bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Packaging Material Technology for Wide Band Gap Power Devices and Its Performance/Reliability Evaluation
Authors: Suganuma Katsuaki , Sato Naoki , Suetake Aishi , Choe Chanyang , Sugahara Toru , Nagao Shijo , Chen Chuantong 
Published: February 2020

Wide band gap semiconductors such as SiC and GaN have been expected to be established as the next generation power semiconductors, which are capable to reduce huge energy-loss in electric power conversion. The application of them will increase power density resulting in operation temperature rise beyond 200 °C. In addition, both increase of current and of frequency will also increase stress on devices. In general, power devices must possess robustness and high reliability for safe control of power conversion. Heat dissipation from the hot die in operation is one of the essential key factors for establishing high performance WBG devices. Here we report the current status of high temperature packaging materials including die-attach, wiring, substrates and molding compounds. In addition, reliability issues including thermal shock, power cycling and transient thermal properties will be summarized.
A series of DBC and DBA substrates, composed of Al and Cu as metal layers and of Al2O3, AlN and Si3N4, were examined by thermal shock test between -50 °C and 250 °C. DBC substrates with Al2O3 and AlN fractured only after 10 cycles due to severe thermal stress while all DBA and DBC with Si3N4 substrates survived. Al and Cu layer of all DBC and DBA substrates severely deformed by thermal shock. By microstructural observation, grain boundary sliding during thermal shock has a key to cause deformation of metal layers on ceramics. Ni and Ni-P plating on metal layer also deformed followed by Al and Cu layer deformation. Ni-P plating showed severe cracking which can be attributed to brittleness of Ni-P plating while Ni plating did not.
Ag sinter joining can be successfully applied for die attach by low temperature and low pressure bonding in air. For better bonding quality, Ag coating is the best metallization due to the specific reaction of Ag in air. By modifying solvent, Ag particles paste was modified to form a good bonding with Au surface finish. It can provide not only high temperature structural stability but also excellent thermal dissipation capability. High die-shear strength beyond 30 MPa was maintained by thermal shock between -50 °C and 250 °C up to 1000 cycles for a DBC die-attach structure. The thermal resistance of Ag sinter joined die attach is much lower than that of solder.　Figure shows the example of a GaN die-attached on DBC substrate with a new Ag sinter materials at 200 °C in air without any pressure. Even on the Au metallization, the GaN die was bonded with high strength. The interface shows a good bonding between Au and Ag.
This work was supported both by JST ALCA project on GaN packaging and by METI standardization project for evaluation methods of thermal properties of ceramics substrates.

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(Invited) A Revolutionary GaN-on-SiC Heteroepitaxy for High-Frequency Power Transistors
Authors: Chen Jr-Tai , Bergsten Johan , Malmros Anna , Janzén Erik , Thorsell Mattias , Rorsman Niklas , Kordina Olof 
Published: February 2020

GaN HEMTs have a great potential to be well suited for the forthcoming 5G communication infrastructures and other millimeter wave applications, where high-power and high-efficient devices are required. For GaN HEMT heterostructures used in high-frequency applications (> 8 GHz), semi-insulating (SI) SiC is the best choice of substrates, owning to its high thermal conductivity and high resistivity, and the maturity in large-wafer mass production (up to 150 mm). Nevertheless, the typical thickness of a GaN layer grown on SiC substrates has to be at least 1.5~2.0 µm to obtain a structural quality manufacturable for device fabrication, due to the large in-plane lattice mismatch with GaN (3.4%). As a result, the thick GaN layer must be doped with acceptor-like impurities like carbon or iron [1] during the epitaxial growth to increase the resistivity, preventing a parallel conduction in the device. However, these impurities introduce deep traps, which capture electrons during the RF operation, rendering a depletion of the channel electrons thus reducing the device current/power density.
We report the realization of a revolutionary heterostructure of III-nitride materials grown on SiC substrates by a unique MOCVD method. Our success in the material growth enabled a new design of HEMT heterostructures requiring no intentional Fe- or C-doping. Excellent DC and RF performances of the highly-scaled GaN-based high electron mobility transistors (HEMTs) using the proposed new heterostructures are demonstrated. The new HEMT heterostructures also open up new opportunities in material growth schemes to further reduce the charge trapping effects that have been prevailing in the field over that last two decades. Consequently, a high RF output power of ~4 W/mm was obtained at a fundamental frequency of 30 GHz in the HEMT devices with a gate length (Lg) of 0.1 µm, biased at VDS= 30 volt. We also found that the thermal resistance of the new HEMT devices exhibits a substantially lower thermal resistance (RTH) of 4.1 oC mm/W, as compared with that of the conventional ones, which is typically around 9~10 oC mm/W [2] The details of the new heterostructures and device characteristics will be presented. Our breakthrough in the material growth has brought the GaN HEMT technology to a new height and will serve as a new route for further improvement.
IV.References
[1] J.-T. Chen et al, Appl. Phys. Lett. 102, 193506 (2013). Impact of residual carbon on two-dimensional electron gas properties in AlGaN/GaN heterostructure.
[2] J. Joh et al, IEEE Trans. Elec. Dev. 56, 2896 (2009) Measurement of Channel Temperature in GaN High-Electron Mobility Transistors.

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Lithium Manganese Oxyfluoride As a New Cathode Material Exhibiting Oxygen Redox
Authors: House Robert A. , Jin Liyu , Maitra Urmimala , Roberts Matthew R. , Bruce Peter G. 
Published: February 2020

The next generation of high performance Li-ion rechargeable batteries relies on the discovery of new positive electrode materials with a greater capacity to store charge. Generally speaking, highly ordered layered materials, such as LiCoO2 (LCO), LiNi0.85Co0.1Al0.05O2 (NCA) and LiNi0.13Mn0.54Co0.13O2 (NMC), are considered to be the best-in-class. One strategy to increase the capacity has been to explore the ordered Li-Rich materials, Li1+xM1-xO2, where x~1.2, where the greater number of Li ions increases the total theoretical capacity. However, an optimal candidate system for commercialisation within this space has yet to be identified.
In contrast to ordered materials, disordered structures have been largely ignored by the scientific community as they are perceived to exhibit poor Li+ mobility. However, recent research has overturned this understanding and several disordered rock salt structures with competitive energy densities have been proposed (such as Li4Mn2O5, Li2VO2F and Li1.2Mn0.4Ti0.4O2). Could these highly disordered Li-rich materials offer better structural stability and performance than their layered counterparts?
Here, we present the discovery of a new Li-rich disordered rocksalt material, lithium manganese oxyfluoride (LMOF), presented in Figure 1, whose structure appears to remain stable even over 100 charge-discharge cycles. Furthermore, LMOF exhibits a large, reversible capacity to store charge and, interestingly, this appears to be unexplained within the limits of transition metal redox capacity alone, raising the question of how such a large charge storage capacity can be achieved. In this work we fully characterise this new material and specifically we examine the role that oxygen plays in this anomalous charge compensation process.

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High Voltage Cobalt Free Cathode Materials for Advanced Lithium Ion Batteries
Authors: Wohlfahrt-Mehrens Margret , Axmann Peter , Gabrielli Giulio , Balasubramanian Prasanth , Mancini Marilena 
Published: February 2020

Lithium ion batteries are widely used in many applications and are the most promising energy storage systems for future mobility. Nevertheless, they still require further improvements in order to meet the energy and cost requirements for the next generation of electric vehicles. The development of cobalt free cathode materials with high capacity and high voltage can contribute significantly to further cost reduction of lithium ion batteries.
We present a series of Co-free, Li-rich Li1+xNi0.5Mn1.5O4 (0<x<1) compounds obtained via a low-temperature synthesis method. Chemically lithiated Li1+yMn1.5Ni0.5O4 (LMNS) (0< y < 1) with spherical particle morphology and high with tap densities (2.2 – 2.5 g/cm3) have been synthesized from coprecipitated mixed nickel manganese hydroxides as precursors. Figure 1 shows the charge/discharge curve of a sample with the composition Li1.8Ni0.5Mn1.5O4. The electrochemical mechanism in the low-potential region and the involved phase transitions, studied by different techniques including HR-TEM and XRD, will be discussed in more detail together with the electrochemical behavior under different operative conditions.
The obtained lithium‐nickel‐manganese oxide samples have been tailored with respect to composition and crystal structure in order to reach high capacities (up to 250 mAh g-1) with good cycling stability. In addition, full cell data with Li1+xNi0.5Mn1.5O4.0 (0<x<1) compounds as cathode materials and either graphite or silicon/carbon composites as anodes will be presented. LiNi0.5Mn1.5O4/Li1.3Ni0.5Mn1.5O4 blend cathodes with adapted extra lithium can be used to compensate irreversible capacity losses of silicon based anodes in full cells [1]. The cycle life of full cells can be further improved by optimizing morphology, particle size distribution and additional surface coating. The influence of electrode preparation and selection of electrolyte additives on long life stability will also be discussed.
[1] G. Gabrielli, M. Marinaro, M. Mancini, P. Axmann, M. Wohlfahrt-Mehrens, J. Power Sources 351 (2017) 35

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Aerosol Chemical Vapor Deposition of One-Dimensional Cu-Doped TiO2 Nanostructured Anodes for High-Rate Lithium Ion Batteries
Authors: Kacica Clayton Thomas , Biswas Pratim 
Published: February 2020

Energy storage has become increasingly important in recent years due to the rapidly increasing number of electric vehicles (EVs) in use and expanded utilization of intermittent renewable energy sources. Improvements in longevity, energy density, and high rate capability are needed for the next generation of batteries. Lithium-ion batteries (LIBs), the most widely commercialized rechargeable batteries are being used in EVs and some pilot grid-scale storage facilities.
One avenue for enhancing the performance of LIBs is the development of novel electrode materials. One such material, titanium dioxide (TiO2) exhibits very high stability during cycling and is capable of ultra-high rate charging and discharging. However, a major drawback to TiO2 is its relatively low electrical conductivity, which limits its performance. Using nanostructured, one-dimensional morphologies the issue of low conductivity can be mitigated. Additionally, metal-doping of TiO2 with various metallic cations such as zinc, copper, or niobium has been shown to increase conductivity as well.
Aerosol chemical vapor deposition (ACVD) is an atmospheric pressure technique used to deposit nanostructured metal oxide thin films. In ACVD, a vapor phase organometallic precursor is fed to a reactor and undergoes thermal degradation forming metal oxide monomers. The monomers nucleate to form particles which undergo condensational growth before depositing onto a heated substrate, where the particles sinter into various morphologies. Controlling the rates of these processes using various system parameters leads to the deposition of one-dimensional, columnar structures. Additionally, by introducing two precursors simultaneously doped materials can be synthesized, with the composition controlled by the relative flowrates into the reactor.
In this work, we aim to investigate the effect of Cu-doping on the properties and performance of nanostructured TiO2 negative electrodes in LIBs. To achieve this, Cu-doped TiO2 films with compositions between 0-10 at% are synthesized on stainless steel using ACVD and directly utilized as anodes in LIBs. In order to determine the effect of Cu-doping on battery performance a rate capability test is performed by cycling the batteries at progressively higher rates. Additionally, long-term cycling is performed to determine the stability of the electrodes. Additionally, characterization of the lithium diffusion coefficient is performed using both cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). Finally, density function theory (DFT) simulations are performed in order to validate the experimentally measured values for the lithium diffusion coefficient and the electrical conductivity.
Improving the Cycling Performance of Lithium Ion Batteries Silicon/Graphite Anodes Using PI Binder
Authors: Oh Jeonghun , Jin Dahee , Jo Hearin , Park Jinkyu , Yoon Byeolhee , Choi Junyoung , Kim Seokwoo , Ryou Myung-Hyun 
Published: February 2020

As the market for Electric Vehicles (EV) and Energy Storage System (ESS) grows, there is a growing demand for Lithium secondary batteries with high energy density.
However, graphite (372 mAh g-1 for LiC6), a commercially available anode active material, is not suitable for large scale battery system such as EV or ESS due to its low theoretical capacity.
Although, Silicon (Si, 4200 mAh g-1 for Li22Si5 or Li4.4Si) has a higher theoretical capacity than graphite, it has not been successfully implemented in commercialized LIBs due to suffering from large volume changes (> 300 %) during alloying and dealloying. Moreover, the stresses accompanying these changes cause mechanical failure and result in severely degraded electrochemical performances of Si electrodes.
Consequently, Si/C composite anodes (Si/C anodes), wherein Si constitutes only a portion of the active material, have been proposed as an alternative to pure Si anodes. This approach exhibits certain advantages, since even if the theoretical anode capacity increases infinitely, the total theoretical capacity of the battery soon reaches saturation due to the limited theoretical capacity of the cathode.
Herein, we used PVdF and P84 binder in high-loading Si/C anodes (~4.0 mg cm-2) and investigated their electrochemical and mechanical properties. Specifically, mechanical properties such as electrochemical stability, cycling performance and rate capability were evaluated using cyclic voltammetry, with the corresponding data recorded using a battery cycler.
The mechanical properties of the above anodes were evaluated using Surface And Interfacial Cutting Analysis System (SAICAS).
Facile Synthesized Nanoporous Si/C Anode for High Power and Energy Applications
Authors: Min Chan-Woo , Nazir Aqsa , Park Chan-Jin 
Published: February 2020

As the development of electric vehicles (EVs) is progressing recently, it is urgent to develop high energy density batteries. Currently, Li-ion batteries (LIBs) have been mainly used for EVs. In LIBs, the most representative commercial anode material for LIBs is graphite. Unfortunately, its low theoretical capacity (372 mAh g−1) and rate capability is not sufficient to be used in emerging applications, such as EVs and large-scale ESS. Si is a promising anode material for LIBs due to its large theoretical capacity (3600 mAh g-1 for Li15Si4), low working potential (< 0.4 V vs. Li/Li+), low cost, large amount resources, low toxicity, and environmental friendliness. However, Si based anodes in LIBs have several drawbacks. During alloying with Li, Si exhibits large volume expansion of >300%, leading to crush of the active materials and capacity drop. Si electrode also has low intrinsic electrical conductivity compared with graphite. In addition, solid electrolyte interface (SEI) layer is not stable when Si is exposed to organic electrolytes, leading to the consumption of electrolyte and low Coulombic efficiency. Recently, studies on using a buffer layer coating have been conducted to alleviate the stress induced by volume change of Si. Recently, we reported an ultra-simple Mg-thermal-reduction method for the production of mass-scalable coral-like Si powders with a high surface area, and 3-dimensionally (3D)-interconnected Si structures. It is noticeable that simple Mg-reduction process can be used at low cost in ambient air.
In the present work, we employed carbon coating to improve the conductivity of the previously obtained porous nano-sized Si electrode and the stability of SEI layer. We prepared a nano-porous Si/C composite through a facile sol-gel route with various amounts of carbon from citric acid precursor. The morphology and phase purity of the synthesized Si/C composites were analyzed by XRD, FE-SEM, TEM, Raman spectroscopy, and BET analysis. Furthermore, electrochemical characteristics of Si/C electrode was analyzed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry, and galvanostatic charge-discharge test. The Si/C electrode exhibited a long cycling stability, good rate capability, and high reversible capacity. In particular, the Coulombic efficiency in the first cycle was improved significantly. This superior performance of the electrode is attributed to the improvement in electrical conductivity, Li-ion accessibility, stability of SEI layer, and the suppression of volume expansion owing to porous nano-sized Si and carbon coating.
Seebeck Coefficient Measurements of Pristine and Tcnq Loaded HKUST-1 Thin Films
Authors: Hassan Zeinab Mohamed , Chen Xin , Zhang Kai , Redel Engelbert , Baumgart Helmut 
Published: February 2020

Seebeck meaurements have been performed on i) quasi-liquid epitaxially highly oriented HKUST-1 Surface Anchored Metal-Organic Framework (SURMOF) films and for comparison on ii) random polycrystalline HKUST-1 thin films; pristine as well as loaded with tetracyanoquinodimethane (TCNQ).
However, the horizontal Seebeck coefficient of highly oriented (001) SURMOF films is practically around 0 µV/K as there is no measurable horizontal carrier transport parallel to the SURMOF surface. Only in the polycrystalline and pristine HKUST-1 thin films exhibit a high and positive Seebeck coefficient of 422.30 µV/K at 330 K. For the TCNQ loaded polycrystalline HKUST-1 thin films a lowering of the Seebeck coefficient of 388.80 µV/K at 330 K.
The high Seebeck coefficients of these random polycrystalline MOF films demonstrates promising application potential of MOF films in future thermoelectric and electronic devices working highly efficient in the RT (Room Temperature) region.

X. Chen, Z. Wang, Z. M. Hassan, P. Lin, K. Zhang, H. Baumgart, E. Redel ECS Journal of Solid State Science and Technology 2017 6(4), 1-4.

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(Invited) Leaving the Simple Models behind: How Surface Mounted Metal-Organic Frameworks (SURMOFs) Grow
Authors: Terfort Andreas 
Published: February 2020

While metal-organic frameworks (MOFs) have been developed to expose many interesting properties, their utilization in devices often relies on the deposition at surfaces: This bonding does not only provide efficient mechanical contact, as it is e.g. useful for quartz-crystal microbalance (QCM) measurements, but also electrical contact, e.g. for electrochemical or even electronic applications. In addition, the deposition at solid surfaces provides means of directed localization and orientation of the MOF materials.
Many methods for the deposition of MOFs have been developed, the most common of which rely on the direct growth of the frameworks onto the surfaces [1]. The effectiveness of this approach has been demonstrated for a handful of systems, leading even to demonstrators e.g. for photovoltaic devices. Nevertheless, the deposition of surface-attached MOFs (SURMOFs) fails to produce well-defined surface layers, but rather results in heterogeneous and/or disordered systems.
In this talk we are going to present strategies on how SURMOF films can be deposited successfully by keeping certain parameters, such as deposition temperature [2], involved concentrations and exposure times within specific limits. The success of the respective combination of parameters can be rationalized be understanding and conjoining principles from coordination chemistry and surface chemistry [3], which typically are well-known in the respective communities but rarely taken into account by the other communities.

References:

[1] J.-L. Zhuang, A. Terfort, C. Wöll, Coord. Chem. Rev. 307 (2016) 391-424.
[2] X-J. Yu, J.-L. Zhuang, J. Scherr, T. Abu-Husein, A. Terfort, Angew. Chem. Int. Ed. 29 (2016) 8348-8352.
[3] J.-L. Zhuang, M. Kind, C.M. Grytz, F. Farr, M. Diefenbach, S. Tussupbayev, M.C. Holthausen, A. Terfort, J. Am. Chem. S
oc. 137 (2015) 8237-8243.
Structure, Properties, and Degradation of Ultrathin Ionomer Films in Catalytic Layers of Fuel Cells Using Atomic Force Microscopy
Authors: Morawietz Tobias , Handl Michael , Friedrich Kaspar Andreas , Hiesgen Renate 
Published: February 2020

The performance of polymer electrolyte fuel cells and electrolysers depends on the nanostructure of its components. Mainly the nanostructured electrodes determine cell performance and degradation. In working fuel cell electrodes, the ionomer films that encapsulate the Pt/C agglomerates fall within the range of ultrathin films. In recent years, an oxygen transport resistance has been identified as a major hurdle in the development of low-loaded MEAs and the ionomer layer has been postulated to be the reason for additional resistance.
The quantitative investigation of the nanostructure of fuel cell electrodes, especially the analysis of the correct dimensions of the ionomer component has proven to be exceptionally difficult. Using electron beam-based techniques that need vacuum the ionomer is drying and significantly shrinking, in addition to a low contrast between ionomer and carbon components. Also cryogenic TEM analysis may alter the sample by use of alcoholic solvents that have an input on structure, despite of beam damage.
Atomic force microscopy (AFM) has the advantage to work in humid environment and at elevated temperatures, close to operational conditions. Using material-sensitive tapping mode, the high contrast between the ionomer- and the Pt/C phase in adhesion force mapping allows studying the distribution and thickness of the ionomer films that cover the Pt/C agglomerates (Figure 1c). With electronic current mapping, the free Pt-surface can be evaluated (Figure 1a,b).
In this contribution, the analysis of cross-sections of Nafion- and Aquivion–based fuel cell electrodes by material-sensitive AFM will be presented. Analysis of pristine electrodes delivers the distribution of the ionomer film thickness, small ionomer clusters, and larger agglomerates. A thickness distribution of the ionomer films ranging from roughly 4 to 20 nm was retrieved (Figure 1d). After operation, significant thinning of the ionomer films depending on location within the membrane-electrode-assembly and preparation was found. Differences of the swelling behavior of the ionomer films, and IR analysis prior and after operation were used as a measure for ionomer degradation caused by radical attack. A dependence of macroscopic cell degradation rate on initial electrode ionomer film thickness was observed.
For further determination of the properties of such ultrathin films model layers of Nafion®, and Aquivion® PFSA were examined. Conductive AFM allowed investigations of through- and in-plane conductivity in dependence of the film thickness. Significant differences in conductivity for films below ~10 nm thickness were detected.

Figure 1