Electron-emitting element

Details Electron-emitting element Electron-emitting element

1998-03-10

2001-02-06

Day, Michael H. (Department: 2879)

Electric lamp and discharge devices

Discharge devices having a thermionic or emissive cathode

C313S309000, C313S336000, C313S351000, C445S050000, C445S051000

Reexamination Certificate

active

06184611

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron-emitting element, a method of making the same, and an electronic device such as field-emission display (FED), field-emission microscope (FEM), or the like which uses an electron-emitting element.
2. Related Background Art
With the recent advance in minute processing in semiconductor technology, the field of vacuum microelectronics has been rapidly developing. Consequently, as an electronic device for the next generation having a function of displaying or the like, the field-emission display (FED) has come into expectation. It is due to the fact that, unlike the conventional CRT displays, the FED has two-dimensionally arranged minute electrodes which function as field-emission type electron-emitting elements, so that it is unnecessary to deflect and converge the electrons in principle, whereby the display can be easily made thinner or flatter.
As a material used for such a minute electrode, diamond has recently been noticed. It is due to the fact that diamond has a very advantageous characteristic as an electron-emitting device, i.e., its electron affinity is negative. Accordingly, when diamond is pointed and employed as a minute electrode, it can emit electrons at a low voltage.
As a method of making pointed diamond, the following methods have been reported. For example, Japanese Patent Application Laid-Open No. 7-94077 discloses that, when a partially masked diamond substrate is etched, pointed diamond projecting from the substrate surface can be obtained. Also,
NEW DIAMOND,
39, vol. 11, No. 4, pp. 24-25 (1995), reports that an isolated particle of diamond having a pointed form with no grain boundary is obtained as being oriented to (111) surface on a Cu substrate.
SUMMARY OF THE INVENTION
The conventional electron-emitting elements, however, have not been capable of sufficiently emitting electrons. In view of such a problem, it is an object of the present invention to provide an electron-emitting element which can sufficiently emit electrons, a method of making the same, and an electronic device.
In order to overcome the above-mentioned problem, the inventors have first taken account of single-crystal diamond with no grain boundary. There are many crystal morphologies in single-crystal diamond.
FIGS. 1A
to
1
E are perspective views respectively showing typical morphologies of single-crystal diamond. As clearly shown in
FIGS. 1A
to
1
E, each of single-crystal diamonds
1
to
5
is pointed at a part surrounded by crystal faces. This part contains only one carbon atom. Here, the pointing reaches its limit at a microscopic atomic level as observed by an electron microscope or the like. In the diamonds
1
,
3
, and
5
in particular, the radius of curvature of the pointed part is very small.
Meanwhile, diamond belongs to the cubic system; and the pointed parts shown in
FIGS. 1A
,
1
C, and
1
E are respectively positioned in the directions of crystal orientations <111>, <110>, and <100>. Also, these directions are respectively perpendicular to faces with face indices of {111}, {110}, and {100}. Here, the crystal orientation refers to a direction inherent in a crystal indicated by a face index with reference to a crystallographic axis which is a coordinate axis of three ridges intersecting at a common point of a unit lattice; whereas the face index refers to a reciprocal of the value obtained when the distance from the common point to a point where the face intersects with the crystallographic axis is divided by a unit length of the crystallographic axis.
Accordingly, when such single-crystal diamond
1
,
3
, or
5
is integrally formed by homo-epitaxial growth or the like at a desired position on a matrix having such a face index, it is pointed perpendicularly above the matrix at an atomic level, thereby overcoming the above-mentioned problem. Therefore, by taking this point into account, the inventors have attained the following invention.
Namely, the electron-emitting element in accordance with the present invention comprises a diamond substrate, and a diamond protrusion grown on a surface of the diamond substrate so as to have a pointed portion in a form capable of emitting an electron. The diamond protrusion formed by growth has a sharply pointed tip portion, thereby being capable of sufficiently emitting electrons.
Preferably, the surface of the diamond substrate is a {100} face, and the diamond protrusion is surrounded by {111} faces. Alternatively, while the surface of the diamond substrate is a {110} face, the diamond protrusion may be surrounded by {111} and {100} faces. Also, the surface of the diamond substrate may be a {111} face, with the diamond protrusion being surrounded by {100} faces.
Each diamond protrusion of such a diamond member, i.e., protruded portion, is surrounded by its inherent crystal faces governed by the symmetric property of the crystal structure of diamond, thereby exhibiting so-called automorphism. In this case, electric and mechanic characteristics and the like of the protruded portion are those inherent in the single-crystal diamond. Also, the protruded portion is pointed at an atomic level and has a shape determined by the face index of the substrate surface. Further, the surface of the protruded portion is very stable in terms of energy. Thus, a diamond member with a uniform quality can be easily obtained.
On the other hand, as mentioned above, diamond is a material having a negative electron affinity and is excellent in terms of electron-emitting characteristic. Accordingly, when its protrusion tip is not completely pointed, i.e., a minute area of plane or ridge line is left at the tip, it can be expected to become effective in increasing the current of emitted electrons. Namely, as the form of the diamond protrusion that can sufficiently emit electrons, the following can be noted.
First, the diamond protrusion preferably has a quadrangular pyramid portion exposing its tip part. In particular, when a {100} diamond substrate is used, a truncated quadrangular pyramid portion is spread on the skirt side of the quadrangular pyramid portion. Specifically, this diamond protrusion has a truncated quadrangular pyramid portion whose upper and bottom surfaces are respectively continuous with the bottom surface of the quadrangular pyramid portion and the surface of the diamond substrate, while the angle formed between a side ridge line of the truncated quadrangular pyramid portion and the surface of the diamond substrate is smaller than the angle formed between a side ridge line of the quadrangular pyramid portion and the surface of the diamond substrate.
The diamond protrusion may have a truncated quadrangular pyramid portion exposing the upper surface thereof.
The diamond protrusion may have a form surrounded by a first ridge line in parallel to the substrate surface, second and third ridge lines extending so as to spread from one end of the first ridge line toward the surface, and fourth and fifth ridge lines extending so as to spread from the other end of the first ridge line toward the surface.
In order for the diamond substrate to match the diamond protrusion in terms of lattice, the diamond substrate is preferably single-crystal diamond. It is due to the fact that crystal defects consequently become hard to be introduced into the protrusion, whereby quality is kept from deteriorating. As the diamond substrate, polycrystal diamond can also be used.
The method of making an electron-emitting element in accordance with the present invention comprises: (a) a step of preparing a diamond substrate; (b) a step of forming a seed projection on a surface of the diamond substrate by diamond; and (c) a step of forming a diamond protrusion by epitaxially growing diamond at the seed projection by vapor-phase synthesis using the seed projection as a nucleus.
As the nucleus of crystal growth is thus intentionally disposed as t

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