Advanced III-V / Si nano-scale transistors and contacts: Modeling and analysis

The exponential miniaturization of Si CMOS technology has been a key to the electronics revolution. However, the continuous downscaling of the gate length becomes the biggest challenge to maintain higher speed, lower power, and better electrostatic integrity for each following generation. Hence, novel devices and better channel materials than Si are considered to improve the metal-oxide-semiconductor field-effect transistors (MOSFETs) device performance. III-V compound semiconductors and multi-gate structures are being considered as promising candidates in the next CMOS technology. III-V and Si nano-scale transistors in different architectures are investigated (1) to compare the performance between InGaAs of III-V compound semiconductors and strained-Si in planar FETs and triple-gate non-planar FinFETs. (2) to demonstrate whether or not these technologies are viable alternatives to Si and conventional planar FETs. The simulation results indicate that III-V FETs do not outperform Si FETs in the ballistic transport regime, and triple-gate FinFETs surely represent the best architecture for sub-15nm gate contacts, independently from the choice of channel material. ^ This work also proves that the contact resistance becomes a limiting factor of device performance as it takes larger fraction of the total on-state resistance. Hence, contact resistance must be reduced to meet the next ITRS requirements. However, from a modeling point of view, the understanding of the contacts still remains limited due to its size and multiple associated scattering effects, while the intrinsic device performance can be projected. Therefore, a precise theoretical modeling is required to advance optimized contact design to improve overall device performance. In this work, various factors of the contact resistances are investigated within realistic contact-to-channel structure of III-V quantum well field-effect transistors (QWFET). The key finding is that the contact-to-channel resistance is mainly caused by structural reasons: 1) barriers between multiple layers in the contact region 2) Schottky barrier between metal and contact pad. These two barriers work as bottleneck of the system conductance. The extracted contact resistance matches with the experimental value. The approximation of contact resistance from quantum transport simulation can be very useful to guide better contact designs of the future technology nodes. ^ The theoretical modeling of these nano-scale devices demands a proper treatment of quantum effects such as the energy-level quantization caused by strong quantum confinement of electrons and band structure non-parabolicity. 2-D and 3-D quantum transport simulator that solves non-equilibrium Green\u27s functions (NEGF) transport and Poisson equations self-consistently within a real-space effective mass approximation. The sp3d5s* empirical tight-binding method is employed to include non-parabolicity to obtain more accurate effective masses in confined nano-structures. The accomplishment of this work would aid in designing, engineering and manufacturing nano-scale devices, as well as next-generation microchips and other electronics with nano-scale features

The COVID-19 Pandemic and Japan’s Anxiety-Suppression Society: Anxiety, Self-Restraint, and Solidarity in a Disaster Community

In this article, I analyze the Japanese government’s response and public discourse during the early part of the COVID-19 pandemic, a period covering the onset of the pandemic, the declaration of a state of emergency, and the decline in the second wave of infections by mid-October 2020. Assessing that the virus was highly contagious but not particularly fatal, the Japanese government adopted a policy focusing on the prevention of large-scale clusters of infections and treatment of severe cases, calling for the public to practice of “self-restraint” in avoiding the “three C’s” of closed spaces, concentrations of people, and close contact. The goal of this measure was to minimize the pandemic’s socioeconomic impact and sustain the health care system. It was successful in terms of infection and fatality rates. Particularly after the state of emergency was lifted on April 7, Japan began to garner global attention as a model for containing the pandemic without coercion. Behind Prime Minister Abe’s resignation, however, lay the “failure” of Japan’s COVID-19 response. The Japanese people lost faith in the government’s response owing to its perceived harm to publicness, as symbolized in the “Abe-no-mask” incident. Japanese society is a “disaster community,” sharing in the anxiety over the experiences and memories of disasters occurring over the past twenty-five years, including the Great Hanshin-Awaji Earthquake in 1995 and Great East Japan Earthquake in 2011. Japan has thus experienced COVID-19 as a part of a greater, more complex chain of disasters. The response to COVID-19 in the form of the request for self-restraint was also rooted in such communal solidarity. Controversy over PCR testing policies or “optimistic” government perceptions pertaining to COVID-19 evince the present state of the disaster-nation that is Japan as it endeavors to suppress anxiety and maintain daily life as usual. I conceptualize Japanese society in this situation as an “anxiety-suppression society.

General interaction mode of CIDE:CIDE complex revealed by a mutation study of the Drep2 CIDE domain

AbstractThe CIDE domain is a well known protein–protein interaction module that is initially detected at the apoptotic DNA fragmentation factor (DFF40/45). The interaction mechanism via the CIDE domain is not well understood. To elucidate CIDE domain mediated interactions in the apoptotic DNA fragmentation system, we conducted biochemical and mutational studies and found that the surface of CIDE domains can be divided into an acidic side and a basic side. In addition, a mutagenesis study revealed that the basic surface side of Drep2 CIDE is involved in the interaction with the acidic surface side of Drep1 CIDE and Drep3 CIDE. Our research supports the idea that a charge–charge interaction might be the general interaction mode of the CIDE:CIDE interaction.Structured summary of protein interactionsDrep2andDrep2bindbymolecular sieving(View Interaction:1,2)Drep1andDrep2bindbymolecular sieving(View interaction)Drep3andDrep2bindbymolecular sieving(View interaction)Drep2andDrep3bindbyblue native page(View interaction)Drep2andDrep1bindbyblue native page(View interaction

Block Design-Based Local Differential Privacy Mechanisms

In this paper, we propose a new class of local differential privacy (LDP) schemes based on combinatorial block designs for a discrete distribution estimation. This class not only recovers many known LDP schemes in a unified framework of combinatorial block design, but also suggests a novel way of finding new schemes achieving the optimal (or near-optimal) privacy-utility trade-off with lower communication costs. Indeed, we find many new LDP schemes that achieve both the optimal privacy-utility trade-off and the minimum communication cost among all the unbiased schemes for a certain set of input data size and LDP constraint. Furthermore, to partially solve the sparse existence issue of block design schemes, we consider a broader class of LDP schemes based on regular and pairwise-balanced designs, called RPBD schemes, which relax one of the symmetry requirements on block designs. By considering this broader class of RPBD schemes, we can find LDP schemes achieving near-optimal privacy-utility trade-off with reasonably low communication costs for a much larger set of input data size and LDP constraint.Comment: 18 pages, 3 figures, and 1 table. This manuscript was submitted to IEEE Transactions on Information Theory and a short version of this manuscript will be presented at 2023 IEEE International Symposium on Information Theor

Stability of hydrogenation states of graphene and conditions for hydrogen spillover

The hydrogen spillover mechanism has been discussed in the field of hydrogen storage and is believed to have particular advantage over the storage as metal or chemical hydrides. We investigate conditions for practicality realizing the hydrogen spillover mechanism onto carbon surfaces, using first-principles methods. Our results show that contrary to common belief, types of hydrogenation configurations of graphene (the aggregated all-paired configurations) can satisfy the thermodynamic requirement for room-temperature hydrogen storage. However, the peculiarity of the paired adsorption modes gives rise to a large kinetic barrier against hydrogen migration and desorption. It means that an extremely high pressure is required to induce the migration-derived hydrogenation. However, if mobile catalytic particles are present inside the graphitic interstitials, hydrogen migration channels can open and the spillover phenomena can be realized. We suggest a molecular model for such a mobile catalyst which can exchange hydrogen atoms with the wall of graphene.open151

Current Developments in Thermochemical Conversion of Biomass to Fuels and Chemicals

Biomass is one of the largest concentrated carbon source available for producing renewable energy. Thermochemical conversion of biomass has been used for centuries in various settings. Biomass typically has a higher oxygen and volatile matter content than other solid carbon feedstocks, resulting in increased reactivity during conversion by thermochemical pathways. Moisture content of the biomass feedstock exerts significant influence on the conversion process and is an important criteria used to classify various thermochemical conversion technologies. This chapter discusses the current status and future outlook of thermochemical biomass conversion processes

Synergistic effect of Indium and Gallium co-doping on growth behavior and physical properties of hydrothermally grown ZnO nanorods

We synthesized ZnO nanorods (NRs) using simple hydrothermal method, with the simultaneous incorporation of gallium (Ga) and indium (In), in addition, investigated the co-doping effect on the morphology, microstructure, electronic structure, and electrical/optical properties. The growth behavior of the doped NRs was affected by the nuclei density and polarity of the (001) plane. The c-axis parameter of the co-doped NRs was similar to that of undoped NRs due to the compensated lattice distortion caused by the presence of dopants that are both larger (In3+) and smaller (Ga3+) than the host Zn2+ cations. Red shifts in the ultraviolet emission peaks were observed in all doped NRs, owing to the combined effects of NR size, band gap renormalization, and the presence of stacking faults created by the dopant-induced lattice distortions. In addition, the NR/p-GaN diodes using co-doped NRs exhibited superior electrical conductivity compared to the other specimens due to the increase in the charge carrier density of NRs and the relatively large effective contact area of (001) planes. The simultaneous doping of In and Ga is therefore anticipated to provide a broader range of optical, physical, and electrical properties of ZnO NRs for a variety of opto-electronic applications

Conventional Vickers and true instrumented indentation hardness determined by instrumented indentation tests

We evaluate Vickers hardness and true instrumented indentation test (IIT) hardness of 24 metals over a wide range of mechanical properties using just IIT parameters by taking into account the real contact morphology beneath the Vickers indenter. Correlating the conventional Vickers hardness, indentation contact morphology, and IIT parameters for the 24 metals reveals relationships between contact depths and apparent material properties. We report the conventional Vickers and true IIT hardnesses measured only from IIT contact depths; these agree well with directly measured hardnesses within ±6% for Vickers hardness and ±10% for true IIT hardness