Small Sidewall Research Articles

High-Precision and Low-Damage Microchannel Construction via Magnetically Assisted Laser-Induced Plasma Ablation for Micro-Thermoelectric Devices.

Thermoelectric devices are developing toward high density and miniaturization with a large filling factor for new applications in chip thermal management and microenergy harvesting. Pulsed laser etching has become one of the most effective tools for the patterning construction of highly integrated micro-thermoelectric devices. However, the laser spot size and Gaussian laser energy distribution restrict the processing size and accuracy of microchannels. Moreover, the rapid temperature rise caused by laser energy injection would also raise serious problems such as element volatilization, cracks, and recast layers. Herein, a liquid-assisted nanosecond laser ablation technology with magnetically controlled plasma is proposed to etch microchannels on thermoelectric thick films. By evaluating the size and shape of microchannels, we theoretically investigated the influence of cavitation bubbles on the laser optical path and surface roughness in laser-induced plasma ablation. In addition, the energy criterion for high-precision ablation is revealed, and the effect of magnetic field on ablation threshold is explained by magnetic constraint on energy and kinetic properties of the laser-induced charged plasma plume. Finally, the high-precision and low-damage microchannels are achieved on Bi2Te3 thermoelectric thick films with a minimum line width of 19.12 μm and a small sidewall inclination degree of tan θ = 0.085. This work provides a promising alternative for the fabrication of high-density three-dimensional (3D) patterning in semiconductor microdevices.

Sidewall controlling large-scale flow structure and reversal in turbulent Rayleigh-Bénard convection

Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling.

Sidewall Slope Control of InP Via Holes for 3D Integration.

This is the first demonstration of sidewall slope control of InP via holes with an etch depth of more than 10 μm for 3D integration. The process for the InP via holes utilizes a common SiO2 layer as an InP etch mask and conventional inductively coupled plasma (ICP) etcher operated at room temperature and simple gas mixtures of Cl2/Ar for InP dry etch. Sidewall slope of InP via holes is controlled within the range of 80 to 90 degrees by changing the ICP power in the ICP etcher and adopting a dry-etched SiO2 layer with a sidewall slope of 70 degrees. Furthermore, the sidewall slope control of the InP via holes in a wide range of 36 to 69 degrees is possible by changing the RF power in the etcher and introducing a wet-etched SiO2 layer with a small sidewall slope of 2 degrees; this wide slope control is due to the change of InP-to-SiO2 selectivity with RF power.

Natural Convection in Tilted Rectangular Cavity subjected to TA

The present study investigates the spectral analysis for natural convection in a tilted rectangular cavity, lled with high Prandtl oil ”Pr =880” by the code CFD. A constant vertical temperature gradient has been performed by subjecting the horizontal walls to constant temperatures Th and Tc; respectively. Other walls are adiabatic except the left small sidewall is differentially heating with temperature TA creating the horizontal temperature gradient. The results are presented for different values of lateral heating and inclination angle. The spectral analysis is used to identify and show effects on the original oscillation of the natural convection by the various investigated parameters (TA and θ).

A numerical study of the effects of bottom and sidewall stiffeners on sloshing behavior considering roll resonant motion

In the present study, aiming to provide practical guidance for the structural design, the effects of the small bottom and sidewall stiffeners on sloshing loads in shallow and intermediate liquid conditions are investigated numerically. The interaction between the highly nonlinear free surface flow and a large number of small stiffeners is modeled based on the Moving Particle Semi-implicit method. 2D models of a rectangular clean tank and tanks with small sidewalls or bottom stiffeners are considered. For filling ratios ranging from 5% to 20%, harmonic angular motions with periods around the analytical sloshing resonant ones are applied. Simulation snapshots and computed pressure time series, pressure variation, wave run-up, maximum fluid velocity, and kinetic energy were provided to clarify the complex interaction between the small baffles and the shallow free surface flow. As a result, except for the tanks with bottom stiffeners in shallow liquid conditions, in which the response under actual resonant frequency should be considered, the response computed using the clean tank excited by its resonant period can be adopted as a conservative estimation for the sloshing loads of actual tanks with small stiffeners.

Effect of U-shape trench etching process on electrical properties of GaN vertical trench metal-oxide-semiconductor field-effect transistor

As reported by several market analysts, GaN-based power devices show great potential applications in the low and medium voltage range ( < 900 V). For high voltage ( > 1200 V), including ship transportation and power grid, the future applications of GaN highly depend on the development of vertical devices based on GaN substrates. Several vertical devices have been reported, such as current aperture vertical electron transistors (CAVETs), U-shape trench metal-oxide-semiconductor field-effect transistors (UMOSFETs), and fin power transistors. And the UMOSFETs show potential advantages due to greater simplicity in material epitaxy and fabrication process. In the fabrication of UMOSFETs, the U-shape trench dry etching is the most critical process. The GaN sidewalls after dry etching directly affect the interface state characteristics in the MOS structure and the channel electron transport. In this work, etching optimization including etching radio-frequency (RF) power and etching mask is investigated and process-dependent electrical characteristics of GaN UMOSFETs are also studied. The appropriate decrease of RF power ensuring the steep sidewalls can effectively improve the channel electron mobility from 35.7 cm<sup>2</sup>/(V·s) to 48.1 cm<sup>2</sup>/(V·s) and consequently increase the ON-state current and reduce the ON-state resistance. Larger etching damage to the p-GaN sidewall caused by higher RF power leads the scattering effects to increase and the mobility of the channel carriers to decrease. The interface state density at the channel can be extracted by the subthreshold swing. The interface state density decreases to 1.90 × 10<sup>12</sup> cm<sup>–</sup><sup>2</sup>·eV<sup>–1</sup> when the RF power is regulated to 50 W, which is only half of the interface state density when RF power is 135 W. Similar breakdown voltages (350－380 V) are measured for these devices with varying RF power, which are governed by gate early breakdown. Positive valence band offset is formed in the SiO<sub>2</sub>/GaN MOS structure and the early breakdown occurs due to the holes accumulating at the SiO<sub>2</sub>/GaN interface. The etching uniformity at the bottom of U-shape trench can be improved by using the SiO<sub>2</sub> hard masks instead of photoresist masks. Sub-trenches at both ends of the trench bottom are observed in the device with photoresist masks, leading the carrier scattering to increase and ON-state current to decrease. Besides, the interface state density decreases from 3.42 × 10<sup>12</sup> cm<sup>–2</sup>·eV<sup>–1</sup> to 2.46 × 10<sup>12</sup> cm<sup>–2</sup>·eV<sup>–1</sup> with a SiO<sub>2</sub> hard mask layer used. Compared with 1.6 μm photoresist mask, the thinner SiO<sub>2</sub> mask with a thickness of 500 nm has a small sidewall area, which weakens the high-energy ion reflection in the inductively coupled plasma system. Consequently, the over-etching at the bottom ends of the trench is improved significantly and therefore the fabricated GaN UMOSFET has higher channel mobility and a lower interface state density.

Formation of SEM Images in the Secondary Electron Mode. 2. Structures with a Trapezoidal Profile and Small Side-Wall Inclinations

The formation of images of silicon microstructures in a scanning electron microscope, operating in the modes of collecting secondary slow electrons (SSEs) and backscattered electrons (BSEs), is studied. Grooves in electronic silicon with a trapezoidal profile and small angles of inclination of the side walls with a nominal width of 1 µm and a depth of 300 nm are used as the object of study. It is shown that among four mechanisms for the formation of BSE images, currently known, only two mechanisms contribute to the formation of SSE images. They take into account the formation of an image by the primary electron probe and by multiply scattered primary and secondary electrons coming from the surface of a solid. Multiply scattered secondary electrons moving in the direction of probe electron motion, which make the main contribution to the formation of the BSE image, do not contribute to the formation of the SSE image.

Groyne spacing role on the effective control of wall shear stress in open-channel flow

ABSTRACTThe objective of an effective configuration for a series of groynes in an open channel is the attainment of large bed shear stress in the main channel for channel deepening and small sidewall shear stress in the groyne fields for bank protection with the lowest cost, i.e. with the largest spacing between groynes. A Reynolds-averaged Navier–Strokes, finite-volume, numerical model was used and it was validated against experimental data for the case of a single groyne. For series of groynes with uniform spacing between them, the most effective configuration was the one with spacing equal to six groyne lengths. For the range of parameters considered, a substantial improvement of the effectiveness was achieved by implementing a novel non-uniform configuration where the spacing between groynes was reduced to one and a half groyne lengths in the first four groyne fields, and remained equal to six groyne lengths in the subsequent ones.

A method for quantifying in plane permeability of porous thin films

The in-plane permeability of porous thin films is an important fluid mechanical property that determines wicking and pressure-driven flow behavior in such materials. This property has so far been challenging to measure directly due to the small sidewall cross-sectional area of thin films available for flow. In this work, we propose and experimentally demonstrate a novel technique for directly measuring in-plane permeability of porous thin films of arbitrary thicknesses, in situ, using a manifold pressed to the top surface of the film. We both measure and simulate the influence of the two dimensional flow field produced in a film by the manifold and extract the permeability from measurements of pressure drop at fixed flow rates. Permeability values measured using the technique for a periodic array of channels are comparable to theoretical predictions. We also determine in-plane permeability of arrays of pillars and electrodeposited porous copper films. This technique is a robust tool to characterize permeability of thin films of arbitrary thicknesses on a variety of substrates. In Supplementary material, we provide a solid model, which is useful in three-dimensional printer reproductions of our device.

Aneurysm outflow angle at MRA as discriminant for accurate diagnosis and differentiation between small sidewall cerebral aneurysms and infundibula

ObjectiveTo evaluate whether the aneurysm outflow angle (OA) at MR angiography (MRA) might serve as discriminant for accurate diagnosis of, and differentiation between, small sidewall cerebral aneurysms (SCAs) and infundibula.MethodsBetween...

Magnetic pulse forming of AZ31 magnesium alloy shell by uniform pressure coil at room temperature

The magnetic pulse forming process of AZ31 magnesium alloy shell using uniform pressure coil at room temperature was investigated. ANSYS FEA software was used to analyze the distribution of magnetic flux density of the uniform pressure coil and magnetic pressure for loading on the AZ31 sheet. The characteristic of forming process of AZ31 shell was revealed, and magnetic pulse forming process of AZ31 shell and effect of Al alloy sheet with different thickness were presented by experiments. Due to impact between sheet and die, the rebound profiles on the bottom of deformed sheets were observed. In order to remove the rebound profile, AA5052 sheets were employed to drive the deformed AZ31 sheets. The section contour of R = 30 mm (R means bottom radius of die) shell deformed by 0.5-mm thickness of driver sheet driving once and R = 15 mm shell deformed by 1-mm thickness of driver sheet driving twice are good agreement with die, not only width direction (AB direction) but also length direction (CD direction). However, there was a big obstacle to deform the AZ31 shell with R = 2 mm, because the die had small bottom radius and sidewall section. Variation of effective strain and velocity with width direction and length direction during magnetic pulse forming without driver sheet and with Al driver sheet were analyzed by simulation.

Hydraulic Performance of Aggregate Beds with Perforated Pipe Underdrains Flowing Full

Results are presented from an experimental study of the stage discharge relationship for a porous pipe buried under loose laid aggregate. A series of steady-state experiments were performed in which the depth of flow over the pipe was measured for a given pipe discharge. The stage-discharge relationship for the entire system is well described by an orifice equation when the water surface in the aggregate trench was horizontal and the pipe was running full at the outlet. An energy equation analysis shows that the dominant energy losses are due to flow through the small side wall orifices into the pipe and from friction losses along the pipe. Friction losses in the aggregate are shown to be negligible, which again supports the orifice equation model. Discharge coefficients are reported for three commonly available porous pipes. The results of this research can be used in the sizing and placement of subsurface drains in aggregate filled storm water infiltration practices such as infiltration trenches and porous pavements.

Sidewall effects in Rayleigh–Bénard convection

AbstractWe investigate the influence of the temperature boundary conditions at the sidewall on the heat transport in Rayleigh–Bénard (RB) convection using direct numerical simulations. For relatively low Rayleigh numbers $Ra$ the heat transport is higher when the sidewall is isothermal, kept at a temperature $T_c+\Delta /2$ (where $\Delta $ is the temperature difference between the horizontal plates and $T_c$ the temperature of the cold plate), than when the sidewall is adiabatic. The reason is that in the former case part of the heat current avoids the thermal resistance of the fluid layer by escaping through the sidewall that acts as a short-circuit. For higher $Ra$ the bulk becomes more isothermal and this reduces the heat current through the sidewall. Therefore the heat flux in a cell with an isothermal sidewall converges to the value obtained with an adiabatic sidewall for high enough $Ra$ (${\simeq }10^{10}$). However, when the sidewall temperature deviates from $T_c+\Delta /2$ the heat transport at the bottom and top plates is different from the value obtained using an adiabatic sidewall. In this case the difference does not decrease with increasing $Ra$ thus indicating that the ambient temperature of the experimental apparatus can influence the heat transfer. A similar behaviour is observed when only a very small sidewall region close to the horizontal plates is kept isothermal, while the rest of the sidewall is adiabatic. The reason is that in the region closest to the horizontal plates the temperature difference between the fluid and the sidewall is highest. This suggests that one should be careful with the placement of thermal shields outside the fluid sample to minimize spurious heat currents. When the physical sidewall properties (thickness, thermal conductivity and heat capacity) are considered the problem becomes one of conjugate heat transfer and different behaviours are possible depending on the sidewall properties and the temperature boundary condition on the ‘dry’ side. The problem becomes even more complicated when the sidewall is shielded with additional insulation or temperature-controlled surfaces; some particular examples are illustrated and discussed. It has been observed that the sidewall temperature dynamics not only affects the heat transfer but can also trigger a different mean flow state or change the temperature fluctuations in the flow and this could explain some of the observed differences between similar but not fully identical experiments.

Discussion of “Experimental Studies on Flow over Labyrinth Weir” by B. V. Khode, A. R. Tembhurkar, P. D. Porey, and R. N. Ingle

Conclusions To conclude, this discussion provides unified equations for the coefficient of discharge of labyrinth weirs, which can be applied across a spectrum of sidewall angles (α ¼ 8–30°) for the prediction of discharge. The proposed equations render the authors’ work more valuable and complete from a practitioner’s perspective. Thus, they can be directly used for the predictions of discharge by real prototype dams. The discussion also reveals that a labyrinth weir with a smaller side wall angle achieves its maximum flow capacity at a relatively lower water head above the crest than a labyrinth weir with a higher side wall angle. Because the occurrences of nappe interference and local submergence (Crookston and Tullis 2012) in labyrinth weirs with low side wall angles cause a reduction in the discharge capacity, it can be inferred that labyrinth weirs are suitable for the low water head conditions above the crest; hence, they need to be designed for the same condition to achieve economy. However, it is suggested to find a suitable modification in the upstream apex of the labyrinth weirs that can avoid or delay the occurrence of the nappe interference phenomenon to preserve the ability of delivering increased discharge with increasing Ht=P value over a relatively wider range of water head above the weir crest.

Size Ratio Performance in Detecting Cerebral Aneurysm Rupture Status Is Insensitive to Small Vessel Removal

The variable definition of size ratio (SR) for sidewall (SW) vs bifurcation (BIF) aneurysms raises confusion for lesions harboring small branches, such as carotid ophthalmic or posterior communicating locations. These aneurysms are considered SW by many clinicians, but SR methodology classifies them as BIF. To evaluate the effect of ignoring small vessels and SW vs stringent BIF labeling on SR ruptured aneurysm detection performance in borderline aneurysms with small branches, and to reconcile SR-based labeling with clinical SW/BIF classification. Catheter rotational angiographic datasets of 134 consecutive aneurysms (60 ruptured) were automatically measured in 3-dimensional. Stringent BIF labeling was applied to clinically labeled aneurysms, with 21 aneurysms switching label from SW to BIF. Parent vessel size was evaluated both taking into account, and ignoring, small vessels. SR was defined accordingly as the ratio between aneurysm and parent vessel sizes. Univariate and multivariate statistics identified significant features. The square of the correlation coefficient (R(2)) was reported for bivariate analysis of alternative SR calculations. Regardless of SW/BIF labeling method, SR was equally significant in discriminating aneurysm ruptured status (P < .001). Bivariate analysis of alternative SR had a high correlation of R(2) = 0.94 on the whole dataset, and R = 0.98 on the 21 borderline aneurysms. Ignoring small branches from SR calculation maintains rupture status detection performance, while reducing postprocessing complexity and removing labeling ambiguity. Aneurysms adjacent to these vessels can be considered SW for morphometric analysis. It is reasonable to use the clinical SW/BIF labeling when using SR for rupture risk evaluation.

Relaxed Dimensional Tolerance Whispering Gallery Microbends

A new class of highly compact photonic microbend exploiting whispering gallery propagation is analyzed. Critical design dimensions are relaxed by using multimode waveguiding. A small outer sidewall radius enables tight arbitrary angle of rotation for the guided light, and the inner radius is reduced beyond the caustic radius to minimize the impact of the microbend dimensions on losses. Whispering gallery operation is compared with single-mode microbend operation using a combination of full-vectorial wave-equation models and 2-D and 3-D finite-difference time domain models. The dependence of loss on fabricated dimension is shown to be reduced by an order of magnitude. Waveguide width variations of ±100 nm lead to loss variations of only ±0.01 dB in the whispering gallery regime, contrasting favorably with ±0.10 dB loss variations for the single-mode regime for a 20 μm radius and for 1.5 μm input waveguide widths. Smaller radius microbends show comparable trends albeit with higher losses and increased sensitivity to width variations. The sensitivity of microbend loss to small changes in narrow waveguide width is attributed to the excitation of a restricted mode group. Moving the inner sidewall beyond the caustic radius allows relaxed tolerance light propagation in the whispering gallery regime. Losses down to 0.2 dB/180° and polarization conversion of down to -25 dB/180 are predicted.

Influence of Side-Insulation Film on Hybrid Process of Micro EDM and ECM for 3D Micro Structures

This paper describes a hybrid process of Micro EDM and ECM to fabricate 3D microstructures. Micro electro discharge servo scanning machining (Micro EDSSM) is used to remove most part of workpiece material with fast machining speed, while Micro electrochemical scanning machining (Micro ECSM) with side-insulated tool electrode is used to remove the residual material and form the final 3D-structure surface. The application of side-insulated electrode during Micro ECSM is a key technological method to improve the machining accuracy of hybrid process. The effect of side-insulation film property to the movement of hydrogen bubble generated during Micro ECSM is discussed. The hydrophobic film can reduce damages to the junction between film edge and tool-electrode through the attraction to hydrogen, and a hydrophilic 704-silica material is firstly introduced for the fabrication of side-insulation film on the micro rod tool electrode by spin-coating technique. The 704-silica insulation film can effectively isolate the side of tool electrode with electrolyte. Micro 3D structures with uniform side-machining gap and small tape side-wall are machined. The surface with no heat-influence layer and 0.52μm Rahas been achieved.

Enterprise stent-within-stent embolization of a basilar artery perforator aneurysm

Objective and Importance—Vertebrobasilar artery aneurysms can be very challenging to treat and are preferentially dealt with using endovascular tech-niques, since they are associated with lower risk than surgical clipping. Small aneurysms located on perfo-rating arteries can pose problems though, as their dimensions may not be favorable for coiling and leave the endovascular surgeon without many options. We present a basilar perforating artery aneurysm that was successfully embolized using a stent-within-stent technique. Clinical Presentation—A 47 year old fe-male presented with a Hunt-Hess 3, Fisher Grade-3 subarachnoid hemorrhage with blood in the pre-pontine cistern. Initial imaging (CT angiogram and digital subtraction angiography) did not reveal an aneurysm. Follow-up angiography on post-bleed day eight demonstrated a three-millimeter basilar perforating artery aneurysm. After an unsuccessful coiling attempt a closed-cell stent-within-stent tech-nique was used to divert flow away from the aneu-rysm neck to induce aneurysm thrombosis. Interven-tion (or Technique)—Multiple attempts were made to access and stabilize a microcatheter in the small basilar perforator artery aneurysm in order to de-liver coils for endovascular embolization; this could not be done safely. Therefore a closed-cell 4.5 × 22 mm Enterprise stent (Cordis Neurovascular, Inc., Miami Lakes, Florida) was deployed in the basilar artery across the origin of the perforator aneurysm in order for the stent tines to divert flow away from the aneurysm neck and induce thrombosis. Persistant brisk flow within the aneurysm continued however, and a second closedcell 4.5 × 22 mm Enterprise stent was placed within the first one to increase the stent metal surface area across the aneurysm neck to further reduce flow into the aneurysm. Subsequently, angiography demonstrated stagnant blood flow in the aneurysm dome and the aneurysm spontaneously thrombosed, sparing all associated vessels. Conclu-sion—Stent-within-stent technique should be consid-ered as a possible endovascular treatment option for small side-wall and perforator artery aneurysms that can’t be safely treated with coils or embolic agents.

Manipulative depolarization and reflectance spectra of morphologically controlled nano-pillars and nano-rods

Depolarization of sub-mum-high Si nano-pillar/nano-rod surface reflectance with morphologically controlled anti-reflection spectrum is demonstrated. Extremely small reflectance dip of 1.5% at 400-450 nm for Si nano-pillars is extraordinary when comparing with Si nano-rods, in which the reflectance vs. L/lambda for Si nano-pillars coincides well with the graded-index multilayer based modeling spectrum. Alternatively, Si nano-rods preserve its flattened reflectance spectrum up to 1700 nm, whereas the Si nano-pillar surface reflectance monotonically increases to approach that of bulk Si. The destructive interference is only induced on Si nano-pillar surface with larger aspect-ratio > or =15 and small sidewall slope <7 to suppress surface reflectance at blue-green wavelength region. Anomalous depolarization observed from disordered Si nano-pillar/nano-rod surface reflection indicates that TM-mode incidence interacts with more bound electrons than TE-mode to preserve its effective dielectric permittivity less deviated from the bulk Si. The degraded depolarization ratio observed under TE-mode incidence which correlates well with a simplified bounded-electron resonance model is elucidated.

Control of Shape and Material Composition of Solid-State Nanopores

Solid-state nanopores fabricated by a high-intensity electron beam in ceramic membranes can be fine-tuned on three-dimensional geometry and composition by choice of materials and beam sculpting conditions. For similar beam conditions, 8 nm diameter nanopores fabricated in membranes containing SiO(2) show large depletion areas (70 nm in radius) with small sidewall angles (55 degrees ), whereas those made in SiN membranes show small depletion areas (40 nm) with larger sidewall angles (75 degrees ). Three-dimensional electron tomograms of nanopores fabricated in a SiO(2)/SiN/SiO(2) membrane show a biconical shape with symmetric top and bottom and indicate a mixing of SiN and SiO(2) layers up to 30 nm from the edge of nanopore, with Si-rich particles throughout the membrane. Electron-energy-loss spectroscopy (EELS) reveals that the oxygen/nitrogen ratio near the pore depends on the beam sculpting conditions.