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Gate voltage and temperature dependent Ti-graphene junction resistance toward straightforward p-n junction formation
摘要： High-quality metal-graphene contact is crucial for the fabrication of high-performance graphene transistors. Although Ti has been widely used as metal electrodes in graphene-based devices owing to its excellent adhesive capability, contact resistance (Rc) for Ti/graphene (Ti/Gr) is typically high and varies largely by three orders of magnitude from ～103 to 106 Ω μm. Here, we have systematically investigated the effects of gate voltage (VG) and temperature (T) on Rc in the Ti/Gr interface. Besides significant VG dependence, Rc in the n branch is always larger than that in the p branch, indicating a Ti induced n-doping in graphene. In addition, Rc exhibits an anomalous temperature dependence and drops significantly as the temperature decreases, reaching ～234 Ω μm at 20 K. Such Ti/Gr contact can adjust the Fermi energy of up to 0.15 eV and can also directly form a well-defined sharp p-n junction without extra gates or chemical doping. These findings pave the way to develop the next generation of graphene-based electronic and optoelectronic devices.
关键词： gate voltage,temperature dependence,Ti-graphene junction,p-n junction,graphene,contact resistance
更新于2025-09-04 15:30:14
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Dielectric Properties of NaCu <sub/>3</sub> Ti <sub/>3</sub> Nb <sub/>1–x</sub> Sb <sub/>x</sub> O <sub/>12</sub> Ceramics
摘要： In order to investigate the influence of Sb doping on the dielectric properties of NaCu3Ti3NbO12 ceramics, a series of NaCu3Ti3Nb1–xSbxO12 ceramics were prepared by conventional solid-state reaction technique. Their crystalline structure, microstructure, dielectric properties and complex impedance were systematically investigated. All these ceramics show giant permittivity phenomenon, and their low-frequency dielectric loss decrease significantly but permittivity remains large with increased Sb doping. Impedance spectroscopic analysis reveals that NaCu3Ti3Nb1–xSbxO12 ceramics are composed of insulating grain boundaries and semiconducting grains, and their resistance of grain boundary increases with increased Sb doping. According to internal barrier layer capacitance effect, the decrease of low-frequency dielectric loss in NaCu3Ti3Nb1–xSbxO12 ceramics with increased Sb doping should be caused by the increase of grain boundary resistance.
关键词： Internal barrier layer capacitance effect,NaCu3Ti3Nb1–xSbxO12 ceramics,Grain boundary resistance,Low-frequency dielectric loss
更新于2025-09-04 15:30:14
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Polydopamine‐coated poly(vinylidene fluoride) membranes with high ultraviolet resistance and antifouling properties for a photocatalytic membrane reactor
摘要： We modi?ed poly(vinylidene ?uoride) (PVDF) membranes with a polydopamine (PDA) coating for photocatalytic membrane reactor application with appropriate UV resistance and studied the effects of the PDA coating conditions (i.e., coating time and dopamine concentration) and UV irradiation time on the modi?ed PVDF membrane properties. The PVDF membrane that was surface-coated with the appropriate dopamine solution concentration and coating time played a key role in controlling the membrane properties and in protecting the modi?ed membrane against UV radiation. The optimization of the coating condition not only completely protected the modi?ed membrane from free-radical attack initiated through UV irradiation but also improved the membrane hydrophilicity, antifouling properties, ?ltration performance, and mechanical strength of the membrane. UV irradiation of the membrane that was surface-coated with a high-concentration dopamine solution for a long coating time resulted in a higher mechanical strength than that of the membrane without the application of UV irradiation.
关键词： free radical scavenger,photocatalytic membrane reactor,polydopamine,UV-resistance
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE Energy Conversion Congress and Exposition (ECCE) - Portland, OR, USA (2018.9.23-2018.9.27)] 2018 IEEE Energy Conversion Congress and Exposition (ECCE) - Stretching in Time of GaN Active Gate Driving Profiles to Adapt to Changing Load Current
摘要： Active gate driving, where the gate signal is actively profiled, has been shown to reduce EMI, overshoot, and switching loss, in silicon power converters. Recently, much faster gate drivers with the ability to profile at a 100 ps resolution have been reported, which has opened up the possibility of actively driving emerging wide-bandgap devices. This could allow Gallium Nitride (GaN) and Silicon Carbide (SiC) FETs to be switched faster than is currently possible, as unwanted switching features such as current ringing at turn-on could be eliminated. However, these drivers have previously only been demonstrated with pre-programmed gate profiles that have been optimized at certain operating conditions, whereas converters typically operate in a range of conditions. In this paper, some limitations of using fixed gate profiles on GaN FETs are reported for the first time, and a new method of profile adaptation is demonstrated. First, the gate profiles in a 400 V GaN bridge-leg are optimized to minimize current ringing at turn-on for a given load current. Then, the load current is varied, showing that the gate signal profile remains close to optimal for ±20% changes in current. Also, over a larger range of at least ±35%, the profiled waveform performs better than a non-profiled gate waveform. It is then demonstrated that by slightly reducing the driver’s internal clock frequency with increasing load current, the profile is re-optimized for new load currents. It is concluded that driver clock frequency adaptation may be a means of adapting gate profiles to load current variation and possibly also to temperature variation.
关键词： Active Gate Driving,Arbitrary Waveform Gate Driver,GaN Gate Driver,Dynamic Output Resistance Gate Driver,GaN FET
更新于2025-09-04 15:30:14
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Characteristics of Graphene Oxide Films Reduced by Using an Atmospheric Plasma System
摘要： The chemical oxidation method can be used to mass-produce graphene oxides (GOs) from highly oriented pyrolytic graphite. However, numerous oxygen-containing functional groups (hydroxyl, epoxy, carbonyl, etc.) exist in typical GO surfaces, resulting in serious electrical losses. Hence, GO must be processed into reduced graphene oxide (rGO) by the removal of most of the oxygen-containing functional groups. This research concentrates on the reduction efficiency of GO films that are manufactured using atmospheric-pressure and continuous plasma irradiation. Before and after sessions of plasma irradiation with various irradiation times, shelters, and working distances, the surface, physical, and electrical characteristics of homemade GO and rGO films are measured and analyzed. Experimental results showed that the sheet resistance values of rGO films with silicon or quartz shelters were markedly lower than those of GO films because the rGO films were mostly deprived of oxygen-containing functional groups. The lowest sheet resistance value and the largest carbon-to-oxygen ratio of typical rGO films were approximately 90 ?/sq and 1.522, respectively. The intensity of the C–O bond peak in typical rGO films was significantly lower than that in GO films. Moreover, the intensity of the C–C bond peak in typical rGO films was considerably higher than that in GO films.
关键词： sheet resistance,oxygen functional group,GO and rGO films,plasma irradiation,carbon-to-oxygen ratio
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Analysis of 1.2 kV 4H-SiC Trench-Gate MOSFETs with Thick Trench Bottom Oxide
摘要： The 1.2 kV-rated trench-gate SiC power MOSFET with thick trench bottom oxide is analyzed and compared with previous trench-gate SiC power MOSFET structures. Speci?c on-resistance (Ron,sp), breakdown voltage (BV), threshold voltage (VT H ), gate-drain capacitance (Cgd,sp) and gate charge (Qgd) were extracted using numerical simulations for trench bottom oxide thickness between 500 ?A and 8000 ?A. It was found that the electric ?eld in the trench bottom oxide was below 4 MV/cm for oxide thickness beyond 4000 ?A. An analytical model is proposed to allow estimation of the electric ?eld in the trench bottom oxide. The Ron,sp for the thick bottom oxide structure was 1.9 m? ? cm2 (at Vgs of 20 V), Cgd,sp (at Vds= 1000 V) was 417 pF/cm2 and Qgd,sp (at Vgs =20 V, Rg=10 ?, Vds=800V) was 671 nC/cm2, which is signi?cantly better than most planar-gate devices. This structure has superior speci?c on-resistance compared with previous trench-gate and planar-gate structures.
关键词： Silicon Carbide,reverse transfer capacitance,speci?c on-resistance,gate charge,trench bottom oxide,breakdown voltage,threshold voltage,Trench-gate MOSFET (UMOSFET)
更新于2025-09-04 15:30:14
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High-Performance PEDOT:PSS/Hexamethylene Diisocyanate-Functionalized Graphene Oxide Nanocomposites: Preparation and Properties
摘要： Graphene oxide (GO) has emerged as an ideal ?ller to reinforce polymeric matrices owing to its large speci?c surface area, transparency, ?exibility, and very high mechanical strength. Nonetheless, functionalization is required to improve its solubility in common solvents and expand its practical uses. In this work, hexamethylene diisocyanate (HDI)-functionalized GO (HDI-GO) has been used as ?ller of a conductive polymer matrix, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The nanocomposites have been prepared via a simple solution casting method, and have been characterized by scanning electron microscopy (SEM), UV–Vis and Raman spectroscopies, X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile tests, and four-point probe measurements to get information about how the HDI-GO functionalization degree (FD) and the HDI-GO concentration in the nanocomposite in?uence the ?nal properties. SEM analysis showed a very homogenous dispersion of the HDI-GO nanosheets with the highest FD within the matrix, and the Raman spectra revealed the existence of very strong HDI-GO-PEDOT:PSS interactions. A gradual improvement in thermal stability was found with increasing HDI-GO concentration, with only a small loss in transparency. A reduction in the sheet resistance of PEDOT:PSS was found at low HDI-GO contents, whilst increasing moderately at the highest loading tested. The nanocomposites showed a good combination of stiffness, strength, ductility, and toughness. The optimum balance of properties was attained for samples incorporating 2 and 5 wt % HDI-GO with the highest FD. These solution-processed nanocomposites show considerably improved performance compared to conventional PEDOT:PSS nanocomposites ?lled with raw GO, and are highly suitable for applications in various ?elds, including ?exible electronics, thermoelectric devices, and solar energy applications.
关键词： hexamethylene diisocyanate,PEDOT:PSS,functionalization degree,nanocomposite,optical transmittance,sheet resistance,graphene oxide,mechanical properties
更新于2025-09-04 15:30:14