CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 97142036, filed on Oct. 31, 2008, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electronic device and more particularly to a method for forming a gas barrier on the electronic device. 
     2. Description of the Related Art 
     Organic light emitting diodes (OLED) have advantages of self-lighting emittance, quick response and high display quality. Thus, OLEDs are one kind of organic electronic device that is widely applied in organic light emitting displays. However, OLEDs are easy permeated by water vapor and oxygen, so that the efficiency and lifespan thereof are reduced. Therefore, OLEDs need to be sealed. 
     For conventional organic light emitting displays, the OLEDs are packaged by metal or glass. For example, U.S. Pat. No. 6,998,776 discloses using a glass plate as a package covering and using a gastight melting material to seal the OLEDs, wherein laser or infrared rays pass through the glass plate to process the gastight melting material. However, this kind of packaging material is not suitable for flexible displays. In addition, U.S. Pat. No. 7,198,832 discloses using a multi-layer structure to form a gas barrier. A film is coated on OLEDs by deposition to form the gas barrier and package the organic light emitting diodes. However, this kind of package needs several steps for its coating process, such that the fabrication thereof is time-consuming and the cost of the multi-layer structure is high. 
     Moreover, because the packaging methods of the conventional organic light emitting displays are performed by directly forming the gas barriers on the OLEDs and the OLEDs can only withstand a process temperature of smaller than 80° C., the process temperature of the gas barrier is limited and the water vapor and oxygen gas anti-permeation ability can not be enhanced. 
     Therefore, a method for forming gas barriers of electronic devices is desired, which is not limited by the acceptable process temperature of the electronic devices and the properties of the gas barriers can be improved. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a method for forming a gas barrier on an electronic device. First, a first substrate is provided, having at least one electronic device thereon. A second substrate is then provided and the gas barrier is formed on the second substrate. The second substrate is disposed over the first substrate, so that the gas barrier faces the electronic device. An electromagnetic wave light source is provided over the second substrate to irradiate the second substrate. Then, the gas barrier is transferred to the electronic device, covering the electronic device. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a schematic cross section of a material for forming and transferring a gas barrier according to one embodiment of the invention; 
         FIG. 2  is a schematic cross section of a material for forming and transferring a gas barrier according to another embodiment of the invention; 
         FIG. 3  is a schematic cross section of a material for forming and transferring a gas barrier according to further another embodiment of the invention; 
         FIG. 4  is a schematic cross section of a material for forming and transferring a gas barrier according to further another embodiment of the invention; 
         FIGS. 5   a - 5   d  are schematic cross sections of fabricating processes for forming and transferring a gas barrier to an electronic device according to one embodiment of the invention; 
         FIG. 6  is a schematic cross section of a structure of forming and transferring a gas barrier on an electronic device according to another embodiment of the invention; 
         FIG. 7  is a schematic cross section of a structure of forming and transferring a gas barrier on an electronic device according to further another embodiment of the invention; 
         FIG. 8  is a schematic cross section of a structure of forming and transferring a gas barrier on an electronic device according to further another embodiment of the invention; and 
         FIGS. 9   a - 9   b  are schematic cross sections of fabricating processes for forming and transferring a patterned gas barrier to a plurality of electronic devices according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. The description is provided for illustrating the general principles of the invention and is not meant to be limiting. The scope of the invention is best determined by reference to the appended claims. 
     The invention is performed by forming a gas barrier on a substrate and then transferring the gas barrier to an electronic device. Therefore, the fabrication of the gas barrier on the electronic device is not limited by the acceptable process temperature of the electronic device. The gas barrier of the inventions can be fabricated by a higher process temperature. 
     In one embodiment of the invention, a cross section of a structure of a material for forming and transferring the gas barrier is shown as  FIG. 1 . A gas barrier  12  is formed on a substrate  10 . The substrate  10  may be a glass substrate, a flexible substrate or a substrate formed from other materials. The glass substrate has a heat-resistant temperature of about 900 to 1000° C. The flexible substrate has a heat-resistant temperature of about 200° C. The gas barrier  12  is a thin film with high transparency and high water vapor and oxygen gas anti-permeation ability. The material of the gas barrier  12  comprise silicon nitride (SiNx), silicon oxide (SiOx), metal nitride, metal oxide (Al 2 O 3 ), diamond-like carbon (DLC), diamond-like compound or the combinations thereof. The gas barrier  12  may be a one layered or multi-layered thin film, and a plurality of particles may be dispersed in the gas barrier to form a complex thin film. In one embodiment, the gas barrier  12  can be formed on the substrate  10  by a plasma enhanced chemical vapor deposition (PECVD) process. The process temperature of the PECVD process is only limited by the heat-resistant temperature of the substrate  10 . Therefore, the process temperature for forming the gas barrier  12  can be about a room temperature to about 1000° C. Because the heat-resistant temperature of the substrate  10  is higher than the acceptable process temperature of the electronic device, the gas barrier of the invention can be fabricated at a temperature higher than the acceptable process temperature of the electronic device. For example, the gas barrier is fabricated at a temperature higher than 80° C., and the water vapor and oxygen gas anti-permeation ability of a one-layered gas barrier formed at the temperature can be enhanced to above 5*10 −3  g/m 2 /day. However, the conventional gas barrier needs to be fabricated at a temperature smaller than 80° C., and the water vapor and oxygen gas anti-permeation ability of the conventional one-layered organic/inorganic stacked gas barrier is only below about 1*10 −2  g/m 2 /day. Additionally, the mechanical stress of the gas barrier of the invention is lower than conventional gas barriers. Moreover, the gas barrier of the invention can be applied to a flexible organic electronic device, as it is not easily broken when flexed. 
     In another embodiment of the invention, a cross section of a structure of a material for forming and transferring the gas barrier is shown as  FIG. 2 . The gas barrier  12  is formed on the substrate  10  and an adhesive layer  14  is formed on the gas barrier  12 . The material of the adhesive layer  14  is a transparent and adhesive material, such as epoxy resin or UV curing glue. The adhesive layer  14  can enhance the adhesion between the gas barrier and the substrate, and between the gas barrier and the electronic device. In one embodiment, the adhesive layer  14  can be formed on the gas barrier  12  by a spin coating process or dispensing. 
     In further another embodiment of the invention, a cross section of a structure of a material for forming and transferring the gas barrier is shown as  FIG. 3 . The difference between the embodiment of  FIG. 3  and the above embodiments is that a stripping layer  16  is formed on the substrate  10  first, and then the gas barrier  12  is formed on the stripping layer  16 . The stripping layer  16  may be an energy transfer layer, a laser etching layer or a laser separating layer. The stripping layer  16  can help to transfer the gas barrier  12 . The material of the stripping layer  16  may be a S1818 positive typed photoresist (product of MicroChem company), a SU-8 negative typed photoresist (product of MicroChem company), polydimethysiloxane (PDMS), or benzoyl peroxide (BPO), or combinations thereof with carbon nano-tubes (CNT). In one embodiment, the stripping layer  16  can be formed on the substrate  10  by a spin coating process. 
     In further one embodiment of the invention, a cross section of a structure of a material for forming and transferring the gas barrier is shown as  FIG. 4 . The stripping layer  16  is formed on the substrate  10  first, and then the gas barrier  12  is formed on the stripping layer  16 . Next, the adhesive layer  14  is formed on the gas barrier  12 . In this embodiment, the materials and the forming methods of the substrate  10 , the stripping layer  16 , the gas barrier  12  and the adhesive layer  14  are mainly the same as the above embodiments. 
     Referring to  FIGS. 5   a  to  5   d , which illustrate cross sections of fabricating processes for forming and transferring a gas barrier to an electronic device according to the embodiment of the material for forming and transferring the gas barrier as shown in  FIG. 4 . Referring to  FIG. 5   a , a substrate  20  is provided. At least one electronic device  22  is disposed on the substrate  20 . The substrate  20  may be a plastic substrate or a flexible substrate formed from other materials. The electronic device  22  comprise an organic light emitting diode (OLED), an organic thin film transistor (OTFT) or an organic thin film solar cell. Next, referring to  FIG. 5   b , the material for forming and transferring the gas barrier as shown in  FIG. 4  is attached to or disposed apart from over the substrate  20 , such that the gas barrier  12  faces the electronic device  22 . If the material for forming and transferring the gas barrier is attached to the substrate  20 , the adhesive layer  14  is adhered to the substrate  20  and the electronic device  22 . 
     Referring to  FIG. 5   c , an electromagnetic wave light source  30  is disposed over the substrate  10 . The electromagnetic wave light source  30  may be a full-wave band laser, an ultraviolet wave band laser or an infrared wave band laser. The laser light source  30  is used to irradiate the substrate  10  and make the laser light source  30  in focus or out of focus to the stripping layer  16  on the substrate  10  for scanning. In one embodiment, the stripping layer  16  absorbs 80 to 90% of the laser light energy. The ratio of the laser light energy absorbed by the stripping layer  16  is determined by the materials of the stripping layer. Then, the light energy absorbed by the stripping layer  16  is changed into a heat energy, such that the gas barrier  12  and the adhesive layer  14  are separated from the stripping layer  16  and transferred to the substrate  20  and the electronic device  22  together, covering the electronic device  22 . The result is shown as  FIG. 5   d . In the steps of stripping and transferring, because the gas barrier  12  is a transparent material, the residual laser energy of about 0 to 10% of laser light energy, resulted from passing through the stripping layer  16  and the gas barrier  12 , may be absorbed by the adhesive layer  14  and cure the material of the adhesive layer  14  by a photo curing reaction. As a result, the electronic device  22  is not damaged by the residual laser energy. Meanwhile, the adhesive layer  14  can enhance adhesion between the gas barrier  12  and the substrate  20  and between the gas barrier  12  and the electronic device  22 . 
     Referring to  FIG. 5   d  again, after the laser transferring process, a portion  12   a  of the gas barrier  12  and a portion  14 a of the adhesive layer  14  irradiated by the laser light source  30  are transferred to the substrate  20  and the electronic device  22 . A portion  12   b  of the gas barrier  12  and a portion  14   b  of the adhesive layer  14  not irradiated by the laser light source  30  are left on the substrate  10 . In addition, a portion of the stripping layer  16  irradiated by the laser light source  30  may be left on the substrate  10 , dispersed by gasification or stripped together to attach onto the portion  12   a  of the gas barrier  12 . 
     Note that in order to avoid incomplete photo curing reaction of the adhesive layer  14 , after the gas barrier  12   a  and the adhesive layer  14   a  are transferred to the electronic device  22 , an ultraviolet light source (not shown) may be further applied to completely cure and attach the adhesive layer  14  by irradiation. 
     In the process of forming and transferring the gas barrier  12 , suitable laser wavelengths for different materials of the stripping layer  16 , the gas barrier  12  and the adhesive layer  14  are needed to be determined. Additionally, the energy distribution of the laser will affect the transfer printing quality of the materials. Therefore, a laser uniformed module for uniform laser energy distribution is needed to improve the quality and the yield of the material transfer printing. For example, if the material of the stripping layer is the S1818 positive typed photoresist or the S1818 positive typed photoresist combined with the carbon nano-tubes, the material of the gas barrier is diamond-like carbon, and the material of the adhesive layer is epoxy resin, an ultraviolet laser with a wavelength of 355 nm, or an infrared laser with a wavelength of 1064 nm can be used. The laser energy of the ultraviolet laser or the infrared laser is about 0.5 to 2 W. 
     In another embodiment of the invention, the material for forming and transferring the gas barrier as shown in  FIG. 2  is used. The gas barrier is formed and transferred to the electronic device and the result is shown in  FIG. 6 . The fabricating processes for  FIG. 6  are mainly the same as the embodiment shown in  FIGS. 5   a  to  5   d . The difference between the fabricating processes for  FIG. 6  and  FIG. 5   d  is that there is no stripping layer on the substrate  10  in the embodiment of  FIG. 6 . The laser light energy is focused on the gas barrier  12 . A bombarded pressure produced from irradiating the gas barrier  12  by a laser, i.e., the gas barrier  12  directly receives photo pressure produced from bombarding photons combined with the molecular bonding broken by laser energy or explosions produced by laser energy, can make the gas barrier  12   a  and the adhesive layer  14   a  separate from the substrate  10  and transfer to the electronic device  22  and the substrate  20  together, covering the electronic device  22 . Meanwhile, the gas barrier  12   b  and the adhesive layer  14   b  not irradiated by the laser are left on the substrate  10 . 
     In another embodiment of the invention, the material for forming and transferring the gas barrier as shown in  FIG. 3  is used. The gas barrier is formed and transferred to the electronic device and the result is shown in  FIG. 7 . The fabricating processes for  FIG. 7  are mainly the same as the embodiment shown in  FIGS. 5   a  to  5   d . The difference between the fabricating processes for  FIG. 7  and  FIG. 5   d  is that there is no adhesive layer on the gas barrier  12  in the embodiment of  FIG. 7 . Only the gas barrier  12   a  is transferred to the electronic device  22  and the substrate  20 . The gas barrier  12   a  directly covers the electronic device  22 . 
     In further another embodiment of the invention, the material for forming and transferring the gas barrier as shown in  FIG. 1  is used. The gas barrier is formed and transferred to the electronic device and the result is shown in  FIG. 8 . The fabricating processes for  FIG. 8  are mainly the same as the embodiment shown in  FIGS. 5   a  to  5   d . The difference between the fabricating processes for  FIG. 8  and  FIG. 5   d  is that there are no stripping layer on the substrate  10  and no adhesive layer on the gas barrier  12  in the embodiment of  FIG. 8 . The laser light energy is focused on the gas barrier  12 , such that the gas barrier  12   a  is formed and transferred to the electronic device  22  and the substrate  20 . 
     In addition, in another embodiment of the invention, a patterned gas barrier can be formed to cover a plurality of electronic devices on the substrate  20 . Referring to  FIGS. 9   a  to  9   b , which illustrate cross sections of fabricating processes for forming and transferring a patterned gas barrier to the plurality of electronic devices according to the embodiment of the material for forming and transferring the gas barrier as shown in  FIG. 4 . Referring to  FIG. 9   a , a substrate  20  having two electronic devices  22  thereon is provided. Although there are only two electronic devices  22  shown in  FIG. 9   a , one skilled in the art should understand that there may be more than two electronic devices  22  on the substrate  20 . In  FIG. 9   a , the material for forming and transferring the gas barrier is attached on the substrate  20 , wherein the gas barrier  12  faces the electronic devices  22  and the adhesive layer  14  is adhered to the substrate  20  and the electronic devices  22 . The difference between this embodiment and the above embodiments is that a mask  40  is disposed between the substrate  10  and the laser light source  30 . The mask  40  may be a one layered or multi layered mask. The opening pattern on the mask  40  correspond to the plurality of electronic devices  22  on the substrate  20 . Therefore, the laser light source  30  passing through the openings of the mask  40  can make the gas barrier  12  and the adhesive layer  14  transfer to the substrate  20  and the electronic devices  22  together. Meanwhile, the laser light source  30  shielded by the mask  40  can prevent the gas barrier  12  and the adhesive layer  14  transferring to the substrate  20 . The result after the laser transferring process is shown in  FIG. 9   b , wherein a patterned gas barrier  12   a  and a patterned adhesive layer  14   a  are formed on the substrate  20  to cover each of the plurality of electronic devices  22 . The gas barrier  12   b  and the adhesive layer  14   b  covered by the mask  40  are left on the stripping layer  16  on the substrate  10 . Although this embodiment is illustrated according to the embodiment of the material for forming and transferring the gas barrier of  FIG. 4 , one skilled in the art should understand that the embodiments of the material for forming and transferring the gas barrier of  FIGS. 1 to 3  also can be used and the mask  40  can be used in  FIGS. 1 to 3  to form the patterned gas barrier  12   a  to cover each of the plurality of electronic devices  22 . 
     The invention is performed by fabricating the gas barrier on a carrier substrate first, and then using laser transfer printing technology to transfer the gas barrier on the electronic devices. Therefore, consideration of the acceptable process temperature of the electronic devices during fabrication is not needed. A gas barrier with a high water vapor and oxygen gas anti-permeation ability and a low mechanical stress can be fabricated by a high temperature deposition process. In addition, the fabrication processes of transfer printing the gas barrier by a laser can be performed under room temperature, such that damage to the electronic devices thereof is minimized. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
A method for forming gas barriers on electronic devices is provided. The fabrication method includes: providing a first substrate having at least one electronic device thereon; providing a second substrate and forming a gas barrier over the second substrate; disposing the second substrate over the first substrate, wherein the gas barrier faces the electronic device; providing an electromagnetic wave light source over the second substrate; and irradiating the second substrate by the electromagnetic wave light source to transfer the gas barrier to the electronic device and cover the electronic device.