Effect Of Thickness Variation Research Articles

Effects of thickness and geometric variations in the oxide gate stack on the nonvolatile memory behaviors of charge-trap memory thin-film transistors

Device designs of charge-trap oxide memory thin-film transistors (CTM-TFTs) were investigated to enhance their nonvolatile memory performances. The first strategy was to optimize the film thicknesses of the tunneling and charge-trap (CT) layers in order to meet requirements of both higher operation speed and longer retention time. While the program speed and memory window were improved for the device with a thinner tunneling layer, a long retention time was obtained only for the device with a tunneling layer thicker than 5nm. The carrier concentration and charge-trap densities were optimized in the 30-nm-thick CT layer. It was observed that 10-nm-thick tunneling, 30-nm-thick CT, and 50-nm-thick blocking layers were the best configuration for our proposed CTM-TFTs, where a memory on/off margin higher than 107 was obtained, and a memory margin of 6.6×103 was retained even after the lapse of 105s. The second strategy was to examine the effects of the geometrical relations between the CT and active layers for the applications of memory elements embedded in circuitries. The CTM-TFTs fabricated without an overlap between the CT layer and the drain electrode showed an enhanced program speed by the reduced parasitic capacitance. The drain-bias disturbance for the memory off-state was effectively suppressed even when a higher read-out drain voltage was applied. Appropriate device design parameters, such as the film thicknesses of each component layer and the geometrical relations between them, can improve the memory performances and expand the application fields of the proposed CTM-TFTs.

Effects of Fabrication Process Variation on Impedance of Neural Probe Microelectrodes

Effects of fabrication process variations on impedance of microelectrodes integrated on a neural probe were examined through equivalent circuit modeling and SPICE simulation. Process variation and the corresponding range were estimated based on experimental data. The modeling results illustrate that the process variation induced by metal etching process was the dominant factor in impedance variation. We also demonstrate that the effect of process variation is frequency dependent. Another process variation that was examined in this work was the thickness variation induced by deposition process. The modeling results indicate that the effect of thickness variation on impedance is negligible. This work provides a means to predict the variations in impedance values of microelectrodes on neural probe due to different process variations.

Post-process wavelength tuning of silicon photonic crystal slow-light waveguides.

Silicon photonic crystal waveguides have enabled a range of technologies, yet their fabrication continues to present challenges. Here, we report on a post-processing method that allows us to tune the operational wavelength of slow-light photonic crystal waveguides in concert with optical characterization, offsetting the effects of hole-radii and slab thickness variations. Our method consist of wet chemical surface oxidation, followed by oxide stripping. Theoretical modelling shows that the changes in optical behavior were predictable, and hence controlled tuning can be achieved by changing the number of processing cycles, where each cycle removes approximately 0.25 nm from all exposed surfaces, producing a blueshift of 1.6±0.1 nm in operating wavelength.

Effect of thickness variation on the physical properties of La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) by pulsed laser deposition

We report the effect of thickness on the structural, morphological, transport and magnetic properties of perovskite oxide La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) single crystal substrate by pulsed laser deposition. We have observed that the transport and magnetic properties of the films depend on the film thickness, surface morphology, and epitaxial strain. The films were characterized by x-ray diffraction that confirms that the films have good crystalline quality, single phase and c-axis orientation. The Atomic force microscopic (AFM) results show that surface roughness and average grain size increase with film thickness. The resistivity measurements show an insulator to metal transition that correlates well with the magnetic ordering temperature. X-ray photoemission spectroscopy measurements suggests that Te ions are in the Te4+ state, while the Mn ions stay in the Mn2+ and Mn3+ valence states.

Thin-Film Piezoelectric Actuators of Nonuniform Thickness and Nonhomogeneous Material Properties for Modulating Actuation Stress

The effects of the thickness variation and the material property variation of thin-film piezoelectric actuators on the actuation shear stress when the actuators are attached to an elastic plate are studied. A system of 2D equations for the flexure and shear of an elastic plate with symmetric piezoelectric actuators on the plate surfaces is derived. The equations are reduced to the case of elementary flexure without shear as a special case. The effects of the actuator thickness variation and material property variation on the actuation stress are examined using the equations obtained. It is shown that the distribution of the actuation stress depends on the thickness and material property variations of the actuators, and that actuators with varying thickness or varying material properties can be used to make modal actuators for producing a particular deformation or exciting a particular vibration mode.

Modelling and validation of Eddy current response to changes in factors affecting pressure tube to calandria tube gap measurement

Procedures employed to non-destructively examine nuclear power plants must undergo inspection qualification to ensure that they meet their respective inspection specification requirements. Modelling is a powerful tool that can be exploited in the inspection qualification process. The gap between pressure tubes (PTs) and calandria tubes (CTs) in CANDU (CANada Deuterium Uranium) fuel channels is periodically measured, as contact can result in localized cooling and potential cracking. This work shows how an analytical model can be employed to characterize the effects of PT wall thickness and resistivity variation on gap measurement, and details its validation against physical experiments.

Snap-Through Buckling Problem of Spherical Shell Structure

This paper presents results of a numerical study on the nonlinear behavior of shells undergoing snap-through instability. This research investigates the problem of snap-through buckling of spherical shells applying nonlinear finite element analysis utilizing ANSYS Program. The shell structure was modeled by axisymmetric thin shell of finite elements. Shells undergoing snap-through buckling meet with significant geometric change of their physical configuration, i.e. enduring large deflections during their deformation process. Therefore snap-through buckling of shells basically is a nonlinear problem. Nonlinear numerical operations need to be applied in their analysis. The problem was solved by a scheme of incremental iterative procedures applying Newton-Raphson method in combination with the known line search as well as the arc- length methods. The effects of thickness and depth variation of the shell is taken care of by considering their geometrical parameter l . The results of this study reveal that spherical shell structures subjected to pressure loading experience snap-through instability for values of l ≥2.15. A form of ‘turn-back’ of the load-displacement curve took place at load levels prior to the achievement of the critical point. This phenomenon was observed for values of l =5.0 to l =7.0.

An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series $RLC$ resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.

On the use of GDQ for vibration characteristic of non-homogeneous orthotropic rectangular plates of bilinearly varying thickness

The generalized differential quadrature (GDQ) method is used to analyze the effect of non-homogeneity, orthotropy, and thickness variation on the vibration characteristics of rectangular plates on the basis of Kirchhoff’s plate theory. The non-homogeneity of the plate material is assumed to arise due to the exponential variations in Young’s moduli, shear modulus, and density of the plate material with the in-plane coordinates. The thickness of the plate is taken as the Cartesian product of linear variations along two concurrent edges of the plate. In the GDQ method, the derivative of a function with respect to a space variable at a given grid point is approximated as a weighted linear sum of the function values at all of the grid points in the computational domain of that variable. Numerical results have been obtained for four different combinations of boundary conditions at the edges, namely: (1) fully clamped; (2) two opposite edges are clamped and the other two are simply supported; (3) two opposite edges are clamped and the other two are free; and (4) two opposite edges are simply supported and the other two are free. The effect of various plate parameters on the natural frequencies is studied for the first three modes of vibration. Three-dimensional mode shapes for a specified plate are plotted. A comparison of results obtained by the present method with those available in the literature is presented.

Effects of thickness variation on properties of ZnO:Al thin films grown by RF magnetron sputtering deposition

Polycrystalline transparent conductive aluminum doped zinc oxide (ZnO:Al) films, have been grown successfully on glass and silicon substrates by RF magnetron sputtering technique at room temperature. The thickness effect on the structural, optical and electrical properties of these samples is then studied. The structural characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The dc electrical resistivity measurement is achieved in dark at room temperature using four-point probes technique. UV–visible spectroscopy was carried out for the optical characterization. The results show that all the deposited films present a crystalline wurtzite structure with a strong preferred (002) orientation. The intrinsic compressive stress was found to decrease with the increase of the film thickness. The electrical resistivity decreases with the increase of the film thickness and the smallest measured value was 8×10−4Ωcm for the 1500nm thick film. The obtained ZnO:Al films, not only have an average transmittance greater than 90% in the visible region, but also have an optical band gap between 3.32 and 3.49eV depending on the film thickness.

Influence of n-doped μc-Si:H back surface field layer with micro growth in crystalline-amorphous silicon heterojunction solar cells.

The back surface field (BSF) plays an important role for the efficiency of the heterojunction intrinsic thin-film (HIT) solar cell. In this paper, the effect of thickness variation in n-type micro crystalline BSF layer was investigated by Raman and spectroscopy ellipsometry. As we increase the crystalline volume fraction (X(c)) from 6% to 59%, the open circuit voltage (V(oc)) increases from 573 to 696 mV with increase in fill factor from 59% to 71%. However, we observed that V(oc) and FF are decreased over 59% X(c) of n-type μc-Si:H BSF layer. It seems that higher X(c) micro layer include lots of defects. The quantum efficiency (QE) measurements were demonstrated on optimized thickness of n-doped micro BSF layer. In the long wavelengths region, the QE slightly increases with increasing the n-type μc-Si:H BSF layer thickness from 10 to 40 nm because of BSF effect, whereas the QE decreases when n-type μc-Si:H BSF layer thickness increases from 40 to 120 nm due to defects in the layer. The performance of heterojunction solar cell device was improved with the optimized thickness on n-doped micro BSF layer the best photo voltage parameters of the device were found to be V(oc) of 696 mV, short-circuit current density of 36.09 mA/cm2 and efficiency of 18.06% at n-doped micro BSF layer thickness of 40 nm.

Effects of thickness and fiber volume fraction variations on strain field inhomogeneity

In this study, variations in thickness and fiber volume fraction are investigated as causes of elastic strain inhomogeneity in composite laminates under an applied transverse load. Standard carbon/epoxy tensile specimens were fabricated from unidirectional pre-impregnated material using two different manufacturing techniques that produced two different levels of surface roughness. Fiber volume fraction variation was computed by analyzing optical micrographs of the samples. During loading and unloading of the samples two-dimensional surface strain fields were measured on the specimen using digital image correlation. It was shown that in both cases the strain in the specimen is not uniform, as is generally assumed. Using finite element simulations the effects of fiber volume fraction variation and thickness variation were modeled individually and in combination. The simulations agree well with the experimental results and suggest that thickness variations are the dominant mechanisms involved in this elastic strain inhomogeneity.

Accurate Leakage/Delay Estimation for FinFET Standard Cells under PVT Variations using the Response Surface Methodology

Among different multi-gate transistors, FinFETs and Trigate FETs have set themselves apart as the most promising candidates for the upcoming 22nm technology node and beyond owing to their superior device performance, lower leakage power consumption, and cost-effective fabrication process. Innovative circuit design and optimization techniques will be required to harness the power of multi-gate transistors, which in turn will depend on accurate leakage and timing characterization of these devices under spatial and environmental variations. Hence, in order to aid circuit designers, we present accurate analytical models using central composite rotatable design (CCRD) based on response surface methodology (RSM) to estimate the leakage current and delay of FinFET standard cells under the effect of variations in gate length ( L G ), fin thickness ( T SI ), gate-oxide thickness (T OX ), gate-workfunction (Φ G ), supply voltage ( V DD ), and temperature ( T ). To the best of our knowledge, this is the first such attempt to develop analytical models for leakage/delay estimation of FinFET logic gates. To derive these models, we employ TCAD device simulations of adjusted 2D device cross sections that have been shown to track TCAD device simulations of 3D device behavior within a 1--3% error range. This drastically reduces the CPU time of our modeling technique (by several orders of magnitude) without much loss in accuracy. We present analytical leakage and delay models for different sizes and logic styles (e.g., shorted-gate (SG) and independent-gate (IG) FinFETs at the 22nm technology node). Both leakage and delay estimates derived from the analytical models are in close agreement with quasi-Monte Carlo (QMC) simulation results (QMC simulations track the accuracy of Monte Carlo simulations, but are several orders of magnitude faster) obtained for different adjusted-2D logic gates with a root mean square error (RMSE) in the 0.23%--5.87% range.

Effect of part thickness variation on the mold filling time in vacuum infusion process

An experimental setup was used to fairly compare mold filling times in vacuum infusion and resin transfer molding, and a 9.5% shorter mold filling time in vacuum infusion was observed than in resin transfer molding. The setup was also used to conduct compaction and permeability characterization experiments, and the results were used in a simplified vacuum infusion model, which is more straightforward to solve than the conventional full and coupled models in the literature. Simulated filling time in vacuum infusion was 31% shorter than in resin transfer molding. The faster resin flow in vacuum infusion is explained by the fact that the thickness in the wetted upstream region increases with time, and thus the effective permeability in that region increases.

Effect of strain rate, thickness, welding on the J–R curve for polyethylene pipe materials

The main purpose of the present paper is to investigate the effect of strain rate, specimen thickness and welding on the fracture toughness for the specimens made from high-density polyethylene (HDPE). The welds at the pipe junction are produced by butt-fusion (BF) welding. Tensile tests specimens are cut longitudinally from the pipe with thickness, T=30mm, and are tested at different crosshead speeds (10–500mm/min), and gauge lengths, G=20mm, to determine the mechanical properties of welded and unwelded specimens. Curved three-point bend (CTPB) fracture specimens are used. The effect of specimen thickness variation for welded and unwelded specimens is studied at room temperature, (Ta=23°C), and at different crosshead speeds, VC.H, (10–500mm/min). The study reveals that the crosshead speed has a significant effect on the fracture toughness of both welded and unwelded specimens. The fracture toughness, JIC, is greater for unwelded than welded specimen.

Effects of cell size and cell wall thickness variations on the stiffness of closed-cell foams

This paper concerns with the micromechanical modelling of closed-cell polymeric foams (M130) using Laguerre tessellation models incorporated with realistic foam cell size and cell wall thickness distributions. The cell size and cell wall thickness distributions of the foam were measured from microscope images. The Young’s modulus of cell wall material of the foam was characterised by nanoindentation tests. It is found that when the cell size and cell wall thickness are assumed to be uniform in the models, the Kelvin, Weaire–Phelan and Laguerre models overpredict the stiffness of the foam. However, the Young’s modulus and shear modulus predicted by the Laguerre models incorporating measured foam cell size and cell wall thickness distributions agree well with the experimental data. This emphasizes the fact that the integration of realistic cell wall and cell size variations is vital for foam modelling. Subsequently the effects of cell size and cell wall thickness variations on the stiffness of closed-cell foams were investigated using Laguerre models. It is found that the Young’s modulus and shear modulus decrease with increasing cell size and cell wall thickness variations. The degree of stiffness variation of closed-cell foams resulting from the cell size dispersion and cell wall thickness dispersion are comparable. There is little interaction between the cell size variation and cell wall thickness variation as far as their effects on foam moduli are concerned. Based on the simulation results, expressions incorporating cell size and cell wall thickness variations were formulated for predicting the stiffness of closed-cell foams. Lastly, a simple spring system model was proposed to explain the effects of cell size and cell wall thickness variations on the stiffness of cellular structures.

Directional flank spreading at Mount Cameroon volcano: Evidence from analogue modeling

AbstractMount Cameroon is characterized by an elongated summit plateau, steep flanks, and topographic terraces around its base. Although some of these features can be accounted for by intrusion‐induced deformation, we here focus on the contribution of edifice‐scale gravitational spreading in the structure of Mount Cameroon. We review the existing geological and geophysical data and morphostructural features of Mount Cameroon and surrounding sedimentary basins. Volcanic ridge gravitational spreading is then simulated by scaled analogue models on which fault formation is recorded using digital image correlation. Three sets of models are presented (i) models recorded in cross section (Type I), (ii) models recorded from above with a uniform (Type IIa), and (iii) nonuniform ductile layer (Type IIb). Type I models illustrate the formation of faults accommodating summit subsidence and lower flank spreading. Type IIa models favor displacement perpendicular to the long axis, with formation of a summit graben and basal folds, but fail to reproduce the steep flanks. Type IIb models investigate the effect of spatial variations in sediment thickness and/or properties consistent with geological evidence. Directional spreading of the volcano's central part perpendicular to the long axis is accounted for by a sediment layer with restricted lateral extent and increasing thickness away from the volcano axis. The later model closely reproduces key features observed at Mount Cameroon: steep upper flanks are accounted for by enhanced lateral spreading of the lower flanks relative to the summit. The relevance of these findings for understanding flank instabilities at large oceanic volcanoes is finally highlighted.

Modeling two sequential coaxial phases of shortening in a foreland thrust belt

Analog sandbox models are used to simulate two sequential coaxial phases of shortening in a foreland thrust belt. A sufficient hiatus is considered so that erosion and sedimentation after the first phase create an angular unconformity that is subsequently deformed. The effect of variation in thickness of post-erosional sediment package and presence of a weak layer at the unconformity level are analyzed. During the second phase, some first phase thrusts are reactivated and new thrusts are also initiated. Thrust reactivation results in a structure spacing that is smaller than the expected spacing for a thicker sediment package. Reactivation of pre-existing structures prevents the weak layer from acting as an intermediate décollement. An increase in thickness ratio tends to weaken reactivation of pre-existing thrusts. Model results also show that total displacement along individual reactivated thrusts generally increases downwards across the unconformity, which could be used to distinguish thrust reactivation in the field. Two regional examples from the northern Eastern Cordillera in Colombia and from the Variscan frontal zone in Western Europe, respectively, where multiphase coaxial shortening occurred, are compared with model results. Both natural cases show features, such as partially eroded first-generation folds and truncated first-generation thrusts that are indicators for two sequential phases of deformation as observed in the models.

Evaluating choroidal thickness in diabetic retinopathy.

Dear editor We read with interest the article by Unsal et al1 and congratulate them on their work assessing choroidal thickness in patients with diabetic retinopathy. We will like to highlight some factors of relevance. Unsal et al state that their measurement of the choroid was from the outer part of the retinal pigment epithelial layer to the choroidal scleral junction.1 However, their Figure 2 seems to draw the upper border of the choroid at various locations (external limiting membrane, inner/outer segment junction, top of the retinal pigment epithelium).1 An illustrative diagram (Figure 1) for measuring choroidal thickness can be seen in the study reported by Copete et al.2 Recent studies of the thickness of the retinal pigment epithelium–Bruch’s membrane complex in normal individuals ranged from 17.5 μm to 28.2 μm.3 Hence, measurement of choroidal thickness has to be drawn correctly and consistently at the same location (outer part of the retinal pigment epithelium) to minimize potential inaccuracies. It is also important to consider the effects of diurnal variation in choroid thickness on their reported results. Previous studies have concluded that the choroid is found to be thickest at night (11 pm) and thinnest at noon (12 pm).4 The difference between the thickest and thinnest choroidal thickness due to diurnal variation can be up to 67 μm.5 Hence, the study could have standardized the timings of the optical coherence tomography scans for both controls and diabetic subjects to minimize any potential differences in choroidal thickness caused by diurnal variation. The results reported by Unsal et al are consistent with those of other studies showing no significant change in choroidal thickness in subjects with nonproliferative diabetic retinopathy and decreased choroidal thickness in subjects with proliferative diabetic retinopathy or diabetic macular edema.6,7 In addition, a recent study by Adhi et al characterized the morphological features of the choroid, ie, the Haller, Sattler, and choriocapillary layers. Their results showed significant thinning of the combined thickness of the Sattler and choriocapillary layers in eyes with proliferative diabetic retinopathy or diabetic macular edema when compared with controls.7 It will be interesting to note if similar results were seen in the Unsal et al study too, since both studies used spectral domain optical coherence tomography. In conclusion, Unsal et al has provided very useful information on choroidal thickness in diabetics. However, measurements of choroid thickness have to be correctly drawn and consideration of diurnal variation is required to improve the accuracy of the results.

Limit Load Determination and Material Characterization of Cracked Polyethylene Miter Pipe Bends1

The quality of Natural Gas Piping Systems (NGPS), must be ensured against manufacturing defects. The main purpose of the present paper is to investigate the effect of loading mode and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB), under different crack depths a/W = 0–0.4 at a crosshead speed 500 mm/min. The geometry of cracked and uncracked multi-miter pipe bends are pipe bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in NGPS. The welds at the miter pipe junction are produced by butt-fusion welding. For all loading modes the limit load is obtained by the tangent intersection (TI) method from the load–deflection curves produced by the specially designed and constructed testing machine at the laboratory5. Tensile tests are conducted on specimens longitudinally extruded from the pipe with thickness, T = 10, 30 mm, at different crosshead speeds (5–500 mm/min), and different gauge lengths (G = 20, 25, and 50 mm) to determine the mechanical properties of welded and unwelded specimens. The fracture toughness is determined on the basis of elastic plastic fracture mechanics (EPFM). Curved three-point bend specimens (CTPB), are used. All specimens are provided with artificial precrack at the crack tip, a/W = 0.5. The effect of specimen thickness variation (B = 10, 15, 22.5, 30, 37.5, and 45 mm) for welded and unwelded specimens is studied at room temperature (Ta = 23 °C) and at different crosshead speeds, VC.H, ranging from 5 to 500 mm/min. The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of MPB for both in-plane, and out-of-plane bending moment. In case of combined load (out-of-plane and in-plane opening; mode), higher load angles lead to an increase in the limit load. The highest limit load value occurs at a loading angle, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode), the limit load decreases with increasing load angles. At a load angle ϕ = 30 deg, the higher limit load value occurred in both cases. For combined load opening case, higher values of limit load are obtained. The crosshead speed has a significant effect on the mechanical behavior of both welded and unwelded specimens. The fracture toughness, JIC, is greater for unwelded than welded specimen.