Abstract:
Provided is an organic EL device having a lower power consumption and high performance and enabling to display separate pictures on bidirectional screens as well as to display the same picture on the bidirectional screens, and a driving apparatus thereof. The organic EL device includes: a first organic EL panel for a unidirectional display; and a second organic EL panel for a unidirectional display, each of the first and second organic EL panels having a substrate, a first electrode, an emitting layer and a second electrode, wherein the first organic EL panel and the second organic EL panel are coupled so as to display pictures in bidirections. According to the present invention, a sufficient brightness can be obtained even under a low power. Also, since an opaque cathode is used, performance and transmittance are enhanced compared with the related art organic EL device using a transparent cathode.

Description:
This application claims the benefit of the Korean Application No. 10-2003-0086839 filed on Dec. 2, 2003 which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic EL device, and more particularly, to an organic EL device and a driving apparatus thereof. 
     2. Discussion of the Related Art 
     Generally, an organic electroluminescent (EL) device is a device to emit light while a pair of electron and hole formed by injecting a charge into a light emitting layer of an organic material disposed between the electron injection electrode (cathode) and the hole injection electrode (anode). 
     Such an organic EL device is characterized by operation at a relatively low voltage and low power consumption. 
     Among the general organic EL devices, the organic EL devices for a unidirectional display can be classified into a bottom emission type and a top emission type. 
     A bottom emission type organic EL device is shown in  FIG. 1 . A method of fabricating the bottom emission type organic EL device shown in  FIG. 1  will now be described. 
     An anode  2  is formed on a transparent substrate  1 . The anode  2  is generally made of indium tin oxide (ITO). 
     Next, a hole injecting layer (HIL)  3  is formed on the anode  2 . The HIL  3  is generally made of copper phthalocyanine (CuPc) and is coated to a thickness of 10-30 nm. The structure of CuPc is shown in  FIG. 8  for your understanding. 
     Next, a hole transport layer (HTL)  4  is formed on the HIL  3 . 
     The HTL is generally made of TPD (N′-diphenyl-N,N′-bis(3-methylphenyl)-(1-1′-biphenyl)4,4′-diamine) or NPD (4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl), and is deposited to a thickness of 30-60 nm. The structures of TPD and NPD are shown in  FIG. 8  for your understanding. 
     Next, an organic emitting layer  5  made of an organic material is formed on the HTL  4 . 
     The organic emitting layer  5  as formed may contain dopants if necessary. 
     In case of green light emission, Alq 3  {tris(8-hydroxy-quinolate)aluminum} is deposited to about 30-60 nm so as to form the organic emitting layer  5 , and coumarin  6  or Qd (Quinacridone) is added as the dopants. 
     In case of red light emission, ECM, DCJT, DCJTB or the like is used. The structure of Alq 3  is also shown in  FIG. 8 . 
     Next, an electron transport layer (ETL)  6  and an electron injecting layer (EIL)  7  are continuously formed on the organic emitting layer  5 , or the ETL  6  and the EIL  7  are formed together with an electron injection transport layer. 
     At this time, the EIL  7  is formed by coating LiF or Li 2 O to a thickness of about 5□, or by depositing alkali metal or alkaline-earth metal such as Li, CA, Mg, Sm, etc. to a thickness less than 200□ for making electron injection better. 
     Also, in case of the green light emission, since Alq3 used as the organic emitting layer  5  has a good electron transport capability, the EIL  7  and the ETL  6  may be not used. 
     Next, aluminum (Al) is coated on the EIL  7  to a thickness of about 1000 □ to form a cathode  8 . 
     In the bottom emission type organic EL device formed by the above method, the material layer used as the cathode serves as a mirror reflection surface. 
     Accordingly, half of the light emitting from the emitting layer of the organic EL device emits toward the transparent electrode (anode)  2 . 
     The remaining half of the light is reflected by the cathode and emits toward the transparent electrode (anode). 
     Next, a top emission type organic EL device is shown in  FIG. 2 . A method of fabricating the top emission type organic EL device shown in  FIG. 2  will now be described. 
     Unlike in the bottom emission type, in the bottom emission type, an organic EL device is formed on an opaque substrate and a transparent electrode is lastly formed such that light emits in an opposite direction to the substrate. 
     An anode  12  is first formed on an opaque substrate  11 . 
     Next, hole injecting layers (HILs)  13  and  14  are formed on the anode  12 . 
     Next, an organic emitting layer  15  made of an organic material is formed on the HTL  14 . 
     Next, an electron transport layer (ETL)  16  and an electron injecting layer (EIL)  17  are formed on the organic emitting layer  15 . 
     Next, a transparent cathode  18  is formed on the EIL  17  such that light is irradiated upward. 
       FIG. 3  is a sectional view of a bidirectional organic EL according to the related art. 
     The organic EL device for bidirectional display employs the bottom emission type shown in  FIG. 1  at the lower side from an emitting layer  25  and the top emission type shown in  FIG. 2  at the upper side from the emitting layer  25  such that light emits in both directions of upper and lower sides. 
     However, the related art organic EL device for bidirectional display has the following drawbacks. 
     First, since light generated by a single emitting layer emits in upper and lower directions, the organic EL device for bidirectional display needs a power at least four times greater than that of the bottom emission type organic EL device so as to obtain the same brightness. 
     Secondly, since the organic EL device for bidirectional display is driven by a pair of electrodes, it is possible to display an identical picture in the upper and lower directions, but it is impossible to display different pictures on the upper screen and the lower screen. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an organic EL device and a driving apparatus thereof that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an organic EL device having a lower power consumption and high performance and enabling to display separate pictures on bidirectional screens as well as to display the same picture on the bidirectional screens, and a driving apparatus thereof. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an organic EL device comprising: a first organic EL panel for a unidirectional display; and a second organic EL panel for a unidirectional display, each of the first and second organic EL panels having a substrate, a first electrode, an emitting layer and a second electrode, wherein the first organic EL panel and the second organic EL panel are coupled so as to display pictures in bidirections. 
     The first organic EL panel and the second organic EL panel may be coupled using a UV hardening material. 
     The above organic EL device may further comprise a buffer layer for electrical contact of the first organic EL panel and the second organic EL panel. 
     The above organic EL device may further comprise an insulating layer for electrical isolation between the first organic EL panel and the second organic EL panel. 
     Also, the first organic EL panel and the second organic EL panel can be selectively driven to display the same picture or different pictures. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  is a sectional view of a bottom emission type organic EL device according to the related art; 
         FIG. 2  is a sectional view of a top emission type organic EL device according to the related art; 
         FIG. 3  is a sectional view of an organic EL device for bidirectional display according to the related art; 
         FIG. 4  is a sectional view of an organic EL device for bidirectional display according to a first embodiment of the present invention; 
         FIG. 5  is a sectional view of an organic EL device for bidirectional display according to a second embodiment of the present invention; 
         FIG. 6  is a sectional view of an organic EL device for bidirectional display according to a third embodiment of the present invention; 
         FIG. 7  is a sectional view of an organic EL device for bidirectional display according to a fourth embodiment of the present invention; 
         FIG. 8  shows molecular structural formulas of CuPC, TPD, Alq3, NPD and phthalocyanine; 
         FIG. 9  is a block diagram of a driving apparatus of an organic EL device according to the present invention; and 
         FIG. 10  is a block diagram of the switching unit of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     First Embodiment 
     As shown in  FIG. 4 , an organic EL device for bidirectional display according to a first embodiment of the present invention is made by bonding a first organic EL panel  30  and a second organic EL panel  30 ′. 
     The first organic EL panel  30  performs a unidirectional display through a transparent anode  32  and a transparent substrate  31 , and the second organic EL panel  30 ′ also performs a unidirectional display through a transparent anode  32 ′ and a transparent substrate  31 ′. 
     Accordingly, the first organic EL panel  30  and the second organic EL panel  30 ′ are coupled by bonding a cathode  38  of the first organic EL panel  30  with a cathode  38 ′ of the second organic EL panel  30 ′ for bidirectional display. 
     Next, a method of fabricating the first and second organic EL panels  30  and  30 ′ will be described. 
     Since the first organic EL panel  30  and the second organic EL panel  30 ′ have the same structure of which upper and lower sides are inverted, their description is made centering on the first organic EL panel  30 . 
     A transparent anode  32  is formed on a transparent substrate  31 . The transparent anode  32  is generally made of indium tin oxide (ITO). 
     Next, a hole injecting layer (HIL)  33  is formed on the transparent anode  32 . The HIL  33  is generally made of copper phthalocyanine (CuPc) and is coated to a thickness of 10-30 nm. The structure of CuPc is shown in  FIG. 8  for your understanding. 
     Next, a hole transport layer (HTL)  34  is formed on the HIL  33 . 
     The HTL  33  is generally made of TPD (N′-diphenyl-N,N′-bis(3-methylphenyl)-(1-1′-biphenyl)4,4′-diamine) or NPD (4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl), and is deposited to a thickness of 30-60 nm. The structures of TPD and NPD are shown in  FIG. 8  for your understanding. 
     Next, an organic emitting layer  35  made of an organic material is formed on the HTL  34 . 
     The organic emitting layer  35  as formed may contain dopants if necessary. 
     In case of green light emission, Alq 3  {tris(8-hydroxy-quinolate)aluminum} is deposited to about 30-60 nm so as to form the organic emitting layer  5 , and coumarin  6  or Qd (Quinacridone) is added as the dopants. 
     In case of red light emission, ECM, DCJT, DCJTB or the like is used. The structure of Alq 3  is also shown in  FIG. 8 . 
     Next, an electron transport layer (ETL)  36  and an electron injecting layer (EIL)  37  are continuously formed on the organic emitting layer  35 , or the ETL  36  and the EIL  37  are formed together with an electron injection transport layer. 
     At this time, the EIL  37  is formed by coating LiF or Li 2 O to a thickness of about 5□, or by depositing alkali metal or alkaline-earth metal such as Li, CA, Mg, Sm, etc. to a thickness less than 200□ for making electron injection better. 
     Also, in case of the green light emission, since Alq3 used as the organic emitting layer  5  has a good electron transport capability, the EIL  7  and the ETL  6  may be not used. 
     Next, aluminum (Al) is coated on the EIL  7  to a thickness of about 1000□ to form a cathode  38 , thereby completing the first organic EL panel  30 . 
     The second organic EL panel  30 ′ is fabricated by the same method as the aforementioned method. 
     The cathode  38  of the first organic EL panel  30  is bonded with the cathode  38 ′ of the second organic EL panel  30 ′, thereby completing the fabrication of the organic EL device for bidirectional display. 
     The bonding of the first and second organic EL panels  30  and  30 ′ is performed using an ultra violet (UV) hardening material, for example, epoxy-based adhesive. 
     Although not shown in the drawings, a buffer layer for electrical connection of the two EL panels may be further formed between the first organic EL panel  30  and the second organic EL panel  30 ′. 
     Also, although not shown in the drawings, an insulating layer for electrical insulation between the two EL panels may be further formed between the first organic EL panel  30  and the second organic EL panel  30 ′. 
     Alternatively, any one of the cathodes of the first and second organic EL panels  30  and  30 ′ may be commonly used. 
     In other words, any one of the first and second organic EL panels  30  and  30 ′ may not have the cathode. 
     According to the above first embodiment, since the respective emitting layers are provided to display pictures through the transparent anode and the transparent substrate, a sufficient brightness for bidirectional display is obtained, so that a low power operation becomes possible. 
     Also, since the opaque cathode is used, performance and transmittance are enhanced compared with the related art EL device using the transparent cathode. 
     This is because the transparent cathode formed by a sputtering causes a thermal stress to lower the device performance and a transparent passivation layer is further required on the transparent cathode, thereby causing drop of the overall transmittance. 
     Second Embodiment 
     As shown in  FIG. 5 , an organic EL device for bidirectional display according to a second embodiment of the present invention is made by bonding a first organic EL panel  40  and a second organic EL panel  40 ′. 
     The first and second organic EL panels  40  and  40 ′ perform a unidirectional display through their respective transparent cathodes  48  and  48 ′. 
     Accordingly, the first organic EL panel  40  and the second organic EL panel  40 ′ are coupled by bonding the transparent cathode  48  of the first organic EL panel  40  and the transparent cathode  48 ′ of the second organic EL panel  40 ′ for bidirectional display. 
     Next, a method of fabricating the first and second organic EL panels  40  and  40 ′ will be described. 
     Since the first organic EL panel  40  and the second organic EL panel  40 ′ have the same structure of which upper and lower sides are inverted, their description is made centering on the first organic EL panel  40 . 
     First, an anode  42  is formed on an opaque substrate  41 . 
     Next, a hole injecting layer (HIL)  43  and a hole transport layer (HTL)  44  are formed on the anode  42 . 
     Next, an organic emitting layer  45  made of an organic material is formed on the HTL  44 . 
     Next, an electron transport layer (ETL)  46  and an electron injecting layer (EIL)  47  are formed on the organic emitting layer  45 . 
     Next, a transparent cathode  48  is formed on the EIL  47  such that light emits, thereby completing the first organic EL panel  40 . 
     The second organic EL panel  40 ′ is fabricated by the same method as the aforementioned method. 
     The substrate  41  of the first organic EL panel  40  is bonded with the substrate  41 ′ of the second organic EL panel  40 ′, thereby completing the fabrication of the organic EL device for bidirectional display. 
     The bonding of the first and second organic EL panels  40  and  40 ′ is performed using an ultra violet (UV) hardening material, for example, epoxy-based adhesive. 
     Although not shown in the drawings, a buffer layer for electrical connection of the two EL panels may be further formed between the first organic EL panel  40  and the second organic EL panel  40 ′. 
     Also, although not shown in the drawings, an insulating layer for electrical insulation between the two EL panels may be further formed between the first organic EL panel  40  and the second organic EL panel  40 ′. 
     Alternatively, any one of the substrates of the first and second organic EL panels  40  and  40 ′ may be commonly used. 
     In other words, after the first organic EL panel  40  is fabricated, the second organic EL panels  40 ′ except for the substrate  41 ′ is formed on an exposed surface of the substrate  41  of the first organic EL panel  40 . 
     Of course, the reverse case will be also possible. 
     According to the above second embodiment, since the respective emitting layers are provided to display pictures through the transparent cathodes, a sufficient brightness for bidirectional display is obtained, so that a low power operation becomes possible. 
     Third Embodiment 
     As shown in  FIG. 6 , an organic EL device for bidirectional display according to a third embodiment of the present invention is made by bonding a first organic EL panel  40  and a second organic EL panel  30 ′. 
     The first organic EL panel  40  performs a unidirectional display through a transparent cathode  48  and has the same structure as the first organic EL panel  40  of  FIG. 5 . 
     The second organic EL panel  30 ′ performs a unidirectional display through a transparent anode  32 ′ and a transparent substrate  31 ′ and has the same structure as the second organic EL panel  30 ′ of  FIG. 4 . 
     Accordingly, the first organic EL panel  40  and the second organic EL panel  30 ′ are coupled by bonding the substrate  41  of the first organic EL panel  40  and the cathode  38 ′ of the second organic EL panel  30 ′ for bidirectional display. 
     Since a method of fabricating the first and second organic EL panels  40  and  30 ′ was described in the first and second embodiments, their repeated description will be omitted. 
     The bonding of the first and second organic EL panels  40  and  30 ′ is performed using an ultra violet (UV) hardening material, for example, epoxy-based adhesive. 
     Although not shown in the drawings, a buffer layer for electrical connection of the two EL panels may be further formed between the first organic EL panel  40  and the second organic EL panel  30 ′. 
     Also, although not shown in the drawings, an insulating layer for electrical insulation between the two EL panels may be further formed between the first organic EL panel  40  and the second organic EL panel  30 ′. 
     According to the above third embodiment, since the respective emitting layers are provided to display pictures through the transparent cathode and the transparent substrate, a sufficient brightness for bidirectional display is obtained, so that a low power operation becomes possible. 
     Fourth Embodiment 
     As shown in  FIG. 7 , an organic EL device for bidirectional display according to a fourth embodiment of the present invention is made by bonding a first organic EL panel  30  and a second organic EL panel  40 ′. 
     The first organic EL panel  30  performs a unidirectional display through a transparent anode  32  and a transparent substrate  31 , and has the same structure as the first organic EL panel  30  of  FIG. 4 . 
     The second organic EL panel  40 ′ performs a unidirectional display through a transparent cathode  48 ′ and has the same structure as the second organic EL panel  40 ′ of  FIG. 5 . 
     Accordingly, the first organic EL panel  30  and the second organic EL panel  40 ′ are coupled by bonding the cathode  38  of the first organic EL panel  30  and the substrate  40 ′ of the second organic EL panel  40 ′ for bidirectional display. 
     Since a method of fabricating the first and second organic EL panels  30  and  40 ′ was described in the first and second embodiments, their repeated description will be omitted. 
     The bonding of the first and second organic EL panels  30  and  40 ′ is performed using an ultra violet (UV) hardening material, for example, epoxy-based adhesive. 
     Although not shown in the drawings, a buffer layer for electrical connection of the two EL panels may be further formed between the first organic EL panel  30  and the second organic EL panel  40 ′. 
     Also, although not shown in the drawings, an insulating layer for electrical insulation between the two EL panels may be further formed between the first organic EL panel  30  and the second organic EL panel  40 ′. 
     According to the above fourth embodiment, since the respective emitting layers are provided to display pictures through the transparent cathode and the transparent substrate, a sufficient brightness for bidirectional display is obtained, so that a low power operation becomes possible. 
     Hereinafter, construction and operation of a driving apparatus of an organic EL device according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIG. 9 , a driving apparatus of an organic EL device includes an organic EL device, a driving unit  50 , a switching unit  60  and a controller  70 . 
     The driving apparatus of the present invention may be used in all organic EL devices each having first and second electrodes and operatable separately as well as in the organic EL devices fabricated according to the first to fourth embodiments of the present invention. 
     The driving unit  50  outputs first and second driving signals such that the organic EL device can display pictures. 
     The driving unit  50  may be constructed to output only one driving signal or two or more driving signals. 
     The switching unit  60  supplies at least one of the first and second organic EL panels with the first and second driving signals outputted from the driving unit  50  according to a control signal. 
     At this time, the switching unit  60 , as shown in  FIG. 10 , includes first and second input terminals receiving the first and second driving signals outputted from the driving unit  50 , a first output terminal outputting one of the first and second driving signals to the first organic EL panel, a second output terminal outputting one of the first and second driving signals to the second organic EL panel, a third output terminal concurrently outputting one of the first and second driving signals to the first organic EL panel and the second organic EL panel, a switch  61  selectively connecting the first and second input terminals with the first to third output terminals, and a diode connected to the third output terminal, for preventing a signal transmission error between the first output terminal and the second output terminal. 
     Alternatively, the switching unit  60  may be designed having a different construction depending on the number of the signals outputted from the driving unit  50 . 
     The controller  70  controls the switching unit  60  according to a preset program or an external control. 
     In the above, the preset program is to automatically perform a picture display. For example, there are the same picture display setting in bidirections, a different picture display setting in bidirections, or a unidirectional picture display setting. 
     Also, the external control means a control signal of when a user manually selects one of the picture display settings. 
     The operation of the driving apparatus of the organic EL device constructed as above will now be described. 
     The organic EL device can display different pictures with respect to the first and second organic EL panels as well as perform bidirectional display. 
     Accordingly, a display operation of the same picture in bidirections, a display operation of different pictures setting in bidirections, or a display of a picture in a single direction will be described with the driving apparatus. 
     First, when a display of the same picture in bidirections is set, the controller  70  controls the switch  61  shown in  FIG. 10  such that the first driving signal (or second driving signal) is supplied to the first organic EL panel and the second organic EL panel at the same time. 
     Accordingly, the first and second organic EL panels operate according to the first driving signal to display the same picture. 
     Next, when a display of different pictures in bidirections is set, the controller  70  controls the switch  61  shown in  FIG. 10  such that the first driving signal (or second driving signal) is supplied to the first organic EL panel through the first output terminal. 
     Concurrently with this, the controller  70  controls the switch  61  such that the second driving signal (or first driving signal) is supplied to the second organic EL panel through the second output terminal. 
     Accordingly, the first and second organic EL panels operate according to the first driving signal and the second driving signal to display the respective different pictures thereon. 
     Next, when a display of a picture in a single direction, for example, a display of a picture on the first organic EL panel according to the first driving signal, is set, the controller  70  controls the switch  61  shown in  FIG. 10  such that the first driving signal is supplied to the first organic EL panel through the first output terminal. 
     Accordingly, the first organic EL panel operates according to the first driving signal to display a picture thereon. At this time, the second organic EL panel does not display a picture. 
     In other words, a selected picture is displayed on a selected panel but a picture is not displayed on a non-selected panel. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.