermally-activated polaronic mechanism. The obtained values of the activation energy for the relaxation processes, estimated from the Arrhenius law for the mean relaxation time, revealed a decrease from 0.29 up to 0.21 eV as the Gd-doping concentration increases, which suggests the conduction process to be associated with the polaronic effects due to the coexistence of Ti4+ and Ti3+ ions in the structure. Analysis from the conductivity formalism, by using the Jonscher universal power-law, confirmed the polaron-type conduction mechanism for the dielectric dispersion, as suggested by the dielectric analysis, being the nature of the hopping mechanism governed by small polaron hopping (SPH) charge transport in the studied Ba1-xGdxTiO3 ceramics.
This thesis outlines the optical characterisation and low-cost fabrication techniques for the creation of nanorod metamaterial structures, using materials aluminum, rhodium and palladium for UV-plasmonics and hydrogen sensing.
Ultraviolet (UV) photodetectors are extensively adopted in the fields of the Internet of Things, optical communications and imaging. Nowadays, with broadening the application scope of UV photodetectors, developing integrated devices with more functionalities rather than basic photo-detecting ability are highly required and have been triggered ever-growing interest in scientific and industrial communities. Ferroelectric thin films have become a potential candidate in the field of UV detection due to their wide bandgap and unique photovoltaic characteristics. Additionally, ferroelectric thin films perform excellent dielectric, piezoelectric, pyroelectric, acousto-optic effects, etc., which can satisfy the demand for the diversified development of UV detectors. In this review, according to the different roles of ferroelectric thin films in the device, the UV photodetectors based on ferroelectric films are classified into ferroelectric depolarization field driven type, ferroelectric depolarization field and built-in electric field co-driven type, and ferroelectric field enhanced type. These three types of ferroelectric UV photodetectors have great potential and are expected to promote the development of a new generation of UV detection technology. At the end of the paper, the advantages and challenges of three types of ferroelectric UV photodetectors are summarized, and the possible development direction in the future is proposed.
The basic aim of our study is to investigate the correlation between structural parameters and the electrocaloric effect in lead-free epitaxial Ba1−xSrxTiO3 (BSTO) based thin film architectures. Therefore, BSTO thin films with Sr contents of x = 0 to x = 0.3 were grown on SrRuO3 buffered SrTiO3 single crystalline substrates by pulsed laser deposition. Structural characterization verified an epitaxial growth for all Sr contents with an additional tetragonal distortion compared to bulk material. Temperature and frequency-dependent measurements of dielectric properties revealed increased permittivity values for thicker films with broad maxima indicating a diffuse phase transition. The temperature of maximum permittivity decreases with increasing Sr content, whereas polarization measurements indicate a relaxor-like behaviour in particular above room temperature. Adiabatic temperature changes were determined with the indirect method resulting in |ΔT| values of up to 2.9 K for a 680 nm thick BSTO layer with x = 0.3 at an applied electric field of 750 kV cm⁻¹.
Cracking and delamination in constrained films and coatings during fabrication and service has been an important subject of scientific inquiry for several decades. Considerable past efforts have focused on developing analytical models based predicting steady state energy release rates to determine the occurrence of either cracking and/or delamination in thin films. Such models have been reconciled into a ‘Design Map’. However, the extent of available experimental validation of such Design Maps is limited. In addition, these analytical Design Maps lack the description of nuances in the processing of layered films such as progressive incremental deposition.
In this study, the interplay between cracking and delamination in progressively deposited plasma sprayed coatings is defined based on the aforementioned models. Following the adaptation of the models and presiding assumptions, a carefully designed set of experiments to probe responses from different ceramics and process conditions have been conducted, which allowed the controlled observation of cracking and/or delamination events. These experiments elucidated the underlying conditions that determine the onset of such stress relaxation events. The experimental data is reconciled with an adapted analytical Design Map for single, isolated, rapidly solidified droplets (splats) and for incrementally deposited thick plasma sprayed coatings, thus providing a framework for the robust design and processing of advanced coatings.
High demands for and rapid development of technologies related to the Internet of Things (IoT) call for a pertinent technological breakthrough in sensing devices to effectively detect various external stimuli or target analytes. Advanced sensing platforms utilizing thin-film transistors (TFTs) are essential for realizing cost-effective and high-performance chemical sensors. Here, it is reported that the utilization of a gas-selective layer based on polymeric chromatographic stationary phases is an unprecedented and facile method to establish simultaneously the desired gas selectivity and responsivity of ZnO thin films at room temperature. With the aid of computational studies, in-depth analysis and comparison of gas-sensing and the charge transfer mechanism between the gas and the resulting sensor devices are performed. ZnO with cyanopropylmethyl-phenylmethyl polysiloxane films provide excellent selective sensing with gas mixtures, and the achieved response to vaporized ethanol is nearly three times higher than the response of pristine ZnO at ~22 °C and atmospheric pressure. This effective enhancement of sensing performance under ambient conditions is attained through the transition from chemisorption to physisorption based on intermolecular interactions between gas molecules and gas-selective polymers. This work demonstrates a potent yet cost-effective method to fabricate low power consumption gas sensor systems based on metal oxide TFT.
The trend of replacing trench and stack capacitors in a dynamic random access memory (DRAM) with a planar configuration has stimulated the development of high dielectric constant materials with reliably low leakage current and high dielectric breakdown strength. In this regard, high dielectric constant materials, such as PbZr x Ti y O 3 (PZT), BaTiO 3 , SrTiO 3 , PbTiO 3 , and Ba x Sr 1-x TiO 3 , have been extensively investigated as dielectrics in the last few decades. Of these, the sol id-solution quaternary Ba x Sr 1-x TiO 3 , (BST) combines the high dielectric constant of BaTiO 3 , with the structural stability of SrTiO 3 , is one of the most promising materials for DRAM cells in very large-scale integrated circuits. BST shows a paraelectric phase for x<0.7 at room temperature, which provides additional features such as no aging or fatigue effects from ferroelectric domain switching. However, so far, there have been few studies of the interfaces between BST and the substrates, particularly at the atomic-resolution level.
Adhesive wear is a significant material loss mechanism that leads to wide scale surface degradation of functional components especially in engineering industries like wind turbine roller bearings. This paper deals with improving the tribological properties of surfaces where adhesive wear is prominent. Adhesive wear is a common problem in gears, bearings, cutting tools, fittings, valves and earth moving equipment. For instance in a planetary gear arrangement, worn out debris from gears cause adhesive wear on the surface of roller bearings. Ceramic coatings are significant for protecting components and to improve the performance of surfaces subjected to adhesive wear over longer periods. Most of the ceramic coatings have high surface roughness owing to which they contribute to further adhesive wear of fine surfaces. In this paper, focus is on studying the performance of ion plated titanium nitride (TiN) and titanium carbide (TiC) PVD coatings against adhesive wear on EN 31 steel (substrate). Surfaces of samples coated with TiN, TiC and uncoated substrate of EN 31 steel are comparatively studied for adhesive wear behavior using wear tests as per ASTM standards. EN 31 steel is composed of 95% Fe, 0.9–1.1% C, 0.35% Mn, and 0.2% Si. Surface morphology and compositional analysis is inferred from Electron Microscopy (SEM and EDS) and surface roughness is estimated using 3-D confocal microscopy and surface profile measurement. The bond strength of coating is analysed from nanoscratch test; the coefficient of friction, material removal rate and hardness of surface is obtained from nano indentation Test. On experimental investigation, it is found that TiN and TiC ceramic coatings have excellent wear resistance, a low coefficient of friction and fine surface finish which are suitable for adhesive wear resistant applications.
Flexible strain sensors have captured a lot of attention since first being proposed. Most studies are focused on adopting new materials or developing novel structures to detect strain, temperature, and even to realize multifunction. The reliability of flexible strain sensors in harsh environments such as at low and high temperatures, however, has so far received little attention because traditional bendable or stretchable substrates, including polyethylene terephthalate, polyimide, polydimethylsiloxane, paper, silk, and cotton, cannot withstand high temperature. The poor thermostability limits their potential applications in harsh conditions such as in interstellar probes, polar exploration, petrochemical, and metal smelting. Here, a heat‐resisting flexible strain sensor is shown, consists of a BaNb0.5Ti0.5O3 film on top of a 4.5 µm thick mica substrate. The device exhibits excellent thermal stability in a wide temperature range from 20 to 773.15 K. Owing to the ultrathin mica substrate and low resistance, the device demonstrates low power consumption (0.96 µW cm⁻²), is lightweight (2.06 g cm⁻³), together with having high stability over 5000 bending cycles. This work opens a path for pressure sensors applying ceramic materials that can be used from an ultralow to a high temperature.
Structural and microstructural properties of lead-free BaBa1−xGdxTiO3 ceramics are investigated. The results confirm the formation of the ferroelectric phase, for all the cases, revealing a decrease in the unit-cell volume (V) with the increase of the gadolinium concentration, which can be associated to the difference between the ionic-radii of the involved ions (Gd³⁺ and Ba²⁺). A decrease in the average grain-size, with the increase of the Gd³⁺ content, was associated to the pinning effect (typical of rare-earths) due to the contribution of minor additional phase, which is not easily detectable by X-ray diffraction technique at very low dopant concentrations.
Barium titanate (BaTiO3) ceramics, prepared by the Pechini’s method, were investigated considering the influence of the samarium-modifier concentration. Nanosized crystallites in the order of 15–20 nm have been successfully obtained by this synthesis process. The structural properties analyzed from the X-ray diffraction technique, confirmed a single ferroelectric phase with no additional secondary-phases, and suggest the amphoteric character (A- or B-site occupancy) of the Sm³⁺ ion into the BaTiO3 structure. This effect, which has not been previously reported, has been also confirmed from microstructural (scanning electron microscopy) analysis. The obtained results reveal to be the starting point for further detailed investigations of the real amphoteric behavior of the Sm³⁺ ion, and other rare-earth elements in perovskite-type structure systems.
The dispersion of dry, cohesive micro- and nanosized powders has wide applications ranging from medical and environmental science to manufacturing technology. Being able to disperse the dry powder at a stable concentration over periods of time (∼hour to several hours) is challenging to achieve, which we attempt to address with a novel dry powder dispersion technology. A portable, cost effective and simple dry powder dispersion device that uses ultrasonic energy for continuous feeding of aerosol particles to a de-agglomeration device is developed and tested with commercially available powders. The study is performed using 5 µm polyamide powder and rutile TiO2 powders of 500, 100, and 30 nm mean size of primary particles. The ultrasonic dispersion device proved to be able to disperse all of these powders, which represent low-density material to high-density metal oxides, with stable concentration over periods that extend to an hour. From aerosol measurements to obtain the size distribution of various size particles, it is seen that the highly agglomerated powder particles are not easy to de-agglomerate as we go to the lower (nominal) sized powders because of the stronger inter-particle adhesion forces between nanoparticles compared to microparticles. The scanning electron microscopy (SEM) images of particles in their native powder state and those collected after the dispersion showed significant difference in the agglomeration of the powder particles, which suggests partial success of the turbulent jet de-agglomeration employed.
© 2019 American Association for Aerosol Research
YSZ film was fabricated by a facile electrophoretic deposition process using commercial YSZ powders. YSZ films with average thickness of around 10 µm were deposited on LSM/YSZ substrate at 20 V for 20 minutes and subsequently sintered at 1200 °C, 1300 °C, and 1350°C. XRD patterns of the deposited and sintered films can be attributed to mostly cubic YSZ phase. On the other hand, SEM images revealed that a sintering temperature above 1300 °C was needed to obtain a denser YSZ film. The film morphology also showed that as the sintering temperature increases, the YSZ grain size also increases.
The aerosol deposition (AD) method is a unique approach to metal and ceramic coating, by which solid-state submicron metal and ceramic particles are accelerated by gas flow up to 100–500 m/s and then impacted onto a substrate. The National Institute of Advanced Industrial Science and Technology (AIST) found an interesting consolidation phenomenon of ceramic particles in this method over 20 years ago. During the collision of fine particles and interaction with the substrate, these ceramic particles, not only for oxide materials but also for non-oxide materials, form thick, dense, and hard ceramic layers at room temperature. No additional heating for the solidification of ceramic powder was required. We named this phenomenon "room-temperature impact consolidation (RTIC)". Consolidated ceramic powder with RTIC via the AD method can be called as a high-density binderless ceramic green. It can rapidly form into a thick dense, uniform, and hard layer at room temperature without additional heating for solidifying starting powders, even at a low vacuum, using relatively cheap and simple production facilities. Metal-based optical scanning devices, tube-type ultrasonic motors, and piezoelectric energy harvesters are fabricated by the AD method have been developed for sensor and actuator applications.
By optimizing laser raster scanning conditions and controlling PbO evaporation, we have grown high quality large area PbZr.52Ti.48O3 (PZT) thin films using custom-built off-axis pulsed laser deposition (PLD) technique. The realization of high quality PZT thin films over a large area with uniform polarization is a challenging task due to the formation of non-ferroelectric or pyrochlore like PbTi3O7 phases at the processing temperature (>600°C). Our results show the polycrystalline nature of the sample with a uniform chemical surface composition. The macroscopic level of polarization mapping shows excellent saturated P-E loops with a narrow variation (6%) of the remnant polarization (2Pr) across the large area thin films. A comparative study of macroscopic and nanoscale level of mapping of polarization switching are performed, to demonstrate the existence of stoichiometry ferroelectric PZT thin films over a large area. The achievement of high quality large area PZT thin films with uniform polarization might be used for under-water SONAR devices and in power harvesting.
The evolution of domain structure with external stress in a free-standing PbTiO3 ferroelectric thin film of ˜100nm in thickness is observed by in-situ TEM technique. The thin film is composed of granular grains of ˜100nm in diameter, most of them appear to be single-domained whereas others are multi-domained showing domains of different sizes(5˜20nm). For some single-domained grains new domains appear during tension. For multi-domained grains, rearrangement of domain walls and coarsening of domains have been observed during tension. In many cases the domain walls disappear under high stress, i.e., a multi-domained grain changes into a single-domained grain. However, it is also observed that a large portion of single-domained grains appear not to respond to external stress. The dynamic behavior of domain walls in very thin ferroelectric thin films may help to understand the switching of these very thin films.
The successful use of pulsed laser deposition (PLD) to fabricate thin film superconductors has generated interest in using the technique to deposit thin films of other materials. The compositional fidelity between laser target and deposited film and the ability to deposit films in reactive gas environments make the PLD process particularly well suited to the deposition of complex multicomponent materials. Cheung and Sankur recently provided an excellent review of the PLD field, including a table of over 100 elements, inorganic and organic compounds, and
superlattices that have been laser evaporated. Over 75 of these materials were deposited as thin films.
The goal of this article is to provide an introduction to some of the newer applications of PLD for thin film fabrication. Four classes of materials are highlighted: ferroelectrics, bioceramics, ferrites, and tribological materials. Ferroelectric materials are structurally related to the high-temperature superconducting oxides and therefore are a direct extension of the recent superconducting oxide work. Bioceramics are dissimilar in structure and application to both ferroelectrics and superconducting oxides, but they are complex multicomponent oxides and, therefore, benefit from the use of PLD. Ferrites, also complex, multicomponent oxides, represent another exciting, but only lightly explored opportunity for PLD. In contrast, tribological materials are typically neither complex nor multicomponent. Nevertheless, interesting structures and properties have been produced by PLD. A few of the more important ones will be discussed. These different types of materials demonstrate the diversity of capabilities offered by PLD.
Technological and scientific activities in the synthesis of ferroelectric thin films have been in progress for approximately 35 years with some very notable achievements taking place along the way. The work started with the simple evaporation of BaTiO3 by Feldman (1955), and accelerated during the 1970’s with the advent of sputtering technologies. Since that time some totally new techniques and innovative processes have been introduced. The ability to routinely fabricate films having good ferroelectric properties in sub- micron thicknesses, and to demonstrate marketable products such as non-volatile memories and electro-optic switches has generated an immense interest in integrated ferroelectrics. Progress has been made in three areas: (1) theresearch and development of new processing technologies, (2) methods for accelerated testing and property measurement, and (3) the development of novel thin film devices utilizing the functional properties of ferroelectrics. Further advances in these areas are linked to an improved understanding of (1) the theory of nucleation and film growth related to composition, (2) the dependence of film properties on thickness, (3) concerns related to the compatibility of ferroelectrics with electrode materials, and (4) reliability issues.
Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high-displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated-circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.
Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.
Temperature and frequency dispersion of the dielectric constant was investigated on the ferroelectric Pb(Zr-0.53 Ti-0.47)TiO3[PZT] thin films, which prepared by sol-gel spin on process using 0.4 M PZT solution. The virgin PZT and fatigued PZT films exhibited a marked dielectric dispersion over the temperature range from room temperature to 300 0 C and over the frequency range from 10(-2) Hz to 100 kHz. The dielectric relaxation was observed below 10 kHz, which was interpreted based on a dipole relaxation of the Cole-Cole type. Low-frequency dielectric relaxation is attributed to the lead and oxygen vacancies complex dipoles in PZT film. The thermal activation energy for the relaxation process of ionized space-charge carriers in the virgin and fatigued PZT film were 1.61 eV and 0.96 eV, respectively.
A new kind of lead-free ferroelectric material, BaTi2O5, which is expected to have good ferroelectricity and high permittivity with a high Curie temperature, was prepared by Spark Plasma Sintering (SPS) method. The influences of sintering temperature on the phase, density and microstructure of the ceramics were mainly investigated. The results show that the relative density of the BaTi2O5 ceramics is increased with higher sintering temperature. When the temperature is lower than 1050 degrees C, single-phase BaTi2O5 ceramics can be obtained, but at the temperature >= 1100 degrees C, it is decomposed into BaTiO3 and Ba6Ti17O40. The optimum SPS conditions are found to be 1050 degrees C, 40 MPa and 10 min, under which the single-phase, dense and large-scale BaTi2O5 ferroelectric ceramics can be obtained.
Microstructural characteristics in the BaSrNb0.3Ti0.7O3 thin film, grown on SrTiO3 substrate by computer-controlled laser molecular beam epitaxy, were characterized by means of transmission electron microscopy (TEM). It is found that the film is single-crystallized and epitaxially grown on the SrTiO3 substrate forming a flat and distinct interface. Anti-phase domains were identified, and the crystallographic features of mismatch dislocations at the interface between film and substrate were clarified. The high conductivity of the present film was discussed from the viewpoint of Nb dopant and the nitrogen atmosphere.
Nano-particles of Nd-doped BaTiO3 were prepared by modified sol-gel method. The microstructure and high-frequency electromagnetic properties were characterized by using X-ray diffraction(XRD), vector network analyzer. The results showed that Nd-doped barium titanate samples crystalline sound with annealed 1h at 700°C. With the increase of Nd content, the lattice size of the BaTiO3 powders decreased with the grain refinement. Within the bandwidth of 2-18 GHz, the real part of dielectric constant of 5% Nd-doped BaTiO3 powders decreased slightly with the stability improved, but the imaginary part of dielectric constant greatly increased. Both the peak of the complex permittivity and permeability has blue shift with Nd-doped. The reflection loss of 5% Nd-doped BaTiO3 powders is greatly increased and reflection peak has blue shift compared with pure BaTiO3 powders. The above shows that Nd-doping can greatly improved the microwave absorption properties of the BaTiO3.
Aerosol deposition (AD) is a unique approach for depositing ceramic films, where submicron ceramics particles (both oxide and non-oxide) are accelerated by gas flow up to 100-500. m/s and then impacted on a substrate. It can rapidly form a thick, dense, uniform and hard ceramic layer at room temperature without additional heating for solidifying ceramic powders, even in low vacuums, using relatively cheap and simple production facilities. It is expected to reduce energy and costs, ease the fabrication of thin or thick film with complicated material compositions, and reduce the number of processes during fabrication of electronic devices, as well as to improve substantially their performance. This technique is particularly useful for fabricating piezoelectric thick films and producing micro-actuator devices. This chapter deals with the mechanism and features of the AD process first, followed by its application for piezoelectric materials and devices.
IntroductionAD MethodRoom Temperature Impact Consolidation (RTIC)Deposition Properties and Film PatterningOther Similar Methods and Comparison with the AD Method
Electrical Properties of AD FilmsDevice ApplicationSummaryAcknowledgmentsReferences
IntroductionMaterialsProcessingPropertiesApplicationsFuture Prospects
We have fabricated multiple layer ZnO acoustic transducers for highly efficient sound wave generation at millimeter‐wave frequencies. The transducers consist of half‐wave‐thick layers of ZnO with alternating crystal structure. The two‐way untuned conversion loss values were 27 dB near 29 GHz and 50 dB at 96 GHz measured at liquid nitrogen temperatures.
Degradation of Ba 2 YCu 3 O 6.9 films on yttria‐stabilized zirconia substrates is shown to proceed by barium depletion from the film and barium zirconate formation. This process is accompanied by a decrease in the temperature of zero resistivity and ultimately produces Y 2 Cu 2 O 5 and CuO. BaZrO 3 is, however, found to be inert to Ba 2 YCu 3 O 6.9 at 950 °C. Use of a truly chemically inert substrate material may permit extended heat treatment of films without degradation due to substrate interactions.
We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO 3 and Al 2 O 3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.
The ferroelectric effect has been demonstrated for sol-gel derived lead zirconate titanate (PZT) (53/47) thin films. The respective values of coercive field and remanent polarization were 4x10(6) V/m and 0.36 C/m(2). The thin-film fabrication process is simple and compatible with Si planar technology, and offers a wide variety of potential uses for counting, memory, and integrated optical circuit applications.
Acoustic lenses made of thin piezoelectric lead zirconate titanate (PZT) films fabricated by a chemical sol-gel process are presented. A frequency range between 50 and 250 MHz has been achieved. PZT films have been successfully coated on substrates such as fused quartz and metals, flat and cylindrical surfaces, and substrates with a large coating area or length. The piezoelectricity of the film is achieved by electric poling. The comparison between PZT and ZnO films for ultrasonic high frequency transducers is outlined.
Ferroelectric PbTiO3 thin films were prepared by a simultaneous deposition of TiO2 and PbO on heated substrates under the reduced pressure of 6 Torr. Titanium tetraisopropoxide and tetraethyl lead were used as source materials. The deposition behaviors of TiO2 and PbO were examined independently. Homogeneous nucleations of the reaction species in the vapor phase were depressed under the reduced pressure. The films obtained at 500° to 650°C of consisted of PbTiO3 of the single perovskite phase, and highly c-axis oriented and epitaxal films were grown on MgO(100). The deposition rate of the film available by adjusting the source temperature and the flow rate of the carrier gas is 50 to 1000Å/min, the maximum value of which is ten or more times that obtained by the conventional sputtering method.
Both longitudinal and shear waves can be generated simultaneously and efficiently using 10° rotated Y‐cut lithium niobate disks and tilted C‐axis zinc oxide thin films. By properly varying the operating frequencies, the ratio between longitudinal and shear excitation strength can be adjusted.
Superconductivity above the temperature of liquid nitrogen in copper oxide-based systems has led to optimism that superconductors
may at last find wide application. The critical temperature, however, is just one of the required parameters. The materials
must be made into usable forms such as wire, thick films, thin films, and bulk ceramics. In addition, the critical current
in these various forms is a crucial test of their utility. This article reviews the processing techniques used to fabricate
potentially useful forms and assesses remaining problems. Considerable improvement in critical current density is necessary
in bulk materials, and thin films need to be made compatible with other thin-film technology.
DOI:https://doi.org/10.1103/RevModPhys.60.585
Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis and condensation of alkoxide complexes with several metals. This requires temperatures only up to the transformation range of the glass in question, usually 500–600 °C. The process does not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances, depending on the composition. The method is particularly suitable for the production of thin, transparent multicomponent oxide layers of almost any composition on substrates. Some of these layers provide protection against climatic attack or against oxidation.
The processing of thin-film semiconducting, optical, and electronic materials by spray pyrolysis processing is reviewed. The major processing parameters, equipment, and chemical solutions utilized in the deposition of sulfides, selenides, oxides, and ternary semiconducting compounds are described in relation to the potential applications of these materials. The prospects of spray pyrolysis processing in photovoltaic, ir optical, and electronic materials technologies and ceramic powder preparation are discussed.
c‐axis oriented thin films of piezoelectric ZnO have been deposited on room‐temperature substrates by rf magnetron sputtering of zinc in a reactive ambient of 100% oxygen over a pressure range from 5–70 mTorr. Below 10 mTorr the film structure, orientation, and physical properties depend on the position of the substrates with respect to the target. This is attributed primarily to resputtering of the film in the region of the target erosion area by high‐energy neutral oxygen. At higher pressures where the mean free path inhibits such effects, the film structure and properties are uniform. At 700‐W sputtering power, the optimum pressure lies between 20–30 mTorr leading to highly oriented ZnO over a large area of plasma with a dielectric constant of 11, conductivity at 300 °C=2×10-10 Ω-1 cm-1, and Rayleigh wave velocity=2600 m/s. The films are characterized using optical transmittance, electrical conductivity, dielectric constant and SAW, and acoustic microscope measurements.
Crack‐free transparent ferroelectric polycrystalline Pb(Zr,Ti)O 3 thin films were prepared by spin‐coating solutions of complex alkoxides. The preparation of stock solution, firing, and annealing of films was described. The coating of the intermediate layer of Al 2 O 3 increased the adhesion between Pb(Zr,Ti)O 3 thin films and glass substrates. The crystalline phases of films with varying Zr/Ti ratios were investigated. The dielectric constants were about 260. The remanent polarization and coercive field were 6.6 μC/cm2 and 26.7 kV/cm, respectively. The refractive index of the perovskite Pb(Zr,Ti)O 3 films was 2.6 at 6328 Å, and the absorption edge was at 3400 Å. The quadratic and linear electro‐optic effects were measured with respect to the Zr/Ti ratio from 40/60 to 60/40 for films grown on glass substrates. The quadratic and linear electro‐optic coefficients were about 1×10-18 m2 /V2 and 2.4×10-11 m/V at 6328 Å, respectively.
Lead zirconate titanate [Pb(Zr,Ti)O 3 or PZT] thin films have been grown by sputtering a multi‐element metal target in oxygen using dc planar magnetron sputtering. Growth parameters and annealing conditions have been optimized. The kinetics of reactive sputtering and the implications of sputtering parameters on film composition have been studied. The studies reveal the requirement for operation at low substrate temperatures (200 °C), high sputtering pressures (4–5 Pa), and a large substrate‐to‐target distance (10 cm) for obtaining good control over composition. The structural and electrical properties of films were found to depend on the compositional ratio of Zr/Ti, similar to that observed in bulk PZT ceramics. Films having a resistivity of 1010 Ω cm and a dielectric constant ϵ’∼820 at room temperature (300 K) have been achieved. Ferroelectric hysteresis loop measurements indicated a remanent polarization of 30.0 μC/cm2 and coercive field of 25 kV/cm for the rhombohedral phase composition (Zr/Ti=58/42). Piezoelectric activity in the films is reported for the first time, through the fabrication of a surface‐acoustic‐wave delay line on a poled polycrystalline PZT thin film.
A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C.
Thin films of ferroelectric Pb 1-x Ca x TiO 3 (x=0.0–0.4) were formed on MgO, Pt/MgO, SrTiO 3 , and Pt/SrTiO 3 substrates by rf magnetron sputtering. Characterization of the films by x‐ray diffraction, x‐ray precession, scanning electron microscopy, and electron probe microanalysis showed them to be epitaxially grown with their c‐axis oriented perpendicular to the substrate. The decrease in the Curie temperature T c and the increase in the pyroelectric coefficient dP s /dT with an increase in Ca doping were successfully explained by assuming that the Ca ions occupied Pb ion sites. Pyroelectric infrared detectors using Pb 0.7 Ca 0.3 TiO 3 thin‐film elements gave better performance than the detectors using PbTiO 3 ceramic elements. The internal bias field E B and fixed polarization P B were observed to be a function of both the Ca content and temperature in ferroelectric hysteresis curves as well as in hysteresis curves of the dielectric constant as a function of the applied electric field. These phenomena were explained by the difference in thermal behavior between the sputtered films and the substrates at temperatures below T c .
Thin films of the high T c superconductor YBa 2 Cu 3 O 7 - δ were prepared and characterized. The films made on SrTiO 3 showed epitaxial growth and high critical current densities in excess of 9×104 at 78 K and 2×106 at 4.2 K. Also, surface pinning in the parallel direction was found to be very high. The measurements put a lower limit on the depairing critical current density of 5×107 A/cm2.
The emergence of high rate sputtering during the past few years is mainly a consequence of the development of high performance magnetron sources. In this paper we discuss several issues which are of importance in scaling magnetron technology to high rates and in extending its application to non-conducting materials. These include (1) considerations concerning magnetron plasma discharges, (2) special problems encountered in r.f. sputtering with magnetrons and (3) observations which illustrate the importance of the total system (including the chamber walls) in reactive sputtering processes. Finally we briefly discuss some of the consequences to coating growth of the low working gas pressures commonly used in magnetrons. The discussion includes coating flux angle-of-incidence and reflected-ion effects which, for example, make the coating growth dependent on the apparatus geometry.
The structural, electrical and optical properties of d.c.-magnetron-sputtered lead zirconate titanate (Pb(Zr, Ti)O3) (PZT) thin films have been investigated, and the influence of the growth conditions on surface morphology has been examined by scanning electron microscopy. PZT films with different crystallographic structures have been achieved by varying the Zr:Ti ratio. Films possess a dielectric constant of 800, a remanent polarization of 0.3 Cm−2 and a coercive field of 2.5 × 106 Vm−1. The optical transparency is 75% in the visible region (λ = 0.6−0.9 μm). The surface morphology of the films was found to depend on processing conditions and the type of substrate used. Formation of hillock structures contributing to surface roughness is discussed in terms of relative thermal expansion between the substrate and the film and the internal stress induced in the films during deposition. Substrate temperatures of 200°C and proper annealing conditions are shown to be of importance in producing device quality films, while thin buffer layers can play an important role in matching films to specific substrates.
In situ neutron powder diffraction measurements show that the orthorhombic-to-tetragonal phase transition in YBa2Cu3O7-x which occurs near 700 C in a pure oxygen atmosphere, is an order-disorder transition in which the disordering of oxygen atoms into a normally vacant site destroys the one-dimensional Cu-O chains present in the room-temperature orthorhombic structure. For both structures, the oxygen stoichiometry decreases monotonically with increasing temperature. The transition temperature depends on the oxygen partial pressure and occurs when the stoichiometry is near YBa2Cu3O6.5. The tetragonal structure has a partially occupied, nearly octahedral Cu-O arrangement, in contrast to the orthorhombic structure which has one-dimensional Cu-O chains. The observed depression of the superconducting transition temperature in tetragonal YBa2Cu3O7-x, which has been quenched from high temperature, could result either from the disordering of oxygen atoms which destroys the one-dimensional chains or from the absence of Cu3+ ions.
Surface and bulk acoustic wave measurements with lead zirconate titanate (PZT) thin films fabricated by a sol gel processing technique are reported for the first time. The piezoelectricity of such films was achieved by poling. Good acoustic properties of these films are confirmed by the acoustic images and V(z) curves obtained by a scanning acoustic microscope.
The structure and operation of ferroelectric thin-film memory capacitors for use in nonvolatile random-access memory applications are described. The search for the ideal ferroelectric material for ferro-electronic memory applications is examined. Possible military and nonmilitary applications of these memories are noted.< >
An experimental 512-b random-access memory based on
ferroelectric-capacitor storage cells has been successfully fabricated
and tested. The device was designed solely for use in process
development and electrical characterization and includes onboard test
circuitry for that purpose. The internal timing of the memory is
controlled externally to allow experimentation with timing algorithms,
hence the name 512 externally controlled device, or 512 ECD. The authors
discuss the properties of the ferroelectric ceramics used in integrated
circuit memories, the operation of a destructively read ferroelectric
memory cell, and the organization of the 512 ECD die, including its
onboard test circuitry. Finally, retention and wear-out properties of
ferroelectric capacitors are discussed as they relate to design
requirements
- P Sigmund
- Theory I Of Sputtering
- Sputtering
- Of
- Polycrystalline Targets
Ceramic Thick and Thin Films
- A N Patel
Ceramic Thick and Thin Films
- G Yi