bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computational Analysis of Joule Heating Effect in Triple Material Gate AlGaN/GaN High Electron Mobility Transistor
Authors: Kashem Md Tashfiq Bin , Subrina Samia 
Published: July 2021

Aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high electron mobility transistor (HEMT) has shown great potential and superiority over other devices in high power and high speed-based systems [1-4]. Recently, a novel AlGaN/GaN HEMT structure named triple material gate (TMG) HEMT has been proposed in [5] in which the gate contact is composed of three metals with different work functions. TMG HEMT ensures high carrier velocity and better suppression of short channel effects. In this work, a two-dimensional electro-thermal model has been developed to investigate the joule heating effect in TMG AlGaN/GaN HEMT using the software COMSOL [6]. The current continuity and heat transport equations are solved self-consistently to obtain the temperature distribution profile in various layers of the device. Thermal efficiency of TMG HEMT is compared with dual material gate and single material gate HEMT. It has been found that, besides providing better current carrying capability, TMG HEMT shows optimum thermal performance. Moreover, the variation of peak temperature in the channel with drain and gate voltages is analyzed to study the bias voltage dependence of the device temperature rise. Effects of several device parameters like total channel length, spontaneous and piezoelectric polarization induced charges and ratio of lengths of control and screen gates, on the thermal performance have also been explored. Simulations are carried out for the device lying on different substrate materials (Sapphire, GaN, Si and SiC) with varying thermal conductivity to demonstrate their performance in heat removal capacity. This simulation model can serve as a very useful tool to comprehend the thermal behavior of the device for high power and high frequency applications.

References:

[1] Fletcher, AS Augustine, et al. "Analysis of AlGaN/GaN HEMT using discrete field plate technique for high power and high frequency applications." AEU-International Journal of Electronics and Communications 99 (2019): 325-330.
[2] Nirmal, D., et al. "Current collapse modeling in AlGaN/GaN HEMT using small signal equivalent circuit for high power application." Superlattices and Microstructures 113 (2018): 810-820.
[3] Chung, Jinwook W., et al. "AlGaN/GaN HEMT With 300-GHz fmax." IEEE Electron Device Letters 31.3 (2010): 195-197.
[4] Shen, L., et al. "AlGaN/AlN/GaN high-power microwave HEMT." IEEE Electron Device Letters 22.10 (2001): 457-459.
[5] Kashem, MTB, and Subrina, S. "Analytical modeling of channel potential and threshold voltage of triple material gate AlGaN/GaN HEMT including trapped and polarization‐induced charges." International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 32.1 (2019): e2476.
[6] COMSOL Multiphysics® (Version 3.5a) [Computer software]. Burlington, MA.
Reducing the Threshold Voltage Instability of β-Ga2O3 Nanobelt Field-Effect Transistors Using Ozone Treatment
Authors: Cho Cheolhee , Park Hyunik , Kim Jihyun 
Published: July 2021

β-Ga2O3 is a promising semiconducting material for next-generation power devices owing to its wide bandgap (4.8 eV), high breakdown electric field (8 MV/cm), and good thermal stability. β-Ga2O3 has a monoclinic crystal structure with weak covalent bonding along the direction of (100), so bulk β-Ga2O3 can be exfoliated into ultra-thin flakes, which can be integrated with van der Waals materials. An example of the application is metal-insulator-semiconductor field-effect transistors (MISFETs) using h-BN as a gate dielectric. H-BN has an atomically flat surface without dangling bond, minimizing interfacial states between the channel and insulator layer. Moreover, the high thermal conductivity of h-BN (30 W/m·K along the c-plane) makes heat management easier (cf. SiO2: 1.4 W/m·K). Therefore, β-Ga2O3/h-BN MISFETs are expected to enhance device performance with a synergetic effect of both materials.
However, there are remaining reliability issues about the gate-bias stress instability (BSI), the temporary or permanent degradation of electrical properties from gate bias stress (ex. threshold voltage, field-effect mobility, on/off ratio). β-Ga2O3 FETs have been developed for high voltage operation in harsh environments, so that suppression of BSI is required. BSI is mainly attributed to charge trapping in the channel, channel/dielectric interface, or dielectric layer under gate-bias stress. In this work, we tried to reduce bias-stress instability of β-Ga2O3/h-BN MISFETs by UV-O3 treatment. Numerous reports demonstrated the annealing of oxygen-related defects by UV-O3 treatment in oxide-based materials. Therefore, UV-O3 treatment was expected to also work on β-Ga2O3.
First, β-Ga2O3 (200-300 nm) and h-BN (40-50 nm) flakes were exfoliated from each bulk crystal with adhesive tape. H-BN flake was dry-transferred on SiO2/p++Si substrate, and subsequently β-Ga2O3 flake was stacked on h-BN. The source, drain, and gate electrodes (Ti/Au 50 nm/100 nm) were defined by e-beam lithography, followed by e-beam evaporation and lift-off processes. Bias-stress characteristics were systematically measured by Measure-Stress-Measure (MSM) method—repeating the sequence of 1) IDS-VGS, 2) VGS stress, 3) IDS-VGS sweep. β-Ga2O3/h-BN MISFET was UV-O3 treated using a commercial UV-O3 cleaning system (PSD-UV, Novascan Technologies, Ames, IA, USA). By following bias-stress characteristics measurement, we could observed reduced shifts of electrical properties regarding as annealing effect on oxygen-related defect by UV-O3 treatment. This work grants facile way to achieve β-Ga2O3 FETs stable to stress and open up new opportunities for the practical implementation of β-Ga2O3 power device. The details of methods and results will be presented at the conference.
(Invited) Shallow Donor Impurities in GaN
Authors: Freitas Jaime A. 
Published: July 2021

Significant advances have been achieved during the last three decades in heteroepitaxial, homoepitaxial, and bulk growth of nitride semiconductors. Despite this remarkable progress, the full realization of the functionality of this material system is often limited by the presence of pervasive residual impurities inherent to the high-temperature growth process, and/or by the presence of lattice point and extended defects. A number of important fundamental aspects of these properties must be understood and controlled in order to realize optimum device performance.
We review here on a systematic investigation, employing a combination of defect-sensitive techniques, carried out on freestanding HVPE-GaN films to identify the chemical nature of the shallow donors. High-resolution, variable temperature PL experiments were performed in the spectral region associated with recombination processes involving the ground and excited states of the neutral donor bound excitons and their two-electron-satellites in GaN substrates and homoepitaxial films. High-sensitivity SIMS and high-resolution FTIR measurements unambiguously identify Si and O shallow donors with ground state binding energies of 30.18 meV and 33.20 meV, respectively. These binding energies are in excellent agreement with values obtained by the analyses of the two-electron-satellite PL spectra considering the participation of ground and excited state donor bound excitons. High-resolution PL studies of homoepitaxial GaN films confirm the SIMS and the FTIR impurity identifications. These results were conveniently employed to verify the incorporation and activation of shallow donors in high crystalline quality GaN substrates.
This work supported by the Office of Naval Research
Topological Supramolecular Network Enabled Intrinsically Stretchable Organic Electronics for Multimodal and Seamless Biointerfaces
Authors: Jiang Yuanwen , Bao Zhenan 
Published: July 2021

Multielectrode arrays that can seamlessly integrate with electrogenic tissues provide critical information to diagnose disease pathophysiology and even augment human functions. Despite extensive efforts to merge rigid inorganic electrodes with soft and curvilinear tissues, the inherent misalignment between their mechanical properties (e.g., stiffness vs stretchability) inevitably leads to a trade-off between the device density and tissue conformability.
Organic electronic materials, on the other hand, offer exciting new opportunities in the formation of minimally invasive and seamlessly integrated biointerfaces due to its potential combination of intrinsic softness, stretchability and electric conductivity. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), as one of the most prominent conducting polymer, has been widely used to reduce interfacial impedance of bioelectronic devices due to its ionic-electronic dual conducting mechanism. However, pristine PEDOT:PSS thin film is stiff and brittle that cannot be stretched to sustain natural tissue deformations.
In this talk, I will elaborate our effort on the development of stretchable, conductive PEDOT:PSS with chronic stability. Through a rationally-designed supramolecule-based topological network, we achieved for the first time simultaneously enhanced conductivity (up to 3000 S/cm) and stretchability (100% strain without cracks) of PEDOT:PSS with even direct photopatternability (down to 2 µm feature size). The as-fabricated stretchable PEDOT:PSS electrode array exhibits low interfacial impedance with excellent conformability with human skin and animal tissue, allowing for high-density mapping of electrophysiological activities as well as precise neuromodulation through unprecedented brainstem based neural interfaces.
(Invited) Flexible Organic Sensors and Actuators in Human-Machine Interfaces
Authors: Ng Tse Nga 
Published: July 2021

My research aims to develop low-cost, flexible, large-area organic devices for different human-machine interfaces.1,2 In this presentation, we discuss case studies for two different point-of-use applications:

1) Motor skills characterization. There is no objective metric for evaluating motor skill training progress, and current assessments rely on qualitative surveys. We have fabricated an instrumented glove with pressure and motion sensors for motor characterization. This glove is useful for characterizing motor skills of people suffering from spasticity, a neuromuscular disorder that causes muscle stiffness/resistance and jerky movement. Analyses of force versus velocity show movement-dependent muscle resistance in a patient with spasticity. Through the flexible sensor systems, the shift from subjective scores to objective measurement will promote better diagnosis and dramatically improve the accuracy in tracking patient response to therapy.

2) Haptic interaction. Haptic actuators generate touch sensations and provide realism and depth in human-machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. We demonstrated the printing integration of multi-material actuators, with an eye toward improving the fidelity and robustness of the printing process. We achieved a compact tactile display by using liquid-crystal elastomers patterned by extrusion.3 Printing with organic materials is a versatile approach that can lead to devices that are ergonomic, readily customizable, and economical for everyone to explore potential benefits and create new haptic applications.
1 M. Amit, L. Chukoskie, A. J. Skalsky, H. Garudadri and T. N. Ng, Advanced Functional Materials, 2019, 1905241.
2 M. Amit, R. K. Mishra, Q. Hoang, A. M. Galan, J. Wang and T. N. Ng, Materials Horizons, 2019, 6, 604–611.
3 Y. Zhai, Z. Wang, K. S. Kwon, S. Cai, D. J. Lipomi, T. N. Ng, Advanced Materials (2020) 2002541.
(Invited) Soft Wireless Optofluidic and Optoelectronic Implants for Advanced Chronic Neural Interfacing
Authors: Jeong Jae-Woong 
Published: July 2021

Optogenetics and neuropharmacology holds immense promise for dissection of neural circuits and cellular signaling in freely behaving animals. However, the full potential of their in vivo applications is limited by the use of conventional tools such as cannulas for drug delivery and fiber optics for photostimulation. These traditional approaches greatly damage neural tissue near the implant, hinder integration with different modalities, and severely limit the animal’s natural behavior and movement, mainly due to their rigid construction, bulky design, and tethered operation, respectively. Furthermore, current methods lack spatiotemporal control of drug delivery, wireless control, and multi-functionality.
To address these fundamental limitations in in vivo neuroscience, we have developed soft wireless optofluidic and optoelectronic implants, which can provide wireless delivery of light and/or drugs in awake, moving animals. The devices consist of ultrathin and flexible probes, which integrate microscale inorganic light-emitting diodes and/or microfluidic channels, and wireless interface with an independent power supply. This design enables compact, lightweight and soft system, thus enabling seamless implantation and operation in the brain without causing disturbance of naturalistic behavior. With integration of smartphone control, replaceable drug cartridges for long-term drug delivery, and wireless energy harvesters for intervention-free charging, they can further facilitate chronic neural interfacing to uncover the basis for brain functions and neuropsychiatric diseases. We have successfully demonstrated chronic wireless capabilities of these devices in freely moving animals that can repeatedly deliver multiple wavelengths of light and drugs for long periods of time to manipulate animals’ behavior. The unique capabilities of the soft wireless implants forecasts their broad utility in chronic in vivo neuropharmacology and optogenetics for various neuroscience research and clinical applications.
Phase Transitions in Correlated Oxides Modulated through Electrochemical Gating
Authors: Smieszek Nicholas , Joshi Siddharth , Chakrapani Vidhya 
Published: July 2021

Strongly correlated oxides have many unusual properties, such as high-temperature superconductivity, colossal magnetoresistance, spin polarization, and metal-insulator phase transitions (MIT) that can be induced by various types of external stimuli, such as temperature, strain, pressure, electron and chemical doping, and light. VO2 undergoes an electronic and structural phase transition at 67°C from a non-magnetic monoclinic (M1) phase to a paramagnetic rutile (R) phase. Modulation of the transition temperature through oxygen over-stoichiometry is difficult to achieve in VO2 through annealing due to nucleation of the V2O5 phase within the VO2 lattice. However, electrochemical doping at room temperature using suitable electrolyte allows for systematic modulation of oxygen stoichiometry in VO2 through the regulation of charge carrier injection. Using this method, the oxygen stoichiometry in VO2 was modulated from 1.86 to 2.44 and its effects on the band structure and MIT was studied through detailed electrical and photoemission studies. In oxygen over-stoichiometric VO2 the TIMT was shifted from 67°C to 118°C, as shown in Figure 1.
The results offer a different perspective on the temperature- and doping-induced IMT process. They suggest that charge fluctuation in the metallic phase of intrinsic VO2 results in the formation of e− and h+ pairs that lead to delocalized polaronic V3+ and V5+ cation states. The metal-to-insulator transition is linked to the cooperative effects of changes in the V–O bond length, localization of V3+ electrons at V5+ sites, which results in the formation of V4+–V4+ dimers, and removal of π* screening electrons. It is shown that the nature of phase transitions is linked to the lattice V3+/V5+ concentrations of stoichiometric VO2 and that electronic transitions are regulated by the interplay between charge fluctuation, charge redistribution, and structural transition.

Figure 1
Performance Degradation in Proton-Conducting Ceramic Electrochemical Cells
Authors: Le Long , Herradon Carolina , Meisel Charlie , Huang Jake , Ricote Sandrine , O'Hayre Ryan , Sullivan Neal P. 
Published: July 2021

Proton-conducting ceramics are a promising new class of electrochemical cells with a lower-temperature operational range in comparison to more-conventional solid-oxide or molten-carbonate counterparts. In the past, we have successfully demonstrated the scalability of this technology from the button-cell to the lab-scale stacks shown in the figure, along with strong performance and stability over thousands of hours under methane fuel at 550 ºC. This encouraging result was achieved through careful tuning of materials, fabrication procedures, and operating conditions. We have found that the degradation rates of protonic-ceramics stacks can be intense, especially at lower temperatures under fuel-cell operating mode. We have observed lower degradation rates under electrolysis operation, and at higher operating temperatures. These are both perhaps counterintuitive; lower-temperature operation is expected to improve the long-term stability, and degradation is typically more pronounced for more-common solid-oxide electrolyzers. In this presentation, we will review our studies on the root causes of performance degradation in protonic ceramics, and approaches to mitigate degradation.
Previous work on performance degradation in oxygen-ion conducting electroceramics provides clues into the sources of degradation in protonic ceramics. That said, a number of degradation mechanisms are avoided by the nature of the protonic-ceramic device. For example, our microstructural characterizations reveal no nickel coarsening or agglomeration in the fuel electrode, likely due to the lower-temperature operation near 550 ºC. Operating conditions are shown to have a large impact on degradation rates in our protonic-ceramics; such conditions provide important clues about degradation’s root causes. Electrochemical Impedance Spectroscopy reveals how the slow kinetics of the electrochemical processes are closely tied to the degradation behaviors observed in our experiments.
While we will continue to explore our root causes of degradation in proton-conducting electrochemical cells, we also report the impact of a gadolinium-doped ceria (GDC) interlayer on improving the durability of the cells, especially at low temperatures. This is perhaps a surprising, as GDC is a common O2--conducting material, and perhaps ill-matched to protonic ceramics. Regardless, the presence of the GDC layer at the air electrode - electrolyte interface has proven to be an effective strategy for minimizing protonic-ceramics degradation throughout our research, falling to 1.2% / 1000 hr for the methane-fueled stack at 600 ºC. While the root causes of this performance improvement remain unclear, we find the use of the GDC interlayer to impactful in reducing performance degradation in protonic ceramics.

Figure 1
Improved Ionic Conductivity of MgM4P6O24 (M = Hf, Zr) Ceramic Solid-State Electrolytes by Sol-Gel Synthesis
Authors: Adamu Mohammed , Kale Girish M 
Published: July 2021

Noticeable improvements in the ionic conductivity of MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes were measured on platinised pellets of 13 mm diameter and 3.8 mm thickness synthesised by the sol-gel method (presented in Figure 1) [1-4]. Electrochemical impedance spectroscopy deployed in this study, demonstrated and evaluated Mg2+-cation conducting species in the characterisation of MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes using the two-probe analysis at a temperature range of 182 - 764 oC and 100 mHz - 32 MHz frequency range to determine the ionic conductivity data. In this study, a promising ionic conductivity of 4.52 x 10-4 Scm-1 and 7.23 x 10-3 Scm-1 for both MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes, respectively, were evaluated at an impedance measurement temperature of 747 oC and 725 oC, respectively, while maintaining service stability of the highly sintered sample pellets at 1000oC ≤ T oC ≤ 1300. Meanwhile, the resultant pellets are believed to find useful applications as solid-state electrolytes in high-temperature electrochemical sensors, solid-state batteries and other electrochemical devices.

References

[1] M. Adamu, and G.M. Kale, The ECS Transactions,
98(12), 17-38 (2020)
[2] G.M. Kale, L. Wang, and Y. Hong, International Journal of Applied Ceramic Technology, 1(2), 180-187 (2004).
[3] M. Adamu, K.T. Jacob, and G.M. Kale, Journal of The Electrochemical Society,
167, 027532 (2020).
[4] M. Adamu, and G.M. Kale, The Journal of Physical Chemistry C,
120, 17909-17915 (2016).

Figure 1. Ionic conductivity of MgZr4P6O24 and MgHf4P6O24 solid-state electrolytes as a function of temperature

Figure 1
Instilling Monovalent Selectivity in Cation Exchange Membranes By Molecular Layer Deposition
Authors: Wormser Eyal , Nir Oded , Edri Eran 
Published: July 2021

Desalination is becoming a vital part of the solution to water scarcity with a current worldwide desalination capacity of approx. 100 million m3/day, which is expected to grow by 40% by 2030. In 2019, 29% of the global desalination capacity was of brackish and river water (500-20000 ppm TDS). Most (98%) of the brackish water nowadays is desalinated by reverse osmosis (RO) which completely deprives the permeate of Mg2+ and Ca2+. Both are critical nutrients needed to sustain human health and agriculture. Replenishing these divalent ions to the desalinated water increases the cost and complexity of the overall process and decreases its sustainability and economic attractiveness. Electrodialysis is energetically more efficient than RO for desalination of brackish water, and using monovalent selective membranes—membranes that enable monovalent ions passage, but retains divalent ions—offer a potential solution to preserve the nutrients in the permeate. However, current methods for instilling ion selectivity uses large macromolecular building blocks to form the selective layer, which increases ion transport resistance and hence the energy demand and cost of selective electrodialysis. To disrupt the resistance-selectivity trade-off, a method for uniformly depositing an ultrathin and highly charged selective layer is needed.
While low-temperature atomic layer deposition is a suitable method for depositing ultrathin metal oxides on membranes, the elastic mismatch between metal oxides and polymers hinders the stability of the selective layer. Instead, we used molecular layer deposition of alucones to resolve the elastic mismatch. We show that the electrostatic charge of alucone surface leads to monovalent selectivity values on par with commercial membranes, but with only a marginal increase in resistivity.