Showing papers on "Field electron emission published in 1987"

Electrical conduction of purified cyclohexane in a divergent electric field

Abstract: The mechanisms of field emission and field ionisation are indeed operative but with very drastic conditions i.e., highly purified liquid and very sharp tips.

Field emission vacuum devices

Abstract: A vacuum valve device comprises a substrate on which is formed an updoped silicon layer from which a silicon dioxide layer is grown. First, second and third electrode structures are formed on the silicon dioxide layer by depositing a metallic layer and etching away unwanted portions of the layer. The first electrode structure has a pointed end and/or a sharp edge and/or is formed of low work function material so that, when a suitable voltage is applied between the first and third electrode structures, electrons are emitted from the first electrode structure due to a field emission process. Electrons therefore flow from the first to the third electrode structure substantially parallel to the substrate. The second electrode structure acts as a control electrode.

Electron trap center generation due to hole trapping in SiO2 under Fowler–Nordheim tunneling stress

Abstract: The relation between generation of neutral electron trap centers and hole trapping in thermally grown SiO2 under Fowler–Nordheim tunneling stress has been investigated. The experimental results show that the density of neutral electron trap centers is proportional to the density of trapped holes under Fowler–Nordheim tunneling stress with various electric fields and the total number of electrons injected into the oxide. The generation mechanism is explained by a model based on strained bonds.

Semiconductor device having a cold cathode

Abstract: In a semiconductor cathode, the electron-emitting part of a pn junction is provided in the tip of a projecting portion of the semiconductor surface which is situated within an opening in an insulating layer on which an acceleration electrode is disposed. Due to the increased electric field near the tip, a reduction of the work function (Schottky effect) is obtained. As a result, cathodes can be realized in which a material reducing the work function, such as caesium, may be either dispensed with or replaced, if required, by another material, which causes lower work function, but is less volatile. The field strength remains so low that no field emission occurs and serarate cathodes can be driven individually, which is favorable for applications in electron microscopy and electron lithography.

Cherenkov free electron laser operation from 375 to 1000 μm

Abstract: The first time operation of a far infrared Cherenkov free electron laser is reported. Continuously voltage tunable radiation from 375 μm to 1 mm wavelengths has been produced from an electron beam driven slow wave supporting structure consisting of two parallel metal plates covered with a thin dielectric film. A cold cathode, field emission diode was used to generate the electron beam of density ∼ 1012 cm−3 with a beam energy that varied between 2 < γ < 3. The measured wavelength agrees well with the wavelength for which the TM01 mode phase velocity is synchronous with the electron beam velocity. The measured power output of the device indicates the production of 10 kW at 400 μm, 75 kW at 500 μm and 200 kW at 1 mm wavelengths, yielding conversion efficiencies up to 0.2%.

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

Abstract: 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 e-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/cm/sup 2/ with leakage in the ..mu..A 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.

Schottky barrier junctions of hydrogenated amorphous silicon‐germanium alloys

Abstract: The current‐transport mechanisms of amorphous Schottky barrier junctions are investigated using both undoped and phosphorus‐doped hydrogenated amorphous silicon‐germanium alloys (a‐Si1−xGex: H) fabricated by rf glow discharges in diode‐ and triode‐reactor systems with and without the dilution of hydrogens. From the experimental results, the forward‐current mechanisms for amorphous Schottky barrier junctions are generally discussed and classified into three categories: (1) field emission, (2) diffusion‐field emission, and (3) diffusion. The diffusion‐field‐emission model (multistep tunneling through a part of the Schottky barrier) used for the first time in this work can interpret the current‐voltage characteristics and their temperature dependence on amorphous Schottky barrier junctions to a high degree. Moreover, the flow chart proposed here classifies the material quality of amorphous semiconductors according to their junction properties. We concluded that one of the better methods to fabricate high‐qua...

Fowler-Nordheim tunneling in implanted MOS devices

Abstract: Current-voltage curves of thermally oxidized silicon with polysilicon gates have been measured and interpreted with the Fowler-Nordheim model of tunneling of electrons through the energy barrier at one of the interfaces of the dielectric. The measurements were done on wafers which have been implanted with various doses As+ ions. From the F-N curves the barrier height and the pre-exponential term have been extracted. The barrier height and the pre-exponential term decrease substantially if the dose was larger than 1014/cm2. Although the Fowler-Nordheim plots shifted and had different slopes, it is shown that the expression following from the model is still applicable. It was verified whether the current density was homogeneous over the area. When however the As+ implantation was performed with the gate as a mask, the Fowler-Nordheim curves turned out to be kinked. This kinked curve suggests that it is composed of two straight lines. The steep part of the curve is thought to correspond to the unimplanted region under the gate and the flat part to the implanted region at the side-wall. This phenomenon can have important implications for self-aligned source and drain implantation techniques. The lowering of the barrier and the pre-exponential term by implantation is interpreted in terms of trap-assisted tunneling.

Electrical conduction mechanism in semi‐insulating polycrystalline silicon films

Abstract: A scanning Auger microprobe (SAM) has been used to measure the equipotential lines and the potential profile across semi‐insulating polycrystalline silicon (SIPOS) film structures, and the electron beam parameters required to prevent charging effects and to minimize beam current relative to sample current have been determined. The conduction process in these SIPOS films was related to Frenkel generation of carriers. This field‐enhanced emission from a localized state results in a field‐dependent current which is added to an ohmic current. The potential profiles obtained with the SAM are in reasonable agreement with those predicted by this model. The effects of potential screening by charge at the SiO2‐SIPOS interface are discussed and related to location‐dependent variations in the potential profile. A zero‐field conductivity of 1.4×10−6 (Ω cm)−1 was obtained for our films.

Physics of Resonant Tunneling in Semiconductors

Abstract: The concept of tunneling through a potential barrier lies at the core of quantum mechanics, and its experimental observation is a manifestation of the wave-like behavior of matter. Since the early days of quantum mechanics, tunneling models have been used to explain fundamental experiments such as the ionization of hydrogen by an electric field and the emission of alpha particles by heavy nuclei. The idea of tunneling was also incorporated very soon into solid-state physics, and, thus, was used in 1928 by Fowler and Nordheim to describe field emission from metals, and by Zener in 1,934 to account for internal field emission in semiconductors.

The conduction properties of SIPOS

Abstract: The electrical characteristics of SIPOS-silicon heterojunctions are presented. The current-voltage characteristics as a function of temperature of SIPOS-silicon heterojunctions, with the SIPOS having different oxygen concentrations from 5.2 to 27.9 at.% and different film thicknesses, from 1200 to 5000 A, are reported. At temperatures above room temperature, the thermionic emission (TE) theory satisfactorily describes the carrier transport through the SIPOS films. At lower temperatures, a competing conduction mechanism comes into play which involves significant tunneling and the carrier transport is governed by thermionic field emission (TFE). Tarng's model, slightly modified to take account of the different device structure used, is presented which enables the current density-voltage characteristics of all four batches to be accurately predicted over the entire measured temperature range of each batch. Material parameters such as grain size, inter-grain barrier heights for electrons and holes, and the effective Richardson's constant, can be derived from the model and the measured current density-voltage temperature data. SIPOS stands for “semi-insulating polycrystalline silicon”.

Fowler-Nordheim tunneling and conduction-band discontinuity in GaAs/GaAlAs high electron mobility transistor structures

Abstract: Oscillatory structure is observed in the dI/dV and d2I/dV2 characteristics of conventional GaAs/GaAlAs high electron mobility transistor samples at liquid‐helium temperature, which can be explained using a Fowler–Nordheim tunneling theory. The position of the oscillations allows a determination of the conduction‐band discontinuity, and the depth of the deep donor levels in the GaAlAs for high aluminum concentrations. The fit of the data gives a value of ΔEc/ΔEg=0.61±0.04 for aluminum concentration 30, 36, and 40%. The deep donor level in the GaAlAs was determined to be 130 meV below the conduction band.

Caractéristiques énergétiques de cathodes à micropointes à émission de champ

Abstract: We present in this paper the characteristics of field emission cathodes consisting of a large number of micron-sized tips, arranged at the surface of a component and realized by using thin film technology. Theoretical results concerning the current-voltage characteristics are presented, as well as the measured properties of cathodes prepared in our laboratory: a current of about 100 μA is emitted at 60 V by a 1 mm 2 surface comprising 10 000 microtips; the emitting area is about 10 A 2 per tip and the field about 5×10 9 Vm ―1 . We consider next the energy distribution of the emitted electrons: the expected theoretical results and the experimental methods are presented. The experiment exhibits a voltage drop at the interface between the tips and the substrate on which they are deposited (depending on the nature of the substrate). The observation of a large energetic spread (2 eV) is correlated to this parasitic phenomenon. As for the cathodes which exhibit a low interface resistance, we measured an energetic spread of 0.9 eV, at a current of 100 μA and an energy of 60 eV; it appears that improvements in this field depend on the control of the interface. The emission of high currents, even at a low temperature (T>100 K), makes it possible to use such cathodes as cold electron sources providing intense beams of low-energy electrons Caracteristiques de cathodes a emission de champ comprenant un grand nombre de pointes de dimensions voisines du micron, regroupees a la surface d'un composant et realisees par les techniques de la microelectronique

Field emission cathode

Abstract: PURPOSE:To make it possible to emit a low energy electron beam without reducing the velocity of the electron beam and at low field emission voltage, by keeping the distance between a cathode and an anode small using a specified work method. CONSTITUTION:It is possible to decrease a field emission voltage required for obtaining the density of a constant field emission current by shortening distance between a cathode 1 and an anode 9. A tungsten single crystal wire 6 is welded on the top position of a V-shaped welded tungsten filament 5, and fixed on an anode cylinder 10 through a support stem 7, insulation glass 8 and a pressure ring 11. A platinum disc 9 with a small hole in its center is placed at the aperture part of the anode cylinder 10. A minute distance is formed by electropolishing between plate 9 and cathode 1 after polishing wire 6, under such a condition that wire 6 is isolated from the edge of the hole of plate 9. Because of this distance, the electron beam with low energy can be emitted at a low voltage.

Field emission studies in superconducting cavities

Abstract: Ctirrent experience with l-cell superconducting (SC) cavities prepared from the highest thermal conductivity material by the best availabie techniques shows that the dominant limitation to achieving high accelerating gradients is field emission loading Emitters dre studiec using high purity Nb single-cell, 1500 MHz elliptical cavities equipped with a new thermomztry system (654 sensors) capable of scanning tne entire surface of the cavity within a few seconds 3peration of this rapid temperature mapping system in superfluid He is a necessary advance for high field study over customarily used subcooled He diagnostics Emitter properties are determined by comparison with calculations of field emitted electron trajectories and their associated power deposition

Stable field emission of electrons from liquid metal

Abstract: Experiments were carried out on the field emission of electrons from Ga-In-Sn liquid alloy and a stable DC emission was observed in addition to the pulse explosion already reported. The emission stability depended on the apex radius of the tungsten tip to which the liquid metal adhered to form a cone. When we used an emitter with an apex radius smaller than 0.5 µm, Fowler-Nordheim plots in the DC mode were heavily influenced by the adhesive state at its surface.

The electrical properties of magnetite-loaded polyethylene composites

Abstract: Magnetite–polyethylene composites containing various concentrations of magnetite have been prepared and their electrical properties have been investigated. The electrical resistivities of the specimens were studied as function of filler concentration and temperature. The current density-electric field characteristic and the current variation with time were measured. The thermionic and field emission models provide good explanations for the electrical conduction in the specimens, and space-charge-limited conduction is discussed based on the results.

Hydrogenation of boron acceptor in silicon during electron injection by Fowler−Nordheim tunneling

Abstract: Hydrogenation of the boron acceptor in silicon is observed during Fowler–Nordheim tunneling injection of electrons for the first time. Experiment is also presented which shows that the existence of free holes at the silicon surface is not important for boron hydrogenation.

Spherical oscillator gauge with field emission cold cathode

Abstract: The spherical oscillator gauge with field emission cold cathode has been successfully developed on the basis of many experiments and theoretical calculations with a computer. It basically keeps the advantage of the high sensitivity (K=15 Pa−1) of an oscillator gauge. The incident electrons move in oscillatory mode and effectively restrain their trajectory. The resulting ion beam is focused and collected. Successfully applying the field emission code cathode to the spherical oscillator gauge is the key step of solving the problem in extremely high‐vacuum measurement.

Field emission type scanning electron microscope and similar apparatus

Abstract: PURPOSE:To enable complete removal of FE noise by detecting a portion of separated electron beam as a information signal through an energy filter while focusing the other portion of the electron beam and irradiating onto a sample to take out an information signal S from a sample then obtaining a ratio between two detection signals as a sample information signal after noise correction. CONSTITUTION:Only such electron beam 21 as having specific energy width in an electron beam 11 projected from FE electron gun 1 will pass through an iris 4 while the remaining electron beam 22 will impinge against the iris 4 to emit secondary electrons 14 which are detected as a detection signal M by means of a detector 8. The electron beam 21 is focused through an objective lens 5 onto the sample 7 face. Secondary electrons 15 emitted from the surface of the sample 7 are detected by means of a detector 9. Here, FE noise of signal S detected by means of the detector 9, is corrected by employing the signal M detected by means of the detector 8 for obtaining S/M by means of a correction circuit 10 which is employed as a corrected sample information signal. Since the electron beam 22 impinging against the iris 4 and the electron beam 21 irradiating onto the sample are emitted from same position of a field radiation cathode, same FE noise is detected and corrected resulting in a complete correction.