bluuebunny/crossref_metadata_2025 huggingface dataset:
Fe-Ni-Co Electrodeposited Nanowires Decorated with Au
Authors: Podlaha Elizabeth J. , Beheshti Mohammadsadegh , Li Deyang , Park Sunggook
Published: July 2022

Alloy nanowires containing Fe, Ni and Co are of interest as electrode materials in miniaturized devices due to their ability to align them under a magnetic field. In order to improve their resistivity while retaining their magnetic behavior, Fe-Ni-Co nanowires were electrodeposited and decorated with Au; single nanowires were then further characterized (Fig. 1). The nanowires were deposition under a constant applied potential within a nanoscale alumina template, followed by dissolution of the membrane, release of the nanowires, and subsequent treatment in a gold acid electrolyte. Au clusters formed on the Fe-Ni-Co surface through simultaneous displacement and corrosion reactions. The morphology, composition and structure was examined before and after modification, revealing a change in crystallinity and composition that impacted the nanowire’s electrical and magnetic properties. Transferring a single nanowire to a lithographically prepared two-point probe enabled the electrical and magnetic characterization of the Au decorated nanowire. Averaging results of quadruplicate replicates, a low coverage of discontinuous Au clusters on Fe-Ni-Co nanowires significantly decreased the resistivity, not attributed entirely to the lower resistivity of Au, but as a consequence of changes of the Fe-Ni-Co crystallinity. A high coverage of the Fe-Ni-Co by Au had no further benefit, and even increased the resistivity. Since bulk gold is diamagnetic and decoration of Au onto the Fe-Ni-Co nanowires may compromise the overall magnetic property, the magnetoresistance and electron mobility were determined. Both decreased, as expected, with coverage of Au clusters on the nanowires, suggesting that there may be an optimal cluster density for modifying the Fe-Ni-Co nanowires.

Figure 1. Electrodeposited nanowires initially amorphous then decorated with Au showing a change in crystallinity and subsequent characterization with a two-point probe.

Figure 1
Development of a Programmable Rastering Open-Source Electrodeposition System
Authors: Avery Hayden , Jurkovic Jacob , Marara Iragi , Salaripoor Hamidreza , Bruce David Robert
Published: July 2022

A prototype rasterizable electroplating system constructed entirely of open-source systems and off-the-shelf electronic components has been developed. The system as proposed can be broken down into separate movement and electroplating systems. The movement system consists of a Creality Ender 3 3D-Printer which has been modified to support the electroplating system. This electroplating system was built using an Arduino microcontroller that controls the voltage and current of the system. The system polarization can be controlled potentiostatically or galvanostatically in an operating window of 0 to 5V with currents up to 300 mA and a stability of 2% accuracy.

The results presented will be a demonstration of the system operation in an electrolytic capacity, with simple water splitting in a bicarbonate solution chosen to examine the controls and system readings when electrodes are moved geometrically throughout a simple two electrode cell with unequal electrode shapes. A discussion of the set-up process for this system follows to elaborate on the challenges of translating STL file decoding to the path the printer must follow, which is then further sliced and translated to Gcode. Limitations to the Gcode generation and further modifications to allow for cross-communication between the Arduino and Ender control systems are discussed, highlighting the limitations of these economic yet powerful system builds.
Protective Coating Layers via Phosphazene Compounds for Stabilizing Silicon Anode Materials
Authors: Ghaur Adjmal , Peschel Christopher , Dienwiebel Iris , Haneke Lukas , Du Leilei , Profanter Laurin , Placke Tobias , Winter Martin
Published: July 2022

In recent years, lithium-ion batteries (LIBs) are widely used in electric vehicles (EVs) and mobile energy storage devices (ESDs), which has led to higher requirements for energy density. To fulfill these requirements, tremendous attention has been paid to design advanced LIBs with various silicon active materials as alternative negative electrodes to replace graphite (372 mAh g-1) due to their high theoretical gravimetric capacity (4200 mA h g-1).[1,2] However, silicon as potential anode material suffers from huge volume changes during charging and discharging and has a poor electronic conductivity which negatively impacts the long-term performance and prevents high silicon contents from practical application.[3] Additionally, an unstable crystalline silicon structure tends to pulverization during the (de)lithiation process.[4] To compensate the volume changes, alleviate pulverization and maintain high electronic conductivity, silicon-doped graphite composites with protecting coating layers are a promising approach. In this context, phosphazene compounds are investigated concerning their silicon protecting properties in silicon-doped graphite composites. In detail electrochemical performance measurements in pouch full-cells (NCM523||SiOx/C), supressing gas formation properties and post-mortem analyzes were carried out to characterize phosphazene compounds as additive materials. The introduction of the dual-additive approach in state-of-the-art electrolytes leads to synergistic effects between FEC and phosphazene compounds which accelerate the durability of silicon particles and results in enhanced electrochemical performance.

Reference:

[1]Zuo X, Zhu J, Muller‐Buschbaum P, Cheng Y, Silicon based lithium‐ion battery anodes: a chronicle perspective review, Nano Energy, 2017, 31, 113‐143.

[2]Jimenez A. R., Klöpsch R., Wagner R., Rodehorst U. C., Kolek M., Nölle R., Winter M., Placke T., A step toward high-energy silicon-based thin film lithium ion batteries, ACS Nano, 2017, 11, 5, 4731-4744.

[3] Berla A. L., Lee S. W., Ryu I., Cui Y., Nix W. D., Robustness of amorphous silicon during the initial lithiation/delithiation cycle, Journal of power sources, 2014, 258, 253-259.

[4] Casimir A., Zhang H., Ogoke O., Amine J. C., Lu J., Wu G., Silicon-based anodes for lithium-ion batteries: Effectiveness of materials synthesis and electrode preparation, Nano Energy, 2016, 27, 359-376.
Advanced Data-Driven Modeling Framework for Predicting Thermal Failures in Li-Ion Pouch Batteries
Authors: Mastrogiorgio Massimiliano , Das Goswami Basab Ranjan , Ragone Marco , Mashayek Farzad , Yurkiv Vitaliy
Published: July 2022

With the rapid development and widespread applications of lithium-ion batteries (LIBs), there is an ongoing need to extend and apply theoretical models that assist LIB’s safety aspects. It is particularly important for electric vehicles (EVs) due to numerous recent fire accidents. Thermal runaway (TRA) is one of the principal causes of LIB’s failures in EVs occurring due to thermal or mechanical breakdown, internal/external short-circuiting, or electrochemical abuse. During EV’s operation, it is impossible to directly monitor the TRA; however, the change in thermo-electrical characteristics (pattern) during TRA-like events could signal the presence of a failure, allowing for the prediction of LIB malfunction. Thus, in this work, we employ machine learning-based techniques informed by multi-physics models to predict and prevent the TRA in large pouch LIBs as presently used in various EVs.

The multi-physics model is implemented in commercial software Comsol, with the P2D electrochemical model1 and a 3D thermal model. The degradation sub-model2 includes oxygen release in the positive electrode to simulate the overcharge phenomenon during EV’s charging. In addition, the oxygen released in the positive electrode may exothermically react with the electrolyte as well as create significant stress in the electrode, which may lead to the mechanical deformation of the electrode and a subsequent TRA. An LG Chem lithium-ion pouch cell consisting of Li(Ni0.6Mn0.2Co0.2)O2 – NMC622 – cathode and graphite anode are studied to address this severe TRA problem.

As a result of the time-varying nature of the variables that affect TRA, we propose three potential machine learning algorithms. These are Support Vector Machine, Deep Neural Network, and Recurrent Neural Network, tailored and implemented for estimating the TRA likelihood, using thermal images acquired from the multi-physics modeling of LIB pouch cells. Hyperparameters optimization has been performed to identify a set of variables for the best performing ML method. The proposed combined multi-physics and machine learning modeling methodology provide interesting insight and predictive capabilities for TRA prediction.

References

J. Newman and W. Tiedemann, J. Electrochem.
Soc., 140, 1–5 (1993).

X. Feng, X. He, M. Ouyang, L. Wang, L. Lu, D. Ren and S. Santhanagopalan, J. Electrochem. Soc., 165, A3748–A3765 (2018).
(Digital Presentation) Effects of Non-Uniform Temperature Distribution on the Degradation of Liquid-Cooled Lithium-Ion Cells
Authors: Iriyama Takuto , Cavalheiro Gabriel M. , Liu Siyi , Poudel Pragati , Zhang Guangsheng
Published: July 2022

Non-uniform temperature distribution develops inside lithium-ion (Li-ion) cells due to heat generation and low thermal conductivity in the thickness direction. Such non-uniform temperature distribution can cause non-uniform and accelerated degradation of Li-ion cells, as shown in our previous work on an air-cooled stack consisting of five Li-ion cells1, 2. Compared with air cooling, liquid cooling is more widely used for large-size Li-ion cells due to its stronger cooling capability. Liquid cooling would cause larger temperature gradient in Li-ion cells than air-cooling. It was therefore hypothesized that the degradation of liquid-cooled Li-ion cells will be more non-uniform than air-cooled cells. To test the hypothesis, a stack of water-cooled parallel-connected Li-ion cells, as schematically shown in Figure 1, were tested and compared with the air-cooled stack. Each cell has a nominal capacity of 3 Ah. As expected, the temperature distribution in the liquid-cooled stack was very non-uniform (Figure 2) and the cells degraded differently (Figure 3). Unexpected, however, the middle cell in the water-cooled stack degraded slower than the side cells, which is opposite to the trend of the air-cooled stack. Further investigation suggested that the opposite trend can be attributed to the combined effects of temperature rise and temperature gradient. Moreover, capacity drop and recovery was observed for the cells in the liquid-cooled stack after reference performance test, which could be attributed to the anode overhang effects3.

References

G. M. Cavalheiro, T. Iriyama, G. J. Nelson, S. Huang and G. Zhang, Journal of Electrochemical Energy Conversion and Storage, 17 (2020).

H. J. Gonzalez Malabet, G. M. Cavalheiro, T. Iriyama, A. Gabhart, G. J. Nelson and G. Zhang, Journal of The Electrochemical Society, 168, 100507 (2021).

B. Gyenes, D. A. Stevens, V. L. Chevrier and J. R. Dahn, Journal of The Electrochemical Society, 162, A278 (2014).

Figure 1
(Digital Presentation) Electrocatalytic Transformations of Phenolic Compounds
Authors: Martic Sanela
Published: July 2022

Electrocatalytic transformations giving rise to new C-C bond formation and new products are of value. We have recently discovered that phenolic compounds undergo selective electrochemical oxidation giving rise to reactive radicals which combine to produce product with new C-C bond formed [1]. A series of phenolic compounds, including butylated hydroxytoluene (BHT), 4-tert-butylphenol (4TBP), 2-tert-butylphenol (2TBP), 2,4,6-tri-tert-butylphenol (TTBP), 2,6,-di-tert-butylphenol (DTBP), diphenylphenol (DPP), and trichlosan were systematically evaluated by electrochemical methods.The selective electrochromic behavior was observed via electrochemical cycling. The electrocatalytic oxidation of substrates resulted in a formation of new compounds due to C-C coupling, or related products. The products were characterized by X-ray diffraction, GC-MS, and NMR, among other methods. The electrochemical synthesis was compared to the traditional chemical synthesis and the reaction yields and products were highly dependent on the synthetic strategy used and a substrate.

References

Zabik, N., Virca, C. N., McCormick, T., Martic-Milne, S. (2016). Selective electrochemical versus chemical oxidation of bulky phenols. J. Phys. Chem. B. 120: 8914-8924.
Defect-Free Metallization of through-Glass Vias (TGV) with Engineered Geometry
Authors: Mazumder Prantik , Jayaraman Shrisudersan , Sevem Matthew , Kanungo Mandakini , Vaddi Rajesh
Published: July 2022

Metallized through-glass vias (TGVs) have attracted interest in recent years due to their promise in enabling 2.5D and 3D electronic architectures and high-density MEMS devices. However, unlike metallization of PCB, metallization of TGV is challenging, and the electroplating processes are not well-established. This is mostly due to the form factor associated with TGVs - high length (L) and small diameter (Φ). During electrolytic process, for example electroplating of Copper inside the TGVs, such form factor often leads to severe transport limitation and subsequent formation of defects such as seams or voids in the samples. This has led to intense research in the past decade to develop special additives and processes to achieve defect-free filling of TGVs. It has been accepted that defect-free filling of TGVs is not possible without specialized additives in the solution. We will first demonstrate through simplified theoretical analysis and numerical modeling why that is the case when the geometry of the TGV has uniform cross-section. Even when the electroplating is carried out in in fully kinetic-controlled regime (Thiele modulus, μ ≤ 1), it will be clear from the analysis that a complete defect-free metallization is not achievable as long as the TGV cross-section is uniform. Next, we will report a novel metallization technique using an engineered via with an X-shape in the middle and operating in the kinetic-limited regime without the requirement of any specialized additives. This leads to Cu bridging of the vias at the waist, after which continued conformal plating ensures void-free filling. It would be emphasized that by combining these two effects – novel shape of TGV and kinetic controlled electroplating – void-free filling is achievable even in the absence of any additives. While additive-based bath is required and will continue to be used to optimize between plating speed, low stress and roughness of plated copper, the objective of this talk is to demonstrate the advantage of engineered vias in which even an additive-free bath could provide defect-free metallization. At very low current densities, an anomalous increase in thickness in the middle compared to the top of the via was observed. This cannot be explained by a simple 1D model and is an interesting next step in understanding additive-free electroplating.
(Digital Presentation) Electrochemical Dewatering of Cellulosic Nanomaterials
Authors: Vijapur Santosh Hanamant , Le Huong , Hall Timothy , Taylor E. Jennings , Inman Maria , Snyder Stephen , Nelson Kim
Published: July 2022

Cellulose is an abundantly available natural resource utilized for cost effective manufacturing of cellulosic nanomaterials that exhibit great potential in a variety of industrial applications. Although cellulosic nanomaterial is cost effective to produce, it is not economical to ship long distance while containing significant water content (>95 wt.%). Therefore, a need has been identified by manufacturers to develop energy-efficient, dewatering or drying of cellulosic nanomaterials.

Accordingly, Faraday Technology in collaboration with GranBio USA, manufacturers of cellulosic nanomaterials, is addressing this need by developing an economical method and system, for electrochemical dewatering of cellulosic nanomaterials including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Innovative reactor designs are utilized to demonstrate the feasibility of an industrially viable and energy efficient ElectroDewatering approach capable of generating >50 wt.% final solid content for both CNC and CNF. The material properties were maintained through dewatering, and materials with ~25-30 wt.% final solids were successfully rehydrated and redispersed via vortexing. The pulse process approach reduced the energy use by at least 50% compared to thermal drying at similar dewatering performance. We have continued to improve our TRL by scaling the electrochemical dewatering system from sub-scale batch to alpha-scale continuous process. Specifically, this talk will discuss the results of these advancements.

Acknowledgements: The financial support of DOE Contract No. DE-SC0018787 is acknowledged.
(Digital Presentation) Electrochemical Finishing of Mo Feedhorn Arrays
Authors: Hall Timothy , Le Huong , Moran Andrew
Published: July 2022

Powder bed methods of additive manufacturing (AM) use an electron beam (EBM) to sequentially melt powder, layer by layer, to build up a 3-dimensional object directly from a powder bed according to a computer aided design file. With EBM. there are four steps to build each layer in a build. First, the beam is scanned to preheat the powder bed without melting, second, the contours (outer edge) of the area to be melted is traced and powder melted, third, the hatch (area within the contours) is melted and finally any supports that need to be built to support higher layers of the part being built are added.

The major concerns for incorporation of AM into structural parts are (1) microstructural anisotropy/inhomogeneity, (2) porosity and (3) surface finish that is strongly dependent on the orientation of the surface relative to the build direction. Improving the surface finish is critical for certain applications. While finish machining can be used where surfaces are accessible, one benefit of the complexity of part shape is the possibility of building parts with internal passages, inaccessible to machining.

Therefore, this paper will discuss recent developments toward the demonstration of a process to electrochemically finish the feedhorn arrays produced with Mo by EBM additive manufacturing. Specifically, we will discuss developments toward achieving optimal electrochemical processing conditions, surface finish, nominal tooling, and performance. Unlike conventional surface finishing processes that either use media or machine tools to physically modify the surface, electrochemistry can be used as a non-contact flexible approach, to finish hard to reach surfaces such as the internal channels of refractory materials that maybe inaccessible to conventional processes. This paper will focus on pulse/pulse reverse electrofinishing processes developed by Faraday Technology and the technique to scale this approach to functional parts of interest.

Acknowledgements: The financial support of DOE Contract No. DE-SC0020783 is acknowledged.
Design of “Low Stress” Post-CMP Cleaning Processes for Advanced Technology Nodes
Authors: Cahue Kiana A. , Dudek Abigail L. , Miliauskas Mantas M. , Cahue Tatiana R. , Mlynarski Amy , Keleher Jason J.
Published: July 2022

As integrated circuit and logic device feature sizes approach the 3-nm node, limiting induced defectivity during Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) is of utmost importance. The CMP process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method involving a poly-vinyl alcohol (PVA) brush is used to transfer cleaning chemistry to the substrate of interest as well as provide the necessary mechanical energy for defect removal. While this process is effective in contaminant removal its reliance on shear forces can induce secondary defect modes, such as scratching. To minimize the aforementioned induced defectivity during contact p-CMP processes, the implementation of non-contact modalities has become of the utmost importance. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials such as SiC, GaN, carbon-doped oxides, and metals. More specifically, “OVER”-cutting and “soft” cleaning processes that balance the modulation of surface reaction kinetics (chemical and adsorption) with advanced low shear force environment will be evaluated. For example, employing supramolecular cleaning chemistries coupled with reactive oxygen species (ROS) generating complexes under megasonic action were evaluated for effective SiC cleaning. Results from a second order kinetic model indicate that processing conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low stress conditions in the megasonic field. Utilizing a suite of dynamic analytical techniques (i.e., atomic force microscopy, quartz crystal microbalance, contact angle, zeta potential, and electrochemical analysis, shear force analysis) a correlation between interfacial reaction mechanisms and effective p-CMP cleaning will be presented.
Reclaim Mode Post Etch Residue Remover Solutions for Advanced Technology Nodes
Authors: Gupta Rohini , Klipp Andreas
Published: July 2022

Back-end-of-line (BEOL) processing for creation of vias in advanced technology node semiconductor manufacturing warrants a wet chemistry capable of removing post-etch residue (PERR), titanium nitride hardmask (TiN HM) and etch stop layer (ESL), while being compatible with metals, such as copper, tungsten and cobalt. In accordance with BASF’s core competency of innovating sustainable solutions with minimal environmental impact, our reclaim mode BEOL PERR chemistries allow semiconductor manufacturers to minimize not only their cost of ownership (COO) but also their waste footprint.

BASF’s reclaim mode PERR chemistries, when mixed with appropriate amount of hydrogen peroxide, facilitate oxidative wet etching of TiN HM. In this paper, we demonstrate that optimization of formulation and spiking protocol extends the bath lifetime of these chemistries beyond 24hr, which is significant improvement vis-à-vis current industry standard of single use (drain mode) chemistries. Beaker-level bath lifetime investigation of BASF’s leading formulation confirms that TiN etch rate (ER) and bath pH are stable for 48hr (Fig. 1a) when bath is loaded with commensurate amount of Ti ions. Beaker-level performance was also corroborated by 300mm wafer level assessment. BASF’s reclaim mode PERR chemistries with bath lifetime greater than 8hr offer progressively favorable cost of ownership (COO) vis-à-vis drain mode chemistry (Fig. 1b).

Figure 1
(Digital Presentation) Two-Step Wet Clean for HKMG TiAl Protection and Polymer-Free
Authors: Chen Tianrui , Tu Wutao , Zhang Haiyang
Published: July 2022

In this paper, a two-step clean method for HKMG TiAl protection is discussed, which could improve TiAl damage and make etch-polymer clean. Using Dupont’s EKC580 chemical before traditional HF clean, the TiAl form TiOx protection layer on the surface, then HF cleans etch by-product polymer. The TiAl loss by HF can improve from 37A to 6A after EKC580 clean. The yield performance is hence much improved.
(Digital Presentation) Efficient Mandrel Cleaning Process for Fin-FET Technology Node
Authors: Zhang Jing
Published: July 2022

In this work, the surface cleaning of amorphous silicon mandrel at Fin-FET technology node is demonstrated. The unclean mandrel surface can cause abnormal growth of the following ALDSIN spacer deposition which may transfer to protrusion or bridge defect at the final structures. We present several mandrel cleaning methods to study the quality of deposited ALDSIN and then put forward a model of abnormal growth of ALDSIN. Finally, it is demostrated that the protrusion or bridge defect can be obviously improved and avoid the yield loss by the optimization of the mandrel cleaning process.
(Invited, Digital Presenter) Semiconductor Technology Challenges, Past, Present and Future
Authors: Sekiguchi Akihisa
Published: July 2022

Even though a large fraction of the global economy has yet to recover, the semiconductor related industry is doing well in spite the pandemic. The sales of electronic goods worldwide is projected to be $500 Billion (US) annually in 2021. And, according to some estimates, the electronics market may top $1 Trillion (US) in sales by 2030, essentially doubling the market in ten years.

There are a few questions that one may want to ask, like: why is this happening and how did we get here? is this projected growth realistic and sustainable for the next decade? speaking of sustainable, how is the industry addressing the need to be consistent with United Nations SDGs? what are the technical challenges that we are facing going forward? ...the list goes on.

Of course, the author does not have a crystal ball, but will attempt to give a balanced view on factors that may explain how we got here, where we might be headed, and what we need to do collectively. Input and views from a wide range of industry and academic experts and institutions will be presented in this invited presentation.
(Digital Presentation) SiGe Epitaxial Growth on Si Substrate Using Al-Ge Paste
Authors: Suzuki Shota , Matsubara Moeko , Minamiyama Hideaki , Dhamrin Marwan , Uraoka Yukiharu
Published: July 2022

Silicon-germanium (SiGe) has been considered as an important alternative material to silicon due to its high carrier mobility, low power consumption and excellent performance [1]. However, due to both material unique phase diagram with melting points separated by 376 °C, it is too difficult to realize a good bulk quality of polycrystalline-free SiGe single crystals with controlled Ge contents.

In this work, crystalline thick epitaxial layers of SiGe with Ge contents exceeding 30% are fabricated by screen-printing technology on Si wafers. As illustrated in Figure 1, Aluminum-germanium (AlGe) paste with a mole ratio of 7:3 was prepared and screen-printed on p-type Cz-Si <111> substrate, dried at 100 °C for 10 minutes and then annealed in Ar ambient using IR image furnace at 900 °C for 5 minutes. The Al begins to melt at 660 °C, dissolving the silicon wafer surface and the Ge in the paste. The melted Al, Si and Ge form the liquid phase of the Al-Si-Ge, which when cooling process start, regrown epitaxially at the melt/Si interface to form the Al-doped SiGe crystalline layer.

The formed SiGe was observed by scanning electron microscope (SEM), and energy dispersive X-ray spectrometry (EDX). As can be seen in the cross-sectional SEM image in Figure 2, SiGe layer of about 20mm was formed on the Si substrate surface. It is worth mentioning that the SiGe/Si interface is formed straight as the reaction stopped perfectly on façade <111> forming SiGe layer. EDX mapping of elements suggests that the Al in the Al-Si-Ge liquid phase formed at high temperature is segregated from the liquid to the Al-Ge paste layer during the cooling process and remains only as dopant in the SiGe layer due to its low solid solubility in Si and Ge. The Al-Ge paste residue layer will be etched chemically and further step of chemical mechanical polishing will be performed to improve the surface flatness of SiGe layer to be an epi-ready SiGe/Si substrate for different semiconductor devices applications.

Reference

[1] M. L. Lee and E. A. Fitzgerald, Strained Si/strained Ge dual-channel heterostructures on relaxed Si0.5Ge0.5 for symmetric mobility p-type and n-type metal-oxide-semiconductor field-effect transistors, Appl. Phys. Lett. 83, 4202 (2003).

Figure 1
(Invited, Digital Presentation) Development of 3D-Stacked Artificial Retina Chip with 3DIC/TSV and Advanced Packaging Technology
Authors: Tanaka Tetsu
Published: July 2022

3DIC/TSV is the most promising candidate for high-performance and low-power computing devices. They have many advantages such as short wiring length, small pin capacitances, high packing density, ultra-parallel operation. Among several types of 3D-IC technologies, multiple chips-to-wafer (MCtW) stacking can stack known-good chips fabricated with different technologies and sizes, leading to a true 3D heterogeneous system. We have developed a fully implantable retinal prosthesis with a 3D-stacked artificial retina (AR) chip. In the 3D-stacked AR chip, the photoreceptor chip and stimulus current generator with image processing circuits are vertically stacked and electrically connected by many TSVs. Furthermore, advanced packaging technology like FOWLP is being developed to implement multiple AR chips in a flexible substrate to obtain a wide viewing angle. This leads to small chip size, lightweight, large fill-factor, high resolution, and high quality of life patients.
Impact of Substrate Defects on Vertical GaN Device Leakage Behavior
Authors: Wang Yekan , Liao Michael Evan , Huynh Kenny , Olsen William , Gallagher James C , Anderson Travis J. , Huang Xianrong , Wojcik Michael , Goorsky Mark S.
Published: July 2022

In this work, the effects of the substrate defects on the reverse leakage behavior of vertical GaN Schottky and p-i-n diodes are investigated. A direct connection between the reverse leakage behavior of GaN based vertical devices and the defect characteristics of the substrate was achieved. The difference in the leakage current can be as high as 6 orders of magnitude for vertical GaN p-i-n diodes at -200V, using HVPE substrate with inhomogeneous defect distributions (with dot-cores). For comparison, using HVPE substrate with uniform defect distribution (no cores), the p-i-n diodes show much more uniform leakage behavior at -200V, varying within only an order of magnitude. The wafers with inhomogeneous defect distribution possess periodically patterned core-centers with higher defect density (up to 108 cm-2) than regions in between cores, which have very low defect concentrations (as low as 104 cm-2). The full width at 0.01 maximum of the triple axis rocking curves (GaN (0004)) shows a large variation ranging from 60 to 930 arcsec. In comparison, wafers without the periodic cores have a uniform defect density (~106 cm-2) and show a small variation in the rocking curve FW0.01M, ranging only from 70 to 280 arcsec. For Schottky diodes fabricated on substrate with cores, positioning the devices away from the core-centers results in a reduction of the reverse bias leakage by 2-4 orders of magnitude at -10 V. Similar trend are also observed in the p-i-n diodes, with device further away from the core-centers showing lower leakage. The devices in the low defect concentration region (> 200 um away from core centers) on the wafer with cores outperform the devices from the wafer without cores, showing up to 2 orders of magnitude lower leakage current at -200 V. The results from this study show that the substrate defect density and distribution play an important role on the device leakage current and avoiding highly defective regions on the substrate will improve the performance of vertical GaN devices.
(Invited, Digital Presentation) Exploring Interfaces and Polarity to Realize Vertical III-Nitride Superjunction Devices
Authors: Pavlidis Spyridon , Khachariya Dolar , Szymanski Dennis , Reddy Pramod , Kohn Erhard , Sitar Zlatko , Collazo Ramon
Published: July 2022

In recent years, there has been a surge of research and commercial interest in gallium nitride (GaN)-based devices for power conversion applications. This is largely motivated by the wide bandgap of GaN, which offers a unipolar limit of performance that is larger than that of silicon and silicon carbide. This performance ceiling, however, can be surpassed with the use of superjunction (SJ) structures, a strategy that has now been experimentally proven in both vertical Si- and SiC-based technologies. The ability to selectively dope lateral regions of a semiconductor is a requirement for SJ fabrication, with typical schemes relying on ion implantation, epitaxial regrowth or a combination of both. However, due to the challenges associated with applying conventional selective area doping techniques to GaN, vertical GaN SJ structures have remained elusive.

Recently, our team proposed the use of lateral polar junctions (LPJs) to form vertical GaN SJ devices. This approach exploits the natural doping asymmetry between the N-polar and Ga-polar crystal orientations to simultaneously grow N-polar GaN for the n-type pillars and Ga-polar GaN for the p-type pillars. The first part of this talk will present a design framework for GaN SJ devices. This will reveal several critical design requirements: 1) doping in N-polar GaN must be reduced below 5 × 1017 cm-3 to achieve kV-class devices, 2) charge must be tightly balanced between neighboring pillars in the SJ structure to obtain efficient performance and 3) the barrier height to the N-polar GaN region must be tuned to suppress leakage currents and avoid bipolar operation.

The next part of the talk will focus on the characterization of rectifying contacts to N-polar GaN. While the analysis of Schottky barrier diodes proved the ability to reduce doping to relevant levels, the low barrier height and enhanced chemical sensitivity of N-polar GaN make it challenging to process adequate devices. Thus, low-pressure chemical vapor deposited (LPCVD) silicon nitride (SiN) interlayers were introduced to increase the barrier height. This approach is enabled by surface-termination dependent barrier height and an amphoteric miniband for enhanced conduction via the interlayer. Moreover, the use of the LPCVD SiN interlayer enables operation of the diodes up to 400 °C compared to less than 200 °C for the reference case. In addition, N-polar GaN camel diodes were also designed, fabricated and tested to better tune the barrier height. The latter structure was incorporated into the first charge-balanced GaN superjunction device. A detailed electrical analysis of the GaN LPJ device will represent the final portion of this talk.

The successful demonstration of these experimental building blocks paves the way for the GaN LPJ to be used in future high-voltage GaN SJ devices.
(Invited) Updated Issues Regarding Threshold-Voltage Instability in SiC MOSFETs
Authors: Lelis Aivars , Habersat Daniel , Urciuoli Damian , Green Ronald
Published: July 2022

This work will provide an updated overview of our understanding of several key reliability issues for SiC power MOSFETs related to threshold-voltage stability. Threshold-voltage instability likely occurs due to the charging and discharging of near-interfacial oxide traps in response to a change in gate bias. If enough traps change charge state, it can lead to significant shifts in the threshold voltage, which may in turn lead to increases in leakage current in the off state, or increases in on-state resistance in the on state. An important question is, what is the best—or most appropriate—test method to use to determine the reliability of these devices. It has recently been observed that one commercial device manufacturer has quite large instabilities, even in previously unstressed devices, and that such large instabilities can result in significant increases in on-resistance during normal switching conditions, thereby degrading circuit performance. Other issues addressed will be the effects of AC Stressing, measuring both static and dynamic threshold voltage, and comparing effects in trench and planar geometry devices.
(Invited, Digital Presentation) Fatigue-Resistant of Ag Sinter Joining on Ni-P/Pd/Au Finished DBA Substrate with Thick Ni-P Layer During Thermal Shock Test
Authors: Chen Chuantong , Suganuma Katsuaki
Published: July 2022

The wide band-gap (WBG) semiconductor, such as silicon carbide (SiC) and gallium nitride (GaN), are widely expected to replace conventional Si-based chips, which provide the power modules with higher working temperature larger than 250 degrees. Ag paste sinter joining emerges as a promising alternative for the die attach material in WBG power devices owing to its superior electrical/thermal conductivity as well as a high melting point of 960℃. For Ag paste sinter joining on WBG chip or substrate, most studies are focusing on Ag metallization layers by which the Ag-Ag interface delivers high bonding strength because of the chemical/structural similarity. However, with the superior anti-oxidation/corrosion property, Au metallization layers ensure the Ag-Au joint much wider usage environment than Ag-Ag joint.

The study was carried out to develop a highly reliable Ag-Au sintering joint in SiC chip and Direct bonded aluminum (DBA) power modules. The DBA substrate was strengthened by an electroless nickel/electroless palladium/immersion gold (ENEPIG) metallization layer. ENEPIG plated DBA substrate was modified to possess superior mechanical strength by thickening the Ni layer with the thickness of 7µm and 20µm. The reliability of SiC/DBA die-attached module by Ag-Au joining was evaluated during a long-term thermal shock test (TST) from -50℃ to 250℃ up to 1000 cycles. In the case DBA with a Ni metallization layer of 7µm, severe plastic deformation occurred at the Ag-Au interface. By thickened ENEPIG layer with Ni-P layer to 20µm, the Ag-Au interfacial deformation derived from Al plastic deformation was successfully suppressed even after 1000 cycles. The shear strength of as-sintered Ag-Au joint was evaluated to be larger than 35 MPa, but degradation was still found to be the interfacial delamination between Ag paste and ENEPIG substrate during thermal shock test for the two ENEPIG metallization cases. The bonding interface and fracture characteristics were systematically investigated, which provide basic understanding between microstructural evolution and reliability of Ag-Au joint during TST.
Mechanism of Reverse Leakage Current in Schottky Diode Fabricated on Large Bandgap Semiconductors like Ga2O3 or Diamond Part II
Authors: Lau Wai Shing
Published: July 2022

The bandgap of Ga2O3 (4.5-4.9 eV) is larger than the bandgap of GaN (3.4 eV). In addition, single crystal bulk Ga2O3 wafers can be more easily manufactured than GaN wafers. Therefore, Ga2O3 has strong potential for applications in high power semiconductor devices [1]. Schottky diodes fabricated on n-type Ga2O3 have strong potential as fast high-power switching devices. Similarly, the bandgap of diamond (5.5 eV) is very large and diamond Schottky diodes have good potential.

One possible mechanism of reverse leakage current in Schottky diodes is image force barrier lowering at the metal-semiconductor interface. Historically, there were 2 theories regarding the image force barrier lowering effect. In 1953, Krömer published his theory that the image force dielectric constant in the equation for Schottky emission should be equal to 1 [2]. Subsequently in 1964, Sze et al. published their theory that the image force dielectric constant in the equation for Schottky emission should be equal to n2 [3], where n is the refractive index of the semiconductor in the infrared or visible light range. In 1969, Sze published a book which has influenced many scientists [4]. Sze’s theory [3]-[4] quickly became the dominating theory whereas Krömer’s theory essentially became a forgotten theory. In 2020, the author pointed out that Krömer’s theory is quite frequently more compatible with experimental results for Ga2O3 or diamond Schottky diodes [5]. In 2021, the author attempted to propose a new theory involving the concept of electron velocity overshoot to unify Krömer’s theory and Sze’s theory, as shown in Fig. 1 [6]; Krömer’s theory is better than Sze’s theory for high reverse bias voltage.

In conclusion, the author pointed out that it is necessary to resurrect an old and forgotten theory from Krömer in order to explain the experimental data on the reverse leakage current of Schottky diodes fabricated on large bandgap semiconductors like Ga2O3 and diamond, etc. A theoretical basis based on quasi-ballistic transport will be provided.

References

[1] M. Higashiwaki, H. Murakami, Y. Kumagai and A. Kuramata, Jpn. J. Appl. Phys., 55, 1202A1 (2016).

[2] H. Krömer, Zeitschrift fur Physik, 134, 435 (1953). (In German.)

[3] S.M. Sze, C.R. Crowell and D. Kahng, J. Appl. Phys., 35, 2534 (1964).

[4] S.M. Sze, Physics of Semiconductor Devices, p. 367, Wiley Interscience, New York (1969).

[5] W.S. Lau, ECS Trans. 97 (4), 99 (2020).

[6] W.S. Lau, CSTIC 2021 (China Semiconductor Technology International Conference, Shanghai, 2021, IEEE), 1 (2021). (Available from IEEE database.)

Figure 1
Subgap Density of States of Amorphous Indium Gallium Zinc Oxide (a-IGZO) Thin Film Transistors
Authors: Mattson George , Vogt Kyle , Wager John F , Graham Matt Werden
Published: July 2022

In amorphous oxide semiconductors such as indium gallium zinc oxide (a-IGZO), subgap states often play an important role in determing thin-film transistor (TFT) operation metrics such as turn-on voltage, mobility, hysteresis, and bias-stress stability. Using a-IGZO TFTs, we are able to resolve (over 6 orders of magnitude) the photoconduction response of a-IGZO spanning the subgap region (from 0.3-3.5 eV) in order to elucidate the subgap density of states (DoS).1 In this presentation, we will focus on two significant findings related to the nature of a-IGZO subgap states. First, hydrogen is found to act as a negative-U donor in a-IGZO, contributing an electron to the conduction band before bonding with valence band oxygen 2p states, thereby forming an [OO
2-H+]- defect complex whose Gaussian-like DoS are positioned 0.4 eV above the valence band mobility edge.2 Second, bottom-gate, back-channel etched a-IGZO TFTs are found to have a Gaussian-like zinc vacancy-related subgap state centered roughly 2.3 eV below the conduction band mobility edge, a feature that is not present in top-gate a-IGZO TFTs.

K. Vogt et al. Phys.
Rev. Research 2 (Sep. 2020). 10.1103/PhysRevResearch.2.033358

G. Mattson et al. arXiv:2111.08588

Figure 1
(Digital Presentation) Fabrication and Characterization for Vanadium Oxynitride Thin Films By Magnetron Sputtering
Authors: Li Chuan , Hsieh J. H. , Papina I
Published: July 2022

Vanadium oxynitride (VNxOy, x+y=1) is a metallic compound between vanadium oxides (VO, V2O3, V2O5) and vanadium nitride (VN) which would have interesting properties and functions that potentially can be supplied for different applications. In this study, vanadium nitride and oxynitride thin films were obtained by reactive magnetron sputtering using vanadium targets, Ar as plasma carrier, and a mix of N2 and O2 as reactive gas. The ratio of mass flow between the two gases is maintained around O2:N2=1:20 during the process. To obtain crystalline phases of oxynitrides a post rapid thermal annealing (RTP) in Ar atmosphere at 600ºC and 700ºC for 5 minutes was done. The purpose of the study is to define the effect of the magnetron sputtering parameters, such as reactive gas flow rates, and annealing temperature on the composition, microstructure, and optical properties of the obtained vanadium oxynitride thin films. The characterization of obtained films includes the examination of thickness and morphology by the surface profiler and SEM; identifying crystal structures and further microstructural vibration modes of molecular polarizability by X-ray diffraction and Raman spectroscopy, respectively; evaluation of the chemical composition of films by XPS analysis; assessing of optical transmittance, reflectance, and absorbance by the UV-visible- NIR spectrometer. Experimental data reveal that the annealed films can be oxynitrides when the oxygen flow rate is below 0.25 sccm and the ratio of oxygen/nitrogen ≤1/20. The annealed vanadium oxynitride films in terms of their properties are closer to vanadium nitrides than to oxides: more metallic than semi-conductive with dark appurtenance and high optical absorbance across the spectrum between 200 and 900 nm. The optical absorbance reaches almost 90% around 300 nm and then slowly reduces to 70% at 900 nm. Thus, these films could be good optical shields. For practical usage, the deposition of O2:N2=1/20, O2<0.25 sccm, and 600ºC annealing are recommended because of the truly low transmittance (<10%) through films.
Control of Hydrogen Concentration in Ingazno Thin Film Using Cryopumping System
Authors: Jung Seyeon , Sung Taehoon , Lee Sein , Kwon J.-Y.
Published: July 2022

Recently, amorphous metal-oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) have attracted great attention with their lower power consumption and higher mobility than amorphous silicon in the display field. However, the threshold voltage (Vth) shift of IGZO thin film transistor (TFT) caused by their poor reliability leads to the drop panel luminance. Therefore, improvement of IGZO TFT reliability is necessary, which is largely influenced by oxygen vacancy and hydrogen. In particular, hydrogen has shown different roles inside the IGZO active layer by hydrogen concentration. At lower concentration, the hydrogen passivation of oxygen deficiency region induces the improvement of initial electrical characteristics and reliability [2]. Meanwhile, Vth shift and degradation reliability are generated at higher concentration owing to the hydrogen related defect states [3]. Therefore, controlling excess hydrogen is necessary for reliability enhancement.

In this work, IGZO thin film was fabricated by cryopumping system instead of a turbo molecular pump (TMP) for radio frequency sputtering to reduce hydrogen concentration. Cryopump is an adsorption type that enables excellent evacuation ability of hydrogen and moisture taking up most of the partial pressure in high vacuum. As a result, deposition of IGZO thin film with lower hydrogen impurity is available. The hydrogen concentration in the IGZO thin film using both cryopump and TMP was quantitatively analyzed by elastic recoil detection (ERD) analysis. Then, electrical characteristics of the self-aligned top-gate structure TFTs fabricated by both pumps were measured with bias stress conditions.

To sum up, we showed the improved reliability of IGZO TFT by controlling excess hydrogen using cryopumping system.

Fig.1. (a) Schematic of RF magnetron sputtering process with cryopump. (b) TOF-SIMS depth profiles of hydrogen concentration in IGZO film using TMP and cryopump

Acknowledgment

This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283)

References

Chung, Ui-Jin, et al. "15‐1: Invited Paper: Manufacturing Technology of LTPO TFT." SID Symposium Digest of Technical Papers. Vol. 51. No. 1. 2020.

Hanyu, Yuichiro, et al. "Hydrogen passivation of electron trap in amorphous In-Ga-Zn-O thin-film transistors." Applied Physics Letters 103.20 (2013): 202114.

Mativenga, Mallory, et al. "Origin of light instability in amorphous IGZO thin-film transistors and its

suppression." Scientific reports 11.1 (2021): 1-12

Figure 1