Abstract:
A passivation structure capping an electrical device disposed on a substrate is introduced. The passivation structure includes a first diamond-like carbon film covering a top surface and the sidewall of the electrical device and the surface of the substrate, a buffer layer positioned on the first diamond-like carbon film, and a second diamond-like carbon film positioned on the buffer layer. Part of the second diamond-like carbon film covers the first diamond-like carbon film directly to form a cyclic structure.

Description:
BACKGROUND OF INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a passivation structure, and more particularly, to a passivation structure comprising a cyclic structure composed of a diamond-like carbon film to resolve the heat issues of OLED devices.  
           [0003]    2. Description of the Prior Art  
           [0004]    The progress of science and technology has led to organic materials being well applied to all kinds of electrical devices. For example, organic light-emitting displays (OLEDs), which are formed by using organic materials, have the advantages of simpler structures, excellent operating temperature, high contrast, and a wide viewing angle, and have the beneficial characteristics of light-emitting diodes (LEDs), such as rectification and luminosity, so as to be used extensively in the field of display devices. Since the OLED uses luminous devices formed of organic materials to provide a light source, the OLED is very sensitive to the moisture. Once the organic light-emitting devices are exposed in the moisture, the cathode thereon may be oxidized and the interface of organic compounds may be peeled. This leads to dark spots being generated in the luminous devices, which deteriorates the brightness and the lifetime of the display devices. As a result, the package material used to package the electrical devices not only needs high anti-abrasiveness and thermal conductivity, but also requires low moisture permeability to prevent the organic materials from being exposed in the external environment effectively and to improve the lifetime of the electrical devices.  
           [0005]    For example, in the conventional package process of display devices, a sealing agent made of polymer materials is often used to combine the container, which is composed of a metal or glass material, with the substrate and desiccants and dry nitrogen are filled into the empty region there between. However, this package structure can be only applied to the display devices with metal or glass substrates, but cannot be used in packaging those with the flexible substrates. In addition, the metal container has disadvantages of having a heavy weight, and being oxidized easily. In the fabricating process, the metal container also has disadvantages of pealing off from the glass materials easily and having the requirement of a high degree of flatness. The glass container has the disadvantages of having heavy weight, cracking easily, and pealing off easily due to stress differences. Moreover, most of the sealing agents composed of polymer materials lack adequate protection from moisture. As a result, although the electrical devices are packaged, the moisture of the external environment still permeates into the packaged device gradually and erodes the display devices so as to deteriorate the display effect and decrease the lifetime of the display devices.  
           [0006]    In order to solve the above-mentioned problems of the metal or glass container, a new passivation process that utilizes films to encapsulate the protected devices was developed. Please refer to FIG. 1, which is a cross-sectional diagram of a passivation structure  16  disclosed in U.S. Pat. No. 5,811,177. As shown in FIG. 1, an OLED  10  mainly comprises a substrate  12 , a display unit  14  positioned on the substrate  12 , and a passivation structure  16  covering the display unit  14  and the substrate  12 . The display unit  14  is composed of a plurality of pixels and further comprises a driving circuit (not shown) disposed on the substrate  12  for driving the pixels to display. The passivation structure  16 , which is a multiple film structure, comprises a metal layer  18 , a buffer layer  20 , a thermal coefficient matching layer  22 , a low permeability layer  24 , and a sealing layer  26  stacked on the display unit  14  in sequence for protecting the display unit  14 .  
           [0007]    Furthermore, another passivation structure which utilizes a metal layer, inorganic materials and hydrophobic polymer materials is disclosed in U.S. Pat. No. 5,952,778. Another moisture-proof multi-layer structure is disclosed in Chinese Taipei Patent 379,531 to improve the above-mentioned problem. The structure includes a moisture-adsorbing resin layer, an adhesive layer, and a transparent resin layer and covers an electroluminescent device to prevent the electroluminescent device from moistening and oxidizing.  
           [0008]    As mentioned above, the conventional passivation structure utilizes inorganic ceramic materials, metal materials and polymer materials stacking on display units as a passivation structure to prevent electrode materials or organic materials in the display device from being eroded or oxidized by the moisture and oxygen in the external environment. Normally, some moisture sensitive electrical devices, such as the OLED, requires a passivation whose permeability is less than 0.05 g/m 2  day. Thus, most of the conventional passivation structures are composed of more than five stacked layers to meet the permeability requirement. However, the heat dispersion ability cannot be satisfied in the aforementioned structures. In other words, although the multi-layer structure can provide a better effect on moisture protection, there is the disadvantage of low heat dispersion ability and a complicated fabricating process which leads to a high fabrication cost and long fabricating time. Thus, it is important to develop a new passivation structure to solve the aforementioned problem.  
         SUMMARY OF INVENTION  
         [0009]    It is therefore a primary objective of the claimed invention to provide a passivation structure which comprises a cyclic structure composed of a diamond-like carbon film to solve the problem mentioned above.  
           [0010]    In a preferred embodiment of the claimed invention, a passivation structure capping an electrical device disposed on a substrate is introduced. The passivation structure comprises a first diamond-like carbon film covering a top surface and the sidewall of the electrical device and the surface of the substrate, a buffer layer positioned on the first diamond-like carbon film, and a second diamond-like carbon film positioned on the buffer layer. Part of the second diamond-like carbon film covers the first diamond-like carbon film directly to form a cyclic structure.  
           [0011]    It is an advantage of the claimed invention that the present passivation structure utilizes a material character of the diamond-like carbon film to obtain a good anti-abrasiveness and a low permeability and uses the formed cyclic structure to provide a high thermal conductivity and improve the lifetime of the protected electrical device in advance. 
       
    
    
       [0012]    These and other objectives of the claimed invention will not doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.  
       BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic diagram of a passivation structure according to prior art.  
         [0014]    [0014]FIG. 2 is a-schematic diagram of a passivation structure according to the present invention.  
         [0015]    [0015]FIG. 3 is a local amplified diagram of the passivation structure shown in FIG. 2.  
         [0016]    [0016]FIG. 4 is a top view of the passivation structure of the present invention.  
         [0017]    [0017]FIG. 5 shows the moisture permeability of DLC films and silicon nitride layers. 
     
    
     DETAILED DESCRIPTION  
       [0018]    The present invention discloses a passivation of an electrical device. In order to show the difference between the passivation structure of the present invention and that of the prior art, an OLED is illustrated in the following to describe the passivation structure in the present invention. It is important that the present invention is not limited in the passivation structure of an OLED, but can be applied to other electrical devices, such as an LCD or semiconductor devices.  
         [0019]    Please refer to FIG. 2, which is a cross-sectional diagram of a passivation structure of an OLED in a preferred embodiment of the present invention. As shown in FIG. 2, the OLED  110  comprises a substrate  112  and a display unit  114  positioned on the surface of the substrate  112  to define a display region  126 , and a peripheral region  128 . In addition, the OLED  110  further comprises a passivation structure  118  covering the display unit  118  to prevent the display unit from being exposed to the external atmosphere.  
         [0020]    Please refer to FIG. 3 of a local amplified diagram of the passivation structure  118  of FIG. 2. As shown in FIG. 3, the display unit  114  is composed of a plurality of pixels. Each pixel, which is a multi-layer. structure, comprises a conductive layer  130 , a luminous layer  132 , a metal layer  134 , and a conductive layer  138  stacked on the substrate  112  in sequence. In the preferred embodiment of the present invention, the substrate  112  is a glass substrate. The conductive layers  130  and  138  are composed of indium tin oxide (ITO) or indium zinc oxide (IZO). The luminous layer  132  is composed of organic materials, such as an organic luminous layer composed of conjugated polymers. The metal layer  134  comprises alloys of Al—Mg, Al—Li, or Al—LiF.  
         [0021]    The passivation structure  118  comprises a first diamond-like carbon (DLC) film  120 , a buffer layer  122  and a second DLC film stacked in sequence. The first DLC film  120  covers a top surface and sidewalls of the display unit  114  and the substrate  112  so that the display unit  114  can be fully enclosed between the substrate  112  and the passivation structure  118 . In the preferred embodiment of the present invention, the first DLC film  120  and the second DLC film  124  are both formed in a plasma-enhanced chemical vapor deposition (PECVD) process with a thickness about 10 to 50000 angstroms. The buffer layer  122  comprises solvent type or non-solvent type thermal curable materials, materials composed of diamond-like carbon layer and polymers, UV curable materials, or thermal evaporation polymer materials. The main function of the buffer layer  122  is for reducing a stress between the first DLC film  120  and the second DLC film  124  and preventing the first DLC film  120  and the second DLC film  124  from cracking  
         [0022]    Please refer to FIG. 3 and FIG. 4. FIG. 4 is a top view of the passivation structure  118  of the present invention. It is clearly shown that an area covered by the buffer layer  122 , is less than that covered by the first DLC film  120  and less than that covered by the second DLC layer  124 . As a result, the second DLC film  124  covers parts of the first DLC film  120  directly so that a cyclic structure is formed of the first DLC film  120  and the second DLC film  124  thereby. In addition, the cyclic structure is located on the peripheral region  128  and therefore has no effect on the permeability of the passivation structure  1129  above the display region  126 .  
         [0023]    The passivation structure  118  of the present invention uses the DLC film as a major package material. The DLC film, which is a carbon film bonded in a state between sp 3 , such as a diamond, and sp 2 , such as graphite, is formed by a magnetically sputtering method, an ion plating method, an arc ion plating method or the PECVD process as shown in the aforementioned preferred embodiment. Furthermore, by controlling the process parameter or using additional dopants, the formed DLC films can have different features, such as a soft polymer-like film with very small stress or an amorphous DLC film with a high hardness. In the present invention, a DLC film with low permeability is used to achieve the purpose of avoiding moisture penetration.  
         [0024]    Nakahigashi et al. (U.S. Pat. No. 6,136,386) disclosed a method of coating polymer or glass objects with carbon films. In Nakahigashis disclosure, a DLC film is deposited on a plastic film by a CVD process to suppress the transmittance of the moisture and oxygen gas.  
         [0025]    As shown in FIG. 5, the DLC filmdeposited on the plastic film can reduce the transmittance of the moisture and oxygen gas effectively. Comparing with the original plastic film, the plastic film coated with the DLC film can reduce the moisture permeability to {fraction (1/14)} and the oxygen permeability to {fraction (1/12)}.  
         [0026]    In the Japan Industrial Material on July 2000 (page 97, Vol. 48 No.6), it also disclosed that depositing a DLC film with a thickness about 10 to 100 nm on a PET film can reduce the oxygen permeability to {fraction (1/30)} of the original.  
         [0027]    Besides the low permeability, the DLC film also has the characteristic of high hardness (3000-5000 kg/mm 2 ), high acid and base resistances, a high dielectric coefficient, high anti-abrasiveness, and high smoothness of the surface. In addition, the thermal conductivity of the DLC film, which is about 1100 W/cm-K, is much higher than the conventional package materials, such as an aluminum nitride (170 W/cm-k), aluminum oxide (28 W/cm-k), silicon nitride (25 W/cm-k), titanic oxide (10.4 W/cm-k), or silicon oxide (0.02 W/cm-k). Furthermore, the-passivation structure of the present invention comprises the cyclic structure formed of the first DLC film  120  and the second DLC film  124 , which can fully develop the high thermal conductivity of the DLC film. In other words, when the display unit  114  generates a lot of heat when operating, the heat is rapidly transferred from the first DLC film  120 , which is the most inner layer of the passivation structure  118 , to the second DLC film  124 , which is the most outer layer of the passivation structure  118 , through the cyclic structure. Then, the heat is dispersed to the external atmosphere rapidly from the second DLC film  124 , which contacts with air directly, so as to improve the heat dissipation of the display device  110  effectively and solve the problem in the conventional OLED devices, which utilize a multi-layer structure to obtain enough waterproof ability but decrease the heat dissipation of the display units.  
         [0028]    It is important that the passivation structure in the aforementioned embodiment is applied to the field of OLED packaging. However, the present invention is not limited in the OLED field. For those skilled in the art, the present invention can be further applied to all kinds of electrical devices which need a passivation structure of high anti-abrasiveness, low moisture permeability, or high thermal dissipation according to the aforementioned descriptions and drawings so as to improve the lifetime of the electrical devices.  
         [0029]    In contrast with the prior art, which uses inorganic materials or the ceramics materials, the present invention uses the DLC film as a major package material so as to obtain a better anti-abrasiveness, a higher thermal dissipating ability, and a lower moisture permeability. Therefore, the passivation structure of the present invention can prevent the electrode materials or the organic materials in the electrical devices from contacting the external atmosphere, which leads to deterioration of the lifetime the electrical devices. In addition, the first DLC film and the second DLC film contact directly and form a cyclic structure thereby. As a result, the DLC film in the top layer of the passivation structure not only provide a high anti-abrasiveness to protect the packaged electrical device, but also use the high thermal conductivity of the DLC film to dissipate the generated heat rapidly from the inner DLC film through the cyclic structure to the external atmosphere. Therefore, the thermal dissipating ability of the passivation structure can be increased effectively so that the stability and lifetime of the electrical devices are both improved in advance.  
         [0030]    Those skilled in the art will readily observe that numerous modifications and alterations of the invention may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of appended claims.