bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconformal Filling of High Aspect Ratio through Glass Vias for Interposer Applications Using Tnbt and Ntbc Additives
Authors: Dimitrov Nikolay , Ogutu Paul , Fey Edmond
Published: February 2020

The drive toward higher circuit density and higher operating frequencies in electronic packaging has led to the employment of interposers between the Si chip and the underlying package. Currently Si or glass, both are considered materials feasible for the fabrication of interposers.   Through-holes are needed to make connections between the top and bottom surfaces of the interposer.  This can be done with conformal Cu plating, but especially in the case of glass it is also desirable to fill the through glass vias (TGVs) with Cu to compensate for its poorer thermal conductivity compared to Si.  Filling also enables formation of a flat surface for subsequent layers or for component attachment.  Techniques have already been developed for filling “blind” holes/vias by Cu electroplating using combinations of suppressors and accelerators.  In the case of Si, through-vias have been generated by first filling holes as blind ones. Then thinning the back side of the wafer by CMP is applied until the bottoms of the filled vias are intersected, thereby producing filled through-holes. Alternatively, sealing one end of the through vias could be made and then one could fill them as blind vias.  In the case of glass, TGVs may be formed directly into the glass without the need for mechanical thinning, but this leaves the problem of filling the holes as through-holes, open on both ends.  The aforementioned plating methods for filling of blind vias do not work well when directly applied to filling of TGVs, and a different approach is needed. 

In this report, Cu superconformal filling of through glass vias (TGV) of aspect ratios (AR) 6:1 and 10:1 for glass interposer applications is achieved by  DC electroplating in the presence of the additives tetranitroblue tetrazolium Cl- (TNBT) and nitroblue tetrazolium Cl-  (NTBC) in acidic CuSO4/ Cl-  formulations.  Filling takes place by the so-called ‘butterfly’ mechanism that nucleates Cu plug in the TGV’s center and keeps low surface coverage.  Holes of AR 6:1 are filled in 3 hours at 2.5 mA.cm-2, using a bath composed of 40 ppm TNBT, 80 ppm Cl-, 0.88M CuSO4, and 0.3M CH3COOH under stagnant conditions.  Increasing [TNBT] to 80 ppm and [Cl-] to 120 ppm in the presence of 0.3 M CH3COOH allows filling of 10:1 AR holes in 12.5 hours at 1.0 mA.cm-2 while maintaining thin surface coverage.  In the case of NTBC, 6:1 holes are filled in 4-5 h at 2.5 – 4.0 mA.cm-2, and 10:1 holes are filled in 12-13 h at 1.0 to 1.5 mA.cm-2 in a slowly stirred bath containing 0.88 M CuSO4, 80 ppm Cl-, 0.6 M H2SO4, and 45-50 ppm  NTBC.  Bath composition is necessary to avoid void-formation in the holes.  Effects of composition on overvoltage and Cu surface topography are discussed. Finally, a critical discussion on some mechanistic aspects of the supeconformal filling process, taking place according to the Figure, is also presented.

Figure 1
Novel Si Etching and Dielectric Liner Film Processing Technologies for Low-Cost TSV Packaging
Authors: Morikawa Yasuhiro
Published: February 2020

In recent years, "2.5D silicon interposers" and "Full 3D stacked" technology for high-performance LSI circuits has attracted much attention since this technology can solve interconnection problems by using TSVs (Through Silicon Vias) to electrically connect stacked LSI circuits. 2.5D and 3D Si integration has great advantages over conventional 2D devices such as a high packaging density, small wire length, high-speed operation, low power consumption, and a high feasibility for parallel processing. Yet, the problem of cost-effective TSV production is still to be solved. In particular, the demand for a new plating bath technology to shorten the Cu plating time is pressing. In addition, TSV isolation liner materials will be necessary with lower cost for the production of future high-frequency devices.

A new etch process has been developed for scallop-free and taper-shaped TSV fabrication [1]. By using a direct etch process instead of cycled etching, TSVs were obtained with smooth-sidewalls and tapered profiles. The absence of scallops has a positive effect on signal transmission speed. Also, the direct etch process allows for shorter TSV fill process times and thus provides lower cost of deposition processes like PE-CVD, PVD and Cu-ECP (electrochemical plating) [2,3]. A cost correlation of taper-shape etching and Cu-ECP (electro-chemical plating) will be included.

For the TSV isolation, polyurea dielectric liners were successfully deposited using a vapor deposition polymerization technology (which is Ulvac’s FPF/PV large panel technology). This process allows for isolation liners in next-generation high-frequency devices and for the film formation into a TSV pattern.

In summary, a novel low-cost TSV fabrication flow can be provided for 2.5 / 3D Si integration in high-frequency applications. The process flow yields scallop-free and taper TSVs, which can be filled effectively with electroplated copper and polyurea dielectric liners.

References

[1] Y. Morikawa, et al., “Scallop Free TSV Etching Method for 3-D LSI Integration”, Proc. Int. Symp. on AVS 57th, Albuquerque, New Mexico, Nov. 1, 2010, p 121.

[2] Y. Morikawa, et al., “A Novel Scallop Free TSV Etching Method in Magnetic Neutral Loop Discharge Plasma”, in Proc. IEEE Electronic Components and Technol. Conf. (ECTC 2012), San Diego, CA, May 29 – June 1, 2012, pp. 794–795.

[3] Y. Morikawa, T. Murayama, Y. Nakamuta,  T. Sakuishi, A. Suzuki, and K. Suu, “Total Cost Effective Scallop Free Si Etching for 2.5D & 3D TSV Fabrication Technologies in 300mm Wafer”, Proc. IEEE Electronic Components and Technol. Conf. (ECTC 2013), Las Vegas, NV, USA, May 28 – 31, 2013, pp. 605–607.
Lithium Plating and Stripping in the Framework of a 3D Electrochemical Model
Authors: Hein Simon , Latz Arnulf
Published: February 2020

The range of application of lithium-ion-batteries (LIB) is vast. It ranges from consumer electronics, like smartphones, to battery packs inside of electric vehicles. While cell size and geometry may differ, the electrodes are subject to the same degradation mechanisms. One of these processes is known as “lithium plating”. While charging a lithium-ion-battery with high currents or during operation at low ambient temperatures ( T < 0 °C), lithium ions can deposit on the surface of the negative electrode. The resulting metallic film can lead to increased solid electrolyte interphase growth, and may even create an electrical short-circuit, potentially causing a thermal runaway of the whole battery. Therefore it is desirable to hinder or, if possible, prevent the deposition of metallic lithium on the electrode surface.

To pursue this objective, a better understanding of which operating conditions, at which spatial locations inside the electrode microstructure and which material most parameters influence the deposition is vital. Since it is not convenient to measure the exact electrochemical situation at the electrode surface during operation, theoretical modeling and simulation is the tool of choice.

We present a model describing the initialization, growth and dissolution of a metallic lithium phase. This model is incorporated into the framework of a 3D microstructure resolved model [1, 2]. This is achieved by extending the mathematical description of the interfaces to consider the governing differential equations of surface species. These surface modifications allow for the simulation of the electrode surfaces, on which metallic lithium nucleates and grows. In the presented model, a complete coverage of the surface with a metallic lithium film results in the blockage of the direct intercalation pathway.

The influence of the geometry of the negative electrode and operating conditions on the cell performance and electrochemical conditions is investigated. The cell voltage plateau during discharge of a LIB, which contains plated lithium, [3, 4] can be attributed to chemical intercalation of metallic lithium into the supporting active material, as well to electrochemical dissolution.

[1] Battery and Electrochemical Simulation Tool, http://www.itwm.fraunhofer.de/best

[2] A. Latz and J. Zausch, J. Power Sources, 196 (2011), pp. 3296–3302.

[3] M. Petzl and M. A. Danzer, J. Power Sources, 254 (2014), pp. 80-87.

[4] B.V. Ratnakumar, M.C. Smart, J. Electrochem. Soc. Trans. 25 (2010), pp. 241-252.
Analyzing Capacitive Characteristics of Lithium-Ion Batteries Using a Distribution Function of the Differential Capacity
Authors: Schoenleber Michael , Ivers-Tiffée Ellen
Published: February 2020

By analyzing the Distribution Function of Relaxation Times (DRT) of a measured impedance spectrum one can separate different loss processes and thereby study which physical mechanisms contribute how strongly to the overall polarization resistance. The method is based on the idea that certain parts of an impedance spectrum can be represented by a serial connection of parallel RC-Elements [1].

The DRT has been successfully used for analyzing the polarization processes taking place in Solid Oxide Fuel Cells (SOFC) as well as in Li-Ion batteries [2][3]. For the latter however, the analysis had to be limited: Due to the structure of the underlying modelling approach using parallel RC-elements, only the non-capacitive region of the impedance could be analyzed using the DRT. Accordingly, information contained within the capacitive region could not be utilized optimally so far.

For analyzing capacitive characteristics we therefore propose to adapt the concept of DRT to capacitive systems yielding a Distribution Function of Differential Capacities (DDC).

By physical means this function states how much load is intercalated how fast into an electrode after applying a voltage step. Figure 1 further exemplifies the concept by showing

(i) a simple model system consisting of three intercalation pathways.

(ii) the non-measurable intercalation currents over time exhibiting the different time constants with which the partial capacity of different-sized particles can be utilized.

(iii) the according shape of the DDC, which allows to quantify time-constants and capacity contributions of different-sized particles from simple impedance measurements.

Hence, using the proposed DDC allows to easily obtain information regarding an electrodes capacitive characteristics and can therefore serve as a supporting tool for custom-tailoring modern electrode microstructures.

A detailed motivation and derivation of the new method will be given and first results will be shown.

REFERENCES

[1]    H. Schichlein, A.C. Müller, M. Voigts, A. Krügel, E. Ivers-Tiffée, “Deconvolution of electrochemical impedance spectra for the identification of electrode reaction mechanisms in solid oxide fuel cells”, J. Appl. Electrochem. 32, p. 875-882 (2002).

[2]    A. Leonide, V. Sonn, A. Weber and E. Ivers-Tiffée, “Evaluation and Modeling of the Cell Resistance in Anode-Supported Solid Oxide Fuel Cells”, J. Electrochem. Soc., 155 (1), p. B36-B41 (2008).

[3]    J. Illig, M. Ender, T. Chrobak, J. P. Schmidt, D. Klotz and E. Ivers-Tiffée, "Separation of Charge Transfer and Contact Resistance in LiFePO4-Cathodes by Impedance Modeling", J. Electrochem. Soc. 159, p. A952-A960 (2012).

Figure 1
Discovery of New Anode SEI Forming Additives Using an in silico Evolutionary Approach
Authors: Murdock Stuart E. , Hughes Thomas F. , Kwak Shaun H. , Goldberg Alexander , Giesen David J , Cao Yixiang , Sanders Jeffrey , Gavartin Jacob , Dathar G. K. Phani , Halls Mathew D.
Published: February 2020

To reduce the capacity fade and improve the performance associated with lithium-ion batteries functional additives are used to reduce damage to the electrolyte by forming SEI layers when the cell is charged. Two major factors defining a successful anode SEI former are a high reduction potential and a high reactivity.  

High throughput quantum chemistry screening of large libraries of structures is an approach that is becoming more popular with the ever decreasing cost of CPU cycles, however this can be a time consuming and highly curated procedure. The automated evolution of a set of input structures and defining the direction in which chemical properties should be automatically adjusted requires less user management and enables knowledge creation rather than knowledge implementation. As the expense of computing resources decreases a monitored genetic algorithm to improve the chemistry of an initial set of structures can be a faster method requiring less user intervention than traditional high throughput chemistry.

In this presentation we show how we reduce the chemical hardness and increase the reduction potential of a set of potential SEI additives or structures having potential SEI additive traits automatically while additionally suggesting optional structural characteristics that the molecules should have. An improvement of these characteristics of a set of input structures is shown using our genetic optimization through supervised learning.
Computational Modelling Study on Electrochemical Activity of Nanoporous and Bulk Beta MnO2
Authors: Ngoepe Phuti Esrom , Sayle Thi X T , Sayle Dean C
Published: February 2020

Nanostructured manganese dioxides (MnO2) are among the promising materials for high-capacity lithium-ion batteries [1], lithium air batteries [2] and supercapacitors [3], that can be used in electric vehicles and other consumer electronics. They further have several advantages owing to their high specific energy capacity, low fabrication cost, abundance of the materials in the earth, and environmentally friendly nature [4]. Various experimental methods have been employed for the synthesis of MnO2 with various nano-architectures such as the spheres, sheets, porous, wires, rods [5,6] etc.

Simulated amorphisation recrystallisation method has been successfully used to nucleate and crystallise bulk and nanoporous β-MnO2 [7]. In the current study molecular dynamics simulation reveals that the reason nanoporous β-MnO2 is electrochemically active, in contrast to the parent bulk material, is because strain imposed upon nanoporous β-MnO2 during lithium intercalation does not influence the structure or dimensions of the 1D tunnels in which the lithium ions intercalate and reside. Conversely, the parent bulk material suffers structural collapse of the 1D tunnels under strain.

[1] B.X. Li, G.X. Rong, Y. Xie, L.F. Huang and C.Q. Feng, Inorg. Chem. 2006, 45, 6404.

[2] A. Débart, A.J. Paterson, J. Bao and P.G. Bruce, Angew. Chem., Int. Ed. 2008, 47, 4521.

[3] W. Wei, X. Cui, W. Chen and D.G. Ivey, Chem. Soc. Rev. 2011, 40, 1697.

[4] S. Devaraj and N. Munichandraiah, J. Phys. Chem. C 2008, 112, 4406.

[5] J.H. Cheng, G.A. Shao, H.J. Yu and J.J. Xu, J. Alloys Compd. 2010, 505, 163.

[6] X. Wang and Y. Li,  Chem. Eur. J. 2003, 9, 300.

[7] P.E.Ngoepe, R.R. Maphanga and D.C. Sayle, (2013), “Towards the Nanoscale”, Chapter 9 in Computational Approaches to Energy Materials, pp 261-290, edited by C.R.A. Catlow, A. Sokol and A. Welsch, John Wiley and Sons Ltd.
(Invited) Predicting the Properties of Interfaces Between Electrolytes and Electrodes: Condensed Matter Physics Meets Electrochemistry
Authors: Galli Giulia
Published: February 2020

We will discuss the results of ab initio simulations of the interfacial properties of water and aqueous electrolyes with insulating and semiconducting electrodes. These simulations are carried out with methods borrowed from condensed matter physics and adapted to tackle complex electrochemical processes. The challenges associated with comparisons with experiments will be addressed as well.
First-Principles Based Modeling of Li-Metal/Solid-Electrolyte Interfaces in Application to Li-Batteries
Authors: Cheng Tao , Merinov Boris V , Kozinsky Boris , Goddard William A
Published: February 2020

All solid-state batteries could store significantly higher energy compared to conventional lithium-ion batteries using liquid electrolytes, simultaneously highly increase the safety. They are promising for future wide applications, such as wearable device, phones and even electric cars. However, several critical issues (e.g. low conductivity of solid electrolyte, mechanical and chemical stabilities of interfaces etc.) need to be solved before commercialization of all solid-state batteries. The knowledge of the fundamental aspects of these issues would highly accelerate the process of searching and designing the advanced materials and structures for efficient and low cost all solid-state batteries. The interfacial interactions are complicate and difficult to characterize experimentally. There is insufficient understanding of the interface formation processes and factors affecting interfacial structures, charge transfer and ion transport, chemical and mechanical stability and degradation. We use first-principles based methods, such as QM and ReaxFF [1] reactive molecular dynamics (MD) to achieve better understanding of these problems. A family of sulfide ceramics, so-called Li-argyrodites, Li6PS5X (X = Cl, Br, I), shows high ionic conductivity (~7 · 10−3 S/cm at 298 K) [2] and might be considered as a possible candidate for solid electrolyte for Li-batteries. These materials can provide a balance of efficiency and price. We have built the Li6PS5Cl structure and Li/Li6PS5Cl interface and performed QM MD and ReaxFF MD simulations on this systems. The results of these simulations will be reported together with results obtained for some other interface systems of interest.

 

Acknowledgements. This work was financially supported by Bosch Energy Research Network Grant No. 13.01.CC11.

References

[1]   A.C.T. van Duin, .C.T., S. Dasgupta, F. Lorant, W.A. Goddard III “ReaxFF: A Reactive Force Field for Hydrocarbons” J. Phys. Chem. A 105,9396-9409, 2001.

[2]   H.-J. Deiseroth, S.-T. Kong, H. Eckert, J. Vannahme, C. Reiner, T. Zaiβ, M. Schlosser ”Li6PS5X: A class of crystalline Li-rich solids with an unusually high Li+ mobility” Angew. Chem. Int. Ed. 47, 755-758, 2008.
(Invited) Insights into Solvation, Dynamics and Stability of Electrolytes for the Design of Novel Multivalent Systems from Coupled Molecular Dynamics and First-Principles Modeling
Authors: Persson Kristin A , Rajput Nav Nidhi , Qu Xiaohui
Published: February 2020

Within the Joint Center for Energy Storage (JCESR) we have developed a high-throughput infrastructure for the automated calculation of molecular properties with a focus on battery electrolytes. Computational screening techniques have been found to be an effective alternative to the trial and error of experimentation for discovery of new materials. Using this infrastructure, we have computed the ionization potential (IP) and electron affinities (EA) of 16,000 molecules relevant to electrolytes targeting both multivalent intercalation as well as non-aqueous redox flow systems. For some potential multi-valent electrolytes we use classical molecular dynamics simulations coupled with ab initio calculations for Mg salts in various solvents. We uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potential, e.g., at the metal anode1. We elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics.

Specifically, we find that multivalent electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. For example, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg2+→Mg+), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI− exhibits a significant bond weakening while paired with the transient, partially reduced Mg+. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt. We use our previous insights to design for new Mg electrolyte anions with the aim to stabilize the electrolyte during possible ion pair formation and charge transfer reactions. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics, we proposed 16 new electrolyte salts. Based on successive property evaluation such as electrochemical stability window, chemical decomposition and hydrolysis vulnerability we down-select 4 potential new anions for Mg electrolytes.

References

[1] N. N. Rajput, X. Qu, N. Sa, A. K. Burrell, K.A. Persson, “The Coupling between Stability and Ion Pair Formation in Magnesium Electrolytes from First-Principles Quantum Mechanics and Classical Molecular Dynamics”, Journal of the American Chemical Society, 2015.

[2] X. Qu, A. Jain, N. N. Rajput,Y.Zhang, S.P.Png, M. Brafman, L.Cheng, E. Maginn, L.A. Curtiss, K.A. Persson, “Electrolyte Genome Project: A Big Data Approach in Battery Materials Discovery”, Computational Materials Science, 2015.
Computational Study of Li2SnO3 and Li2SnS3
Authors: Howard Jason David , Holzwarth Natalie A. W.
Published: February 2020

First principles simulations were used to study Li ion mobilities in Li2SnO3 and Li2SnS3.  These simulations determined the activation energies (Ea) for Li ion migration primarily considering the vacancy mechanism; calculations for the interstitial mechanism are ongoing.  Experimental values for Ea
 are available for each material [1, 2 ]. For over a decade,  Li2SnO3 has been of interest as a promising anode material.  It is known that when lithiated, Li2SnO3 will undergo an irreversible decomposition to Li2O and  SnLix alloys [3].  The residual Li2O matrix is said to stabilize the volume change during charging/discharging of the SnLix anode [4]. It is of primary interest to investigate both Li2SnO3  and Li2SnS3 for these properties using simulations.

Acknowledgments

            The computational portion of this work was supported by NSF grant DMR-1105485. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the University.

References

[1]   J. A. Brant et al,   Chemistry of Materials 
27, 189-196 (2015)

[2]   L. P. Teo et al,    Ionics
18, 655–665 (2012)

[3] I. A. Courtney and J. R. Dahn,  J Electrochem. Soc.
144, 2045–2052 (1997)

[4] D.W. Zhang et al,  Journal of Alloys and Compounds
415, 229–233  (2006)
(Keynote) Imaging Electrochemical Growth Using Liquid Cell Transmission Electron Microscopy
Authors: Ross Frances M
Published: February 2020

Transmission electron microscopy is very helpful in measuring structure and composition after electrochemical growth has finished. However, it is also possible to image structures while they are still growing, by carrying out electrodeposition inside the electron microscope. The trick is to confine the electrolyte in a layer that is thin enough to be transparent to the imaging electrons – of the order of a few hundred nanometers – and to include electrodes with a geometry that allows the reaction to be controlled and visualized. To do this, we use microfabrication techniques to build liquid cells with thin windows of silicon nitride. Once filled with electrolyte, a liquid cell is placed in the microscope and controlled by a potentiostat during imaging. We can then relate changes in morphology to electrochemical parameters, providing a detailed probe of growth mechanisms with good temporal and spatial resolution.

In this presentation, we first describe practical aspects of liquid cell electron microscopy, particularly the competing requirements of resolution and diffusion – in other words, the extent to which a liquid layer that is thin enough to provide high resolution images can also replicate a process of interest. We then describe measurements of nucleation and growth during the deposition of metal films, and quantify the onset of growth instabilities. We show movies of the interface evolution of galvanostatically deposited Cu from an acidic electrolyte: initially, the kinetics are consistent with kinetic roughening theory, and later, with diffusion limited growth models. Macroscale models appear to predict the behavior over long length and time scales, but short scale behavior differs from spatially averaged measures, affecting the onset of the instability. We demonstrate some control of interface evolution through pulse plating and inorganic additives. We finally discuss liquid cell microscopy of electroless deposition and of corrosion processes in metal films, and combine metal dissolution with reduction by the electron beam to produce nanostructures. Developments in equipment and modelling are making liquid cell microscopy increasingly quantitative, suggesting exciting possibilities for detailed interrogation of a wider range of electrochemical growth physics.
(Invited) A Coverage Dependent Behavior of Pt on Au Deposited Using Surface Limited Redox Replacement
Authors: Vasiljevic Natasa , Al Amri Zakiya
Published: February 2020

Different Pt bimetallic nanostructures, such as ultrathin Pt overlayers, alloys and nano-clusters, have been a focus of intense research because of their enhanced catalytic activity compared to the bulk Pt. Over the last few decades our fundamental understanding of the effects responsible for their electro catalytic behavior, such as bifunctional, electronic and ensemble effects, has advanced by the development of theoretical models and studies on model 2D systems enabled by development of new electrodeposition methods and routines to control their structure [1-4].

Studies of Pt-nanoclusters have shown strong correlation of surface activity with the structure and distribution of Pt on the surface [4, 5]. An enhancement of CO tolerance on supported Pt/Ru catalysts obtained by spontaneous deposition has been shown at a considerably lower Pt loading than on the commercial catalysts [6]. The modified Au surface with Pt nanosize clusters coverage as low as 15-25% of the substrate area, exhibit very high activity and improved selectivity toward dehydrogenation of formic acid (HCOOH) [7]. Most recently formation of Pt monolayer catalysts and nanoclusters using Surface Limited Redox Replacement (SLRR) method has been used to show the effect of strain and morphology on the catalytic behaviour [4].  

Here in this work we present the study of Pt-nanoclusters on Au substrate as a function of their size, and areal coverage. We compared the design of Pt nanoclusters using two electrochemical approaches: i) spontaneous deposition (SD) i.e. reduction of the spontaneously adsorbed Pt-complex and ii) the surface limited redox replacement (SLRR) method based on the redox  replacement of  Pb underpotentially deposited layers.  For each method successive application of optimized electrodeposition protocols yielded increased Pt surface coverage ranging from 0.25 to 1 area fraction. Using two different methods enabled design of nanocluster with varied cluster sizes and the areal coverage of Au. The structure and distribution of Pt nanoclusters was determined by electrochemical techniques (H-UPD and CO adsorption) and scanning tunneling microscopy (STM). Their catalytic behavior was analyzed and compared during formic acid electro-oxidation.

References:

1. W. Chrzanowski; H. Kim and A. Wieckowski, Catal. lett., 50 (1998),  69.

2. S. R. Brankovic, J. X. Wang, R. R. Adzic. Surf. Sci. 474, (2001), L173.

3. L. Bromberg, M. Fayette, B. Martens, Z. Luo, Y. Wang, D. Xu, J. Zhang, J. Fang, and N. Dimitrov, Electrocatalysis, 2013, 4 (2013), 24.

4. R. Loukrakpam, Q. Yuan, V. Petkov, L. Gan, S. Rudi, R. Yang, Y. Huang, S.R. Brankovic and P. Strasser, Phys.Chem.Chem.Phys.,16 (2014), 18866.

5. B. Du and Y. Tong, J. Phys. Chem. B, 109 (2005), 17775.

6. S. Brankovic; J. McBreen and R. Adzic, J. Electroanal. Chem., 503 (2001),  99.

7. M. Obradović; A. Tripković and S. Gojković, Electrochim. Acta, 55 (2009),  204.
Cu Underpotential Deposition on Ru(0001)
Authors: Brankovic Stanko , Wu Dongjun
Published: February 2020

The underpotential deposition (UPD) has attracted research attention for many years due to its fundamental and practical importance[i]. Development of scanning probe methods (STM and AFM), and X-ray scattering techniques has enabled mechanistic in situ studies for many substrate-adlayer systems with great insight in details of UPD adlayer formation and structure, alloying and anion co-adsorption[ii]. However, in some cases, the noble metal surfaces with complex reactivity and interaction with water based electrolytes have rendered UPD studies a very difficult endeavor. One example is Ru surface for which a just few UPD studies have been reported[iii]-,[iv],[v],[vi],[vii].  

Our talk presents a study of Cu UPD on Ru(0001). The Ru(0001) surface was prepared by annealing at 1400 C for one hour in Ar+H2 atmosphere (96:4), Figure 1. After cooling the Ru surface was protected by CO-saturated 0.1 M HClO4 solution and transferred to the electrochemical cell or STM cell for further studies.  The example of the cyclic voltammetry and insitu STM results are shown in Figure 1. The potential has been gradually changed towards the region where Cu UPD on Ru(0001) occurs and high resolution/quality STM images were recorded. The morphological change of Ru(0001) surface due to Cu UPD process were correlated with CV data and characteristic cathodic and anodic peaks in CV were associated with particular features/process occurring during Cu UPD deposition and/or stripping. The Cu UPD process and adlayer structure on Ru(0001) is compared with corresponding Cu UPD process on other closed pack surfaces such as Au(111) and Pt(111). The apparent similarities and differences were identified and discussed during the talk. 

The authors acknowledge the support from NSF Chemistry division under the contract # 0955922.

Figure 1. Cyclic voltammetry for Cu UPD on Ru(0001), scan rate 10 mV/s. Solution: 0.1 M HClO4 + 10-3 M Cu2+. Inset shows Ru crystal during inductive annealing.

[i] S. Trasatti, J. Electroanal. Chem.
33, 351 (1971),

[ii] E. Budevski, G. Staikov and W. J. Lorenz in Electrochemical Phase Formation and Growth, ed. R.C. Alkire et al. VCH, Berlin (1996), see Ref. herein.

[iii] M. Vukmirovic, in Modern Aspects of Electrochemistry, vol. 42, ed. C. Vayenas et al. Springer, NY (2008).

[iv] N. Bogolowski, S. Huxter, A. –E.  Abd-El-Latif,G.A. Attard, H. Baltruschat, Journal of Electroanalytical Chemistry, 646, 68 (2010).

[v] D. K. Gebregziabiher,Y-G. Kim, C. Thambidurai, V. Ivanova, P-H. Haumesser, J.L. Stickney, Journal of Crystal Growth,
312 1271 (2010).

[vi] Y. Zhang, L. Huang, T. N. Arunagiri, O. Ojeda, S. Flores, O. Chyan, R. M. Wallace, Electrochemical and Solid-State Letters, 7 C107 (2004).

[vii] M. A. Quiroz, L. Salgado, Y. Meas, Electrochimica Acta, 33 435 (1988).

Figure 1
(Invited) Advanced Materials for Integrated on-Chip Power Converter
Authors: Deligianni Hariklia (Lili) , Wang Naigang , Jinka Oblesh , Yoon Joonah , O'Sullivan E. J. , Romankiw Lubomyr , Gallagher W. J.
Published: February 2020

We describe electrolessly plated magnetic material
s
required for the demonstration of a monolithically integrated on-chip inductors. Miniaturization of magnetic inductors and integration on semiconductor chips requires the choice of high performance magnetic materials. The requirements are soft magnetic properties with low coercive force (Hc < 1.0) and high saturation magnetization, high resistivity (r >=110 mohm cm) to reduce inductor losses at high frequencies from eddy currents, and excellent thermal stability to a processing temperature that is dictated by the integration process on-chip (>200~250oC).  This work demonstrates that a Co85W5P10 thin film deposited using electroless chemistry on a Pd activated Ni80Fe20 seed layer meets all the materials requirements for a low process temperature integrated inductor.  A 1.2 mm thick CoWP layer deposited on a 60nm Ni80Fe20 seed layer has a resistivity of 110 mohm cm and its moment and anisotropy are stable after 200oC thermal cycling.  The work also shows that the initial stages of growth, starting from the magnetic Ni80Fe20 seed layer surface, affect greatly the growth and thermal stability of the CoWP film.  As far as maintaining a higher ~250°C thermal processing limit, we obtained encouraging data for CoWP and NiFeBP films thinner than 300nm grown by electroless deposition. We will also discuss approaches to achieving laminated films incorporating these materials.
Light Assisted Electrodeposition for the Metallization of Silicon Solar Cells
Authors: Huang Qiang , Papa Rao Satyavolu , Fisher Kathryn
Published: February 2020

Cu electroplating is of a great deal of interest for the metallization of silicon solar cells due to its comparable resistance with the current silver metallizaion, and its lower cost for both the material and the operation.[1,2] However, the notorious Cu diffusion into Si is of great concern to the devices performance degradation during the life cycle of the cells. Ni silicide and Ni metal layers have been recently reported as part of the integration scheme to enable the Cu metallizaion and greatly improved the solar cell reliability.[3,4] The formation of this Ni silicide and Ni stack structure is to provide a low-resistance contact between the silicon and metal grid, a good adhesion of metal grid, and a diffusion barrier for the Cu. Among them, the Ni silicide formation needs to be well controlled so that it is not too thick to shunt the solar cell.

This paper will present the light assisted plating of Ni and the silicide formation on single crystalline silicon solar cells fabricated with CMOS p-Si on a semiconductor line. The solar cell substrates for plating comprise ~ 60 ohm/sq emitter formed by POCl diffusion, PECVD SiN passivation layer, and evaporated Al back surface field. Electrodeposition of Ni was studied on 4 cm x 4 cm solar cells in different solutions containing Ni salt and other plating additives. Back contact through the Al BSF was used and front-side illumination was applied. Silicidation was achieved by rapid thermal annealing at different temperatures for different time. The study is focused on the effect of light, chemistry and the plating current on the film in terms of morphology, impurity and its salicidation.

Figure 1 shows the relation between the applied potential and the light intensity at different constant current densities. Two regions of operation were clearly observed with a threshold light intensity. At high illumination, when enough carriers were generated by the light, the plating occurs at the forward bias mode of the diode. As the light intensity decreases below a threshold value, the potential increases significantly and stays at a high value indicating the diode operates at reverse bias mode. The threshold light intensity is dependent on the illumination energy spectrum, solution absorbance, anode shadowing and applied current density.

REFERENCES

D. A. Yates, US Patent 4,609,565 (1986).

K. Holdermann, US patent 5,543,333 (1996).

J Bartsch, A Mondon, K Bayer, C Schetter, M Horteis, and S W Glunz, J. Electrochem. Soc., 157, H942 (2010).

J Bartsch, A Mondon, C Schetter, M Horteis, S W Glunz, IEEE 35th PVSC, Honolulu HI (2010).

Figure 1
Hybrid Electro-Electroless Deposition (HEED)
Authors: Petro Robert , Schlesinger M.
Published: February 2020

Hybrid electro-electroless deposition (HEED) is a novel thin film metal deposition technique developed in Windsor.  The process combines both electroplating and electroless deposition within a single electrolyte.  The two deposition processes upon which HEED is based are combined such that each individual process targets a distinct metal ion for reduction.  The nature of the deposit is determined by the composition of the electrolyte and electroplating potential applied, among other well established factors for both individual techniques.  The process of HEED allows the formation of composite, alloyed, and multi-layered, or compositionally modulated alloy, deposits.  Composite HEED deposits are somewhat uncommon as one of the two techniques must produce well defined grains.  Alloyed HEED deposits are produced under two sets of conditions.   Either each individual technique comprising HEED, electroplating and electroless deposition, is made to deposit an alloy [1], or each technique deposits a thin layer for the purpose of interlayer diffusion.  Multi-layered HEED deposits are produced wherein each technique deposits pure, or nearly pure, metallic layers which nominally do not diffuse into one another [2].  The novelty of the HEED process may be illustrated with the deposition of metals of similar nobility, such as nickel and cobalt, in a multi-layered deposit [2].  The HEED multi-layers are in contrast to the standard method of electroplated multi-layers wherein the deposition potential and electrolyte support nearly pure layer deposition where the metals are of differing nobility [3].   

[1] Robert Petro and Mordechay Schlesinger, “Development of Hybrid Electro-Electroless Deposit (HEED) Coatings and Applications”, Journal of The Electrochemical Society, 161(10), (2014), p.D1-D6

[2] Robert Petro and Mordechay Schlesinger, “Deposition of Cobalt-Nickel Hybrid Electro-Electroless Deposited (HEED) Modulated Multilayers”, Journal of The Electrochemical Society, 162(4), (2015), p.D154-D158

[3] K. D. Bird, M. Schlesinger, “Giant Magnetoresistance in Electrodeposited Ni/Cu and Co/Cu Multilayers”, Journal of The Electrochemical Society, 142(4), (1995), p.L65-L66
Properties of Pulse Electrodeposited CuInGaSe2 Films
Authors: Murali Kollegal Ramakrishna , Chitra V
Published: February 2020

CuIn1-xGaxSe2 films of different composition (0< x <1), were pulse electrodeposited on indium tin oxide coated glass and molybdenum substrates at 50 % duty cycle and at room temperature. The precursors used were 20 mM SeO2, 30 mM CuCl2 and the concentration of the Indium chloride and gallium chloride precursors were varied to obtain films of different composition.  The deposition potential was maintained at – 0.8V (SCE). The pH was maintained at 1.5 by HCl. A microprocessor controlled pulse plating unit was used. Thickness of the films measured by Mitutoyo surface profilometer was in the range of 0.5 – 1.4 micrometer with increase of Indium concentration.

The x-ray diffraction patterns of CuIn1-xGaxSe2 films of different composition. All the figures indicate the prominent peaks corresponding to (112), (220)/(204), (312)/(116). These care characteristic of the chalcopyrite phase. No other phases were observed in the x-ray diffractograms indicating the formation of single phase material. The peaks shifted from CuInSe2 side to CuGaSe2 side as the concentration of Ga increased in the films.

Composition of the films was estimated by recording the EDS spectrum of the films deposited of different composition. It is observed that films with lower concentrations of Gallium were copper rich. As the gallium concentration increased, the films became nearly stochiometric.

The tranmssion spectra exhibits interference fringes and the value of the refractive index was estimated by the envelope method. The refractive index decreases from 2.80 to 2.35 with wavelength. The band gap of the films increased from 1.11 eV to 1.62 eV  as the gallium concentration increased ( from(αhν)2 vs hν plot ). The increase in band gap at lower duty cycles is due to the small crystallites. The values of the band gap agree well with the earlier report.

The room temperature transport parameters were measured by Hall Van der Pauw technique by providing gold ohmic contact. The magnitude of the resistivity increased from 0.8 ohm cm to 23.52 ohm cm as the gallium concentration is increased. The resistivity values are comparable with an earlier report.

The PEC cells using these films exhibited low photocurrent and photovoltage. The intensity of the light falling on the films deposited at different duty cycles was kept constant at 60 mW cm-2. Films of composition CuIn0.9Ga0.1Se2 exhibited maximum photo output. The photooutput was low, hence, in order to increase the photo outpout, the films of different composition were post heated in argon atmosphere at different temperatures in the range of 450 - 550°C for 15 min. Films of composition CuIn0.7Ga0.3Se2 exhibit maximum Voc. The power output characteristics after 80s photoetching indicates a Voc of 0.70V, Jsc of 20.0 mA cm-2, ff of 0.71 and h of 14.33 %, for 60 mW cm-2 illumination.
Effect of Different Palladium Nanoparticles on the Adhesion Between Electroless-Deposited Nickel-Phosphorus Film and Silane-Compound-Modified Silicon Surface
Authors: Hsu Chin Wei , Wang Wei-Yan , Wei Tzu Chien , Lai Kuei-Chang , Chen Chih-Ming
Published: February 2020

Eletroless deposition of nickel/phosphorus (Ni/P) film is a very promising skill for preparing diffusing barrier layer on silicon wafer. In general, palladium metal is needed as the catalyst to initiate electroless Ni/P deposition. In this study, we synthesized two types of palladium nanoparticles which is capped by polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA), coded as PVP-Pd & PVA-Pd, as the catalysts of electroless deposition. In order to enhance the adsorption of PVP-Pd or PVA-Pd on silicon surface, we apply 3- 2-(2-aminoethylamino)ethylamino propyl trimethoxysilane (ETAS) as a coupling agent to modify silicon surface then followed by electroless Ni/P deposition. Evidenced by transmission electron microscopy and scanning electron microscopy, PVP-Pd reveals slightly aggregated, while the particle shape of PVA-Pd is clearly defined; this makes a better distribution when PVA-Pd nanoparticles are adsorbed on silicon surface so that the adhesion of catalyst as well as Ni/P film is further improved. Finally, the interaction between ETAS and PVA-Pd were further explained by X-ray photoelectron spectroscopy. Compared with the adhesion of Ni/P layer catalyzed by commercial Sn/Pd colloids on unmodified silicon surface, the adhesion of Ni/P layer catalyzed by PVP-Pd or PVA-Pd on the ETAS modified silicon surface improved significantly by 2~3 times without the need of post-annealing treatment.
Copper Oxide Layers Obtained Via Anodization for Electrowetting on Dielectrics
Authors: Bernasconi Roberto , Bellantone Andrea , Liberale Francesco , Magagnin Luca
Published: February 2020

Electrowetting is a technique which allows to modify the wettability of a surface through the action of an electric field. At the time of its discovery the phenomenon was believed to have no practical use due to the electrochemical reactions occurring on the surface, which in fact limit the overall effect obtainable. In the last few decades the interest toward this technique arose and the first applications appeared. Fundamental to allow such renewed interest was the use of a dielectric hydrophobic layer interposed between the metallic surface and the electrolyte: it is known in this case as Electrowetting on Dielectric (EWOD). Possible applications of this technique include variable focal lenses, microfluidic systems and displays. The latter in particular can find possible wide industrial diffusion due to the development of the Liquavista technology by Samsung. The challenge of the next future is the transfer of the electrowetting technology from rigid and planar displays to flexible and curved ones. Flexible electronics are expected to be the technology of the future and applications include wearable devices, flexible screens and smart labels for packaging.

The present work investigates the possibility of creating compact layers of copper oxide via copper anodization for the EWOD technology. Copper was chosen instead of metals that can be more efficiently anodized due to its ease of deposition by mean of wet techniques. In fact copper can be easily electroless deposited on flexible substrates, while metals like aluminium or titanium need PVD deposition or thermal coupling techniques. Other advantages of copper include high conductivity and good mechanical properties. The first part of the study involves the fundamental study of electrowetting on copper oxide coated with a fluoropolymer. Hysteresis and saturation of contact angle are analysed, as well as the adherence of the behaviour to the Young-Lippman equation. In the second part a flexible substrate is tested for electrowetting on a curved surface. Such specimen is manufactured by electroless plating of copper on PET, anodizing the resulting layer and coating the oxide layer thus obtained with a fluoropolymer. Finally the result is compared with an equivalent sample obtained coupling an aluminium layer with a polymeric substrate and thermally bonding them. The result is then anodized to obtain a compact oxide layer and coated with the fluoropolymer.
Development of Silver-Carbon-Nanotube Metal Matrix Composites for Metal Contacts on Space Photovoltaic Cells
Authors: Abudayyeh Omar Kamal , Nelson Cayla , Han Sang , Gapp Nathan , Wilt David
Published: February 2020

The advanced solar cells used in space vehicles today are rapidly moving towards thin-film-based inverted metamorphic multijunction (IMM) solar cells mounted on flexible substrates.  However, the IMM cells are more prone to cracking than state-of-the-art triple junction cells.  The cell cracking can lead to metal contact failure on IMM cells, compromising the power generation.  To mitigate the power loss and increase the lifetime of IMM cells, silver metal films imbedded with carbon nanotubes (CNTs), otherwise known as metal matrix composites, have been developed and investigated for the reinforced mechanical strength against stress-induced cracking.  We have primarily focused on (1) surface functionalization of CNTs to make their surface more hydrophilic and wetting to metals, (2) optimization of a cyanide-free electrochemical deposition of silver, (3) electrochemical deposition, drop casting and nanospreader technique to control the composite microstructure, and (4) mechanical and electrical characterization of the composite films.  We observe that carboxylation of CNTs produces a stable, homogeneous suspension of negatively charged CNTs at pH > 6.  Lustrous-mirror-finish silver films are also successfully deposited, using a commercial cyanide-free silver-plating solution with precise control of current density.  Currently, one of the microstructures being explored is a silver-carbon-nanotube layer-by-layer structure, where the surface coverage of CNTs is an important parameter that directly affects the CNT packing fraction and metal intercalation through the CNT network.  We quantify the CNT surface coverage as a function of different deposition variables by digitally analyzing scanning electron microscopy images.  In this presentation, we will further discuss how this surface coverage correlates to the mechanical and electrical properties of the MMC films.  We characterize the mechanical properties, using nanoindentation and strain failure tests.  The initial nanoindentation analysis reveals that the composite film has a lower elastic modulus (10 GPa) than pure silver (73 GPa), which is contrary to our initial prediction given the high elastic modulus of CNTs (1000 GPa).  The lower elastic modulus is attributed to the electroplating process of silver, in which hydrogen is incorporated and trapped within the composite.  Our finite element analysis also corroborates this speculation, where the elastic modulus near 10 GPa is predicted with approximately 4% void fraction.  While the composite elastic modulus is lower than that of pure silver, the strain failure tests show that carbon nanotubes can bridge 20 to 50-μm-wide microcracks, maintaining electrical conductivity of the composite