JPH10312736A - Electron emitting element and method for forming cathode thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron emitting element by which stable emission electric current is obtained by decreasing the diameter of respective cathodes and the integration degree of the cathodes. SOLUTION: This element comprises cathodes 3 made of pole-like or needle- like conductive ceramics or conductive oxides projected approximately vertically on the surface of a substrate 1 and gate electrodes 5 installed near the tip end sides of the cathodes 3 and electrically insulated from the cathodes 3 and the element is so composed as to emit electrons out of the cathodes 3 by applying electric field between the cathodes 3 and the gate electrodes 5. Since the cathodes 3 are formed into a pole-like or needle-like shape by utilizing the etching speed difference in the grain parts and grain boundary parts composing the conductive oxide film of the cathodes, the diameter of respective cathodes 3 is easily narrowed and the degree of integration of the cathodes 3 is heightened. The diameter of the respective cathodes 3 is controlled to be several nanometer or several-tens nanometer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a manufacturing method of a cold cathode type electron-emitting device used as an electron source of a field emission display (FED), a high-sensitivity photodetector, a high-speed electronic device, and the like. It is about.

[0002]

2. Description of the Related Art As a conventional cold cathode type electron-emitting device,
A Spindt type having a conical or pyramidal cathode (cold cathode) as shown in FIG. 4 is known (US Pat. No. 3,947,947). A gate electrode 42 is formed in an annular shape around the tip of the cathode 41.
By applying a voltage between the gate electrode 1 and the gate electrode 42, electrons are emitted from the tip of the cathode 41. The cathode 41 has a conductive layer 4 on a glass substrate 43.
4 is formed on the resistance layer 45 formed by lamination. The gate electrode 42 is electrically insulated from the cathode 41 and the resistance layer 45 by the insulating layer 46. As a material of the cathode 41, a semiconductor or metal such as Si, Mo, Nb, or W is used. Since the tip shape and diameter of the cathode 41 greatly affect the magnitude and stability of the current due to electron emission, it is necessary to precisely control the three-dimensional shape and dimensions of the cathode 41 during the manufacturing process. A method for manufacturing such a Spindt-type electron-emitting device includes, for example,
There is one disclosed in Japanese Patent Publication No. 1132. FIG.
(F) is a manufacturing process diagram of the field emission type cold cathode disclosed in the above-mentioned publication, and firstly, a flat Si single crystal substrate 51 as shown in (a) and a bottom surface as shown in (b). A sharp quadrangular pyramid-shaped recess 52 is formed by anisotropic etching, and SiO 2 remaining on the surface of the Si single crystal substrate 51 is formed.
2 After removing the oxide film 53, as shown in FIG.
A thermal oxidation process is performed on the surface (first main surface) of the single crystal substrate 51 including the inner wall surface of the concave portion 52 to form a thermal oxide layer 54, on which an emitter material layer 55 made of W or Mo is formed. Form. Next, as shown in (d), a glass substrate 57 having a back surface coated with an Al layer 56 is placed on the emitter material layer 5.
Glue on 5 After that, the entire substrate is turned upside down, and as shown in (e), the Si single crystal substrate 51 is etched off partway to expose the thermal oxide layer 54 covering the tip of the projection 55 'of the emitter material layer 55. Next, the thermal oxide layer 54 covering the tip of the projection 55 'is removed by etching, and the projection 5' is removed.
Expose the 5 'pointed tip. As described above, the cathode 58 as a quadrangular pyramid-shaped emitter is obtained.

[0003]

When a Spindt-type electron-emitting device manufactured by the above-described manufacturing method is used as an electron source for a display, even if the emission current from individual cathodes varies, the integration of the cathodes can be improved. If the degree is increased and a plurality of cathodes constitute one pixel, variations in emission current can be averaged. However, in the case of a Spindt-type electron-emitting device, the diameter of each cathode is at least about 10 μm, which limits the degree of integration. Therefore, an object of the present invention is to provide an electron-emitting device that can obtain a stable emission current by reducing the diameter of each cathode and increasing the degree of integration of the cathode.

[0004]

According to a first aspect of the present invention, there is provided an electron-emitting device having a columnar or needle-like conductive shape projecting substantially perpendicular to a substrate surface. A cathode made of ceramics or a conductive oxide;
A gate electrode that is disposed near the front end side of the cathode and is electrically insulated from the cathode, and configured to emit electrons from the cathode by applying an electric field between the cathode and the gate electrode. It is characterized by doing. An electron-emitting device according to a second aspect of the present invention is the electron-emitting device according to the first aspect, wherein a surface of a tip portion of the cathode is covered with a film having a composition different from that of the cathode. . The electron-emitting device according to a third aspect of the present invention is the electron-emitting device according to the first aspect, wherein the conductive ceramic or the conductive oxide has a property of transmitting visible light. It is characterized by doing. According to a fourth aspect of the present invention, there is provided the method for forming a cathode of an electron-emitting device according to any one of the first to third aspects, wherein the polycrystalline structure includes a crystal grain having a columnar structure substantially perpendicular to the substrate surface. After the conductive oxide film is formed, the cathode is formed by performing a wet etching process to selectively remove a grain boundary portion around the crystal grain.

According to the above-described electron-emitting device, the use of a columnar or needle-like cathode made of conductive ceramics or conductive oxide projecting substantially perpendicular to the substrate surface is achieved. Since the diameter of each cathode can be reduced and the degree of integration of the cathode can be increased, a stable emission current can be obtained. According to the electron-emitting device of the second aspect, the front end surface of the cathode is coated with a film having a different composition from that of the cathode.
Since the surface of the tip portion of the cathode can be modified and the durability of the cathode can be increased, a stable emission current can be obtained for a long time. According to the electron-emitting device of the third aspect, since the conductive ceramics or the conductive oxide that is a material of the cathode and has a property of transmitting visible light is used, the substrate or the substrate By using an electrode or the like having a property of transmitting visible light, a field emission display that can display a display image from the electron-emitting device side can be realized. According to the method of forming a cathode according to claim 4, a columnar or needle-like cathode is formed by utilizing a difference in etching rate between a crystal grain constituting a conductive oxide film and a portion of a grain boundary. Therefore, the diameter of each cathode can be reduced, and the degree of integration of the cathode can be increased.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view showing an example of an embodiment of an electron-emitting device according to the present invention. The electron-emitting device 10 is a field emission display (hereinafter referred to as an FED
It is written. ) Which constitutes an electron source,
A large number of Pt electrodes 2 are formed corresponding to each pixel on the top,
A plurality of cathodes 3 having a needle-like structure made of a conductive oxide are provided on each Pt electrode 2 substantially perpendicularly to the Si substrate 1. As the conductive oxide, for example, a mixture of indium and tin is used. An insulating layer 4 made of a silicon oxide film is provided around the Pt electrode 2. The insulating layer 4 protrudes from the tip of the cathode 3, and a gate electrode 5 is provided on the insulating layer 4. The cathode 3 forms a Pt film to be a Pt electrode 2 on a Si substrate 1, and then forms a conductive oxide film on the Pt film by a sputtering method. It is formed into a needle shape by etching with an iron-based liquid. The diameter of each cathode 3 is from several nanometers to several tens of nanometers, and can be controlled by changing conditions for forming a conductive oxide film or the like, etching conditions, and the like.

[0007] The FED is schematically constructed by arranging an electron-emitting device 10 and a glass substrate (light-emitting substrate) (not shown) coated with a phosphor so as to face each other, and keeping a vacuum between them. The predetermined Pt electrode 2 of the electron-emitting device 10
By applying a voltage between the Pt electrode 2 and the gate electrode 5, electrons are emitted from the tips of the plurality of cathodes 3 on the Pt electrode 2, and some of the electrons are transferred between the electron-emitting device 10 and the light emitting substrate. By drawing out by the applied acceleration voltage and colliding with the inner surface of the light emitting substrate, the phosphor of a predetermined pixel emits light to perform display. Since the electron-emitting device 10 can form a large number of extremely small needle-like cathodes 3 on the Pt electrode 2 corresponding to each pixel at a high density, it is possible to average the variation of the emission current from each cathode 3. it can. Therefore, by using the electron-emitting device 10 as the electron source of the FED, stable display without uneven brightness can be performed.

FIG. 2 is a side sectional view showing another embodiment of the electron-emitting device according to the present invention. In the electron-emitting device 20 of this embodiment, a lower portion of a plurality of cathodes 3 'corresponding to a common pixel is formed of a common conductive oxide film.
Such a structure can be realized by forming a conductive oxide film on a Pt film to be the Pt electrode 2 and then etching the conductive oxide film halfway with a ferric chloride-based solution. . In the above embodiment, the electron-emitting devices 10, 20
Although a Si substrate is used as the substrate, a glass substrate may be used instead of the Si substrate. Further, cathodes 3 and 3 ′ made of a conductive oxide are formed on Pt electrode 2,
If the resistance of the conductive oxide to be used is sufficiently small, the conductive oxide film is formed directly on the substrate, and then the conductive oxide film is partially etched in the same manner as in FIG. In this case, a cathode having a structure in which the lower part is not separated may be formed. In the above example, an oxide made of indium and tin is used as the conductive oxide. However, the conductive oxide is not limited thereto, and aluminum nitride, zinc oxide, tin oxide, or the like may be used.

The surfaces of the cathodes 3, 3 'may be covered with a film having a composition different from that of the cathode, such as a carbon-based film. The carbon-based film is hard, resistant to damage caused by electron emission, has a stable surface, and is resistant to adsorption of ions such as hydrogen. Therefore, by providing this kind of film as a protective film, the cathode can be protected for a long time and a stable emission current can be obtained. Plasma CVD using methane as raw material
A carbon film having a diamond structure formed by a method is most suitable. Also, by using a transparent glass substrate for the substrate of the electron-emitting device, directly forming a light-transmitting conductive oxide film on the glass substrate, and then etching the conductive oxide film halfway, A cathode having a structure in which the lower portion is not separated may be formed. Then, a display image, that is, light emission of the phosphor on the inner surface of the light emitting substrate can be seen from the electron emitting element side (the direction of arrow A in the figure)
Can be realized. By making the display image visible from the electron-emitting device side, light loss and discoloration due to the glass coated with the phosphor can be reduced, and a clear image display can be performed.

Next, the manufacturing method will be described. FIG. 3 is a diagram showing an example of an embodiment of a method for manufacturing an electron-emitting device according to the present invention. First, as shown in FIG.
A conductive oxide film (ZnO) 12 having a thickness of about 500 nm is formed on an i-substrate 11 by MOCVD or plasma CVD.
Laminate. As a result, C-axis oriented crystal grains 1 having a grain size of about 100 nm and having a columnar structure substantially perpendicular to the Si substrate 11.
Thus, a transparent conductive oxide film 12 having a polycrystalline structure of 3 is obtained. Of course, an electrode metal may be stacked on the Si substrate 11 and the conductive oxide film 12 may be stacked thereon,
In this manufacturing method, it is better to directly laminate on the Si substrate 11. The reason is that ZnO grows in a form affected by the value of the lattice constant of the single-crystal Si constituting the Si substrate 11, so that the C-axis orientation can be easily obtained. Then
The conductive oxide film 12 is etched using an etching solution of an acidic solution. Then, a large number of spike-shaped cathodes 15 are formed as shown in FIG. 3B due to the etching rate difference between the crystal grains 13 and the grain boundaries 14 constituting the conductive oxide film 12.

As described above, the spire-shaped cathodes 15 are formed by utilizing the etching rate difference between the crystal grains 13 constituting the conductive oxide film 12 and the portion of the grain boundary 14, so that each cathode 15 is formed. The diameter can be reduced, and the degree of integration of the cathode 15 can be increased. As described above, the diameter of each cathode 15 can be controlled by changing the conditions for forming the conductive oxide film 2, the etching conditions, and the like, and can be several nanometers to several tens of nanometers. Note that in the above description, a conductive ceramic film may be formed instead of the conductive oxide film. The method for forming the conductive oxide film or the conductive ceramic film is not limited to the MOCVD method or the plasma CVD method, and a sputtering method, a sol-gel method, or the like can be applied. At that time, in the case of the sputtering method, crystallization is performed by the particle energy at the time of vapor deposition, and in the case of the sol-gel method, crystallization is performed by the heat energy of the sintering step, and a large number of crystals having a columnar structure almost perpendicular to the substrate are formed. A polycrystalline film composed of grains is formed.

[0012]

As described above, the present invention has the following excellent effects. According to the electron-emitting device according to claim 1, each cathode is formed by using a columnar or needle-like cathode made of conductive ceramic or conductive oxide projecting substantially perpendicular to the substrate surface. Can be reduced in diameter and the degree of integration of the cathode can be increased, so that a stable emission current can be obtained. Further, according to the electron-emitting device according to the second aspect,
In addition, by coating the tip surface of the cathode with a film having a different composition from that of the cathode, the surface of the cathode tip can be modified and the durability of the cathode can be increased, so that a stable emission current can be maintained for a longer time. Can be obtained. According to the electron-emitting device of the third aspect, in addition to the first aspect, a conductive ceramic or a conductive oxide that is a material of the cathode and has a property of transmitting visible light is used. Therefore, by using a substrate or an electrode formed on the substrate having a property of transmitting visible light, a field emission display that can display a display image from the electron-emitting device side can be realized. According to the method of forming a cathode according to claim 4, a columnar or needle-like cathode is formed by utilizing a difference in etching rate between a crystal grain constituting a conductive oxide film and a portion of a grain boundary. Therefore, the diameter of each cathode can be easily reduced, and the degree of integration of the cathodes can be increased.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an example of an embodiment of an electron-emitting device according to the present invention.

FIG. 2 is a side sectional view showing another embodiment of the electron-emitting device according to the present invention.

3A and 3B are views showing an example of an embodiment of a method for manufacturing an electron-emitting device according to the present invention, wherein FIG. 3A is a perspective view and FIG. 3B is a side sectional view.

FIG. 4 is a side sectional view showing an example of the structure of a conventional cold cathode type electron-emitting device.

5A to 5F are views showing a series of manufacturing steps of a conventional electron-emitting device.

[Explanation of symbols]

Reference Signs List 1 Si substrate, 2 Pt electrode, 3 cathode, 3 'cathode, 4 insulating layer, 5 gate electrode, 10 electron-emitting device, 11 Si substrate, 12 conductive oxide film, 13
Crystal grains, 14 grain boundaries, 15 cathodes, 20 electron emission devices.

Claims (4)

[Claims] 1. A method according to claim 1, wherein a columnar or needle-shaped cathode made of conductive ceramics or conductive oxide protruding substantially perpendicular to the surface of the substrate and a gate electrode arranged near the tip of the cathode. An electron-emitting device characterized in that electrons are emitted from the cathode by applying an electric field to the electron-emitting device. 2. The electron-emitting device according to claim 1, wherein a front end surface of the cathode is coated with a film having a composition different from that of the cathode. 3. The electron-emitting device according to claim 1, wherein the conductive ceramic or the conductive oxide transmits visible light. 4. The method for forming a cathode of an electron-emitting device according to claim 1, wherein the conductive oxide film has a polycrystalline structure comprising crystal grains having a columnar structure substantially perpendicular to the substrate surface. Forming the cathode by performing a wet etching process to selectively remove a grain boundary portion around the crystal grain after forming the cathode.