RU2654522C1 - Method for increasing current density and degradation resistance of auto-emission codes on silicon plates - Google Patents

Abstract

FIELD: electronics.

SUBSTANCE: invention relates to electronic engineering and can be used in the manufacture of light-indicating technology products and emission electronics based on field emission of a matrix of multi-point carbon emitters on single-crystal silicon plates. Production of a matrix of a multi-tip auto-emission cathode is performed on a single-crystal silicon plate of the hole-type conductivity in the plasma of a microwave gas discharge by precipitation from vapors of carbonaceous substances, for example ethanol, carbon coatings on silicon columnar nanostructures that are up to several tens of nanometers in height. Emission layers with a low transverse electric conductivity are used to increase the densities of field emission currents.

EFFECT: technical result is an increase in the stability and efficiency of field emission.

1 cl, 2 dwg

Description

Technical field

The invention relates to the field of electronic technology and can be used in the manufacture of products of light-indicating equipment and emission electronics based on field emission from composite nanodiamond graphite structures.

State of the art

Known multi-edge field emission cathodes in which the matrix is formed by layers of woven fabric impregnated with a high-temperature binder, for example pyrocarbon [1].

In the manufacture of the matrix, all fabric threads are oriented at an acute angle to the direction of electron emission, and the working surface, which is an emitter of electrons and consists of many fibers forming fibers, is polished.

However, during the operation of such autocathodes in a technical vacuum, the binder is destroyed by ion bombardment. This leads to stratification of the material and significantly limits the density of field emission currents and the life of the cathode.

Also known are regular multi-tip arrays of field emission cathodes made of glassy carbon made by the thermochemical method [2]. The packing density of such matrix glassy carbon emitter structures reaches 10 ⁶ cm ^-2 . The points in the matrix have the shape of a truncated cone with a height of up to 15-20 microns. To increase the electric field gain, the tips of the tips were specially sharpened in the oxygen plasma. After sharpening, their radius was 0.3-0.5 μm.

However, glassy carbon matrices of multi-tip cathodes do not provide a high packing density of emitting centers. This reduces the density of currents from emitters, and the application of high electric fields to enhance the field emission process leads to an increase in heat release by ion bombardment and, as a consequence, to the degradation of multi-tip cathodes. In addition, the multi-stage and complexity of the technology limits its application and competitiveness.

Matrices of multi-edge field emission cathodes consisting of single-walled carbon nanotubes are also known [3]. The surface density of randomly oriented single-walled nanotubes was 10 ⁸ cm ^-2 . The coefficient of increase in the electric field at the top of the tube varies in the range from 2500 to 10000 with an average value of 3600, which is approximately three times higher than the corresponding value for multilayer nanotubes.

However, the emission characteristics of such structures are unstable - for ten hours of continuous operation, the emission current density (at a constant applied voltage) decreases by about an order of magnitude. This, apparently, is associated with the destruction of nanotubes under the action of fast electrons.

The closest in technical essence and technical result to the proposed are multi-edge field emission cathodes based on single-crystal silicon [4]. In such autocathodes, in order to increase the electric field gain and reduce working voltages when obtaining increased field emission currents, emission centers are formed on crystalline silicon in the form of nanodiamond graphite islands on integrated columnar nanostructures up to several tens of nanometers high and with a surface density of up to (5-14) 10 ⁹ cm ^-2 .

The disadvantage of multi-edge field emission cathodes based on single-crystal silicon is the insufficiently high stability and density of field emission currents.

Disclosure of invention

The aim of the invention is the creation of such a matrix of field emission cathodes, which, with a simplified manufacturing technology compatible with the technology for the production of silicon integrated circuits, would provide high density and stability of field emission current collection with a longer service life.

This goal is achieved by the fact that a multi-edge cathode matrix in the form of island field emission carbon coatings on silicon columnar nanostructures up to several tens of nanometers high and a surface density of up to (5-14) 10 ⁹ cm ^{-2 is} made on a substrate of single-crystal silicon of the hole type conductivity. An increase in the density and stability of field emission currents in such a cathode matrix is achieved by increasing the resistance to the transverse transport of charge carriers through the emission layer.

Brief Description of the Drawings

FIG. 1 - structure of the field emission element:

1 - anode;

2 - field emission carbon coating;

3 - p-type semiconductor.

FIG. 2 is a graph of field emission current density versus surface layer conductivity at a field strength of 20 V / μm.

The implementation of the invention

When field emission is carried out from a planar structure made on a silicon wafer with a hole type of conductivity, a “reverse inclusion” of the diode structure is realized at the semiconductor-diamond-graphite layer boundary, in which the current of minority carriers (electrons) passes across the structure to the positive anode (1) (Fig. 1 )

As is known [5], when the semiconductor contact layer is switched back on, it is depleted in the main carriers, and the transverse current through the semiconductor structure (3) - metal (conducting emission layer (3)) tends to the value of the saturation current, which depends on the potential ϕ _s on it surface. The potential ϕ _s on the surface of the semiconductor is determined by the potential difference at the anode (V _a ) and the potential drop in the emission layer (ϕ _s = V _a -V _c ). With fluctuations in the field emission current I _a , the potential drop in the emission layer changes, since V _c = I _a ⋅ R _c , where R _c is the transverse resistance of the emission layer. The result of this is a change in ϕ _s and the current passing through the semiconductor. When turned back on, the dependence of the saturation current on the potential ϕ _s is very weak, and the resistance is very large. This does not allow current fluctuations to transfer the emission process to an anomalous discharge mode and, thereby, helps to increase the stability of the field emission current and the durability of the cathode by eliminating the phenomena associated with the “burnout” of the emission centers of the cathode as a result of current fluctuations.

With an increase in the transverse resistance of a planar emission structure made on a p-type semiconductor, the potential drop in it increases and, thus, the value of the positive potential ϕ _k on the surface of the semiconductor decreases. By reducing the thickness and resistance of the barrier layer in the semiconductor, this contributes to an increase in field emission current from a planar structure made on a p-type silicon substrate (Fig. 2).

Field emission cathodes were fabricated in the form of island coatings of a composite nanodiamond-graphite film formed on the surface of p-type single-crystal silicon wafers in a plasma of a microwave gas discharge of ethanol vapor in the pressure range from 0.05 to 0.08 Pa and the substrate temperature from 200 to 350 ° C. The fabricated carbon multi-edge field emission cathode arrays with different surface densities and aspect ratio of columnar emission centers during the tests showed good characteristics, namely, high stability of emission with an amplitude of current fluctuation of less than 3.5% at the initial stage, which allows predicting the cathode life of at least 10,000 hours, as well as high current densities. So, with a decrease in the electrical conductivity of the emission layer from 1.35⋅10 ^-4 cm to 2⋅10 ^-5 cm due to an increase in the thickness of the carbon layer from 1.0 nm to 10 nm and more than the density of emission currents from the cathode matrices on silicon substrates p- type at a field strength of 20 V / μm increased from 3 to 19 mA / cm ² (Fig. 2).

Literature

1. USSR author's certificate No. 767858, MKI H01J 1/30, 1978.

2. Patent RU 1738013, MKI H01J 1/30, 1993.

3. Bonard J. - M., Salvetat J. - P., Stockli T., Heer W. A., Forro L. and Chatelain A. Appl. Phys. Lett, 1998, 73, p. 918.

4. Patent RU 2484548, IPC H01J 1/30, H01J 9/02, 2011.

5. Bonch-Bruevich V.L., Kalashnikov S.G. Semiconductor Physics. M .: 1977, p. 672.

Claims (1)

A method for increasing the current density, stability and degradation resistance of multi-edge field emission cathodes in the form of a composite nanodiamond-graphite film on columnar nanostructures of single-crystal silicon with a height of up to several tens of nanometers and a surface density of up to (5-14) 10 ⁹ cm ^-2 , characterized in that multi-edge field emission cathodes are made on wafer-type single-crystal silicon wafers with a nanodiamond-graphite film thickness of at least 10 nm with a transverse conductive a bone that needs to be reduced to increase the field emission current density.

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