Abstract:
An ElectroLuminescent (EL) device includes a transparent electrode layer, a luminescent layer, and insulation layer, a rear electrode layer, a first protection layer adapted to cover the luminescent layer and the insulation layer and the rear electrode layer, and an electrode layer for noise reduction sequentially arranged on an insulated substrate; and a second protection layer adapted to cover the electrode layer for noise reduction.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an ElectroLuminescent (EL) device used as parts such as backlight of cellular phone, more particularly, to an EL device capable of reducing audio noise and electrical noise by alternating current power and a fabrication method of the EL device. 
   2. Description of Related Art 
   An inorganic EL (electroluminescent) device driven by alternating current power is possessed of electrical noise by characteristics of the alternating current power that is a driving power source. Particularly, a power source used in mobile phone is a direct current power, wherein transforming direct current power into a power source of sine wave similar to alternating current through an inverter and providing the transformed power source of sine wave to the EL device generally use the mobile phone. The transformed power source of sine wave used in the mobile phone generates electrical noise and audio noise as polarity of dielectric layer is being changed by alternating current power a phase of which is changed. 
   An EL device used as a backlight of a mobile phone, for example, comprises a transparent electrode layer that is formed of ITO and formed on a transparent insulation substrate such as PolyEthylene Terephthalate (PET) film as a first electrode, a luminescent layer and an insulation layer as a dielectric layer sequentially formed on the transparent electrode layer, a rear electrode layer as a second electrode formed on the insulation layer, and a protection layer formed to envelope the luminescent layer, the insulation layer and the rear electrode layer. 
   The EL device further comprises a ground electrode that is formed on the protection layer, and a dielectric rear tape that is formed on the ground electrode, wherein the ground electrode is formed of a copper plate, and the dielectric rear tape is adhered onto the ground electrode to insulate the ground electrode from the outside. 
   In such an EL device, the transparent electrode layer and rear electrode layer are used as two electrodes of front electrode and rear electrode respectively to be connected to an output terminal of an inverter, wherein AC power is supplied to the two electrodes. Furthermore, the ground electrode is grounded to a substrate. Therefore, the EL device has three terminals including two electrodes that are connected to the output terminal of the inverter and the ground electrode that is connected to a ground terminal. 
   The EL device transforms DC power of battery through the inverter and provides transformed sinusoidal AC power to the electrodes, since the DC power of battery is used as a power source of the EL device. 
   Therefore, light is emitted from the luminescent layer, if the sinusoidal AC power that is transformed through the inverter is supplied to the transparent electrode layer and the rear electrode layer that act as two electrodes in an EL device having the foregoing structure. 
   However, there have been problems in such an EL device in that electrical noise is generated by the AC power, and audio noise is generated from the dielectric layer as phase of an AC power is alternately being changed. 
   Furthermore, there have been problems in that although a copper plate used as the ground electrode is formed on the protection layer to reduce noise, the copper plate has to be adhered to the EL device through a separate process, and a ground electrode has to be formed additionally so that the additionally formed ground electrode is grounded to the substrate. 
   Furthermore, there have been problems in that since an insulation tape surely has to be adhered to the copper plate so that the insulation tape encircles the copper plate so as to insulate the copper plate from the outside, not only process is cumbersome and complex, but also it is difficult to apply the insulation tape to a device to which the insulation tape is not required to be adhered, or to which the insulation tape is partially adhered although it is possible to apply the insulation tape to a backlight of LCD (liquid crystal display) to all over the front of which the insulation tape is required to be adhered. 
   SUMMARY OF THE INVENTION 
   The present invention is suggested to solve the foregoing problems, and it is an object of the present invention to provide an EL device with electrode capable of reducing audio noise and electrical noise generated by AC power. 
   It is another object of the present invention to provide an EL device capable of simplifying processes by forming an electrode for noise removal during the fabrication process of the EL device, thereby excluding separate copper plate adhering process, ground electrode forming process and insulation tape adhering process, and a fabrication method of the EL device. 
   It is another object of the present invention to provide an EL device in which an electrode for noise removal is integrally fabricated to be applied to various flat panel devices, and a fabrication method of the EL device. 
   It is the other object of the present invention to provide an EL device capable of removing noise by forming two terminals only with the EL device itself without separate copper plate and ground electrode for noise removal, and a fabrication method of the EL device. 
   In order to achieve the foregoing objects, the present invention provides an EL device comprising: a transparent electrode layer, a luminescent layer, and insulation layer, a rear electrode layer, a first protection layer adapted to cover the luminescent layer and the insulation layer and the rear electrode layer, and an electrode layer for noise reduction sequentially arranged on an insulated substrate; and a second protection layer adapted to cover the electrode layer for noise reduction. 
   Furthermore, the present invention provides an ElectroLuminescent (EL) device comprising: a transparent electrode layer formed on an insulation substrate; a luminescent layer formed on the transparent electrode layer; an insulation layer formed on the luminescent layer; a rear electrode layer formed on the insulation layer; a first protection layer adapted to cover the luminescent layer, the insulation layer and the rear electrode layer; an electrode layer adapted to reduce noise, the electrode layer formed on the first protection layer; and a second protection layer adapted to cover the electrode layer for noise reduction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the present invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which: 
       FIG. 1  is a cross-sectional view of an EL device on which a ground electrode is formed; and 
       FIG. 2  is a cross-sectional view of an EL device according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross-sectional structure of an EL device used as a backlight of a mobile phone, for example. 
   Referring to  FIG. 1 , an EL device comprises a transparent electrode layer  11  that is formed of ITO and formed on a transparent insulation substrate  10  such as PolyEthylene Terephthalate (PET) film as a first electrode, a luminescent layer  12  and an insulation layer  13  as a dielectric layer sequentially formed on the transparent electrode layer  11 , a rear electrode layer  14  as a second electrode formed on the insulation layer  13 , and a protection layer  15  formed to envelope the luminescent layer  12 , the insulation layer  13  and the rear electrode layer  14 . 
   The EL device further comprises a ground electrode  16  that is formed on the protection layer  15 , and a dielectric rear tape  17  that is formed on the ground electrode  16 , wherein the ground electrode  16  is formed of a copper plate, and the dielectric rear tape  17  is adhered onto the ground electrode  16  to insulate the ground electrode  16  from the outside. 
   In such an EL device, the transparent electrode layer  11  and rear electrode layer  14  are used as two electrodes of front electrode and rear electrode respectively to be connected to an output terminal of an inverter (not illustrated in drawing), wherein AC power  18  is supplied to the two electrodes  11  and  14 . Furthermore, the ground electrode  16  is grounded to a substrate. Therefore, the EL device has three terminals including two electrodes  11  and  14  that are connected to the output terminal of the inverter and the ground electrode  16  that is connected to a ground terminal. 
   The EL device transforms DC power of battery through the inverter and provides transformed sinusoidal AC power  18  to the electrodes  11  and  14 , since the DC power of battery is used as a power source of the EL device. 
   Therefore, light is emitted from the luminescent layer  12 , if the sinusoidal AC power  18  that is transformed through the inverter is supplied to the transparent electrode layer  11  and the rear electrode layer  14  that act as two electrodes in an EL device having the foregoing structure. 
   The present invention will now be described in detail in connection with an exemplary embodiment with reference to the accompanying drawings. For reference, like reference characters designate corresponding parts throughout several views. 
     FIG. 2  illustrates a cross-sectional structure of an EL device used as backlight of cellular phone according to an embodiment of the present invention. 
   Referring to  FIG. 2 , an EL device of the present invention comprises a transparent electrode layer  21  formed of ITO and formed on a transparent insulation substrate  20  such as a PolyEthylene terephthalate (PET) film as a first electrode, a luminescent layer  22  as a phosphor layer formed on the transparent electrode layer  21 , an insulation layer  23  as a dielectric layer formed on the luminescent layer  22 , and a rear electrode layer  24  as a second electrode formed on the insulation layer  23 . 
   Furthermore, the EL device of the present invention further comprises a first protection layer  25  formed to envelope the luminescent layer  22 , the insulation layer  23  and the rear electrode layer  24 , an electrode layer  26  for noise reduction formed on the first protection layer  25 , and a second protection layer  27  formed to envelope the electrode layer  26  for noise reduction. 
   The electrode layer  26  for noise reduction is commonly grounded along with the transparent electrode layer  21  that is first electrode, and is connected to one of the output terminals of an inverter (not shown in the drawings) so that the substrate is grounded. 
   Conductive electrode materials can be used as the electrode layer  26  for noise reduction, and the electrode layer  26  for noise reduction is formed on the first protection layer  25  by printing a metallic electrode material such as Ag in one preferred embodiment of the present invention. 
   The first protection layer  25  and the second protection layer  27  not only prevent penetration of moisture from the outside, but also function as an insulation layer between electrodes. The first protection layer  25  and the second protection layer  27  are formed by printing a material having superior moisture resistance, pressure resistance and insulating characteristics, e.g. polyester. 
   In an EL device of the present invention, light is emitted from the luminescent layer  22  since DC power of a battery is transformed through an inverter (not shown in the drawings) so that sinusoidal AC power  28  is provided to the transparent electrode layer  21  and the rear electrode layer  24  that are used as two electrodes. 
   The EL device of the present invention not only reduces electrical noise generated from the transparent electrode layer  21  and the rear electrode layer  24  due to the AC power, but also reduces audio noise generated from the dielectric layer by the AC power by forming the electrode layer  26  for noise reduction on the first protection layer  25 , commonly grounding the electrode layer  26  along with the transparent electrode layer  21  and connecting the electrode layer  26  to one electrode in output electrodes of the inverter, thereby grounding the substrate. 
   The foregoing EL device according to an embodiment of the present invention has merits in that electrical noise and audio noise due to AC power are reduced by forming an electrode layer for noise reduction between protection layers, commonly grounding the electrode layer together with a transparent electrode layer. 
   The present invention simplifies processes by excluding the cumbersomeness that occurs when a separate copper plate is adhered to the EL device and a ground electrode is formed and grounded with the substrate or adhering an insulation tape to the copper plate, since an electrode for noise removal is formed during the process of fabricating the EL device, and insulation is performed by a protection film. Therefore, an EL device of the present invention has merits in that noise is removed by the EL device itself, and the EL device can be applied to various flat display devices. 
   While the present invention has been particularly shown and described with reference to an exemplary embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail can be made therein without departing from the spirit and scope of the invention.