Patent Grant
7495381
This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0012633 filed on Feb. 25, 2004 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.
The present invention relates to an electron emission device, and more particularly, to an electron emission device equipped with a metal grid electrode that focuses electrons emitted from an electron emitting region.
An electron emission device (EED) generally comprises a display apparatus from which an arbitrary image is realized when electrons emitted from an electron emitting region of a cathode electrode irradiate. The electrons irradiate through the tunneling effect of quantum mechanics, by colliding with a phosphor layer formed on an anode. A triode consisting of a cathode electrode, a gate electrode, and an anode electrode is a widely used structure for an EED.
A commonly used triode consists of a vacuum container comprising a rear substrate comprising a cathode electrode and a gate electrode and a front substrate comprising an anode electrode. The vacuum container is put together using a sealant, such as a frit. The vacuum container includes several spacers creating a fixed gap between the rear and front substrates to keep the rear substrate away from the front substrate.
An arc discharge is generated in the vacuum container by the electron emission device. It can be inferred that the arc discharge is generated by the simultaneous ionization of a great deal of gas by outgassing, which occurs in the vacuum container. Generally, the arc discharge generated becomes more severe as the anode voltage increases. Due to this arc discharge, the gate electrode can be easily damaged because the anode electrode can be electrically shorted with the gate electrode.
To resolve this problem, an electron emission device has been proposed in which a metal grid electrode is equipped between the rear substrate and the front substrate. The grid electrode can protect the electrodes equipped on the rear substrate from damage due to generation of the arc discharge, and improves the capability of focusing the emitted electrons.
However, when the thermal expansion coefficient of the metal grid electrode differs remarkably from the thermal expansion coefficient of heat-reinforced glass used for the front and rear substrate of a flat panel display, several problems occur during the sealing and exhaust processes of the electron emission device. One such problem is the limited availability of high temperature processes. Another problem is that the panel can be damaged during the exhaust process when the grid electrode and underplate are misaligned. Moreover, electrons emitted from the electron emitting region may collide with the phosphor layer of a surrounding territory instead of the selected territory due to the misalignment of the grid electrode, and the color purity can depreciate.
To solve these problems, a design has been introduced which compensates for the misalignment of the grid electrode generated during the heat treatment process. However, this design uses a troublesome process and has certain limitations in quality control.
In one embodiment of the present invention, an electron emission device is provided that is capable of preventing misalignment due to a difference of thermal expansion coefficients between the grid electrode and front and rear substrates by providing a metallic grid electrode having a thermal expansion coefficient similar to those of the first and second substrates.
In a first embodiment, the electron emission device (EED) comprises a first substrate and a second substrate constituting a vacuum container, positioned opposite each other with a predetermined gap therebetween; cathode electrodes and gate electrodes provided in an insulating state on an insulating layer on the first substrate; electron emitting regions comprising an electron emitting material, formed on the cathode electrode; at least one anode electrode and phosphor layers of a red, a green, and a blue color provided on the second substrate; and a grid electrode installed in the vacuum container, and equipped with holes for passing of electrons emitted from the electron emitting region, wherein a thermal expansion coefficient of the grid electrode is in the range of 80 to 120% of the thermal expansion coefficient of the first and second substrates.
In a second embodiment, the electron emission device (EED) comprises a first substrate and a second substrate constituting a vacuum container, positioned opposite each other with a predetermined gap therebetween; cathode electrodes and gate electrodes provided in an insulating state on an insulating layer on the first substrate; electron emitting regions comprising an electron emitting material, formed on the cathode electrode; at least one anode electrode and phosphor layers of a red, a green, and a blue color provided on the second substrate; and a grid electrode installed in the vacuum container, and equipped with holes for passing of electrons emitted from the electron emitting region, wherein the grid electrode comprises a nickel-iron alloy.
The above and other advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:
In the first embodiment, the electron emission device (EED) comprises a first substrate and a second substrate constituting a vacuum container, positioned opposite each other with a predetermined gap therebetween; cathode electrodes and gate electrodes provided in an insulating state on an insulating layer on the first substrate; electron emitting regions comprising an electron emitting material, formed on the cathode electrode; at least one anode electrode and phosphor layers of a red, a green, and a blue color provided on the second substrate; and a grid electrode installed in the vacuum container, and equipped with holes for passing of electrons emitted from the electron emitting region, wherein a thermal expansion coefficient of the grid electrode is in the range of 80 to 120% of the thermal expansion coefficient of the first substrate and the second substrate.
In the second embodiment, the electron emission device (EED) comprises a first substrate and a second substrate constituting a vacuum container, positioned opposite each other with a predetermined gap therebetween; cathode electrodes and gate electrodes provided in an insulating state on the other side of an insulating layer on the first substrate; electron emitting regions comprising an electron emitting material, formed on the cathode electrode; at least one anode electrode and phosphor layers of a red, a green, and a blue color provided on the second substrate; and a grid electrode installed in the vacuum container, and equipped with holes for passing of electrons emitted from the electron emitting region, wherein the grid electrode comprises a nickel-iron alloy.
The present invention is described in more detail with reference to the accompanying drawings. However, the present invention is not limited by the structure of the drawings. Rather, the drawings illustrate examples of the electron emission device of the present invention.
As used herein, the “first substrate” refers to a front substrate comprising the phosphor layers, and the “second substrate” refers to a rear substrate comprising the electron emitting regions.
With reference to
More particularly, the gate electrodes 10 are positioned on the first substrate 2 in a striped pattern, and each gate electrode 10 extends along the Y direction. An insulating layer 12 is positioned over the gate electrodes 12 on the side of the first substrate 2 facing the second substrate 4. The cathode electrodes 14 are positioned on the insulating layer 12 in a striped pattern, and each cathode electrode 14 extends along the X direction, perpendicular to the gate electrodes 10. An electron emitting region 16 for an electron emission source is positioned on the edge of the cathode electrode 14 at each point where the cathode electrodes 14 intersect the gate electrodes 10.
If desired, a counter electrode 18 can be positioned on the first substrate 2. The counter electrode 18 is electrically connected to the gate electrode 10 by contact through a hole 12a formed in the insulating layer 12. The counter electrode 18 is positioned between the cathode electrodes 14 and separated from the electron emitting region 16 by a predetermined distance. The counter electrode 18 provides a stronger electric field in the area surrounding the electron emitting region 16, such that electrons are favorably emitted from the electron emitting region 16.
Additionally, an anode electrode 20 is formed on the side of the second substrate 4 facing the first substrate 2. Red, green and blue phosphor layers 22 are provided on the anode electrode 20. Phosphor screens 26 consisting of black color layers 24, are formed on the anode electrode 20 and positioned between the phosphor layers 22. The anode electrode 20 comprises a transparent electrode such as indium tin oxide (ITO). As shown in
Moreover, a grid electrode 8 for focusing the electron beam is positioned between the first substrate 2 and the second substrate 4, but is positioned closer to the first substrate 2. The grid electrode 8 comprises a metal plate having several openings 6 to allow passage of the electron beam. The grid electrode 8 is positioned in the vacuum container by upper spacers 28 situated between the second substrate 4 and the grid electrode 8 and lower spacers 30 situated between the first substrate 2 and the grid electrode 8. The spacers 28 and 30 separate the grid electrode 8 from first and second substrates by a predetermined, constant distance.
With reference to
An emission structure to enable the emission of electrons by an electric field is formed on the second substrate 4, and an illumination structure to enable the realization of predetermined images by interaction with electrons is formed on the first substrate 2.
In more detail, for the emission structure, cathode electrodes 14 are formed in a stripe pattern, and an insulating layer 12 is formed over an entire surface of the second substrate 4 covering the cathode electrodes 14. Further, gate electrodes 10 are formed in a stripe pattern on the insulating layer 12. Holes 10a and 12a are formed in the gate electrodes 10 and the insulating layer 12, and electron emitting regions 16 are formed on the cathode electrodes 14 in the same areas exposed through the holes 10a and 12a.
With respect to the illumination structure for realizing predetermined images, anode electrodes 20 are formed on a surface of the first substrate 2 opposing the second substrate 4. Also, phosphor layers 22 and black color layers 24 are formed on the anode electrodes 20. The phosphor layers 22 are illuminated by electrons emitted from the electron sources 16 of the second substrate 4.
With this structure, if electrons are emitted from the electron emitting regions 16 by the voltage difference between the cathode electrodes 14 and the gate electrodes 10, the electrons are attracted by a high voltage applied to the anode electrodes 20 to strike the phosphor layers 22 and excite the same.
A grid electrode 8 is mounted between the first substrate 2 and the second substrate 4 to prevent arc discharge between these elements and to aid in focusing the emitted electrons. Preferably, the grid electrode 8 includes a plurality of openings 6, each opening 6 corresponding to one electron emitting region 16. The grid electrode 8 is positioned in the vacuum container by upper spacers 28 situated between the second substrate 4 and the grid electrode 8 and lower spacers 30 situated between the first substrate 2 and the grid electrode 8. The spacers 28 and 30 separate the grid electrode 8 from the first and second substrates by a predetermined, constant distance.
In the said EEDs, the electron emitting regions 16 comprise a carbon-based material. Preferably, the carbon-based material is selected from the group consisting of carbon nanotubes, graphite, diamond, diamond-like carbon, fullerene (C60), and mixtures thereof.
Preferably, the first and second substrates comprise glass substrates having thermal expansion coefficients ranging from about 1.0×10−6 to about 10.0×10−6/° C. More preferably, the first and second substrates comprise heat-reinforced glass substrates having thermal expansion coefficients ranging from about 1.0×10−6 to about 10.0×10−6/° C.
The thermal expansion coefficient of the grid electrode ranges from about 80 to about 120% of the thermal expansion coefficient of the first and second substrates 2 and 4, preferably about 90 to about 110%, and more preferably about 95 to about 105%. When the thermal expansion coefficient of the grid electrode is less than about 80% or more than about 120% of the thermal expansion coefficient of the glass substrate, the possibility of a misalignment increases. Therefore, the difference in thermal expansion coefficients between the grid electrode and the glass substrates is preferably as small as possible.
The thermal expansion coefficient of the grid electrode is controllable by controlling the nickel content of a nickel-iron alloy. For example, when the first and second substrates 2 and 4, respectively, comprise heat-reinforced glass having a thermal expansion coefficient ranging from about 1.0×10−6 to about 10.0×10−6/° C., a grid electrode comprising a nickel-iron alloy with a nickel content ranging from about 42 to about 52 wt % can be used. Preferably, the nickel content ranges from about 45 to about 50 wt. %, more preferably about 47 to about 49 wt. %.
A 36 nickel-iron alloy, i.e. an alloy with a nickel content of 36 wt. %, has previously been used as the grid electrode or the shadow mask for a cathode-ray tube (CRT). However, such an alloy is inadequate for high temperature processes and misalignment easily occurs between the grid electrode and the lower plate because the thermal expansion coefficient of this 36 nickel-iron alloy is substantially smaller than the thermal expansion coefficient of the first and second substrates in the flat panel display. However, the nickel-iron alloy having a nickel content in the range of 42 to 52 wt %, as used in the present invention, has a thermal expansion coefficient in the desired range, substantially eliminating the misalignment problems and the problems associated with high temperature processes.
The grid electrode of the present invention mainly comprises the nickel-iron alloy. In addition, however, a metal selected from the group consisting of chromium, cobalt, or titanium, may optionally be included to impart desired physical and mechanical properties, for example etching and workability. Chromium, cobalt, or titanium are present in the nickel-iron alloy in an amount according to necessity. Preferably, however, chromium is present in an amount ranging from about 0.01 to about 10 wt. %.
In one embodiment, the thickness of the grid electrode ranges from about 0.05 to about 0.2 mm. When the thickness of the grid electrode is less than about 0.05 mm, mechanical handling of the electrode is difficult. When the thickness of the grid electrode is greater than about 0.2 mm, processing of a microscopic hole is difficult.
The electron emission device comprising a grid electrode of the present invention can be fabricated according to a top-gate form, an under-gate form, or a modified form with reference to the position of the gate electrode, and is not limited by an electron emission device of a specific structure.
Hereafter, examples of the present invention are described. The examples described below are only examples of the present invention, and the present invention is not limited by these examples.
Heat-reinforced glass (PD-200) having a thermal expansion coefficient (TEC) of 8.6×10−6/° C. was used as the first and second substrates. The grid electrode was manufactured using a nickel-iron alloy comprising 42 wt % nickel. An electron emission device was fabricated according to the structure shown in
An electron emission device was fabricated according to the method described in Example 1, except that the grid electrode was manufactured using a nickel-iron alloy comprising 45 wt % nickel.
An electron emission device was fabricated according to the method described in Example 1, except that the grid electrode was manufactured by using a nickel-iron alloy comprising 47 wt % nickel.
An electron emission device was fabricated according to the method described in Example 1, except that the grid electrode was manufactured using a nickel-chromium-iron alloy comprising 42 wt % nickel, 6 wt % chromium and 52 wt % iron.
An electron emission device was fabricated according to the method described in Example 1, except that the grid electrode was manufactured using a nickel-iron alloy comprising 36 wt % nickel.
The following table lists the thermal expansion coefficients (TEC) of the grid electrodes used in Examples 1 to 4 and Comparative Example 1.
Misalignment does not occur during the sealing and exhausting processes in the electron emission devices of Examples 1 to 4, but does occur during the sealing and exhausting processes in the electron emission device of Comparative Example 1, which generates a damaged part.
The misalignment occurs due to a difference of the thermal expansion coefficient between the grid electrode and the front or rear substrate. This misalignment can be prevented, as it is in the present invention, by adopting a metallic grid electrode having a thermal expansion coefficient similar to that of the first and second substrates. In so doing, alignment precision is improved, high temperature processes are possible, and the reliability of the device is improved.
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