Patent Publication Number: US-2011059560-A1

Title: Organic Electroluminescence Pixel, Organic Electroluminescence Device, and Manufacturing Method Thereof

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This is a divisional application of patent application Ser. No. 11/838,987 filed on Aug. 15, 2007. The prior application Ser. No. 11/838,987 claims the benefit of Taiwan Patent Application No. 096115627 filed on May 2, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic electroluminescence (OEL) pixel with high color saturation and high luminescent efficiency, an organic electroluminescence device comprising OEL pixels, and a manufacturing method thereof. 
     2. Descriptions of the Related Art 
     With the advantages of self-emission, high luminescent efficiency, high contrast ratio, and ultra wide viewing angle, the organic electroluminescence display (OELD) is increasingly becoming a focus of research in the electronic display field. The OELD can be divided into two categories: the active matrix organic electroluminescence display (AMOELD) and the passive matrix organic electroluminescence display (PMOELD). 
     Since the OELD technology eliminates the need of backlit modules and features self-emission capability, higher contrast ratio, lower power consumption, wider viewing, slimmer thickness as well as a higher response speed compared to liquid crystal display (LCD) technology, it is better suited for electronic products for future generations. It is therefore considered as one of the most promising display technologies of the future. 
     As shown in  FIG. 1 , an OEL device  1  in a conventional AMOELD comprises a plurality of OEL pixels  1   r,    1   g,    1   b,  a substrate  11 , an active matrix circuitry layer  12 , a plurality of transparent lower electrodes  13   r,    13   g,    13   b,  a pixel insulation layer  15 , an organic emitting layer  17 , and an upper electrode  19 . The OEL pixels  1   r,    1   g,    1   b  are configured to emit red light, green light, and blue light, respectively. The substrate  11  further comprises a plurality of thin film transistors (TFTs)  111 ,  113 ,  115  and a plurality of signal lines  116 . The TFT  111  is configured to control the OEL pixel  1   r  in the OEL device  1  to emit red light, the TFT  113  is configured to control the OEL pixel  1   g  in the OEL device  1  to emit green light, and the TFT  115  is configured to control the OEL pixel  1   b  in the OEL device  1  to emit blue light. The pixel insulation layer  15  is configured to define the emitting area of respective OEL pixels  1   r,    1   g,    1   b.  The signal lines  116  are configured to transfer signals. 
     In order for the aforesaid OEL device  1  to emit red light, the TFT  111  is turned on to energize the lower electrode  13   r,  thus allowing the OEL pixel  1   r  to emit red light. At the same time, the TFTs  113  and  115  are turned off, so as not to allow the OEL pixels  1   g  and  1   b  to emit light. As a result, the OEL device  1  only emits red light. 
     However, in this type of conventional bottom-emission AMOELD, constraints imposed by the materials used often leads to insufficient color saturation in the OEL device  1 . Therefore, in the conventional technologies, microcavity structures are further fabricated to improve the luminescent efficiency and color saturation of the OEL pixels  1   r,    1   g,    1   b.  As shown in  FIG. 2 , the OEL device  2  is similar to the OEL device  1  in most of its structure, and comprises a plurality of OEL pixels  2   r,    2   g,    2   b,  a substrate  21 , an active matrix circuitry layer  22 , a plurality of transparent lower electrodes  23   r,    23   g,    23   b,  a pixel insulation layer  25 , an organic emitting layer  27 , and an upper electrode  29 . The OEL pixels  2   r,    2   g,    2   b  are configured to emit red light, green light, and blue light, respectively. The substrate  21  further comprises a plurality of TFTs  211 ,  213 ,  215  and a plurality of signal lines  216 . 
     In conventional technology as shown in  FIG. 2 , in order to fabricate OELDs with microcavity structures, a photo-etching process is utilized to form patterned semi-trans-flective metal electrodes  24   r,    24   g,    24   b  on the transparent lower electrodes  23   r,    23   g,    23   b.  The pixel insulation layer  25  is then formed thereon to define an emitting area for the pixel. However, this requires an additional photo-etching process in the existing TFT process, which adds to the manufacturing costs. Moreover, surfaces of the semi-trans-flective metal electrodes exposed in the photo-etching process may suffer from at least one of oxidation, increased surface roughness, residue of conductive substances, and/or residue from organic substances, all which will have adverse effect on the properties of the device (e.g., incurrence of short circuits, variation of electrical property, and variation of operation voltage). 
     In addition to the need of forming patterned semi-trans-flective metal electrodes on the transparent lower electrodes  23   r,    23   g,    23   b,  the microcavity structure described above also requires an organic film layer with appropriate thickness in the OEL device  2 . The thickness of the organic film layer must be selected appropriately in order to improve the color saturation and luminescence efficiency of the OEL device  2 . A thinner organic film layer (i.e. the organic emitting layer  27 ) will undoubtedly endow the OEL device  2  with better luminescent efficiency and color saturation. However, due to the uneven surface of the transparent lower electrodes  23   r,    23   g,    23   b  and /or the semi-trans-flective metal electrodes  24   r,    24   g,    24   b  (e.g., protrusions on the semi-trans-flective metal electrodes  24   g  in  FIG. 2 ), an unduly thin organic film layer tends to cause a current leakage or even a short circuit between the upper electrodes  29  and the transparent lower electrodes  23   r,    23   g,    23   b  or the upper electrodes  29  and the semi-trans-flective metal electrodes  24   r,    24   g,    24   b  in the OEL device  2 . On the other hand, if the organic film layer has its thickness increased in order to eliminate the aforesaid current leakage phenomenon in the OEL device  2 , variation of its luminescent efficiency and color saturation will be increased due to an uneven thickness of the organic film layer. 
     Accordingly, an effort still has to be made in this field to enhance the luminescent efficiency and color saturation of the OEL devices in OELDs without introducing any additional process, and without modifying the existing manufacturing process and yield thereof. 
     SUMMARY OF THE INVENTION 
     One of the objectives of this invention is to provide an organic electroluminescence pixel, which comprises a substrate, a first electrode, a first carrier-injection layer (CIL), a semi-trans-flective metal layer, a first organic emitting layer, and a second electrode. The first electrode is formed on the substrate. The first CIL, the semi-trans-flective metal layer, and the first organic emitting layer are formed between the first electrode and the second electrode. At least one of the first electrode and the second electrode comprises a transparent electrode. 
     Another objective of this invention is to provide an OEL device, which comprises a plurality of OEL pixels electrically connected with each other. At least one of the OEL pixels is the OEL pixel defined above. 
     Yet a further objective of this invention is to provide a method for manufacturing an OEL device. The method comprises: providing a substrate; forming a first electrode on the substrate; forming a first pixel on the first electrode; and forming a second electrode on the first pixel. The step of forming a first electrode on the substrate further comprises the steps of: forming a first CIL; forming a semi-trans-flective metal layer; and forming an organic emitting layer. At least one of the first electrode and the second electrode comprises a transparent electrode. 
     As a result, this invention can improve the luminescent efficiency and the color saturation of OEL devices and effectively mitigate the current leakage therein without introducing any additional manufacturing process or modifying the existing manufacturing process and yield thereof. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a conventional OEL device; 
         FIG. 2  is a schematic diagram illustrating another conventional OEL device; 
         FIG. 3  is a schematic diagram illustrating the first embodiment of this invention; and 
         FIG. 4  is a flow chart illustrating the second embodiment of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIG. 3 , the first embodiment of the present invention is an organic electroluminescence (OEL) device  3 . The OEL device  3  may be (but is not limited to) a bottom emitting type, a top emitting type, a dual emitting type, or a combination thereof. In this embodiment, the OEL device  3  is the bottom emitting type, and will be used as an example for the following description. 
     The OEL device  3  comprises a plurality of OEL pixels  3   r,    3   g,    3   b,  a substrate  31 , a plurality of first electrodes  33   r,    33   g,    33   b,  a first carrier-injection layer (CIL)  33 , a semi-trans-flective metal layer  34 , an organic emitting layer  35 , a second electrode  36 , an insulation layer  37 , and an active matrix circuitry layer  38 . The OEL pixels  3   r,    3   g,    3   b  are configured to emit red light, green light, and blue light, respectively. The active matrix circuitry layer  38  further comprises an active matrix layer  381 , a gate dielectric layer  382 , an interlayer dielectric layer  383 , a passivation layer  384 , a plurality of TFTs  311 ,  313 ,  315 , a plurality of signal lines  316 , and a plurality of line segments  385 ,  386 ,  387  electrically connected to their respective signal lines. The types of the TFTs include a top-gate type, a bottom-gate type, other similar types, or a combination thereof. The TFTs of various types all include an active layer  381  therein, that comprises Si-containing amorphous materials, Si-containing single crystal line materials, Si-containing microcrystalline materials, Si-containing polycrystalline materials, Ge-containing amorphous materials, Ge-containing single crystalline materials, Ge-containing microcrystalline materials, Ge-containing polycrystalline materials, other similar materials, or a combination thereof. In this embodiment, a top-gate type of TFT is made of Si-containing polycrystalline materials (e.g., polycrystalline silicon) is used as an example, and this invention is not limited thereto. The TFTs  311 ,  313 ,  315  are configured to control the OEL pixels  3   r,    3   g,    3   b  of the OEL device  3  to emit red light, green light, and blue light, respectively. The signal lines  385 ,  386 ,  387  are configured to supply signals (e.g., signal levels) to the TFTs  311 ,  313 ,  315 , respectively. The first CIL  33 , the semi-trans-flective metal layer  34 , and the organic emitting layer  35  are formed between the first electrodes  33   r,    33   g,    33   b  and the second electrodes  36 . 
     In the OEL device  3 , at least one of the first electrodes  33   r,    33   g,    33   b  and the second electrode  36  is a transparent electrode, a reflective electrode, or a combination thereof (e.g., a partly transparent and partly reflective electrode). In this embodiment, since the OEL device  3  is a bottom-emitting type, the first electrodes  33   r,    33   g,    33   b  are made of a transparent material which renders them transparent. The transparent material includes indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), aluminum tin oxide (ATO), cadmium tin oxide (CTO), hafnium oxide (HfO), other similar materials, or a combination thereof. The second electrode  36  is made of a reflective material which renders it non-transparent. The reflective material may includes Au, Ag, Cu, Fe, Tin, Al, Ti, Ta, Mo, W, Nd, Hf, Li, Mg, Ca, alloys thereof, nitrides thereof, oxides thereof, or a combination of the above materials. 
     On the contrary, if the OEL device  3  is a top emitting type, the first electrodes  33   r,    33   g,    33   b  may be made of a reflective material which renders them non-transparent. The reflective material includes Au, Ag, Cu, Fe, Tin, Al, Ti, Ta, Mo, W, Nd, Hf, Li, Mg, Ca, alloys thereof, nitrides thereof, oxides thereof, or a combination of the above materials. The second electrode  36  may be made of a transparent material which renders it transparent. The transparent material may include ITO, IZO, AZO, ATO, CTO, HfO, other similar materials, or a combination thereof. Alternatively, if the OEL device  3  is a dual emitting type, both the first electrodes  33   r,    33   g,    33   b  and the second electrode  36  are made of a transparent material, including ITO, IZO, AZO, ATO, CTO, HfO, other similar materials, or a combination thereof. Even further, if the OEL  3  is a combination of two of the top emitting type, the bottom emitting type, and the dual emitting type, the material for making at least one of the first electrodes  32   r,    32   g,    32   b  and the second electrode  36  comprises at least one of the transparent materials and the reflective materials described above. 
     Although the first CIL  33  is formed on the first electrodes  33   r,    33   g,    33   b  in the OEL device  3  of the first embodiment, it is not limited in that the first CIL  33  must be formed on all of the first electrodes  33   r,    33   g,    33   b;  instead, it can be formed on only at least one of the first electrodes  33   r,    33   g,    33   b.  Also, the thickness X of the first CIL  33  can be adjusted on each first electrode respectively in an attempt to obtain the optimum luminescent efficiency of respective OEL pixels  3   r,    3   g,    3   b.  In other words, depending on the design requirements, the first CIL  33  may have the same or different thickness on different pixels. 
     The organic emitting layer  35  further comprises a second CIL  351 , a carrier transport layer (CTL)  353 , and a light emitting layer  355 , which constitutes the basic structure that forms a microcavity structure. In this embodiment, the CTL  353  is formed on the second CIL  351 . The light emitting layer  355  is formed on the CTL  353 , and comprises a metal complex compound, such as Al complex oxides and Bi complex oxides. The metal complex compounds may include organic materials, inorganic materials, or a combination thereof. 
     However, the organic emitting layer  35  in this invention is not limited to the aforesaid combination that forms the microcavity structure, and may have additional layers as desired. In this embodiment, the combination that forms the microcavity structure comprises the following ordered sequence: the light emitting layer  355 /the CTL  353 /the second CIL  351 . Additionally, layers may be in other ordered sequences; for example, a multilayer structure may be (but is not limited) in the following ordered sequences: the CTL  353 /the light emitting layer  355 /the second CIL  351 , the second CIL  351 /the CTL  353 /the light emitting layer  355 , or the light emitting layer  355 /the second CIL  351 /the CTL  353 . 
     The semi-trans-flective metal layer  34  is formed between the first CIL  33  and the first electrodes  33   r,    33   g,    33   b.  In this embodiment, in order to improve the color saturation and luminescent efficiency of the OEL pixel  3   b  that emits blue light in the OEL device  3 , the semi-trans-flective metal layer  34  is formed only between first CIL  33  and the first electrode  33   b,  and is fabricated in the following way without addition of any shadow masking process: a photomask with a particular design is employed in conjunction with a particular evaporation deposition angle to make the semi-trans-flective metal layer  34  only deposit on, and entirely overcoat, the area of the OEL pixel  3   b  that emits blue light, but not on the OEL pixels  3   r,    3   g  that emit red and green light. In other words, the semi-trans-flective metal layers  34  in adjacent OEL pixels are not connected to each other. However, the formation of the semi-trans-flective metal layer  34  is not limited to the OEL  3   b  that emits blue light, and instead, it can be formed on at least one of the OEL pixels  3   r,    3   g,    3   b.  Also, the semi-trans-flective metal layer  34  formed on at least one of the OEL pixels  3   r,    3   g,    3   b  may have the same or different thickness. Light reflectivity and transmissivity of the semi-trans-flective metal layer  34  depend on its thickness. The thicker the layer is, the higher its reflectivity will be. In contrast, the thinner it is, the higher its transmissivity will be. In this sense, whether an OEL pixel reflects or transmits light can be judged through its thickness. However, sometimes its resistance does not comply with the constraints for driving the OEL pixel, even if its thickness does. Therefore, whether an individual OEL pixel reflects or transmits light can be preferably judged by both its thickness and resistance. To ensure the high luminescent efficiency of the OEL device  3  with the semi-trans-flective metal layer  34 , a boundary has to be defined for the emitting area of the OEL device  3 . The insulation layer  37  is used to define a pixel range area  341  from the semi-trans-flective layer  34 . A lateral dimension of the pixel range area  341  is substantially smaller than that (not shown) of the semi-trans-flective metal layer  34 . Located outside of the pixel range area  341  of the semi-trans-flective metal layer  34  are the boundary areas  343 . Also, to ensure the high luminescent efficiency of the OEL device  3 , a maximum brightness of the boundary areas  343  from outside of the pixel range area  341  to the boundary of the semi-trans-flective metal layer  34  should be substantially smaller than or substantially equal to 50% of that of the pixel range area  341 . 
     Formation of the semi-trans-flective metal layer  34  in this invention is not limited to the position between the first CIL  33  and the first electrodes  33   r,    33   g,    33   b.  Instead, it can be formed inside the first CIL  33 , between the first CIL  33  and the second CIL  351 , inside the second CIL  351 , between the second CIL  351  and the CTL  353 , inside or on the CTL  353 , all of which can be effective in improving the color saturation and luminescent efficiency of the OEL device  3 . 
     As shown in  FIG. 4 , the second embodiment of the present invention is a method for manufacturing an OEL device. This OEL device may be the OEL device  3  described in the first embodiment, and this method is described as follows. 
     In step  401 , a substrate is provided. Then, a first electrode is formed on the substrate in step  403 , which is followed by step  405  where a first CIL is formed. In step  407 , a semi-trans-flective metal layer is formed. Subsequently, an organic emitting layer is formed in step  409 , which combines with steps  405  and  407  to form a first pixel. In step  411 , a second electrode is formed on the first pixel formed through step  405  to  409 . Then step  403  is repeated to form another first electrode on the substrate, which is followed by the formation of another CIL in step  413 . Thereafter, another organic emitting layer is formed in step  415 , which combines with step  413  to form a second pixel. Finally in step  417 , the second electrode is formed on the second pixel formed through steps  413  and  415 . The process proceeds by repeating in this way. As with the first embodiment, at least one of the first electrodes and the second electrodes formed in the second embodiment is a transparent electrode. 
     The position where the semi-trans-flective metal layer of the first pixel is formed is not limited in this invention, and it can be formed instead on the first pixel, between the first CIL and the organic emitting layer, or on the organic emitting layer, all of which can be effective in improving the color saturation and luminescent efficiency of the OEL device. 
     In addition to the first and the second pixel formed through the aforesaid steps, in the method for the second embodiment, additional pixels can also be formed through the same steps. 
     In addition to the steps depicted in  FIG. 4 , the second embodiment can also execute all the operations of the first embodiment. Those skilled in the art can understand the corresponding steps and operations of the second embodiment by following the descriptions of the first embodiment, and thus no unnecessary details are given. 
     It follows from the above description that, as compared to the conventional OEL device with a microcavity structure, the OEL device of this invention can be formed with a semi-trans-flective metal layer and/or a CIL in the individual OEL pixels that the OEL device comprises, and the CIL can be adjusted in the vertical dimension (i.e. the thickness). These properties can effectively improve the luminescent efficiency and the color saturation of the OEL device and effectively mitigate the current leakage therein without introducing any additional process or modifying the existing manufacturing process and yield, thus achieving the goal of technical advancement. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.