Material Properties Of Thin Films Research Articles

Dynamic Behavior of Thermal Stress in a Functionally Graded Material Thin Film Subjected to Thermal Shock

In the present article, a one-dimensional dynamic thermoelastic problem in a functionally graded material (FGM) thin film subjected to a thermal shock loading is analyzed. An exact analytical solution is obtained by employing techniques of the space-variable transformation and Laplace transform, in the case where variations in material properties of the FGM thin film are expressed as exponential functions of the space-variable. Numerical calculations for time histories of thermal stresses have been carried out. Obtained numerical results reveal that the thermal stress oscillation is unsteady when the mechanical impedance depends on the space-variable, whereas it is monotonic and periodic when the impedance is independent of the space-variable. The factor which causes the different behavior of the thermal stress oscillations is also investigated based on the analytical and numerical results.

Synthesis and Characterization of LPCVD Polysilicon and Silicon Nitride Thin Films for MEMS Applications

Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated MEMS devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not very well controlled during deposition. The residual stress, for example, tends to vary significantly for different deposition conditions; experiments were carried out to study the polysilicon and silicon nitride deposited by Low Pressure Chemical Vapor Deposition (LPCVD) method at wide range of process conditions. High temperature annealing effects on stress in case polysilicon are also reported. The reduced residual stress levels can significantly improve device performance, reliability, and yield as MEMS devices become smaller.

A Review Paper on Tribological and Mechanical Properties of Ternary Nitride based Coatings

Abstract The nanotribological studies are needed to develop fundamental understanding of interfacial phenomena on a smaller scale in nanostructures used in magnetic storage systems and other industrial applications. In several fields of technical application, e.g., in the automotive or aircraft industries, the reduction of friction and wear is a very important aspect with respect to longer lifetimes, increased service intervals and lower operation costs of tools, machines and other devices or mechanically loaded elements. Many researchers have studied tribological properties of various binary thin film materials to investigate various properties like adhesion, hardness and friction coefficients according to the respective applications. The different deposition techniques they used are Unbalanced Magnetron Sputtering. Ion Beam Assisted Deposition, Physical Vapour Deposition etc. Recently ternary nitride based coatings are invesitgated as they exhibit improved tribological, mechanical and thermal properties compared to binary nitride based coatings. This review paper is aimed to summarize tribological properties of three ternary nitride based coatings such as Titanium Aluminium Nitride, Titanium Vanadium Nitride and Titanium Molybdenum Nitride.

Photoluminescence Characterization of Phosphorus Diffusion and Hydrogenation in Continuous Wave Diode Laser Crystallized Si Thin-Film on Glass.

ABSTRACTIn this paper, the effect of phosphorus diffusion and hydrogen passivation on the material properties of laser crystallised silicon on glass is investigated. Photoluminescence imaging, as well as Hall effect and Suns-Voc techniques are applied for the characterisation of laser crystallized silicon thin-film material properties. Hall effect as well as Suns-Voc measurements supports the photoluminescence imaging results; phosphorus diffusion and hydrogen passivation of laser crystallized films improves the overall material quality. Hydrogen passivation is more effective at improving the electronic properties of the laser crystallized films than phosphorus diffusion. Hydrogen passivated samples improved the photoluminescence intensity even further by a factor of 3. In addition, a correlation between photoluminescence intensity and open-circuit voltage is demonstrated: samples with highest photoluminescence intensity (1678 counts/s), gave the highest voltage (530 mV). Hall effect measurement shows a significant improvement in the bulk material, with carrier mobility increasing from 208 cm2/Vs to 488 cm2/Vs.

Investigation of Loading-Unloading Curve and Stress Distribution of Thin Hard Coating by Finite Element Analysis during Nanoindentation Process

This study applies the finite element method (FEM) in conjunction with an nanoindentation test to predict the loading curve and stress distribution of thin hard coatings. To verify the prediction of FEM simulation for loading and unloading process, the experimental data are compared with the results of current simulation. Loading curve is investigated for different material parameters, such as elastic modulus E, yield stress Y0 and tangent modulus ET of nanoindentation process, by finite element analysis. The effects of material properties of thin film on the stress distribution for loading and unloading in the nanoindentation are also investigated. Therefore, the loading curve and stress distribution will be prediction for the different material parameters of nanoindentation process.

Molecule motion at polymer brush interfaces from single‐molecule experimental perspectives

ABSTRACTPolymer brushes have been widely used as functional surface coatings for broad applications including antifouling, energy storage, and lubrications. Understanding the molecule dynamics at polymer brush interfaces is important in unraveling the structure–property relationships in these materials and establishing a new materials design paradigm of novel functional polymer thin films with efficient interfacial transport. By applying modern fluorescence‐based single‐molecule spectroscopic and microscopic techniques, molecule dynamics at varied polymer brush interfaces have been experimentally investigated in recent years. New insights are given to the understandings of some unique and unusual materials properties of polymer brush thin films. This review summarizes some recent studies of molecular diffusion at polymer brush interfaces, highlights some new understandings of the interfacial properties of polymer brushes, and discusses future research opportunities in this field. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014, 52, 85–103

The Analysis of the Film Morphology

Thin film technologies are widely used in modern scientific and technological fields .The theory of thin film growth is guidance for developing a new-type materials and improving the properties of custom thin film materials .In this article , the studies of thin film growth are carried out. The studies are made a simulation of surface growth of the GaxIn1-xAs1-ySby and YBCO film, Schematic diagram of the surface morphology under different substrate temperature of thin film growth are obtained and analyzed .Many significant results are found. First of all ,the background of the topic ,research purpose and significance are described in this article .Then the studies of thin film growth are carried out ，to analyse the effects of different elements on the surface of the crystal film.

Accurate characterization of thin films on rough surfaces by spectroscopic ellipsometry

Spectroscopic ellipsometry (SE) is the technique of choice to determine material properties of thin films in a fast and non-destructive way. However, its ability to accurately extract the material properties of thin films deposited on rough substrate surfaces still remains a challenge, due to depolarization of specularly reflected light. In this paper we present a method based on SE to determine the properties of thin films on rough surfaces. It is shown that, by analyzing SE data only at discrete photon energies, information such as the film thickness and the refractive index at these photon energies can be extracted. The discrete photon energies selected in this method can be related to destructive interference of light at the thin-film surfaces, which significantly reduces the depolarization problem. The method is demonstrated using thin amorphous hydrogenated silicon nitride (a-SiNx:H) films deposited on both polished and rough silicon wafer substrates. By varying the a-SiNx:H film thickness, it is shown that the depolarization effect of light is strongly dependent on the incident photon energies due to light interference at the surface of the a-SiNx:H film. Based on this observation, energy selective ellipsometry (ESE) is proposed as a technique for analyzing thin films on random rough surfaces. It is shown that a-SiNx:H films with a wide range of thickness and optical properties on rough silicon surfaces can be studied accurately by means of ESE. This technique is expected to have useful practical applications, for example in photovoltaics where films are typically deposited onto textured substrates as a means of enhancing light trapping.

Use of radiation effects for a controlled change in the chemical composition and properties of materials by intentional addition or substitution of atoms of a certain kind

This study is a continuation of works [1–12] dealing with the field developed by the authors, namely, to widen the possibilities of radiation methods for a controlled change in the atomic composition and properties of thin-film materials. The effects under study serve as the basis for the following two methods: selective atom binding and selective atom substitution. Such changes in the atomic composition are induced by irradiation by mixed beams consisting of protons and other ions, the energy of which is sufficient for target atom displacements. The obtained experimental data demonstrate that the changes in the chemical composition of thin-film materials during irradiation by an ion beam of a complex composition take place according to mechanisms that differ radically from the well-known mechanisms controlling the corresponding chemical reactions in these materials. These radical changes are shown to be mainly caused by the accelerated ioninduced atomic displacements in an irradiated material during irradiation; that is, they have a purely radiation nature. The possibilities of the new methods for creating composite structures consisting of regions with a locally changed chemical composition and properties are demonstrated for a wide class of materials.

Combinatorial Techniques to Efficiently Investigate and Optimize Organic Thin Film Processing and Properties

In this article we present several developed and improved combinatorial techniques to optimize processing conditions and material properties of organic thin films. The combinatorial approach allows investigations of multi-variable dependencies and is the perfect tool to investigate organic thin films regarding their high performance purposes. In this context we develop and establish the reliable preparation of gradients of material composition, temperature, exposure, and immersion time. Furthermore we demonstrate the smart application of combinations of composition and processing gradients to create combinatorial libraries. First a binary combinatorial library is created by applying two gradients perpendicular to each other. A third gradient is carried out in very small areas and arranged matrix-like over the entire binary combinatorial library resulting in a ternary combinatorial library. Ternary combinatorial libraries allow identifying precise trends for the optimization of multi-variable dependent processes which is demonstrated on the lithographic patterning process. Here we verify conclusively the strong interaction and thus the interdependency of variables in the preparation and properties of complex organic thin film systems. The established gradient preparation techniques are not limited to lithographic patterning. It is possible to utilize and transfer the reported combinatorial techniques to other multi-variable dependent processes and to investigate and optimize thin film layers and devices for optical, electro-optical, and electronic applications.

Measurement system of dynamic microscopic deformation for membrane based on fringe projection

The bulge test has been utilized extensively in determining the mechanical properties of thin film materials. We develop a bulge-test system that consists of three main components, including an optical system, a loading system, and a control system. A telecentric lens is adopted as an imaging camera in an optical system to provide high imaging quality along with a constant angle of view across the entire field of view. The out-of-plane deformation is obtained by projecting a sinusoidal fringe pattern onto a specimen surface and analyzing recorded images with a digital image correlation algorithm. A least-squares polynomial fitting is presented to solve the problem that the out-of-plane calibration coefficient is not a constant. Experiments were performed to validate the availability and reliability of this proposed bulge-test system in the measurement of a dynamic microscopic deformation of membrane. The measuring range of deformation is from several microns to hundreds of microns with an accuracy of 0.6 μm.

Measuring methods for the investigation of in‐plane and cross‐plane thermal conductivity of thin films

AbstractThe characterization of the thermal properties of thin film materials is important both for understanding of their structure and conduction mechanisms and for their technical applications. Thermal conductivity and diffusivity are crucial parameters for the design of integrated devices, thermal microsensors and actuators. Reliable system simulation and design optimization of such devices is based on the accurate determination of thermophysical properties. It is therefore highly desirable to acquire such data. Usually, thermal properties of thin films differ considerably from the bulk values, since the parasitic surface effects are much stronger due to the smaller dimensions and aspect ratios. The measurement of these properties is sophisticated and associated with various problems. We report on steady‐state and transient methods for the characterization of in‐plane and cross‐plane film properties by using microelectrothermal chips.

Substrate-biasing during plasma-assisted atomic layer deposition to tailor metal-oxide thin film growth

Two substrate-biasing techniques, i.e., substrate-tuned biasing and RF biasing, have been implemented in a remote plasma configuration, enabling control of the ion energy during plasma-assisted atomic layer deposition (ALD). With both techniques, substrate bias voltages up to −200 V have been reached, which allowed for ion energies up to 272 eV. Besides the bias voltage, the ion energy and the ion flux, also the electron temperature, the electron density, and the optical emission of the plasma have been measured. The effects of substrate biasing during plasma-assisted ALD have been investigated for Al2O3, Co3O4, and TiO2 thin films. The growth per cycle, the mass density, and the crystallinity have been investigated, and it was found that these process and material properties can be tailored using substrate biasing. Additionally, the residual stress in substrates coated with Al2O3 films varied with the substrate bias voltage. The results reported in this article demonstrate that substrate biasing is a promising technique to tailor the material properties of thin films synthesized by plasma-assisted ALD.

Characterization of piezoelectric polymer composites for MEMS devices

Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (k). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low k value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2–2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.

Molecular dynamics simulation based size and rate dependent constitutive model of polystyrene thin films

Rate and size-dependent properties dominate the mechanical behavior of polymeric thin films used in a variety of applications related to generation, transmission and storage of energy. In this paper, molecular dynamics (MD) simulations of polystyrene thin films are used to develop a size and rate dependent finite deformation elastic–plastic constitutive relations. Different modes of deformation are considered in the MD model, and results of simulations are homogenized to yield parametric representations of the constitutive model. The hyperelastic behavior is represented by a modified Ogden type model for films of different thicknesses at different strain rates. The MD simulations suggesting a rate-dependent yield strength is developed for a perfect plasticity model with mitigated size effects. The softer material properties of thin films are found to be the consequence of a large surface layer, which has a low density with high local chain mobility.

Stress Monitoring of Post-processed MEMS Silicon Microbridge Structures Using Raman Spectroscopy

Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated Micro-Electro-Mechanical Systems (MEMS) devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not well controlled during deposition. The residual stress; for example, tends to vary significantly for different deposition methods. Currently, few nondestructive techniques are available to measure residual stress in MEMS devices prior to the final release etch. In this research, micro-Raman spectroscopy is used to measure the residual stresses in polysilicon MEMS microbridge devices. This measurement technique was selected since it is nondestructive, fast, and provides the potential for in-situ stress monitoring. Raman spectroscopy residual stress profiles on unreleased and released MEMS microbridge beams are compared to analytical and FEM models to assess the viability of micro-Raman spectroscopy as an in-situ stress measurement technique. Raman spectroscopy was used during post-processing phosphorus ion implants on unreleased MEMS devices to investigate and monitor residual stress levels at key points during the post-processing sequences. As observed through Raman stress profiles and verified using on-chip test structures, the post-processing implants and accompanying anneals resulted in residual stress relaxation of over 90%.

On the Origin of the Energy Gain in Epitaxial Growth of Molecular Films.

The material properties of organic thin films depend strongly on their order. The different types of epitaxy may complicate the exploration of the large variety of ordered systems and its exploitation in potential electronic devices. In this Letter, we develop a coherent description of the driving force that creates epitaxial systems. We focus on flat-lying organic adsorbates and explain the energy gain in commensurate, point-on-line, and line-on-line epitaxy. We use potential energy maps to visualize our concept and to derive a relation that allows anticipating epitaxial growth from low-energy electron diffraction (LEED) data. A unified description facilitates the identification and interpretation of experimentally observed adsorbate structures, whereas the rationalized expectation from LEED means a considerable speed gain if suitable candidates for organic-organic epitaxy are searched for in a combinatory approach.

P‐168: Room Temperature Deposition of Transparent Conducting Anode for Organic Light‐emitting Diodes

AbstractPoly‐crystalline Indium tin oxide (ITO) film, which shows high optical transmittance and low resistivity, is the essential material to realize OLED device as a transparent anodic electrode. However, this anode material has some problems for flexible displays or OLEDs due to the high manufacturing temperature and imperfect work function alignment in each layer of device. This study examined the anode material properties of ITO, GZO, and IZTO thin films deposited at room temperature using pulsed DC magnetron sputtering along with the device performance of organic emitting diodes (OLEDs). In conclusion, the IZTO film is an alternative material for conventional ITO anodes used in OLEDs and flexible displays.

Mechanical, Electrical, and Optical Properties of (Pr,Ce)O2 Solid Solutions: Kinetic Studies

Praseodymium doped cerium oxide (PCO) shows mixed ionic and electronic conducting (MIEC) characteristics at relatively high pO2 (e.g. air) and enhanced oxygen storage capacity (OSC), of interest for solid oxide fuel cell (SOFC) cathodes and three way catalysts, resulting from the ready reduction of Pr to its trivalent state. This reduction also results in a change of lattice parameter, known as chemical expansion, and changes in optical absorption related to the formation of a Pr impurity band. These properties can be measured as a function of time, yielding oxide ion diffusion and surface exchange coefficients. In this manuscript, the diffusivity and/or surface exchange of PCO is explored using TGA and dilatometry of bulk specimens and HTXRD and optical absorption of thin films. The HTXRD and optical absorption measurements promise the ability to monitor both thermodynamic and kinetic properties of thin film materials exhibiting wide swings in oxygen stoichiometry.

A closer look at polymer annealing

Solvent vapour annealing processes are used to optimize the material properties of thin films of semiconducting polymers used in electronic devices. One such process has now been examined at the molecular level.