bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Copper Surface Passivation for Low Temperature Cu-to-Cu Bonding Applications
Authors: Park Hae-Sung , Seo Han Kyeol , Kim Gahui , Park Young-Bae , Kim Sarah Eunkyung 
Published: December 2020

As the IC devices are rapidly scaled down, IC integration has faced several technical bottlenecks: further miniaturization, power delivery and distribution, signal/power integrity, and heat dissipation. In this regard, chip or wafer stacking processes have attracted attention to improve an interconnect delay and an inter-die bandwidth, reduce a form factor, and decrease manufacturing costs. Vertically stacking technology not only enhances device performance, but also can realize heterogeneous packaging systems for the next generation heterogeneous integration. Of the three unit processes in the vertical stacking system, Cu-to-Cu bonding has emerged as a core technology for efficient power density, high bandwidth, and fine-pitch connecton.
Various Cu-to-Cu bonding studies have been reported, such as thin metal passivation on Cu surface, self-assembled monolayer that passivates Cu surface with alkane-thiol, surface activated bonding that removes surface oxide layers and contaminants by plasma treatment, and direct bonding interconnect that enables Cu/SiO2 hybrid bonding. Despite many studies, Cu surface oxidation and high bonding temperature are still major issues to be resolved in high volume manufacturing. Sustainable, oxidization-free copper surface prior to Cu-to-Cu bonding is critical, especially since chip-to-chip bonding must still be performed in the air. Therefore, in this study, the copper surface passivation using the two-step plasma treatment has been investigated.
The Cu-to-Cu bonding process of less than 300℃ was investigated using the copper nitride passivation. The copper nitride passivation layer was formed on 8-inch Si/SiO2/50nm Ti/1μm Cu using the two-step Ar-N2 plasma treatment process. The purpose of two step plasma treatment is first to remove copper oxides and any contaminants through Ar plasma, activate the Cu surface, and then form a copper nitride layer through N2 plasma. This metastable passivation of couple nanometer thickness prevents further oxidation and reduces surface roughness. In addition, since a copper nitride tends to decompose at 300oC or lower it does not adversely affect Cu bonding interface. The two-step plasma treatment was optimized to improve Cu bonding quality, and optimization was systematically carried out by the response surface methodology (RSM) based on a central composite design (CCD) in design of experiment (DOE). It has been found that copper nitride passivation lasts at lasts for 1 week.. The two-step plasma treatment showed the Cu2O removal and Cu4N formation on the Cu surface. Under the optimized two step Ar-N2 plasma treatment at 300℃, Cu-to-Cu bonding quality has significantly improved compared to the Cu-to-Cu bonding without any surface treatment. The interfacial strength measured by 4-point bending test and shear test and electrical measurements will be discussed.
Nanostructural Investigation on GaAs//Indium Tin Oxide/Si Junctions for III-V-on-Si Hybrid Multijunction Cells
Authors: Hara Tomoya , Liang Jianbo , Araki Kenji , Kamioka Takefumi , Sodabanlu Hassanet , Watanabe Kentaroh , Sugiyama Masakazu , Shigekawa Naoteru 
Published: December 2020

Hard X-ray photoemission spectroscopy (HAXPES) measurements and transmission electron microscopy (TEM) observations are performed on GaAs thin film//Indium tin oxide (ITO)/Si junctions fabricated by surface-activated bonding and selective wet etching. Both of the Ga-O/Ga-As ratio in the Ga 2p3/2 HAPES core spectrum (Fig. 1(a)) and As-O/As-Ga ratio in the As 2p3/2 HAXPES core spectrum (Fig. 1(b)) demonstrate that the GaAs layers are oxidized after annealing at 400 °C. This observation is consistent with the formations of a ~1-nm-thick intermediate layer in the cross-sectional TEM image of the junctions after the 400 °C annealing, as is shown in Figs. 2(a) and 2(b). It is found by using in-house X-ray photoelectron spectroscopy in combination with Ar+ bombardment that the oxide layers are formed at GaAs//ITO bonding interfaces after annealing at 200 °C or higher temperatures. The observation of the oxide layers corresponds with the onset of resistivity increase in GaAs//ITO/Si junctions due to the annealing [1]. These results suggest that annealing brings about the reaction between GaAs and ITO layers and hence the oxidation of GaAs layers, which causes the degradation of the electrical properties of GaAs//ITO/Si junctions. A fabrication process at lower temperatures is likely to be required so as to fully exploit the advantage of ITO as intermediate layers in III-V//Si hybrid tandem solar cells with lower series resistance.
[1] Tomoya Hara, Tomoki Ogawa, Jianbo Liang, Kenji Araki, Takefumi Kamioka, and Naoteru Shigekawa, "Electrical properties of GaAs//indium tin oxide/Si junctions for III-V-on-Si hybrid multijunction cells", Jpn. J. Appl. Phys. 57, 08RD05 (2018). DOI: 10.7567/JJAP.57.08RD05

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Promoting Lithium Electrodeposition Towards the Bottom of 3-D Copper Meshes in Lithium-Based Batteries
Authors: Kim Sujung , Kim Yena , Nguyen Chi Thang , Jang Taegyu , Lee Han-Bo-Ram , Byon Hye Ryung 
Published: December 2020

Lithium (Li) has been considered as the promising negative electrode in rechargeable batteries, owing to the negative redox potential (-3.04 V vs. SHE), low density (0.534 g/cm3), and high theoretical specific capacity (3,860 mAh/g). However, the non-uniform stripping/plating process of the metallic Li is still challenging.[1] As one of the solutions, three-dimensional (3-D) metallic scaffolds were introduced to the negative electrode. The uniform electric field applied in the porous scaffolds could suppress the dendritic growth of the Li during the plating process. In addition, a decrease in the effective current density prolonged Sand’s time.[2] However, such a Li deposition mainly proceeded on the top surface and led to rapid surface clogging due to the strong surface electric field. In this presentation, we show the preferred Li deposition inside the 3-D copper (Cu) scaffold using gold nanoparticles (Au NPs). The lower Li nucleation energy barrier on the Au surface than that on the typical Cu current collector was investigated intensively.[3] However, the role of Au for spatially promoting Li deposition was not studied in depth. We added the Au NPs with an average particle size of ~7.5 nm to the bottom of 3-D Cu. The Au NPs with a total ~28 nmol reduced the charge-transfer resistance, which suggested the fast Li nucleation on the Au. In addition, we coated aluminum oxide (Al2O3) layer with ~ 26 nm of thickness on the top surface of 3-D Cu scaffold through the atomic layer deposition (ALD) process. This insulating layer further suppressed the Li deposition on the surface. As a result, apparent Li deposition towards the bottom of 3-D Cu was clearly demonstrated. During Li plating/stripping cycles, the surface clogging of the 3-D Cu/Au by an accumulation of solid electrolyte interphase (SEI) was also dramatically alleviated even in the absence of Al2O3 layer. It demonstrated the continuous Li deposition towards the bottom of the 3-D Cu/Au scaffold. Besides, symmetric 3-D Cu/Au cells exhibited over 95 % of Coulombic efficiency (CE) for ~120 cycles. The full cells comprised of the 3-D Cu/Au and LiFePO4 (LFP) electrodes delivered stable 300 cycles with a capacity of ~140 mAh/g at 1 C-rate. I will discuss the detailed role of the Au NPs and the Al2O3 layer, and comparative cell performances in the presentation.
References
[1] D. Lin, Y. Liu, and Y. Cui, Nat. Nanotechnol.
12 (3), 194-206 (2017).
[2] P. Bai, J. Li, F. R. Brushett, and M. Z. Bazant, Energy Environ. Sci.,
9 (10), 3221-3229 (2016).
[3] K. Yan, Z. Lu, H.-W. Lee, F. Xiong, P.-C. Hsu, Y. Li, J. Zhao, S. Chu, and Y. Cui, Nat. Energy,
1 (3), 16010-16017 (2016).

Figure 1
Parametric study of lithium-ion battery using electrochemical model in conjunction with machine learning techniques
Authors: Pathak Anil Daliprasad , Gogineni Ajay K , Pati Soobhankar , Sahu Kisor Kumar 
Published: December 2020

Lithium-ion batteries (LIBs) are widely used in consumer electronics because of its high energy density, superior rate capability, and long cycling life. Lately, the demand for LIBs in other sectors such as automobiles and grid level storage has been growing because of emphasis on renewable energy. However, performance such as rate of charging, energy density, and cost of storing energy ($/kWh) of LIBs does not meet the US-DOE targets for battery electric vehicles. Since, the LIB consists of several components like cathode, anode, electrolyte and separator, its performance is limited by the performance of individual components in the assembled LIB. Further, the performance represents the full LIB and it is difficult to isolate the performance of individual components in the assembled battery. Electrochemical modelling can be extensively used to identify the limitation and improve the performance of individual components since it is an efficient, and cost effective tool. In this work, an isothermal electrochemical model is developed for LIBs with LiC6 anode; LiPF6 based electrolyte, and LiMnO4 cathode. A porous electrode theory is used to describe the insertion and de-insertion of Li+ ions into electrode. A concentrated solution theory is used to describe the transport mechanism in the electrolyte. The Butler-Volmer kinetics is used to model reactions at the electrode/ electrolyte interface.
The electrochemical model developed is solved using COMSOL Multiphysics® 5.1a finite element modelling software. The modeling results are verified with the experimental results available in the literature. The model is used to evaluate the influence of various design parameters that influence the performance of LIB such as the electrode dimensions, structure, conductivity, etc. Furthermore, the electrochemical model data was used to develop machine learning techniques such as random forests (RF), support vector machine (SVM) and gradient boosting (GB) for feature-analysis of the LIB parameters. Feature analysis, an extremely important metric for estimating relative importance of a particular parameter, were studied towards understanding the relative importance of other parameters for maximizing energy and power density of a battery. Random forest techniques performed well for predicting the energy density which is depend on thickness (after current) but gradient boosting failed to predict it (as shown in Fig.1). However, gradient boosting techniques performed well for forecasting power density which depend on conductivity (after current), here random forest failed to predict this. Without such feature-analysis by machine learning techniques, it would have been very difficult to have a quantitative estimation of their ranking towards understanding the relative importance of other battery parameters for maximizing energy and power density of LIBs.

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Development of Non-Deteriorating Lithium-Sulfur Battery
Authors: Machida Kazuki , Ushioda Yusuke , Inaba Kohei , Miyauchi Hibiki , Takahashi Keitaro , Seki Shiro 
Published: December 2020

To resolve energy issues, the demand of large-scaled capacity storage batteries are increasing. Therefore, the realization of lithium-sulfur (Li-S) battery, which is one candidate of the next-generation high-performance innovative battery systems, is strongly desired. In general, lithium metal is used as the negative electrode for Li-S batteries. On the other hand, elemental sulfur (S8) is also used as the positive electrode, and it has high theoretical reversible capacity of 1,672 mAhg-1. However, effect of Li metal negative electrode is unclear due to their chemical properties with charge/discharge process. In this study, we applied Li-doped negative electrode for suppressing the Li-dendrite formation. Therefore, we obtained Li4Ti5O12 (LTO) electrode as stable negative electrode, which is strain-free intercalation material, and high reversible characteristics of battery system are expected.
To applying LTO for Li-S batteries, electrochemical doping of Li into LTO is required owing to their lack of carrier ion into LTO. Therefore, at first [Li| electrolyte |LTO] cells were assembled by using disassemble cell, which can be easily taken out cell materials without short circuit into inert atmosphere (e.g., glove box). After takeoff of Li-doping LTO (Li-LTO), lithium (Li-doped) -sulfur battery was fabricated by using SPAN as sulfur positive electrode ([Li-LTO|1M-LiFSI EC/DEC=3/7|SPAN] cell). (SPAN:developed non-degraded S positive electrode). Charge / discharge performance of prepared cells were evaluated.
Fig. 1 (a) and (b) shows the charge and discharge profiles and the cycle number dependences of coulombic efficiency for prepared cell at 303K. Although operating voltage and capacity are relatively low, charge and discharge over 2000 cycles were observed. Therefore, this cell has suitable constitution in battery materials. Within 200 cycles, high coulombic efficiencies (about 99.9%) were always observed. Therefore, it suggests the possibility of realizing a non-degraded battery, which has high reversible characteristics by using Li-LTO electrode and SPAN electrode.

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Modifying Carbon Felt Electrodes Using High-Temperature Ammonia Treatment to Improve the Performance of All-Vanadium Redox Flow Batteries
Authors: Gass Kaycee , Bera Bapi , Aaron Douglas , Mench Matthew M 
Published: December 2020

High temperature ammonia treatments were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.
Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without intervention, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to make it more effective, which has been historically accomplished with thermal treatments to promote oxygen functional groups. [1] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [2-4] Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. [5]
For our experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at 900°C for varying lengths of time. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.
The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. A pitting effect was observed in SEM images, preceded by surface blistering at shorter lengths of exposure.
Greatly increased active surface area, along with a substantial increase in cell performance, was achieved with the ammonia-modified carbon felts described in this work.

Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment. Electrochimica Acta, 1992. 37(7): p. 1253-1260.

Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces. Energy & Environmental Science, 2016. 9(7): p. 2319-2325.

Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries. Journal of Power Sources, 2016. 325: p. 329-336.

Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries. Energy Storage Materials, 2020. 25: p. 885-892.

Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016.

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(Invited) Spatial ALD Challenges and Opportunities in Advanced Integrated Circuit Manufacturing
Authors: O'Meara David , Dip Anthony , Igeta Masanobu , Clark Robert D. , Higuchi HIsashi , Liu Eric , Raley Angelique , Smith Jeffrey , Tapily Kandabarra , Triyoso Dina , Leusink Gert J. 
Published: December 2020

Miniaturization in Integrated Circuit fabrication has scaled to atomic dimensions in recent times. With critical device dimensions moving into the range of ~10nm, atomic layer processing control is becoming essential. Atomic Layer Deposition (ALD) uses separated film components at (or near) self-limiting conditions for atomic level uniformity and thickness control. The unique nature of ALD processing has opened the opportunity for a deposition technique that presents deposition components in a spatially separated method compared to sequential component exposure of traditional systems. Spatial ALD has differentiating characteristics that can benefit IC Fabrication at current fabrication dimensions.
Historically, deposition systems for IC fabrication use batch furnace or single wafer configurations. The economic benefit of batch furnace processing has been challenged by the enhanced capabilities of single wafer processing as IC scaling emphasized critical film properties and uniformity. ALD processing has rejuvenated batch furnace benefits since separate exposures of deposition components provides excellent uniformity from self-limiting deposition layers, and lower particle defectivity since the components don’t mix. However, the sequential processing of individual components has strained the efficiencies of batch furnace and single wafer ALD processing.
Spatial ALD moves substrates (wafers) through each deposition component separately in space, compared to the time sequential processing of batch furnaces and single wafer processing. There are several advantages to Spatial ALD processing, and several unique capabilities that can apply to IC fabrication. By depositing through movement, the deposition components can be maintained through a steady state, which is advantageous for plasma processing and for limiting peripheral equipment film accumulation. By its nature, the deposition rate of Spatial ALD is controlled by the speed of substrates passing through the deposition zones, which can provide unique controls for deposition. Deposition chemistry and process conditions can be designed to take advantage of Spatial ALD properties for unique benefits in IC fabrication. The presentation will explore some fundamental aspects of Spatial ALD processing, the dependency and opportunities of relevant chemistries, and potential applications for the unique capabilities of Spatial ALD, including unsaturated process conditions.
Atomic Layer Deposition for Surface Area Characterization of Porous Solid Oxide Fuel Cell Electrodes and Beyond
Authors: Schmauss Travis Anthony , Barnett Scott A 
Published: December 2020

Conventional surface area determination techniques are inadequate for calculating the surface areas of porous solids with absolute totals less than ~1 m2, but with nm-scale feature sizes, such as state-of-the-art, lab-scale solid oxide fuel cell electrodes. Meaningful contextualization of their electrochemical performance requires knowing system surface area, but the two predominant classes of techniques, tomography and gas adsorption theory, either lack the resolution or require prohibitive amounts of material. Presented here is a new method for the accurate determination of absolute surface areas on the order of 1-1000 cm2 with precision ±0.3 cm2 utilizing atomic layer deposition (ALD) of commonly available trimethylaluminum (TMA) and water vapor to conformally deposit alumina over internal features. The area of alumina can then be quantified using plasma spectroscopy and the known nm-scale thickness of the layer. As a model system, scaffolds of La0.8Sr0.2MnO3-δ/Ce0.9Gd0.1O2-δ (LSM/GDC) of 2.6 m2/g were measured under the new technique and compared against the B.E.T. method, with remarkably similar results obtained, but with ~1000 times less mass needed for the experiment. Under the modest ALD reactor soak times used (~10 s), and with conservative precursor pulse durations, the penetration depth of the coating was found to be ~50 µm, exceeding the requirement for the electrodes under study. To demonstrate the technique’s capabilities further, the LSM/GDC scaffolds were infiltrated with PrOx nanoparticles of ~50 nm, and the increase in surface area (+ ~25%) and enhanced electrochemical performance were measured. After annealing for 1000 hours at 700°C, both were again measured, and the surface area was found to have reverted to non-infiltrated levels, despite the infiltrated cells maintaining their higher performance. The technique, due to its ease versus other surface area determination methods and its pairing with an established analytical chemistry method, enables a useful combined chemical/morphological approach to the characterization of next-generation solid oxide cell electrodes, and may find other uses among nanostructured yet low absolute surface area systems in the broad field of heterogeneous catalysis.
Figure 1. Measured specific surface areas for La0.8Sr0.2MnO3-δ/Ce0.9Gd0.1O2-δ (LSM/GDC) scaffolds and the ALD Al2O3-based technique, in lab-scale mg quantities, versus the B.E.T. method result for gram-scale LSM/GDC flakes. Shown is ALD-derived surface area quantified both via inductively coupled plasma-optical emission spectroscopy (ICP-OES) (Blue) and gravimetrically (Green), with the ICP-OES offering comparable accuracy and precision to the B.E.T. (Purple). Error bars reflect repetition of the same sample (intra-cell) and among different samples (inter-cell).

Figure 1