Search

For solitary waves on a horizontal bed, the study deals experimentally with the high ratio of wave height (H0) to still water depth (h0) that amplifies the wave nonlinearity. The value of H0/h0 tested in a wave flume ranges from 0.050 to 0.550, indicating the shift from a quasi-linear solitary wave to a highly nonlinear one. A high-speed particle image velocimetry (HSPIV) and a flow visualization technique of particle-trajectory tracking method are utilized to measure velocity fields and identify near-bed flow structures. The unsteady free-stream velocities with equal magnitude take place in a free-stream zone, FSZ). The FSZ underlies the internal flow zone, over which the external free surface of solitary wave exists and is situated beyond the boundary layer. The spatio-temporal variation of free-stream velocity, moving in phase with the free surface elevation, characterizes the pattern of pressure gradient in the FSZ and thus dominates the behavior of boundary layer flow. Accordingly, nonlinear effects on the time series as well as the maximum values of horizontal velocity, particle acceleration, and pressure gradient in the FSZs of solitary waves are presented. Before, at, and after the wave crest’s intersection with a given measurement location, favorable, zero, and adverse pressure gradients occur in the FSZ, respectively. For H0/h0 = 0.179, 0.363, and 0.550, the values of the dimensionless maximum free-stream velocity are about 3.10, 5.32, and 6.20 times that (= 0.0473) for H0/h0 = 0.050; and the corresponding values of the dimensionless maximum adverse pressure gradient are about 5.74, 14.54 and 19.84 times that (= 0.0061) for H0/h0 = 0.050. This evidence highlights the nonlinear effect on the kinematic and hydrodynamic features of solitary waves. Finally, the effect of nonlinearity on the relationship between the dimensionless time for the maximum adverse pressure gradient in the FSZ and that for the incipient flow reversal in the bottom boundary layer is explored for the first time. It is found that the incipient flow reversal takes place immediately after the maximum adverse pressure gradient, together with a decrease in the dimensionless time for flow reversal if H0/h0 increases. The fact accentuates the nonlinear effect on the incipient flow reversal right above the bed.

This study presents experimental data on the hydrodynamic features of a nonlinear solitary wave of height H0 = 2.9 cm propagating over a horizontal bed in otherwise still water depth h0 = 8.0 cm. High-speed particle image velocimetry is used to quantify the local and convective particle accelerations and pressure gradients under the solitary wave. It is found that the magnitudes of the horizontal and vertical particle local accelerations are invariably larger than their convective counterparts, highlighting the important contribution of local acceleration to the pressure gradient in a solitary wave. The dimensionless pressure gradient in the horizontal direction is favorable, zero, and adverse for time before, at, and after the wave crest passes the section of interest. The dimensionless adverse pressure gradient exhibits a maximum for the dimensionless time T[=t(g/h0)1/2, where g is the gravitational acceleration and t is the time with respect to the crest passing the section] = 1.39, at which the dimensionless local acceleration has a negative maximum. Subsequently, flow reversal takes place above the bed surface. The relationship is elucidated between flow reversal at the bed surface and the evolution of the adverse pressure gradient in the near-bed zone, where uniform horizontal/free stream velocity exists.

This paper describes a four-layer-stacked chip with 45-nm dynamic random access memory (DRAM) dice and 65-nm logic controller, which are interconnected by backside-via-last through-silicon via (TSV) processes. Fabrication of backside-via-last process and multiple die stacking using chip-to-chip bonding are presented with electrical connection between TSV (5-μm-diameter/50-μm-length) and Cu interconnects. Excellent fabrication of stacked dice verified that the micro bumps with 12-μm diameter are bonded using three step temperature bonding profile. Further stacked DRAM/Logic performance and system verifications are demonstrated successfully using 3-D heterogeneous integration.

The hydrodynamic characteristics, including local and convective accelerations as well as pressure gradient in the horizontal direction, of the external stream of an undular bore propagating on a 1:20 sloping beach are experimentally studied. A bore with the water depth ratio of 1.70 was generated downstream of a suddenly lifted gate. A high-speed particle image velocimetry was employed to measure the velocity fields during the run-up and run-down motions. The time series of free surface elevation and velocity field/profile of the generated bore, comprising a pure bore accompanied by a series of dispersive leading waves, are first demonstrated. Based on the fast Fourier transform (FFT) and inverse FFT (IFFT) techniques, the free surface elevation of leading waves and the counterpart of pure bore are acquired separately at a specified measuring section (SMS), together with the uniform horizontal velocity of the pure bore. The effect of leading-wave-induced velocity shift on the velocity profiles of the generated bore are then evaluated at the SMS. To understand the calculation procedure of accelerations and pressure gradient, three tabulated forms are provided as illustrative examples. Accordingly, the relationships among the partially depth-averaged values of the non-dimensional local acceleration, convective acceleration, total acceleration and pressure gradient of the generated/pure bore acquired at the SMS versus the non-dimensional time are elucidated. The trends in the non-dimensional accelerations and pressure gradient of the external stream of generated bore are compared with those of the pure bore. During the run-up motion from the instant of arrival of the bore front to the moment of the peak level at the SMS, continuous decrease in the onshore uniform horizontal velocity, and successive deceleration of the pure bore in the onshore direction are evidenced, exhibiting the pure bore under the adverse pressure gradient with decreasing magnitude. However, the pure bore once ridden by the leading waves is decelerated/accelerated spatially and accelerated/decelerated temporally in the onshore direction during the rising/descending free surface of each leading wave. This fact highlights the effect of pre-passing/post-passing of the leading wave crest on the velocity distribution of generated bore. It is also found that, although the leading waves have minor contribution on the power spectrum of the free surface elevation as compared with that of the pure bore, the leading waves do play an important role on the magnitudes of both accelerations and pressure gradient. The largest magnitude of the acceleration contributed by the leading waves is around 26 times the counterpart contributed by the pure bore. Further, during the run-down motion right after the moment for the peak level of the bore, a linear increase in the magnitude of the offshore uniform horizontal velocity and a constant local acceleration with increasing time are both identified. The partially depth-averaged value of the non-dimensional pressure gradient is equal to a small negative constant (−0.0115) in the offshore direction, indicating that the bore is subject to a constant favorable pressure gradient.

An experimental results on the spatio-temporal variation of velocity field and vortex structure, generated from the separated boundary layers on the offshore side of the still-water shoreline, during the run-down process of non-breaking solitary waves over a 1:3 sloping beach are presented. Three waves having the incident wave-height to water-depth ratios (H0/h0) of 0.363, 0.263, and 0.171 were generated in a wave flume. Two flow visualization techniques and high-speed particle image velocimetry were employed. The primary topics and new findings are: (1) Mechanism of the incipient flow separation, accompanied by formation of the separated shear layer from the beach surface, is elucidated under the adverse pressure gradient, using the fine data of velocity measurements very close to the sloping boundary. (2) Occurrence of hydraulic jump subsequently followed by development of the tongue-shaped free surface and projecting jet is demonstrated through spatio-temporal variation in the Froude number. It is confirmed by a change in the Froude number from supercritical to subcritical range as the free surface rapidly rises from the onshore to offshore side. (3) A complete evolution of the primary vortex structure (including the core position, vortex size, and velocity distribution passing through the vortex core) is first introduced systematically, together with the illustration of temporal variation in the topological structure. The non-dimensional shoreward distance of the vortex core section decreases with the increase in the non-dimensional time. However, the non-dimensional size height of the primary vortex increases with increasing non-dimensional time. (4) Two universal similarity profiles for both the wall jet flow and the shear layer flow demonstrate independency of the two similarity profiles of the wave-height to water-depth ratio and the beach slope. The similarity profiles indicate the promising collapse of the data from three previous studies for 1:20, 1:10, and 1:5 sloping beaches.

Four image-based techniques—i.e., shadowgraphic image method (SIM), high-speed particle image velocimetry (HSPIV), bubble tracking method (BTM), and bubble image velocimetry (BIV)—are employed to investigate an aerator flow on a chute with a 17° inclination angle. The study focuses on their applications to the following issues: (1) to explore the characteristic positions of three water–air interfaces; (2) to interpret the evolution process of air bubbles shed from the wedged tip of the air cavity; (3) to identify the probabilistic means for characteristic positions near the fluctuating free surface; (4) to explore the probability distribution of intermittent appearance of air bubbles in the flow; (5) to obtain the mean streamwise and transverse velocity distributions of the water stream; (6) to acquire velocity fields, both instantaneous and mean, of air bubbles; (7) to construct a two-phase mean velocity field of both water flow and air-bubbles; and (8) to correlate the relationship among the probability distribution of air bubbles, the mean streamwise and transverse velocity profiles of air bubbles, and water stream. The combination of these techniques contributes to a better understanding of two-phase flow characteristics of the chute aerator.

A novel memory cell consisting one transistor and two uneven magnetic tunnel junctions (MTJs) (IT2UMTJ) is proposed and implemented to shrink the bit size with a potential down to 6 [F.sup.2] by an extended via process and to reduce the writing current by a factor of 2, making the magnetoresistive random access memory suitable for universal memory applications. As a result, a high density of bit size potentially down to 6 [F.sup.2], a high reading speed and a throughput of less than 100 ns for two sharing bits can be realized.

The gate voltage swings with efficient transconductances, greater saturation current densities and greater linear and power applications can be obtained by applying three kinds of delta-doped GaAs/In(x)Ga(1 - x)As/GaAs pseudomorphic heterostructures. By applying the compositionally graded In(x)Ga(1 - x)As, embodied by In with a reduced buffer/channel interface facing outward and ungraded single and double delta-doped GaAs layer channels, the gate voltage swings can be made more effective. The graded In(x)Ga(1 - x)As channel helps in deriving a flat transconductance area.

The brief thermal treatment effects on the magnetoresistance of microstructured [Co.sub.60][Fe.sub.20][B.sub.20]-based magnetic tunneling junctions are analyzed. The survival of magnetoresistance at higher annealing temperature is because of boron conservation in the amorphous CoFeB ferromagnetic layer at higher annealing temperature for only a short time.

The interfacial and annealing effects on magnetic properties of CoFeB thin films were studied and the thickness of magnetically dead layer of as-deposited CoFeB film with Ta and Ru interfaces was investigated. CoFeB film with Ta interfaces was observed to remain amorphous while that with Ru interface started crystallizing during the annealing above 250 degrees Celsius.

A study of switching behaviors in elliptic shaped submicron tunnel junctions is conducted. The results reveal that under considerable stray originating from pinned layers, junctions with single free layer show complex switching behaviors with larger Hc variations.

The velocity characteristics of a solitary wave shoaling in the prebreaking zone and near the breaking point are investigated experimentally. The study focuses on the near-bottom and boundary layer flows on a 1:10 slope, with the incident wave steepness varying from0.133 to 0.384. Both a flow visualization technique (FVT)with thin-layered dye as well as particle image velocimetry (PIV)with a high-speed camera were used. Results fromFVT reveal that laminar boundary layer flow occurs not only in the prebreaking zone during the shoaling phases, but also in the postbreaking zone during the run-up and run-down phases.However, the laminar boundary layer disappears soon after breaking but before the run-up motion, and immediately after the flow separation followed by hydraulic jump during the later stage of the run-down motion. Results from the PIV measurement show that the maximum horizontal velocity appears under the wave crest and increases during the shoaling process. Flow reversal is observed after the passage of the wave crest. Three unique similarity profiles are then obtained for the velocity distributions in the acceleration phases and in the layers of flow reversal with overshooting, as well as for the maximum onshore and offshore velocities in the boundary layer. In addition, the nondimensional time for the beginning of flow reversal at each measuring section is found to be exponentially proportional to the dimensionless distance to the slope origin, but nearly independent of the incident wave steepness. This study also investigates the lead-time effects of the horizontal velocity at different heights in the boundary layer and at different measuring sections along the slope. The maximum value of the nondimensional lead time, occurring very close to the sloping bottom, decreases linearly with the dimensionless distance to the toe of the slope. [ABSTRACT FROM AUTHOR]

In this investigation, Cu-Sn lead-free solder microbumps on 10-μm pads with a 20-μm pitch are designed and fabricated. The chip size is 5 × 5 mm with thousands of microbumps. A daisy-chain feature is adopted for the characterization and reliability assessment. After pattern trace formation, the microbump is fabricated on the trace by an electroplating technique. A suitable barrier/seed layer thickness is designed and applied to minimize the undercut due to wet etching but to still achieve good plating uniformity. With the current process, the undercut is less than 1 μm and the bump height variation is less than 10%. In addition, the shear test is adopted to characterize the bump strength, which exceeds the specification. Also, the Cu-Sn lead-free solder microbumped chip is bonded on an Si wafer using chip-to-wafer bonding technique. Furthermore, the microgap between the bonded chips is filled with a special underfill. The shear strength of the bonded chips without the underfill is measured and it exceeds the specification. The bonding and filling integrity is further evaluated by open/short measurement, scanning acoustic tomography analysis, and cross-section with scanning electron microscopy analysis. The stacked ICs are evaluated by reliability (thermal cycling) test (-55 to 125°C). Finally, ultrafine-pitch (5-μm pads on a 10-μm pitch) lead-free solder microbumping is explored. [ABSTRACT FROM PUBLISHER]

Thermal performance of 3D IC integration is investigated in this study. Emphasis is placed on the determination of a set of equivalent thermal conductivity equations for Cu-filled TSVs with various TSV diameters, TSV pitches, TSV thicknesses, passivation thicknesses, and microbump pads. Also, the thermal behavior of a TSV cell is examined. Furthermore, 3D heat transfer simulations are adopted to verify the accuracy of the equivalent equations. Finally, the feasibility of these equivalent equations is demonstrated through a simple 3D IC integration structure. [ABSTRACT FROM AUTHOR]

In this study, key enabling technologies such as the oxide liner by the PECVD, the barrier and seed layers by the PVD, and Cu plating of blind TSVs on 300 mm wafers for 3D integration are investigated. Emphasis is placed on the determination and optimization of the important parameters for each of the key enabling technologies. Also, the leakage current of the fabricated Cu-filled TSVs is measured. Furthermore, cross sections and SEM of the fabricated TSVs are examined. [ABSTRACT FROM AUTHOR]

This paper proposes a 3D IC integration TSV testing apparatus, primarily using at least one set of TSV component testing devices with a specific design. Under complex technological conditions, such as varying depth-width ratios of TSVs and heterogeneous IC integration, as well as the principle of different coupling parasitic parameters between TSVs, the TSV coupling measuring device designed for specific purposes in coordination with a measuring method for high-frequency coupling TSV Sparameters, achieves the function of monitoring the SiO2 thickness completeness of TSVs. This feasible approach further allows judgment of whether subsequent processes can continue, effectively reducing costs. [ABSTRACT FROM AUTHOR]

The magnetic random access memory (MRAM) is considered one of the potential candidates that will replace current on-chip memories (RAM, EEPROM, and flash memory) in the future. The MRAM is fast and does not need a high supply voltage for read/write operations, and is compatible with the CMOS technology. It can also endure almost unlimited read/write cycles. These combined advantages of RAM and flash memory make it a potential choice for SOC. In this paper, we present the write disturbance fault (WDF) model for MRAM, i.e., a fault that affects the data stored in the MEAM cells due to excessive magnetic field during the write operation. We also construct the SPICE macro model for the magnetic tunneling junction (MTJ) device of the toggle MRAM to obtain circuit simulation results. We then present an MRAM fault simulator called RAMSES-M, based on which we derive the shortest test for the proposed WDF model. The test is shown to be better and more robust as compared with the conventional March C-test algorithm. We also present a March 17 N diagnosis algorithm for identifying WDF. A 1 Mb MRAM chip has been designed and fabricated using a CMOS-based 0.18-µ technology. The proposed WDF model is justified by chip measurement results, with the march test results reported. Finally, specific MRAM fault behavior and test issues are discussed. [ABSTRACT FROM AUTHOR]

Novel cell structures based on one transistor and two uneven magnetic tunnel junction cell and pillar write word line architecture are proposed to shrink the bit size with a potential down to 6 F² by a so-called extended via process, and to reduce the writing current by a factor of 2, combined with the nature of nonvolatility and high speed, making the magnetoresistive random access memory suitable for universal memory applications. [ABSTRACT FROM AUTHOR]

A composite free layer (CFL) consisting of a soft layer and a hard layer exchange coupled in parallel is proposed. The experimental results showed that the critical current density (Jc) can be reduced from 7.05×106 A/cm2 of strong coupled CoFeB(12.5 Å)/Ru(4 Å)/NiFe(17.5 Å) CFL to 2.65×106 A/cm2 of weak coupled CoFeB(12.5 Å)/Ru(15 Å)/NiFe(17.5 Å) CFL. The macrospin simulations showed that the soft layer of CFL can assist the hard layer of CFL to switch at a lower Jc. These results suggest that by using CFL, it is possible to reduce the Jc of spin torque transfer switching without compromising the thermal stability. [ABSTRACT FROM AUTHOR]

A novel phase-change memory cell with a double-confinement structure was proposed and fabricated in this work. By having an additional bottom Ge2Sb2Te5 layer under the electrically confined active region, the heat loss can be effectively prevented. The temperature uniformity over the active region significantly improves and so does the thermal efficiency. Therefore, a low IRESET of about 0.3 mA and a reset power can be achieved. For the SET performance, a pulsewidth as low as 200 ns can be used without compromising the RSET. [ABSTRACT FROM AUTHOR]

The capping effects on the properties of magnetic tunneling junctions (MTJs) have been investigated to improve the magitetoresistive (MR) ratio [Nagamine et al. Applied Physics, vol. 99, p. 08K703, 2006] and thermal stability [Fukumoto et al. Japanese Journal of Applied Physics, vol. 45, p. 3829, 2006. In this paper, MgO/Mg and MgO capping layers for MTJs were used to replace our previously used Ta and Ru capping layer [Yen et al., IEEE Transactions on Magnetics, vol. 42, no. 10, p. 862, 2004]. The MTJs with NiFe and CoFeB free layers were patterned to ellipses of 0.36 µm × 0.72 µm. The MR ratios of the MTJs with an NiFe free layer were enhanced from 26% to about 33% by capping MgO/Mg bilayers. A great improvement was also found on the MTJs with the CoFeB free layer, where the MR ratio was 50.4% with the MgO cap layer enhanced from 44.7% of Ru-capped MTJs. In addition, the influences of those capping layers included Ta, Ru, MgO, and MgO/Mg on thermal stability were also discussed. [ABSTRACT FROM AUTHOR]

The writing probability of toggle magnetic random access memory (MRAM) at built-in bias field is studied by micromagnetic simulation and a dual polarity write pulse scheme has been proposed to enhance the toggle probability at low writing field. The critical writing field can be reduced to 19 Oe at strong built-in bias field from CoFe(1.0 nm)/CoFeB(2.0 nm)/Ru/CoFe(5.0 nm) pinned layer structure. From the simulation and experimental results, it is proven that the toggle MRAM can be operated at lower writing field by dual polarity write pulse scheme. [ABSTRACT FROM AUTHOR]

A Ru/Ta capping layer for magnetic tunneling juctions (MTJs) was used to replace the routinely used Ta capping layer. The MTJs with CoFeB used as the free layer were shaped to ellipses of 0.36 × 0.60 μm. The magnetoresistive (MR) ratio of Ru/Ta capped MTJs was found to be 47.3%, slightly lower than the value of 52.8% of Ta capped MTJs. In the meantime, the switching field of Ru/Ta capped MTJs with 30Å of Ru was found to be 37.7 Oe, greatly reduced from 63 Oe of Ta capped MTJs. The switching field varition of Ru/Ta capped MTJ5 was 6 Oe, also better than the value of 11 Oe of Ta capped MTJs. The different switching behaviors of Ru/Ta and Ta capped MTJs were discussed from the aspects of oxygen diffusion, intermixing, and magnetostriction. [ABSTRACT FROM AUTHOR]

In this work, a writing scheme with preceding negative pulse wave form for toggle magnetic random access memory (MRAM) is proposed to enhance the switching yield and enable a low current switching. The failure mechanism of toggle switching is studied by micromagnetic analysis. As a result of broadened operation window and reduced switching current, the scalability of MRAM is feasible with the robust toggle operation. [ABSTRACT FROM AUTHOR]

Editor's note:Especially for microcontroller and mobile applications, embedded nonvolatile memory is an important technology offering to reduce power and provide local persistent storage. This article describes a new resistive RAM device with fast write operation to improve the speed of embedded nonvolatile memories.—Leland Chang, IBM T.J. Watson Research Center [ABSTRACT FROM PUBLISHER]