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Post-arc breakdowns of vacuum circuit breakers during capacitive operation can be possibly caused by particles. In this work, we experimentally observe the generation and dynamics of particles in capacitive interruptions and their resultant effects on post-arc breakdowns. We further constructed a synthetic test circuit for the capacitive current switching and adopted the laser-shadow technique to observe the dynamics behaviors of particles, formed by different electrode materials and inrush currents. CuCr10 electrodes tend to generate particles with high probability and quantity, owing to their weak refractoriness and lower mechanical strength. Furthermore, we find that the higher inrush current facilitates the formation of particles. Additionally, under the influence of recovery voltages and variable charges, particles show complex and diverse dynamic behavior, such as bouncing, oscillating, levitating, lifting, and rotating. Essentially, all particles relevant to breakdowns moved at a low speed (below 0.5 m/s), besides, almost all non-sustained disruptive discharges and restrikes are concerned with the particles closed to electrodes under near-peak recovery voltage. Therefore, we think neither energy accumulation nor high-speed bombardment of particles can explain post-arc breakdowns, conversely, the joint effect of particle-induced field enhancement and resulting field electron emission is responsible for breakdowns. [ABSTRACT FROM AUTHOR]

Surface upward longwave radiation (SULR) is a key parameter that regulates surface radiation budget balance and matter–energy exchange. However, the state-of-the-art SULR retrieval methods based on remotely sensed data are only effective under clear skies, which mean that the existing methods are unable to generate spatiotemporal continuous SULR product at regional or global scale. Herein, taking the advantage of long-pending abundant ground-based radiation observations, satellite products, and meteorological reanalysis data, a data-driven random forest (RF) method is proposed to retrieve the instantaneous SULR under all-sky conditions. Based on spectral samples of different surface types and simulation results from the moderate resolution atmospheric transmission (MODTRAN), spectral transformation is carried out to transform SULR of various measured domains into the defined 4–100 $\mu \text{m}$ domain at first. SULR and surface downward shortwave radiation (SDSR) observations from seven stations of the surface radiation budget network (SURFRAD) and nine stations of the baseline surface radiation network (BSRN) are used in model’s training and testing procedures, and the RF model achieves a high accuracy with the root-mean-square error (RMSE) of 10.45 W/ $\text{m}^{2}$ on test set. In model evaluation, ground measurements from 14 stations of FLUXNET have been used, and the overall RMSE is 18.40 W/ $\text{m}^{2}$. In the actual application process, SDSR is estimated by remotely sensed data of Meteosat Second Generation (MSG). The accuracy of RF model has been validated with the observations from five stations of BSRN in 2021, and RMSEs are 17.00, 10.94, 12.17, 27.89, and 12.54 W/ $\text{m}^{2}$ , respectively. Validation result shows that the data-driven method is capable of estimating SULR under all-sky conditions with a high accuracy. Finally, sensitivity analysis has been carried out, and the established RF model keeps robust even though there are great uncertainties among input parameters. [ABSTRACT FROM AUTHOR]

Dry air is promising as an alternative insulation medium for SF6 gas in high-voltage equipment. Since its dielectric strength is about one-third of that of SF6 gas, one of the most effective ways to apply dry air to high-voltage gas-insulated switchgears (GISs) is to further increase gas pressure. In this article, impulse breakdown strength of dry air at high pressure under quasi-uniform electric field is measured. Furthermore, the probability distribution of breakdown voltage is predicted using the volume-time theory in consideration of initial electron generation probability in gas gap and field electron emission from an electrode. The predicted distribution of breakdown voltage by the volume-time theory is in line with the experimental results. [ABSTRACT FROM AUTHOR]

In this work, the parallel micro-light-emitting diode ($\mu $ LED) arrays based on via-holes structure with various array numbers from $1\times 1$ to $6\times 6$ are proposed. The photoelectric characteristics and frequency response characteristics of the $\mu $ LED arrays under different array numbers are analyzed. The experiment and analysis results show that the −3 dB bandwidth of parallel $\mu $ LED arrays based on via-holes structure improves as the number of arrays increases, and this result is attributed to the decrease in device RC time constant. However, the maximum withstand current density of $\mu $ LED arrays decreases as the number of arrays increases, and the $1\times 1\,\,\mu $ LED array achieves an extremely high withstand current density of 15.82 kA/cm2. Among all the arrays, the $3\times 3\,\,\mu $ LED array can reach the highest −3 dB bandwidth of 606 MHz at 7.91 kA/cm2 under the combined effect of withstand current density and array numbers. Meanwhile, the light output power for $3\times 3\,\,\mu $ LED array is above 15.0 mW. This work sheds light on preparation of high-performance LEDs for visible light communication. [ABSTRACT FROM AUTHOR]

AlGaN alloys are promising for field emission devices due to their low electron affinities. However, there have been limited demonstrations of AlGaN vacuum transistors so far. This letter combines a new self-aligned-gate (SAG) process and digital-etching tip sharpening to demonstrate three-terminal AlGaN SAG field emitter arrays (FEAs). These devices show a turn-on voltage of 19.5 V and an anode current density (JA) of 100 mA/cm2 at an overdrive voltage of 20 V, which are comparable with best Si devices. The AlGaN SAGFEAs can operate in DC mode at a fixed gate-emitter voltage ($\text{V}_{\textit {GE}}$) with JA of 3–5 mA/cm2 for at least 5 hours without a significant degradation. The gate leakage does not increase after the long DC operation, suggesting high-performance and stable AlGaN vacuum transistors. [ABSTRACT FROM AUTHOR]

Uniform electron emission (EE) from on-chip micro-emitter arrays based on SiOx tunneling diodes (STDs) in electroformed SiOx is reported. EE from STDs is found to be accompanied with visible light emission, which enables us to resolve the spatial distribution of EE from the micro-emitter arrays and emitter-to-emitter uniformity at the microscale resolution via optical imaging. Up to 99% micro-emitters in a 15 $\times15$ array is observed to work simultaneously with good emitter-to-emitter uniformity, showing an emission current of 0.56 mA and an emission density of 626 mA/cm2. The good uniformity is attributed to the insensitivity of EE from STDs to the microfabricated structures of micro-emitters. [ABSTRACT FROM AUTHOR]

There exist lots of impurities and micro-protrusions on the surface of metallic electrode, which lower the electron emission threshold. Since intense pulsed ion beam (IPIB) irradiation can melt and vaporize metal material, it is expected to increase the electron emission threshold by removing the impurities and micro-protrusions with this method. In our work, effects of IPIB treatment on electron emission threshold of metallic electrodes were studied. The electron emission threshold tests were done on a platform named 1 MV generator (the output voltage is higher than 1 MV with a rise time of ~25 ns when the load impedance $> 10~\Omega $). The pressure of the test vacuum chamber was kept at ~10−3 Pa. The results show that the electron emission threshold of as-machined 304L SS electrode was ~250 kV/cm, and it increased to 316 kV/cm after polish, and IPIB treatment enhanced the average electron emission threshold to 367 kV/cm. For bare machined aluminum electrodes, the average threshold was 255 kV/cm, and it also increased to 368 kV/cm after IPIB treatment. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) super junction (SJ) JFETs fabricated by sidewall implantation with different mesa-widths (MWs) and termination designs are characterized in this article. The device with an MW of $1.8 \mu \text{m}$ and active area of 0.104 mm2 achieves a breakdown voltage of 1086 V and a specific ON-resistance of 0.98 $\text{m}\Omega \,\cdot $ cm2. The first-quadrant output and transfer characteristics are presented, from which the ON-resistance and pinch-off voltage are extracted and analyzed. The pinch-off voltage shows great stability against the variation of temperature. The forward blocking characteristics under different gate voltages and with different terminations are presented. The gate needs to be negatively biased below the hold-off voltage to prevent the premature breakdown caused by drain-induced barrier-lowering (DIBL) effect. The termination with narrow mesas in the ${x}$ -direction and trapezoidal mesas in the ${y}$ -direction is found to have the highest breakdown voltage, due to its optimized net charge distribution. The third-quadrant output characteristics are presented. Under forward-off gate voltage, the third-quadrant turn-on voltage is found to be determined by the difference of hold-off and pinch-off voltages, and there is a tradeoff between the absolute third-quadrant voltage drop ($\vert {V}_{\text{on}}\vert $) and the maximum current before gate junction turn-on (${J}_{\text{umax}}$). The third-quadrant performance can be improved by using forward-on gate voltage, a $\vert {V}_{\text{on}}\vert $ lower than 0.2 V (at 100 A/cm2) and a ${J}_{\text{umax}}$ larger than 500 A/cm2 are achieved. Finally, the whole output characteristics are modeled to facilitate the device design in different applications. [ABSTRACT FROM AUTHOR]

Microchannel plate photomultiplier tubes (MCP-PMTs) with high temporal resolution and low dark count rates will be used as single-photon detectors for the Super Tau-Charm Facility (STCF) proposed in China. Similar to other RICH or DIRC detectors, MCP-PMTs in the STCF need to operate properly in an axial magnetic field of about 1.5 T. We study the magnetic field tolerance of MCP-PMTs with the simulation methods based on the Furman model as a secondary electron emission model and the particle-in-cell method for tracking electrons. The effects of MCP structural parameters (aperture $D$ , length-to-diameter ratio $L/D$ , bias angle $\theta $ , and applied voltage $U$) on the magnetic field tolerance are simulated. The results show that the smaller the $D$ and the smaller the $L/D$ of the MCP, the better its magnetic field tolerance. By increasing the MCP bias angle, its magnetic field tolerance increases first and then weakens. The applied voltage does not affect its magnetic field tolerance. Changing the angle between the magnetic field and the normal direction to the microchannel plate (MCP), the gain decays fastest when the magnetic field direction is parallel to the axial direction of the MCP channels; at a magnetic field direction of 60°, the MCP gain decays the slowest. For MCP-PMTs, the change in the magnetic field direction causes the alteration of the motion direction of the electron cloud in the gaps (cathode-MCP1, MCP1-MCP2, and MCP2-anode), which is the principal reason for the difference in its gain in different magnetic field directions with the same magnetic field strength. The magnetic field tolerance of different assembly methods of two MCPs (i.e., two, three, or four electrodes for applying high voltage) is simulated. The results show that two MCPs’ multiplication structure with the four-electrode assembly method is an appropriate choice. [ABSTRACT FROM AUTHOR]

Gated Si-tip with on-tip integrated gate-all-around field effect transistor using hyperbolic nano-channel (Hy-GAAFET) for actively controlled field electron emission is presented. Fully IC compatible nano-fabrication procedures were developed to obtain the Hy-GAAFET and the on-tip integration with the Si-tip emitter. The Hy-GAAFET exhibit characteristics of ${I}_{\textit {on}}/{I}_{\textit {off}} =\sim 10$ 4, ${I}_{\textit {sat}} = 0.25 ~\mu \text{A}/\mu \text{m}$ at ${V}_{\textit {gaa}}=-0.4$ V and 20 mV of drain-induced barrier lowering. The emission current of the gated Si-tip can be actively regulated by the Hy-GAAFET gate voltage, i.e., 0.4 pA/mV with an extractor voltage of 53 V and showed a well-optimized current stability. This on-chip integrated device is promising for applications in modern miniature vacuum nano electronics. [ABSTRACT FROM AUTHOR]

The results of preparation and post-treatment conditions on the long-term stability of Co-substituted nanostructured manganite La0.81Sr0.19Mn1.09Co0.06O3 films are presented. The films were grown on polycrystalline Al2O3 substrates by pulsed-injection metal-organic chemical vapor deposition technique at 600 °C keeping different growth rates (9, 13, and 27 nm/min), thus inducing different levels of disorder in the films. For comparison, the reference epitaxial films were deposited on the LaAlO3 substrate. The changes of resistivity and magnetoresistance (MR; up to 20 T) during the long-term storage of the films and accelerated aging by annealing the films in O2 or Ar atmosphere at ~100 °C were studied. It was found that the annealing atmosphere and long-term storage have a significant influence on the film resistivity and metal–insulator transition temperature, while MR magnitude is affected insignificantly. The aging effects have the highest influence on the nanostructured film grown at the highest growth rate, while for epitaxial films, the changes are negligible. The observed changes were analyzed using Mott’s variable-range hopping model and explained by oxygen depletion and diffusion in grain boundaries of nanostructured films. The ways to stabilize the main parameters of the manganite–cobaltite films for the development of high magnetic field sensors are discussed. [ABSTRACT FROM AUTHOR]

A planar lateral Vacuum Field Emission Triode (VFET) with a double gate structure is proposed to improve the gate modulation characteristics in this letter. The preparation of this double gate structure is obtained by using the mature bottom gate VFET manufacturing process without any additional dedicated masks. The emission characteristics of the fabricated VFET under vacuum and atmosphere condition are measured. The experimental results demonstrate that both the bottom gate and the top gate can effectively control the emission electrons in the vacuum channel with width of about 110–200 nm which is successfully prepared by the electro-forming process. The operating mechanism of the device is basically the same as that of the plane-bottom gate VFET, and the device has achieved good field electron emission characteristics and double-gate modulation characteristics. Meanwhile, the vacuum channel is covered by the top gate insulator layer, which relaxing the vacuum requirement and improving the collection efficiency of emitted electrons by drain electrode about 50% in air. [ABSTRACT FROM AUTHOR]

This article designed a Ka-band traveling wave tube (TWT) with the single wall carbon nanotubes (SWCNTs) field emission cathode electron gun. The designed cold-cathode TWT was miniaturized and could instantly startup at room temperature because of the field emission cathode. First, SWCNT cathode was made by imprinting. The field emission measurement results showed that its turn-on field was as low as 0.57 MV/m, and the maximum emission current was about 10 mA. Then, a grid-controlled electron gun with planar field emission cathode was simulated based on the experiment results, which had low operation voltage of the electron gun and would prevent their grid mesh from burning. The optimized electron beam waist radius of the electron gun was 0.15 mm with the structure of the focusing magnetic field. According to experiment and simulation results, we preliminarily designed a Ka-band helix TWT with an average output power of 8.6 W and a gain of 24.6 dB at 28 GHz. The designed miniaturized TWT with a low-operation-voltage field emission cathode electron gun is expected to be used in low-power applications including 5G communication. [ABSTRACT FROM AUTHOR]

A 600 V-rated insulated gate bipolar transistor (IGBT) with improved turn-on transient characteristics is proposed and investigated by simulation. The proposed IGBT features a built-in voltage-clamping structure. The floating ${p}$ -body adjacent to the trench gate is clamped at an appropriately high voltage before turn-on. This slows down the hole accumulation process in the floating p-body during turn-on transient, and thus the self-charging displacement current through the gate capacitance is reduced. The increasing rate for the gate voltage (dVGE/dt) is then reduced. As a result, the proposed IGBT achieves a 25% decrease in collector current ($I_C$) overshoot and 34% decrease in dIC/dt, when compared with the conventional IGBT with the same turn-on loss (EON), at IC = 250 A/cm2 under hard-switching. Its fabrication process is compatible with conventional trench IGBT. [ABSTRACT FROM AUTHOR]

An effective design for cold cathode named as the interdigitated field electron emission driving-secondary electron emission (FEE-SEE) cathode is proposed in this article. The cathode consists of an FEE region and an SEE region, which integrates the advantages of the field emission and secondary emission on the M-type device. The excellent FEE performance of the directional single-wall carbon nanotubes (SWCNTs) with an effective method of directly imprinting the SWCNTs sludge on a substrate is studied for obtaining higher primary excitation current. Meanwhile, the cathode prebunch technique is implemented by imposing a fivefold azimuthal variation on the SEE cathode of a ten-cavity magnetron, which could prebunch the electrons into the desired mode at birth to enhance stability and speed startup time. A 3-D particle-in-cell simulation analysis is used to predict a novel cold cathode magnetron with high output power of 3144 W with 6.2% efficiency enhancement with reference to the conventional thermionic cathode applied to the 2450-MHz magnetron. Its startup time is about 100 ns with excellent stability and pure output spectrum. [ABSTRACT FROM AUTHOR]

A miniature ionization vacuum sensor (IVS) based on an on-chip SiOx-based tunneling electron source is reported. The vacuum sensor fabricated by microfabrication technologies exhibits a compact multilayered structure with overall dimensions of $13\times 9\times2.7$ mm3, where the electron source chip, Si layer of the electron collector, Si layer of the ion collector, and glass spacers between them are stacked together by an anodic bonding method. Electron impact ionization occurs in a semiclosed cavity through the electron and ion collector layers and glass spacers. Because of the compact structure, low working voltage of SiOx-based tunneling electron sources, and stable electron emission of the electron sources in a poor vacuum, a wide linear detection range from $1.3\times 10^{-2}$ to 133 Pa and a sensitivity of $8.3\times 10^{-4}$ Pa−1 have been demonstrated for the devices. These advantages, including miniature size, a detection range up to the rough vacuum regime, and the capability of batch fabrication with microfabrication technologies, make our IVSs promising in vacuum measurements. [ABSTRACT FROM AUTHOR]

A miniaturized radio frequency (RF) excited grid-free field emission cathode made by single-wall carbon nanotubes (SWCNTs) is suggested and studied. The $\lambda $ /4 coaxial resonant cavity is used as field-emitted electron source with length of 26.5 mm and diameter of 12.8 mm. Electrons can be pulled out by a small electrostatic field and an RF electric field without interception. The RF electric field of inner conductor surface at the open end, which pasted SWCNTs, can reach 3 MV/m when the input power is 30 W, and the field is larger than the turn-on field of SWCNTs. The results of simulation and experiment both show that the maximum emission current under input RF power of 30 W is 30 times larger than without RF excitation, which can reach 24 mA at the anode voltage of 950 V. This miniaturized RF excited grid-free field emission cathode electron source can be used as electron source, in a high repetition frequency vacuum electronic devices, e.g., terahertz (THz) devices, and X-ray tubes. [ABSTRACT FROM AUTHOR]

An investigation of runaway electron (RE) kinetics under the influence of a strongly inhomogeneous electric field was carried out by means of 2-D analytical and 2-D numerical Monte–Carlo approaches. Several shapes of cathodes generating an inhomogeneous electric field were studied. Within the developed 2-D analytical model, blade-shaped and cone-shaped cathodes were considered. The voltage values which allow electrons to scatter at large angles close to $\pi $ /2 near a blade-shaped cathode were determined. Also, it was shown that the RE scatter angles are larger for the blade (in comparison with the ones for the cone) due to the electric field defocusing effect. Within the framework of the numerical 2-D Monte–Carlo model, a cathode was assumed to have a parabolic shape. Inapplicability of the classical runaway criterion in strongly inhomogeneous electric fields was demonstrated. Also, it was shown that the cathode surface domain of electron emission and an initial direction of electron motion have a strong influence on their energy balance and, hence, on the probability for electrons to transit into the continuous accelerating regime. Energy losses of REs were estimated. A correlation between the full-width at half-maximum of the RE energy spectrum and an inelastic energy loss value was proposed. [ABSTRACT FROM AUTHOR]

An electron source with an array of individually controllable single tips allows the observation of each emitter current simultaneously as well as the measurement of the integral current. Furthermore, the initial activation process of the individual tips and current distribution of the source can be examined. The Si cathode consists of an array of $2\times2$ conically shaped emitter structures on a borosilicate glass substrate. The emitters were fabricated by laser micromachining and wet etching. Integral field emission (FE) measurements were performed in a diode configuration in a vacuum chamber at pressures of about 10−9 mbar with a self-aligned Si extraction grid, due to adjustment pins. The total emission current was regulated to a predefined value (4.0, 10, 20, 40, and 50 $\mu \text{A}$) by an external regulating circuit and recorded individually during the measurement. The onset voltage for a current of 1 nA varied between 320 and 430 V. The voltage conversion factor is in the range of $7.6\times 10^{{4}}$ cm−1 to $1.3\times 10^{{5}}$ cm−1. Constant current measurements over a longer period of time (1800 values with a sample rate of 0.5 Hz) were performed and show a total current fluctuation less than 0.6% due to the regulation circuit. Despite the stable total current in regulated operation, it was observed that the individual emitters fluctuate up to 75% for low (~10−8 A) and 5% for high (~10−5 A) currents. [ABSTRACT FROM AUTHOR]

The gate voltage overshoot during the turn-on transient in the trench gate U-shaped (TGU) channel silicon-on-insulator lateral insulated gate bipolar transistor (SOI-LIGBT) is investigated and novel structures are proposed for the first time with numerical simulation in this article. The TGU SOI-LIGBT features two U-shaped trench gates, G1 and G2, connected together. The U-shaped trench for G2 serves as a hole barrier trench. A large number of holes accumulate in the U-shaped region during the turn-on transient because of the U-shaped architecture and the hole-blocking effect of G2. The displacement current induced by the nonuniform distributed holes overcharges the gate and leads to high di/dt. In this article, the novel structures (Novel-1 and Novel-2) with G2 partially filled by the polysilicon are proposed for the improvement in gate voltage overshoot while keeping superior turn-on loss (${E}_{ \mathrm{ON}}$). The novel structures (Novel-1 and Novel-2) can suppress the hole accumulation and slow down the rising of the electric potential in the silicon region near the G2. The di/dt can be lowered and the displacement current that overcharges G2 can be effectively shielded. Compared with the conventional TGU structure, the di/dt of the Novel-2 are improved by 56.3% at the same ${E}_{ \mathrm{ON}}$ of 2.4 mJ/cm2. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) cold-cathodes hold much promise in a variety of millimeter-wave and terahertz vacuum electronic radiation devices due to their inherent near instantaneous temporal turn-on and near-ideal ideal field electron emission performance. Here we report on the development of a CNT cold-cathode Ka-band backward-wave oscillator (BWO). Using a novel beam compression stage, theoretical studies, simulation results, and empirical findings collectively demonstrate that this device affords an unprecedentedly high output power of 230 W at a technologically important operating frequency of 33.65 GHz. The developed magnetic injection electron gun achieves a high emission current of 265.5 mA (emission current density of 188.3 mA/cm2) and a high focused beam current density of 18.5 A/cm2, which our studies suggest, is essential to the BWOs high output power. [ABSTRACT FROM AUTHOR]

This work reports a $\beta $ -Ga2O3 double-barrier Schottky barrier diode (DBSBD) with both low turn-on voltage and low reverse leakage current by using Ni and PtOx as the anode electrode. The barrier height of PtOx-based diode can be effectively modulated from 1.26 to 1.62 eV by adjusting oxygen pressure during sputtering processes. Combining the maximum work function of PtOx electrode with the optimization of the electrode ratio of Ni and PtOx, the DBSBD with an electrode diameter ratio of $\text{D}_{\text {Ni}} /\text{D}_{\text {PtOx}}= {75}/{150} \mu \text{m}$ not only exhibits a high forward current of 470.9 A/cm2 (at 3.5 V), a low on-resistance of 4.1 $\text{m}\Omega ~\cdot $ cm2 and a low turn-on voltage of 1.13 V, but also possesses a relatively low reverse leakage current of ${1.2}\times {10}^{-{7}}$ A/cm2 (at −100 V), which is more than one order of magnitude lower than that of the Ni-SBD. Silvaco TCAD simulation reveals that such optimization can be attributed to the suppression of edge leakage current due to the double-barrier contact. Therefore, the strategy of double-barrier design can balance the forward and reverse characteristics in SBD, providing a new device structure for advanced power electronics. [ABSTRACT FROM AUTHOR]

Large-size vertical β-Ga2O3 Schottky barrier diodes (SBDs) with various device areas were demonstrated on a Si-doped n-type drift layer grown by hydride vapor phase epitaxy (HVPE) on bulk Sn-doped (001) n-type β-Ga2O3 substrate. In this letter, the devices have two circular contacts with a diameter of 1500 and 500 μm and two square contacts with dimensions of 1600 × 1600 μm2 and 800 × 800 μm2, corresponding to the area of 0.2 × 10−2 cm2 (the smallest device), 0.6 × 10−2, 1.8 × 10−2, and 2.6 × 10−2 cm2 (the largest device). The breakdown voltage (BV) was determined to be −261 V for the largest device and −427 V for the smallest device. Also, the ideality factor (η) of vertical Ga2O3SBDs with different device areas exhibited the same value of 1.07, except for the largest device area of 2.6 × 10−2 cm2 with an ideality factor of 1.21. At an applied forward bias of VF = 2 V, the specific on-state resistance (RonA) of all the Ga2O3 SBDs remains relatively low with values ranging from 1.43 × 10−2 Ω cm2 to 7.73 × 10−2 Ω cm2. The measured turn-on voltage (Von) of all the SBDs remains low with a narrow distribution. [ABSTRACT FROM AUTHOR]

Integrated field emission electron sources with low driving voltage are desired for micro/nano vacuum electronics. Herein, we demonstrate the enhanced and stable electron emission from crystalline gold–silver (Au–Ag) alloy nanoparticle capped Si nanowires (SiNWs) and the achieved gated electron sources with low driving voltage (<50 V). Thermally induced self-assembly hemispherical (50–80 nm) crystalline Au–Ag nanoparticles were prepared and used as masks in plasma etching to form vertically aligned high aspect ratio (~14) SiNWs. The nanoparticles were preserved after the etching, forming in situ integrated Au–Ag/Si junctions with each individual SiNWs. The SiNWs with capped nanoparticles possess superior field emission current density (45.80 mA/cm2) and current stability (fluctuation ~6%). A self-aligned process was developed to fabricate gated field emission devices, using the Au–Ag nanoparticle capped SiNWs as cathode. The gated devices showed field emission at low gate voltage (69.52-μA/cm2 at 42.1 V). Experimental and numerical simulation studies demonstrated the Au–Ag/Si contact behaved as space-charge-limited (SCL) Schottky conduction. The idea behind the enhancing and stable emission is that the SCL–Schottky junction undergoes a process of negative feedback and thus suppressed the current and shot-noise from the outstanding SiNWs. Accordingly, more SiNWs were activated and contributed stable and higher field emission current. [ABSTRACT FROM AUTHOR]

In this letter, a high-performance GaN quasi-vertical Schottky barrier diode (SBD) is demonstrated via oxygen plasma termination. A specific on-resistance of 0.2 $\text{m}\Omega \cdot $ cm2, turn-on voltage of 0.71 V, and breakdown voltage of 193 V are achieved with a GaN SBD of $1.3~\mu \text{m}$ drift layer. The average breakdown electric field is calculated to be about 1.48 MV/cm, which is much higher than the state-of-art value for GaN vertical SBDs. The temperature-dependent forward and reverse I-V characteristics confirm the high-temperature stability of the oxygen plasma treated SBDs. X-ray spectroscopy and Kelvin Probe Force Microscopy reveal that the surface potential is increased after the oxygen plasma treatment, which results in the suppression of the leakage current and improvement of the breakdown electric field. [ABSTRACT FROM AUTHOR]

The green InGaN/GaN micro light-emitting diode (Micro-LED) is a significant component in micro-display whereas lack of size dependence and high injected current analysis. In this letter, different size Micro-LEDs were fabricated and the electro-optical characteristics were measured. The size-dependence phenomenon for EQE “efficiency droop”, luminous flux and brightness were observed and discussed. All sizes Micro-LEDs exhibited an extremely high brightness as 37.5k and 67.6k nits at 1 A/cm2, 2.89M and 3.81M nits at 300 A/cm2 for 25 and $200~\mu \text{m}$ respectively. In addition, the elevating current densities from 160 to 6400 A/cm2 were injected into $25~\mu \text{m}$ Micro-LED and the electroluminescence (EL) spectra transformation of different current densities were depicted. The green to blue shift and secondary peak effect, which promise an opportunity to modulate the emission wavelength for higher quality and lower the barrier of mass transfer technology, were observed and analyzed through the spectra. [ABSTRACT FROM AUTHOR]

Fabrication of single crystal hydrogen-terminated diamond MOSFET with dielectrics of LiF/Al2O3 has been successfully carried out. After patterning source and drain electrodes, 60nm LiF/20nm Al2O3 were deposited as dielectrics. The output and transfer characteristics were investigated, indicating the typical p-type channel MOSFET. The on/off ratio was ∼ 109, which was high enough for practical applications. The fixed and trapped charge in LiF/Al2O3 were also examined. Based on the capacitance-voltage curves, the dielectric constant of LiF/Al2O3 was calculated to be 36.1, which was ascribed to the LiF supercapacitor structure. To the best of our knowledge, this LiF supercapacitor structure was first used in hydrogen-terminated diamond MOSFET to improve the dielectric constant. [ABSTRACT FROM AUTHOR]

In this article, a novel tri-gated hybrid anode AlGaN/GaN power diode (TG-HAD) with intrinsic low turn-on voltage (VON) is demonstrated. A novel forward VON modulation technique based on an ultrathin barrier (UTB) AlGaN/GaN heterostructure is proposed. VON of the diode is determined by the intrinsic threshold voltage of the two-dimensional electron gas (2DEG) channel of the UTB heterostructure, which can be precisely controlled and which fundamentally features excellent uniformity by tailoring the AlGaN barrier thickness. On the other hand, compared with the planar GaN diodes, the proposed TG-HAD achieves significant reverse leakage current reduction originating from the effectively suppressed buffer leakage by the tri-gate design. The detailed device characteristics and the underlying mechanisms are investigated by TCAD simulation. The TG-HAD, together with the proposed turn-on voltage modulation technique, is promising for fabricating high performance large periphery devices for power applications. [ABSTRACT FROM AUTHOR]

Paschen’s law (PL), derived based on the Townsend avalanche (TA) condition, is commonly used to predict gas breakdown. For microscale gaps near atmospheric pressure, TA is insufficient to drive breakdown and ion-enhanced field emission (FE) dominates. Accurately predicting breakdown voltages for these gaps is critical for numerous applications, including environmental remediation, medicine, combustion, and propulsion. This tutorial summarizes theoretical and computational approaches for predicting this behavior and demonstrating the transition between the TA and FE mechanisms. It focuses on the derivation of closed-form solutions from a theory that accounts for the generation of additional positive space charge at the cathode due to electrons generated by the strong FE-induced electric fields. Appropriate simplifications using a matched asymptotic analysis in terms of the total ionization in the gap agree well with simulations and experiments and show the transition from FE for small gaps to PL at larger gaps. Specifically, this theory shows that the breakdown voltage varies linearly with gap distance when FE dominates, agreeing with both the experimental and simulation results. The particle-in-cell Monte Carlo collision (PIC/MCC) simulations used to predict the ionization coefficient provide additional insight into the mechanisms involved. Future benefits of extended theoretical and computational research for examining microscale and nanoscale breakdown and electron emission, particularly assessing the impact of electrode surface structure and device design and coupling with additional emission mechanisms, will be discussed. [ABSTRACT FROM AUTHOR]

Organolead halide perovskites provide tremendous opportunities for ideal radiation detection due to their high atomic numbers, large carrier mobilities, and long lifetimes. Here, we synthesized high-quality single crystal CH3NH3PbBr3 with a high mobility-lifetime product of $\text {4.1} \times \text {10}^{\text {-2}}$ cm2/V by the developed inverse low temperature crystallization method. The sensitive X-ray detector was fabricated by depositing 50 nm of gold on both sides of the perovskite crystal. This device exhibited a high sensitivity up to $259.9~\mu \text{C}$ /Gy $_{\text {air}}$ /cm2 under the 39 keV X-ray exposure at a small electric field of ~0.83 V/mm and yielded a low noise of $\text {3.1} \times \text {10}^{-\text {23}}\,\,\text{A}^{\text {2}}$ /Hz. Additionally, the sensitivity can be further improved by increasing operating voltage. Our results provided a solution for constructing high-performance X-ray detectors. [ABSTRACT FROM AUTHOR]

In this study, ZnO and gold-adsorbed ZnO (Au-ZnO) nanorods (NRs) are successfully synthesized by hydrothermal method. The result of scanning electron microscopy verifies that high-density ZnO NRs are successfully grown on the substrate. The NRs are mostly perpendicular to the substrate surface. The J – E curves in the dark and under UV indicate that the turn-on field values of the ZnO and Au-ZnO NRs are 6.85 and 5.85 V/μm and 4.85 and 4.14 V/μm, respectively. The F – N plot in the dark and under UV demonstrates that the field enhancement factors of the ZnO and Au-ZnO NRs are approximately 700, 1896 and 1796, 4109, respectively. The performance of ZnO NR field emission (FE) is improved by adsorbed Au. The results show that the FE properties remain stable and that the manufactured device features excellent characteristics. [ABSTRACT FROM AUTHOR]

This letter demonstrates novel hydrogen-plasma based guard rings (GRs) for high voltage vertical GaN p-n diodes grown on bulk GaN substrates by metalorganic chemical vapor deposition (MOCVD). The GR structure can significantly improve breakdown voltages (BV) and critical electric fields (${E}_{c}$) of the devices. Not having field plates or passivation, the p-n diodes with a $9~\mu \text{m}$ drift layer and 10 GRs showed BV /on-resistance (${R}_{\textit {on}}$) of 1.70 kV/0.65 $\text{m}\Omega \cdot $ cm2, which are close to the GaN theoretical limit. Moreover, the device also exhibited good rectifying behaviors with an on-current of ~ 2.6 kA/cm2, an on/off ratio of ~ 1010, and a turn-on voltage of 3.56 V. This work represents one of the first effective GR techniques for high performance kV-class GaN p-n diodes. [ABSTRACT FROM AUTHOR]

Due to their unique characteristics of instant responses and low-power consumption, vacuum electronic devices based on field emission cold-cathode have potentials for realizing compact and novel high frequency electromagnetic wave radiation sources. Herein, a cold-cathode radiation source operating in the frequency range from gigahertz to terahertz is developed, which is based on frequency multiplication by taking advantage of nonlinearity of field electron emission. The radiation source is realized by introducing a compact structure with two re-entrant cavity resonators. Based on such a structure, radiation sources of frequencies at 12.10 GHz and 0.1 THz were, respectively, designed and simulated numerically. Based on the simulation results, the 12.10-GHz radiation source using carbon nanotubes cold-cathode was fabricated and tested experimentally. The results showed that an electromagnetic wave output at 12.10 GHz with power of $98~\mu \text{W}$ can be achieved upon excitation by a 6.05 GHz input signal with power of 1.05 mW. Our study provides an approach for microwave and terahertz wave generation. [ABSTRACT FROM AUTHOR]

We report a dual-gate, amorphous In-Ga-Sn-O (a- IGTO) thin-film transistor (TFT) exhibiting high field-effect mobility ($\mu _{\text {FE}}$) and very low subthreshold swing. The TFT has a bottom-gate having $5~ \mu \text{m}$ overlap with source/drain (S/D) and a top-gate with $0.5~\mu \text{m}$ offset with S/D electrodes. The bottom-gate potential is swept at various top-gate voltages. The $ \mu _{\text {FE}}$ of a-IGTO TFT is found to be 39.1 cm $^{\text {2}}\text{V}^{-\text {1}}\text{s}^{-\text {1}}$ which is almost independent of top-gate potential. The subthreshold swing is ~0.19 Vdec−1 and also does not change much with top-gate potential variation between −50 V and +90 V, indicating very low density of states in the gap. The a-IGTO TFT exhibits no effect of negative bias illumination stress. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCBs) are widely used in the medium voltage class. In VCBs, late breakdowns sometimes occur after the circuit current has been interrupted, and these late breakdowns are thought to be triggered by microparticles. In this paper, the motion of the microparticles and the breakdown triggered by the microparticles are observed under the application of dc voltage. It turns out that the motion of microparticles can be grouped into three patterns: attaching to electrodes, bouncing at electrodes, and bouncing up and down between electrodes. Some microparticles gain positive/negative charge during the flight as the acceleration changes despite application of dc voltage. The microparticles are positively charged by the secondary electron emission under the bombardment of field emission electrons from the cathode, while they are negatively charged by absorbing field emission electrons. The patterns of breakdowns triggered by the microparticles can be grouped into six patterns according to the motion of the microparticles before/after the breakdown and the location of light emission. The occurrence frequencies of each breakdown pattern are also measured with changing the microparticle size. It can be said that contamination of the gap with big and attaching microparticles should be avoided in order to prevent degradation of the withstanding voltage of the gap. [ABSTRACT FROM AUTHOR]

A two-stage compact bushing has been developed by CEA-Cadarache and installed on its 1-MV testbed. This bushing acts as high-voltage feedthrough between a transmission line under pressurized nitrogen or sulfur hexafluoride (SF6) gas and a vacuum tank with a volume of 30 m3. The bushing has been successfully tested up to 420 kV. Electron field emission causes a dark current to flow between the electrodes in the vacuum, both inside or outside the bushing in the vacuum tank. High-voltage conditioning leads to a significant reduction in this dark current. The dark current can be further reduced or even suppressed by adding low-pressure (~1 mPa) nitrogen or SF6 gas to the vacuum. [ABSTRACT FROM AUTHOR]

A magnetic-focused X-band traveling wave tube (TWT) based on carbon nanotube (CNT) cathode is presented. The CNT TWT has a simple structure of the electron gun, consisting of a CNT emitter electrode and a ring-shaped anode, with no metallic mesh extracting electrode, nor electrostatic focusing electrode. The field emission electrons are extracted directly by the ring-shaped anode, while the electron beam focusing is realized by an extra magnetic field. Apart from the CNT electron gun, the TWT mainly has a high-frequency interaction circuit and a collector. All these components are totally immersed in a uniform axial magnetic field, and thus, electrons are confined by the Lorentz force during their traveling process from the cathode surface toward the collector. The fabricated CNT TWT was tested in a superconducting system providing a uniform axial magnetic field. The dc mode testing showed about 86% of the emission electrons can reach collector, which is better than a common gate-controlled CNT electron gun. [ABSTRACT FROM AUTHOR]

The improving of tip-to-tip electron emission uniformity in an array is one of the essential issues for the vacuum microelectronic/nanoelectronic applications. Here, we report the achieving of quasi-saturated ultrahigh arsenic concentration ($\sim 6.7\times 10^{{21}}$ /cm3) at the Si nanotip apex, in the mechanisms of dopant segregation during the thermal oxidation and the limitation of arsenic solubility in Si. The tips with quasi-saturated high-level arsenic concentration possess a well tip-to-tip uniformity in surface work function. The measured work function for the tips in an array with saturated dopant concentration is in a narrow range of 4.347–4.371 eV (~2.1% fluctuation). This merit not only resulted in high emission current density (~418.36 mA/cm2) from the devices at a relatively lower gate voltage but also brought well spatially uniform electron emission in an array. The work inspired vital insight into the interpretation for mechanisms in dopant density control and the improving of emission uniformity of the Si-tip array. It could be used as an essential approach to acquire high-performance Si-based vacuum electronic devices. [ABSTRACT FROM AUTHOR]

A voltage-driven, continuously-tuned beam shifting device is proposed, simulated, and demonstrated in an InP photonic integrated circuit. Electrodes are applied on the left and right side of a mode-expanded waveguide to electronically control the refractive index profile and shift the optical beam by means of reverse bias voltage. The feasibility of a beam shifting of $4.9~\mu \text{m}$ with a power consumption of the order of 4.5 pW and voltage of 10 V is numerically predicted for a beam shifting element with ideal electrical isolation and fundamental input mode excitation. The reduction in beam-shifting efficiency is subsequently quantified for imperfect electrical isolation and in the presence of higher order mode excitation at the input to the beam shifting element. An experimental proof of concept is implemented by realizing the device on a generic photonic integration platform and co-integrating an on-chip tunable laser. High-resolution near-field measurements show near-field beam shifting of $1~\mu \text{m}$ with an applied voltage range from −4 to 0 V. [ABSTRACT FROM AUTHOR]

In this paper, Al-doped ZnO nanorods (AZO NRs) were successfully applied on glass substrates through hydrothermal synthesis growth with a fabrication field-emission (FE) device. The enhanced FE properties of AZO NRs were measured. The turn-on fields were reduced by 2.35 and 1.51 V/ \mu \textm in the dark and under UV light, and the enhanced field enhancement factors ( $\beta $ ) were 5708 and 10137, respectively. Results show that the FE performances of AZO NRs were enhanced by the combined effect of increased carrier concentration and UV light illumination. [ABSTRACT FROM AUTHOR]

Field electron emission from metal (tungsten, molybdenum, and tantalum) surfaces with different surface morphology was measured. Fuzz and loop samples had small increment in the emission current, whereas bubble samples marked huge increment in the current, accompanied by breakdown. The emission current became greater on the fuzzy samples than the loop samples probably because of more elongated morphology of fuzzy fiber. Among the materials, molybdenum had the lowest current. From Fowler–Nordheim plot analysis, it was revealed that fuzz samples had higher field enhancement factor than loop samples. Bubble samples marked the highest value in the field enhancement factor among the three types of morphology, likely due to the continuous emission from the craters formed after the breakdown. Molybdenum showed favorable properties in terms of suppressing the field emission and preventing the breakdown and the arcing in fusion reactor. From the scanning electron microscope observation, the size of the crater increases with the emission current on the bubble samples. Fuzzy structure was observed at the crater on the tantalum bubble surface after breakdown even without stationary plasma irradiation or stationary incidence of ion flux. [ABSTRACT FROM PUBLISHER]

The carrier mobility of MoS2 transistors can be greatly improved by the screening effect of high-k gate dielectric. Therefore, in this paper, atomic layer deposited HfTiO annealed in different ambients (N2, O2, and NH3) is used to replace SiO2 as gate dielectric for fabricating back-gated multilayer MoS2 transistors. As a result, excellent electrical properties are achieved for the sample annealed in NH3 at 400 °C for 10 min: the field-effect mobility of 31.1 cm ^\mathrm \mathbf 2 /(V $\cdot $ s) and the subthreshold swing of 100 mV/decade, which are six times higher and three times smaller compared with that of the control sample, respectively. The enhanced electrical performance should be associated with the passivation effects of the NH3 annealing, which reduces defective states in the HfTiO dielectric and at/near the HfTiO/MoS2 interface. The capacitance equivalent thickness of the gate dielectric (HfTiO) is only 6.79 nm, which is quite small for back-gated MoS2 transistor and is conducive to the scaling down of the device. [ABSTRACT FROM AUTHOR]

A theory is developed which describes the processes of dust particle charging in the situation when dust particles are subjected to the action of a beam of electrons. It is shown that in this situation it is necessary to consider the electron field emission in addition to the influence of the electron beam on the dust particle. We calculate the current of the electron field emission modified by the Schottky effect and find the steady-state dust particle charge. We show that in the situation considered the electrostatic energy of the dust particle is much smaller than the electron energy in the beam. [ABSTRACT FROM AUTHOR]

A simple analytical low-field electron mobility model to be employed for technology computer-aided design of thin-body MOSFETs based on III-V compound semiconductors is presented. The scattering sources accounted for in the model are Coulomb centers, lattice vibrations (i.e., phonons), and surface roughness. The dependence of the thin-body effective thickness on the transverse electric field is calculated through 1-D Schrödinger–Poisson numerical simulations and is introduced in the model by means of an appropriate analytical function. Then, the free-electron density distribution is determined by considering both quantization effects and oxide–semiconductor interface traps. The model is calibrated on the experimental data collected on In0.53Ga0.47As-on-InP thin-body MOSFETs featuring body thicknesses as low as 5 nm. In particular, the model accurately reproduces CG – V\mathrm{ GS} characteristics, effective mobility against inversion layer charge plots, and I\mathrm{ DS} – V\mathrm{ GS} curves at low V\mathrm{ DS} . [ABSTRACT FROM AUTHOR]

A 2-D hydrodynamic model has been developed that describes the pre-explosion processes in a microprotrusion of a vacuum arc cathode based on a self-consistent calculation of the electric potential drop in the near-cathode region. The model includes a calculation of the cathode temperature in view of the surface heat fluxes carried by electrons and ions during the interaction of the cathode surface with the cathode spot plasma and the Joule heating of the cathode. The near-cathode space charge sheath is considered in the 1-D local Bohm approximation. It has been shown that the heat flux from a cathode plasma having parameters characteristic of low-current vacuum arcs can induce thermal instability (thermal runaway) in a cathode microprotrusion and heat it to a critical temperature within some tens of nanoseconds. Comparative analysis of the volumetric Joule mechanism and the surface electron-plasma mechanism underlying the development of thermal instabilities in a cathode has been performed in one numerical experiment. It has been shown that the instability induced by the surface mechanism can arise at lower densities of the cathode spot plasma and its growth rate is lower compared with the instability induced by the Joule mechanism. [ABSTRACT FROM PUBLISHER]

The microengineered MEMS-type ion-sorption micropump with field-emission electron source has been shown. Effective emission properties of the carbon nanotubes cathode ensure satisfactory efficiency of residual gas ionization, showing possibility of active pumping of circa 0.05 cm3 volume down to 10-5 hPa. Measurement of ion current allows estimation of vacuum level inside the microcavity. [ABSTRACT FROM AUTHOR]

In this paper, we present investigations of picosecond effects in atmospheric gaps at the stage of a pulsed breakdown delay. It is shown that in centimeter gaps with rapid achievement of multiple overvoltages, the breakdown point, its stability, and development time are determined by the advance emission of runaway electrons. Methods for controlling and stabilizing the temporary and energy characteristics of the flows of these particles are proposed. [ABSTRACT FROM AUTHOR]

In this paper, we discuss and analyze the design of a high-frequency, broadband distributed amplifier (DA) based on a 2-D array of field-emission nanotriodes (FENT) consisting of self-aligned gate around a nanomaterial field emitter. We propose here a physics-based device model to characterize dc properties of individual FENTs and a transmission-line circuit for evaluating and optimizing relevant ac properties, including power gain and impedance matching. Our discussion starts from the FENT array's dc characteristics and covers its radio frequency and microwave properties, considering effects of array density, geometry, FENT dimensions, and nanoemitter work function, in order to maximize power gain and bandwidth for high-frequency applications (30–100 GHz). Finally, we consider the practical design of a transmitter front end for wireless systems, combining the FENT-array DA with a tapered open-ended waveguide antenna, significantly improving matching and power radiation efficiency. Our results are of interest for imaging, sensing, satellite communications, defense, and security at 94 GHz. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel method to enhance the emission characteristics of carbon nanotubes (CNTs). It is extremely possible for CNTs to adsorb moisture and other contaminants during the fabrication processes, leading to the degraded field emission characteristics. In this work, CNT emitters are activated with commonly used heating process and supercritical carbon dioxide (SCCO2) fluids technology for removing adsorbed residue moisture. Experimental results have demonstrated that the electrical stability and field emission enhancement of CNT emitters are effectively achieved by the SCCO2 fluids treatment compared to the heating process, due to the minimization of residuary moisture in CNTs [ABSTRACT FROM PUBLISHER]

We report here an excellent field emission performance from periodic patterned graphene nanomesh (GNM) field emitter. A simulation of the relationships between external electric field and the local electric field enhancement on the GNM edges was conducted to optimize the parameters of the nanostructure. Experimental results revealed that the gate driving voltage was as low as 20 V. This kind of emitters also shows good field emission stability. It is expected that the GNM introduced here will generate impacts for the further advancement of graphene field emission devices in emerging technologies and applications. [ABSTRACT FROM AUTHOR]