Advanced Research Systems

In this work, we describe the instrumentation used to perform the first operando transmission X-ray microscopy (TXM) and simultaneous X-ray diffraction of laser melting simulating laser powder bed fusion on the XCS instrument at the Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL). Our TXM with 40× magnification in the X-ray regime at 11 keV gave spatial resolutions down to 940 nm per line pair, with effective pixel sizes down to 206 nm, image integration times of <100 fs, and frame rates tunable between 2.1 and 119 ns for two probe frames (0.48 GHz to 8.4 MHz). Images were recorded on Zyla and Icarus (UXI) detectors to trade off between spatial resolution and time dynamics. A 1 kW CW IR laser was coupled into the interaction point to conduct pump-probe studies of laser melting and solidification dynamics. Our temporal and spatial resolution with attenuation-based contrast exceeds that currently possible with synchrotron-based high-speed radiography. This system was sensitive to feature velocities of 10-12000 m s-1 but we did not observe any motion in this range in the laser melting of Al6061 alloy. Shockwaves were not observed and hot cracking proceeded at velocities below the detection limits. Pore accumulation was observed between successive shots, indicating that bubble escape mechanisms were not active. With proper experimental design, the spatial resolution, contrast and field of view could be further improved or modified. The increased brightness and narrower bandwidth of the XFEL allowed for this imaging technique and it lays the groundwork for a wide range of operando techniques to study additive manufacturing.

To meet the increasing market demand for next-generation electronic devices, 3D system integration is getting greater and greater attention. However, traditional methods such as soldering or bump bonding cannot handle high density interconnection. Therefore, hybrid bonding technology, which simultaneously bonds Cu wiring layer and SiO2 dielectric layer, is indispensable. In the hybrid bonding process, hydrophilic bonding is commonly used to bond SiO2 to SiO2. This technique involves bonding of hydrophilic bonding surfaces, followed by post-bonding annealing to achieve a reliable bonding interface. For Cu bonding, it is necessary to break the oxide layer at the Cu bonding interface and allow Cu atoms to diffuse into each other to achieve electrical connection.However, since post-bonding annealing at high temperatures can damage the device or induce residual stress at the bonding interface, low temperature process below 200°C is preferable. Currently, the most widely adopted process is hydrophilic bonding using N2 plasma, which also achieves hybrid bonding through heating at around 350°C to 400°C.In this study, we propose to apply sequential plasma activation bonding (SPAB), which has been shown to be effective for low-temperature bonding of quartz glass, to the bonding of TEOS SiO2 and Cu. SPAB is a technique that forms a highly reactive oxynitrides on the substrate by continuously irradiating the bonding surface with O2 plasma, N2 plasma, and nitrogen radicals. This then adsorbs a large amount of OH groups by reacting with moisture, leading to a strong bond after bonding and post-bonding annealing at 200°C. Since this technique is effective for quartz, it is expected to be effective for TEOS SiO2 as well, and we also investigate its effect on Cu in this study.For this, we investigated the effect of SPAB for blanket TEOS SiO2 and Cu wafer separately. Cu layers were deposited on 4 inch, 525 µm thick Si wafers, and TEOS SiO2 layers on 6 inch, 625 µm thick Si wafers. The Cu layers were deposited by sputtering with a 1 µm thickness, while the SiO2 layers were deposited using plasma-enhanced TEOS process for a 1 µm thickness. Both types of deposited layers were planarized by CMP.The SPAB process was carried out using RIE plasma and microwave radicals of N2 and O2 gas. The bonding surfaces were activated by O2 plasma, N2 plasma, and N radicals sequentially. After the surface activation, the wafers were exposed to ambient air to adsorb water on the surface, followed by bonding in air and post-bonding annealing at 200°C for 2 hours.For comparison, bonding was also carried out using only N2 plasma and only O2 plasma activation, respectively. Results show that when surface activation was performed using only N2 plasma, the bond strength was 0.75 J/m2 for TEOS SiO2 and 0.33 J/m2 for Cu. In the case of O2 plasma activation, the bond strength was 0.57 J/m2 for TEOS SiO2 and 0.98 J/m2 for Cu.On the other hand, the SPAB technique improves the bond strength to 1.13 J/m2 for TEOS SiO2 and 1.03 J/m2 for Cu. Therefore, it can be concluded that the SPAB technique enhances the bond strengths of both TEOS SiO2 and Cu compared to single gas plasma activation. Since the SPAB improves the bond strength of both SiO2 and Cu in the same process condition with annealing temperature of 200°C, this technique will contribute low temperature hybrid bonding applications.

3D-stacked memory plays a vital role in achieving high-throughput and low-power operation in various devices. The 3D integration of memory chips, such as SRAMs and DRAMs, enables high-bandwidth, large-capacity, and low-power memory. However, conventional wired integration using TSVs and $\mu -$bumps has challenges of additional TSV process cost, area overhead cost, and low yield [1–4]. Wireless integration using inductive coupling known as ThruChip Interface (TCI) has low cost and high yield thanks to its compatibility with standard CMOS fabrication processes [5]. Furthermore, a physical placement method of placing coils over SRAM macros proposed in [6] reduces the area overhead to just that of transceiver circuits while minimizing the resultant loss in communication efficiency. A synchronous transceiver topology is a key enabler for the method since it can detect the lower received amplitude due to the over-SRAM placement. In [6], Manchester encoding is employed to enable synchronous communication, but the data-rate is limited to 8.5 Gbps, where the distribution of the high-frequency clock required for encoding is the bottleneck. This paper proposes a new receiver circuit that eliminates the need for encoding, achieving a 12.8-Gbps data-rate.

Physical inactivity has become a prevalent problem among elderly people. Although digital wellness technologies have been proposed as one promising solution to it, our understanding on the antecedents of the acceptance and use of these technologies among elderly people remains limited. In this study, our objective is to promote this understanding by examining the potential changes in the use intention of digital wellness technologies and its antecedents over time in the case of the young elderly segment and physical activity logger applications. We base this examination theoretically on UTAUT2 and empirically on survey data that is collected from 99 Finnish young elderly users of a physical activity logger application and analysed with partial least squares structural equation modelling (PLS-SEM). We find the scores of both use intention and most of its antecedents to decline over time as well as some changes in the effects of the antecedents on use intention.

The ability to predict and understand phases in high-entropy alloys (HEAs) is still being debated, and primarily true predictive capabilities derive from the known thermodynamics of materials. The present work demonstrates that prior work using high-throughput first-principles calculations may be further utilized to provide direct insight into the temperature- and composition-dependent phase evolution in HEAs, particularly Al-containing HEAs with a strengthening multiphase microstructure. Using a simple model with parameters derived from first-principles calculations, we reproduce the major features associated with Al-containing phases, demonstrating a generalizable approach for exploring potential phase evolution where little experimental data exists. Neutron scattering, in situ microscopy, and calorimetry measurements suggest that our high-throughput Monte Carlo technique captures both qualitative and quantitative features for both intermetallic phase formation and microstructure evolution at lower temperatures. This study provides a simple approach to guide HEA development, including ordered multi-phase HEAs, which may prove valuable for structural applications.

An integrated portfolio of wide-area real-time reliability tools is addressing one of the major recommendations from the most recent blackouts in North America's Eastern and Western interconnections: The lack of common, simultaneous, adequate and accurate reliability information during major disturbances. The functional specifications for the tools were defined through guidance provided by NERC reliability Subcommittees and Reliability Coordinators addressing wide-area real operational reliability problems. The tools' intelligent alarms, multi-view, geo-graphic displays and automatic reliability reports enable Balancing Authorities and Reliability Coordinators to rapidly and jointly interpret and use consistently presented real-time data to monitor load-generation-frequency resources adequacy and grid health. The data and functional architectures are being adapted to make the tools useful for the integration of emergent dynamic distributed systems into the traditional centralized systems of today. The paper focus on the most intensively used tools, and illustrates how the tools are used in practice with five examples drawn from four interconnections.

GO-imbedded nanocomposite hollow fiber membranes were investigated for oily water treatment, with the aim to improve GO-polymer interfacial interaction and membrane anti-fouling properties via the formation of a simultaneously covalent and ionic inter-network.