Patent Publication Number: US-6710536-B2

Title: Display device using filament

Description:
FIELD OF THE INVENTION 
     The present invention relates to a display device such as a fluorescent display device using a cathode filament; and, more particularly to a cathode filament serving as an electron source for the display device. 
     BACKGROUND OF THE INVENTION 
     FIGS. 10A and 10B show schematic internal structures of conventional display devices  800  and  850 , respectively. Referring to FIG. 10A, the display device  800  includes a glass substrate  81 , a filament  84 , a filament support  82  and an anchor  83  for the filament  84 . While one end of the filament  84  is fixed to a support member  821  of the filament support  82 , the other end of the filament  84  is fixed to a support member  831  of the anchor  83 . The height of the filament support  82  and that of the anchor  83  define the height (i.e., a distance between the substrate  81  and top end thereof) of the filament  84  (e.g., see, Japanese utility model laid open publication No. 61-7856). 
     The support member  831  of the anchor  83  is formed as a plate spring structure. A preset tension force is applied to the filament  84  to prevent the filament from hanging down due to the thermal expansion thereof. Accordingly, the plate spring structure of the support member  831  should be fabricated so that a uniform tension force is applied to the filament  84 . Further, the support member  831  should be fabricated with high precision since the support member  831  should fixedly support the filament  84  and maintain the height of the filament  84  at a preset level. The anchor  83  is of a complex structure, requiring a fabrication with high accuracy, and therefore, its fabrication is not easy and the cost thereof is expensive. In addition, it is not easy to make the anchor  83  of a small size, thereby rendering the fabrication of a thin and small display device difficult. FIG. 10B illustrates a schematic internal structure of a conventional display devices  850  which does not use an anchor. Like reference numerals represent like parts in FIGS. 10A and 10B. 
     Referring to FIG. 10B, the display device  850  includes a glass substrate  81 , a left filament support  82 , a right filament support  82 ′ and a filament having a coiled portion  842  and a linear portion  841 . The filament supports  82  and  82 ′ are fixed at a left and right end portion on top of the substrate  81 , respectively. While the left end of the coiled portion  842  is fixed at a support member  821  of the left filament support  82 , the right end of the linear portion  841  is fixed at a support member  821 ′ of the right filament support  82 ′. The coiled portion  842  applies a tension force on the linear portion  841 , thereby functioning similar to the anchor  83  in the device  800  shown in FIG. 10A (e.g., see, Japanese utility model laid open publication No. 61-7856). 
     The device  850  solves the problem of the anchor  83  as shown in FIG. 10A but entails another problem in that a temperature of the coiled portion  842  becomes higher than that of the linear portion  841  during the operation of the display device  850 . Namely, for example, during normal turning-on period of the display device  850 , the temperature of the coiled portion  842  reaches to about 800° C. while that of the linear portion  841  approaches to about 600° C. Under this condition, the coiled portion  842  emits red light to thereby prevent a normal display operation thereof. 
     In a manufacturing process of a conventional display device, in order to activate the filament, a flushing is performed at a high voltage. During the flushing, the temperature of the coiled portion  842  reaches to about 1500° C. to 2000° C. while that of the linear portion  841  reaches to 1000° C. As a result, electron emitting source material, e.g., a carbonate, coated on the coiled portion  842  is decomposed and flies around thereby contaminate fluorescent material deposited on an anode. This prevents the display device from operating normally. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a simple and inexpensive display device of high display quality by employing a filament free from above-mentioned problems, i.e., display quality degradation due to red light emission from the coiled portion and contamination of fluorescent material deposited on the anode due to flight of carbonate of a coiled portion, originated from an excessively high temperature of the coiled portion of the filament. 
     The display device of the present invention overcomes the above-mentioned problems of the conventional display device by adopting a cathode filament having a coiled portion and a linear portion and applying a tension force with the coiled portion and providing electrons only to the linear portion of the filament. 
     In accordance with a preferred embodiment of the present invention, there is provided a display device including: a cathode filament containing a coiled portion and a linear portion thereof; and a power feeding member, wherein an end of the coiled portion is fixed either to a substrate made of an insulating material or to an insulated support, the power feeding member being installed to contact with the linear portion of the cathode filament. 
     In accordance with another preferred embodiment of the present invention, there is provided a display device including: a cathode filament containing a coiled portion and a linear portion thereof; and a power feeding wiring for feeding power to the cathode filament, wherein an end of the coiled portion is fixed on either the power feeding wiring or a support member fixed on the power feeding wiring, the coiled portion being insulated. 
     In accordance with yet another preferred embodiment of the present invention, there is provided a display device including: an anode substrate; a back substrate having either a transparent conductor film or a control electrode formed thereon; a cathode filament installed between the anode substrate and the back substrate, the cathode filament having a coiled portion and a linear portion thereof; and a plurality of spacers fixed to either the transparent conductor film or the control electrode of the back substrate, wherein an end of the coiled portion is fixed either on an insulated support fixed on one of the anode substrate and the back substrate or on one of the anode substrate and the back substrate, a power feeding member being installed to contact with the linear portion of the cathode filament and the substrate on which the end of the coiled portion is fixed being made of insulating material. 
     In accordance with still yet another preferred embodiment of the present invention, there is provided a display device including: an anode substrate; a back substrate having either a transparent conductor film or a control electrode formed thereon; a cathode filament installed between the anode substrate and the back substrate, the cathode filament having a coiled portion and a linear portion thereof; and a plurality of spacers fixed to either the transparent conductor film or the control electrode of the back substrate, wherein an end of the coiled portion is fixed on either a support member fixed on a power feeding wiring of the cathode filament or the power feeding wiring, the coiled portion being insulated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, wherein: 
     FIGS. 1A and 1B illustrate schematic views of an internal structure of a display device, respectively, in accordance with a first preferred embodiment of the present invention; 
     FIGS. 2A and 2B depict schematic views of a structure of another power feeding member of the display device, respectively, in accordance with the first preferred embodiment of the present invention; 
     FIGS. 3A and 3B depict schematic views of a structure of yet another power feeding member of the display device, respectively, in accordance with the first preferred embodiment of the present invention; 
     FIGS. 4A and 4B present another example of means for fixing a left end of a filament instead of a filament support in FIG. 1; 
     FIGS. 5A and 5B describe schematic views of an internal structure of a display device, respectively, in accordance with a second preferred embodiment of the present invention; 
     FIGS. 6A and 6B illustrate schematic views revealing another internal structure of a unit for insulating the coiled portion shown in FIGS. 5A and 5B; 
     FIGS. 7A and 7B set forth schematic views revealing an internal structure of a display device, respectively, in accordance with a third preferred embodiment of the present invention; 
     FIGS. 8A to  8 C represent another example of a cylindrical conductor and a support shown in FIG. 7; 
     FIGS. 9A and 9B present another example of means for fixing a left end of a filament instead of a filament support in FIG. 7; and 
     FIGS. 10A and 10B show internal structures in accordance with conventional display devices, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 to  9 , preferred embodiments of the present invention will be described. Like reference numerals in FIGS. 1 to  9  represent like parts. A display device of the present invention overcomes the problems of the conventional display device by providing an electric power only to a linear portion of a filament. 
     FIG. 1A illustrates a schematic plan view revealing an internal structure of a display device  100  in accordance with a first preferred embodiment of the present invention. FIG. 1B is a cross sectional view taken along a line X—X of FIG.  1 A. Referring to FIGS. 1A and 1B, the display device  100  includes a glass substrate  11 , a display region  12  thereof, a power feeding wiring  131 , e.g., made of aluminum, for feeding power to a filament, a metallic contact member  141  of a plate shape, a coiled portion  152  and a linear portion  151  of the cathode filament and a filament support  161 . 
     The cathode filament having the coiled portion  152  and the linear portion  151  is a wire whose core wire is made of a tungsten or tungsten alloy (e.g., Re—W alloy) and carbonate is deposited on the surface thereof. The metallic contact member  141  serves as a power feeding member for providing electrons from the power feeding wiring  131  to the linear portion  151  of the filament. The metallic contact member  141  also defines the height of the linear portion  151 , i.e., a distance between the substrate  11  and a top of the metallic contact member  141 . 
     The filament support  161  is made of metal and electrically insulated. A left end of the coiled portion  152  of the filament is fixed by welding on a top part of the filament support  161  as depicted in FIG.  1 B. The height of the filament support  161  is set to be equal to or lower than that of the metallic contact member  141 . A bottom end and the top end of the metallic contact member  141  are fixed to the power feeding wiring  131  and the linear portion  151  of the filament, respectively. A right end of the linear portion  151  of the filament is connected to another power feeding wiring (not shown). A voltage is applied on the linear portion  151  of the filament between the power feeding wiring  131  and another power feeding wiring mentioned above. The coiled portion  152  of the filament serves to apply a preset tension force on the linear portion  151  of the filament to prevent the filament from hanging down due to the thermal expansion thereof. 
     The vertical cross sectional shape of the metallic contact member  141  may be a rectangle, a triangle, a circle or any other polygonal shape. If the vertical cross sectional shape of the contact member is a triangle, heat dissipation of the filament through the metallic contact member  141  can be decreased. 
     As can be seen from FIGS. 1A and 1B, the left end of the coiled portion  152  is fixed by welding on a top part of the filament support  161  and the linear portion  151  is in contact with top end of the metallic contact member  141 . In this condition, since the support  161  is electrically insulated, no voltage is applied on the coiled portion  152 . As a result, since the coiled portion  152  is not heated, in the coiled portion  152 , there are no emission of red light, decomposition and flight of the carbonate coated thereon. 
     FIG. 2A shows a schematic plan view revealing a structure of another power feeding member of the display device  100 . FIG. 2B is a cross sectional view taken along a line X—X of FIG.  2 A. 
     In FIGS. 2A and 2B, a numeral  142  represents a contact wire. A numeral  17  stands for a support member of the contact wire  142 . The support member  17  made of metal is fixed to a power feeding wiring  131 . A linear portion  151  of a filament is in contact with the contact wire  142 . Electrons are fed from the power feeding wiring  131  to the linear portion  151  of the filament through the contact wire  142 . In this internal structure of the display device  100 , only the support member  17  and the contact wire  142  act as a power feeding member, thereby simplifying the structure of the display device  100 . Further, since the heat capacity of the wire  142  is smaller than that of a metal plate, the heat dissipation therefrom is reduced. 
     FIG. 3A depicts a schematic plan view revealing a structure of yet another power feeding member of the display device  100 . FIG. 3B is a cross sectional view taken along a line X—X of FIG.  3 A. 
     In FIGS. 3A and 3B, a numeral  143  stands for a metal wire. One end of the metal wire  143  is connected to a linear portion  151  of a filament while the other end thereof is connected to a power feeding wiring  131 . Electrons are fed from the power feeding wiring  131  to the linear portion  151  of the filament through the metal wire  143 . The height of the linear portion  151  of the filament is defined as the height of a support  161 . 
     In this internal structure of the display device  100 , only the metal wire  143  acts as a power feeding member to the linear portion  151  of the filament, thereby simplifying the structure of the display device  100 . Further, since the heat capacity of the metal wire  143  is smaller than that of a metal plate, the heat dissipation therefrom decreases. 
     FIGS. 4A and 4B present another example of means for fixing the left end of the filament instead of the filament support  161  in FIG.  1 . In FIG. 4, a numeral  18  represents a fixing part formed by employing a glass paste for fixing a left end of a coiled portion  152  of the filament. In this case, the height of a linear portion  151  of the filament is defined as the height of a metallic contact member  141  as viewed in FIG.  4 B. This configuration employing the fixing part  18  is simpler than that using the filament support  161  illustrated in FIG. 1B which requires a very accurate fabrication, entailing a high cost. Further, the fixing procedure thereof becomes easy by employing the fixing part  18 . 
     FIG. 5A illustrates a schematic plan view revealing an internal structure of a display device  500  in accordance with a second preferred embodiment of the present invention. FIG. 5B is a cross sectional view taken along a line X—X of FIG.  5 A. 
     The display device  500  overcomes the problems of the conventional display device by insulating a coiled portion of a filament and providing an electric power only to a linear portion of the filament. 
     Referring to FIGS. 5A and 5B, the display device  500  includes a glass substrate  11 , a display region  12  thereof, a power feeding wiring  132  for feeding power to a filament, a coiled portion  152  and a linear portion  151  of the filament, a metallic contact member  1621  and a filament support  162 . The filament support  162  made of a metal also serves as a power feeding member for feeding power from the power feeding wiring  132  to the linear portion  151  of the filament. 
     A left end of the coiled portion  152  of the filament is fixed by welding on top of the filament support  162  as depicted in FIG.  5 B. Since the coiled portion  152  is insulated by the filament support  162 , electrons are fed only to the linear portion  151  of the filament through the filament support  162  fixed on the power feeding wiring  132 . As a result, the coiled portion  152  of the filament is not heated. The height of the linear portion  151  of the filament is defined as the height of a vertical part  1621  of the support  162 . 
     In this case, since the support  162  serves as a support member for the filament and a power feeding member to the filament, a space needed to install the power feeding wiring  132  between the filament support  162  and the display region  12  is greatly saved. Further, the filament fixing process can be performed with ease. 
     FIG. 6A illustrates a schematic top view revealing another internal structure of the unit, i.e., the support  162 , for insulating the coiled portion  152  shown in FIGS. 5A and 5B. FIG. 6B is a cross sectional view taken along a line X—X of FIG.  6 A. In FIGS. 6A and 6B, a numeral  19  indicates a cylindrical conductor or a cylindrical insulator having conductor material deposited thereon. 
     A left end of a coiled portion  152  of a filament is fixed on top of a power feeding wiring  132  as depicted in FIG.  6 B. Since the coiled portion  152  is insulated by means of the power feeding wiring  132  and the cylindrical conductor  19 , electrons are fed only to the linear portion  151  of the filament. This is similar to the case of FIGS. 5A and 5B. The height of the linear portion  151  of the filament is defined as the height of the cylindrical conductor  19 . 
     In this case, since the cylindrical conductor  19  is fixed on the power feeding wiring  132 , the structures of the support and the power feeding wiring become simple and space for installation of the power feeding member between the filament support  162  and the display region  12  is saved. Further, the filament fixing process can be performed with ease. 
     FIG. 7A illustrates a schematic plan view revealing an internal structure of a display device  700  in accordance with a third preferred embodiment of the present invention. FIG. 7B is a cross sectional view taken along a line X—X of FIG.  7 A. FIG. 7A is a plan view taken along a line Y—Y of FIG.  7 B. 
     Referring to FIGS. 7A and 7B, the display device  700  includes a glass anode substrate  11 , a power feeding wiring  133 , a cylindrical conductor  144 , a linear portion  151  of a filament, a coiled portion  152  of the filament, a filament support  163  made of a metal, a glass fiber  20  serving as a spacer, a back glass plate  21 , an anode  22  having a fluorescent layer formed thereon, a transparent conductor film (or a control electrode)  25  and side glass plates  241 ,  242  and  243 . The anode substrate  11 , the back plate  21  and the side glass plates  241  to  243  constitute a sealed vacuum vessel. A bottom part of the support  163  is fixed to the back plate  21 . A left end of the coiled portion  152  is fixed by welding to a top part of the support  163 . 
     The cylindrical conductor  144  serves as a power feeding member for feeding power from the power feeding wiring  133  to the linear portion  151  of the filament. The cylindrical conductor  144  defines the height of the linear portion  151  of the filament. The transparent conductor film  25  aims for electromagnetic shielding. Instead of the transparent conductor film, the part represented by the numeral  25  may be a control electrode for controlling electrons emitted from the filament to the anode. 
     The glass fiber  20  is fixed to the transparent conductor film  25  or the control electrode  25 . If the control electrode  25  is divided into electrode parts, it is preferable that the glass fiber  20  is fixed between the electrode parts. Both cases discussed in the above are considered in this description. The glass fiber  20  can be made of any material which has insulating characteristic. 
     In a thin display device, since spacing between the linear portion  151  of the filament and an inner surface of the back substrate  21  and that between the linear portion  151  and an inner surface of the anode substrate  11  range about 1.0 mm and about 1.4 mm, respectively, if a vibration is applied on the display device, the linear portion  151  may contact with the transparent conductor film or the control electrode  25  or other electrode. A glass fiber  20  ameliorates this contact problem. 
     Meanwhile, since heat is dissipated from the linear portion  151  when the linear portion  151  of the filament contacts with the glass fiber  20 , thereby deteriorating the electron emission capability thereof, it is preferable that there is no contact between the linear portion  151  and the glass fiber  20  under a normal state, i.e., a state that there is no vibration thereof. Accordingly, a diameter of the glass fiber  20  is equal to or preferably smaller than that of the cylindrical conductor  144 . 
     In this preferred embodiment, in a thin display device employing a glass fiber as a spacer, a coiled portion  152  of a filament is used as a unit for applying tension force to the filament and a cylindrical conductor  144  for electron feeding is installed between the coiled portion  152  and the linear portion  151 , thereby removing heat dissipation from the coiled portion  152 . 
     FIGS. 8A to  8 C represent another example of the cylindrical conductor  144  and the support  163  shown in FIG.  7 . In FIG. 8A, the support  163  is fixed to a back plate  21  while a power feeding wiring  133  and a cylindrical conductor  144  are installed on an anode substrate  11  in sequence. In FIG. 8B, the support  163  is fixed to the anode substrate  11  while the power feeding wiring  133  and the cylindrical conductor  144  are also installed on the anode substrate  11  in sequence. In FIG. 8C, the support  163  is fixed to the anode substrate  11  while the power feeding wiring  133  and the cylindrical conductor  144  are installed on the back plate  21  in sequence. 
     FIGS. 9A and 9B present another example of means for fixing a left end of the coiled portion  152  of the filament instead of the filament support  163  in FIG.  7 . In FIG. 9A, a left end of a coiled portion  152  of a filament is directly fixed to an anode substrate  11 ; and an electron feeding wire  133  and a cylindrical conductor  144  are also fixed to the anode substrate  11 . The height of a linear portion  151  of the filament is defined as that of the cylindrical conductor  144 . In FIG. 9B, a left end of a coiled portion  152  of a filament is directly fixed to a back plate  21 ; and an electron feeding wire  133  and a cylindrical conductor  144  are also fixed to the back plate  21 . 
     A structure of a display device is determined or selected based on conditions for electrodes and spaces of the wiring with reference to the structures thereof illustrated in FIGS. 7 to  9 . 
     In FIGS. 7 to  9 , the end of the coiled portion  152  of the filament is insulated to thereby provide electrons only to the linear portion  151  thereof. This is also applied to the cases of FIGS. 5 and 6 for insulating the end of the coiled portion  152  of the filament. 
     As discussed in the above, since the display device of the present invention uses a cathode filament having a coiled portion and a linear portion thereof, it is not necessary to use a high cost anchor of high fabrication accuracy. 
     The display device of the present invention uses a filament having a coiled portion and a linear portion thereof, wherein an end of the coiled portion is insulated and a power feeding member is installed to contact with the linear portion. As a result, electrons are not fed to the coiled portion but fed only to the linear portion. Accordingly, since the coiled portion is not heated, the emission of red light therefrom deteriorating the display function, decomposition and flight of the carbonate coated thereon contaminating the display device are avoided. Further, since the power feeding member can be used as a member for defining the height of the filament, thereby realizing the display device without a high cost support of a complex shape. 
     Since in the display device of the present invention the end of the coiled portion is insulated to avoid feeding electrons to the coiled portion, there can be obtained a same effect as that obtained when the power feeding member is installed in the linear portion. Further, in this case, there is no need to install the support to fix the end of the coiled portion and the power feeding member simultaneously, thereby saving necessary components and simplifying the structure of the display device. 
     Even though the display device of the present invention uses a filament having a coiled portion and a linear portion thereof, electrons are not fed to the coiled portion. As a result, since there entails no power consumption in the coiled portion, the power consumption of the display device is decreased. 
     The display device of the present invention avoids heating of the coiled portion by employing the filament having the coiled portion and the linear portion thereof, thereby rendering the display device slimmer by using a space such as a glass fiber. 
     While the present invention has been described with respect to certain preferred embodiments only, other modifications and variations may be made without departing from the scope of the present invention as set forth in the following claims.