Abstract:
A flat panel display is disclosed. In one embodiment, the display includes a first substrate and an organic light emitting device formed over the first substrate, wherein the organic light emitting device comprises a first electrode layer, an organic light emitting layer, and a second electrode layer, and wherein the organic light emitting layer is interposed between the first and second electrode layers. The display also includes a second substrate attached to the first substrate by the use of a sealant and an In-Plane Switching (IPS) mode electrode layer formed between the first and second substrates, wherein the IPS mode electrode layer is closer to the second substrate than the first substrate, wherein the IPS mode electrode layer has first and second surfaces opposing each other, and wherein the first surface is closer to the second substrate than the first surface. The display further includes a first alignment layer formed on the second surface of the IPS mode electrode layer and a liquid crystal layer filled in a space formed between the first substrate and the second substrate, wherein at least part of the liquid crystal layer is formed over the organic light emitting device.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2010-0016334, filed on Feb. 23, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     The described technology generally relates to a flat panel display, and more particularly, to a dual flat panel display of an organic light emitting display (OLED) and a liquid crystal display (LCD). 
     2. Description of the Related Technology 
     Flat panel displays such as LCDs or OLEDs have recently received considerable attention for commercial applications. 
     The OLED is a self-luminous type display that electrically excites fluorescent organic compounds interposed between an anode electrode and a cathode electrode. Thus, the OLED may be operable at a low voltage and may be manufactured with a thin panel. In addition, the OLED has a wide viewing angle and a fast response time. 
     The LCD is a device that changes an optical anisotropy of liquid crystal by applying an electric field to the liquid crystal having liquidity and crystal optical properties, and has less power consumption than a conventional cathode ray tube. In addition, the LCD has additional advantages such as being light weight, thin, simple, and portable, such that a large-scaled screen and high definition may be easily obtained. 
     SUMMARY 
     One inventive aspect is a dual flat panel display of an organic light emitting display (OLED) and a liquid crystal display (LCD). 
     Another aspect is a flat panel display device including: a first substrate; an organic light emitting device on the first substrate and including a first electrode layer, an organic light emitting layer, and a second electrode layer; a sealant on the edges of the first substrate; a second substrate attached to the first substrate by using the sealant as a medium and including an In-Plane Switching (IPS) mode electrode layer on a side facing the first substrate; a first alignment layer on a side of the IPS mode electrode layer facing the first substrate; and a liquid crystal layer filled in a space formed between the first substrate and the second substrate. 
     At least one of the first electrode layer and the second electrode layer may be a reflective electrode and the IPS mode electrode layer may be a transparent electrode. 
     Once a predetermined voltage is applied to the IPS mode electrode layer, an image may be realized by distortion of the liquid crystal layer. 
     The IPS mode electrode layer may be connected to an external terminal on the second substrate. 
     Once a predetermined voltage is applied to the first electrode layer and the second electrode layer, an image may be realized according to light emission of the organic light emitting layer. 
     The first electrode layer and the second electrode layer may be connected to an external terminal on the first substrate. 
     The flat panel display device may further include a second alignment layer on the first substrate and the organic light emitting device, the second alignment layer being aligned in the same direction as the first alignment layer. 
     The first and second alignment layers may be aligned at 45 degrees with respect to the surface of the first substrate or the second substrate. 
     The first and second alignment layers may include polyimide. 
     The sealant may include glass frit. 
     The flat panel display device may further include a linear polarization film on a side that is opposite to a side of the second substrate facing the first substrate. 
     The first electrode layer serves as a reflective electrode; the second electrode layer serves as a transparent electrode; and the IPS mode electrode layer serves as a transparent electrode. 
     The flat panel display device may further include an adhesive material between the second substrate and the linear polarization film. 
     Another aspect is a method of manufacturing a flat panel display device, the method including: preparing a first substrate and a second substrate, the first substrate including a first electrode layer, an organic light emitting layer, and a second electrode layer, the second substrate including an In-Plane Switching (IPS) mode electrode layer; coating a first alignment layer on a side of one of the first substrate and the second substrate and aligning the first alignment layer; filling liquid crystal in a space formed by the first substrate and the second substrate; and bonding the first substrate and the second substrate and hardening the liquid crystal. 
     During the preparing of the first substrate and the second substrate, at least one of the first and second substrates may be formed as a reflective electrode and the IPS mode electrode layer may be formed as a transparent electrode. 
     During the preparing of the first substrate and the second substrate, an external terminal that connects to the first and second electrode layers may be formed on the first substrate and an external terminal that connects to the IPS mode electrode layer may be formed on the second substrate. 
     During the coating of the first alignment layer and the aligning of the first alignment layer, a second alignment layer may be further coated on one side of one substrate without the coated first alignment layer among the first and second substrates. 
     The second alignment layer may be aligned in the same direction as the first alignment layer. 
     The first and second alignment layers may be aligned at 45 degrees with respect to the first substrate or the second substrate. 
     The first and second alignment layers may include polyimide. 
     The first and second alignment layers may be aligned through an ultraviolet (UV) photo alignment method. 
     During the bonding of the first and second substrate and the hardening of the liquid crystal, the liquid crystal may be hardened by UV light. 
     The method may further include attaching a linear polarization film on a side that is opposite to a side of the second substrate facing the first substrate. 
     The method may further include disposing an adhesive material between the second substrate and the linear polarization film. 
     During the bonding of the first and second substrate and the hardening of the liquid crystal, the first substrate and the second substrate may be bonded using a sealant on edge portions of the first substrate or the second substrate. 
     Another aspect is a flat panel display comprising: a first substrate; an organic light emitting device formed over the first substrate, wherein the organic light emitting device comprises a first electrode layer, an organic light emitting layer, and a second electrode layer, and wherein the organic light emitting layer is interposed between the first and second electrode layers; a second substrate attached to the first substrate by the use of a sealant; an In-Plane Switching (IPS) mode electrode layer formed between the first and second substrates, wherein the IPS mode electrode layer is closer to the second substrate than the first substrate, wherein the IPS mode electrode layer has first and second surfaces opposing each other, and wherein the first surface is closer to the second substrate than the first surface; a first alignment layer formed on the second surface of the IPS mode electrode layer; and a liquid crystal layer filled in a space formed between the first substrate and the second substrate, wherein at least part of the liquid crystal layer is formed over the organic light emitting device. 
     In the above display, at least one of the first electrode layer and the second electrode layer is formed at least partially of a reflective material and wherein the IPS mode electrode layer is formed at least partially of a transparent material. In the above display, the liquid crystal layer is configured to display an image based on a voltage applied to the IPS mode electrode layer. In the above display, the IPS mode electrode layer is electrically connected to an external terminal formed on the second substrate. 
     In the above display, the organic light emitting layer is configured to display an image based on a voltage applied to the first electrode layer and the second electrode layer. In the above display, the first electrode layer and the second electrode layer are electrically connected to an external terminal formed on the first substrate. 
     The above display further comprises a second alignment layer formed over the first substrate and the organic light emitting device, wherein the second alignment layer is aligned in substantially the same direction as the first alignment layer. In the above display, the first and second alignment layers are aligned at about 45 degrees with respect to at least one of a first surface of the first substrate and a second surface of the second substrate, and wherein the sealant contacts the first surface of the first substrate and the second surface of the second substrate. In the above display, the first and second alignment layers are formed at least partially of polyimide. In the above display, the sealant is glass frit. 
     The above display further comprises a linear polarization film, wherein the second substrate has first and second surfaces opposing each other, wherein the first surface of the second substrate contacts the sealant, and wherein the linear polarization film is formed over the second surface of the second substrate. In the above display, the first electrode layer is formed at least partially of a reflective material, wherein the second electrode layer is formed at least partially of a transparent material and wherein the IPS mode electrode layer is formed at least partially of a transparent material. The above display further comprises an adhesive material formed between the second substrate and the linear polarization film. 
     Another aspect is a method of manufacturing a flat panel display, the method comprising: providing a first substrate and a second substrate, wherein an organic light emitting device is formed over the first substrate, and wherein an In-Plane Switching (IPS) mode electrode layer is formed on the second substrate; forming a first alignment layer on a first surface of one of the first substrate and the second substrate; filling liquid crystal in a space formed between the first substrate and the second substrate; bonding the first substrate and the second substrate with a sealant; and hardening the liquid crystal. 
     In the above method, at least one of the first and second substrates is formed at least partially of a reflective material and wherein the IPS mode electrode layer is formed at least partially of a transparent material. In the above method, the organic light emitting device comprises a first electrode layer, an organic light emitting layer and a second electrode layer, wherein the organic light emitting layer is interposed between the first and second electrode layers, and wherein the providing comprises: forming an external terminal on the first substrate to be connected to the first and second electrode layers; and forming an external terminal on the second substrate to be connected to the IPS mode electrode layer. 
     The above method further comprises forming a second alignment layer on a second surface of the other substrate, wherein the second surface faces the first surface. The above method further comprises aligning the first and second alignment layers through an ultraviolet (UV) photo alignment method. In the above method, the hardening is performed with the use of UV radiation. 
     Another aspect is a flat panel display comprising: first and second substrates opposing each other; an organic light emitting layer formed between the first and second substrates; a liquid crystal layer formed between the first and second substrates; and a circuit configured to selectively drive the organic light emitting layer or liquid crystal layer so as to display an image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a flat panel display device according to an embodiment. 
         FIG. 2  is a cross-sectional view illustrating a flat panel display device according to another embodiment. 
         FIGS. 3 through 7  are cross-sectional views illustrating a method of manufacturing a flat panel display device, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments will be described with reference to the drawings. 
       FIG. 1  is a cross-sectional view illustrating a flat panel display device  100  according to an embodiment. As shown in  FIG. 1 , the flat panel display device  100  includes a first substrate  110 , an organic light emitting device  120 , a second substrate  130 , a sealant  140 , a first alignment layer  150 , a second alignment layer  160 , and a liquid crystal layer  170 . 
     The first substrate  110  may be formed of a transparent glass material including SiO 2  as a main component. However, in a case of a top emission type in which an image is realized in an opposite direction of the first substrate  110 , the first substrate  110  may not be necessarily formed of a transparent material. 
     Although not illustrated in  FIG. 1 , a buffer layer (not shown), for example, SiO 2  and/or SiN x , (where x is a natural number) may be further formed on the top surface of the first substrate  110  to smoothen the first substrate  110  and prevent penetration of impurities. 
     An organic light emitting device  120  is formed on a part of the first substrate  110 . The organic light emitting device  120  includes a first electrode layer  121 , a second electrode layer  123  facing the first electrode layer  121 , and an organic light emitting layer  122  interposed therebetween. 
     In one embodiment, a pattern of the first electrode layer  121  has line stripes (which are respectively spaced a predetermined interval apart from each other) in a case of a passive matrix (PM) type and has a form corresponding to a pixel in an active matrix (AM) type. In the AM type, a thin film transistor (TFT) layer including at least one TFT may be further provided on the first substrate  110  to be below the first electrode layer  121 , and the first electrode layer  121  may be electrically connected to the TFT layer (not shown). The first electrode layer  121  is electrically connected to an external terminal (not shown) on the first substrate  110  and thus may serve as an anode electrode. 
     The second electrode layer  123  is disposed on the first electrode layer  121  and is electrically connected to an external terminal (not shown) on the first substrate  110  and thus may serve as a cathode electrode. The second electrode layer  123  may have a stripe form substantially perpendicular to the pattern of the first electrode layer  121  in the PM type or may be formed over an entire active region where an image is realized in the AM type. Of course, polarities of the first and second electrode layer  121  and  123  may be reversed. 
     The flat panel display device  100  may be a top emission type in which an image is realized in an opposite direction of the first substrate  110 . In this embodiment, the first electrode layer  121  may serve as a reflective electrode and the second electrode layer  123  may serve as a transparent electrode. Further, in this embodiment, the first electrode layer  121  may be formed at least partially of a reflective material and the second electrode layer  123  may be formed at least partially of a transparent material. In one embodiment, after a reflective layer is formed using Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, or a compound thereof, ITO, IZO, ZnO, or In 2 O 3  having a high work function is formed on the reflective layer in order to form the reflective electrode of the first electrode layer  121 . In one embodiment, after a metal having a small work function such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, or a compound thereof is deposited, an auxiliary electrode layer or a bus electrode line is formed thereon using a transparent conductive material such as ITO, IZO, ZnO, or In 2 O 3  in order to form the transparent electrode of the second electrode layer  123 . 
     The flat panel display device  100  may be a bottom emission type where an image is displayed in a direction of the first substrate  110 . In this embodiment, the first electrode layer  121  may be formed at least partially of a transparent material and the second electrode layer  123  may be formed at least partially of a reflective material. In one embodiment, the first electrode layer  121  is formed of ITO, IZO, ZnO, or In 2 O 3  having a high work function and the second electrode layer  123  is formed of a metal having a small work function such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, and Ca. 
     Moreover, in a case of a dual-sided emission type, the first electrode layer  121  and the second electrode layer  123  may be formed as a transparent electrode. 
     The organic light emitting layer  122  may be interposed between the first electrode layer  121  and the second electrode layer  123 . The organic light emitting layer  122  emits light by the electrically driven first and second electrode layers  121  and  123 . The organic light emitting layer  122  may be formed of a high or low molecular weight organic matter. 
     If the organic light emitting layer  122  is formed of a low molecular weight organic matter, a hole transport layer (HTL) and a hole injection layer (HIL) are stacked in a direction of the first electrode layer  121  with respect to the organic light emitting layer  122 , and an electron transport layer (FTL) and an electron injection layer (EIL) are stacked in a direction of the second electrode layer  123  with respect to the organic light emitting layer  122 . Besides these layers, various kinds of layers may be stacked, depending on the embodiment. Available organic matters may include copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminium (Alq3). 
     In addition, in a case of a high molecular weight organic layer formed of a high molecular weight organic matter, only the HTL may be included in a direction of the first electrode layer  121  with respect to the organic light emitting layer  122 . The HTL may be formed of poly-(2,4)-ethylene-dihydroxy thiophene (PEDOT) or polyaniline (PANI), and the high molecular weight organic light emitting layer  122  may be formed of PPV, Soluble PPVs, Cyano-PPV, or Polyfluorene. 
     Accordingly, the flat panel display device  100  displays an image on an organic light emitting device because the organic light emitting layer  122  emits light. The organic light emitting layer  112  emits light through the combining of electrons and holes when voltage is externally applied. 
     The second substrate  130  for sealing the organic light emitting device  120  from the outside is disposed on the organic light emitting device  120 . In a case of the top emission type, the second substrate  130  is a transparent substrate. 
     An electrode layer  131  of an In-Plane Switching (IPS) mode (hereinafter referred to as an IPS mode electrode layer  131 ) is disposed on the bottom surface of the second substrate  130  facing the first substrate  110 . The IPS mode electrode layer  131  is formed to be substantially parallel to the side of the second substrate  130  facing the first substrate  110  and drives the liquid crystal layer  170  (described below) in a horizontal electric field mode, such that a wider viewing angle can be realized than a conventional vertical electric field mode. 
     Although not illustrated in the drawings, the IPS mode electrode layer  131  may include a pixel electrode (not shown) or a common electrode (not shown), and may be formed through various kinds of patterning processes. The IPS mode electrode layer  131  including the pixel electrode (not shown) and the common electrode (not shown) is electrically connected to an external terminal (not shown) on the second substrate  130 , and thus may serve as an anode or a cathode. In the present embodiment, the IPS mode electrode layer  131  serves as a transparent electrode formed of, for example, ITO, IZO, ZnO, or In 2 O 3 . 
     In one embodiment, the sealant  140  is formed at the edge portions of the first substrate  110  or the second substrate  130 . The second substrate  130  is attached to the first substrate  110  by the sealant  140 , and thus the organic light emitting device  120  is protected from external moisture or oxygen penetration. Like the present embodiment, if a glass substrate is used as the second substrate  130 , frit glass may be used as the sealant  140 . By using a sealant with an excellent sealing force such as the frit glass, external moisture and oxygen penetration can be prevented without an additional moisture absorbent in a sealing space. 
     The first alignment layer  150  is formed on the IPS mode electrode  131  of the second substrate  130 . The first alignment layer  150  is used to arrange the liquid crystal layer  170  (described below) in a predetermined direction, and is formed by coating a high molecular layer such as a polyimide layer. Especially, according to the present embodiment, the first alignment layer  150  may be aligned at about 45 degrees with respect to the surface of the first substrate  130 . 
     The second alignment layer  160  is formed over the first substrate  110  and on the organic light emitting device  120 . The second alignment layer  160  is aligned in substantially the same direction as the first alignment layer  150 . Thus, the second alignment layer  160  is aligned at about 45 degrees with respect to the surface of the second substrate  130 . 
     The liquid crystal layer  170  is disposed in an inner space formed by the first substrate  110 , the second substrate  130 , and the sealant  140 . The liquid crystal layer  170  absorbs and cools heat emitted from the organic light emitting device  120 , and fills the inner space of the flat panel display device  100 , thereby preventing damage to the flat panel display device  100  from an external impact. 
     Furthermore, the liquid crystal layer  170  where an initial alignment is determined between the first alignment layer  150  and the second alignment layer  160  is driven by a parallel electric field, which is formed on the IPS mode electrode layer  131  of the second substrate  130 , once a voltage is externally applied. Therefore, an image is displayed by a liquid crystal display (LCD). Moreover, the LCD according to the present embodiment may be configured as a reflective type device without an additional backlight. 
     In summary, the display device functions as an LCD if an electrical signal such as voltage is applied to the IPS mode electrode layer  131 . Further, the display device functions as an OLED if an electrical signal such as voltage is applied to the first and second electrode layers  121  and  123 . Accordingly, the flat panel display device may include a dual display of an LCD and an OLED. Moreover, since the liquid crystal is used as a filling material, heat dissipation and internal impact resistance can be improved. 
     Hereinafter, a flat panel display device according to another embodiment is described with reference to  FIG. 2 . 
       FIG. 2  is a cross-sectional view illustrating a flat panel display device  100 ′ according to another embodiment of the present invention. 
     As shown in  FIG. 2 , the flat panel display device  100 ′ includes a first substrate  110 , an organic light emitting device  120 , a second substrate  130 , a sealant  140 , a first alignment layer  150 , a second alignment layer  160 , a liquid crystal layer  170 , and a linear polarization film  180 . Hereinafter, differences between the  FIG. 1  embodiment and the  FIG. 2  embodiment will be mainly described and like reference numerals refer to like elements. 
     The organic light emitting device  120  including the first electrode layer  121 , the organic light emitting layer  122 , and the second electrode layer  123  is disposed on a part of the first substrate  110 . 
     A pattern of the first electrode layer  121  and the second electrode layer  123  may include an AM type pattern or a PM type pattern, and may be electrically connected to an external terminal (not shown) on the first substrate  110  to serve as an anode or a cathode. Once a voltage is externally applied, the organic light emitting layer  122  emits light because of the combining of electrons and holes such that an image is realized on the flat panel display device  100 . 
     In one embodiment, the flat panel display device  100 ′ is a top emission type. Thus, the first electrode layer  121  serves as a reflective electrode and the second electrode layer  123  serves as a transparent electrode. 
     In one embodiment, after a reflective layer is formed using Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca or a compound thereof, ITO, IZO, ZnO, or In 2 O 3  having a high work function is formed thereon in order to form the first electrode layer  121 . 
     In one embodiment, after a metal of a small work function such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca or a compound thereof is deposited, an auxiliary electrode layer or a bus electrode line is formed thereon using a transparent conductive material such as ITO, IZO, ZnO, or In 2 O 3  in order to form the second electrode layer  123 . 
     The second substrate  130  for sealing the organic light emitting device  120  from the outside is disposed on the organic light emitting device  120 . In the present embodiment, the second substrate  130  is a transparent substrate. 
     The IPS mode electrode layer  131  is disposed with various kinds of patterns on the side of the second substrate  130  facing the first substrate  110 . The IPS mode electrode layer  131  is electrically connected to an external terminal (not shown) on the second substrate  130 , and thus may serve as an anode or a cathode. 
     In the present embodiment, the IPS mode electrode layer  131  serves as a transparent electrode formed of, for example, ITO, IZO, ZnO, or In 2 O 3 . 
     The first substrate  110  and the second substrate  130  are bonded using the sealant  140 . The first alignment layer  150  is formed on the IPS mode electrode layer  131  of the second substrate  130 , and the second alignment layer  160  is formed on the first substrate  110  and the organic light emitting device  120 . The first and second alignment layers  150  and  160  are used to align the liquid crystal layer  170  in a predetermined direction, and a high molecular layer such as polyimide is coated therefor. In one embodiment, the first alignment layer  150  is aligned at about 45 degrees with respect to the second substrate  130 . 
     The liquid crystal layer  170  is provided in an inner space formed by the first substrate  110 , the second substrate  130 , and the sealant  140 . The liquid crystal layer  170  absorbs and cools heat emitted from the organic light emitting device  120 , and fills the inner space of the flat panel display device  100 ′, thereby preventing damage to the flat panel display device  100 ′ from an external impact. 
     In addition, the liquid crystal layer  170  of which an initial alignment is determined between the first alignment layer  150  and the second alignment layer  160  is driven by a parallel electric field formed at the IPS mode electrode layer  131  of the second substrate  130  once a voltage is externally applied. Thereby, an image is realized on an LCD. In one embodiment, the LCD may include a reflective device without an additional backlight. 
     Moreover, the liquid crystal layer  170  is aligned at about 45 degrees with respect to the surface of the second substrate  130  when no external voltage is applied. Therefore, the liquid crystal layer  170  serves as a ¼ of the wavelength phase difference plate in an OLED device. 
     The linear polarization film  180  is provided on the side of the second substrate  130 , which is opposite to a side of the second substrate  130  facing the first substrate  110 . 
     Due to external light, contrast and visibility are deteriorated in an OLED device. To resolve this, a conventional OLED device includes a circular polarization film, which is manufactured by bonding a multi-layered polarization film and phase difference film. However, since the circular polarization film is manufactured using the bonded multi-layered films, it is difficult to produce a thin display device because of its complex manufacturing process, expensive cost, and thick thickness. 
     In one embodiment, in the flat panel display device  100 ′, since the liquid crystal layer  170  serves as a ¼ wavelength phase difference plate, only the thin linear polarization film  180  instead of a thick circular polarization film is provided. Accordingly, a thin display device can be realized. 
     Furthermore, an adhesive layer (not shown) may be further provided between the second substrate  130  and the linear polarization film  180 . 
     In one embodiment, the flat panel display device may have a dual display of an LCD and an organic light emitting device. In addition, since liquid crystal is used as a filling material, heat dissipation and internal impact resistance can be improved. In one embodiment, since liquid crystal serving as a ¼ wavelength phase difference plate is used and only a linear polarization film instead of a conventional circular polarization film is attached at an external light incident side, external light visibility can be improved and the thickness of a device can be reduced. 
     Hereinafter, a method of manufacturing a flat panel display device, according to an embodiment, will be described with reference to  FIGS. 3 through 7 . 
       FIGS. 3 through 7  are cross-sectional views illustrating a method of manufacturing a flat panel display device, according to an embodiment. 
     Referring to  FIG. 3A , a second substrate  130  having an IPS mode electrode layer  131  is prepared and a first alignment layer  150  is coated on the second substrate  130  to cover the IPS mode electrode layer  131 . In addition, referring to  FIG. 3B , a first substrate  110  is prepared as a light emitting substrate having an organic light emitting device  120 , and a second alignment layer  160  is coated on the first substrate  110 . In the present embodiment, a high molecular weight layer such as polyimide is coated and used as the first and second alignment layers  150  and  160 . 
     An external terminal (not shown) that is electrically connected to a first electrode layer  121  and a second electrode layer  123  of the organic light emitting device  120  is formed on the first substrate  110  substantially simultaneously during the forming of the first electrode layer  121  and the second electrode layer  123 . Moreover, an external terminal (not shown) that is electrically connected to the IPS mode electrode layer  131  is formed on the second substrate  130  substantially simultaneously during the forming of the IPS mode electrode layer  131 . 
     Referring to  FIG. 2B , although a sealant  140  is formed first on the edge portions of the first substrate  110  before the coating of the second alignment layer  160 , the order may be changed. That is, after the second alignment layer  160  is coated, the sealant  140  may be disposed at the edge portions of the first substrate  110 . In addition, as shown in  FIG. 2B , after the sealant  140  is formed on the edge portions of the first substrate  130 , the sealant  140  is attached to the second substrate  130 , but it is possible that after the sealant  140  is formed on the edge portions of the second substrate  130 , the sealant  140  is attached to the first substrate  110 . 
     In one embodiment, as shown in  FIGS. 4A and 4B , ultraviolet (UV) light is projected on the first and second alignment layers  150  and  160 . The first and second alignment layers  150  and  160  may be aligned through various kinds of methods in order to align the liquid crystal layer  170  in a predetermined direction. A method of manufacturing an alignment layer may be a contact type method such as a rubbing method where a polyimide surface is rubbed in a predetermined direction with a fiber such as nylon or polyester, and a non-contact type method such as a photo alignment method, an energy beam alignment method, a vapor deposition alignment method, and a lithography alignment method. In the present embodiment, the photo alignment method, in which UV light is projected on the coated polyimide thin layer to control molecular characteristics of an alignment layer, is used. 
     In the present embodiment, the first alignment layer  150  is aligned at a tilt angle θ (e.g., about 45 degrees) with respect to the second substrate  130 . Since the second alignment layer  160  is aligned in substantially the same direction as the first alignment layer  150 , the second alignment layer  160  is aligned at about 45 degrees with respect to the second substrate  130 . 
     Referring to  FIG. 5 , a liquid crystal material is injected into the second substrate  130  having the first alignment layer  150  to form the liquid crystal layer  170 . 
     Referring to  FIG. 6 , the second substrate  130  with the injected liquid crystal layer  170  is attached to the first substrate  110  by using the sealant  140 , and the liquid crystal layer  170  injected into an inner space formed by the first substrate  110 , the second substrate  130 , and the sealant  140  is hardened by UV light. Thereby, the liquid crystal layer  170  serves as a ¼ wavelength phase difference plate. In addition, the liquid crystal layer  170  absorbs and cools heat emitted from the organic light emitting device  120 , and fills the inner space of a device, thereby preventing damage to the flat panel display device from an external impact. 
     Referring to  FIG. 7 , a linear polarization film  180  is attached on the top surface of the substrate  130  of the flat panel display device using a liquid crystal layer  170 . Furthermore, although not illustrated in the drawings, it is apparent that an adhesive layer (not shown) may be further provided between the second substrate  130  and the linear polarization film  180 . The liquid crystal layer  170  serves as a ¼ wavelength phase difference plate and the linear polarization film  180  may serve as a circular polarization film. 
     According to at least one embodiment, a dual display of an OLED and an LCD is realized. In addition, since liquid crystal is used as a filling material, heat dissipation and internal impact resistance can be improved. Moreover, a liquid crystal serving as a ¼ wavelength phase difference plate is used and only a linear polarization film instead of a conventional circular polarization film is attached such that external light visibility can be improved and the thickness of a device can be reduced. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.