Microwave and Millimeter-Wave GaN HEMTs: Impact of Epitaxial Structure on Short-Channel Effects, Electron Trapping, and Reliability

Application of gallium nitride high-electron-mobility transistors (GaN HEMTs) to millimeter-wave power amplifiers requires gate length scaling below 150 nm: in order to control short-channel effects, the gate-to-channel distance must be decreased, and the device epitaxial structure has to be completely redesigned. A high 2-D electron gas (2DEG) carrier density can be preserved even with a very thin top barrier layer by substituting AlGaN with AlN, InAl(Ga)N, or ScAlN. Moreover, to prevent interaction of hot electrons with compensating impurities and defects in the doped GaN buffer, the latter has to be separated from the channel by a back barrier. Other device designs consist in adopting a graded channel (which controls the electric field) or to adopt nitrogen-polar (N-polar) GaN growth (which decreases the distance between gate and channel, thus attenuating short-channel effects). The aim of this article is to review the various options for controlling short-channel effects, improve off-state characteristics, and reduce drain–source leakage current. Advantages and potential drawbacks of each proposed solution are analyzed in terms of current collapse (CC), dispersion effects, and reliability

Comorbidities and causes of death in SARS-CoV-2-infected patients from the Amazon region / Comorbidades e causas de morte em pacientes infectados com SARS-CoV-2 na região amazônica

COVID-19 may be more severe in elder people and/or people presenting comorbidities, possibly leading to death. Therefore, we analyzed the profile of deaths caused by SARS-CoV-2 in part of the Amazon region, associating them to risk factors. 467 cases of death caused by COVID-19 from October 2020 to July 2021 were analyzed and correlated to age group, gender, comorbidities, and other risk factors, using the Chi-squared Test or Fisher's Exact Test as necessary. Deaths occurred in the age group between 17 and 98 years, with a predominance of men (57.4%) and higher concentration in the period between March and April 2021. Systemic arterial hypertension was the most prevalent disease, followed by smoking, cardiovascular disease, and diabetes mellitus. Smoker men and obese women (and/or with cardiovascular disease) presented higher chances to die, as well as obese people under 65 years and people over 65 years with cardiovascular disease, smokers, or hypertensive (p<0.05). The description of risk groups contributes for the adoption of strategies directed to the most vulnerable populations, as disease monitoring and an increase in vaccination rate, reducing the probability of overloading Brazil's Unified Health System

Elastic Shape Analysis for Anomaly Detection in Fabric Images

In this paper, the problem of quality control in the textile industrial field is addressed. Because of the general unavailability of labelled data from real production plants and the imbalanced nature of the problem, this task is faced with novelty detection methods that monitor the behaviour of the system and identify whether shifts from the nominal conditions arise. In particular, we utilize techniques from Elastic Shape Analysis to analyse the shapes created by the yarns intersections of the fabrics and to extract features used to define distance metrics that quantify the shapes variability. The proposed approach is applied to images of four different textiles, where only some defect free images are needed for the training phase. The results of this preliminary study confirm the effectiveness of the proposed approach

Letramentos acadêmicos no ensino superior: aspectos verbo-visuais no processo de textualização em contexto semipresencial

Este trabalho situa-se na discussão sobre escrita na universidade e investiga o processo de textualização verbo-visual e extraverbal em contexto de Educação a Distância (EaD) semipresencial. Com base no conceito de letramentos acadêmicos, advindo dos Novos Estudos de Letramento, busca problematizar relação entre cor escolhida e imagem, no processo de produção do texto realizado por universitários (professores em formação), num Curso de Pedagogia semipresencial de uma universidade pública do Estado de São Paulo. Procura, assim, contribuir com os estudos da linguagem no que se refere ao estabelecimento de critérios para investigação da integração entre semioses diversas na constituição de conceito de “texto” não restrito ao reconhecimento de sua base gráfica

Current collapse and high-electric-field reliability of unpassivated GaN/AlGaN/GaN HEMTs

Long-term ON-state and OFF-state high-electric-field stress results are presented for unpassivated GaN/AlGaN/GaN high-electron-mobility transistors on SiC substrates. Because of the thin GaN cap layer, devices show minimal current-collapse effects prior to high-electric-field stress, despite the fact that they are not passivated. This comes at the price of a relatively high gate-leakage current. Under the assumption that donor-like electron traps are present within the GaN cap, two-dimensional numerical device simulations provide an explanation for the influence of the GaN cap layer on current collapse and for the correlation between the latter and the gate-leakage current. Both ON-state and OFF-state stresses produce simultaneous currentcollapse increase and gate-leakage-current decrease, which can be interpreted to be the result of gate–drain surface degradation and reduced gate electron injection. This study shows that although the thin GaN cap layer is effective in suppressing surface-related dispersion effects in virgin devices, it does not, per se, protect the device from high-electric-field degradation, and it should, to this aim, be adopted in conjunction with other technological solutions like surface passivation, prepassivation surface treatments, and/or field-plate gate