Array Cathode Research Articles

Vacuum field emission from a Si-TaSi2 semiconductor-metal eutectic composite

We report on measurements of vacuum field emission from ungated field emission cathode arrays fabricated from Si-TaSi2 eutectic composite wafers. The Si-TaSi2 material is an ideal candidate for large area field emission array cathodes due to the large density of TaSi2 fibers incorporated into the Si matrix, the high melting point of the TaSi2 material, the ease with which single-crystal large diameter (2.5 cm) material can be fabricated, and the promise of integrability of the field emission array with conventional Si technology through the use of epitaxial Si layers grown on the cathode backplane.

GaAs field emitter arrays

The authors report on technological peculiarities of fabrication of large-area gallium arsenide multipoint cathodes. The topics discussed are fabrication methods, noise characteristics and uniformity of emission, and lifetime and degradation of semiconductor multipoint cathodes. The results of the emission characteristics investigation are described. Expressions for the noise power spectral density function and the time constant of degradation for such cathode arrays are obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A multiple-cathode arc-discharge plasma source

A plasma source for obtaining a 1-cm length of high-fractional ionized plasmas with electron densities in the range of 10/sup 15/-10/sup 17/ cm/sup -3/ is described. The source consists of a capacitive discharge between a metal anode and an array of small metal cathodes embedded in epoxy, each with a current-limiting resistor. The effect is to have an array of sources which merge into each other, producing the plasma as a whole. The design and performance of the plasma source are presented. The entire system consists of the main electrode and shielding structures, the preionization circuit, and the main discharge circuit. Each of these components is described and the operating parameters and results are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Emission properties of Spindt-type cold cathodes with different emission cone material

Emission properties of thin film field emission array cathodes with molybdenum, hafnium, diamond-like carbon, and lanthanum hexaboride cones were investigated. Each array consisted of 681 holes and cones (microcells), spaced on 10- mu m centers on a silicon substrate. At work functions of more than 5 eV carbon cones had the lowest operating voltage-less than 50 V-due to the high value of the form factor of the cones, which have a sharp ribbed pyramidal shape. However, high current density was not achieved with such cathodes because of the low conductance of this type of diamond-like carbon. Different approaches to increase transconductance provided by one cell are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer simulation of micro-triode performance

A computer code for the simulation of electron beams from field emitter cathodes has been applied to typical micro-cathode configurations. The program (SPEED) solves Poisson's equation using relaxation techniques on a rectangular mesh for triodes with arbitrary, axisymmetric electrode shapes. It employs the Fowler-Nordheim law at emitter surfaces to determine the emission current density distribution. The calculations are part of Spindt cathode arrays for use in fast oscillography. By varying tip radius and work function, one can reproduce the measured I-V curves of prototype arrays. The authors then compare calculated brightness with experimental results using Spindt arrays in a 1.0-kV cathode ray tube.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field-emitter arrays for vacuum microelectronics

An ongoing program on microfabricated field-emitter arrays has produced a gated field-emitter tip structure with submicrometer dimensions and techniques for fabricating emitter arrays with tip packaging densities of up to 1.5*10/sup 7/ tips/cm/sup 2/. Arrays have been fabricated over areas varying from a few micrometers up to 13 cm in diameter. Very small overall emitter size, materials selection, and rigorous emitter-tip processing procedures have contributed to reducing the potential required for field emission to tens of volts. Emission current densities of up to 100 A/cm/sup 2/ have been achieved with small arrays of tips, and 100-mA total emission is commonly produced with arrays 1 mm in diameter containing 10000 tips. Transconductances of 5.0 mu S per tip have been demonstrated, indicating that 50 S/cm/sup 2/ should be achievable with tip densities of 10/sup 7/ tips/cm/sup 2/. Details of the cathode arrays and a variety of performance characteristics are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-voltage field emission from tungsten fiber arrays in a stabilized zirconia matrix

Field emitter array cathodes were fabricated from unidirectionally solidified composites of tungsten fibers in an insulating yttria-stabilized-zirconia (YSZ) matrix. A close-spaced molybdenum gate film (extractor) was formed utilizing c-beam evaporation of alumina as an insulator, which was overlayed by the molybdenum extractor. The high resistivity of the composite matrix coupled with the alumina insulator resulted in low leakage current and permitted dc operation of the device. Emission testing demonstrated current densities of 1–5 A/cm2 with leakage in the μA range for applied potentials of 125–200 V. Variation of emitter tip geometries from hemispheres to right circular cylinders to pointed cones produced increases in emission consistent with reduced tip radii.

Finite element analysis of current pathways with implanted electrodes

A technique for numerical solution to complex electric field distribution problems has been devised. The specific application for which it was developed is the analysis of current density and isopotential line spacing from implanted neuro stimulation electrodes. Three configurations of cerebellar stimulation electrodes in clinical use were studied for current spread to regions distant from the cerebellum using a planar model of the human head, neck, and upper torso in mid-saggital section. It was found that an array of cathodes on the superior cerebellar surface and an array of anodes on the inferior cerebellar surface causes significant current spread to the brainstem, a prediction confirmed by clinical observation in patients with previously implanted electrodes of this configuration. Results modelling other electrode configurations are also presented, along with a study of the effects of possible inaccuracies in available impedance data for neural tissue.

The application of thin-film field-emission cathodes to electronic tubes

The emission properties of arrays of field emission cathodes, fabricated using thin film technology and microlithography are reviewed. It is argued that from the standpoint of life, stability, energy distribution, current fluctuation noise, and average current density over the array, these cathodes have demonstrated sufficient promise to justify their trial use in a range of electronic devices. Specific applications and possible problem areas are also discussed.

Glow discharge with an array of hollow cathodes

Glow discharge with an array of hollow cathodes

The spatial correlation of fluctuations of the blood flow in forearm skin.

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.

Transient and optical studies of free convective mass transfer during electrodeposition at single and multi-cylinder cathodes

A recent paper [1 ] described measurements of free convective mass transfer using the limiting electrolysis current technique at vertical arrays of horizontal cylindrical cathodes. The distribution of mass transfer up an array was measured and for any particular cylinder the current was found to depend on the concentration and velocity fields rising from cylinders immediately below. The purpose of the present communication is to present further visual evidence of the existence and properties of the convective plumes above cylinders in free convection and also to describe simple transient experiments demonstrating the convective interaction between cylinders. In the experiments to be described, the apparatus was basically similar to that previously described except that for the optical experiments the electrolyte was contained in a tank fitted with plane glass sides, the tank being incorporated into a conventional Schlieren optical system which allowed photography of the convective phenomena using a 35 mm camera.

The Generation and Diagnosis of Pulsed Relativistic Electron Beams above 1010 Watts

A review of the several approaches to the generation of intense electron streams in the megavolt energy regime is presented. The techniques used in the diagnosis of the 30,000 ampere, 3 Mev beam from a gas insulated coaxial system with a characteristic pulse length of 25 nanoseconds are discussed. The general features of such a stream drifting under self-focused conditions are presented and the results compared with the theory of such an idealized beam. The results of work conducted with cathode arrays of varying geometry are discussed. In particular, the dynamics of 20,000 ampere streams at 2 Mev, from arrays with 1 ? n ? 4, are presented. Based on these data, a prognosis is made for the limitations of future high peak power electron accelerators at energies in the 10 Mev range.

High-current injection into liquid hexane using field emitters

Currents of up to 05 mA have been injected into commercial grade hexane, using a simple array of field-emitting razor-edge cathodes. The electrical power input resulted in bulk liquid motion, which aided charge transfer from the injection region. The magnitude of the resulting conduction current was found to depend on the hydrodynamic impedance of the test arrangement. The ability to inject large currents into liquid dielectrics, non-destructively, opens up the possibility of a new range of high-voltage devices.