Power Devices Research Articles

A review of carbon nanotube field effect transistor from structure and properties to applications

Abstract. In the pursuit of next-generation electronic devices that overweigh the limitations of traditional silicon-based technologies, Carbon Nano Tube Field Effect Transistors (CNTFETs) have garnered significant attention. Unlike conventional Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), CNTFETs utilize the exceptional properties of Carbon Nanotubes (CNTs) as the channel material, promising substantial improvements in performance, power consumption, and scalability. This paper presents a comprehensive overview of CNTFETs, delving into their fundamental structures and underlying principles. It critically examines the unique characteristics that make CNTFETs an attractive alternative, including their superior carrier mobility, reduced leakage currents, and compatibility with nanoscale fabrication techniques. This review explores the application prospects of CNTFETs, spanning from high-speed digital circuits to energy-efficient sensors and beyond. Despite their promising potential, the paper also acknowledges recent challenges associated with CNTFETs, such as challenges in material synthesis, integration with existing semiconductor processes, and cost considerations. By addressing these challenges and fostering interdisciplinary research collaborations, the widespread adoption of CNTFETs in integrated circuits could revolutionize the electronics industry, enabling the development of more efficient, powerful, and sustainable devices for the future.

Operation of Photoeelectron Spectrometers for Non-Invasive Photon Diagnostics at the European X-Ray Free Electron Laser

Angle-resolved photoelectron spectrometers with microchannel plate detectors and fast digitizer electronics are versatile and powerful devices for providing non-invasive single-shot photon diagnostics at a MHz repetition rate X-ray free-electron lasers. In this contribution, we demonstrate and characterize the performance of our two operational photoelectron spectrometers for the application of hard X-rays and soft X-rays as well as new automation tools and online data analysis that enable continuous support for machine operators and instrument scientists. Customized software has been developed for the real-time monitoring of photon beam polarization and spectral distribution both in single-color and two-color operation. Hard X-ray operation imposes specific design challenges due to poor photoionization cross-sections and very high photoelectron velocities. Furthermore, recent advancements in machine learning enable resolution enhancement by training the photoelectron spectrometer together with an invasive high-resolution spectrometer, which generates a response function model.

Design and research of high voltage β-Ga2O3 /4H-SiC heterojunction LDMOS

Abstract In recent years, gallium oxide (Ga2O3), one of the ultra-wide band-gap semiconductor materials, has been regarded as one of the most promising materials in the field of high-voltage and high-power electronic devices in the future because of its unique electrical properties and low preparation cost. However, it is difficult for β-Ga2O3 materials to form effective P-type doping, so the PN junction is not formed in most of its power devices, which greatly limits the improvement of its voltage resistance. A novel lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOS) is proposed to realize a junction β-Ga2O3 power device and improve the voltage resistance performance of β-Ga2O3 power devices. In this device, a β-Ga2O3 power device with a junction is realized by using P-type 4H-SiC to form a PN junction with N-type β-Ga2O3, and the voltage resistance of the β-Ga2O3 power device is improved. Sentaurus TCAD software was used to simulate the device structure and electrical performance. The device is optimized by adjusting the length of the drift zone, drift zone concentration, SiC channel concentration, and gate oxide thickness. Optimized, the device exhibits a positive threshold voltage of 3.42 V, a breakdown voltage of 2203 V, a specific on-resistance of 7.80 mΩ·cm2, and a power figure of merit of 622 MW/cm2. The results show that the heterojunction device is significant for realizing high-performance junction β-Ga2O3 power devices.

Bulk Single Crystals and Physical Properties of Rutile GeO2 for High‐Power Electronics and Deep‐Ultraviolet Optoelectronics

The top‐seeded solution growth for rutile GeO2 single crystals using alkali carbonates or fluorides as flux is applied. Structural data of obtained single crystals confirm the rutile phase with a = b = 4.3966 Å and c = 2.8612 Å. The crystals with diameter of 5–15 mm are either undoped or intentionally doped with Sb5+, Sn4+, Al3+, Ga3+, and F− ions. It is found that Sb5+ is a very efficient n‐type donor enabling free electron concentration even above 1020 cm−3; thus, Sb‐doped GeO2 is a potential substrate for vertical power devices. In contrast, crystals doped with Al and Ga do not show p‐type conductivity suggested by the theory. The onset of the absorption occurs at 5.0 and 5.5 eV perpendicular and parallel to the c‐axis, respectively. Rutile GeO2 shows a very intense photoluminescence peaking at 420 nm (blue) and 520 nm (green). Raman spectra show narrow lines, in particular at high phonon energy (B1g, 170 cm−1). Prepared wafers show FWHM values of rocking curves below 30 arcsec and polishing is achieved down to RMS roughness of 0.15 nm. Transmission electron microscopy images do not show point or extended structural defects with uniform Sb distribution.

Improved lateral figure-of-merit of heteroepitaxial α-Ga2O3 power MOSFET using ferroelectric AlScN gate stack

In this Letter, we demonstrate heteroepitaxial α-Ga2O3 MOSFETs using an aluminum scandium nitride (AlScN) ferroelectric gate stack. Owing to ferroelectric effects, α-Ga2O3 MOSFETs with the AlScN/HfO2 gate stack (FGFET) exhibited enhanced electrical performance compared with a HfO2 gate dielectric (IGFET) for variable gate–drain lengths (10, 15, 20 μm). A remnant polarization value of the AlScN deposited on a HfO2 layer was measured to be about 30 μC/cm2. The subthreshold swing (SS) and field-effect mobility (μFE) of IGFET was extracted at 1814 mV/dec and 13.9 cm2/V s, respectively. However, the FGFET exhibits a reduced SS of 552 mV/dec with enhanced μFE of 42.7 cm2/V s owing to the negative capacitance of the ferroelectric AlScN. Furthermore, a lateral figure-of-merit of 17.8 MW/cm2 was achieved for the FGFET, far surpassing the 8.3 MW/cm2 of the IGFET. The proposed ferroelectric AlScN/HfO2 stack can be a promising gate structure for improving both transfer and breakdown characteristics in heteroepitaxial α-Ga2O3 power devices.

Advances in defect characterization techniques using polarized light observation in SiC wafers for power devices

This short review provides an overview of advancements in the characterization of defects in silicon carbide (SiC) wafers using polarized light observation. SiC, which has a wide bandgap and excellent thermal and electrical properties, is widely used in power devices. However, various defects such as threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD) can significantly affect device performance and reliability. Polarized light observation offers a nondestructive method for visualizing these defects and analyzing the stress fields induced within the SiC crystal structure. This paper summarizes recent developments in this technique, including the application of analyzer rotation to enhance the contrast in defect visualization. Furthermore, the development of automated systems for rapid wafer evaluation is discussed, highlighting the role of polarized light observation in improving quality control and production efficiency in SiC power device manufacturing.

Deep learning assisted prediction on main factors influencing shear strength of sintered nano Ag-Al joints under high temperature aging

Bonding strength of sintered nano silver (Ag) joints has been an important index for evaluating the reliability of power module packages, which has been reported to be influenced by many factors. However, it is hard to evaluate and predict those factors affecting bonding strength. With the help of artificial intelligence (AI), the utilization of AI tools to assist in finding science solutions has become a mainstream consensus. In this paper, we will show how to evaluate and predict those sintered nano Ag-Al bonded joints bonding strength with deep learning (DL) methods. Firstly, a reliable extended dataset was obtained using the conditional formal condition table generation Induction Network (CTGAN) based on the die shear test dataset of sintered Ag-Al interface shear strength with four different metallization layers under different high-temperature aging time. Subsequently, four DL models were adopted to predict the shear strength of Ag-Al interface under different metallization layers to evaluate the interface bonding strength, all with high level of determination coefficient (R2, above 0.99) and classification accuracy (above 85%). Last but not least, factors influencing the shear strength of Ag-Al interface were analyzed and ranked by weight analysis and SHapley Additive exPlanations (SHAP) method. This research could provide a novel perspective on understanding those factors affecting the shear strength of sintered nano Ag interconnect layer in power devices.

Capabilities of cellebrite universal forensics extraction device in mobile device forensics

The powerful digital forensics tool cellebrite universal forensics extraction device (UFED) extracts and analyzes mobile device data, helping investigators solve criminal and cybersecurity cases. Advanced methods and algorithms allow Cellebrite UFED to recover data from erased or obscured devices. Cellebrite UFED can pull data from call logs, texts, emails, and social media, providing valuable evidence for investigations. The use of smartphones and tablets in personal and professional settings has spurred the development of mobile device forensics. The intuitive user interface speeds up data extraction and analysis, revealing crucial information. It can decrypt encrypted data, recover deleted files, and extract data from multiple devices. The sector's best data extraction functionality, Cellebrite UFED, helps forensic analysts gather crucial evidence for investigations. Legal and ethical considerations are crucial in mobile device forensics. Legal considerations include allowing access to data, protecting privacy, and adhering to chain of custody protocols. Ethics include transparency, defamation, and information exploitation protection. Using Cellebrite UFED, researchers can navigate complex data on mobile devices more efficiently and precisely. Artificial intelligence (AI) and machine learning (ML) algorithms may automate data extraction in future tools. Examiners must train, maintain, and establish clear protocols for using Cellebrite UFED in forensic investigations.

Impact of overvoltage on the mode transition of the spark gap switch: from edge breakdown to stochastic breakdown

Abstract Spark gap switch (SGS) is a fundamental but critical component for large-scale pulsed power devices, whose reliable operation is significantly affected by the breakdown characteristics of SGS. It is observed experimentally that, with the increase of overvoltage, the bridging position of the spark channel transits from edge to stochastic center. In this work, the influence of overvoltage on the breakdown process of a parallel-plate SGS with low geometric distortion of static electric field (<13%) between an atmospheric-pressure air gap of 5 mm is investigated by particle-in-cell/Monte Carlo collision simulation. It is found that, under a low overvoltage (ratio of applied voltage U a to static breakdown voltage U 0, U a/U 0 = 1.5), the streamers at the edge first bridge the gap before that in the central region, due to the field enhancement induced by the electrode curvature. Under higher overvoltage (U a/U 0 = 3), the synchronicity between streamers initiating from the center and those from the edge is greatly improved during the inception stage. After the streamers pass the middle of the gap, the field enhancement at the streamer front is more intensified and promotes the generation of fast electrons. These fast electrons rapidly magnify the difference among the propagating streamers by providing abundant seed electrons ahead of the discharge channel, which leads to the randomness of the bridging position. The results in this work demonstrate the relationship between overvoltage and streamer dynamics, which is beneficial for the performance improvement of SGS.

Expanded graphite encapsulation of nitrates for enhanced thermal transport: Mechanism insight and component screening

The efficient improvement of the heat transfer capability of high-temperature molten salts and the accurate measurement within the operating temperature range is vital for improving the efficiency of concentrating solar power devices. Through theoretical investigation, this paper explores different thermal properties including thermal conductivity, phase transition properties and interfacial interactions using a range of expanded graphite/nitrates (EG/nitrates). Molecular dynamics simulations reveal that the EG/eutectic salt (ES) exhibits optimal comprehensive properties. Experimentally prepared EG/ES composite phase change materials (PCMs), coupled with theoretical predictions, demonstrate exceptional thermal conductivity (2.2 W m−1 K−1) and a significant latent heat of phase change (>80 J g−1). The calculation results of the interaction energy between the host-guest indicate that the strong interaction of the EG to ES restricts the molecule movement, leading to a weak temperature dependence of the thermal conductivity of the EG/ES composite PCM. This contrasts with the conventional understanding of PCM thermal conductivity, which typically exhibits a sharp change during the phase transition from solid state to liquid state. Additionally, the thermal response of 15 wt% EG/ES is increased by 27.2 % compared to pure ES, which effectively helps alleviate local overheating in practical applications. The progress made so far sheds light on the mechanism behind the improved heat transfer and storage performance of nitrate from a microscopic view, offering valuable theoretical insight for developing high-efficient nitrate PCMs in solar thermal power generation systems.

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

Discontinuous Pulse Width Modulation Strategy for Single-phase Five-level T-type NPC Inverter considering Symmetric Thermal Loadings of Power Devices

Research on Fault Prediction of Power Devices in Rod Control Power Cabinets Based on BiTCN-Attention Transfer Learning Model

The Insulated Gate Bipolar Transistor (IGBT) is the key power device in the rod control power cabinet of nuclear power plants; its reliable operation is of great significance for ensuring the safe and economical operation of the nuclear power plants. Therefore, it is necessary to conduct fault prediction research on IGBT to achieve better condition-based maintenance and improve its operational reliability. However, power cabinets often operate under multiple, complex working conditions, so predicting IGBT faults from single working condition data usually has limitations and low accuracy. Its failure probability has an important relationship with the actual operating conditions of the cabinet. In order to improve the reliability and maintainability of the control power cabinet in nuclear power plants, this paper takes IGBTs in the rod control power cabinet as the object and makes full use of the data of IGBTs under multiple working conditions to carry out research on the cross-condition fault prediction of IGBTs under multiple-source working conditions. A transfer learning (TL) model based on a bidirectional time convolutional network (BiTCN) combined with attention was proposed to solve the problem of low accuracy of cross-operating fault prediction in a multi-source domain. Firstly, an IGBT fault simulation model was built to collect the life cycle state data of the module under different working conditions. Then, after pre-processing such as removing outliers, kernel principal component analysis (KPCA) was used to integrate all source domain data, obtain source domain characterization data, and train the BiTCN-attention model. Finally, the BiTCN-attention model trained in the source domain was transferred, and the model was fine-tuned according to the target domain data. Simulation results show that the accuracy of the proposed BiTCN-attention transfer learning prediction method can reach more than 99%, which is significantly better than that of the recurrent neural network transfer learning (RNN-TL) model, long short-term memory network transfer learning (LSTM-TL) model, gated cyclic unit transfer learning (GRU-TL) model, and time convolutional network transfer learning (TCN-TL) model. This method can not only reduce the inconsistency of fault characteristic values caused by changes in working conditions but also accurately predict the degradation trend when only early fault data are available, providing an effective solution for IGBT fault prediction across working conditions in multi-source domains.

Weird Ghosts of the Anthropocene: The Spectral Encounter in New Weird Fiction as a Conceptual Metaphor for Ecocritical Theory

In The Great Derangement, Amitav Ghosh links the reluctance of contemporary fiction to tackle the environmental crisis to the inadequacy of realism, with which Western “high” literature has been associated since the rise of the modern novel, to describe the “hyperobject” quality (Clark 140) of the Anthropocene. This paper argues that the genre labeled as New Weird, which strives to portray the Unheimlich, the eerie, or precisely the weird in our familiar reality, offers an answer to this aesthetic challenge, having found an especially powerful literary device in spectral encounters. In the works of New Weird author China Miéville, environmental concerns are often embodied by the encounter of human protagonists with the ghostly apparitions of non-human entities, from icebergs floating in the sky over London to a sunken oil platform re-emerging from the sea. A close reading of three stories from his collection Three Moments of an Explosion, “Polynia”, “Covehithe” and “Estate”, will show how Miéville’s portrayal of people’s behavior in encountering ‘weird’ spectral presences bear a specific ecological significance. This significance, which is common to many different authors of New Weird fiction, reverberates in the use of spectrality as a conceptual metaphor in contemporary ecocritical theory, thus corroborating the claim of this genre as the most productive for our historical times.

High-temperature time-dependent dielectric breakdown of 4H-SiC MOS capacitors

—With the rapid applications of silicon carbide metal–oxide–semiconductor field-effect transistor (SiC MOSFET) power devices, further improving the performance of SiC MOSFET device through enhancing its gate oxide reliability is one of the crucial directions. The density of interface states in a SiC MOSFET is a significant parameter that affects the reliability of the gate oxide layer. In this paper, the SiC MOS capacitors (MOSCAPs) were prepared by the 1250 °C dry oxidation and 1350 °C NO annealing process. Then, we analyzed the mechanisms of the breakdown by two group of ramped experiment. And we still evaluated the reliability of oxide layer via the high-temperature time-dependent dielectric breakdown (TDDB) tests on the prepared MOSCAPs, meanwhile, the temperature effect on the reliability was considered. Furthermore, the E, 1/E, and E models with Weibull plotting were used to calculate the tBD lifetimes and failure analysis was carried on the failed samples finally. The results indicate that: (1) the impact of the generation and accumulation of the traps in the oxide, which is the main mechanisms of device failure; (2) The prediction of lifetime was calculated with three models at different acceleration factors; (3) at high-temperature, although the lower the density of interface states is, the Si epitaxial growth and C cluster will manifest in the oxide surface and lead to the breakdown of SiC MOSCAPs.

200 cm2/Vs electron mobility and controlled low 1015 cm−3 Si doping in (010) β -Ga2O3 epitaxial drift layers

We report on metalorganic chemical vapor deposition (MOCVD) growth of controllably Si-doped 4.5 μm thick β-Ga2O3 films with electron concentrations in the 1015 cm−3 range and record-high room temperature Hall electron mobilities of up to 200 cm2/Vs, reaching the predicted theoretical maximum room temperature phonon scattering-limited mobility value for β-Ga2O3. Growth of the homoepitaxial films was performed on Fe-doped (010) β-Ga2O3 substrates at a growth rate of 1.9 μm/h using TEGa as the Gallium precursor. To probe the background electron concentration, an unintentionally doped film was grown with a Hall concentration of 3.43 × 1015 cm−3 and Hall mobility of 196 cm2/Vs. Growth of intentionally Si-doped films was accomplished by fixing all growth conditions and varying only the silane flow, with controllable Hall electron concentrations ranging from 4.38 × 1015 to 8.30 × 1015 cm−3 and exceptional Hall mobilities ranging from 194 to 200 cm2/Vs demonstrated. C-V measurements showed a flat charge profile with the ND+–NA− values correlating well with the Hall-measured electron concentration in the films. SIMS measurements showed the silicon atomic concentration matched the Hall electron concentration with carbon and hydrogen below detection limit in the films. The Hall, C-V, and SIMS data indicate the growth of high-quality 4.5 μm thick β-Ga2O3 films and controllable doping into the mid 1015 cm−3 range. These results demonstrate MOCVD growth of electronics grade record-high mobility, low carrier density, and thick β-Ga2O3 drift layers for next-generation vertical β-Ga2O3 power devices.

Analysis and Design of an SiC CMOS Three-Channel DC-DC Synchronous Buck Converter for High-Temperature Applications

In this study, we present the design, simulation, and implementation of a DC-DC synchronous buck converter utilizing IISB’s 2 μm 4H-silicon carbide (SiC) complementary metal–oxide–semiconductor (CMOS) technology. The converter is designed to meet the demands of modern integrated circuits, particularly in the field of integrated power management. The SiC technology offers enhanced performance and reliability at high temperatures, making it especially suitable for applications that operate in these conditions, including automotive systems, and aerospace, among others. The power transistors and gate drivers are fully integrated on-chip, optimizing efficiency and minimizing footprint. Additionally, the study contributes to the understanding of SiC technology and its application in integrated circuit design. Simulation results demonstrate a peak efficiency of 86.6% at 120 mA load current and 84.8% at 300 mA load current, showing the converter performance under different operating conditions. Furthermore, at high temperatures (295 °C), the converter achieves an efficiency of 89.6%, demonstrating its robustness and versatility in extreme environments. These findings contribute to the advancement of integrated circuit design and facilitate advancements in more efficient and robust power management solutions.

Modelling of Power Semiconductor Devices Switching and Conduction Losses in a Power Electronic System

In power converters, power semiconductor devices, mainly Insulated-Gate Bipolar Transistor (IGBT), are generally used as they are less costly and capable of converting electrical energy into high frequency and voltage. It is critical to accurately determine the switching and conduction losses of power devices before they are assembled into an electronic system. The accurate values help to minimize power loss in a power converter system. With the aid of simulation, design problems are identified to help eliminate device destruction, and critical parameters are monitored. In addition, costly equipment for measuring purposes and testing prototypes is not required at the initial design stage. This research uses simulation work in a power converter system to predict IGBT and diode losses with varied frequencies and voltages. The predictive modelling is produced using regression analysis. The models have been validated by R square (R2) and Mean Absolute Percentage Error (MAPE) techniques. This work is aimed at providing a supervised learning technique mainly used in a machine learning environment, in line with the technological development in the semiconductor industry. With the simulation performed in this work, the efficiency of a boost converter system is enhanced as it shows the models have a good fit with an R2 value of almost 1, and MAPE values are noticed to be less than 5%.

‘Like to comment on that?’

Abstract Questions are powerful interactional devices which academic lecturers may use to facilitate learning, engage students and add to a lecture’s interactivity. This contrastive and corpus-based study examines student-oriented questions, i.e. those initiating a student response, in British and Montenegrin university linguistics lectures. It aims to answer research questions regarding what forms of this question category are employed; how frequent they are, what functions they commonly perform, and whether there are any similarities and differences in these respects between the two groups of lectures. The data include 12 lectures in linguistics from several British academic corpora and a specially created corpus of 12 Montenegrin linguistics lectures. We combine quantitative and qualitative approaches to arrive at results which point to certain similarities and differences between the corpora. Some of these might be explained by the language differences between English and BCMS (Bosnian/Croatian/Montenegrin/Serbian), while others seem to have stemmed from academic lecturing style differences. The findings add to the literature on questions in academic lectures and, together with other contrastive studies, may contribute to revealing the universal and culturally-specific discourse features of academic lectures across academic cultures, as well as be pedagogically useful for lecturers, particularly novices, who are teaching linguistics in English and BCMS.

Out‐Diffusion and Uphill‐Diffusion of Mg in Czochralski‐Grown (100) β‐Ga2O3 Under High‐Temperature Annealing and Its Influence on Lateral MOSFET Devices

AbstractIn this work, the out‐diffusion and uphill‐diffusion of Mg inside (100) β‐Ga2O3 epilayers and substrates are reported. The Mg accumulates toward the (100) surface upon annealing under an oxidizing environment, whereas the concentration profile changes with annealing temperatures and durations. Furthermore, the out‐diffusion of Mg from the substrate into the epilayer is observed at temperatures above 800 °C, which continues during the film growth. The substitutional‐interstitial‐diffusion (SID) mechanism is suggested to be the driving mechanism for the former, and the latter is related to the diffusion of mobile Mg interstitials. The accumulation profile of Mg can be used to identify the interface between the epilayer and the substrate. Furthermore, significant differences in device performance are observed for power transistors fabricated on annealed and non‐annealed epitaxial β‐Ga2O3 wafers. Increased breakdown voltages of annealed samples are attributed to the Mg diffusion into the first few nanometers of the epitaxial layer close to the interface to the semi‐insulating substrate, leading to compensation of residual dopants (donors) in that region.

A strategy for enhancing interfacial thermal transport in Ga2O3-diamond composite structure by introducing an AlN interlayer

Heat dissipation issues have emerged in power devices due to miniaturization and high power density, particularly for materials like low-thermal-conductivity gallium oxide (Ga2O3). Increasing interfacial heat transfer has been identified as a critical strategy for tackling these issues. This study first explored the thermal transport of Ga2O3-diamond interfaces in composite structures containing an AlN interlayer. First-principles calculations revealed that the AlN interlayer improved interfacial bonding between Ga2O3 and diamond. Subsequently, Ga2O3 membranes were deposited on diamond substrates with and without interlayers using pulsed laser deposition (PLD), and the structural and thermal characteristics were examined. The interlayer strategy was shown to be effective in improving the quality of Ga2O3 thin films, including improved crystallinity, a smoother surface, and fewer oxygen vacancies. The thermal characteristics were accordingly improved: the thermal conductivity of Ga2O3 increased from 5.5±0.3–6.0±0.3 W/m·K, and the thermal boundary conductance of Ga2O3-diamond interface (TBCGaO-dia) increased from 46.1±2.3–60.9±3.0 MW/m2·K. Molecular dynamics (MD) analysis further revealed that the enhancement in phonon transmission was due to the increase in the low-frequency phonon participation rate. Additionally, the electro-thermal simulation using COMSOL confirmed the effectiveness of the AlN interlayer in mitigating the self-heating effect. These findings offer a new route for improving interface heat transport and pave the way for the optimization and design of reliable Ga2O3-based devices.