Patent Application
20060066216
1. Field of the Invention
The present invention relates to a field emission display (FED) utilizing a field emission electron source.
2. Description of Related Art
Conventionally, cathode ray tubes (CRTs) have been the standard for displays (image displays) of color televisions, personal computers and the like. However, with the recent increasing demand for the reduction in the size, weight and thickness of the image displays, various thin image displays are being developed and manufactured.
Under such circumstances, the research and development of a variety of flat panel displays has been conducted recently. In particular, extensive research is being conducted on liquid crystal displays, plasma displays and the like. Liquid crystal displays are applied to various products such as portable personal computers, portable televisions, video cameras and car navigation systems, whereas plasma displays are applied to products such as 20-inch-to 40-inch-class large displays. However, liquid crystal displays have the problems of a narrow viewing angle and a slow response, and plasma displays have the problems, for example, in that high brightness is difficult to achieve and their power consumption is high.
Therefore, as a flat panel display that can solve these problems, an image display utilizing a phenomenon called field emission in which electrons are emitted in a vacuum at room temperature (hereinafter, referred to as “field emission display”) is receiving attention. This field emission display is self-emitting, and therefore can achieve a wide viewing angle and high brightness. Furthermore, its basic principle (causing phosphors to emit light using electron beams) is the same as that of conventional cathode ray tubes, so that it can display an image that is natural and has high color reproducibility.
As a conventional field emission display of this type, a field emission display having a configuration as described below (see e.g., JP2001-110343A) is known.
As shown in
In the field emission display 200 having the above-described configuration, by applying predetermined voltages (a gate voltage, an anode voltage and a shield voltage) to the gate electrode 104, the anode electrode 107 and the shield electrode 109, respectively, electrons having a certain divergence angle that are emitted from the emitter 105 are focused by the shield electrode 109, while being accelerated in the direction of the anode substrate 106, so that they collide with the phosphor layer 110. Consequently, the phosphor layer 110 emits light, and an image is displayed.
When a field emission display having the above-described configuration is used in applications requiring a high brightness of at least 1×104 cd/m2, it is necessary to set the anode voltage to at least 5 kV.
However, in the case of a field emission display having the above-described configuration, although it is possible to set the potential of the shield electrode to an optimum value when the anode voltage is in the range of 1 kV or lower, it is difficult to set the potential of the shield electrode to an optimum value when the anode voltage is in a high voltage region of 5 kV or higher, since it is not possible to maintain the withstand voltage between the shield electrode and the anode electrode safely. If the potential of the shield electrode cannot be set to an optimum value, then the focusing performance of the shield electrode decreases, so that inter-pixel crosstalk occurs, which undesirably causes a pixel that is adjacent to the actual light-emitting pixel to emit light. This leads to degradation of the resolution.
Therefore, in view of such problems, a field emission display that can achieve high brightness without increasing the anode voltage has been proposed (see e.g., JP2004-47140A).
As shown in
With the configuration of the field emission display shown in
When electrons that are emitted from a field emission electron source hit a phosphor layer, these electrons have sufficient excitation energy, so that light with a wavelength in the visible band is excited from the phosphor layer. Upon reaching the adjacent pixel, this excited light becomes a stray light component, causing inter-pixel crosstalk.
Nevertheless, in the case of the field emission display having the configuration shown in
The present invention has been made in order to solve the above-described problems in the related art, and it is an object of the invention to provide a field emission display that can achieve high brightness without increasing the anode voltage, and can realize high resolution by preventing inter-pixel crosstalk resulting from light excited from phosphor layers.
In order to achieve the above-described objects, a first configuration of a field emission display according to the present invention includes: a field emission electron source disposed in a vacuum container; and a phosphor screen that is disposed in the vacuum container, opposite to the field emission electron source, and that has a plurality of recessed portions on its surface opposing the field emission electron source, with phosphor layers being formed in the recessed portions, the field emission display displaying an image by causing the phosphor layers to emit light by collision of electrons emitted from the field emission electron source. An inner wall surface of the recessed portions widens in a tapered shape from the bottom surface side toward the opening side of the recessed portions. The adjacent recessed portions are divided by a rib structure made of a material having a light-absorbing effect (Black effect) with respect to light of the light-emitting wavelength. The phosphor layers are formed substantially all over the bottom surface and the inner wall surface of the recessed portions.
It is preferable that the above-described first configuration of the field emission display according to the present invention further includes an electron beam shield plate that is disposed in the vicinity of the phosphor screen on the field emission electron source side and that has openings corresponding to an opening size of the recessed portions. With this preferable configuration, by applying an intermediate (positive) voltage between the outgoing voltage (gate voltage) and the anode voltage to the electron beam shield plate, electrons that are emitted from the field emission electron source move straight ahead, with no lens effect exerted thereon, and only peripheral electrons are shielded (blocked) mechanically by the spatial filtering effect of the electron beam shield plate. Consequently, it is possible to prevent the electron beam from entering the adjacent pixel, thus achieving high resolution by suppressing the occurrence of inter-pixel crosstalk. Furthermore, in this case, it is preferable that a getter film having a gas-adsorbing effect is formed on at least one surface of the electron beam shield plate. According to this preferable configuration, outgassing components that are produced by, for example, the collision of electrons on the phosphor layer can be absorbed efficiently, so that the vacuum degree in the field emission display can be maintained favorably. As a result, it is possible to prevent the emitters constituting the field emission electron source from becoming inoperable due to discharge breakdown, thus making it possible to extend the life of the field emission electron source and that of the field emission display as well.
It is preferable that the above-described first configuration of the field emission display according to the present invention further includes an electron beam shield plate that is disposed in contact with the phosphor screen on the field emission electron source side and that has openings corresponding to an opening size of the recessed portions. Furthermore, in this case, it is preferable that a getter film having a gas-adsorbing effect is formed on a surface of the electron beam shield plate that is on the field emission electron source side.
In the above-described first configuration of the field emission display according to the present invention, it is preferable that the plurality of the recessed portions is arranged in a matrix form or a line form.
With the present invention, the effective surface area of the phosphor layers of the phosphor screen that correspond to each pixel can be increased significantly, and it is therefore possible to improve the emission brightness. Consequently, it is possible to realize a field emission display that can achieve high brightness without increasing the anode voltage. Furthermore, since the inner wall surface of each of the recessed portions in which the phosphor layers are formed widens in a tapered shape from the bottom surface side toward the opening side of the recessed portions, an electron beam (reflection component) that has been reflected after entering each of the phosphor layers on the inner wall surface of the recessed portions can be made incident again on the same phosphor layer in the recessed portions, and this also makes it possible to achieve an improved emission brightness. Furthermore, since the adjacent recessed portions are divided by a rib structure made of a material having a light-absorbing effect (Black effect) with respect to light of the light-emitting wavelength, it is possible to achieve high brightness by suppressing the occurrence of inter-pixel crosstalk resulting from light excited from the phosphor layers.
A second configuration of a field emission display according to the present invention includes: a field emission electron source disposed in a vacuum container; and a phosphor screen that is disposed in the vacuum container, opposite to the field emission electron source and that has a plurality of recessed portions on its surface opposing to the field emission electron source, with phosphor layers being formed in the recessed portions, the field emission display displaying an image by causing the phosphor layers to emit light by collision of electrons emitted from the field emission electron source. An inner wall surface of the recessed portions widens in a tapered shape from the bottom surface side toward the opening side of the recessed portions. The phosphor layers are formed substantially all over the bottom surface and the inner wall surface of the recessed portions. The second configuration of a field emission display further includes an electron beam shield plate that is disposed in the vicinity of the phosphor screen on the field emission electron source side and that has openings corresponding to an opening size of the recessed portions, and a getter film has a gas-adsorbing effect is formed on at least one surface of the electron beam shield plate.
A third configuration of a field emission display according to the present invention includes: a field emission electron source disposed in a vacuum container; and a phosphor screen that is disposed in the vacuum container, opposite to the field emission electron source and that has a plurality of recessed portions on its surface opposing to the field emission electron source, with phosphor layers being formed in the recessed portions, the field emission display displaying an image by causing the phosphor layers to emit light by collision of electrons emitted from the field emission electron source. An inner wall surface of the recessed portions widens in a tapered shape from the bottom surface side toward the opening side of the recessed portions. The phosphor layers are formed substantially all over the bottom surface and the inner wall surface of the recessed portions. The third configuration of a field emission display further includes an electron beam shield plate that is disposed in contact with the phosphor screen on the field emission electron source side and that has openings corresponding to an opening size of the recessed portions, and a getter film having a gas-adsorbing effect is formed on a surface of the electron beam shield plate that is on the field emission electron source side.
Hereinafter, the present invention will be described more specifically by way of an embodiment with reference to the accompanying drawings.
As shown in
The field emission electron source 2 includes: a cathode substrate 4 made of glass or the like; cathode electrodes 5 that are made of a metal film or the like formed as a thin film on the cathode substrate 4; a plurality of cathode portions 6 formed on the cathode electrodes 5; an insulating layer 7 that is made of an insulating film of silicon oxide or the like also formed on the cathode electrodes 5, surrounding the cathode portions 6; and a gate electrode 8 that is made of a film of, for example, Nb metal or polysilicon formed on the insulating layer 7. Here, the cathode portions 6 are arranged in a matrix form, and each of the cathode portions 6 is configured as an emitter array that includes a plurality of conical emitters (namely, several hundreds of emitters per pixel) constituted by a high-melting metal such as molybdenum, or a semiconductor such as silicon. Further, the gate electrode 8 serves as an outgoing electrode for applying a voltage to each of the emitters such that electrons are emitted from the tip of each emitter.
The phosphor screen 3 includes: an anode substrate 9 made of glass or the like; anode electrodes 10 that are formed by, for example, a metal film formed as a thin film on the anode substrate 9; a plurality of recessed portions 11 formed on the anode electrodes 10, opposite to the respective cathode portions 6; and phosphor layers 12 formed in the recessed portions 11. That is, each of the recessed portions 11, in which the phosphor layers 12 are formed, corresponds to a single display pixel, and the recessed portions 11 are arranged in a matrix form, as with the cathode portions 6 (see
In the field emission display 1 having the above-described configuration, by applying predetermined voltages (a gate voltage and an anode voltage) to the gate electrodes 8 and the anode electrodes 10, respectively, electrons that are emitted from each of the cathode portions 6 of the field emission electron source 2 are accelerated in the direction of the phosphor screen 3 and then collide with the corresponding phosphor layer 12, thereby causing the phosphor layers 12 to emit light to display an image.
As shown in
Preferably, the tapered angle α of the inner wall surface of the recessed portions 11 is in the range of 60°<α<90°. Since the phosphor layers 12 are formed on the bottom surface and the tapered inner wall surface of the recessed portions 11, it is preferable to increase the tapered angle α, in order to increase the effective surface area of the phosphor layers 12 of the phosphor screen 3 that correspond to each pixel. On the other hand, increasing the tapered angle α gives rise to the problem of increased technical difficulty of the formation process. By using a sandblasting technique used for the rib formation for plasma display panels (PDPs), it is possible to perform processing that provides a tapered angle α of 60° or more.
When electrons that are emitted from the cathode portions 6 of the field emission electron source 2 collide with the phosphor layers 12, these electrons have sufficient excitation energy, so that light with a wavelength in the visible band is excited from the phosphor layers 12. Then, upon reaching the adjacent pixel, this excited light becomes a stray light component, causing inter-pixel crosstalk. In order to prevent the occurrence of this crosstalk, the rib structure 13 dividing the adjacent recessed portions 11 is formed of a material having a light-absorbing effect (Black effect) with respect to light with a wavelength in the visible band (light-emitting wavelength). Examples of a suitable material having a light-absorbing effect (Black effect) include a black matrix resist, which is used commonly for the phosphor screens of CRTs. By using a material having a light-absorbing effect to light with a wavelength in the visible band (light-emitting wavelength) to form the rib structure 13 forming the inner wall surface of each of the recessed portions 11 in this way, it is possible to achieve high resolution by suppressing the occurrence of inter-pixel crosstalk resulting from light excited from the phosphor layers 12.
Preferably, an electron shield plate 14 that has openings 14a corresponding to the size of the opening surface (opening size) of the recessed portions 11 is disposed in the vicinity of the phosphor screen 3 on the field emission electron source 2 side. With this preferable configuration, by applying an intermediate (positive) voltage between the outgoing voltage (gate voltage) and the anode voltage to the electron beam shield plate 14, electrons that are emitted from the field emission electron source 2 move straight ahead, with no lens effect exerted thereon, and only peripheral electrons are shielded (blocked) mechanically by the spatial filtering effect of the electron beam shield plate 14. Consequently, it is possible to prevent the electron beam from entering the adjacent pixel, thus achieving even higher resolution by suppressing the occurrence of inter-pixel crosstalk.
As described above, with the configuration according to this embodiment, it is possible to realize a field emission display 1 that can achieve high brightness and high resolution at the same time.
Furthermore, when electrons that are emitted from the cathode portions 6 of the field emission electron source 2 collide with the phosphor layers 12, gas components are released into the field emission display 1 and thus the vacuum degree decreases, which in the worst case renders the emitters constituting the cathode portions 6 inoperable due to discharge breakdown. To prevent such a decrease in the vacuum degree, it is preferable to form a getter film 17 having a gas-adsorbing effect on at least one surface of the electron beam shield plate 14 disposed in the vicinity of the phosphor screen 3. Since the gettering effect of the getter film 17 greatly varies depending on the gas component, it is important to select an optimum material as the material of the getter film 17. As the material of the getter film 17, a Ba compound material and a Ti compound material, for example, can be used. By forming the getter film 17 having the gas-adsorbing effect on the surface of the electron beam shield plate 14 disposed in the vicinity of the phosphor screen 3 in this way, outgassing components that are produced by, for example, the collision of electrons with the phosphor layer 12 can be absorbed efficiently, so that the vacuum degree in the field emission display 1 can be maintained favorably. As a result, it is possible to prevent the emitters constituting the cathode portions 6 of the field emission electron source 2 from becoming inoperable due to discharge breakdown, thus making it possible to extend the life of the field emission electron source 2 and that of the field emission display 1 as well.
Here, a method for producing the phosphor screen 3 will be described with reference to
First, as shown in
Next, as shown in
Next, as shown in
Finally, as shown in
It should be noted that although the recessed portions 11 are formed in the shape of a truncated quadrangular pyramid in this embodiment, the recessed portions are not necessarily limited to this configuration, and may be in the shape of a truncated cone or a truncated polygonal pyramid, for example.
Further, although the recessed portions 11 in which the phosphor layers 12 are formed are arranged in a matrix form so as to correspond to each pixel in this embodiment, the recessed portions 11 are not necessarily limited to this configuration, and may be arranged in a line form, as shown in
Furthermore, although the electron beam shield plate 14 is spaced apart from the phosphor screen 3 in this embodiment, the electron beam shield plate 14 also may be disposed in contact with the phosphor screen 3, as shown in
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-284553 | Sep 2004 | JP | national |
