Increasing Substrate Thickness Research Articles

Effects of Processing Parameters on the Temperature Field of Melts in Aluminothermic Reaction to Prepare Bulk Nanocrystalline Fe<sub>3</sub>Al

Making use of the finite element analysis software ANSYS, we calculated the effects of different processing parameters on temperature, cooling rate and superheating time of Fe3Al melt in aluminothermic reaction to prepare bulk Nanocrystalline Fe3Al. The results showed that, with the increase of substrate thickness and reduction of reactant’s quantity, cooling rate of the Fe3Al melt at the initial cooling stage became larger, while the melt purification became worse. With the increase of argon pressure, the Fe3Al melt cooled a little quicker. The cooling rate of melt cooled by glass substrate was lower than that of the melt cooled by 1045 steel and Cu substrate, while the melt purification became better. With the increase of Al2O3, Fe3Al diluents content, the cooling rate at the initial cooling stage became lower, and the melt purification became worse. The experiment verified that the calculated results were in good coincident with the experimental results.

On the Reflection Characteristics of a Reflectarray Element with Low-Loss and High-Loss Substrates

This paper revisits the loss phenomenon (particularly, the dielectric loss) for a microstrip patch in reflectarray mode, and discusses the reflection characteristics (magnitude and phase) for a reflectarray element with low- and high-loss substrates. First, the dielectric losses that occur in a lossy slab backed by a perfect electric conductor are both analytically and numerically investigated. Using similar numerical analysis, the reflectarray element (a patch on top of a slab backed by a conductor) is characterized, based on dielectric losses and reflection behavior. It is observed that for low-loss substrates, the dielectric loss decreases with increasing substrate thickness (as previously suggested in the literature). More importantly, for high-loss substrates, the dielectric loss no longer follows the expected trend (decreasing loss with increasing substrate thickness). The dielectric loss becomes a complex phenomenon, involving the dielectric loss tangent and substrate thickness. It is therefore noted that it is important to recognize the well-behaved and misbehaved phase-swing region for high-loss substrates for a reflectarray element. A simple circuit-model representation is provided for the reflectarray element. The anomalous phase behavior observed for high-loss substrates is explained using pole-zero analysis. Waveguide measurements are performed to quantify these reflectarray losses for low- and high-loss substrates. Finally, the loss mechanisms in a patch reflectarray (scattering mode) are compared to a patch antenna (radiation mode), using parameters such as reflection power and radiation efficiency, and similar loss mechanisms for both structures are apparent.

Effects of film and substrate dimensions on warpage of film insert molded parts

AbstractThree‐dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in‐mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in‐mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Flexural deformation and bending mode of magnetoelectric nanobilayer

A model is discussed for magnetoelectric (ME) coupling in a nanobilayer of ferromagnetic and piezoelectric phases on a substrate. The theory is applied to a specific case, nickel ferrite and lead zirconate titanate bilayer on strontium titanate substrate. Both low-frequency coupling and ME interactions at frequencies corresponding to bending oscillations have been considered. The influence of lattice mismatch between the substrate and piezoelectric and piezomagnetic layers on material parameters has been estimated using the Landau–Ginsburg–Devonshire phenomenological thermodynamic theory. At low frequencies, the model predicts a maximum in the ME coupling strength when the substrate is of the same thickness as the bilayer. The ME voltage coefficient drops with further increase in substrate thickness due to clamping effects. The bending oscillations in nanobilayers are expected to occur at ultralow frequencies (<5 Hz) compared to longitudinal acoustic modes at 100–200 kHz for bilayers of nominal dimensions. The mode frequency shows an increase with increasing substrate thickness, and the resonance value of the ME coefficient is predicted to show a minimum when the substrate-to-bilayer thickness ratio is 0.3.

Modelling of magneto-acoustic resonance in ferrite–piezoelectric bilayers

A model is discussed for magnetoelectric (ME) effects in a single-crystal ferrite–piezoelectric bilayer on a substrate. The specific focus is on coupling at magneto-acoustic resonance (MAR) at the coincidence of ferromagnetic resonance in the ferrite and thickness modes of the electromechanical resonance in the piezoelectric. The clamping effect of the substrate has been considered in determining the ME voltage coefficient and applied to a model system of a bilayer of lead zirconate titanate (PZT) and yttrium iron garnet (YIG) on a gadolinium gallium garnet substrate. The theory predicts a giant ME effect at MAR due to interaction and transfer of energy between elastic modes and the uniform precession spin-wave mode. It is shown that the ME coupling strength decreases with increasing substrate thickness. Estimates for YIG–PZT for nominal film parameters predict MAR at 5 GHz and ME coefficients on the order of 5–70 V cm−1 Oe−1. The phenomenon is of importance for the realization of multifunctional ME sensors and transducers operating at microwave frequencies.

Internal strains and crystal structure of the layers in AlGaN/GaN heterostructures grown on a sapphire substrate

In this paper, we investigate the structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses using high-resolution x-ray diffraction and Raman scattering methods. We discuss the microscopic nature of spatial-inhomogeneous deformations and dislocation density in the structures. Microdeformations within mosaic blocks and the sizes of regions of coherent diffraction are determined. We reveal a gradient depth distribution of deformations in the mosaic structure of nitride layers, as well as at the interface regions of the sapphire substrate on the microscale level using confocal micro-Raman spectroscopy. We determine that an increase in substrate thickness leads to a reduction in dislocation density in the layers and an increase in the elastic deformations. The features of the block structure of nitrides layers are shown to have a significant influence on their elastic properties.

Band gaps of lamb waves in one- dimensional piezoelectric composite plates: effect of substrate and boundary conditions

We theoretically study the band structures of Lamb waves in one-dimensional phononic crystal plates consisting of piezoelectric ceramics placed periodically in epoxy with epoxy or piezoelectric ceramic substrate by the virtual plane wave expansion method. The dependences of the widths and starting frequencies of first band gaps (FBG) on the substrate's thickness, the filling fraction, and the lattice spacing are calculated for different materials of substrate under different electric boundary conditions, i.e., short circuit (SC) and open circuit (OC). The FBG width decreases gradually as the substrate's thickness increases and the FBG starting frequency increases progressively as the thickness increases on the whole. The FBG widths and starting frequencies with SC are always larger than with OC. Our research shows that it is possible to control the width and starting frequency of the FBG in the engineering according to need by choosing suitable values of the substrate's thickness, the filling fraction, and the lattice spacing.

Enhancement of magnetoelectric coupling in functionally graded ferroelectric and ferromagnetic bilayers

A model is presented for magnetoelectric (ME) effects in a functionally graded ferroelectric-ferromagnetic bilayer. A linear grading of the piezoelectric coefficient and permittivity in the ferroelectric and a similar grading of piezomagnetic coefficient in the ferromagnet are assumed. The ME coupling at low frequencies and at mechanical resonance due to bending oscillations have been estimated and applied to the specific case of bilayers of nickel zinc ferrite and lead zirconate titanate with the grading axis perpendicular to the sample plane. Both free-standing bilayers and bilayer on a substrate have been considered. The thickness dependence of piezomagnetic and piezoelectric coefficients leads to an additional flexural strain and the theory predicts an enhancement in the strength of ME coupling compared to homogeneous compositions. The enhancement in the case of a free-standing bilayer is on the order of 50% at low frequencies and at electromechanical resonance (EMR). For the case of a bilayer on a substrate, the low-frequency ME coefficient is maximum when the substrate and the bilayer are of equal thickness. The coupling weakens with increasing substrate thickness. With increasing substrate thickness, the ME coefficient at EMR is expected to show an initial rapid decrease, followed by an increase and a broad maximum. The resonance frequency is predicted to show a linear increase with increasing substrate thickness.

Effect of sapphire-substrate thickness on the curvature of thick GaN films grown by hydride vapor phase epitaxy

The effect of sapphire-substrate thickness on the curvature and stress in thick hydride vapor phase epitaxial GaN films was studied by high-resolution x-ray diffraction at variable temperatures. The curvature was found to have the maximum value for comparable thicknesses of the film and the substrate, while the stress at the film surface decreases with increasing film thickness and increases with increasing substrate thickness, which is in very good agreement with the simulation results. The curvature at the growth temperature was found to be strongly influenced by the value of the intrinsic tensile strain, which is determined by the film/substrate thickness ratio.

A parametric study of laser induced thin film spallation

We report parametric studies of elastic wave generation by a pulsed laser and associated spalling of thin surface films by the corresponding high stresses. Two different substrate materials, single crystal Si (100) and fused silica, are considered. Spallation behavior of Al thin films is investigated as a function of substrate thickness, film thickness, laser energy, and various parameters governing the source. Surface displacement due to the stress wave is measured by Michaelson interferometry and used to infer the stresses on the film interface. Consistent with previous studies, the maximum stress in the substrate and at the film/substrate interface increases with increasing laser fluence. For many of the conditions tested, the substrate stress is large enough to damage the Si. Moreover, the maximum interface stress is found to increase with increasing film thickness, but decrease with increasing substrate thickness due to geometric attenuation. Of particular significance is the development of a decompression shock in the fused sillica substrates, which results in very high tensile stresses at the interface. This shock enhances the failure of thin film interfaces, especially in thicker samples.

Influence of the silicon substrate thickness on the response of thin film pyroelectric detectors

The effect of silicon substrate thickness on the performance of thin film PZT pyroelectric detectors is theoretically and experimentally investigated. As the silicon substrate thickness increases, the pyroelectric current responsivity drastically decreases. The current responsivity of a pyroelectric thin film detector with no silicon substrate is about two orders higher than that of a similar detector with 450 μm thick silicon substrate. To verify the theoretical analysis, micromachined Pb(Zr 0.3Ti 0.7)O 3 (PZT30/70) thin film pyroelectric detectors with different silicon substrate thickness are fabricated and characterised. The experimental results agree well with the theoretical analysis.

磁性材料 有機可塑基板上に堆積させたＣｏ含有酸化鉄薄膜

Co-containing ferrite thin films were successfully deposited on organic flexible substrates by the reactive sputtering method using-an electron cyclotron resonance microwave plasma at a temperature lower than 150°C. The ferrite thin films had an amorphous-like structure, perpendicular magnetic anisotropy and high perpendicular coercivity of about 170kA/m. The perpendicular coercivity increased with increasing substrate thickness. Inserting SiO2 underlayer between organic flexible substrate and ferrite thin films enhanced the perpendicular coercivity.

Flip-Chip BGA Design to Avert Die Cracking

Fracture mechanics is applied to flip-chip BGA design to avert die cracking from its backside. Fracture mechanics is integrated with the finite element analysis (FEA) and design of virtual experiments (virtual DOE) to analyze the effects of location and length of a die crack, and the effects of some key material properties and package dimensions on die cracking of flip-chip BGA. The stress intensity factor (SIF) and the strain energy release rate (ERR) are taken as the design indices. The FEA is used to calculate the fracture parameters, and the virtual DOE is employed to determine contributions of each design parameter to die cracking and their acceptable design windows. The investigation consists of two parts. The first is relations of length and location of a die crack with the fracture parameters. The relations are established through sweeping along crack length for a crack located at the center of the die backside, and along the die backside surface. The critical crack length is determined for a specific design. The second is the virtual DOE based on fracture mechanics. Several key material properties and package dimensions are used as the design inputs. The main effects and interactions of these design parameters to die cracking are calculated. Based on it, some generic design guidelines are made. It is concluded that substrate and die thicknesses are the two most significant factors to die cracking of flip-chip BGA. Increasing substrate thickness and reducing die thickness are the most effective measures to design a package with high resistance to die cracking.

Transient non-Darcian forced convection flow in a pipe partially filled with a porous material

In this paper, a numerical simulation is presented for the transient forced convection in the developing region of a cylindrical channel partially filled with a porous substrate. The porous substrate is attached to the inner side of the cylinder wall, which is exposed to a sudden change in temperature. The flow within the porous domain is modeled by the Brinkman-Forchheimer-extended Darcy model. The effects of several parameters on the hydrodynamic and thermal characteristics of the present problem are studied. These parameters include the porous substrate thickness, Darcy number and Forchheimer coefficient. Results of the current model show that the existence of the porous substrate may improve the Nusselt number at the fully developed region by a factor of 8. However, there is an optimum thickness of the porous substrate beyond which no significant improvement in the Nusselt number is achieved. Also, in the present work, the macroscopic inertial term in the porous domain momentum equation is included due to its significant effect. It is found that the steady state time increases as the substrate thickness increases up to a certain limit and then the steady state time decreases upon further increase in the substrate thickness. Also, increasing the Forchheimer coefficient and decreasing the Darcy number increase the steady state time.

YBa2Cu3O7−δ infrared bolometers: Temperature-dependent responsivity and deviations from the dR/dT curve

The phase and amplitude of the response to infrared radiation of superconducting bolometers was investigated. The detectors were fabricated with 120–550 nm Y1Ba2Cu3O7−δ films on MgO, SrTiO3, and LaAlO3 substrates. A model for the response is developed and compared to the experimental results. The response versus frequency of the samples shows bolometric behavior, in agreement with the measured time dependence of the signals at low frequencies. Different techniques were developed to measure the key parameter in the response of the bolometers, G, the thermal conductance. Several anomalies were observed in the study that provide insight into heat conduction in these devices. The dc or low modulation frequency thermal conductance, G(0), of the samples is found to be limited by the substrate/cold-head thermal boundary resistance. It was also found to decrease with increasing substrate thickness, but still limited by the substrate/cold-head interface. This thickness dependence of G(0) is attributed to scattering of phonons within the substrate, that changes their transmission rate through the substrate/cold-head interface. The results from simultaneous measurements of the IR response and dR/dT (using R versus T) at low modulation frequencies (20 Hz) show that the magnitude of the response differs by up to 30% from the dR/dT curve. The discrepancy is found to be frequency dependent, increasing with decreasing modulation frequency. This can be treated by use of temperature-dependent thermal constants (G and the heat capacity, C) in the model for the bolometric response. The discrepancy is also observed to be dependent on the superconducting transition, which suggests a possible correlation between the heat conduction through the substrate (and its interfaces) and the absorption mechanism in the superconductor. The phase of the response versus temperature shows an abrupt change at the transition. This is evidence for a change in thermal constants in the bolometer as it goes through the superconducting transition, affecting both the phase and magnitude of the response. Joule heating at even high bias currents has little effect on the response (and its deviation from the dR/dT curve) in our samples, and the effect of noise on the response is significant only at very low bias currents.

Analysis of Rubbed Polyimide Films by Polarized Infrared Spectroscopy

Abstract Polarized infrared spectroscopy was applied to the analysis of rubbed polyimide films. N2 purge of a sample chamber and increased substrate thickness enhanced the detection sensitivity. Dichroic differences were measured for the rubbed polyimide films at varied translating speed of the rubbing roller and at varied substrate temperature. The results suggest that the orientation of the polyimide was enhanced by increased polyimide surface temperature brought about by the heat of friction or the external heat. Moreover, a correlation between the LC alignment and the orientation of the polyimide chains was revealed by the analysis of the dichroic difference of the rubbed polyimide films immersed in organic solvents and the LC alignment on the films.

Simulation of the effect of creep on stress fields during vacuum plasma spraying onto titanium substrates

Boron carbide has been deposited by vacuum plasma spraying onto thin substrates of Ti−6wt.%Al−4wt.%V alloy. Substrate/deposit curvature histories have been measured by analysis of a series of video images. These results, together with thermal histories, have been compared with predictions obtained from a numerical process model describing the development of residual stresses. It is shown that, when using the standard form of the model, a discrepancy arises between predicted and observed curvature histories. This is attributed to the effect of creep in the substrate under the influence of the residual stresses. A modification to the model accounting for the effect of creep allowed good agreement to be obtained between theory and experiment. It is shown that creep effects can be significant with titanium, although they become less significant as the substrate thickness increases. In general, the effect of creep is to lower the stress levels during spraying, although the final residual stresses can actually be higher than would be the case in the absence of creep.

Microstrip dipoles on electrically thick substrates

Certain basic radiation properties of microstrip dipoles on electrically thick substrates are investigated, and a comparison is made with the case of dipoles printed on a dielectric half-space. It is concluded that the microstrip dipole radiation properties become sensitive to substrate loss as the substrate thickness increases, with the half-space properties obtained for an adequate amount of loss. Asymptotic formulas for radiated power and efficiency are given for both the thick substrate and half-space problems, showing the behavior with increasing dielectric constant. The method of moments is used to extend the analysis to center-fed strip dipoles, and a method of improving both the efficiency and gain of a printed antenna by using a superstrate layer is discussed.

Study of planar-helix slow-Wave structure for application to travelling-wave tubes

A planar helix, constituted of a pair of unidirectionally conducting screens conducting in different directions, is suggested as a slow-wave structure for application in a travelling-wave tube (TWT). Circuit parameters, such as interaction impedance and space-charge parameter, are derived for the suggested planar-helix TWT. Computed results for the planar helix indicate a performance comparable with that of its circular helix counterpart. Also, the change in interaction impedance and the dispersion characteristics of the planar helix, are considered in the presence of dielectric substrates and a metal shield. Results are obtained for a few different possible configurations of the planar helix on dielectric substrates with or without a metal shield. The phase velocity and interaction impedance reduce, both as the substrate thickness increases and as the metal shields are brought closer to the planar helix. However, the resulting degradation in the characteristics of the structure with commonly used substrate materials, for example alumina and beryllia, is less severe than in the case of the circular helix.

Studies of enzyme systems at a solid-liquid interface. I. The system chymotrypsin-serum albumin

The proteolytic activity of chymotrypsin at a liquid-solid interface has been studied. Bovine serum albumin, as substrate, constituted the solid phase. After adding enzyme to the liquid phase it is adsorbed onto the substrate or removes substrate from the solid phase or both reactions occur simultaneously, depending on buffer concentration and pH. The Arrhenius coefficient of the reaction is 8–9 kcal./mole between 10 and 40 °C. The reaction velocity increases with increasing substrate thickness.