Anode-cathode Spacing Research Articles

On the Child–Langmuir law in one, two, and three dimensions

We consider the limiting current from an emitting patch whose size is much smaller than the anode–cathode spacing. The limiting current is formulated in terms of an integral equation. It is solved iteratively, first to numerically recover the classical one-dimensional Child–Langmuir law, including Jaffe's extension to a constant, nonzero electron emission velocity. We extend to two-dimensions in which electron emission is restricted to an infinitely long stripe with infinitesimally narrow stripe width so that the emitted electrons form an electron sheet. We next extend to three-dimensions in which electron emission is restricted to a square tile (or a circular patch) with an infinitesimally small tile size (or patch radius) so that the emitted electrons form a needlelike line charge. Surprisingly, for the electron needle problem, we only find the null solution for the total line charge current, regardless of the assumed initial electron velocity. For the electron sheet problem, we also find only the null solution for the total sheet current if the electron emission velocity is assumed to be zero, and the total maximum sheet current becomes a finite, nonzero value if the electron emission velocity is assumed to be nonzero. These seemingly paradoxical results are shown to be consistent with the earlier works of the Child–Langmuir law of higher dimensions. They are also consistent with, or perhaps even anticipated by, the more recent theories and simulations on thermionic cathodes that used realistic work function distributions to account for patchy, non-uniform electron emission. The mathematical subtleties are discussed.

Effects of a modified argon glow plasma source on PET polymeric surface properties

A homemade plasma source with a Langmuir electrical probe was built in this work to create a plasma beam that could be utilized successfully in a range of uses. By modifying the operational parameters, including the discharging voltage, cathode–anode spacing and argon (Ar) pressure, a steady discharging medium was achieved. Additionally, a locally designed electrical probe was introduced into the discharging plasma to monitor the current–voltage (I–V) characteristics curve in order to assign plasma properties. The probe was moved to any intended destination in the plasma volume and had the following dimensions: 1 mm length and 0.5 mm diameter. The gas pressure and probe–cathode separation were modified to measure the plasma characteristics, including the electron density and electron temperature. It is found that as the pressure rises from 0.15 to 0.3 Torr, the electron temperature T e varies from 4.66 × 104 to 2.91 × 104 eV. When a poly(ethylene terephthalate) (PET) polymeric film is subjected to argon plasma beams, its surface wettability is altered. When the plasma period is increased from 0 to 8 min, the overall surface free energy rises from 32.2 to 67.7 mJ/m2. Additionally, the developed plasma source is highly efficient and tailored to satisfy the needs of applications such as polymeric surface modifications.

Numerical determination of field emission performance of GaN nanowire arrays

Determining the field emission turn-on field of the GaN nanowire array can better adapt to the application of field-assisted photocathode. A numerical simulation of the field emission behavior based on the finite difference method is proposed. Considering the influence of nanowire radius, height, cathode-anode spacing and interwire spacing on the field emission of GaN nanowires. The simulation proves that field enhancement factor of a single GaN nanowire is the most excellent, while emission electrons is relatively small. When GaN nanowires have a larger aspect ratio, it will have a larger enhancement factor and a small required turn-on electric field. Due to an enhanced field shielding, the enhancement factor of the GaN nanowire array reduces as interwire spacing reduces. Cathode-anode spacing hardly influences enhancement factor of GaN nanowire array, while potential distributions are affected by cathode-anode spacing to a certain extent.

MILLIMETER-WAVELENGTH RELATIVISTIC MAGNETRON: PROBLEMS OF MICROWAVE POWER EXTRACTION

The relativistic magnetrons operating at millimeter wavelengths demonstrate problems with microwave power extraction, both in the radial and in axial direction. The preferred axial extraction concept can be implemented ei-ther as ‘diffractional output’ or via introduction of additional resonant elements into the output waveguide. In this paper several solutions for axial-directed extraction are discussed, including circular ring ‘antennas’ at the end of the anode-cathode space, and resonance-length rods at the faces of the anode-block cavities. These have allowed increasing the power extraction efficiency by a factor of 101 to 102.

Hybrid BaTiO3/SiNx/AlGaN/GaN lateral Schottky barrier diodes with low turn-on and high breakdown performance

In this Letter, we demonstrate hybrid GaN lateral Schottky barrier diodes with enhanced breakdown characteristics and a low turn-on voltage. These diodes incorporate a lateral Schottky barrier in combination with a high permittivity material beneath the field plate, enabling high average breakdown fields and a low turn-on voltage. Average electric fields up to 2.38 MV/cm were achieved for devices with an anode–cathode spacing of 4 μm, while maintaining with a turn-on voltage of 0.48 V. In contrast, SiNx/AlGaN/GaN control lateral Schottky diodes displayed an average breakdown field of ∼0.7 MV/cm for devices with similar dimensions with a turn-on voltage of 0.46 V. The use of a high-permittivity dielectric can more effectively utilize the high breakdown fields in wide bandgap materials by proper management of the electric field. This demonstration provides an innovative way to integrate high-permittivity materials with GaN lateral devices for improved breakdown and resistance characteristics.

Numerical Optimization of Electrodeposition Thickness Uniformity with Respect to the Layout of Anode and Cathode

Electrodeposition has been widely used in many fields due to its unique advantages, especially in the mold manufacturing of transfer printing by roll-to-roll. Electrodeposition thickness uniformity becomes prominent when surface areas to be electrodeposited are large and have strict geometrical accuracy requirements as well. For achieving uniformity of deposition thickness, the available methods range from adjusting anode-cathode spacing, the surface areas of anode and cathode, and partially shielded cathode. The three methods have been proved to be easy to implement and effective in practice. However, determining the optimized layouts of anode and cathode poses a challenge. This paper illustrates how to optimize the layout for thickness uniformity for solving a real electrodeposition problem encountered in electroplating nickel on a large copper mold with its length and width of 600 mm × 600 mm. Combined application of the three methods to optimize the deposition thickness uniformity can achieve better results than the single method. The results of simulation and electrodeposition tests show that the ratio of sideline thickness to central line thickness decreased from 1.16 to less than about 1.05. The optimization was performed through solving mathematical equations of electric charge transport plus boundary conditions. This paper also explains the influences of the layout of anode and cathode on deposition thickness uniformity from the perspective of electric current distribution and electric field distribution, which would help designers of electrodeposition processes develop an intuitive feeling about the interplay among the layout parameters.

Demonstration of Al0.85Ga0.15N Schottky barrier diode with > 3 kV breakdown voltage and the reverse leakage currents formation mechanism analysis

In this paper, high performance lateral Al0.85Ga0.15N Schottky barrier diodes (SBDs) with a field-plate structure and a heavily doped GaN cap layer in the Ohmic region are demonstrated. Employing Al0.85Ga0.15N rather than AlN for the channel layer effectively reconciles the tension between electron mobility and dopant activation caused by AlN material dilemma. The lateral Al0.85Ga0.15N SBD with an anode-cathode spacing (LAC) of 20 μm achieves a specific on-resistance (Ron,sp) of 0.19 Ω·cm2 and a breakdown voltage exceeding 3 kV, rendering Baliga's power figure of merit of more than 47 MW/cm2, which is the highest value among all AlN- or Al-rich-AlGaN (Al ratio > 70%)-based diodes. Reverse leakage current mechanisms of Al0.85Ga0.15N SBDs are dominated by a variable range of hopping and trap-assisted space charge-limited conduction before destructive breakdown occurs in the field-plate oxide, which are verified by analyzing the reverse leakage characteristics. Combined with the stable performance with temperature up to 275 °C, the Al0.85Ga0.15N SBD shows great promise for next--generation high power electronics applications after further resolving the Ohmic and electron mobility issues.

Towards the Stability of Low-Temperature Aluminum Electrolysis

The results of several different tests related to the low-temperature aluminum electrolysis were considered in this work. The role of mass transfer processes in the anode-cathode space was recommended to be significant during electrolysis in the low-temperature KF-AlF3 and NaF-AlF3-based melts. The stationary polarization and voltammetry methods were applied in order to study the kinetics of the electrode processes on the carbon and metal electrodes in the KF-AlF3-Al2O3 melts and to select the electrolysis parameters. The schemes of electrode processes were suggested on the basis of electrochemical tests, the flows of substances in the anode-cathode distance were analyzed and the main reasons of the cathode current efficiency decrease during the low-temperature electrolysis in the KF-AlF3-Al2O3 and KF-NaF-AlF3-Al2O3 melts were discussed. It was revealed that the cathode current density should not exceed 0.4–0.55 A cm−2 during the electrolysis at 750 °C–800 °C.

2.7-kV AlGaN/GaN Schottky barrier diode on silicon substrate with recessed-anode structure

In this paper, we demonstrate high-performance lateral AlGaN/GaN Schottky barrier diodes (SBD) on Si substrate with a recessed-anode structure. The optimized rapid etch process provides results in improving etching quality with a 0.26-nm roughness of the anode recessed surface. By using the high work function metal Pt as the Schottky electrode, a low turn-on voltage of 0.71 V is obtained with a high uniformity of ±0.023 V for 40 devices. Supported by the flat anode recess surface and related field plate design, the SBD device with the anode–cathode spacing of 15 μm show the specific on-resistance (Ron,sp) of 1.53 mΩ·cm2 only, the physical breakdown voltage can reach 1678 V with a high power figure-of-merit (P-FOM) of 1840 MW/cm2. For the SBD device with the anode–cathode spacing of 30 μm, the physical breakdown voltage can be as high as 2705 V and the power FOM is 2217 MW/cm2.

Experimental and mathematical analysis of electroformed rotating cone electrode

In this study, we present results of a mathematical model in which the governing equations of electroforming process were solved using a robust finite element solver (COMSOL Multiphysics). The effects of different parameters including applied current density, solution electrical conductivity, electrode spacing, and anode height on the copper electroforming process have been investigated. An electroforming experiment using copper electroforming cell was conducted to verify the developed model. The obtained results show that by increasing the applied current density, the electroforming process takes place faster, thereby resulting in a higher thickness of the electroformed layer. In addition, higher applied current density led to non-uniformity of the coated layer. It was revealed that by increasing electrolytic conductivity from 5 to 20 S/m, the electroformed layer became thicker. By considering three different anode heights, it was found that if the cathode and anode are the same height, the process will be more effective. Finally, it was concluded that there is an optimum value of anode-cathode spacing: above it, energy consumption and plating time are high; while below it, the resultant layer is non-uniform. The present study demonstrates that the developed model can accurately capture the physics of electroforming with a reasonable computational time.

A Breakdown Enhanced AlGaN/GaN Schottky Barrier Diode with the T-Anode Position Deep into the Bottom Buffer Layer.

In this paper, an AlGaN/GaN Schottky barrier diode (SBD) with the T-anode located deep into the bottom buffer layer in combination with field plates (TAI-BBF FPs SBD) is proposed. The electrical characteristics of the proposed structure and the conventional AlGaN/GaN SBD with gated edge termination (GET SBD) were simulated and compared using a Technology Computer Aided Design (TCAD) tool. The results proved that the breakdown voltage (VBK) in the proposed structure was tremendously improved when compared to the GET SBD. This enhancement is attributed to the suppression of the anode tunneling current by the T-anode and the redistribution of the electric field in the anode–cathode region induced by the field plates (FPs). Moreover, the T-anode had a negligible effect on the two-dimensional electron gas (2DEG) in the channel layer, so there is no deterioration in the forward characteristics. After being optimized, the proposed structure exhibited a low turn-on voltage (VT) of 0.53 V and a specific on-resistance (RON,sp) of 0.32 mΩ·cm2, which was similar to the GET SBD. Meanwhile, the TAI-BBF FP SBD with an anode-cathode spacing of 5 μm achieved a VBK of 1252 V, which was enhanced almost six times compared to the GET SBD with a VBK of 213 V.

A Comparison Study of Diode-String ESD Clamps for CMOS Input Protection

Based on 2-D device simulations and mixed-mode transient simulations, DC and transient discharge characteristics of a usual diode string utilizing a standard CMOS process, and a diode string utilizing a triple-well CMOS process, which can serve as an essential VDD-VSS clamp device for CMOS input ESD protection were compared. Transient discharge characteristics including peak voltages developed across gates oxides of transistors in input buffers, lattice heating inside ESD protection devices, and ratios of discharge current components at its peak inside the diode-string clamp were compared. DC standby current levels added per each input pad structure, which are the critical parameters determining usefulness of the devices, were also compared. We showed that the diode-string devices in comparison can serve successfully as a VDD-VSS clamp device for ESD protection by virtue of the dominant pnpn thyristor-related conduction mechanisms. Optimization of design parameters including anode-cathode contact spacing in each diode in the string, device width of the diode string, and number of diodes in the diode string was performed to present transient discharge and DC characteristics of some recommendable design examples, which can serve as a guideline in designing diode-string clamp devices.

Impact of flow recirculation and anode dimensions on performance of a large scale microbial fuel cell

Many design and operational parameters that can impact power generation in microbial fuel cells (MFCs), such as flow over the electrodes, can only be effectively examined in larger-scale systems. A maximum power density of 0.101 ± 0.006 W m−2 (0.74 ± 0.05 W m−3) was obtained in an 85-L MFC with graphite fiber brushes (5.1 cm diameter, 61 cm long) and flat air cathode (0.62 m2 exposed area; anode-cathode spacing of 1.3 cm) in batch mode. Recirculating the anolyte diagonally through the chamber (entering the top right side of the reactor and exiting the bottom left side) further improved performance by 17% to 0.118 ± 0.006 W m−2, at a hydraulic retention time (HRT) of 22 min (3.9 L min−1), compared to static flow conditions. This power density was also higher than that obtained with parallel flow through the chamber (more evenly distributed using a manifold; 0.109 ± 0.009 W m−2). Reducing the diameter of the anode brushes from 5.1 cm to 2.5 cm did not improve the anode performance. These results demonstrate the importance of electrode spacing and hydraulic flow on large-scale MFC performance.

Preparation of Tungsten Nanoparticles from Spent Tungsten Carbide by Molten Salt Electrolysis

Tungsten carbide was used as sacrificial anode in NaCl-KCl molten salt to form tungsten ion dissolution, with increasing anode potential of the charge transfer resistance decreases, tungsten ions in molten salt of average valence of +6, reduction of tungsten ion for the reversible behavior of diffusion control. Increasing the cathode distance and changing the cathode position can effectively avoid the pollution of the anode residual carbon to the tungsten powder of cathode products. The particle size of tungsten powder increases with the increase of cathode current density. When the cathode current density is 0.01Acm-2, anode potential 1.2V and anode cathode spacing 45mm, the particle size of tungsten powder is about 50nm.

Field-Plated Lateral β-Ga2O3 Schottky Barrier Diode with High Reverse Blocking Voltage of More Than 3 kV and High DC Power Figure-of-Merit of 500 MW/cm2

In this letter, we report on demonstrating high-performance field-plated lateral <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Schottky barrier diode (SBD) on a sapphire substrate with a reverse blocking voltage of more than 3 kV and a low dc specific ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{{ \mathrm{\scriptscriptstyle ON}, \text {sp}}}$ </tex-math></inline-formula> ) of 24.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an anode–cathode spacing ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24~\mu \text{m}$ </tex-math></inline-formula> . To the best of our knowledge, this lateral breakdown voltage (BV) >3 kV with dc power figure-of-merit (FOM) >370 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is the highest BV achieved among all the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBDs. Meanwhile, lateral <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBD with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}} = \text {16}\,\,\mu \text{m}$ </tex-math></inline-formula> also demonstrates a high BV of 2.25 kV and low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{{ \mathrm{\scriptscriptstyle ON}, \text {sp}}} = \text {10.2}\,\,\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , yielding a record high dc power FOM of 500 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Combining with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> high-current ON/OFF ratio, 1.15-eV Schottky barrier height and 1.25 ideality factor, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBD with field-plate structure shows its great promise for power electronics applications.

Quasi-monoenergetic ultrashort microbunch electron source

By combining static electric and laser fields for generation of field-emitted electrons, it is possible to generate a quasi-monoenergetic train of electron microbunches by controlling the anode–cathode spacing such that the time of flight of the electrons becomes independent of the laser field. Such quasi-monoenergetic microbunches with pulse durations that are a fraction of the laser wavelength would be ideal for radiation sources as well as compact accelerators.

H2 production in membraneless bioelectrochemical cells with optimized architecture: The effect of cathode surface area and electrode distance

In this work we report on the hydrogen production capacity of single-chamber microbial electrohydrogenesis cell (MEC) with optimized design characteristics, in particular cathode surface area and anode-cathode spacing using acetate as substrate. The results showed that the maximal H2 production rates and best energetic performances could be obtained using the smallest, 71 cm2 stainless steel cathode and 4 cm electrode distances, employing a 60 cm2 bioanode. Cyclic voltammetric analysis was employed to investigate the dominant electron transfer mechanism of the architecturally optimized system.

Investigation on multi-frequency oscillations in InGaAs planar Gunn diode with multiple anode-cathode spacings

Abstract Current oscillations in an AlGaAs/InGaAs/AlGaAs-based two-dimensional electron gas (2DEG)-based hetero-structure have been investigated by means of semiconductor device simulation software SILVACO, with an interest on the charge domain formation at large biases. Single-frequency oscillations are generated in planar Gunn diodes with uniform anode and cathode contacts. The oscillation frequency reduces as the applied bias voltage increases. We show that it is possible to create multiple, independent charge domains in a novel Gunn diode structure with designed multiple anode-cathode spacings. This enables simultaneous generation of multiple frequency oscillations in a single planar device, in contrast to traditional vertical Gunn diodes where only single-frequency oscillations can be achieved. More interestingly, frequency mixing in multiple-channel configured Gunn diodes appeared. This proof-of-concept opens up the possibility for realizing compact self-oscillating mixer at millimeter-wave applications.

Simulation investigation of multiple domain observed in In0.23Ga0.77As planar Gunn diode

A numerical study for an AlGaAs/InGaAs-based quantum well structure planar Gunn diodes was performed by initially proposing imperfect metallic contacts that can introduce multiple anode–cathode spacings caused by etching process during the fabrication. Through Fast Fourier transform (FFT) algorithm, the result reveals that, at moderate bias voltage above the threshold, multi-channel planar Gunn diode exhibits multiple oscillations which were consistent with experimental observation due to non-uniformity of contact terminal. A downwards shift of oscillation frequency by varying the applied voltage across terminal was observed due to Gunn effect. The finding may be utilized not only to generate multiple millimeter wave or even terahertz signal sources on single chip, but also to achieve frequency tunability through tuning the applied bias voltage.

Evaluation of Carbon Foams and Membranes As the Cathode in Non-Flow Zinc Bromine Energy Storage Cells to Mitigating Liquid Bromine Convection

Zinc Bromine (Zn-Br2) secondary batteries have been extensively studied as a low cost, fully rechargeable, high density energy storage system. However, large scale and widespread commercial implementation of this battery technology has been retarded due to two key limitations [1]: i) self discharging of the cell due to Br2 (l) convection and diffusion through the liquid electrolyte towards the Zn anode. ii) shorting due to zinc dendrite formation after multiple cycles of the cell. Zn-Br2 flow-cells alleviate these limitations by adding Br2 (l) complexing agents, and flowing electrolyte to improve Zn plating, [2] respectively, at the cost of cell resistance, battery efficiency, size, and capital costs. In this work, we address the Br2 (l) convection issue by designing a simple, low cost non-flow Zn-Br2 cell without the use of expensive complexing agents, via modification of the bromine cathodic electrode material composition and geometry. The Zn dendrite issue is addressed elsewhere [3]. We take advantage of the difference in density of the Br2 (l) (~3.1g/cc) and a 2M ZnBr2 electrolyte (~1.5 g/cc) to contain the liquid bromine below the cathode while cycling the cell. First, we demonstrate a thin membrane electrode composed of carbon black/graphite/PVDF having a density of 1.88 g/cc. The densities are matched such that the membrane electrode floats at the interface between the dense Br2 (l) and the electrolyte. During charging bromine forms and drops below the semi-porous membrane electrode while the cathode rises, reducing the anode-cathode spacing and, hence, the cell resistance. During discharge the Br2 (l) is prevented from convecting through the electrolyte by the physical membrane barrier, while allowing a small degree of diffusion. Second, we also demonstrate the use of highly conductive carbon foam bromine electrode, which selectively traps the non-polar Br2 (l) in its highly porous structure and thus addresses the bromine convection issue. The electrochemical characteristics of the non-flow Zn-Br2 cell based on both these bromine electrodes designs are discussed in terms of cell resistance, specific capacity, energy and coulombic efficiencies, energy storage capability and cycle life. The physical properties of the membrane and foam electrodes are analyzed using SEM, AFM and XRD.