bluuebunny/crossref_metadata_2025_split huggingface dataset:
Overview of Aging Mechanisms in Sige Hbts
Authors: Raghunathan Uppili , Ioannou Dimitris , Jain Vibhor , Pekarik Jack 
Published: November 2022

SiGe HBTs offer significant performance advantage over Si BJTs with improved base resistance and base transit time. However, each faster technology iteration usually comes at the cost of reduced breakdown parameters. As a result, devices are often restricted to smaller operation biases, and rely on fully utilizing these imposed limits to attain maximum circuit performance. Both high voltage and high current operation have been shown to take a toll on a device’s aging behavior. One unintended consequence of technology scaling is that it forces designers to consider alternate circuit architectures and operate these devices under non-traditional modes such as reverse active, off-state, and saturation. Although not as optimal for device performance as forward active operation, these modes enable improved radiation hardening, power savings and even simpler circuit design.
A bipolar transistor’s operation can be categorized into four main modes as shown in the figure below based on the applied voltage to the base-emitter (VBE) and base-collector (VCB) junctions. Due to the asymmetrical junction engineering for vertical HBTs, the forward-active mode is usually the most optimized for device performance. Because it is the most utilized mode, it is also the most characterized for device reliability. In this paper, in addition to the mixed mode stress used to characterize SiGe bipolars, we will discuss some of the recent learning in SiGe HBT reliability in the other less-understood modes of operation. We begin with a brief overview of SiGe HBT reliability physics including hot carrier generation (Auger vs. Impact-Ionization), the temperature dependence of competing mechanisms and the physical damage responsible for electrical degradation. Using measurements and simulations, we discuss in detail the device degradation under off-state and saturation modes. We demonstrate how the hot carrier generation physics responsible for degradation in the forward-active mode is still applicable in the other regions of operation.

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Analysis of Graphite Lithiation Behaviour in Li-Ion Full Cells Using a Novel Cross-Sectional in Situ Optical Microscopy Method
Authors: Hogrefe Christin , Waldmann Thomas , Benavente Molinero Miguel , Wildner Ludwig , Axmann Peter , Wohlfahrt-Mehrens Margret 
Published: November 2022

In Li-Ion batteries, the graphite anode undergoes chromatic changes from grey (unlithiated graphite) to blue (LiC18) to red (LiC12) to gold (LiC6) during lithiation.1 When charged with high current rates, lithiation gradients are observable due to mass transport limitations within the anode.2 Due to high lithiation degrees at the surface, the anode potential decreases locally and the possibility of Li deposition is increased.3

We introduce a new in situ optical microscopy set-up, which allows a direct observation of the cross-section of Li-ion full cells in combination with simultaneous recording of electrochemical data (Figure 1). Extensive analysis of the chromatic changes from the graphite electrode surface to the current collector gives insights into the lithiation processes on electrode and particle level. The set-up was validated by comparing the electrochemical results with data from coin full cells. The propagation of lithiation fronts for LiC12 (~ 3300 µm2 min-1) and LiC6 (~1260 µm2 min-1) at 1C through the graphite electrode coating were determined as well as the estimation of apparent solid-state diffusion coefficients in the order of 10-10 cm2 s-1 from analyzing the phase propagation within single particles at C/10. Additionally, the expansion of all components of the whole cell can be observed individually. We found that the graphite contributes mainly to the cell expansion, both irreversibly (4%) and reversibly (4-13%). Directly observing the described phenomena in the full cell can give insights into aging mechanisms of the materials.
Figure 1 Exemplary image from the video at the end of charge of an in situ measurement (cycling at C/10) of a graphite-NMC 622 full cell cross-sections.
References

P. Maire, A. Evans, H. Kaiser, W. Scheifele and P. Novák, J. Power Sources,
155(11), A862 (2008).

M. Weiss, R. Ruess, J. Kasnatscheew, Y. Levartovsky, N. R. Levy, P. Minnmann, L. Stolz, T. Waldmann, M. Wohlfahrt-Mehrens, D. Aurbach, M. Winter, Y. Ein-Eli and J. Janek, Adv.
Energy Mater.,
11(n/a), 2101126 (2021).

T. Gao, Y. Han, D. Fraggedakis, S. Das, T. Zhou, C.-N. Yeh, S. Xu, W. C. Chueh, J. Li and M. Z. Bazant, Joule (2021).

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Performance Optimization of High Ni (≥90%) Cathode Materials: Synthesis & Modification
Authors: Gim Jihyeon , Han Jinhyup , Kahvecioglu Ozgenur , Zuo Peng , Zou Lianfeng , Dogan Fulya , Mane Anil U. , Darapaneni Pragathi , Wang Chongmin , Elam Jeffrey W. , Lee Eungje , Amine Khalil , Croy Jason R. 
Published: November 2022

The significant growth rate of the electric vehicles (EVs) market, powered by rechargeable lithium-ion batteries (LIBs), in favor over of the internal combustion engine (ICE), represents an opportunity to massively reduce CO2 emissions and help limit global warming issues. EVs should have a similar performance to that of ICE-powered vehicles in terms of fulfilling driving range as well as lifetime of the battery to appeal the potential consumers. However, the driving range of EV’s is limited by the battery performance, which is related to the properties of the cathode material. Therefore, the development of advanced cathodes is needed.
Current state-of-the-art, Li-ion cathodes for EV batteries are derived from layered LiNiO2 (LNO) by substitution of Ni with other elements such as Mn, Co, and Al – so called LiNixMnyCozAl1-x-y-zO2 (NMCA). Substitutions are used to offset the inferior structural stability and poor cycle-life performance of typically-produced, high-capacity NMCAs. In this regard, pure LNO has been reported as a baseline material for gauging the improvements, via doping/coating strategies, for the NMCA-class of cathodes. However, for the purposes of a fully understanding the roles of Mn, Co, Al, and other dopants in NMCAs, the development of a truly state-of-the-art, LNO cathode should be accomplished. This presentation will discuss the various parameters affecting the synthesis and performance of LNO and LNO-based oxides, from precursors to final products, and the strategies that have been pursued at Argonne National Laboratory towards the realization of high-performance LNO baselines and derivatives thereof. Their potential applicability to battery applications will be also reviewed.
Tailoring Redox Reactions for Stable Cycling of High-Capacity Li-Ion Cathodes
Authors: Tong Wei 
Published: November 2022

Development of new cathode materials with even better performance and lower cost is needed to meet the ever-increasing global demand on lithium-ion batteries. As such, extensive efforts have been devoted to developing next-generation cathodes for high-energy Li-ion batteries, e.g., Li-rich transition metal oxides. As a counterpart to the conventional cation-ordered layered oxides, cation-disordered rocksalts (DRXs) have emerged as a new class of high-capacity cathode materials. One unique advantage of the DRX chemistry is the structural flexibility that substantially lessens the elemental constraints and enables the incorporation of a wide variety of TMs and fluorine anion at a decent amount in the crystal lattice. As a result, the dominant TMs have been extended from redox-active Ni and Co in layered cathodes to cost-effective and earth-abundant Mn and Fe as well as redox-inactive TM (e.g., Nb, Ti, Zr, Mo) to facilitate the DRX phase formation. This exceptional chemical diversity largely opens up the opportunity to tune the material compositions for optimal performance through the control of redox reactions.
In this talk, I will present our recent work on several high-capacity cathodes based on Mn and Ni redox centers. We specifically focused on understanding the redox chemistry, including cationic and anionic redox, using combined electrochemical, soft X-ray absorption (XAS), and resonant inelastic X-ray spectroscopy (RIXS) techniques. This presentation summarizes the different TM and O redox behaviors and their roles in the electrochemical processes of these high-capacity cathodes. I will then show some examples on how this understanding leads to improved cathodes with enhanced performance by tailoring the redox reactions.
Characterization of ALD Ta2O5, Al2O3, and Ta2O5/Al2O3 Nanolaminate as Metal-Insulator-Metal Capacitor Dielectric for GaAs HBT Technology
Authors: Yota Jiro 
Published: November 2022

In order to reduce die size and increase capacity, the metal-insulator-metal (MIM) capacitor area in circuit designs fabricated using GaAs hetero-junction bipolar transistor (HBT) technology has to be reduced. This can be achieved by using a capacitor dielectric material that has a high dielectric constant or high capacitance density. In GaAs HBT technology, the MIM capacitor dielectric film is typically also required to have a high breakdown voltage (>20 V) and low leakage current. Furthermore, the deposited dielectric film has to be compatible with GaAs processing and has to be deposited at a temperature of < 300oC, due to the limited process thermal budget in the HBT technology. As a result of these requirements, there are only a few materials available for MIM capacitor dielectric application in GaAs HBT technology.
In this study, 60 nm tantalum pentoxide (Ta2O5), aluminum oxide (Al2O3), and Ta2O5/Al2O3 nanolaminate deposited using atomic layer deposition (ALD) have been characterized and evaluated as MIM capacitor dielectric for GaAs HBT technology. The results show that the capacitor with 60 nm of ALD Ta2O5 has the highest capacitance density (3.84x10-15 F/μm2), followed by the capacitor with 60 nm Ta2O5/Al2O3 nanolaminate, and the capacitor with 60 nm Al2O3 capacitor dielectric film with a capacitance density of 2.40x10-15 F/µm2 and 1.37x10-15 F/μm2, respectively. The calculated dielectric constant of ALD Ta2O5 and Ta2O5/Al2O3 nanolaminate is 26.1 and 16.3, respectively, while that of ALD Al2O3 is 9.3, as shown in Figure 1.
Figure 2 shows the I-V characteristics of MIM capacitors with 4055 μm2 area and with 60 nm of ALD Ta2O5, Ta2O5/Al2O3 nanolaminate, and Al2O3 capacitor dielectric. As can be seen, the capacitor with Al2O3 capacitor dielectric has significantly lower leakage and higher breakdown voltage (46 V), while the capacitor with Ta2O5/Al2O3 and Ta2O5 capacitor dielectric has higher leakage current and lower breakdown voltage of 32.7 V and 22.4 V, respectively. Figure 3 shows the C-V characteristics of capacitors with the 3 ALD capacitor dielectric films. The results show that the capacitance of MIM capacitor using these three films increased marginally by 2.2% to 4.3%, when the temperature was increased from 25oC to 125oC. No significant change in capacitance density of these ALD capacitor dielectric films was observed, when the applied voltage was varied from -5 V to +5 V.

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Micro LED Display Pixel Circuit Using Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistor
Authors: Kang Seo Jin , Yu Eun Seong , Lee Hyuk Su , Bae Byung Seong 
Published: November 2022

Micro LED (μ-LED) refers to a micro-light emitting diode with a chip size of 5 to 100 μm. Since micro-LED displays use individual LED chips as a light source of the pixel, they do not need backlight and color filters, which are suitable for implementing flexible displays. In addition, micro-led displays have many advantages over OLED displays, such as excellent color gamut, power consumption, lifetime, and response time. With these advantages, micro-LED displays are attracting attention as next-generation displays, and accordingly, interest in micro-LED driving technology is increasing. While existing OLED displays express grayscale by controlling the amount of current flowing through the light-emitting device, micro-LED can have a problem of color change depending on the grayscale because the light-emitting wavelength shifts when the amount of current changes. Therefore, in order to express a certain color, it is necessary to express the grayscale by adjusting the emission time at the same current density. That is, it is more suitable to use the PWM(pulse width modulation) for each pixel than to use the PAM(pulse amplitude modulation) for the grayscale representation of the OLED display. Therefore, unlike OLED, the micro-LED display requires a new pixel circuit because it must use a PWM driving. In addition, unlike LCDs, micro-led displays are sensitive to changes in electrical characteristics of TFTs depending on the location of each pixel or external stress. Thus, threshold voltage compensation is essential because changes and degradation of the characteristics of the thin film transistor backplane, such as threshold voltage shift, cause non uniform brighteness. Therefore, we propose a PWM compensation pixel circuit based on a-IGZO TFT that can be fabricated on a flexible substrate and has a lower process cost than LTPS and greater mobility than a-Si TFT.
The operation of proposed pixel is divided into (1) reset 1, (2) PWM data compensation, (3) reset 2, (4) CCG (constant current generation)compensation, and (5) emission. The circuit is divided into a CCG unit that generates a constant current and a PWM unit that adjusts emission time by a ramping signal. Figure 1 (a) shows the output current simulation result according to PWM data voltage variation. When the PWM data voltages vary from -1 to ~ - 5V, the currents were constant at 70.9 μA, and the smaller the PWM data voltage, the longer the emission time was. In addition, Figure 1 (b) shows the effect of the threshold voltage compensation. The current and emission time are constant for various threshold voltages such as 1, 2, and 3 V.

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(Invited, Digital Presentation) Aqueous Zinc Battery for Safe Energy Storage
Authors: Zhi Chunyi 
Published: November 2022

Development of energy storage system in the past year focus on improvement of energy density. While the progress is remarkable, safety problems of lithium-ion batteries (LIB) have been intensively exposed. On one hand, LIB is not intrinsically safe with very active anode, flammable electrolyte and oxygen-releasing cathode; on the other hand, many application scenarios actually don’t require very high energy density.
We work on aqueous electrolyte batteries to achieve both high energy density and superior safety performance. We developed a few approaches to improve stability of Zn anode and figured out potential problems of the current Zn anode studies. We tackled the challenge of stability of Zn anode at high areal capacity and high current density by developing artificial SEI film, electrolyte regulation and organic anode development. In addition, we develop Zn powder based anode and improve their stability for more practical applications.
In terms of cathode of cathode materials, we develop various Mn, PBA, organic materials and MXenes based materials, targeting on a stable and high-capacity ones. We also develop a few cathode materials based on conversion mechanism, providing extraordinary capacity and decent voltage output. We also developed a few approaches to regulate conventional cathode materials for better stability.
Our research purpose is to develop aqueous Zn batteries for large scale energy storage with ultimate safety performance and integrate them with renewable energy systems. We hope our research can contribute to sustainable society development.
(Invited, Digital Presentation) Ternary III-Sb Nanowires: Synthesis and Their Electronic and Optoelectronics Applications
Authors: Yip Sen Po , Wang Wei , Ho Johnny C 
Published: November 2022

Nowadays, the increasing demand for low power and highly efficient electronics and optoelectronics has driven the semiconductor industry to look for the alternatives of Si which is approaching its physical limit. Materials like graphene, carbon nanotube, III-V materials and so on, are the most promising candidates as the replacement of silicon. Among them, III-Sb materials, a sub-group of III-V materials, have been extensively researched due to their narrow and direct bandgap, high charge carrier mobility and high g-factor which makes them suitable for transistor, infra red detection and so on. Their nanowire counterparts have also been explored as the geometry of nanowire provide unique advantages.
One of the research directions of III-Sb nanowire is to study their ternary counterpart (III-V-Sb or III-III’-Sb) like InAsSb, GaAsSb and InGaSb. Compares with binary compounds, ternary compound provides more room for engineering freedom like lattice parameter engineering and bandgap tuning. In this presentation, the synthesis and the electronic and optoelectronic applications of ternary III-Sb nanowires will be introduced. The high-crystal quality and high-aspect ratio ternary III-Sb nanowires were synthesized by using solid-source chemical vapor deposition method. Composition tunability was demonstrated successfully by adjusting the precursor ratio which allowed us to control the physical properties. We further integrated these nanowires into transistors and photodetectors which exhibit good performance like high carrier mobility and good photoresponse.
(Invited) From Bulk to Nanostructured Perovskites
Authors: Ho Johnny C 
Published: November 2022

The dimensionality of semiconductors has a crucial role in determining their properties. Recently, metal halide perovskites have been demonstrated with many exciting applications, attracting wide attention to further their development for advanced optoelectronics, such as photovoltaics, photodetectors, light-emitting diodes, and lasers. At length scales down to nanoscale regimes, surface features as well as quantum confinement effects become dominant in regulating the material properties of perovskite materials. In past years, our group focus on the synthesis and characterization of metal halide perovskites with different configurations, ranging from bulk films, microplates, nanosheets, to nanowires. The corresponding physical properties and device applications were also systematically studied based on their widely tunable dimensionality, morphologies, and compositions.
Specifically, for perovskite bulk films, surface defects and bulk structural order significantly affect their device performance. Through optimizing processing techniques, self-assembled quasi-2D perovskite films with graded phase distribution were successfully prepared. Gradient type-II band alignments along the out-of-plane direction of perovskites with spontaneous separation of photo-generated electrons and holes are obtained, which is later employed to construct self-powered vertical-structure photodetectors for the first time. Without any driving voltage, the device exhibited impressive performance with the responsivity up to 444 mA/W and ultrashort response time down to 52 µs. In addition, to assess the intrinsic material properties of crystalline perovskites, freestanding MAPbI3 nanosheets and lead-free Cs3Sb2I9 microplates were fabricated by two-step chemical vapor deposition method, in which excellent optoelectronic performance (e.g., responsively of MAPbI3 nanosheet is measured to be 40 A/W) together with ultra-fast response speed (down to 58 µs) and superior thermal stability were obtained.
For nanostructured perovskites, understanding the dimensional features and their impact on the materials and devices is becoming increasingly important. Lately, we reported the direct vapor-liquid-solid growth of single-crystalline all-inorganic lead halide perovskite (i.e., CsPbX3; X = Cl, Br, or I) NWs. These NWs exhibited high-performance photodetection with the responsivity exceeding 4489 A/W and detectivity over 7.9 × 1012 Jones toward the visible light regime. Field-effect transistors based on individual CsPbX3 NWs were also fabricated to show the impressive carrier mobility of 3.05 cm2/Vs, being higher than other all-inorganic perovskite devices. Besides, the realization of high-mobility CsPbBr3 NW devices is reported via a simple surface charge transfer doping strategy. After MoO3 decoration and device fabrication, the hole mobility of CsPbBr3/MoO3 core-shell NW device is significantly enhanced to 23.3 cm2/Vs. All these results provide important guidelines for the further improvement of these perovskite nanostructures for practical utilization.
Preparation and Characterisation of Microporous Layers Derived from Graphene Foam
Authors: Lee Florence Cecilia , Kusdhany Irfan , Ismail Mohammed , Ingham Derek , Hughes Kevin , Lyth Stephen , Ma Lin , Pourkashanian Mohamed 
Published: November 2022

Proton exchange membrane fuel cells (PEMFC) are a viable means to meet global energy demand, reduce dependence on fossil fuels, and mitigate carbon dioxide emissions. Despite recent progress in their development, water saturation remains a challenge to current PEMFC design and efficiency. The addition of a microporous layer improves fuel cell performance largely from the reduction of water accumulation and the enhancement of mass transfer capacity at high current densities. However, optimisation of the microporous layer is necessary to improve its capability to manage liquid water and facilitate mass transfer. In this study, the viability of microporous layers produced from synthesised graphene foams was assessed.
Graphene foam was synthesised from the pyrolysis of sodium ethoxide, the resulting carbon was then subject to pyrolysis in different atmospheres in order to enhance the conductivity. The graphene foams underwent characterisation by electron microscopy and x-ray fluorescence which showed high carbon purity open foams with micron scale pores and graphene-thin walls. Microporous layers were then produced from these graphene foams, commercial graphene and from carbon black; they were then characterised ex-situ and through polarisation curves.
Ex-situ characterisation of the microporous layers was used to determine the micro-structure and physical properties, as well as its ability to repel liquid water and to conduct electron and mass transfer. Electron microscopy and mercury intrusion porosimetry enabled the analysis of morphology and microstructure, and the transport properties of the layer were determined through permeability, electrical conductivity and contact angle measurements. Polarisation curves were performed at low and high relative humidities in order to understand the capability of these microporous layers in a range of operating conditions.

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