Patent Grant
7064479
The present invention relates to a cold cathode display device, and more particularly to a cold cathode display device having a small thickness and a large display area.
A cold cathode display device is a display device which causes electrons emitted from an electron emitting part thereof to collide with a phosphor in a space formed by disposing a pair of substrates, at least one of which is transparent, opposite to each other, thereby displaying a desired pattern.
A back substrate 101 and a face substrate 102 are disposed opposite to each other with a spacer 103 interposed therebetween, to form a chamber. The chamber is evacuated. Each of the back substrate 101 and the face substrate 102 is attached to the spacer 103 by glass frit 104, and at least a portion of the face substrate 102 which serves as a display surface is required to be transparent in view of properties of a cold cathode display device. A light emitting part is formed on an inner side of the face substrate 102 in order to display a desired pattern. The light emitting part is formed by depositing a phosphor 108 on a transparent electrode 109 serving as a positive electrode (, which part will hereinafter be also referred to as an “anode”).
On the other hand, an electron emitting part is formed on an inner side of the back substrate 101, so as to be opposite to the anode. The electron emitting part is formed by depositing a cold cathode material 106 on a substrate electrode 105 serving as a negative electrode (, which part will hereinafter be also referred to as a “cathode”). While a filament has conventionally been employed as such an electron emitting part, a conductive layer including a carbon nanotube which can be manufactured by a printing process has become used as a material for a field emission type cold cathode, recently. Reasons for recent use of a conductive layer including a carbon nanotube as an electron source are higher brightness and a longer life time as compared to those provided by use of a filament. Also, as a conductive layer can be manufactured by a printing process, low cost manufacture is possible. Meanwhile, details of a technique for employing a conductive layer including a carbon nanotube as a material for a field emission type cold cathode are provided in Japanese Patent Application Laid-Open No. 2001-155666.
Further, an extraction electrode 107 for controlling electrons is provided between the anode and the cathode. The extraction electrode 107 has many apertures through which electrons emitted from the cathode pass, the apertures being located at positions at which the extraction electrode 107 and the cathode intersect each other. The extraction electrode 107 is configured such that a leg portion, formed by bendin6fritg a portion of the extraction electrode 107, is attached to the back substrate 101 by glass frit, and is secured to the back substrate 101. There is a need of externally supplying a potential to the extraction electrode 107. For this reason, the extraction electrode 107 is connected to a copper wire electrode 110, a portion of which penetrates the glass frit 104 to protrude from the chamber, within the chamber. As there is a need of externally supplying a potential also to each of the substrate electrode 105 and the transparent electrode 109, each of the substrate electrode 105 and the transparent electrode 109 is connected to the copper wire electrode in an analogous manner to the extraction electrode 107. It should be noted that
Next, principles of operations of the cold cathode display device will be explained. Basically, operations of the cold cathode display device are similar to those of a triode. Upon application of a potential to the substrate electrode 105 of the cathode within the chamber holding therein a vacuum with a pressure in a range between approximately 10□3 and 10□5 Pa, electrons are emitted from the cold cathode material 106. The emitted electrons are controlled by the extraction electrode 107, and are accelerated because of a potential difference between the transparent electrode 109 of the anode and the substrate electrode 105 of the cathode. The accelerated electrons reach the phosphor 108 of the anode, and excite the phosphor. The excited phosphor emits light when returning to a normal energy state. The cold cathode display device provides a desired display by utilizing the light emission of the phosphor.
The conventional cold cathode display device is a simple triode which is composed of an anode, an extraction electrode and a cathode. With this composition, the following problems have been caused.
A structure of the extraction electrode of the conventional cold cathode display device has been designed to have an optimum diameter of the aperture in the extraction electrode, an optimum plate thickness of the extraction electrode and an optimum distance between the extraction electrode and the cathode, taking into account mainly an extraction voltage and an extraction efficiency. However, optimization of a diameter of the aperture in the extraction electrode, a plate thickness of the extraction electrode and a distance between the extraction electrode and the cathode could not allow sufficient reduction of a size of electrons (which will hereinafter be also referred to as an “electron beam”) emitted from the cathode, which is measured on a surface of the anode. As such, a distance which the electron beam travels until it reaches the surface of the anode should be reduced, thereby making the size of the electron beam as measured on the surface of the anode (which will hereinafter be also referred to an “electron beam diameter”) smaller than a size of the phosphor of the anode. This requires a distance between the anode and the extraction electrode to be reduced.
Due to the requirement that the distance between the anode and the extraction electrode be reduced, a voltage which can be applied between the anode and the extraction electrode is limited, so that a high voltage can not be applied. Being unable to apply a high voltage to the anode results in a failure to sufficiently enhance an efficiency in light emission of the phosphor. This causes a problem of non-achievement of a cold cathode display device providing a satisfactory brightness.
The requirement that the distance between the anode and the extraction electrode be reduced, on the other hand, results in reduction of a distance between the cathode and the anode. Accordingly, there is a need for configuring the cold cathode display device to have a ratio of approximately 1:1 between a size of the electron emitting part of the cathode and a size of the phosphor of the anode. As a result, in a situation where a voltage on the extraction electrode is varied in order to adjust a current value so that a degree of convergence in the vicinity of the extraction electrode is varied to further vary an electron beam diameter, the variation in electron beam diameter directly affects light emission of the phosphor of the anode, resulting in variation in brightness among pixels.
Moreover, the requirement that the distance between the anode and the extraction electrode be reduced makes a required level of an accuracy in assembling, high. A low accuracy in assembling results in positional shift of an electron beam, to bring about emission of mixed colors in which another phosphor located next to an intended phosphor emits light. This causes a problem of degradation in color purity.
A further problem of localization of electrons in emission thereof from a surface of the cathode is caused. Causes of this problem are as follows. In a typical cold cathode electron source, emission characteristic thereof is determined by a strength of an electric field and a work function of an uneven surface of a cathode with protrusions. However, an electric field strength is very responsive to respective configurations of the protrusions. Even if a work function of the surface of the cathode can be made uniform in some way, it is technically difficult to planarize the surface of the cathode with an accuracy on the order of μm or smaller. Accordingly, variation in height among the protrusion of the surface of the cathode is unavoidable, to allow an amount of electrons emitted from the cathode to depend greatly on an electric field of the surface of the cathode. Hence, there are created a portion which can easily emit electrons and a portion which can not easily emit electrons due to subtle variation in configuration among the protrusions in the surface of the cathode. In the portion which can easily emit electrons, a current value increases exponentially in accordance with an increase of the electric field of the surface after electron emission is initiated. As a result, localization of an electron emitting region occurs on the surface of the cathode so that light emitting points are interspersed like dots in a pixel which is lighted up, which causes a problem of degrading an image quality.
It is an object of the present invention to solve the foregoing problems and provide a structure of a cold cathode display device in which an anode can be sufficiently distant from an extraction electrode to ensure a breakdown voltage, an electron beam diameter can be made sufficiently smaller than a size of a phosphor, and light emitting points of a pixel can be prevented from being interspersed like dots, thereby suppressing degradation of an image quality, as well as a method of manufacturing such a cold cathode display device.
According to the present invention, a cold cathode display device includes: a pair of substrates of first and second substrates which are disposed opposite to each other so as to form a space therebetween which is evacuated, at least a display portion of the second substrate serving as a display surface being transparent; a light emitting part which is disposed at a predetermined position on a side of the second substrate on which the space is formed, and includes a positive electrode and phosphors provided on the positive electrode; an electron emitting part which is disposed on a side of the first substrate on which the space is formed so as to be opposite to the light emitting part, and emits an electron upon application of a predetermined potential; an extraction electrode provided between the electron emitting part and the light emitting part, for controlling the electron emitted from the electron emitting part; and a focus electrode which is provided between the light emitting part and the extraction electrode, and is,provided with windows through which the electron emitted from the electron emitting part pass.
The cold cathode display device according to the present invention allows an anode to be sufficiently distant from an extraction electrode to ensure a breakdown voltage, allows an electron beam diameter to be sufficiently reduced as compared to a size of a phosphor, and prevents light emitting points of a pixel from being interspersed like dots to degrade image quality.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
a)–6(c) are sectional views showing electron beam paths according to the first preferred embodiment of the present invention.
a)–7(c) are sectional views showing electron beam paths according the first preferred embodiment of the present invention.
a)–12(g) illustrate processes in manufacturing a structure in the vicinity of a cathode according to the third preferred embodiment of the present invention.
On the other hand, a back substrate 9 according to the first preferred embodiment has a structure in which cathodes 7 are formed on the back substrate 9 so as to be opposite to the anodes 2, respectively, and barriers 8 are formed adjacent to the cathodes 7, respectively, on the back substrate 9. According to the first preferred embodiment, lines of the cathodes 7 and lines of the barriers 8 are arranged in stripes. The lines of the cathodes 7, each of which is 100 μm wide, are arranged so as to have a pitch of 200 μm.
Further, extraction electrodes 5 arranged in stripes are provided over the back substrate 9 on which the cathodes 7 are formed, so as to be orthogonal to the stripes of the cathodes 7. The extraction electrodes 5 are provided with electron passage windows 6, and the extraction electrodes 5 are disposed such that the electron passage windows 6 are located on the cathodes 7. The extraction electrodes 5 are attached to, and supported by, the barriers 8 via glass frit.
The structure of the back substrate 9 according to the first preferred embodiment further includes a focus electrode 3. The focus electrode 3 is formed of a single metal plate and provided over the back substrate 9 on which the extraction electrodes 5 and the cathodes 7 are formed. Also, the focus electrode 3 is provided with electron passage windows 4, and the focus electrode 3 is disposed such that the electron passage windows 4 are located on the cathodes 7 and the electron passage windows 6 of the extraction electrodes. The focus electrode 3 is attached to, and supported by, the extraction electrodes 5, via an insulating material, with a predetermined distance being kept therebetween.
The cold cathode display device according to the first preferred embodiment has a structure in which the face substrate 1 with the foregoing structure and the back substrate 9 with the foregoing structure are disposed so as to allow the anodes 2 and the cathodes 7 to be opposite to each other, and respective peripheries of the face substrate 1 and the back substrate 9 are attached to, and supported by, each other via a spacer so that a predetermined distance can be kept therebetween. Additionally, another spacer is optionally provided inside the device in order to keep the predetermined distance between the face substrate 1 and the back substrate 9. To drive the cold cathode display device requires that a potential be externally supplied to electrodes such as the focus electrode 3 and the extraction electrodes 5. For this reason, those electrodes are connected to external electrodes as needed. However,
It is noted that values noted above for parameters such as dimensions of the windows and the plate thickness are provided for illustrative purposes, and can be arbitrarily determined depending on a specification of an individual cold cathode display device. Further, though the phosphors provided on the anodes 2 and the cathodes 7 are arranged in stripes according to the first preferred embodiment, such arrangement is a mere example. The phosphors provided on the anodes 2 and the cathodes 7 may alternatively be arranged in a matrix.
Next, operations of the focus electrode according to the first preferred embodiment will be explained.
First, description will be made about an electron beam path in the section A—A parallel to the X direction (
After the electrons pass the extraction electrode 5, the electrons are moderately accelerated by a potential difference between the extraction electrode 5 and the focus electrode 3. Also, as the focus electrode 3 causes a force in the X direction to be exerted on the electron beam path, the electron beam path expands. However, by reducing a distance between the extraction electrode 5 and the focus electrode 3, the expansion of the electron beam path is suppressed, to prevent the electrons from colliding with the focus electrode 3. Also, the shorter side of each of the electron passage windows 4 of the focus electrode 3 extends along the X direction, and the focus electrode 3 is located in the vicinity of the electron beam path. A region in the vicinity of the focus electrode 3 is affected by an electric field from the anodes 2, so that a force in a direction which causes the electron beam path to converge is exerted on the electron beam path. Therefore, the electron beam path in the section A—A parallel to the X direction gradually converges and is focused onto a surface of one of the anodes by the focus electrode 3.
Next, description will be made about an electron beam path in the section B—B parallel to the Y direction (
After the electrons pass the extraction electrode 5, the electrons are moderately accelerated by a potential difference between the extraction electrode 5 and the focus electrode 3. Also, as the focus electrode 3 causes a force in the Y direction to be exerted on the electron beam path, the electron beam path expands. Further, the longer side of each of the electron passage windows 4 of the focus electrode 3 extends along the Y direction, and the focus electrode 3 is not present in the vicinity of the electron beam path. Accordingly, a force which is generated under influence of an electric field from one of the anodes 2 and causes the electron beam path to converge in the vicinity of the focus electrode 3 is not substantially exerted on the electron beam path. Therefore, the electron beam path in the section B—B parallel to the Y direction gradually expands to be focused onto the surface of the anode without converging.
Though
Next,
Variation in electron beam diameter on the surface of one of the anodes in accordance with variation in a potential difference between one of the extraction electrodes 5 and one of the cathodes 7 as described above is shown in
As is made clear from the foregoing, the provision of the focus electrode 3 in the cold cathode display device makes it possible to control an electron beam diameter on the surface of each of the anodes so as to be smaller than a size of each of the phosphors. Also, an electron beam diameter can be controlled independently of a potential difference between one of the extraction electrodes 5 and one of the cathodes 7. Accordingly, there is no need for limiting a distance between the anodes 2 and the extraction electrodes 5 in order to control an electron beam diameter, which allows the anodes 2 to be distant from the extraction electrodes enough to ensure a breakdown voltage.
Since a distance between the anodes and the extraction electrodes can be broad, also a distance between the cathodes and the anodes can be broad. This eliminates a need for configuring the cold cathode display device to have a ratio of approximately 1:1 between a size of a light emitting part of each of the cathodes and a size of the phosphor of each of the anodes. Even in a situation where a voltage on one of the extraction electrodes is varied in order to adjust a current value so that a degree of convergence in the vicinity of the extraction electrode is varied to further vary an electron beam diameter, possible influence by the variation in electron beam diameter is prevented from being exerted directly on light emission of the phosphors of the anodes, to suppress problematic variation in brightness among pixels.
Further, since a distance between the anodes and the extraction electrodes can be broad, a required level of an accuracy in assembling can be reduced. This relieves the problem of degradation in color purity due to a positional shift of an electron beam and resulting emission of mixed colors in which a phosphor adjacent to an intended phosphor emits light, which are caused by a low accuracy in assembling.
Moreover, the problem of degradation in image quality due to localization of an electron emitting region in the surface of each of the cathodes which causes a lighted pixel to be interspersed with light emitting points like dots is relieved by provision of the focus electrode 3 in the cold cathode display device. Specifically, when electrons are emitted from one localized electron emitting region, a corresponding electron beam path is caused to expand in the Y direction by the focus electrode 3. As a result of this expansion of the electron beam path, the electron beam path and another electron beam path coming from another localized electron emitting region overlap each other on the surface of one of the anodes, to cause the phosphor to emit light on the surface of the anode. Accordingly, dot-like light emission in a lighted pixel is made uniform, to relieve a problem of degradation of image quality.
The cold cathode display device according to the first preferred embodiment includes a pair of substrates, the face substrate 1 and the back substrate 9 disposed opposite to each other, so as to form a space therebetween, which is evacuated. At least a display portion of the face substrate 1 serving as a display surface is transparent. The cold cathode display device according to the first preferred embodiment further includes: the anodes 2 which are disposed at predetermined positions on a side of the face substrate 1 on which the space is formed, and positive electrodes and phosphors formed on the positive electrodes; the cathodes 7 which are disposed at positions opposite to the anodes 2 on a side of the back substrate 9 on which the space is formed and which emit electrons upon application of a predetermined potential; the extraction electrodes 5 provided between the cathodes 7 and the anodes 2, for controlling the electrons emitted from the cathodes 7; and the focus electrode 3 which is provided between the anodes 2 and the extraction electrodes 5 and is provided with the electron passage windows 4 through which the electrons emitted from the cathodes 7 pass. The cold cathode display device according to the first preferred embodiment makes it possible: to dispose the anodes 2 at a sufficient distant from the extraction electrodes 5 to ensure a breakdown voltage; to sufficiently reduce an electron beam diameter relative to a size of each of the phosphors; and to prevent light emitting points from being interspersed like dots in each pixel to suppress degradation in image quality.
In the cold cathode display device according to the first preferred embodiment, the focus electrode 3 is made of a plate-shaped material, and the electron passage windows 4 are provided in the plate-shaped material so as to form a grid including elongate rectangles. The cold cathode display device according to the first preferred embodiment makes it possible: to dispose the anodes 2 at a sufficient distant from the extraction electrodes 5 to ensure a breakdown voltage; to sufficiently reduce an electron beam diameter relative to a size of each of the phosphors; and to prevent light emitting points from being interspersed like dots in each pixel to suppress degradation in image quality.
The configuration of the focus electrode 3 according to the first preferred embodiment, however, requires that the electron passage windows 4 be aligned with the cathodes 7 and the electron passage windows 6 of the extraction electrodes because each of the electron passage windows 4 contributes to formation of one pixel. A level of an accuracy in this alignment should be high because of a small size of each of the electron passage windows 4 with a 500 μm-long longer side and a 100 μm-long shorter side. If the focus electrode 3 is misaligned, a sufficient electron beam does not reach each of the anodes 2, to reduce light emission of each of the phosphors resulting in degradation of image quality.
In view of the foregoing, the focus electrode 3 according to the second preferred embodiment has a configuration in which the electron passage windows 4 are arranged in stripes. In other words, the focus electrode 3 according to the second preferred embodiment is formed of a multiplicity of spaced parallel metal lines. As such, there is no portion of the focus electrode 3 in a direction orthogonal to the line of each of the cathodes 7. To employ such configuration with stripes for the focus electrode 3 eliminates a need for a high accuracy alignment in a direction parallel to the line of each of the cathodes 7, to facilitate manufacture.
It is noted that also the focus electrode 3 with the configuration according to the second preferred embodiment functions to narrow a diameter of an electron beam in the direction orthogonal to the line of each of the cathodes 7, (i.e., the X direction), and to increase a diameter of an electron beam in the direction parallel to the line of each of the cathodes 7 (i.e., Y direction), in the same manner as the focus electrode 3 according to the first preferred embodiment.
In a cold cathode display device according to the second preferred embodiment, the focus electrode 3 is made of a multiplicity of lines, and the multiplicity of lines are disposed so as to be parallel to, and spaced from, one another so that the electron passage windows 4 are arranged in stripes. The cold cathode display device according to the second preferred embodiment provides for reduction of a required level of an accuracy in alignment between the electron passage windows 4 of the focus electrode 3 and the electron passage windows, 6 of the extraction electrodes 5, or the like.
To employ a printing process in forming the focus electrode 3 and the extraction electrode 5 makes it possible to form the focus electrode 3 and the extraction electrode 5 with a high accuracy. Also, a further advantage of eliminating a need for a process of assembling the focus electrode 3 and the extraction electrode 5 is produced. Also the focus electrode 3 manufactured by such a manufacturing method as described above according to the third preferred embodiment functions to narrow a diameter of an electron beam in the direction orthogonal to the line of the cathode 7 (i.e., the X direction) and to increase a diameter of an electron beam in the direction parallel to the line of the cathode 7 (i.e., the Y direction) in the same manner as the focus electrode 3 according to the first preferred embodiment.
A method of manufacturing a cold cathode display device according to the third preferred embodiment includes a step of forming the extraction electrode 5 on the back substrate 9 by a printing process, and a step of forming the focus electrode 3 over the back substrate 9 by a printing process. The method of manufacturing a cold cathode display device according to the third preferred embodiment makes it possible to form the extraction electrode 5 and the focus electrode 3 with a higher accuracy, and eliminates a need for a process of assembling the extraction electrode 5 and the focus electrode 3.
Also, in the method of manufacturing a cold cathode display device according to the third preferred embodiment, the step of forming the focus electrode 3 over the back substrate 9 by a printing process includes forming the barrier 8 over the back substrate 9 and then forming the focus electrode 3 on the barrier 8 by a printing process. The method of manufacturing a cold cathode display device according to the third preferred embodiment makes it possible to form the extraction electrode 5 and the focus electrode 3 with a higher accuracy, and eliminates a need for a process of assembling the extraction electrode 5 and the focus electrode 3.
A cold cathode display device according to a fourth preferred embodiment is characterized by the window in the focus electrode. Description will be made with reference to
Further, the extraction electrodes 5 formed in stripes are provided over the back substrate 9 on which the cathodes 7 are formed, so as to be orthogonal to the stripes of the cathodes 7. The extraction electrodes 5 are provided with the electron passage windows 6, and the extraction electrodes 5 are disposed such that the electron passage windows 6 are located on the cathodes 7. The extraction electrodes 5 are attached to, and supported by, the barriers 8 via glass frit. More than one electron passage window 6 is provided at each position for one pixel. For example, one pixel includes approximately 10 electron passage windows 6. Each of the electron passage windows 6 is provided such that a longer side thereof and a shorter side thereof extend along the X direction and the Y direction, respectively. A length of the longer side is 100 μm, and a length of the shorter side is 20 μm, for example.
Moreover, the focus electrode 3 is formed over the back substrate 9 on which the extraction electrodes 5 and the cathodes 7 are formed. Also the focus electrode 3 is provided with the electron passage windows 4. Though
Because of such a structure in which more than one electron passage window 6 of the extraction electrodes 5 is provided so as to be matched with each of the electron passage windows 4 of the focus electrode 3, an electron having passed through one of the electron passage windows 6 and an electron having passed through another one of the electron passage windows 6 travel the same path when they pass through one of the electron passage windows 4. Accordingly, unevenness in distribution of electrons passing through the electron passage windows 6 can be eliminated when the electrons pass through the electron passage windows 4 so that evenness is achieved. Thus, it is possible to supply even distribution of electrons to the anodes 2.
Also, a configuration in which each longer side of the electron passage windows 6 extends along the X direction and each longer side of the electron passage windows 4 extends along the Y direction, allows for control of convergence of electrons in the X direction when the electrons pass through the electron passage windows 4. In a situation where a voltage applied between one of the extraction electrodes 5 and one of the cathodes 7 is controlled to vary a current value of electrons in order to allow a cold cathode display device to provide gradational display, converge of electrons in the X direction would not be affected by a change in voltage on the extraction electrode 5, in the foregoing configuration. Thus, it is possible to prevent electrons from being scattered too widely in the X direction before the electrons reach one of the anodes 2, to prevent a pixel different from an intended pixel from problematically emitting light.
In the cold cathode display device according to the fourth preferred embodiment, the focus electrode 3 is provided with the electron passage windows 4 each of which is rectangular or non-circular. A longer diameter or side of each of the electron passage windows 4 is parallel to a longer side of each of the phosphors formed on the anodes 2, and orthogonal to a longer diameter or side of each of the non-circular or rectangular electron passage windows 6 formed in the extraction electrodes 5. More than one electron passage window 6 is provided so as to be matched with each of the electron passage windows 4. In the cold cathode display device according to the fourth preferred embodiment, evenly distributed electrons can be supplied to the anodes 2. Further, no influence is exerted on convergence of electrons when the cold cathode display device provides gradational display.
According to a fifth preferred embodiment, a relationship between the window of the focus electrode 3 and a plate thickness of the focus electrode 3 is numerically limited. A structure according to the fifth preferred embodiment is substantially identical to that described in the first preferred embodiment and illustrated in
The back substrate 9 according to the fifth preferred embodiment has a structure in which the cathodes 7 are formed on the back substrate 9 so as to be opposite to the anodes 2, respectively, and the barriers 8 are formed adjacent to the cathodes 7, respectively, on the back substrate 9. According to the fifth preferred embodiment, lines of the cathodes 7 and lines of the barriers 8 are arranged in stripes. The lines of the cathodes 7, each of which is 100 μm wide, are arranged so as to have a pitch of 200 μm.
On the other hand, the anodes 2 are formed of R/G/B phosphors arranged in stripes, and sets each including one R phosphor, one G phosphor and one B phosphor are arranged so as to have a pitch of 0.6 mm. Further, black stripes are formed between the phosphors in order to improve contrast. Each of the phosphors is 100 μm wide, and an aluminum back is formed on each of the anodes 2 for the purposes of improving an efficiency in light emission and establishing electrical conduction. Moreover, a distance between the anodes 2 and the cathodes 7 is approximately 9 mm, and a voltage of 9 kV is applied between one of the anodes 2 and one of the cathodes 7.
Further, the extraction electrodes 5 arranged in stripes are provided over the back substrate 9 on which the cathodes 7 are formed, so as to be orthogonal to the stripes of the cathodes 7. The extraction electrodes 5 are provided with the electron passage windows 6, and the extraction electrodes 5 are disposed such that the electron passage windows 6 are located on the cathodes 7. The extraction electrodes 5 are attached to, and supported by, the barriers 8 via glass frit. In each of the extraction electrodes 5, more than one electron passage window 6 is provided at each position for one pixel. One pixel includes approximately 10 electron passage windows 6 of the extraction electrodes 5. The electron passage windows 6, each with a 100 μm-long longer side and a 20 μm-long shorter side, are arranged so as to have a pitch of 60 μm. In the fifth preferred embodiment, a width of each of the cathodes 7 serving as an electron emitting part is 100 μm.
Then, the focus electrode 3 is formed over the back substrate 9 on which the extraction electrodes 5 and the cathodes 7 are formed. The focus electrode 3 is provided with the electron passage windows 4.
To overcome this, according to the fifth preferred embodiment, the shorter-side-length/plate-thickness ratio is made smaller than 2 by utilizing the relationship between the electric field strength ratio and the shorter-side-length/plate-thickness ratio shown in
In a cold cathode-display device according to the fifth preferred embodiment, a shorter diameter or a length of a shorter side of each of the electron passage windows 4 is smaller than twice the plate thickness of the focus electrode 3. In the cold cathode display device according to the fifth preferred embodiment, influence of a voltage applied to each of the anodes 2 which is exerted on the cathodes 7 does not become great, thereby preventing degradation of controllability of the extraction electrodes 5 over electrons.
According to a sixth preferred embodiment, a positional relationship between the focus electrode 3 and the cathodes 7 is numerically limited. Also a structure according to the sixth preferred embodiment is substantially identical to that described in the first preferred embodiment and illustrated in
On the other hand, the anodes 2 are formed of R/G/B phosphors arranged in stripes, and sets each including one R phosphor, one G phosphor and one B phosphor are arranged so as to have a pitch of 0.6 mm. Further, black stripes are formed between the phosphors in order to improve contrast. Each of the phosphors is 100 μm wide, and an aluminum back is formed on each of the anodes 2 for the purposes of improving an efficiency in light emission and establishing electrical conduction. Moreover, a distance between the anodes 2 and the cathodes 7 is approximately 9 mm, and a voltage of 9 kV is applied between one of the anodes 2 and one of the cathodes 7.
Further, the extraction electrodes 5 arranged in stripes are provided over the back substrate 9 on which the cathodes 7 are formed, so as to be orthogonal to the stripes of the cathodes 7. The extraction electrodes 5 are provided with the electron passage windows 6, and the extraction electrodes 5 are disposed such that the electron passage windows 6 are located on the cathodes 7. Then, the focus electrode 3 is formed over the back substrate 9 on which the extraction electrodes 5 and the cathodes 7 are formed. The focus electrode 3 is provided with the electron passage windows 4.
The foregoing relationship indicates that an electrostatic lens is formed because of the distance between the focus electrode 3 and the cathodes 7. Accordingly, it can be interpreted that an image of electrons emitted from the cathodes 7 is formed on each of the anodes 2 using the focus electrode 3. In view of this, to formulate a model by representing the distance between the focus electrode 3 and the cathodes 7 by d, a distance between the anodes 2 and the cathodes 7 by D, a width of each of the cathodes 7 by w, a pitch of the R/G/B phosphors by W (0.2 mm in the sixth preferred embodiment), and a voltage on each of the anodes by Va (kV), results in establishment of a relationship of F×w×((D−d)/d)×(9/Va)1/2<W. As d=200 μm, D=9000 μm, w=100 μm, W=200 μm, and Va=9 kV in the sixth preferred embodiment, F is smaller than 1/22. Accordingly, the distance d between the focus electrode 3 and the cathodes 7 should be determined so as to establish a relationship of (D/d−1)×w×(9/Va)1/2/W<22 It is noted that the distance between the anodes 2 and the cathode 7 is a minimum distance between one of the anodes 2 and one of the cathodes 7, more specifically, a distance between a bottom surface of the one anode 2 and a top surface of the one cathode 7.
In a cold cathode display device according to the sixth preferred embodiment, the distance d between the focus electrode 3 and the cathodes 7 is correlated with the distance D between the cathodes 7 and the anodes 2, the width w of each of the cathodes 7, the pitch W of the phosphors and the voltage Va on each of the anodes, such that the relationship of (D/d−1)×w×(9/Va)1/2/W<22 is satisfied. The cold cathode display device according to the sixth preferred embodiment prevents other phosphors than an intended phosphor from emitting light due to emission of electrons to the other phosphors. Thus, a cold cathode display device having a high display quality can be achieved.
According to a seventh preferred embodiment, a relationship between a distance between the focus electrode 3 and the extraction electrodes 5 and an interval between the electron passage windows 4 are determined. It is noted that the distance between the focus electrode 3 and the extraction electrodes 5 is a minimum distance between the focus electrode 3 and one of the extraction electrodes 5, more specifically, a distance between a bottom surface of the focus electrode 3 and a top surface of the one extraction electrode 5.
Electrons attracted by the extraction electrodes 5 move toward the focus electrode 3. However, the electrons, which have just been emitted from the cathodes 7, have an extremely large divergence angle. For this reason, there may occur a situation in which an electron emitted from one of the cathodes 7 does not pass through one of the electron passage windows 4 immediately on the one cathode 7, but travels the first electron path 10 illustrated in
According to the seventh preferred embodiment, a relationship between the interval WG between the electron passage windows 4 and the distance dFG between the focus electrode 3 and the extraction electrodes 5 is adjusted in order to eliminate an electron passing through one of the electron passage windows 4 which is located diagonally to one of the cathodes 7 from which the electron is emitted, as described above. More specifically, a condition under which an electron with an initial energy emitted from one of the cathodes 7 should be attracted by the focus electrode 3 or one of the extraction electrodes 5 when the electron is located out of one of the electron passage windows 4 immediately on the one cathode 7 and is passing through a region between the interval WG between the electron passage windows 4 and the extraction electrode 5, is determined. By determining such condition, it is possible to eliminate an electron which causes a pixel different from a predetermined pixel to emit light to degrade display quality of the cold cathode display device. It is noted that the following discussion will be made assuming that a potential on one of the cathodes 7 is a reference value.
The condition under which an electron should be attracted by the focus electrode 3 or one of the extraction electrodes 5 before the electron passes through the interval WG between the electron passage windows 4 is expressed as WG>initial energy of the electron/abs(VF−VG)×dFG where VF represents a voltage on the focus electrode 3, and VG represents a voltage on the extraction electrode. It is additionally noted that abs(VF−VG) indicates an absolute value of (VF−VG). The initial energy is equal to the voltage VF on the focus electrode 3, provided that an electron emitted from an electron emitting material does not collide with any of the extraction electrodes. Accordingly, the condition under which an electron should be attracted by the focus electrode 3 or the extraction electrode 5 is expressed as WG>VF/abs(VF−VG)×dFG.
When the voltage VF on the focus electrode 3 is 200V, the voltage VG on the extraction electrodes 5 is 450V, the interval WG between the electron passage windows 4 is 200 μm, and the distance. dFG between the focus electrode 3 and the extraction electrodes 5 is 100 μm, for example, the right side of the foregoing expression is 200/250×100 μm=80 μm, and the left side is 200 μm. Thus, the foregoing condition is satisfied. Also, in actual experiments using the foregoing values, an electron is prevented from being emitted from one of the electron passage windows 4 located diagonally to one of the cathodes 7 from which the electron is emitted. When an electron is emitted from one of the extraction electrodes 5, an initial energy of the electron is 450V, so that the right side of the foregoing expression is 400/250×100 μm=160 μm and the left side is 200 μm. Thus, the foregoing condition is satisfied. Hence, a structure in which an electron is prevented from being emitted from one of the electron passage windows 4 located diagonally to one of the cathodes 7 from which the electron is emitted is provided.
Further, a length of a shorter side of each of the electron passage windows 4 is occasionally made smaller than a width of each of the phosphors in order to improve a focusing performance of an electron beam on a screen. In such a case, an electron is likely to collide with the focus electrode 3, which causes the electron hit by the focus electrode 3 to be emitted from one of the electron passage windows 4 located diagonally to one of the cathodes 7 from which the electron is emitted, to one of the anodes. For example, when a length of a shorter side of each of the electron passage windows 4 is 60 μm, the voltage VF on the focus electrode 3 is 200V, a sub-pixel pitch on the surface of each of the anodes is 0.2 mm, a width of each of the phosphors is 0.1 mm, the voltage VG on the extraction electrode 5 is 450V, the interval WG between the electron passage windows 4 is 140 μm, and the distance between the focus electrode 3 and the extraction electrodes 5 is 100 μm, the right side of the foregoing expression is 200/250×150 μm=120 μm and the left side is 200 μm. Thus, the foregoing condition is satisfied. Also, in actual experiments using the foregoing values, an electron is prevented from being emitted from one of the electron passage windows 4 located diagonally to one of the cathodes 7 from which the electron is emitted.
In the cold cathode display device according to the seventh preferred embodiment, the interval WG between adjacent ones of the electron passage windows 4 is correlated with the distance dFG between the focus electrode 3 and the extraction electrodes 5 and the voltages VF and VG on the focus electrode 3 and one of the extraction electrodes 5, respectively, which are set when a voltage on one of the cathodes 7 is a reference value, such that the relationship of WG>VF/abs(VF−VG)×dFG is satisfied. The cold cathode display device according to the seventh preferred embodiment provides for elimination of an electron which causes a pixel different from a predetermined pixel to emit light to degrade display quality of the cold cathode display device.
According to an eighth preferred embodiment, a length of a longer side of each of the electron passage windows 6 and a width of each of the cathodes 7 as an electron emitting part are numerically limited in order to suppress divergence of electrons attracted by the extraction electrodes 5. A structure according to the eighth preferred embodiment is substantially identical to that described in the first preferred embodiment and illustrated in
Then, a distance between the extraction electrodes 5 and the cathodes 7 is set to 10 μm. It is noted that the distance between the extraction electrodes 5 and the cathodes 7 is a minimum distance between one of the extraction electrodes 5 and one of the cathodes 7, more specifically, a distance between a bottom surface of the one extraction electrode 5 and a top surface of the one cathode 7.
In view of this, from the length of 60 μm of the longer side of each of the electron passage windows 6 and the distance of 10 μm between the extraction electrodes 5 and the cathodes 7, an expression for the width of each of the cathodes 7 can be derived as (L−2G) where L represents a length of the longer side of each of the electron passage windows 6 and G represents the distance between the extraction electrodes 5 and the cathodes 7. While the distance G between the extraction electrodes 5 and the cathodes 7 is set to 10 μm in
A cold cathode display device according to the eighth preferred embodiment, each of the extraction electrodes 5 is provided with more than one electron passage window 6 which is non-circular or rectangular, at each position therein for one pixel. The electron passage windows 6 are arranged in a line parallel to a direction in which each of the cathodes 7 extends, at each of portions at which the extraction electrodes 5 and the cathodes 7 intersect each other. In the cold cathode display device according to the eighth preferred embodiment, an aperture ratio of each of the electron passage windows 6 can be increased, to produce an advantage of enhancing an efficiency in electron emission as compared to a device in which the electron passage windows 6 are arranged in plural lines at each of portions at which the extraction electrodes 5 and the cathodes 7 intersect each other.
Also, in the cold cathode display device according to the eighth preferred embodiment, the width of each of the cathodes 7 is equal to a length obtained by subtracting twice the distance between the extraction electrodes 5 and the cathodes 7 from a longer diameter or a length of a longer side of each of the electron passage windows 6 of the extraction electrodes 5. The cold cathode display device according to the eighth preferred embodiment provides for suppression of divergence of electrons when they pass through the electron passage windows 6, thereby avoiding degradation of focusing characteristics observed in the anodes 2. Thus, a cold cathode display device having a high image quality can be achieved.
According to a ninth preferred embodiment, a size of each of the electron passage windows 6 of the extraction electrodes 5 is limited. A structure according to the ninth preferred embodiment is substantially equal to that described in the first preferred embodiment and illustrated in
According to the ninth preferred embodiment, a distribution of an electric field on each of the cathodes 7 is determined by varying a distance between the extraction electrodes 5 and the cathodes 7. An electric field on each of the cathodes 7 distributes such that it becomes strongest in a peripheral region of each aperture of the extraction electrodes 5 and becomes weaker in a region closer to a center of each aperture of the extraction electrode 5.
As shown in
In a cold cathode display device according to the ninth preferred embodiment, each of the extraction electrodes 5 is provided with more than one electron passage window 6 which is non-circular or rectangular. A longer diameter or a length of a longer side of each of the electron passage windows 6 is orthogonal to a lengthwise direction of each of the cathodes 7, and a shorter diameter or a length of a shorter side of each of the electron passage windows 6 is equal to, or larger than, a half of a distance between the cathodes 7 and the extraction electrodes 5. The cold cathode display device provides for a uniform electric field strength on the cathodes 7. Thus, a cold cathode display device capable of satisfactorily emitting electrons can be achieved.
While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-108661 | Apr 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/03754 | 3/26/2003 | WO | 00 | 2/5/2004 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO03/085692 | 10/16/2003 | WO | A |
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| 20040232823 A1 | Nov 2004 | US |
