1
FIELD EMISSION DISPLAY DEVICE AND
METHOD OF MANUFACTURING SAME
BACKGROUND OF THE INVENTION
5
1. Field of the Invention
The present invention relates to a field emission display device capable of improving light emission uniformity of a phosphor surface (or display surface) of the field emission display device, and a method of manufacturing the same. 10
2. Description of the Background Art
In general, a field emission display device principally includes a cathode substrate formed with cathode electrodes, an insulating layer formed on the cathode substrate and the cathode electrodes, control electrodes formed on the insu- 15 lating layer, electron emission material layers received in openings formed through the control electrodes and the insulating layer and formed on exposed portions of the cathode electrodes at the bottom of the openings, and an anode substrate located at the front of the control electrodes 20 and formed with anode electrodes and phosphors (U.S. Pat. No. 3,500,102 (See FIGS. 1 to 4) and U.S. Pat. No. 4,857, 799 (See FIGS. 2 and 3)). In the conventional field mission display devices of this type, the openings of the control electrodes are circular in shape. 25
Some of such field emission display devices further include a shield electrode located between the control electrodes and the anode electrodes and formed with electron pass apertures through which an electron beam flowing from the electron emission material layers to the phosphors passes 30 (Japanese Patent Application Laid-Open No. 2002-324501). In the conventional field emission display devices of this type, the openings of the control electrodes are circular in shape, as described above. Each of the electron pass apertures of the shield electrode is, for example, circular in shape 35 and sized so that all of the opening areas of the corresponding openings of the control electrodes are within the opening area of each electron pass aperture (neither too large nor too small in size) (See FIG. 4 of Japanese Patent Application Laid-Open No. 2002-324501). In this structure, the intensity 40 of the electron beam flowing from each of the electron emission material layers through the corresponding openings of the control electrodes and the corresponding electron pass aperture of the shield electrode to the corresponding phosphor is proportional to the area in which the opening 45 areas of the corresponding openings of the control electrode overlap the opening area of the electron pass aperture of the shield electrode.
In the conventional field emission display devices, the openings through the control electrodes and the insulating 50 layer are formed by a photograph manufacturing process. Specifically, a photosensitive control electrode material layer is formed on the insulating layer, and only portions of the photosensitive control electrode material layer which are to be formed as the control electrodes are exposed to light to 55 change to the control electrodes, while portions to be formed as the openings are unexposed. A developer is caused to flow over the photosensitive control electrode material layer to erode and remove the unexposed portions (to be formed as the openings) of the photosensitive control electrode mate- 60 rial layer and portions of the insulating layer corresponding to the unexposed portions, thereby forming the openings through the control electrodes and the insulating layer.
In the field emission display device including the shield electrode, each electron pass aperture of the shield electrode 65 is sized so that all of the opening areas of the corresponding openings of the control electrodes are within the opening
2
area of each electron pass aperture. Therefore, the shield electrode is required to be assembled between the control electrodes and the anode electrodes with high assembly accuracy so that all of the opening areas of the corresponding openings of the control electrodes are within the opening area of each electron pass aperture of the shield electrode without extending off.
Further, if a shift of the assembly position of the shield electrode causes a difference between phosphors in the area in which the opening area of the corresponding electron pass aperture of the shield electrode overlaps the opening areas of the corresponding openings of the control electrodes, variations in the intensity of the electron beam flowing to the phosphors give rise to nonuniform amounts of light emission from the phosphors, resulting in a problem such that the light emission uniformity of a phosphor surface (display surface) of the field emission display device is impaired. Moreover, such defective products lead to increased manufacturing costs.
Furthermore, because the openings formed through the control electrodes and the insulating layer are circular in shape, the reduction in the diameter of the openings makes it difficult for the developer flow to spread to the bottoms of the openings during the formation of the openings. This requires much time for the formation of the openings and makes it difficult to form the openings. For this reason, the diameter of the openings must be large, which results in a problem such that the openings cannot be formed densely, and the intensity of the electron beam decreases.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a field emission display device capable of achieving the assembly of a shield electrode without the need for high assembly accuracy so that the light emission uniformity of a phosphor surface (or a display surface) of the field emission display device is maintained.
It is a second object of the present invention to provide a method of manufacturing a field emission display device capable of densely forming openings in a control electrode and an insulating layer, thereby to increase the intensity of an electron beam.
According to the present invention, a field emission display device includes a cathode substrate, an electron emission material layer, a control electrode, an anode substrate, and a shield electrode. The cathode substrate has a cathode electrode formed thereon. The electron emission material layer is formed on the cathode electrode. The control electrode is located at the front of the electron emission material layer and is formed with at least one opening opposed to the electron emission material layer. The anode substrate has an anode electrode and a phosphor formed thereon, and is located at the front of the control electrode. The shield electrode is located between the control electrode and the anode electrode and is formed with an electron pass aperture through which an electron beam flowing from the electron emission material layer via the opening of the control electrode to the phosphor passes. An opening dimension in a predetermined direction of the opening of the control electrode is greater than an opening dimension in the predetermined direction of the electron pass aperture of the shield electrode. The shield electrode is located at the front of the control electrode so that the entire range of the opening dimension in the predetermined direction of the electron pass aperture of the shield electrode is
within the range of the opening dimension in the predetermined direction of the opening of the control electrode.
Therefore, if the assembly position of the shield electrode is shifted in the predetermined direction, the field emission display device can eliminate variations in the area in which 5 the opening area of each electron pass aperture of the shield electrode overlaps the opening area of the corresponding opening of the control electrode. Thus the field emission display device can eliminate variations in the intensity of the electron beam flowing to each of the phosphors. This achieves the assembly of the shield electrode without the need for high assembly accuracy so that light emission uniformity of a phosphor surface (or display surface) of the field emission display device is maintained. 15
The present invention is also intended for a method of manufacturing a field emission display device. According to the present invention, the method includes the following steps (a) to (d). The step (a) is to form a cathode electrode on a cathode substrate. The step (b) is to form an insulating 20 layer on the cathode substrate and the cathode electrode, and to form a photosensitive control electrode material layer on the insulating layer. The step (c) is to expose to light a portion of the photosensitive control electrode material layer to be formed as a control electrode to change the portion into the control electrode, while a portion of the photosensitive control electrode material layer to be formed as an opening is left unexposed. The step (d) is to erode and remove the unexposed portion of the photosensitive control electrode 3Q material layer and a portion of the insulating layer lying under the unexposed portion by using a chemical solution, thereby to form the control electrode on the insulating layer and to form the opening through the control electrode and the insulating layer. In the step (c), the unexposed portion of 35 the photosensitive control electrode material layer is formed into a substantially rectangular shape. In the step (d), the chemical solution is caused to flow on the surface of the photosensitive control electrode material layer in a longitudinal direction of the unexposed portion of the photosensi- 4Q tive control electrode material layer to erode and remove the unexposed portion of the photosensitive control electrode material layer and the portion of the insulating layer lying under the unexposed portion.
The method produces the effects of: (1) allowing the flow 45 of chemical solution to effectively spread to the bottom of the opening formed through the control electrode and the insulating layer; and (2) forming the opening in a relatively short period of time. The above-mentioned effect (1) allows the flow of chemical solution to spread sufficiently to the 50 bottom of the opening if an opening dimension in a direction orthogonal to the longitudinal direction of the substantially rectangular opening of the control electrode is decreased to some extent. This achieves the formation of the opening of an elongated shape. The above-mentioned effect (2) prevents 55 the chemical solution from eroding the periphery of the opening more than expected and, accordingly, providing the greater opening area of the opening than expected. This reduces the spacing between the opening and its adjacent opening. These effects provide the elongated openings 60 closely spaced apart from each other (or densely formed), to increase the intensity of the electron beam flowing to each phosphor.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the 65 following detailed description of the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view of a field emission display device according to a preferred embodiment of the present invention;
FIG. 2 is a schematic side view showing the construction of the field emission display device according to the preferred embodiment of the present invention;
FIG. 3 is a schematic plan view of openings of a control electrode as seen from an electron pass aperture of a shield electrode in the field emission display device according to the preferred embodiment of the present invention;
FIGS. 4A to 4C are views for illustrating a method of manufacturing the field emission display device according to the preferred embodiment of the present invention;
FIG. 5 is a schematic side view showing the construction of a conventional field emission display device; and
FIG. 6 is a schematic plan view of openings of the control electrode as seen from an electron pass aperture of the shield electrode in the conventional field emission display device.
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
As shown in FIGS. 1 and 2, a field emission display device 1 according to this preferred embodiment of the present invention includes a cathode substrate 3, cathode electrodes 5 formed on the cathode substrate 3, flat electron emission material layers 13 formed on the cathode electrodes 5 and substantially similar in shape to, for example, openings 11 of a control electrode 9 to be described later, the control electrode 9 located at the front of the electron emission material layers 13 and having the openings 11 opposed to the electron emission material layers 13, a transparent anode substrate 15 located at the front of the control electrode 9, for example, transparent anode electrodes 17 formed on the rear surface of the anode substrate 15, phosphors 19 formed on the anode electrodes 17, and a shield electrode 23 located between the control electrode 9 and the anode electrodes 17 and formed with electron pass apertures 21 through which an electron beam B flowing from the electron emission material layers 13 via the openings 11 of the control electrode 9 to the phosphors 19 passes.
In this preferred embodiment, an insulating layer 7 is formed on the cathode substrate 3 and above the cathode electrodes 5, and the control electrode 9 is formed on the insulating layer 7. The openings 11 are formed through the control electrode 9 and the insulating layer 7. The electron emission material layers 13 are formed on the cathode electrodes 5 exposed at the bottom of the openings 11 in such a manner as to be accommodated in the openings 11.
The shield electrode 23 functions herein to protect the electron emission material layers 13 against a high voltage applied to the anode electrodes 17. The control electrode 9 functions as an extraction electrode (or gate electrode) for emission (or extraction) of electrons from the electron emission material layers 13.
The plurality of cathode electrodes 5 (only three of which are shown in FIG. 1) are, for example, in the form of strips each extending in the y direction and having a predetermined width, and are in parallel spaced apart relation to each other.
A plurality of control electrodes 9 (only one of which is shown in FIG. 1) are, for example, in the form of strips each extending in the x direction and having a predetermined
5
width, and are formed on the insulating layer 7 so as to be orthogonal to the cathode electrodes 5 and in parallel spaced apart relation to each other.
The above-mentioned openings 11 of a substantially rectangular (herein rectangular) configuration are formed at 5 intersections of the cathode electrodes 5 and the control electrodes 9. The openings 11 (herein three openings 11a, lib and 11c) extend in orthogonal relation to the longitudinal direction (the y direction) of the phosphors 19 and are in parallel spaced apart relation to each other (although only 10 one opening 11 may be required). The openings 11a, lib, 11c are formed so that an opening dimension Wl in a predetermined direction (herein a direction (the x direction) orthogonal to the longitudinal direction of the phosphors 19) thereof is greater than an opening dimension W2 in the 15 above-mentioned predetermined direction (the x direction) of the corresponding electron pass aperture 21 of the shield electrode 23. The electron emission material layers 13 are geometrically similar in shape to the corresponding openings 11a, lib and 11c of the control electrode 9. 20
The phosphors 19 are formed, for example, one for each of the portions of the anode electrodes 17 opposed to the respective intersections of the cathode electrodes 5 and the control electrodes 9. The phosphors 19 are, for example, of the same size and of a linear shape (i.e., elongated rectan- 25 gular shape), and extend in the same direction (herein the y direction).
The shield electrode 23 is, for example, in the form of a plate approximately coextensive with the cathode substrate 3. The above-mentioned electron pass apertures 21 are 30 formed in portions of the shield electrode 23 opposed to the respective phosphors 19 on the anode electrodes 17. The electron pass apertures 21 are of a substantially rectangular shape and of substantially the same size as the phosphors 19. Each of the electron pass apertures 21 is provided so that the 35 longitudinal direction thereof extends along the longitudinal direction (or in the y direction) of a corresponding one of the phosphors 19.
The shield electrode 23 is located between the control electrode 9 and the anode electrodes 17 so that each of the 40 electron pass apertures 21 thereof is positioned in front of the corresponding phosphor 19 on the anode substrate 15 and so that each of the electron pass apertures 21 is orthogonal to the corresponding openings 11 of the control electrode 9 (i.e., with reference to FIG. 3, so that the entire range of 45 the opening dimension W2 in the x direction of each electron pass aperture 21 is within the range of the opening dimension Wl in the x direction of the corresponding openings 11 of the control electrode 9 and so that the entire range of an opening dimension W4 in the y direction of all of the 50 corresponding openings 11a, lib and 11c of the control electrode 9 is within the range of an opening dimension W3 in the y direction of each electron pass aperture 21).
Although not shown, the field emission display device 1 further includes spacing holding elements for holding the 55 spacing between the substrates 3,15 and the shield electrode 23, an envelope for hermetically sealing a space between the substrates 3 and 15 to maintain a vacuum therein, and drive circuits for applying voltages to the respective electrodes 5, 9, 17, and 23. 60
In the field emission display device 1, a high voltage (e.g., 14 kV) for electron acceleration is normally applied to the anode electrodes 17. A voltage lower than the voltage applied to the anode electrodes 17 (e.g., a voltage as high as a voltage applied to the control electrode 9) is normally 65 applied to the shield electrode 23 for the purpose of shielding against a high-voltage electric field from the anode
6
electrodes 17. A scanning voltage is scanned and applied to one of the cathode electrode 5 and the control electrode 9, and a display voltage is selectively applied to the other. A voltage (e.g., 500 V) required for electron emission due to a difference between the scanning voltage and the display voltage is applied to the electron emission material layers 13 at the intersections of the cathode electrodes 5 and the control electrodes 9 applied with the scanning voltage and the display voltage, whereby electrons (or the electron beam B) are emitted from the electron emission material layers 13. The emitted electron beam B passes through the corresponding openings 11 of the control electrodes 9 and the corresponding electron pass aperture 21 of the shield electrode 23, and are accelerated by the high voltage of the anode electrodes 17 to impinge upon the corresponding phosphor 19, thereby causing the phosphor 19 to emit light.
Next, a method of manufacturing the field emission display device 1 will now be described.
First, as shown in FIG. 4A, the cathode electrode 5 is formed on the cathode substrate 3, and the insulating layer 7 is formed on the cathode substrate 3 and the cathode electrode 5. A photosensitive control electrode material layer 27 is formed on the insulating layer 7.
Then, as shown in FIG. 4B, ultraviolet light is selectively directed through a photomask onto the formed photosensitive control electrode material layer 27, to expose only a portion 27b of the photosensitive control electrode material layer 27 which is to be formed as the control electrode 9 to light, thereby curing the portion 27b into the control electrode 9, while a portion 27a of the photosensitive control electrode material layer 27 which is to be formed as the opening 11 is unexposed. The unexposed portion 27a (which is to be formed as the opening 11) is formed in a substantially rectangular shape.
Then, as shown in FIG. 4C, a chemical solution (herein, a developing solution) is sprayed onto the photosensitive control electrode material layer 27 (27a and 27b) so as to flow on an upper surface of the photosensitive control electrode material layer 27 in the longitudinal direction (the x direction) of the unexposed portion 27a of the photosensitive control electrode material layer 27, thereby to erode and remove the unexposed portion 27a of the photosensitive control electrode material layer 27 and a portion of the insulating layer 7 which lies under the unexposed portion 27a. This provides the substantially rectangular opening 11 formed through the control electrode 9 and the insulating layer 7 and having a bottom at which the cathode electrode 5 is exposed. Since the chemical solution is caused to flow on the surface of the photosensitive control electrode material layer 27 in the longitudinal direction of the unexposed portion 27a of the photosensitive control electrode material layer 27, the flow of the chemical solution can effectively spread to the bottom of the opening 11 formed through the control electrode 9 and the insulating layer 7.
Then, as shown in FIG. 2, the electron emission material layer 13 is formed on the cathode electrode 5 exposed at the bottom of the opening 11 in such a manner as to be accommodated in the opening 11 formed through the control electrode 9 and the insulating layer 7.
Next, as shown in FIGS. 2 and 3, the shield electrode 23 formed with the substantially rectangular electron pass apertures 21 is assembled, for example, to the cathode substrate 3 so as to be located at the front of the control electrode 9 and so that each electron pass aperture 21 thereof is orthogonal to the corresponding openings 11 of the control electrode 9.
|
